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Arabinogalactan-Proteins: Structure, Biosynthesis, and Function
... Hydroxyproline-rich glycoproteins (HRGP) are found in the walls of all plant cells. The HPRP super-family is considered as a continuum of glycosylated proteins ranging from the no or slightly glycosylated proline-rich proteins (PRPs) to the moderately glycosylated extensins and the highly glycosylated AGPs (Fincher and Stone, 1983;Sommer-Knudsen et al., 1998;Lamport et al., 2011;Draeger et al., 2015). ...
... AGPs are ubiquitous in land plants and are located at the cell surface, anchored to the plasma membrane, in the cell wall, in the apoplastic space and/or in secretions (Fincher and Stone, 1983;Nothnagel, 1997;Ellis et al., 2010). AGPs have also been recently identified in the cell walls of brown algae (Herve et al., 2016). ...
... N-glycosylation sites have been identified in some AGPs (Tan et al., 2012a). The glycan-to-protein ratio of most, but not all, AGPs is ≥9:1 (Fincher and Stone, 1983;Ellis et al., 2010). AGPs are diagnostically identified by their ability to bind to a class of synthetic phenylazo dyes, the β-glucosyl (β-Glc) and β-galactosyl (β-Gal) Yariv reagents (Fincher and Stone, 1983). ...
Arabinogalactan-proteins (AGPs) are proteoglycans found in all plants and are involved in plant growth and development. AGPs consist of a protein core generally rich in hydroxyproline (Hyp) that is O-glycosylated with type II arabino-β-(1,3;1,6)-galactans (AGs) and some oligo-arabinosides. For decades little had been known about the enzymes involved in the glycosylation of the AGP protein core. In 2008, Qu et al. sugested that the enzymes responsible of the synthesis of AGs were found in the CAZy GT 31 family. In the present study the role of the two putative galactosyltransferases (GalT), At1g74800 (AtGALT5) and At1g77810 (AtGALT9), in the synthesis of AGPs was investigated through genetic and biochemical approaches. The aims of this thesis were: 1) Characterise the expression patterns of AtGALT5 and AtGALT9, 2) Investigate the consequence of the loss-of-function and over-expression of AtGALT5 and AtGALT9 in Arabidopsis and 3) Characterise the in vitro enzyme activity of AtGALT5 and AtGALT9.
Gene expression analysis carried out using in silico expression data, RT-PCR and GUS reporter promoter fusions indicated that AtGALT5 and AtGALT9 expression is developmentally regulated and located to all organs but in specific cell types. AtGALT5 and AtGALT9 were strongly expressed in mature pollen grains. atgalt5 and atgalt9 mutants had shorter stems and roots compared to wild type and displayed salt root growth hypersensitivity. Lower amounts of AGPs were present in the flowers of atgalt5 and atgalt9 plants suggesting a possible role of AtGALT5 and AtGALT9 in AGP glycosylation. AtGALT5 and AtGALT9 were localised to the Golgi apparatus (GA), an organelle where the synthesis of type II AGs (β-(1,3;1,6)-galactans) takes place. Interestingly, over-expression of AtGALT5-VENUS in Arabidopsis led to alterations in cell size and higher levels of AGP epitopes recognised by the LM2, MAC204, JIM16, JIM17, and CCRCM7 AGP antibodies. This suggested an impairment in cell expansion likely due to abnormal glycosylation of cell surface AGPs in AtGALT5-VENUS overexpressing plants. In vitro GalT assays using β-Gal-NBD as an acceptor indicated that AtGALT9 transiently expressed in Nicotiana benthamiana has β-(1,3)-GalT activity. In conclusion, AtGALT5 is a GA-localised putative GalT involved in the synthesis of type II AGs of AGPs whose function is important in cell expansion. AtGALT9 is a β-(1,3)- GalT likely to be involved in the elongation of the β-(1,3)-D-galactan backbone of AGPs. Both AtGALT5 and AtGALT9 being required for normal root and stem growth.
... The amino acids of AGPs are often arranged in characteristic dipeptide repeats: Ala-Hyp, Ser-Hyp, Thr-Hyp, introduced as AG glycomodules (Tan et al., 2003;Ellis et al., 2010). The carbohydrate moiety of AGPs represents more than 90% of their total molecular mass, and it is composed mainly of arabinose (Ara) and galactose (Gal), as well as minor sugars such as glucuronic acid (GlcA), fucose (Fuc), rhamnose (Rha), and xylose (Xyl; Clarke et al., 1979;Fincher et al., 1983;Showalter, 1993;Chasan, 1994). AGPs have different molecular weights that reflect different extents of glycosylation of their specific protein cores. ...
... Positive reactions with β-Yariv reagent, a chemical reagent that specifically binds to the β-(1→3)-linked D-Galp backbone of AGPs (Yariv et al., 1967;Kitazawa et al., 2013), and immunolocalization studies with monoclonal antibodies that recognize AGP epitopes have shown that AGPs are ubiquitous in the plant kingdom, from bryophytes to angiosperms, and are also present in many algae (Clarke et al., 1979;Fincher et al., 1983;Showalter, 1993;Serpe and Nothnagel, 1999;Lee et al., 2005;Hervé et al., 2016). These glycoproteins were conserved during evolution, presumably because of their vital roles in plants (Serpe and Nothnagel, 1999). ...
... Three models have been proposed for the molecular structure of AGPs: the wattle-blossom, the twisted hairy rope, and the necklace (Fincher et al., 1983;Qi et al., 1991;Du et al., 1996;Lamport et al., 2014). The wattle blossom model predicts globular units of polysaccharide chains anchored to a protein core of a spheroidal molecule, and the twisted hairy rope model foresees an alignment of AG chains along the protein backbone, whereas the recent necklace model compares AGP structure to an ancient gold necklace from Afghanistan with pendant glycomodules. ...
Arabinogalactan-proteins (AGPs) are a large, complex, and highly diverse class of heavily glycosylated proteins that belong to the family of cell wall hydroxyproline-rich glycoproteins. Approximately 90% of the molecules consist of arabinogalactan polysaccharides, which are composed of arabinose and galactose as major sugars and minor sugars such as glucuronic acid, fucose, and rhamnose. About half of the AGP family members contain a glycosylphosphatidylinositol (GPI) lipid anchor, which allows for an association with the outer leaflet of the plasma membrane. The mysterious AGP family has captivated the attention of plant biologists for several decades. This diverse family of glycoproteins is widely distributed in the plant kingdom, including many algae, where they play fundamental roles in growth and development processes. The journey of AGP biosynthesis begins with the assembly of amino acids into peptide chains of proteins. An N-terminal signal peptide directs AGPs toward the endoplasmic reticulum, where proline hydroxylation occurs and a GPI anchor may be added. GPI-anchored AGPs, as well as unanchored AGPs, are then transferred to the Golgi apparatus, where extensive glycosylation occurs by the action of a variety glycosyltransferase enzymes. Following glycosylation, AGPs are transported by secretory vesicles to the cell wall or to the extracellular face of the plasma membrane (in the case of GPI-anchored AGPs). GPI-anchored proteins can be released from the plasma membrane into the cell wall by phospholipases. In this review, we present an overview of the accumulated knowledge on AGP biosynthesis over the past three decades. Particular emphasis is placed on the glycosylation of AGPs as the sugar moiety is essential to their function. Recent genetics and genomics approaches have significantly contributed to a broader knowledge of AGP biosynthesis. However, many questions remain to be elucidated in the decades ahead.
... Histochemical analysis of the taro corm revealed that arabinogalactan (AG, also called galactoarabinan) is the main biopolymer of taro WS-NSP (Harris et al. 1992;Taki, Yamada, and Nakaya 1972). Arabinogalactans (AGs) are classified into three types, Type I, Type II, and Type III, based on their structural composition (Fincher, Stone, and Clarke 1983;Clarke, Anderson, and Stone 1979). Type I AGs is characterized by b-(1-4) galactan backbone substituted with 5-linked and terminal arabinose residues and has a linear (1-4)-b-D-Galq backbone, bearing 20 to 40% a-L-Araf residues (1-5)-linked short chains. ...
... Type I AGs is characterized by b-(1-4) galactan backbone substituted with 5-linked and terminal arabinose residues and has a linear (1-4)-b-D-Galq backbone, bearing 20 to 40% a-L-Araf residues (1-5)-linked short chains. Type II AGs, also known as arabino-3, 6-galactan, is characterized by b-(1-3, 6) linked galactose polymers associated with 3-or 5-linked arabinose residue and has a (1-3)-b-D-Galq backbone which is heavily substituted at position 6 by mono and oligosaccharide side chain composed of arabinosyl and galactosyl units (Ebringerov a, Hrom adkov a, and Heinze 2005;Fincher, Stone, and Clarke 1983). Type II is more widespread than Type I and is found in different sources such as mosses, coniferous woods, gums, saps, and exudates of angiosperms and various plant parts such as seeds, leaves, roots, and fruits (Ebringerov a, Hrom adkov a, and Heinze 2005). ...
... Type II is more widespread than Type I and is found in different sources such as mosses, coniferous woods, gums, saps, and exudates of angiosperms and various plant parts such as seeds, leaves, roots, and fruits (Ebringerov a, Hrom adkov a, and Heinze 2005). It occurs in the extracellular space of the plant and is not a structural component of cell walls unlike Type I. Type II AGs are also associated with protein and together make up the arabinogalactan-protein (AGP) complex (Fincher, Stone, and Clarke 1983). AGPs are high molecular weight proteoglycans found mainly in plant cell walls, secretions, and plasma membrane where polysaccharide comprises the bulk of the molecule and with less than 10% protein moiety (Suzuki et al. 2017;Doco and Williams 2013;Johnson et al. 2003). ...
This review critically evaluates and discusses groundwork and recent studies on the extraction, characteristics, properties, bioactivities, and applications of the water-soluble non-starch polysac-charides (WS-NSPs) of root and tuber crops. Early studies have focused on the use of conventional extraction methods for the extraction of the WS-NSPs and there are limited information on the characteristics and properties of the extracted materials. In recent years, novel extraction techniques such as microwave, ultrasound, and enzyme-assisted extractions have been utilized to improve the yield and functionality of the WS-NSPs. However, low yield and co-extraction of other biological compounds remain a challenging obstacle for commercial uses. A better understanding of the characteristics and properties was recently afforded by employing advanced analytical techniques to investigate the chemical composition and molecular structures of the WS-NSPs. Recent bioactivities of the WS-NSPs that demonstrated their potential in the prevention and management of metabolic diseases like diabetes, obesity, cancer, and in improving gut health and immunity had received considerable attention. Also, many studies have confirmed the potential use of the WS-NSPs of root and tuber crops in a wide range of food and pharmaceutical applications. These bioactivities of WS-NSPs warrant further investigations on this interesting biomaterial.
... The arabinose/xylose ratio (Ara/Xyl) indicates the number of Ara units attached to the Xyl backbone and is routinely used for the determination of arabinoxylans in a biological sample (Morales-Ortega et al., 2013). On the other hand, the ratio arabinose/galactose (Ara/Gal) helps to identify arabinogalactans (Saeed et al., 2011), often represented as a linear skeleton of Gal with short lateral branches of different sugars, mainly Ara (Fincher et al., 1983). Table 1 shows the composition of neutral sugars of the WBAE, where glucose (Glc) was the most abundant. ...
... In the present work, these sugars belong to water-extractable polysaccharides, such as starch, β-glucans, arabinoxylans, or arabinogalactans (Loosvel et al., 1997). The last two are usually attached to peptides and proteins through covalent bonds (Fincher et al., 1983;Cipriani et al., 2009). The WBAE Ara/Xyl ratio (Table 1) was very close to that reported by Maes & Delcour (2002) and Khan & Shewry (2009), who reported ratios of 0.45 for water-extractable arabinoxylans from wheat bran and 0.60 for whole wheat grain, respectively. ...
The objective of this work was to explore whether the formation of protein nanoparticles, reported in a previous study, occurs in a fraction of an aqueous extract of wheat bran with a particular
composition. Using a bottom-up strategy, an aqueous extract of wheat bran was first fractionated by size exclusion chromatography. Each of the chromatographic fractions was hydrolyzed with V8 protease in a reaction medium containing Ca2+. The chromatographic fractions and their hydrolysates were subjected to chemical characterization, electrophoresis, UV-Vis spectroscopy, infrared spectroscopy, and scanning electron microscopy. Six chromatographic fractions from 0.3
to 102.8 kDa were obtained. The chemical and spectroscopic characterization results revealed the presence of protein-polysaccharide-ferulic acid complexes in four of the fractions. In the hydrolysate of a 15.1 kDa fraction, longitudinally fused nanospheres were found, forming chains. Occasionally, fusion occurred at different angles, providing attachment sites for branching. It is discussed how the composition of this fraction and the added Ca2+ ions could determine both the formation of the nanospheres and their arrangement.
... La relación arabinosa/xilosa (Ara/Xyl) indica el número de unidades de Ara unidas al esqueleto de Xyl y se utiliza de forma rutinaria para la determinación de arabinoxilanos en una muestra biológica (Morales-Ortega et al., 2013). Por otro lado, la relación arabinosa/galactosa (Ara/Gal) ayuda a identificar los arabinogalactanos (Saeed et al., 2011), a menudo representados como un esqueleto lineal de Gal con ramificaciones laterales cortas de diferentes azúcares, principalmente Ara (Fincher et al., 1983). La Tabla 1 muestra la composición de azúcares neutros del WBAE, donde la glucosa (Glc) fue la más abundante. ...
... En el presente trabajo, estos azúcares pertenecen a los polisacáridos extraíbles en agua, como el almidón, los -glucanos, los arabinoxilanos o los arabinogalactanos (Loosvel et al., 1997). Los dos últimos suelen estar unidos a péptidos y proteínas a través de enlaces covalentes (Fincher et al., 1983;Cipriani et al., 2009 (2009), quienes informaron relaciones de 0.45 para los arabinoxilanos extraíbles en agua del salvado de trigo y 0.60 para el grano de trigo integral, respectivamente. Así, se confirma la presencia de arabinoxilanos en el WBAE. ...
Protein-rich wheat bran aqueous extract was fractionated by size exclusion chromatography. Each of the chromatographic fractions was hydrolyzed with V8 protease in a reaction medium containing Ca2+. Both the fractions and the hydrolysates were characterized physically and chemically. The objective was to obtain information about which components are involved in the formation of nanoparticles, reported in previous works. Six chromatographic fractions from 0.3 to 102.8 kDa were obtained. The results of chemical characterization, electrophoresis, UV-Vis spectroscopy, and infrared spectroscopy revealed the presence of protein-polysaccharide complexes in four of the fractions. Fused nanospheres at different angles were found by scanning electron microscopy after proteolysis of a 15.1 kDa fraction. It was proposed that such binding could provide sites to form branched nanostructures.
... In this manuscript, I will focus on hydroxyproline-rich glycoproteins (HRGPs) belonging to the group of cell wall glycoproteins, including arabinogalactan proteins (AGPs) and extensins (EXTs). AGPs are known as a large heterogeneous family of HRGPs found both within the cell and on the surface of plant cells (Fincher et al., 1983;Nguema-Ona et al., 2012). They typically bound to the plasma membrane through a glycosylphosphatidylinositol (GPI) anchor (Marzec et al., 2015). ...
... Root tip from perennial ryegrass respond to water stress by producing enhance quantity of mucilage and / or changing the adhesion and structure of the mucilage. AGPs are known as the glycoproteins extremely hydroscopic and have a high water-holding capacity (Fincher et al. 1983;Showalter 2001), the widespread distribution of AGPs epitopes in the mucilage that we found supports the role of these proteins toward the root tip in water deficit condition. ...
To date, root immunity remains poorly investigated as compared to the aerial part. In this thesis, we aimed to evaluate the role of glycomolecules in root defense with a particular interest on fructans and fructan metabolizing enzymes. Lolium perenne (perennial ryegrass), a Poaceae of regional interest due to its role as a grassland forage plant was chosen as fructan accumulating plant. Two non-fructan Brassicaceae were also selected: the plant model Arabidopsis thaliana and oilseed rape (Brassica napus) for its agronomical interest. Fructans are water-soluble fructose polymers containing β-(2,1) and/or β-(2,6) linked fructose residues found in some plant species and in exopolysaccharides produced by some beneficial or pathogenic bacteria. In plants, fructans constitute a carbohydrate reserve and act in the protection against abiotic and biotic stresses according to the theory of the « sweet immunity ». To unravel the mechanisms of action of fructans, their precise localization at tissue and cellular level in various environmental conditions need to be clarified. One of the major task of our study is the production of two novel monoclonal antibodies (mAbs) named BTM15A6 and BTM9H2 towards plant fructans with β-(2,1) and/or β-(2,6) linkages. In depth characterization of their specificity was performed by immune-dot blot assays using a wide range of carbohydrates including polysaccharides. Immunolocalization of fructans by cell imaging confirmed that the recognized epitopes were detected in three fructan plant species but not in the non-fructan plant Arabidopsis. Interestingly the presence of fructan epitopes was also detected in the root system of perennial ryegrass. The root extracellular trap (RET) is known to be an important actor of root protection. By investigating the RET composition of L. perenne, we found that both mucilage and cell wall surface of border cells were particularly enriched in arabinogalactan-proteins (AGPs) epitopes. The amount of the AGP-containing mucilage was increased in response to treatment with the bacterial elicitor flagellin 22 and the water-stress inducer PEG. This suggests that AGPs play an essential role in root protection in L. perenne. Although fructan epitopes were not detected within the mucilage, their presence in the root cap cells suggests that they might also be involved in biotic and/or abiotic stress protection. In addition, we evaluated the regulation of fructan exohydrolases (FEHs) found in non-fructan-accumulating plant species including A. thaliana and B. napus in response to root treatment with defense-related phytohormones. Salicylic acid increased the transcript level of the two FEHs (6-FEH and 6&1-FEH) in both species. These data support a role of these FEHs in root immunity. Furthermore, preliminary results obtained with Arabidopsis FEH knockout mutants suggest a role of these enzymes in root interaction with the beneficial bacteria Pseudomonas brassicacearum.
... Arabinogalactan (AG) is a long, highly branched neutral polysaccharide composed of arabinose and galactose [12]. The main chain of AG is galactan, and its branches are predominantly arabinose side chains, which are connected to galactose through β-1,3 or β-1,6 bonds [12]. ...
... Arabinogalactan (AG) is a long, highly branched neutral polysaccharide composed of arabinose and galactose [12]. The main chain of AG is galactan, and its branches are predominantly arabinose side chains, which are connected to galactose through β-1,3 or β-1,6 bonds [12]. AG is a water-soluble polysaccharide. ...
Background: This study aimed to explore the mechanism by which arabinogalactan (AG) inhibited N-acetyl-para-aminophenol (APAP)-induced acute liver injury in mice. The balance of the mouse intestinal flora and the relationship between AG treatment and the PI3K/AKT and NF-κB signaling pathways were evaluated to confirm a liver-gut interaction. Methods: Mice were administered 2 different doses of AG (150 or 300 mg/kg body weight) by gavage for 7 days and liver injury was induced by a single injection of APAP (250 m/kg). Hematoxylin-eosin staining, terminal deoxynucleotidyl transferase dUTP nick-end labeling, and Hoechst 33258 fluorescence staining of liver tissue were used to analyze liver damage. Western blots were used to evaluate expression of proteins related to PI3K/AKT and NF-κB signaling pathways, and changes in the hierarchical structure of the intestinal flora were determined. Results: AG pretreatment increased the proportion of Lactobacillus and decreased the abundance of species from norank_o_Clostridiaceae and Prevotella in mouse feces compared with APAP-only treated mice. AG pretreatment reversed glutathione depletion and CYP2E1 overexpression, reduced the production of malondialdehyde and 4-hydroxynonenal, and decreased the levels of alanine aminotransferase, aspartate aminotransferase, tumor necrosis factor-α and interleukin-1β compared with the APAP-only treated mice. The levels of proteins related to the PI3K/AKT signaling pathway were similar between the AG and control groups. AG pretreatment significantly reduced APAP-induced hepatocyte apoptosis and necrosis and inflammatory infiltration into the liver. Conclusion: PI3K/AKT pathway-mediated BAX expression and the NF-κB signaling cascade were inhibited by AG. AG protected the intestinal flora composition, which subsequently suppressed oxidative stress in the liver, improved the inflammatory response, and reduced hepatocyte apoptosis and necrosis.
... Arabinogalactan (AG) is a long, highly branched neutral polysaccharide composed of arabinose and galactose [12]. The main chain of AG is galactan, and its branches are predominantly arabinose side chains, which are connected to galactose through β-1,3 or β-1,6 bonds [12]. ...
... Arabinogalactan (AG) is a long, highly branched neutral polysaccharide composed of arabinose and galactose [12]. The main chain of AG is galactan, and its branches are predominantly arabinose side chains, which are connected to galactose through β-1,3 or β-1,6 bonds [12]. AG is a water-soluble polysaccharide. ...
Background: This study aimed to explore the mechanism by which arabinogalactan (AG) inhibited N-acetyl-para-aminophenol (APAP)-induced acute liver injury in mice. The balance of the mouse intestinal flora and the relationship between AG treatment and the PI3K/AKT and NF-κB signaling pathways were evaluated to confirm a liver-gut interaction. Methods: Mice were administered 2 different doses of AG (150 or 300 mg/kg body weight) by gavage for 7 days and liver injury was induced by a single injection of APAP (250 m/kg). Hematoxylin-eosin staining, terminal deoxynucleotidyl transferase dUTP nick-end labeling, and Hoechst 33258 fluorescence staining of liver tissue were used to analyze liver damage. Western blots were used to evaluate expression of proteins related to PI3K/AKT and NF-κB signaling pathways, and changes in the hierarchical structure of the intestinal flora were determined. Results: AG pretreatment increased the proportion of Lactobacillus and decreased the abundance of species from norank_o_Clostridiaceae and Prevotella in mouse feces compared with APAP-only treated mice. AG pretreatment reversed glutathione depletion and CYP2E1 overexpression, reduced the production of malondialdehyde and 4-hydroxynonenal, and decreased the levels of alanine aminotransferase, aspartate aminotransferase, tumor necrosis factor-α and interleukin-1β compared with the APAP-only treated mice. The levels of proteins related to the PI3K/AKT signaling pathway were similar between the AG and control groups. AG pretreatment significantly reduced APAP-induced hepatocyte apoptosis and necrosis and inflammatory infiltration into the liver. Conclusion: PI3K/AKT pathway-mediated BAX expression and the NF-κB signaling cascade were inhibited by AG. AG protected the intestinal flora composition, which subsequently suppressed oxidative stress in the liver, improved the inflammatory response, and reduced hepatocyte apoptosis and necrosis.
... AGPs have a carbohydrate component and a protein fraction. [54] Accounts for around 90% (dry weight basis) that carbohydrate fraction mainly contains arabinose and galactose residues (90% dry weight basis), while protein fraction is composed of hydroxyproline residues (approximately 10% dry weight basis). [54] Furthermore, glycoprotein that has been isolated from Codium decorticatum contains 36.24% ...
... [54] Accounts for around 90% (dry weight basis) that carbohydrate fraction mainly contains arabinose and galactose residues (90% dry weight basis), while protein fraction is composed of hydroxyproline residues (approximately 10% dry weight basis). [54] Furthermore, glycoprotein that has been isolated from Codium decorticatum contains 36.24% carbohydrate. ...
Seaweeds, as a dietary protein source originated in Asian countries and later expanded towards France, Chile, etc. Food applications have been narrowed down due to complications in extraction. Therefore, products are not yet available in the market. Extraction of other phytochemicals along with seaweed proteins provides value addition in food products. Therefore, a trend has emerged to extract protein from edible seaweeds with many health beneficial applications. Also, consumption of many animal proteins like meat are now becoming a threat on humans due to infectious viral diseases. Hence, seaweed proteins are emerging as a global alternative source of protein.
... AGPs are a diverse class of HRGPs, known for their heterogenous glycan chains which take up 90-98% (w/w) of the entire molecule, especially characterized by large arabino-(3,6)galactan (type II AG) polysaccharides ). The glycan side chains have a β-(1,3)-Gal backbone monosubstituted with β-d-1,6 Gal residues, which can be extended with l-Ara, l-Rha, l-Fuc, methylated and unmethylated d-GlcA and d-Xylp (Fincher et al. 1983). The l-Araf residues in type II AGs include α-1,2, α-1,3 and/or α-1,5-linked residues (Seifert and Roberts 2007). ...
... The enzymatic activity of RAY1 was tested using microsomal fractions from Nicotiana benthamiana leaves heterologously expressing RAY1. Low levels of AraT activity were observed with UDP-l-Araf, but not UDP-l-Arap and l-Ara, as a donor and d-Gal or methyl-β-d-Galactoside (minor sugar component in AGPs) as the acceptor (Fincher et al. 1983). Although the evidence for RAY1 being an AGP AraT is strongly supported by mutant and enzymatic activity studies, the result indicating the anomeric configuration of the product is puzzling, as l-Ara in the β-configuration has not been previously reported in AGPs (Knoch et al. 2014). ...
Growth, development, structure as well as dynamic adaptations and remodelling processes in plants are largely controlled by the properties of their cell walls. These intricate wall structures are mostly made up of different sugars connected through specific glycosidic linkages but also contain many glycosylated proteins. A key plant sugar that is present throughout the plantae, even before the divergence of the land plant lineage, but is not found in animals, is L-Arabinose (L-Ara). Here, we summarize and discuss the processes and proteins involved in L-Ara de novo synthesis, L-Ara interconversion, and the assembly and recycling of L-Ara-containing cell wall polymers and proteins. We also discuss the biological function of L-Ara in a context focused manner, mainly addressing cell wall related functions that are conferred by the basic physical properties of arabinose containing polymers/compounds. In this article we explore these processes with the goal of directing future research efforts to the many exciting yet unanswered questions in this research area.
... They take part in the regulatory and functional continuum of the plasmalemma, cell wall, and environment (Ellis et al., 2010). AGPs occur in all plant organs (Clarke et al., 1979;Fincher et al., 1983;Nguema-Ona et al., 2012;He et al., 2019) but molecular mechanisms of their function remain rather puzzling. They are involved in the regulation of plant growth and development, affect cell wall properties, structure, and architecture (Seifert, 2018(Seifert, , 2021Tucker et al., 2018), play a role in stem development and differentiation (Ito et al., 2005;MacMillan et al., 2010;Liu et al., 2020), root growth and differentiation (Dolan et al., 1995;Bossy et al., 2009;Nguema-Ona et al., 2012), sexual reproduction (Cheung et al., 1995;Cheung and Wu, 1999;Nguema-Ona et al., 2012;Pereira et al., 2015;Su and Higashiyama, 2018), embryogenesis (Kreuger and van Holst, 1993;Yu and Zhao, 2012;Perez-Perez et al., 2018), fruit ripening (Leszczuk et al., 2020a,b), response to abiotic and biotic stress factors (Mareri et al., 2018;Seifert, 2021), and interactions with microorganisms (Nguema-Ona et al., 2013;Rashid, 2016). ...
... Arabinogalactan proteins have the most extensive glycosylation of Pro/Hyp-rich glycoproteins. Their carbohydrate moiety forms 90 to 99% of their molecular mass, combining galactose and arabinose as major sugars with fucose, rhamnose, and glucuronic acid as minor sugars (Fincher et al., 1983;Ellis et al., 2010;Showalter and Basu, 2016;Silva J. et al., 2020). AGPs form a complex family (Showalter, 2001). ...
Responsiveness to environmental conditions and developmental plasticity of root systems are crucial determinants of plant fitness. These processes are interconnected at a cellular level with cell wall properties and cell surface signaling, which involve arabinogalactan proteins (AGPs) as essential components. AGPs are cell-wall localized glycoproteins, often GPI-anchored, which participate in root functions at many levels. They are involved in cell expansion and differentiation, regulation of root growth, interactions with other organisms, and environmental response. Due to the complexity of cell wall functional and regulatory networks, and despite the large amount of experimental data, the exact molecular mechanisms of AGP-action are still largely unknown. This dynamically evolving field of root biology is summarized in the present review.
... AGs-II are frequentely attached to hydroxyproline-rich peptides to form glycoproteins known as AGP (Bartetzko, Schuhmacher, Hahm, Seeberger, & Pfrengle, 2015). AGs-II are highly complex polysaccharides, more common than AGs-I (Fincher, Stone, & Clarke, 1983). They are widely distributed in plants and are considered as one of the most complex natural molecules. ...
... For example, high amounts of Glc in AG composition of tamarillo fruit pulp indicated the presence of starch (do Nascimento et al., 2015) and the detection high amounts of GalA and Rha revealed the presence of pectin in AG from Heracleum sosnowskyi Manden (Shakhmatov, Makarova, & Belyy, 2019). Usually, the Gal content is higher than the Ara one in AGs and the Ara/ Gal ratio can vary between 90:10 and 15:85 (Fincher et al., 1983). Higher Ara/Gal ratio has been reported notably for Combreturn fiartmonnianum gum exudate (Anderson & Bell, 1976), Averrhoa carambola L. fruits (Leivas, Iacomini, & Cordeiro, 2016), Viscum album fruits (Wagner & Jordan, 1988), Panax notoginseng flower (Wang, P. et al., 2015), Diospyros kaki leaves (Duan, Wang, Dong, & Fang, J.-n., Li, X., 2003) and Pinus radiata greenery parts (Putoczki et al., 2007) (Table 1 and 2). ...
Arabinogalactans (AGs) are plant heteropolysaccharides with complex structures occasionally attached to proteins (AGPs). AGs in cell matrix of different parts of plant are freely available or chemically bound to pectin rhamnogalactan. Type I with predominantly β-d-(1 → 4)-galactan and type II with β-d-(1 → 3) and/or (1 → 6)-galactan structural backbones construct the two main groups of AGs. In the current review, the chemical structure of AGs is firstly discussed focusing on non-traditional plant sources and not including well known industrial gums. After that, processes for their extraction and purification are considered and finally their techno-functional and biological properties are highlighted. The role of AG structure and function on health advantages such as anti-tumor, antioxidant, anti-ulcer- anti-diabetic and other activites and also the immunomodulatory effects on in-vivo model systems are overviewed.
... Chemically, these materials are known to be comprised to varying extents either by arabinogalactan heteropolysaccharides (e.g., larchwood arabinogalactan) or occur as complex mixtures of other acetylated polysaccharides such as rhamnogalacturonan (e.g., gum karaya), mixtures of galacturonan regions and type II AG as gum tragacanth (Verbeken, Dierckx, & Dewettinck, 2003), or macromolecular complexes of type II AG and proteoglycans (arabinogalactan-protein, AGP) comprising 2%-7% of protein such as mesquite gum (Fincher et al., 1983;Goycoolea et al., 1998;López-Franco et al., 2013, 2008, 2012Orozco-Villafuerte et al., 2003). As a consequence of this heterogeneous and complex chemical structural diversity, these polysaccharides exhibit unique and versatile functional properties. ...
... By contrast, in the material from P. laevigata, a small concentration of L-Rha of $1.3 mol% has been reported (Orozco-Villafuerte et al., 2003). In addition to the polysaccharide component, mesquite gum contains a small amount of protein (2%-7%) (Fincher et al., 1983;Goycoolea et al., 1998;López-Franco et al., 2013, 2008, 2012Orozco-Villafuerte et al., 2003) which is formed mainly by Hyp, Ser, Gly, and Val (López-Franco et al., 2013). Different studies have reported that the protein plays a vital role on its emulsification properties (Goycoolea et al., 1995;Vernon-Carter, Gómez, et al., 1996;Vernon-Carter et al., 1998). ...
The collection, processing, and trading of plant exudate gums, other than gum Arabic, and the production of arabinogalactan from the heartwood of Western larch tree continue to represent an essential economic activity in many regions of the world. This family of materials share in common to be comprised of highly branched heteropolysaccharide structures. This chapter reviews the updated aspects of the manufacture, chemical structure, functional properties, main applications, and regulatory issues for three well-established hydrocolloids, namely gum tragacanth, gum karaya, and larchwood arabinogalactan along with those of mesquite gum, whose full potential utilization is still to be exploited in several fields of application.
... The arabinogalactans are essential for root development and are present in the cell walls (GPI-anchored), and in extracellular exudates, constituting a functional continuum of the plasma membrane, cell wall, and environment (Fincher et al. 1983;Komalavilas et al. 1991;Hromadová et al. 2021). The arabinogalactans recognized by LM2 are related to cell differentiation, and signaling by the GPI anchor cleavage releasing mobile signaling molecules (Lamport et al. 2006;Hromadová et al. 2021). ...
In response to the restrictions imposed by their epiphytic habit, orchids have developed structural traits that allow greater efficiency in water uptake and use, such as a complex adventitious root system with velamen. The composition of cell wall of this specialized epidermis can be altered according to the substrate to which it is fixed, influencing wall permeability, absorption, and storage of water in roots. The current study aimed to evaluate the cell wall composition of adventitious roots of Vanilla phaeantha (Orchidaceae) that grow attached to the phorophyte, fixed in the soil, or hung free. Immunocytochemical analyses were used to determine the protein, hemicellulose, and pectin composition of the cell walls of aerial and terrestrial roots. We observed that pectins are present in the different tissues of the aerial roots, while in the terrestrial roots, they are concentrated in the cortical parenchyma. The deposition of xyloglucans, extensins, and arabinogalactans was greater in the epidermis of the free side of the roots attached to the phorophyte. The strong labeling of pectins in aerial roots may be related to the influx of water and nutrients, which are generally scarce in this environment. The arrangement of hemicelluloses and proteins with the pectins may be associated with increased cell rigidity and sustainability, a feature of interest for the aerial roots. In summary, the habit of roots can interfere with the non-cellulosic composition of the cell walls of V. phaeantha, possibly related to changes in cell functionality.
... senegal, the distribution of the amino acids overall is not significantly different [27]. Since it is thought that hydroxyproline and maybe serine are responsible for the peptide chain's attachment to the polysaccharide, the hydroxyproline level is important [28]. Fraction 2 of Acacia nilotica var. ...
This study aimed to characterize the exudate gum from Acacia nilotica var. nilotica in Sudan and compare its physicochemical properties to Acacia seyal var. seyal and Acacia senegal var. senegal (gum Arabic). Samples were collected from six different states in Sudan over three seasons. The gum had a moisture content of 10.50%, ash content of 1.86%, pH value of 5.19, specific optical rotation of +94.70, intrinsic viscosity of 10.44 cm3 g-1, nitrogen content of 0.024%, protein content of 0.16%, acid equivalent weight of 1907.82, and total uronic acid content of 10.18%. Sugar content analysis revealed arabinose (41.20%), galactose (17.43%), and rhamnose (10.68%). Potassium was the predominant cation, followed by calcium, magnesium, sodium, lead, and iron. Acacia nilotica was classified as part of the Gummeferae series and exhibited a positive specific optical rotation. The Number average molecular weight (Mn) was estimated using osmometric measurements and gel permeation chromatography. The gum had a higher molecular weight and lower intrinsic viscosity compared to gum Arabic, suggesting a spheroidal shape of molecule. Amino acid analysis showed similarities with gum Arabic, with hydroxyproline and serine as principal amino acids. Variations in cationic composition were attributed to differences in soil type among collection locations. KEY WORDS: Physicochemical characterization, Acacia senegal var. senegal gum, Acacia seyal var. seyal gum, Acacia nilotica var. nilotica gum, gammiferae Bull. Chem. Soc. Ethiop. 2024, 38(4), 839-852. DOI: https://dx.doi.org/10.4314/bcse.v38i4.2
... UOLE was mainly composed of uronic acid, galactose, and arabinose, followed by glucose and lower proportions of fucose, xylose, rhamnose, and mannose. These predominant components indicated the backbone of the pectic polysaccharide with side chains from the neutral sugar, which is protein-and phenolic-associated (Fincher et al. 1983;Varner and Lin 1989). The phenol content measured was 21%, a finding that aligns relatively with the reported polysaccharides content obtained from olive leaves by Mehrnia et al. (2020). ...
Polysaccharide-rich materials were extracted from the alcohol-insoluble solids of Olea europaea l. **leaves. Structural
characteristics were determined by colorimetric techniques, FT-IR, GC–MS, SEC/MALS/VD/DRI, and NMR (1H,13C). The
extract and its main macromolecular components were characterized to assess their ability toward antioxidant, α-amylase
inhibition, and antiproliferative activities. Results revealed that the ultrasound olive leave extract comprises polysaccharides
with uronic acid, galactose, arabinose, and glucose in molar percentages of 11.7%, 11.3%, 7.5%, and 4.9% respectively, constituting
41% of the total mass. In addition, polyphenols (21%) and proteins (9%) are associated with these polysaccharides.
Further, the extract showed noticeable ORAC and free radical scavenging abilities, in addition to high in vitro antiproliferative
activity against Caco-2 colon carcinoma cell lines. Similarly, the extract exhibited a strong, uncompetitive inhibition of
α-amylase by 75% in the presence of the extract with 0.75 μg/mL of concentration. This research concludes that ultrasound
extraction method can be used for the extraction of polysaccharide–polyphenol–protein complexes. These conjugates exhibit
the potential for combined biological activities resulting from a synergistic effect of its compounds, making them promising
ingredients for the development of functional food.
... AGPs not GPI-anchored may also liberate sugars by the action of glycoside hydrolases (GHs), which may also function as signalling molecules in specific signalling pathways (Showalter, 2001). AGPs may be destined to degradation by proteolytic cleavage (Fincher et al., 1983;Faye et al., 2005) or by transport to the vacuole through endocytic multivesicular bodies (Herman and Lamb, 1992;Šamaj et al., 2000). ...
... The first fragment is an important constituent of the primary plant cell wall, which is well known to play key roles in the development and differentiation of plant cells. [32] It has a β(1,3)-D-Gal backbone branched by β(1,6)-D-Gal, which in turn are extended by β(1,3) and β(1,6)-L-Arbfs. Therefore, we planned to synthesize a partial trisaccharide L-Arbfβ-(1,6)Galpβ(1,6)Galp 38 (Scheme 2). ...
Regio‐ and stereoselective formation of the 1,2‐cis‐furanosidic linkage has been in great demand for efficient synthesis of biologically active natural glycosides. In this study, we developed a regioselective and β‐stereospecific d‐/l‐arabinofuranosylation promoted by a boronic acid catalyst under mild conditions. The glycosylations proceeded smoothly for a variety of diols, triols, and unprotected sugar acceptors to give the corresponding β‐arabinofuranosides (β‐Arbf) in high yields with complete β‐stereoselectivity and high regioselectivity. The regioselectivity was completely reversed depending on the optical isomerism of the donor used and was predictable a priori using predictive models. Mechanistic studies based on DFT calculations revealed that the present glycosylation occurs through a highly dissociative concerted SNi mechanism. The usefulness of the glycosylation method was demonstrated by the chemical synthesis of trisaccharide structures of arabinogalactan fragments.
... The type II AGs which decorate AGPs are characterized by the presence of b-D-1,3-linked galactan backbones substituted with b-D-1,6-galactan side chains that are decorated further with L-arabinofuranosyl (L-Araf), and less often with L-rhamnosyl (l-Rhap), L-fucosyl (L-Fuc), D-Xyl, and D-glucuronosyl (D-GlcA with or without 4-O-methyl) (Fincher et al., 1983). The glycan structure and length (up to 120 sugar residues ranging from 5 to 25 kDa) vary depending on the developmental stage and tissue type (Tsumuraya et al., 1988), adding to the heterogeneity. ...
Arabinogalactan-proteins (AGPs) are hydroxyproline-rich glycoproteins containing a high sugar content and are widely distributed in the plant kingdom. AGPs have long been suggested to play important roles in sexual plant reproduction. The synthesis of their complex carbohydrates is initiated by a family of hydroxyproline galactosyltransferase (Hyp-GALT) enzymes which add the first galactose to Hyp residues in the protein backbone. Eight Hyp-GALT enzymes have been identified so far, and in the present work a mutant affecting five of these enzymes (galt2galt5galt7galt8galt9) was analyzed regarding the reproductive process. The
galt25789 mutant presented a low seed set, and reciprocal crosses indicated a significant female gametophytic contribution to this mutant phenotype. Mutant ovules revealed abnormal callose accumulation inside the embryo sac and integument defects at the micropylar region culminating in defects in pollen tube reception. In addition, immunolocalization and biochemical analyses allowed the detection of a reduction in the amount of glucuronic acid in mutant ovary AGPs. Dramatically low amounts of high-molecular-weight Hyp- O-glycosides obtained following size exclusion chromatography of base-hydrolyzed mutant AGPs compared to the wild type indicated the presence of underglycosylated AGPs in the galt25789 mutant, while the monosaccharide composition of these Hyp-O-glycosides displayed no significant changes compared to the wild-type Hyp-O-glycosides. The present work demonstrates the functional importance of the carbohydrate moieties of AGPs in ovule development and pollen–pistil interactions.
... The polysaccharide arabinogalactan is found as an essential structural polymer of the cell wall of plants and as a major component of many gums and exudates (Delgobo et al., 1998;Fincher et al., 1983). Several plants have been reported to contain polysaccharides of this type, and its presence has been correlated with a variety of biological activities such as antiviral, antitumour, immune-stimulating, anti-infl ammatory, anti-coagulant, hypoglycemic, and antiulcer (Capek et al., 2003;Nergard et al., 2005;Srivastava and Kulshreshtha, 1989;Yamada, 1994). ...
Type II arabinogalactan (AG) is a polysaccharide found in Maytenus ilicifolia (Celastraceae), a plant reputed as gastroprotective. Oral and intraperitoneal administration of the AG protected rats from gastric ulcers induced by ethanol. No alteration of mechanisms related to acid gastric secretion and gastrointestinal motility were observed. In vitro, the AG showed a potent scavenging activity against the radical of DPPH (2,2-diphenyl-1-picrylhydrazyl) with an IC50 value of 9.3 μM. However, the mechanism of the gastroprotective action remains to be identified.
... Type II AGs are generally found as carbohydrate moieties of arabinogalactan-proteins (AGPs) that are conserved extracellular glycoproteins in plants (Fincher et al., 1983;Seifert and Roberts, 2007;Ma et al., 2018). Type II AGs are necessary for AGP functions. ...
Arabinogalactan-proteins (AGPs) are mysterious extracellular glycoproteins in plants. Although AGPs are highly conserved, their molecular functions remain obscure. The physiological importance of AGPs has been extensively demonstrated with β-Yariv reagent, which specifically binds to AGPs and upon introduction into cells, causes various deleterious effects including growth inhibition and programmed cell death. However, structural features of AGPs that determine their functions have not been identified with β-Yariv reagent. It is known that AGPs are decorated with large type II arabinogalactans (AGs), which are necessary for their functions. Type II AGs consist of a β-1,3-galactan main chain and β-1,6-galactan side chains with auxiliary sugar residues such as L-arabinose and 4-O-methyl-glucuronic acid. While most side chains are short, long side chains such as β-1,6-galactohexaose (β-1,6-Gal6) also exist in type II AGs. To gain insight into the structures important for AGP functions, in vivo structural modification of β-1,6-galactan side chains was performed in Arabidopsis. We generated transgenic Arabidopsis plants expressing a fungal endo-β-1,6-galactanase, Tv6GAL, that degrades long side chains specifically under the control of dexamethasone (Dex). Two of 6 transgenic lines obtained showed more than 40 times activity of endo-β-1,6-galactanase when treated with Dex. Structural analysis indicated that long side chains such as β-1,6-Gal5 and β-1,6-Gal6 were significantly reduced compared to wild-type plants. Tv6GAL induction caused retarded growth of seedlings, which had a reduced amount of cellulose in cell walls. These results suggest that long β-1,6-galactan side chains are necessary for normal cellulose synthesis and/or deposition as their defect affects cell growth in plants.
... Around 90% of the proteins identified in maize RM of seedlings grown axenically were close homologues to the ones identified in pea, Arabidopsis and rapeseed mucilage (Ma et al. 2010). This suggests common biotic functions such as protection from fungal infections (Ma et al. 2010;Nazari et al. 2020) and abiotic functions such as water binding by arabinogalactan proteins (Fincher et al. 1983;Knee et al. 2001) also identified in maize RM (Bacic et al. 1986). Still, the question remains non-answered: despite their low concentration in mucilage, how do proteins affect mucilage physical properties? ...
Aims
High viscosity, low surface tension and hydrophobicity are specific properties of maize root mucilage which contribute to modulate the spatial configuration of the liquid phase in soil pores. Several processes in the rhizosphere, in particularly nutrient absorption, root exudation and microbial activity, may cause strong temporal variations in the chemistry of the soil solution of the rhizosphere. Although the physical properties of maize root mucilage have been repeatedly measured in the last years, their variation upon a changing chemical environment and understanding of the chemical mechanisms governing these properties remain unexplored.
Methods
We investigated how flow and surface properties of maize root mucilage varied by changes in pH, calcium chloride (CaCl2) and lecithin concentrations.
Results
The physical properties of mucilage can strongly vary depending on the environmental conditions. Low surface tension of maize root mucilage at pH7 was increased by addition of calcium. Upon pH change and lecithin addition, hydrophobic mucilage turned hydrophilic. High Ca concentration above 0.83 mmol Ca (g dry mucilage)⁻¹, the addition of 167 μg lecithin (g dry mucilage)⁻¹ and a pH rise to 9 decreased the viscosity of mucilage.
Conclusion
Such variations strongly suggest that the role of mucilage in hydraulic processes in the rhizosphere depends on changes of solutes concentration and composition, which themselves vary according to plant growth and soil water content. It seems that mucilage can best serve as a hydraulic bridge only under certain chemical environments, whose spatio-temporal occurrence in the changing rhizosphere remains to be defined.
... Plant-based diets are also rich in pectin and related glycans such as arabinan and arabinogalactan, which are particularly abundant in some fruits, berries, and processed foods like jams (Mohnen, 2008). Arabinogalactan is also found in the form of arabinogalactan proteins (AGPs) (Fincher et al., 1983), which are particularly enriched in red wine (Vidal et al., 2003), instant coffee (Capek et al., 2010), and natural gums used in food processing (Phillips, 1998;Atgié et al., 2019). Fungal biomass represents an additional nutrient source for diverse microbiota, and is arguably even more abundant and important in soils than gut systems. ...
The Bacteroidetes phylum is renowned for degradation of a wide range of complex carbohydrates, a trait that has enabled its dominance in many diverse environments. The best studied species inhabit the human gut microbiome and use Polysaccharide Utilisation Loci (PULs), discrete genetic structures that encode proteins involved in the sensing, binding, deconstruction, and import of target glycans. In many environmental species, polysaccharide degradation is tightly coupled to the phylum‐exclusive Type IX Secretion System (T9SS), which is used for the secretion of certain enzymes and is linked to gliding motility. In addition, within specific species these two adaptive systems (PULs and T9SS) are intertwined, with PUL‐encoded enzymes being secreted by the T9SS. Here, we discuss the most noteworthy PUL and non‐PUL mechanisms that confer specific and rapid polysaccharide degradation capabilities to the Bacteroidetes in a range of environments. We also acknowledge that literature showcasing examples of PULs is rapidly expanding and developing a set of assumptions can be hard to track back to original findings. Therefore, we present a simple universal description of conserved PUL functions and how they are determined, while proposing a common nomenclature describing PULs and their components, to simplify discussion and understanding of PUL systems. This article is protected by copyright. All rights reserved.
... The overall structure of AGPs is often consistent with the so-called wattle-blossom model, first proposed by Fincher, Stone, and Clarke (1983), where several Hyp residues bear AG substituents resulting in a spheroidal molecule. AGPs are involved in important processes like cell growth, cell proliferation, pattern formation and sexual reproduction (Seifert & Roberts, 2007), but functions of single AGPs are in most cases not identified and may also differ depending on tissue or developmental stage. ...
Arabinogalactan-proteins (AGPs), important signalling molecules of the plant cell wall, are structurally extensively investigated in angiosperms, but information on AGPs in gymnosperms is still limited. We characterized AGPs from the gymnosperms Ginkgo biloba, Ephedra distachya, Encephalartos longifolius and Cycas revoluta. The protein contents are comparable to that of angiosperm AGPs. Hydroxyproline is the site of linking the carbohydrate part and was detected in all AGPs with highest concentration in Cycas AGP (1.1 % of the AGP). Interestingly, with the exception of Cycas, all AGPs contained the monosaccharide 3-O-methylrhamnose not present in angiosperm polysaccharides. The carbohydrate moieties of Cycas and Ephredra showed the main components 1,3,6-linked galactose and terminal arabinose typical of angiosperm AGPs, whereas that of Ginkgo AGP was unique with 1,4-linked galactose as dominant structural element. Bioinformatic search for glycosyltransferases in Ginkgo genome also revealed a lower number of galactosyltransferases responsible for biosynthesis of the 1,3-Gal/1,6-Gal AGP backbone.
... Arabinogalactan-proteins (AGPs) are conserved extracellular proteoglycans consisting of a hydroxyproline-rich core-protein and a large portion of glycan moieties, called type II arabinogalactans (AGs) (Fincher et al. 1983;Majewska-Sawka and Nothnagel 2000;Seifert and Roberts 2007). As the Arabidopsis sos5/fla4 mutant with a defect in the core-protein gene exhibits a root swelling phenotype under salt stress, AGPs are presumed to participate in the regulation of cell shape (Shi et al. 2003). ...
Arabinogalactan-proteins (AGPs) are extracellular proteoglycans, which are presumed to participate in the regulation of cell shape, thus contributing to the excellent mechanical properties of plants. AGPs consist of a hydroxyproline-rich core-protein and large arabinogalactan (AG) sugar chains, called type II AGs. These AGs have a β-1,3-galactan backbone and β-1,6-galactan side chains, to which other sugars are attached. The structure of type II AG differs depending on source plant, tissue, and age. Type II AGs obtained from woody plants in large quantity as represented by gum arabic and larch AG, here designated gum arabic-subclass, have a β-1,3;1,6-galactan structure in which the β-1,3-galactan backbone is highly substituted with short β-1,6-galactan side chains. On the other hand, it is unclear whether type II AGs found as the glycan part of AGPs from herbaceous plants, here designated AGP-subclass, also have conserved β-1,3:1,6-galactan structural features. In the present study we explore similarities of type II AG structures in the AGP-subclass. Type II AGs in fractions obtained from spinach, broccoli, bok choy, komatsuna, and cucumber were hydrolyzed into galactose and β-1,6-galactooligosaccharides by specific enzymes. Based on the proportion of these sugars, the substitution ratio of the β-1,3-galactan backbone was calculated as 46–58% in the five vegetables, which is consistently lower than what is seen in gum arabic and larch AG. Although most side chains were short, long chains such as β-1,6-galactohexaose chains were also observed in these vegetables. The results suggest a conserved β-1,3;1,6-galactan structure in the AGP-subclass that distinguishes it from the gum arabic-subclass.
... (Family-Anacardiaceae). Cashew tree resin is synthesized in the epithelial cells lining pockets or canals and is then secreted into these internal cavities [86]. It can be used as a binding agent and suspending agent. ...
Background
Objective: Various natural gums can be synergistically used in nanoparticulate drug delivery systems to treat cardiovascular diseases. Nanotechnology has been integrated into healthcare in terms of theranostics. In this review, we consider various natural gums that can be used for the preparation of nanoparticles and their role to treat cardiovascular disease.
Methods
Nanoparticles can carry drugs at nanoscales and deliver them to the targeted sites with the desired pattern of drug release. They have specialized uptake mechanisms (e.g. - absorptive endocytosis) which improve the bioavailability of drugs.
Results
By considering cardiovascular diseases at the molecular level, it is possible to modify the materials with nanotechnology and apply nano-formulations efficiently as compared with conventional preparations, due to the fact that the extracellular matrix (ECM) comprises components at the nanoscale range. The interactions of ECM components with cellular components occur at the nanoscale, therefore the nanomaterials have the potential to maintain the nanoscale properties of cells. The synthetic materials used to develop the nanoparticulate drug delivery system may cause toxicity.
Conclusion
This problem can be overcome by using natural polymers. Natural gums can be used in nanoparticulate drug delivery systems as reducing and stabilizing agents and in some cases; they may directly or indirectly influence the rate of drug release and absorption from the preparation.
... [6,7] Unfortunately,t he compositiono ft he structurally microheterogeneous AG is very complex and difficult to analyse. [8,9] There is literature evidence that the allergy-protective activity of AG could originate from recognition of particular (terminal) arabinose containing epitopes by the immune system,s ince it is known that ac leavage of these significantly reduced the allergy-protective activity of the polysaccharide. [6] Moreover,i tw as shown in the same work that AG from other plants, namely Acacia or Larix, does not showa llergy-protective activity.T his is probablyb ased on ad iffering molecular structure, however,t he exact chemical structure of the different AG is unknown. ...
Arabinogalactan, a microheterogeneous polysaccharide occurring in plants, is known for its allergy‐protective activity, which could potentially be used for preventive allergy treatment. New treatment options are highly desirable, especially in a preventive manner, due to the constant rise of atopic diseases worldwide. The structural origin of the allergy‐protective activity of arabinogalactan is, however, still unclear and isolation of the polysaccharide is not feasible for pharmaceutical applications due to a variation of the activity of the natural product and contaminations with endotoxins. Therefore, a pentasaccharide partial structure was selected for total synthesis and subsequently coupled to a carrier protein to form a neoglycoconjugate. The allergy‐protective activity of arabinogalactan could be reproduced with the partial structure in subsequent in vivo experiments. This is the first example of a successful simplification of arabinogalactan with a single partial structure while retaining its allergy‐preventive potential.
Plant cell walls are complex, multifunctional structures, built up of polysaccharides and proteins. The configuration and abundance of cell wall constituents determine cellular elongation and plant growth. The emphasis of this review is on rice, a staple crop with economic importance, serving as model for grasses/cereals. Recent advancements have contributed to a better understanding of the grass/cereal cell wall. This review brings together current knowledge of the organization and metabolism of the rice cell wall, and addresses gaps in the information regarding the cell wall and enzymes involved. Several cell wall fractions, including cellulose, mixed-linkage glucans, and glucuronoarabinoxylans, are well understood in rice and other grasses/grains. Conversely, there are still open questions and missing links in relation to xyloglucans, glucomannans, pectin, lignin, and arabinogalactan proteins. There is still a large and untapped potential to identify carbohydrate-active enzymes (CAZymes), to characterize their activity, and to elucidate their involvement in the metabolism of the mentioned cell wall fractions. This review highlights the involvement of carbohydrate-active enzymes in rice cell wall metabolism, providing an update of current understanding with the aim of demarcating research areas with potential for further investigations.
The combined use of MALDI-MS and statistical analysis to study paint binders in artworks from ancient Egypt indicated that Vachellia species, most likely V. nilotica or V. tortilis , were used as a source of gums for paint binders.
Regio‐ and stereoselective formation of the 1,2‐ cis ‐furanosidic linkage has been in great demand for efficient synthesis of biologically active natural glycosides. In this study, we developed a regioselective and β‐stereospecific d ‐/ l ‐arabinofuranosylation promoted by a boronic acid catalyst under mild conditions. The glycosylations proceeded smoothly for a variety of diols, triols, and unprotected sugar acceptors to give the corresponding β‐arabinofuranosides (β‐Arb f ) in high yields with complete β‐stereoselectivity and high regioselectivity. The regioselectivity was completely reversed depending on the optical isomerism of the donor used and was predictable a priori using predictive models. Mechanistic studies based on DFT calculations revealed that the present glycosylation occurs through a highly dissociative concerted S N i mechanism. The usefulness of the glycosylation method was demonstrated by the chemical synthesis of trisaccharide structures of arabinogalactan fragments.
Highly stereoselective construction of 1,2-cis-Arap linkages has been achieved, which featured a broad range of alcoholic acceptors, including strong nucleophiles and complex bioactive molecules. This method was applied to a regioselective and orthogonal one-pot synthesis of a pentasaccharide, which was the structural motif of a side chain in type II arabinogalactan.
The aggregation in dry state of mineral-loaded arabinogalactan-proteins (AGPs) from Acacia seyal gum (GA) generally occurs above 70 °C. This study focuses on the aggregation sensitivity of AGPs after their demineralization. The dry incubation in mild temperature (25 °C to 70 °C) of demineralized AGPs induced the formation of aggregates, not observed with GA. AGPs aggregated following a self-assembly mechanism for which temperature only modulated the aggregation rate. The activation energy was around 90-100 kJ·mol-1 that could correspond to chemical condensation reactions induced by the AGPs surface dehydration. The aggregation kinetics were characterized by the formation of soluble aggregates during the first times of incubation, whose molar mass increased from 1 · 106 g·mol-1 to 6.7 · 106 g·mol-1 (SEC MALS) or 12 · 106 g·mol-1 (AF4 MALS) after 1.66 days of dry heating at 40 °C. These soluble aggregates revealed they adopted a similar conformation to that of not aggregated AGPs with a νh value around 0.45. Above 1.66 days at 40 °C, the soluble aggregates grew up to form microparticles with sizes ranging from 10 to around 200 μm. This study highlighted the protective role of cations from AGPs whose demineralization increased their sensibility to dry heating and their chemical reactivity for aggregation.
Background: This study aimed to explore the mechanism by which arabinogalactan (AG) inhibited N-acetyl-para-aminophenol (APAP)-induced acute liver injury in mice. The balance of the mouse intestinal flora and the relationship between AG treatment and the PI3K/AKT and NF-κB signaling pathways were evaluated to confirm a liver-gut interaction. Methods: Mice were administered 2 different doses of AG (150 or 300 mg/kg body weight) by gavage for 7 days and liver injury was induced by a single injection of APAP (250 mg/Kg). Hematoxylin-eosin staining, terminal deoxynucleotidyl transferase dUTP nick-end labeling, and Hoechst 33258 fluorescence staining of liver tissue were used to analyze liver damage. Western blots were used to evaluate expression of proteins related to PI3K/AKT and NF-κB signaling pathways, and changes in the hierarchical structure of the intestinal flora were determined. Results: AG pretreatment increased the proportion of Lactobacillus and decreased the abundance of species from norank_o_Clostridiaceae and Prevotella in mouse feces compared with APAP-only treated mice. The AG pretreatment reversed glutathione depletion and CYP2E1 overexpression, reduced the production of malondialdehyde and 4-hydroxynonenal, and decreased the levels of alanine aminotransferase, aspartate aminotransferase, tumor necrosis factor-α and interleukin-1β compared with the APAP-only treated mice. The levels of proteins related to the PI3K/AKT signaling pathway were similar between the AG and control groups. AG pretreatment significantly reduced APAP-induced hepatocyte apoptosis and necrosis and inflammatory infiltration into the liver. Conclusion: PI3K/AKT pathway-mediated BAX expression and the NF-κB signaling cascade were inhibited by AG. AG protected the intestinal flora composition, which subsequently suppressed oxidative stress in the liver, improved the inflammatory response, and reduced hepatocyte apoptosis and necrosis.
Gum Arabic (GA) is a polysaccharide widely used in industry as an emulsifier and encapsulating agent. Nevertheless, its physicochemical properties can be largely improved. The objective of this study was then to modify its structure to improve its functionalities or to provide new ones. To do so, a heterogeneous catalysis process using a laccase and a phenolic compound, curcumin, in aqueous solution was performed. The laccase allowed the oxidation of curcumin, which was then able to be grafted onto the polymer. Therefore, this environmentally friendly process allowed the modification of GA with curcumin oxidation products (OXP) by creating ester bonds between GA and OXP. The molecular mass of GA was largely increased after functionalization. This product contained two fractions of approximately ∼1.165 × 10⁸ g.mol⁻¹ and ∼5.057 × 10⁶ g.mol⁻¹. All these modifications impacted greatly the polymer properties such as its thermal behaviour, with a significant decrease of its glass transition, its hydrophilicity and its hygroscopicity. They also brought antioxidant properties to the modified GA. Moreover, the modification led interestingly to the spontaneous formation of spherical monodisperse micrometric particles in water.
In the present study, a water-soluble neutral polysaccharide (CAPW-1) with an average molecular weight of 64 kDa was purified from the root of Cynanchum atratum Bunge (Apocynaceae). The monosaccharide residue analysis revealed that CAPW-1 was composed of arabinose and galactose with a relative molar ratio of 7: 3. The backbone of CAPW-1 was consisted of 1,3-Galp and 1,3,6-Galp, the branches were attached to the O-6 of 1,3-Galp, and the side chains contained 1,6-Galp, 1,3,6-Galp, 1,5-linked, 1,3-linked, 1,3,5-linked, and terminal-Araf, which was attached to the O-3 of side 1,6-Galp. The bioactivity study indicated CAPW-1 could stimulate the proliferation of RAW264.7 cells and promote the secretion of nitric oxide (NO), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) with no cytotoxicity. The results suggested a potential application of CAPW-1 as an immunostimulant for the treatment of diseases such as infection and tumor.
The increased use of nanoparticles (NP) in different industries inevitably results in their release into the environment. In such conditions, plants come into direct contact with NP. Knowledge about the uptake of NP by plants and their effect on different developmental processes is still insufficient. Our studies concerned analyses of the changes in the chemical components of the cell walls of Hordeum vulgare L. roots that were grown in the presence of gold nanoparticles (AuNP). The analyses were performed using the immunohistological method and fluorescence microscopy. The obtained results indicate that AuNP with different surface charges affects the presence and distribution of selected pectic and arabinogalactan protein (AGP) epitopes in the walls of root cells.
The human gut microbiota (HGM) contributes to the physiology and health of its host. The health benefits provided by dietary manipulation of the HGM require knowledge of how glycans, the major nutrients available to this ecosystem, are metabolized. Arabinogalactan proteins (AGPs) are a ubiquitous feature of plant polysaccharides available to the HGM. Although the galactan backbone and galactooligosaccharide side chains of AGPs are conserved, the decorations of these structures are highly variable. Here, we tested the hypothesis that these variations in arabinogalactan decoration provide a selection mechanism for specific Bacteroides species within the HGM. The data showed that only a single bacterium, B. plebeius, grew on red wine AGP (Wi-AGP) and seaweed AGP (SW-AGP) in mono- or mixed culture. Wi-AGP thus acts as a privileged nutrient for a Bacteroides species within the HGM that utilizes marine and terrestrial plant glycans. The B. plebeius polysaccharide utilization loci (PULs) upregulated by AGPs encoded a polysaccharide lyase, located in the enzyme family GH145, which hydrolyzed Rha-Glc linkages in Wi-AGP. Further analysis of GH145 identified an enzyme with two active sites that displayed glycoside hydrolase and lyase activities, respectively, which conferred substrate flexibility for different AGPs. The AGP-degrading apparatus of B. plebeius also contained a sulfatase, BpS1_8, active on SW-AGP and Wi-AGP, which played a pivotal role in the utilization of these glycans by the bacterium. BpS1_8 enabled other Bacteroides species to access the sulfated AGPs, providing a route to introducing privileged nutrient utilization into probiotic and commensal organisms that could improve human health. IMPORTANCE Dietary manipulation of the HGM requires knowledge of how glycans available to this ecosystem are metabolized. The variable structures that decorate the core component of plant AGPs may influence their utilization by specific organisms within the HGM. Here, we evaluated the ability of Bacteroides species to utilize a marine and terrestrial AGP. The data showed that a single bacterium, B. plebeius, grew on Wi-AGP and SW-AGP in mono- or mixed culture. Wi-AGP is thus a privileged nutrient for a Bacteroides species that utilizes marine and terrestrial plant glycans. A key component of the AGP-degrading apparatus of B. plebeius is a sulfatase that conferred the ability of the bacterium to utilize these glycans. The enzyme enabled other Bacteroides species to access the sulfated AGPs, providing a route to introducing privileged nutrient utilization into probiotic and commensal organisms that could improve human health.
Arabinogalactan-proteins (AGPs) are highly glycosylated proteins (glycoproteins) found in the cell walls of plants. AGPs account for only a small portion of the cell wall, usually no more than 1% of dry mass of the primary wall. AGPs are members of the hydroxyproline-rich glycoprotein (HRGP) superfamily that represent a large and diverse group of glycosylated wall proteins. AGPs have attracted considerable attention due to their highly complex structures and potential roles in signalling. In addition, they have industrial and health applications due to their chemical/physical properties (water-holding, adhesion and emulsification). Glycosylation can account for more than 90% of the total mass. AGPs have been reported in a wide range of higher plants in seeds, roots, stems, leaves and inflorescences. They have also been reported in secretions of cell culture medium of root, leaf, endosperm and embryo tissues, and some exudate producing cell types such as stylar canal cells are capable of producing lavish amounts of AGPs.
The galactosyltransferases (GalTs) have been extensively studied in mammals where they are involved in the synthesis of both N ‐ and O ‐glycans on glycoproteins. In contrast, only a few studies have been published characterizing plant GalTs even though plants assemble many complex carbohydrates and glycoconjugates not found in other eukaryotes or bacteria, such as pectins, galactomannans, xyloglucans, arabinogalactan‐proteins (AGPs), proline‐rich proteins and extensins. Many enzymes characterized within family GT31 are mammalian and include the fringe proteins (GlcNAc‐β‐(1,3)‐Fuc), the chondroitin synthases (GlcUA‐β‐(1,3)‐GalNAc), and the β‐(1,3)‐GalTs. We attempted to categorize the putative β‐(1,3)‐GalTs and, where possible, we predicted their putative substrate specificity based on secondary structure and motifs shared with known β‐(1,3)‐GalTs. Ninety‐four plant sequences are assigned to CAZy family GT31, including 33 from Arabidopsis thaliana ( At ), and 39 from Oryza sativa ( Os ), but only one plant enzyme has as yet been biochemically characterized, At‐GalT1, which is involved in the production of the Lewis a structure of N ‐glycans (Gal β‐(1,3)‐GlcNAc). Phylogenetic analysis identified 11 distinct clades, of which 4 are plant‐specific. Clade 1 proteins contain the plant‐specific DUF604 domain. Clade 7 is defined by a galectin‐containing domain and both clades 7 and 10 contain GalT domains. The possible substrate specificity of these enzymes is predicted. Clade 11 proteins contain no obvious domains so no function can be assigned. Enzymes in clades 7 and 10 are speculated to be involved in the synthesis of both proteoglycans, such as AGPs, and N ‐glycans.
The sections in this article are
Introduction
Hydroxyproline‐Rich Glycoproteins ( HRGPs )
Glycine‐Rich Proteins ( GRPs )
Other Wall Proteins
Conclusion
Acknowledgements
Abstract: The glycosyltransferase 64 (GT64) family includes members from a diverse range of species including human, Xenopus and Drosophila as well as plant species including Arabidopsis, the moss Physcomitrella and poplar. The majority of the animal GT64 proteins are bimodular, consisting of an N-terminal GT47 domain linked to a GT64 domain. The animal GT64 domain has been found to have GlcNAc transferase activity and functions during heparan sulphate biosynthesis.
However, the biochemical activity of the plant GT64 proteins has yet to be established. Arabidopsis has three GT64 members which have been named ECTOPICALLY PARTING CELLS1 (EPC1), EPC-LIKE1 (EPC-L1) and EPC-LIKE2 (EPC-L2). The EPC1 and EPC-L1 proteins are comprised of a single GT64 domain whereas the EPC-L2 protein has an additional N-terminal domain which does not show homology to any other protein other than EPC-L2 homologues from other plants. Mutation of the Arabidopsis GT64 EPC1 results in a plant with severely reduced stature, demonstrating the importance of its function for normal plant development. Neutral sugar analysis of the epc1 cell wall shows a reduction in galactose but there is currently no enzymatic activity demonstrated to explain this
alteration. In contrast to EPC1, EPC-L2 is specifically expressed in reproductive tissues and mutations in the gene result in defects in pollen development, reduced seed formation and embryo abortions at the late globular stage.
Arabinogalactan proteins (AGPs) are important plant proteoglycans involved in many development processes. In roots, AGPs occur in the cell wall of root cells and root cap–derived cells as well as in the secreted mucilage. Detection, localization, and quantification techniques are therefore essential to unravel the AGP diversity of structures and functions. This chapter details root-adapted immunocytochemical methods using monoclonal antibodies, and a collection of biochemical analysis protocols using β-d-glucosyl Yariv reagent for comprehensive AGP characterization.
Arabinogalactan proteins are a diverse group of cell wall-associated proteoglycans. While structural and molecular genetic analyses have contributed to the emerging improved understanding of the wide-range of biological processes in which AGPs are implicated; the ability to detect, localize, and quantify them is fundamentally important. This chapter describes three methods: histological staining, radial gel diffusion, and colorimetric quantification, each of which utilize the ability of Yariv reagent to bind to AGPs.
Water- and alkali-soluble arabinoxylans from isolated wheat endosperm cell walls were examined by ammonium sulphate fractionation and gel-exclusion chromatography.
This chapter discusses the structure and function of plant glycoproteins. Glycoproteins are proteins that contain glycosidic substituents; a firm covalent attachment is present between sugars and protein. Glycoproteins are not the easiest molecules to purify and characterize partly because of variable glycosylation produced during or after their biosynthesis, and partly because the carbohydrate component often imparts anomalous properties to the protein. A given glycoprotein often exhibits varying degrees of glycosylation and microheterogeneity can appear chromatographically or electrophoretically as a puzzling collection of closely physically related peaks or bands but of uncertain affinity. Compositional heterogeneity implies that the composition of similar oligosaccharide units varies. This variation can occur at the periphery of the oligosaccharide or in the central region or core. Microheterogeneity can be because of the lack of glycosyltransferase specificity or it can result from tissue-specific glycosylation or artifactually by enzymatic attack during extraction or by chemical changes during extraction and purification procedures involving alkaline conditions.
It was recognized as early as the end of the last century that proteins (“Fermente”) extracted from the seeds of certain plants exhibit the unusual property of agglutinating animal erythrocytes. Extracts from the seeds of various plant species showed a high degree of specificity when the appropriate source of red blood cells was chosen. For instance, pea extract was very effective in agglutinating erythrocytes from rabbit but far less so with those from sheep or pigeon, whereas human red blood cells were strongly agglutinated by bean and more weakly by pea or lentil extracts (reviewed by Lis and Sharon 1981). The phenomenon was not understood until Sumner and Howell (1936) showed that a protein crystallized from the seeds of Canavalia ensiformis [concanavalin A (ConA) Table 1] was able to precipitate glycogen and starch out of solution and that agglutination of erythrocytes by the same protein was prevented by the presence of sucrose. Both findings taken together suggested that the agglutinins of plant origin (“phytohemagglutinins”) may exert their action by binding to sugar residues located at the erythrocyte surface. It became evident later that certain phytohemagglutinins exhibit ABO blood group specificity. For this reason Boyd and Shapleigh (1954) proposed the term “lectin” (lat. “legere” — to select, to pick out). As proteins or glycoproteins that exhibit hemagglutination activity can also be found in some animals and bacteria, the primary implication of “lectin” was broadened and this term is now in general use. Literature on lectins has increased so much in recent years that throughout this article citation must often be restricted to recent reviews or to the apparently most siginificant paper out of a series.
Morphogenetic machines perform according to preprogrammed design by assembling a vastly intricate pattern woven out of cell secretions. Thus eukaryotic cells, both plant and animal, embed themselves in a surprisingly similar extracellular matrix containing hydroxyproline-rich glycoproteins. Mention any other amino acid and the comparison would be trivial; but hydroxyproline occurs in few proteins, has no codon, and must be synthesized by post-translational modification of prolyl residues via prolyl hydroxylase, a remarkable enzyme catalyzing the direct fixation of molecular oxygen and a concomitant stoichiometric decarboxylation of α-ketoglutaric acid with ascorbic acid as a cofactor. Furthermore, hydroxyproline-rich glycoproteins have been with us virtually since the origin of the Chlamydomonas type where they comprise the major, if not the only component of a cellulose-free cell wall. Thus from an evolutionary point of view we can regard cell surface glycoproteins as exceedingly primitive features, probably first elaborated by wall-less Archaebacteria as cell surface protection (Lamport 1980). The role of plant cell wall proteins is less clear (Lamport 1965, 1970, 1977). This chapter will summarize recent results and major conclusions.
Glycoproteins are interesting molecules because they play important roles in morphogenesis. But glycoproteins are not always as sweet as their name sounds; they are often very slippery both conceptually and in experimenters’ hands. 33 We can if we wish wrestle with the problem of deciding between Eylar’s suggestion13 that sugar residues are the passport for secretion, and the proposal of Winterburn and Phelps50 that sugars are a code not for secretion per se but for topographical location of the “secreted” glycoproteins. Such unifying concepts are always good for a few years of controversy! In this chapter are presented several additional suggestions which may help in understanding the origin of the extracellular matrix in plants and animals.
Formation of a precisely organized, functional tissue or organ is the culmination of a complex series of specific cellular events, usually termed morphogenesis. These events involve several common types of cell behavior, notably movement, proliferation, shape change, recognition, and adhesion. At each stage of morphogenesis of an organ or tissue, the macromolecules present in the extracellular matrix or associated with the external cell surface are important in providing structural support for and environmental signals to the cells involved. These contributions in turn exert a considerable influence on the course of morphogenesis.
The distribution of arabinose-containing macromolecules in suspension-cultured tobacco cells was examined using sucrose density gradients. Exogenously applied 14Carabinose was scarcely converted into other sugars, and concentrated in the Golgi-rich fraction (1.15 g/cm 3) and then secreted to the cell wall. 14C-Arabinose was also incorporated in a lower sucrose density fraction (1.11 g/cm 3), which contains small vesicles presumably originated from the Golgi apparatus. The arabinose-containing macromolecules in this fraction was more easily solubilized in water than those in the Golgi-rich fraction. Alkaline hydrolysis of the macromolecules indicated that cell-wall glycoprotein is a major component of the macromolecules and that the degree of glycosylation is slightly greater in the lower density fractions than in the Golgi-rich fraction. Based on these results, a scheme is suggested in which the glycoproteins and polysaccharides are glycosylated in the Golgi apparatus and secreted to the cell wall via secretion vesicles in the low density fraction. The possibility of 14C-arabinose-containing macromolecules, in the early phase of synthesis, being a marker of the plant Golgi apparatus is also proposed.
The presence of a class of arabinogalactan proteins, known as β-lectins, as detected by their interaction with the Yariv antigen, has been extended from earlier work (Jermyn and Yeow 1975) to include a number of lower plants. A comparison is made of the amino acid and carbohydrate composition of β-lectins isolated from green leaves and seeds from a number of species. The protein content of the isolated β-lectins from leaves has a range of 3-8%, while those examined from seeds have a more variable protein content. The amino acid compositions of the β-lectins from both leaves and seeds are generally similar, usually with high levels of serine, glycine, alanine and hydroxyproline. The monosaccharide compositions are also similar with an overall range of galactose/arabinose values between 1.3 and 2.8. Trace amounts of fucose, rhamnose, mannose and xylose are often detected.
The β-lectins were localized in various tissues using the Yariv antigen as a histochemical reagent. Intense staining was observed within the secretory canals of both the stem and leaves of Hedera helix. However, the staining of the leaves and petioles of Zantedeschia and Alocasia species was mainly associated with the plasma membrane and the cell wall of the aerenchyma. Specific staining is also reported in the reproductive tissues of Gladiolus and the possible function of the β-lectins is these highly specialised tissues is discussed.
A flavonol glycoside has been isolated from aqueous extracts of the flowers of Dryandra praemorsa (Proteaceae) that inhibits the reaction between β-lectins and the Yariv 'artificial antigens'. The flavonol is myricetin; the sugars are galactose (~ 90 %) and glucose (~ 10 %). The material analyses as a myricetin hexoside monohydrate, thus appearing to be a mixture of two components that have not been separated. The optical rotation is consistent with a β-configuration; experiments with compounds of known structure show that inhibitory activity is characteristic of flavonols glycosylated in the 3-position. Hyperin (the 3-β-D-galactopyranoside of the pentahydroxyflavone, quercetin) and the related quercitrin and rutin are somewhat less inhibitory but can be used to demonstrate the general characteristics of the inhibition with compounds of known structure. The inhibitory material can be attached to agarose to give a column packing that shows some capacity to bind β-lectins.
The seeds of both angiosperms and gymnosperms (91 of 104 families tested) contain a specific glycoprotein lectin, which gel-diffusion experiments suggest to be widely present in plant tissues. This lectin will form an insoluble complex with tris-(4-glycosyloxyphenylazo)phloroglucinol where glycosyl = ß-D-gluco-, D-galacto-, D-xylo-, malto-, lacto- or cellobiopyranosyl. In legume seeds the major part of the lectin is concentrated in the intercellular spaces as distinct globular bodies. The purification and analysis of the glycoprotein from a selection of species is described. Both protein and carbohydrate composition show little variation over the range. Hydroxyproline and glucosamine are present and the major sugars are galactose and arabinose. From ultracentrifugation studies the weight-average molecular weight of the Brassica napus lectin is 126 000. Since the carbohydrate:protein ratio is c. 8: 1, the protein moiety has a molecular weight of approx. 15 000. The sole N-terminal amino acid detected in the very similar Allium porrum lectin is tyrosine, suggesting that a single type of peptide chain is present. Neither the function of the lectin nor the reasons for its extraordinary evolutionary stability are known.
Hydroxyproline is rapidly removed from the medium by suspension-cultured endosperm cells of ryegrass (Lolium multiflorum) in a process which exhibits Michaelis-Menten kinetics and is dependent on temperature and metabolic energy. Following uptake by the cells, hydroxyproline is rapidly converted to proline by a route which appears to be more direct than the pathways of hydroxyproline metabolism in mammalian and bacterial systems and which results in substantial conservation of the pyrrolidine ring. Four hours after providing the cells with 5.5 nM [3H]hydroxyproline, approximately 50% of the radioactivity is recovered as intracellular imino acids, intracellular protein and extracellular peptide material. The radioactivity is associated predominantly with proline and hydroxyproline residues.
In common with other plant and animal systems, hydroxyproline is not incorporated directly into protein. However, radioactivity originating in extracellular hydroxyproline is detected eventually in peptide linkage, where it appears first as peptidyl proline. In the extracellular fraction which contains arabinogalactan-protein, peptidyl proline is hydroxylated to form peptidyl hydroxyproline and, after 4 h, approximately 18% of the original 3H label is found in this fraction.
A soluble extract from purified cell walls of C. reinhardii has been separated by gel filtration into three fractions which together account for 94% of the cell wall. The major fraction (accounting for 70% of the extract) is a glycoprotein, with a molecular wt. in sodium perchlorate of 298,000, which can be split into 4 electrophoretically distinct species. It contains 35% protein with high levels of hydroxyproline, arabinose and galactose, and is capable of self assembly into crystalline structures identical to those found within the cell wall. The second fraction (25% of the extract) is a similar glycoprotein, but contains 24% protein, a higher proportion of mannose, and is incapable of self assembly. The third fraction (3-6% of the extract) is shown to be an adsorbed impurity from the growth medium used.
The biochemistry of cell-wall regeneration in protoplasts obtained from Vinca rosea L. (Catharanthus roseus (L.) G. Don) cells grown in suspension culture by isolating the regenerated wall and the extracellular polysaccharides of protoplasts cultured for various periods, and investigating their composition. Gas-liquid chromatography and tracer studies with D-[U-(14)C]glucose showed that the sugar composition of the extracellular polysaccharides was similar to that of the original cell culture, consisting mainly of polyuronide and 3,6-linked arabinogalactan. the regenerated cell wall was composed of non-cellulosic glucans having 1,3- and 1,4-linkages, while its content in pectic and hemicellulosic components was very low.
The arabinosylation patterns of wall-bound hydroxyproline in Phaseolus vulgaris L. cell suspension cultures were determined by separating free hydroxyproline and hydroxyproline-arabinose oligomers over a Bio-Gel P-2 column. Total hydroxyproline accounted for about 3.3% of wall dry weight during all growth phases of batch-cultured bean cells. The chemical arabinosylation patterns of wall-bound hydroxyproline varied during the lag phase and early log phase of the culture. First, an increase in nonglycosylated hydroxyproline occurred accompanied by a corresponding decrease in hydroxyproline tetra-arabinoside. During the early log phase the reverse happened. In later stages of growth the chemical arabinosylation patterns remained constant. The radiochemical arabinosylation patterns were also determined, after pulselabeling the cultures with [(14)C]proline at various times during growth, to be able to distinguish recently incorporated hydroxyproline. The time course of the arabinosylation pattern of this fraction indicated that the initial changes in the chemical pattern were due to the temporary incorporation of less extensively glycosylated hydroxyproline-containing protein into the cell wall.
The major structural glycoprotein of the cell wall of Chlamydomonas reinhardii has a protein core, at least 50% of which is in the unusual polyproline II conformation. This has been demonstrated by examining the circular dichroism of the cell wall, its constituent glycoproteins, and thermolysin released wall glycopeptides. One of these glycopeptides, T2, has a high hydroxyproline and sugar content, and possesses upward of 85% polyproline II structure. The main extracellular matrix glycoprotein therefore has a rigid, rod-like structure and the significance of this and its relation to higher plant cell wall glycoproteins is discussed. The unusual conformation appears to confer great stability on the glycoprotein as it is unchanged either by certain denaturing agents or during the transition from protomer to assembled cell wall.
An enzymatic method is described for the preparation of viable and stable protoplasts from cell suspension cultures of Lolium endosperm. A new purification method was developed using a conjugate of Sepharose 4B and the mouse myeloma protein J539 (an anti-galactan agglutinin). The particulate contaminants bound to Sepharose-J539 forming large aggregates which could be separated from the protoplast suspension by simple filtration.
Carbohydrate-containing polymers have been extracted with water from the fleshy, lobed stems of Opuntia ficus-indica cv “Burbank's Spineless”. By ion exchange chromatography, the material was separated into one neutral and two acidic fractions. Each fraction was separated in two by gel filtration. The neutral fractions consisted of two glucans and a glycoprotein, containing arabinose and galactose. All four acidic fractions contained galacturonic acid, arabinose, rhamnose, galactose and xylose in different proportions. The cell wall structure of O. ficus-indica is discussed.
An analytical study has been made of gum specimens from Acacia hebeclada, A. kirkii, A. newbrownii and A. reficiens (all of the series Gummiferae) and of Acacia erubescens, A.fleckii, A. mellifera ssp. mellifera and A. mellifera ssp. detinens (all of the series Vulgares). The data obtained give further support for the main chemotaxonomic differences between the Gummiferae and Vulgares species recorded previously. In addition, two of the species studied have exceptional features; the gum exudate from A. hebeclada contains 9.4% of nitrogen; that from A. erubescens contains 12% of glucose.
The gum polysaccharides from two species of Prosopis, namely, P. glandulosa and P. chilensis, growing in different locations in South Africa, have been found to have similar structural features, closely resembling those reported in the literature for the gum of the North American species P.juliflora (mesquite). On smith degradation, both of the gums examined in the present study yielded a single polysaccharide product, having molecular weight 6,000, a value also found for the corresponding products from several Acacia species. Successive, Smith degradations of the polysaccharide produced by a sample of P. glandulosahave shown that a simple, (1-→3)-linked d-galactan is obtained after only two such degradations. This suggests the presence of uniform blocks of (1→3)-linked d-galactopyranosyl residues in the skeletal chain of the gum polysaccharide similar to those postulated for gums fromAcacia species.
The behavior of the polysaccharide gum of Acacia elata on acid hydrolysis has been studied by gel chromatography. The changes in the clution pattern and weight-average molecular weight as hydrolysis progresses resemble those found on hydrolysis of the structurally similar polysaccharide of A. Podalyriaefolia gum. The molecular weights corresponding to several persistent peaks in the elution patterns of the hydrolyzates approximate closely to values predicted for the products obtained on complete hydrolysis of peripheral arabinofuranoside and rhamnopyranoside linkages, and subsequent preferential removal of galactopyranose end-groups, from the various components of the polymolecular gum. The hydrolysis rate-constant, which decreases continuously with increasing degree of depolymerization under given conditions, approaches the value for 6-O-β-D-galactopyranosyl-D-galactose in 50nM sulfuric acid when hydrolysis of the gum in this acid is almost complete.
The purified, gum exudate from Chorisia speciosa (Palo borracho) was studied. It contains, in moles per mole, l-arabinose, ∼1; l-rhamnose, 2; d-mannose, 1; d-galactose, 8; and d-glucuronic acid, 3; and a trace of d-xylose. The results from methylation analysis and selective, alkaline degradation, combined with the characterization of the oligosaccharides resulting from partial hydrolysis with acid, made possible the assignment of a tentative “average structure”.
A water-soluble arabinogalactan-peptide from wheat endosperm was degraded by treatment with mild acid, alkali and enzymes. 4-Hydroxyproline-galactoside was isolated from the degradation products and was shown to be identical with synthetic trans-4-hydroxyproline-β-d-galactopyranoside. This linkage compound connects the arabinogalactan side chains to the peptide core in the arabinogalactan-peptide. A possible structural model for this glycoprotein is discussed.
Turnover of cell wall components was examined in two growth phases of a batch suspension culture of Vinca rosea L. Three-day-cultured cells (cell division phase) and 5-day-cultured cells (cell expansion phase) were incubated with d-[U-14C]glucose. After various periods of incubation, extra-cellular polysaccharides (ECP) and cell walls were isolated, and then the cell walls were fractionated to pectic substance, hemicellulose, and cellulose fractions. The results of the measurement of radioactivities and amounts of total carbohydrate in the ECP and cell wall fractions indicated that synthesis of pectic substance was more active in the cell division phase than in the cell expansion phase. From the results of the pulse-chase experiments, in which cells prelabelled by incubation with d-[U-14C]glucose for 3 h were incubated in a medium containing unlabelled glucose for various periods, the gross degradation, net synthesis, and gross synthesis of cell wall components were estimated. Active degradation and synthesis were observed in the hemicellulose fraction, indicating that active turnover occurred in the hemicellulose fraction, while little degradation was found in the pectic substance and cellulose fractions.
The water-soluble glycoproteins obtained from Cannabis leaves of plants grown from South African seeds have been further studied. Treatment of the glycoprotein fractions with NaOH in the presence of NaBH4, resulted in a significant decrease in the serine content and a corresponding increase in alanine. The carbohydrate side chains released contained the sugar alcohol, galactitol. By treatment of the glycoprotein fractions with NaOH in the presence of Na2SO3, and subsequent acid hydrolysis, cysteic acid was formed. These data indicate that carbohydrate and protein are connected via serine-O-galactoside linkages. Further investigation of the structure of the carbohydrate part of the glycoproteins was carried out by methylation analysis, Smith-degradation and enzyme incubation. The present glycoprotein material of plants grown from South African seeds is similar to the material previously investigated, but in contrast to the latter, it is devoid of hexosamine.
Hydroxyproline occurs in many plant proteins and is especially abundant in the proteins associated with the primary cell wall. In vivo evidence indicates that the synthesis of peptidyl hydroxyproline occurs by the hydroxylation of peptidyl proline. We have shown that plant cells contain an enzyme which catalyzes this hydroxylation reaction. The hydroxylase has the following characteristics: it requires O2, Fe2+, ascorbate and an α-keto acid for activity; it does not react with free proline; it is localized in the soluble cytoplasm; it readily hydroxylates prolyl residues of protocollagen isolated from chick embryos. A partial purification of the enzyme was achieved by the use of (NH4)2SO4 and Ca3(PO4)2 gel fractionations.
Autohydrolysis of an aqueous solution of purified, exudate gum from Spondias dulcis trees yielded a degraded gum containing d-galactose, l-arabinose, and d-galacturonic acid in the mole ratios of 3:3:1. Methylation studies were conducted on the degraded gum and its carboxyl-reduced derivative. Three neutral and three acidic oligosaccharides were obtained on graded hydrolysis of the degraded gum, and these were characterized. Based on the results, a tentative structure was proposed for the repeating unit in the polysaccharide. The results of periodate oxidation supported the structure assigned. The anomeric configurations of the sugar residues were determined by studies of oxidation with chromium trioxide.
Purified, exudate gum from the bael (Aegle marmelos) tree contains d-galactose, l-rhamnose, l-arabinose, and d-glucuronic acid in the molar ratios of ∼9:3:1:3. Degraded gum was prepared by autohydrolysis in its aqueous solution at 100°. Methylation analyses were conducted on the degraded gum, the whole gum, and the carboxyl-reduced, whole gum, and the results were corroborated by those from periodate oxidation followed by Smith degradation. The anomeric configurations of the different sugar residues in the whole-gum polysaccharide were determined by chromium trioxide oxidation of the acetylated polysaccharide. Finally, the oligo-saccharides obtained by autohydrolysis of the whole gum, and by graded hydrolysis of the degraded gum, were characterized. From these results, a tentative structure was assigned to the average repeating-unit in the polysaccharide.
C14-proline is readily absorbed by growing tissue cultures of carrot root phloem and of potato tuber in experiments carried out
under aseptic conditions. The C14-proline rapidly enters into the protein of the tissue, appearing there in as short a period as 15 minutes, and, thereafter,
the amount incorporated into the protein bears a linear relation to time. Virtually all the C14 appears in the protein hydrolysate in the form of proline and hydroxyproline. It is shown that the conversion from proline
to hydroxyproline occurs after the C14-proline is combined into the protein and that this conversion proceeds progressively with time. The ratio of C14 as proline to C14 as hydroxyproline declined progressively from a value of 4.0 after 30 minutes of contact and seemed to become stabilized
eventually at 0.7. C14-hydroxyproline, which can be absorbed by the tissue, seems not to be incorporated into the protein as such. The protein moiety which contains the C14-hydroxyproline from C14-proline represents a stable protein which is not metabolized and whose carbon does not ‘turn over’. This inert protein seems
to be characteristic of cells which are in rapid division under the influence of coconut milk or are synthesizing protein
in response to other stimuli such as the events at a cut tissue surface. The protein in question seems to be present mainly
in the cytoplasm rather than in its paniculate inclusions. These results are compatible with earlier views which require that
part of the protein in the cell ‘turns over’ its carbon, whereas another part does not do so.
An extracellular arabinogalactan-protein was obtained from suspension-cultured tobacco cells. It seemed to be a homogeneous preparation from the results of gel-filtration, ultracentrifugation and disc gel electrophoresis. Its MW was estimated to be 2.24 × 105 and its sedimentation coefficient (S20,w) was calculated to be 5.07 S. It consisted of arabinose (40.0%), galactose (36.2%), rhamnose (0.8 %), glucuronic acid (10.0 %), glucosamine (0.2 %), galactosamine (0.1%) and protein (5.5 %). The sugar moiety appeared to be a typical arabino-3,6-galactan. A d-glucuronic acid residue was present as the non-reducing terminal group and was attached to C(O)-6 of a d-galactosyl residue by β-linkage.
Classical methods of polysaccharide characterization are often inadequate for the evaluation of the number and nature of sugar residues associated with side-branches. This investigation demonstrates that controlled, alkaline degradation may be used to eliminate the backbone of the molecule and to convert branches linked through position 6 of the backbone into individual entities containing saccharinic acid end-groups. Application of alkaline degradation to an arabinogalactan revealed that arabinose residues are present not only in the branches but also in the backbone of the molecule. Furthermore it has been shown that, in addition to single-unit and two-unit branches, a few branches contain as many as ten residues.
Lipid intermediates, or lipid-linked saccharides, were first discovered in bacteria where they were shown to be involved in the biosynthesis of cell wall polymers such as peptidoglycan, lipopolysaccharide, teichoic acid and capsular polysaccharides (Osborn 1969, Hemming 1974). Those studies set the stage for later experiments in eukaryotic systems which also showed the synthesis and utilization of similar types of lipid intermediates in the biosynthesis of complex carbohydrates (Waechter and Lennarz 1976). In this chapter, the lipid intermediates that have been identified in higher plants will be discussed and their role in biosynthetic reactions will be considered. The plant systems will be compared to those studies that have been done in animal and yeast systems. Figure 1 outlines a series of reactions that have been proposed to account for the formation of the lipid-linked oligosaccharide that serves as the final donor in the glycosylation of protein. These reactions are considered in detail in the ensuing pages.
Gum arabic was found to have an osmotic molecular weight of 250,000, in agreement with earlier determinations. A molecular weight of 365,000 was found by light scattering, somewhat higher than obtained earlier by sedimentation equilibrium analysis but lower than light-scattering values reported by other investigators. The M̄w/Mn ratio, 1.46, is quite low in gum arabic. The angular dependence of light scattering exhibited the upward curvature to be expected of a spherical molecule and a radius of gyration of about 100 A. or less, as estimated from a Zimm plot. Fractionation of the original gum arabic was done by precipitation of a 0.5% solution in aqueous 0.5% NaCl with acetone. Comparison of the curves of viscosity versus molecular weight and the estimated radius of gyration shows that the hydrodynamic volume is less than that of branched dextran of similar molecular weight. The electroviscous effects for gum arabic in aqueous solution were shown by reduced viscosity curves at various acidities and in salt. The degree of dissociation was calculated for each pH level. The minimum intrinsic viscosity was found in 0.04N HCl where the degree of dissociation at pH 1.5 was found to be 0.049. When the acidity was increased, further reduction in viscosity was found to be negligible. Routine determination of the viscosity and molecular weight of the fractions was done in 0.35M NaCl at pH 10 to which 0.25% of the sodium salt of ethylenediaminetetraacetic acid was added as a sequestrant. The intrinsic viscosity in this solvent was nearly as low as in 0.04N HCl. Light-scattering dissymmetries in water and in 0.35M NaCl plus EDTA at pH 10 were similar, 1.13 and 1.09, respectively, which showed that actual expansion of the macroion is not the cause of the large increase in viscosity of gum arabic when the ionic strength of the solvent is reduced. Periodate oxidation of the polymer confirmed the existence of a 1–3-linked backbone of galactose. Subsequent treatment of the oxidized polymer with alkali reduced the osmotic molecular weight to 45,000 but failed to remove oxidized side branches. The oxidized polymer was fractionated by gel permeation chromatography and the intrinsie viscosity–molecular weight relation compared with relations for fractions of the unoxidized polymer and for other branched and crosslinked polymers.
The occurrence, isolation, chemistry and physico-chemistry of plant arabino-3,6-galactans and arabino-3,6-galactan-proteins is reviewed. The structural relationships between arabino-3,6-galactans from gymnosperm wood, gum exudates of Acacia and other trees, and from plant callus cells and whole tissues are discussed. The nature of these proteoglycans is compared with the arabinose and galactose containing cell wall glycoproteins. Interactions of the arabino-3,6-galactan proteoglycans with carbohydrate binding proteins and with Yariv antigens are described. The utility of these reactions for both cellular and subcellular localization of the proteoglycans is discussed. The possible biological roles of the arabinogalactans and the arabinogalactan-proteins are reviewed.
Arabinogalactans are present in extracts of the sexual and somatic tissues of two monocotyledons, Gladiolus and Lilium. The arabinogalactans precipitated from plant extracts by the β-glucosyl artificial antigen (Yariv antigen) show differences in the proportions of the major monosaccharides, galactose and arabinose. Gladiolus stigma and style preparations contain a single arabinogalactan component, but the other tissues examined contained at least two distinct groups of arabinogalactans. These groups can be separated electrophoretically or by lectin affinity chromatography.
Analytical data are presented for gum specimens from Grevillea agrifolia, G. candelabroides, G. robusta, G. striata, and G. wickhamii (two specimens), and brief botanical details of this large, complex genus are given. The gum exudates, which are of high molecular weight, show good solubility and give solutions that are much more viscous than any of the Acacia exudates studied so far; they may therefore be of industrial interest.
Fractionation of the cell wall material of parenchyma of mature runner beans with and without chlorite-HOAc treatment, clearly showed that at least two main types of wall proteins were present. One relatively rich in hydroxyproline (HP) associated with α′-cellulose, from which most (90%) of it could be readily liberated by chlorite-HOAc treatment and the other relatively poor in HP associated with hemicellulose A. The chlorite HOAC solubilized “glycoprotein” contained a high proportion of arabinose and galactose. It was purified by PhOH-H2O fractionation and the molar ratios of HP, arabinose, galactose, xylose, rhamnose, glucose and uronic acid in the purified glycoprotein (“glycoprotein X”) were 1:2·6:2·4:0·2:0·2:0·1:0·3. The principal amino acids of glycoprotein X were HP (43·5 mol%), serine and proline which together comprised 66 mol% of the total. These results suggest that the HP-rich wall glycoprotein is associated with cellulose microfibrils and approximates in conformation to polyhydroxyproline carrying arabinose and galactose oligosaccharide side chains.
Glycoproteins were extracted with water from leaves of Cannabis sativa grown from seeds of Thailand origin. By ion exchange chromatography the material was separated into a neutral and an acidic fraction. Both glycoprotein fractions contained arabinose, galactose, glucose, mannose and xylose, and in addition rhamnose and galacturonic acid were present in the acidic fraction. The carbohydrate moieties were investigated by methylation analysis and Smith-degradation, whereas the glycopeptide linkage was studied by alkaline hydrolysis in the presence of NaBH4 and Na2SO3, respectively. This linkage was shown to be of the serine-O-galactoside type. The carbohydrate structure is highly branched, the majority of branches terminating in arabinofuranose end groups. Arabinose is also present in the chain, predominantly (1 → 4)- and/or (1 → 5)-linked. Galactose makes up most of the main chain as (1 → 3)-linked residues but also constitutes end groups and branch points, as do mannose and/or glucose. Xylose and rhamnose are present as (1 → 4)- and (1 → 2)-linked units, respectively. Galacturonic acid is assumed to be (1 → 4)- linked with some branching at 3 position. The amino acid hydroxyproline, present in the glycoprotein of South African Cannabis leaves, was absent in the corresponding Thailand material.