[Show abstract][Hide abstract] ABSTRACT: We explored the behavior and the characteristics of xyloglucan polysaccharide chains extracted from tamarind seeds in aqueous media. The initial solubilization is achieved by using a 0.01 M NaOH solution. The absence of compact aggregates in the solution and the average molecular mass of the individual chains were unambiguously demonstrated by size exclusion chromatography with multi-angle light scattering detection. The composition and the stability of the solution were quantitatively checked over weeks by using liquid state nuclear magnetic resonance with DMSO as internal standard. The conformational characteristics of the chains were measured using nondestructive small-angle neutron scattering (SANS). The unambiguous determination of the Flory exponent (ν = 0.588) by SANS enabled us to directly prove that xyloglucan chains in water behave like semiflexible worm-like chains with excluded volume statistics (good solvent), contrary to most of the neutral water-soluble polymer chains that rather exhibit Gaussian statistics (θ-solvent). In addition to the Flory exponent, the persistence length l(p) and the cross section of the chains were also determined by SANS with utmost precision, with values of 80 and of 7 Å, respectively, which provides a complete description of the conformational characteristics of XG chains at all relevant length scales.
[Show abstract][Hide abstract] ABSTRACT: We report a study of xyloglucan (XG)-cellulose interactions made possible by the preparation of various well-defined cellulosic and xyloglucosidic substrates. Bacterial microcrystalline cellulose (BMCC) as well as cellulose whiskers (CellWhisk) were used as cellulosic substrates. Xyloglucosidic substrates were obtained from Rubus cells and Tamarindus indica seeds. Different primary structure characteristics of XGs such as the backbone length and the nature of the side chains, as well as their repartition, were considered in order to examine the influence of the primary structure on their interaction capacity. Two complementary approaches were carried out: first, the determination of adsorption isotherms and its associated models, and second, an enthalpic study using isothermal titration calorimetry (ITC). This study highlighted that an increase of XG interaction capacity occurred with increasing XG molecular weight. Furthermore, we determined that a minimum of 12 glucosyl residues on the backbone is required to observe significant interactions. Moreover, both the presence of trisaccharidic side chains with fucosyl residues and an increase of unsubstituted glucosyl residues enhanced XG-cellulose interactions. The evolution of adsorption isotherms with temperature and ITC measurements showed that two different processes were occurring, one exothermic and one endothermic, respectively. Although the presence of an exothermic interaction mechanism has long been established, the presence of an endothermic interaction mechanism has never been reported.
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to assess the exopolysaccharide (EPS) production capacities of various strains of Oenococcus oeni, including malolactic starters and strains recently isolated from wine.
Fourteen O. oeni strains displaying or not (PCR check on genomic DNA) the gtf gene generally associated with beta-glucan formation and ropiness were grown on grape juice medium, dialysed MRS-derived medium or synthetic medium. The soluble polysaccharides (PS) remaining in the culture supernatant were alcohol precipitated, and their concentration was quantified by the phenol-sulfuric method. Most of the O. oeni strains studied produced significant amounts of EPS, independently of their genotype (gtf+ or gtf-). The EPS production was not directly connected with growth and could be stimulated by changing the growth medium composition. The molecular weight distribution analysis and attempts to determine the PS chemical structure suggested that most strains produce a mixture of EPS.
Oenococcus oeni strains recently isolated from wine or cultivated for many generations as a malolactic starter are able to produce EPS other than beta-glucan.
These EPS may enhance the bacteria survival in wine (advantage for malolactic starters) and may contribute to the wine colloidal equilibrium.
[Show abstract][Hide abstract] ABSTRACT: In this study, contributions of hemicellulose, cellulose and lignin to the mass and the porous properties of chars and activated carbons from various lignocellulosic materials were studied. A predictive calculation was established using the experimental results obtained for the three components separately to evaluate the carbonization and activation yields and their respective contributions to the chars and to the subsequent activated carbons of various precursors in term of weight fraction. These equations were validated. The results showed that lignin can be considering as being the major contributor of all chars and activated carbons. Besides, the evolution of the mean pore size versus the specific porous volume showed that each component contributes to the porosity of chars and activated carbons whatever is its weight contribution.
[Show abstract][Hide abstract] ABSTRACT: Layer-by-layer assembly was used to build thin films, consisting of multiple layers alternating cellulose nanocrystals and xyloglucan, benefiting from the strong non-electrostatic cellulose-xyloglucan interaction. Data from atomic force microscopy and neutron reflectivity showed that these well-defined films exhibited a thickness increasing linearly with the number of layers, without increase in surface roughness. These "green" nanocomposite films, reminiscent of plant cell wall, are composed of a regular stack of single layers of cellulose nanocrystals separated by very thin xyloglucan spacers. Such architecture differs from the one formed by cellulose/polycations multilayers, where the cellulose phase itself consists of a double layer.
[Show abstract][Hide abstract] ABSTRACT: The development of therapeutic agents inhibiting the activity of glucosyltransferases (GTF) and their production of glucans is a potential strategy to reduce dental decay. The aim of this study was first to characterize a GTF preparation from Streptococcus sobrinus ATCC 33478 and then to evaluate the effects of select compounds and mouthrinses on insoluble glucan (ISG) formation by combined GTFs.
The purity of the crude GTF mixture was assessed by electrophoresis. The effects of pH, temperature, sucrose, and dextran T10 concentrations on GTF activity were analyzed and the chemical structure of the products was investigated. Finally, the inhibition of GTF by commercial mouthrinses used in oral hygiene and their active components (chlorhexidine, polyphenolic compounds, fluoride derivatives, polyols, cetylpyridinium chloride, and povidone iodine) was analyzed through the reductions in the overall reaction rate and the quantity of ISG synthesized.
The S. sobrinus ATCC 33478 crude GTF preparation obtained contains a mixture of four different GTFs known for this species. For optimal adherent ISG formation, the reaction parameters were 37 degrees C, pH 6.5, sucrose 50 g/l, and dextran T10 2 g/l. Under these conditions, the most effective agents were chlorhexidine, cetylpyridinium chloride, and tannic acid. Eludril, Elmex, and Betadine were the most effective inhibitors of all the mouthrinses tested.
As the formulation of commercial products considerably influences the efficiency of active components, the fast representative ISG inhibition test developed in this study should be of great interest.
[Show abstract][Hide abstract] ABSTRACT: alpha1,2-linked fucose can be found on xyloglucans which are the main hemicellulose compounds of dicotyledons. The fucosylated nonasaccharide XXFG derived from xyloglucans plays a role in cell signaling and is active at nanomolar concentrations. The plant enzyme acting on this alpha1,2-linked fucose residues has been previously called fucosidase II; here we report on the molecular identification of a gene from Arabidopsis thaliana (At4g34260 hereby designed AtFuc95A) encoding this enzyme. Analysis of the predicted protein composed of 843 amino acids shows that the enzyme belongs to the glycoside hydrolase family 95 and has homologous sequences in different monocotyledons and dicotyledons. The enzyme was expressed recombinantly in Nicotiana bentamiana, a band was visible by Coomassie blue staining and its identity with the alpha1,2-fucosidase was assessed by an antibody raised against a peptide from this enzyme as well as by peptide-mass mapping. The recombinant AtFuc95A is active towards 2-fucosyllactose with a Km of 0.65 mM, a specific activity of 110 mU/mg and a pH optimum of 5 but does not cleave alpha1,3, alpha1,4 or alpha1,6-fucose containing oligosaccharides and p-nitrophenyl-fucose. The recombinant enzyme is able to convert the xyloglucan fragment XXFG to XXLG, and is also active against xyloglucan polymers with a Km value for fucose residues of 1.5mM and a specific activity of 36 mU/mg. It is proposed that the AtFuc95A gene has a role in xyloglucan metabolism.
[Show abstract][Hide abstract] ABSTRACT: "Ropiness" is a bacterial alteration in wines, beers, and ciders, caused by beta-glucan-synthesizing pediococci. A single glucosyltransferase, Gtf, controls ropy polysaccharide synthesis. In this study, we show that the corresponding gtf gene is also present on the chromosomes of several strains of Oenococcus oeni isolated from nonropy wines. gtf is surrounded by mobile elements that may be implicated in its integration into the chromosome of O. oeni. gtf is expressed in all the gtf(+) strains, and beta-glucan is detected in the majority of these strains. Part of this beta-glucan accumulates around the cells forming a capsule, while the other part is liberated into the medium together with heteropolysaccharides. Most of the time, this polymer excretion does not lead to ropiness in a model medium. In addition, we show that wild or recombinant bacterial strains harboring a functional gtf gene (gtf(+)) are more resistant to several stresses occurring in wine (alcohol, pH, and SO(2)) and exhibit increased adhesion capacities compared to their gtf mutant variants.
[Show abstract][Hide abstract] ABSTRACT: The substrate specificity of an arabinofuranosidase (AbfD3) from family 51 of glycoside hydrolase classification was investigated in order to precisely evaluate its catalytic abilities. AbfD3 activity on destarched wheat bran was poor and less than 1% of total arabinose was released. AbfD3 was also tested on arabinoxylans derived from destarched wheat bran that present different degrees of polymerization, A/X ratios, ferulic acid content and solubility. Results indicated that AbfD3 can hydrolyze polymeric arabinoxylans, even if this action was moderate when compared to the efficient hydrolysis of oligosaccharides. The limited action of AbfD3 on polymeric arabinoxylans is discussed with regard to the heterogeneous distribution of the arabinose residues along the xylan main chain, the insolubility of arabinoxylans and to the presence of disubstituted xylose or feruloylated arabinose.
[Show abstract][Hide abstract] ABSTRACT: Structural and physicochemical characteristics of mesquite gum (from Prosopis velutina) were investigated using FT-IR spectroscopic, mass spectrometric and chromatographic methods. Four fractions (F-I, F-IIa, F-IIb and F-III) were isolated by hydrophobic interaction chromatography. The samples were characterized and analyzed for their monosaccharide and oligomers composition by high performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). L-Arabinose (L-Ara) and D-galactose (D-Gal) were found as the main carbohydrate constituent residues in the polysaccharides from mesquite gum and their ratio (L-Ara/D-Gal) varied within the range 2.54 to 3.06 among the various fractions. Small amounts of D-glucose (D-Glc), D-mannose (D-Man) and D-xylose (D-Xyl) were also detected, particularly in Fractions IIa, IIb and III. Infrared spectroscopy identified polysaccharides and protein in all the samples. Data from mass spectrometry (MALDI-TOF MS) was consistent with the idea that the structure corresponding to the periphereal chains of Fraction I is predominantly a chain of pentoses attached to uronic acid.
[Show abstract][Hide abstract] ABSTRACT: The polysaccharide content of wine is generally assumed to originate from grapes and yeasts, independent of bacterial metabolism, except for the action of certain spoilage species. This study shows that malolactic fermentation (MLF) significantly modifies the soluble polysaccharide (SP) concentration of various red Bordeaux wines. Wines with the highest initial SP concentration go on to present decreased SP concentration, whereas those with the lowest initial SP concentration rather go on to have a higher SP concentration after MLF. These tendencies were observed whatever the Oenococcus oeni strain (indigenous or starter) used for MLF. Neutral and charged SPs were affected, but to a degree that depended on the microorganisms driving the MLF. The SP modifications were directly linked to bacterial development, because non MLF controls did not present any significant change of SP concentration.
Journal of Agricultural and Food Chemistry 12/2007; 55(23):9592-9. DOI:10.1021/jf071677+ · 3.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Polysaccharides were sequentially extracted from Gracilaria corticata which is collected from south-west coast of Madagascar. Chemical analysis combined with 1H, 13C NMR and Fourier transform infrared spectroscopies showed that the fraction extracted with water/ethanol 60% (v/v) as solvent has low methoxyl and pyruvate contents and a great ability to form relatively strong physical gels in the presence of KCl. Rheological properties of extracted fractions are discussed as well as the ionic selectivity.
[Show abstract][Hide abstract] ABSTRACT: Selective chemical modification of both β-cyclodextrin (β-CD) and sodium alginate (alg) was performed in order to produce an alginate derivative possessing pendant β-CD cavities along the chain. The latter was then fully characterized in terms of chemical integrity and purity, complexation properties and ability to form hydrogels. Thus, a sodium alginate derivative modified with adipic dihydrazide (alg-ADH) and a β-cyclodextrin derivative possessing an aldehyde function on the primary face were synthesized, and both were selectively coupled by a reductive amination-type reaction. Comparison of the complexation properties of the grafted and natural β-CDs by isothermal titration calorimetry using sodium adamantane acetate as a model guest gave similar enthalpy values suggesting similar mechanisms of binding. However, the association constant for the grafted CD is slightly lower as a result of a less favorable change in the binding entropy. Investigation of the gelation ability in the presence of calcium ions led to the following order: alg > alg-ADH > alg-CD. The decrease of gelation efficiency for the modified alginate samples reflected the reduction of ionic interchain bonds as a result of the unavailability or non-accessibility of G units on the alginate backbone, due to the chemical modification and steric effect of the CD molecule for alg-CD.
[Show abstract][Hide abstract] ABSTRACT: Plant pathogens, like animal ones, use protein-carbohydrate interactions in their strategy for host recognition, attachment, and invasion. The bacterium Ralstonia solanacearum, which is distributed worldwide and causes lethal wilt in many agricultural crops, was shown to produce a potent L-fucose-binding lectin, R. solanacearum lectin, a small protein of 90 amino acids with a tandem repeat in its amino acid sequence. In the present study, surface plasmon resonance experiments conducted on a series of oligosaccharides show a preference for binding to alphaFuc1-2Gal and alphaFuc1-6Gal epitopes. Titration microcalorimetry demonstrates the presence of two binding sites per monomer and an unusually high affinity of the lectin for alphaFuc1-2Gal-containing oligosaccharides (KD = 2.5 x 10(-7) M for 2-fucosyllactose). R. solanacearum lectin has been crystallized with a methyl derivative of fucose and with the highest affinity ligand, 2-fucosyllactose. X-ray crystal structures, the one with alpha-methyl-fucoside being at ultrahigh resolution, reveal that each monomer consists of two small four-stranded anti-parallel beta-sheets. Trimerization through a 3-fold or pseudo-3-fold axis generates a six-bladed beta-propeller architecture, very similar to that previously described for the fungal lectin of Aleuria aurantia. This is the first report of a beta-propeller formed by oligomerization and not by sequential domains. Each monomer presents two fucose binding sites, resulting in six symmetrically arranged sugar binding sites for the beta-propeller. Crystals were also obtained for a mutated lectin complexed with a fragment of xyloglucan, a fucosylated polysaccharide from the primary cell wall of plants, which may be the biological target of the lectin.
[Show abstract][Hide abstract] ABSTRACT: The sorption of xyloglucan (XG) on cellulose is a basic feature of the supramolecular assembly of plant cell walls. The binding to cellulose of xyloglucan fractions from Rubus fruticosus suspension-cultured cells with different substitution patterns was assayed on celluloses having various degrees of crystallinity between 20 and 95%. The primary structure of XGs differing in their Xyl/Glc ratio affected their binding to cellulose. The less substituted XGs gave the highest binding yields. Selective removal of the terminal fucosyl residues of XGs differentially affected the binding depending on the crystallinity of cellulose. The results showed large variations on the way cellulose crystallinity affects the binding interaction of XGs. Interestingly, one of the highest binding capacities was exhibited by the primary cell wall cellulose isolated from the actual R. fruticosus cells which also had the lowest crystallinity. Differences in binding to primary wall cellulose appeared to be inversely related to the global substitution of the glucan main chain of XGs.
[Show abstract][Hide abstract] ABSTRACT: The results of a comparative study of two thermostable (1-->4)-beta-xylan endoxylanases using a multi-technical approach indicate that a GH11 xylanase is more useful than a GH10 xylanase for the upgrading of wheat bran into soluble oligosaccharides. Both enzymes liberated complex mixtures of xylooligosaccharides. 13C NMR analysis provided evidence that xylanases cause the co-solubilisation of beta-glucan, which is a result of cell-wall disassembly. The simultaneous use of both xylanases did not result in a synergistic action on wheat bran arabinoxylans, but instead led to the production of a product mixture whose profile resembled that produced by the action of the GH10 xylanase alone. Upon treatment with either xylanase, the diferulic acid levels in residual bran were unaltered, whereas content in ferulic and p-coumaric acids were unequally decreased. With regard to the major differences between the enzymes, the products resulting from the action of the GH10 xylanase were smaller in size than those produced by the GH11 xylanase, indicating a higher proportion of cleavage sites for the GH10 xylanase. The comparison of the kinetic parameters of each xylanase using various alkali-extractable arabinoxylans indicated that the GH10 xylanase was most active on soluble arabinoxylans. In contrast, probably because GH11 xylanase can better penetrate the cell-wall network, this enzyme was more efficient than the GH10 xylanase in the hydrolysis of wheat bran. Indeed the former enzyme displayed a nearly 2-fold higher affinity and a 6.8-fold higher turnover rate in the presence of this important by-product of the milling industry.
Carbohydrate Research 11/2004; 339(15):2529-40. DOI:10.1016/j.carres.2004.08.012 · 1.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Previous work showed that the fucose→galactose moiety of the xyloglucan nonasaccharide XXFG is responsable for its biological activity. We used this side chain of XXFG (α-l-Fuc (1→2)-β-d-Gal (1→)) in ligand-binding experiments to demonstrate its role as a signal molecule in plant cells. Proteins solubilized from plasma membrane enriched fractions isolated from Rubus fruticosus protoplasts were tested for their ability to bind the side chain of XXFG, using a digoxigenin- or biotin-conjugated neoglycoprotein specific for 2′-fucosyl-lactose in blots and k-ELISA tests. A putative receptor for the signaling sugar was identified, and the ligand specificity is reported. The role of structural elements important for biological activities was investigated using compounds structurally related to xyloglucan, and a variety of phytohormones such as 2,4-D.
[Show abstract][Hide abstract] ABSTRACT: Previous work showed that the fucose-->galactose moiety of the xyloglucan nonasaccharide XXFG is responsable for its biological activity. We used this side chain of XXFG (alpha-L-Fuc (1-->2)-beta-D-Gal (1-->)) in ligand-binding experiments to demonstrate its role as a signal molecule in plant cells. Proteins solubilized from plasma membrane enriched fractions isolated from Rubus fruticosus protoplasts were tested for their ability to bind the side chain of XXFG, using a digoxigenin- or biotin-conjugated neoglycoprotein specific for 2'-fucosyl-lactose in blots and k-ELISA tests. A putative receptor for the signaling sugar was identified, and the ligand specificity is reported. The role of structural elements important for biological activities was investigated using compounds structurally related to xyloglucan, and a variety of phytohormones such as 2,4-D.
[Show abstract][Hide abstract] ABSTRACT: Several xyloglucan polysaccharides were biotinylated through their galactosyl residues, by combination of partial galactose oxidation and biotinamidocaproylhydrazide coupling. They were shown to easily bind to avidin activated ELISA plates by specific recognition of plant lectins Ulex europeaus (UEA-I) and Ricinus communis agglutinin (RCA-I). Subsequent chemical reduction of aldehyde groups after biotinylation was shown to improve immobilisation. UEA-I bound to cell wall xyloglucan but not to tamarind seed xyloglucan, due to the lack of fucose in the latter. RCA-I bound to all xyloglucans we tested, however, a higher affinity was observed with seed xyloglucan, suggesting it specifically clusters with the polysaccharide. The usefulness of using biotinylated xyloglucans for antibodies characterization was investigated.1. Presented at the XVIIIth International Carbohydrate Symposium, Milan, Italy, July 21-26, 1996.