Chihiro Sato

Nagoya University, Nagoya, Aichi, Japan

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Publications (86)257.49 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Polysialic acid (polySia) is a linear polymer of sialic acid that modifies NCAM in the vertebrate brain. PolySia is a large and exclusive molecule that functions as a negative regulator of cell-cell interactions. Recently, we demonstrated that polySia can specifically bind FGF2 and BDNF; however, the protective effects of polySia on the proteolytic cleavage of these proteins remain unknown although heparin/heparan sulfate has been shown to impair the cleavage of FGF2 by trypsin. Here, we analyzed the protective effects of polySia on the proteolytic cleavage of FGF2 and proBDNF/BDNF. We found that polySia protected intact FGF2 from tryptic activity via the specific binding of extended polySia chains on NCAM to FGF2. Oligo/polySia also functioned to impair the processing of proBDNF by plasmin via binding of oligo/polySia chains on NCAM. In addition, the polySia structure synthesized by mutated polysialyltransferase, ST8SIA2/STX(SNP7), which was previously identified from a schizophrenia patient, was impaired for these functions compared with polySia produced by normal ST8SIA2. Taken together, these data suggest that the protective effects of polySia toward FGF2 and proBDNF may be involved in the regulation of the concentrations of these neurologically active molecules. © The Author 2015. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
    No preview · Article · Jul 2015 · Glycobiology
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    Yoichiro Harada · Chihiro Sato · Ken Kitajima
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    ABSTRACT: The 70-kDa heat shock protein (Hsp70), one of the major stress-inducible molecular chaperones, is localized not only in the cytosol, but also in extracellular milieu in mammals. Hsp70 interacts with various cell surface glycolipids including sulfatide (3'-sulfogalactosphingolipid). However, the molecular mechanism, as well as the biological relevance, underlying the glycolipid-Hsp70 interaction is unknown. Here we report that sulfatide promotes Hsp70 oligomerization through the N-terminal ATPase domain, which stabilizes the binding of Hsp70 to unfolded protein in vitro. We find that the Hsp70 oligomer has apparent molecular masses ranging from 440 kDa to greater than 669 kDa. The C-terminal peptide-binding domain is dispensable for the sulfatide-induced oligomer formation. The oligomer formation is impaired in the presence of ATP, while the Hsp70 oligomer, once formed, is unable to bind to ATP. These results suggest that sulfatide locks Hsp70 in a high-affinity state to unfolded proteins by clustering the peptide-binding domain and blocking the binding to ATP that induces the dissociation of Hsp70 from protein substrates.
    Preview · Article · Jun 2015
  • Ken Kitajima · Nissi Varki · Chihiro Sato
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    ABSTRACT: Although the structural diversity of sialic acid (Sia) is rapidly expanding, understanding of its biological significance has lagged behind. Advanced technologies to detect and probe diverse structures of Sia are absolutely necessary not only to understand further biological significance but also to pursue medicinal and industrial applications. Here we describe analytical methods for detection of Sia that have recently been developed or improved, with a special focus on 9-O-acetylated N-acetylneuraminic acid (Neu5,9Ac), N-glycolylneuraminic acid (Neu5Gc), deaminoneuraminic acid (Kdn), O-sulfated Sia (SiaS), and di-, oligo-, and polysialic acid (diSia/oligoSia/polySia) in glycoproteins and glycolipids. Much more attention has been paid to these Sia and sialoglycoconjugates during the last decade, in terms of regulation of the immune system, neural development and function, tumorigenesis, and aging.
    No preview · Article · May 2015 · Topics in current chemistry
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    ABSTRACT: Neurons have well-developed membrane microdomains called "rafts" that are recovered as a detergent-resistant membrane microdomain fraction (DRM). Neuronal tissue-enriched acidic protein of 22 kDa (NAP-22) is one of the major protein components of neuronal DRM. To determine the cellular function of NAP-22, interacting proteins were screened with an immunoprecipitation assay, and calcineurin (CaN) was detected. Further studies with NAP-22 prepared from DRM and CaN expressed in bacteria showed the binding of these proteins and a dose-dependent inhibitory effect of the NAP-22 fraction on the phosphatase activity of CaN. On the other hand, NAP-22 expressed in bacteria showed low binding to CaN and a weak inhibitory effect on phosphatase activity. To solve this discrepancy, identification of a nonprotein component that modulates CaN activity in the DRM-derived NAP-22 fraction was attempted. After lyophilization, a lipid fraction was extracted with chloroform/methanol. The lipid fraction showed an inhibitory effect on CaN without NAP-22, and further fractionation of the extract with thin-layer chromatography showed the presence of several lipid bands having an inhibitory effect on CaN. The mobility of these bands coincided with that of authentic ganglioside (GM1a, GD1a, GD1b, and GT1b), and authentic ganglioside showed an inhibitory effect on CaN. Treatment of lipid with endoglycoceramidase, which degrades ganglioside to glycochain and ceramide, caused a diminution of the inhibitory effect. These results show that DRM-derived NAP-22 binds several lipids, including ganglioside, and that ganglioside inhibits the phosphatase activity of CaN. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.
    Full-text · Article · May 2015 · Journal of Neuroscience Research
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    ABSTRACT: As acidic glycocalyx on primary mouse microglial cells and a mouse microglial cell line Ra2, expression of polysialic acid (polySia/PSA), a polymer of the sialic acid Neu5Ac, was demonstrated. PolySia is known to modulate cell adhesion, migration and localization of neurotrophins mainly on neural cells. PolySia on Ra2 cells disappeared very rapidly after an inflammatory stimulus. Results of knockdown and inhibitor studies indicated that rapid surface clearance of polySia was achieved by secretion of endogenous sialidase Neu1 as an exovesicular component. Neu1-mediated polySia turnover was accompanied by the release of brain-derived neurotrophic factor (BDNF) normally retained by polySia molecules. Introduction of a single oxygen atom change into polySia by exogenous feeding of the non-neural sialic acid Neu5Gc caused resistance to Neu1 induced polySia turnover, and also inhibited the associated release of BDNF. These results indicate the importance of rapid turnover of the polySia glycocalyx by exovesicular sialidases in neurotrophin regulation. Copyright © 2015, The American Society for Biochemistry and Molecular Biology.
    No preview · Article · Mar 2015 · Journal of Biological Chemistry
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    ABSTRACT: Mammalian sperm acquire fertility through a functional maturation process called capacitation, where sperm membrane molecules are drastically remodeled. In this study, we found that a wheat germ agglutinin (WGA)-reactive protein on lipid rafts, named WGA16, is removed from sperm surface on capacitation. WGA16 is a prostate-derived seminal plasma protein that has never been reported, and is deposited on the sperm surface in the male reproductive tract. Based on protein and cDNA sequences for purified WGA16, it is a homologue of human zymogen granule protein 16 (ZG16) belonging to Jacalin-related lectin (JRL) family in crystal and primary structures. Glycan array shows that WGA16 binds heparin through a basic patch containing K53/K73 residues, but not conventional lectin domain of the JRL family. WGA16 is glycosylated, contrary to other ZG16 members, and comparative mass spectrometry clearly shows its unique N-glycosylation profile among seminal plasma proteins. It has exposed GlcNAc and GalNAc residues without additional Gal residues. The GlcNAc/GalNAc residues can work as binding ligands for a sperm surface galactosyltransferase (GalT), which actually galactosylates WGA16 in situ in the presence of UDP-Gal. Interestingly, surface removal of WGA16 is experimentally induced by either UDP-Gal or heparin. In the crystal structure, N-glycosylated sites and potential heparin-binding site face to opposite sides. This geography of two functional sites suggest that WGA16 is deposited on sperm surface through interaction between its N-glycans and the surface GalT, while its heparin-binding domain may be involved in binding to sulfated glycosaminoglycans in female tract, enabling removal of WGA16 from sperm surface. Copyright © 2015, The American Society for Biochemistry and Molecular Biology.
    No preview · Article · Jan 2015 · Journal of Biological Chemistry
  • Masaya Hane · Ken Kitajima · Chihiro Sato
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    ABSTRACT: It has been shown that polysialic acid (polySia) is an indispensable component for viability of mouse during development. Especially, it is deeply involved in normal brain function in mouse and human, affecting cell adhesion, cell migration, cell growth, neurogenesis, and synaptogenesis. PolySia is synthesized by two polysialyltransferases, ST8SIA2 and ST8SIA4. Mice deficient in both enzymes show lethality soon after birth. Mice deficient in either ST8SIA2 or ST8SIA4 show significant impairments in learning, memory, circadian rhythm, and social behavior. Interestingly, different phenotypes are often observed between ST8SIA2- and ST8SIA4-deficient mice. Therefore, characterization of these enzymes in vitro and in vivo and precise understanding of the structurefunction relationship of polySia become more and more important. In this chapter, assay procedures for in vitro activity of the polysialyltransferases are focused on to obtain clear results of their in vitro activities that are often said to be very weak compared with other sialyltransferases.
    No preview · Article · Jan 2015
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    ABSTRACT: Very little knowledge has been available on structure and function of heavily glycosylated proteins, whose glycan parts amount to more than 90 % of the whole molecules, mainly because of technical difficulties in detection and determination of structure. In 2004 flagellasialin was discovered as a major cell surface component in the lipid rafts of sea urchin sperm. The extremely high content of glycan chains completely prevented detecting this glycoprotein by conventional protein staining methods, such as Coomassie Brilliant Blue and silver staining. To make this glycoprotein visible, monoclonal antibodies 4F7 and 3G9 were developed as specific probes for detecting glycan chains of flagellasialin. The frequent occurrence of GPI-anchored proteins in lipid rafts is well recognized. Flagellasialin was actually demonstrated to contain a GPI-anchor, based on three lines of experiments. In addition to the computational predictions from the cDNA sequence and the phosphatidylinositolspecific phospholipase C treatment of the sperm membrane fraction, nitrous acid deamination of a flagellasialin-blotted membrane was newly introduced. The immunostaining of flagellasialin on the membrane disappeared after the nitrous acid treatment of the blotted membrane. This method was easy and effective for identifying flagellasialin as a GPI-anchored protein.
    No preview · Article · Jan 2015
  • Chihiro Sato · Ken Kitajima
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    ABSTRACT: Polysialic acid (polySia), particularly α2,8-linked polyNeu5Ac (DP ¼ 8 ~ 400), is a unique polymer of sialic acid (Sia) and modifies neural cell adhesion molecule (NCAM) spatiotemporally in embryonic brains. PolySia is involved in cell migration, neural outgrowth, axonal guidance, synaptic plasticity, and the development of normal neural circuits and neurogenesis due to its anti- adhesive property and spatiotemporal expression. Recent improvements of polySia-detection methods have told us that polySia expression persists in certain areas of the adult brain, such as the olfactory bulb, hippocampus, subventricular zone, thalamus, prefrontal cortex, and amygdala, where neural plasticity, remodeling of neural connections, or neural generation is ongoing. Importantly, several lines of evidence have raised a new concept of polySia function that polySia works as an attractive field that associates with particular ion channels and neurologically active molecules, such as neurotrophic factor (BDNF), growth factor (FGF2), and neurotransmitter (dopamine), to regulate their involved signaling. It has been shown that polySia is involved in learning, memory, circadian rhythm, and social behaviors using polySia-impaired mice. In addition, SNPs and some deletions in genes encoding the polysialyltransferase and NCAM have been reported from patients of schizophrenia, mood disorder and autism. Such impairments of polySia structure derived from polysialyltransferase gene alterations might influence the polySia function not only as the repulsive field but also as the attractive field.
    No preview · Article · Jan 2015
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    ABSTRACT: Thyroid-stimulating hormone (TSH; thyrotropin) is a glycoprotein secreted from the pituitary gland. Pars distalis-derived TSH (PD-TSH) stimulates the thyroid gland to produce thyroid hormones (THs), whereas pars tuberalis-derived TSH (PT-TSH) acts on the hypothalamus to regulate seasonal physiology and behavior. However, it had not been clear how these two TSHs avoid functional crosstalk. Here, we show that this regulation is mediated by tissue-specific glycosylation. Although PT-TSH is released into the circulation, it does not stimulate the thyroid gland. PD-TSH is known to have sulfated biantennary N-glycans, and sulfated TSH is rapidly metabolized in the liver. In contrast, PT-TSH has sialylated multibranched N-glycans; in the circulation, it forms the macro-TSH complex with immunoglobulin or albumin, resulting in the loss of its bioactivity. Glycosylation is fundamental to a wide range of biological processes. This report demonstrates its involvement in preventing functional crosstalk of signaling molecules in the body.
    Full-text · Article · Nov 2014 · Cell Reports
  • Karen J Colley · Ken Kitajima · Chihiro Sato
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    ABSTRACT: Abstract As an anti-adhesive, a reservoir for key biological molecules, and a modulator of signaling, polysialic acid (polySia) is critical for nervous system development and maintenance, promotes cancer metastasis, tissue regeneration and repair, and is implicated in psychiatric diseases. In this review, we focus on the biosynthesis and functions of mammalian polySia, and the use of polySia in therapeutic applications. PolySia modifies a small subset of mammalian glycoproteins, with the neural cell adhesion molecule, NCAM, serving as its major carrier. Studies show that mammalian polysialyltransferases employ a unique recognition mechanism to limit the addition of polySia to a select group of proteins. PolySia has long been considered an anti-adhesive molecule, and its impact on cell adhesion and signaling attributed directly to this property. However, recent studies have shown that polySia specifically binds neurotrophins, growth factors, and neurotransmitters and that this binding depends on chain length. This work highlights the importance of considering polySia quality and quantity, and not simply its presence or absence, as its various roles are explored. The capsular polySia of neuroinvasive bacteria allows these organisms to evade the host immune response. While this "stealth" characteristic has made meningitis vaccine development difficult, it has also made polySia a worthy replacement for polyetheylene glycol in the generation of therapeutic proteins with low immunogenicity and improved circulating half-lives. Bacterial polysialyltransferases are more promiscuous than the protein-specific mammalian enzymes, and new studies suggest that these enzymes have tremendous therapeutic potential, especially for strategies aimed at neural regeneration and tissue repair.
    No preview · Article · Nov 2014 · Critical Reviews in Biochemistry and Molecular Biology
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    ABSTRACT: Interaction of Hsp70 with natural and artificial acidic glycans is demonstrated based on the native PAGE analysis. Hsp70 interacts with acidic glycopolymers that contain clustered sulfated and di-sialylated glycan moieties on a polyacrylamide backbone, but not with neutral or mono-sialylated glycopolymers. Hsp70 also interacts and forms a large complex with heparin, heparan sulfate, and dermatan sulfate that commonly contain 2-O-sulfated iduronic acid residues, but not with other types of glycosaminoglycans (GAGs). Hsp70 consists of the N-terminal ATPase domain and the C-terminal peptide-binding domain. The interaction analyses using the recombinant N- and C-terminal half domains show that the ATPase domain mediates the direct interaction with acidic glycans, while the peptide-binding domain stabilizes the large complexes with particular GAGs. To our knowledge, this is the first demonstration of direct binding of Hsp70 to the particular GAGs. This property may be involved in the physiological functions of Hsp70 at the plasma membrane and extracellular environments.
    Preview · Article · Jun 2014 · Biochemical and Biophysical Research Communications
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    ABSTRACT: Polysialic acid is a linear homopolymer of α2-8 linked sialic acids attached mainly onto glycoproteins. Cell surface polysialic acid plays roles in cell adhesion and differentiation events in a manner that is often dependent on the degree of polymerization (DP). Anti-oligo/polysialic acid antibodies have DP-dependent antigenic specificity, and such antibodies are widely utilized in biological studies for detecting and distinguishing between different oligo/polysialic acids. A murine monoclonal antibody mAb735 has a unique preference for longer polymers of polysialic acid (DP>10), yet the mechanism of recognition at atomic level remains unclear. Here we report the crystal structure of mAb735 single chain variable fragment (scFv735) in complex with octasialic acid at 1.8 Å resolution. In the asymmetric unit, two scFv735 molecules associate with one octasialic acid. In both complexes of the unit, all the complementarity-determining regions except for L3 interact with three consecutive sialic acid residues out of the eight. A striking feature of the complex is that 11 ordered water molecules bridge the gap between antibody and ligand while the direct antibody-ligand interaction is less extensive. The dihedral angles of the trisialic acid unit directly interacting with scFv735 are not uniform, indicating that mAb735 does not strictly favor the previously proposed helical conformation. Importantly, both reducing and non-reducing ends of the bound ligand are completely exposed to solvent. We suggest that mAb735 gains its apparent high affinity for a longer polysialic acid chain by recognizing every three sialic acid unit in a paired manner.
    Preview · Article · Oct 2013 · Journal of Biological Chemistry
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    ABSTRACT: Oligo/polysialic acids consisting of consecutive α(2,8)-linkages on gangliosides and glycoproteins play a role in cell adhesion and differentiation events in a manner that is dependent on the degree of polymerization (DP). Anti-oligo/polysialic acid antibodies often have DP-dependent antigenic specificity, and such unique antibodies are often used in biological studies for the detection and differentiation of oligo/polysialic acids. However, molecular mechanisms remain unclear. We here use NMR techniques to analyze the binding epitopes of the anti-oligo/polysialic acid monoclonal antibodies (mAb) A2B5 and 12E3. The mAb A2B5, which has a preference for trisialic acid, recognizes sialic acid residues at the non-reducing terminus and those in nascent units. On the other hand, mAb 12E3, which prefers oligo/polysialic acids of more than six sugar units, recognizes inner sialic acid residues. In both structural complexes, the interresidue transferred NOE correlations are significantly different from those arising from analogs of the free states, indicating that the bound and free sugar conformations are distinct. The ability of the two mAbs to distinguish the chain lengths comes from different binding epitopes and possibly from the conformational differences in the oligo/polysialic acids. Information on the recognition modes is needed for the structural design of immunoreactive antigens for the development of high-affinity anti-polysialic acid antibodies and of related vaccines against pathogenic, polysialic acid-coated bacteria.
    No preview · Article · Jul 2013 · Bioorganic & medicinal chemistry
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    Chihiro Sato · Ken Kitajima
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    ABSTRACT: Sialic acids (Sia) are involved in many biological activities and frequently exist as monosialyl residues at the non-reducing terminal end of glycoconjugates. Occasionally, polymerized structures in the form of disialic acid (diSia), oligosialic acid (oligoSia), and polysialic acid (polySia) are also found in glycoconjugates. In particular, polySia, which is an evolutionarily conserved epitope from sea urchin to humans, is one of the most biologically important glycotopes in vertebrates. The biological functions of polySia, especially on neural cell adhesion molecules (NCAMs), have been well studied and an in-depth body of knowledge concerning polySia has been accumulated. However, considerably less attention has been paid to glycoproteins containing di- and oligoSia groups. However, advances in analytical methods for detecting oligo/polymerized structures have allowed the identification and characterization of an increasing number of glycoproteins containing di/oligo/polySia chains in nature. In addition, sophisticated genetic techniques have also helped elucidate the underlying mechanisms of polySia-mediated activities. In this review, recent advances in the study of the chemical properties, distribution, and functions of di-, oligo-, and polySia residues on glycoproteins are described.
    Preview · Article · Jun 2013 · Journal of Biochemistry
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    Chihiro Sato · Ken Kitajima
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    ABSTRACT: Psychiatric disorders are a group of human diseases that impair higher cognitive functions. Whole-genomic analyses have recently identified susceptibility genes for several psychiatric disorders, including schizophrenia. Among the genes reported to be involved in psychiatric disorders, a gene encoding a polysialyltransferase involved in the biosynthesis of polysialic acid (polySia or PSA) on cell surfaces has attracted attention for its potential role in emotion, learning, memory, circadian rhythm, and behaviors. PolySia is a unique polymer that spatio-temporally modifies neural cell adhesion molecule (NCAM) and is predominantly found in embryonic brains, although it persists in areas of the adult brain where neural plasticity, remodeling of neural connections, or neural generation is ongoing, such as the hippocampus, subventricular zone (SVZ), thalamus, prefrontal cortex, and amygdala. PolySia is thought to be involved in the regulation of cell-cell interactions; however, recent evidence suggests that it is also involved in the functional regulation of ion channels and neurologically active molecules, such as Brain-derived neurotrophic factor (BDNF), FGF2, and dopamine (DA) that are deeply involved in psychiatric disorders. In this review, the possible involvement of polysialyltransferase (ST8SIA2/ST8SiaII/STX/Siat8B) and its enzymatic product, polySia, in schizophrenia is discussed.
    Preview · Article · May 2013 · Frontiers in Cellular Neuroscience
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    ABSTRACT: We previously reported on the accumulation of a substantial amount of free N-acetylneuraminic acid (Neu5Ac)-containing complex-type N-glycans in human pancreatic cancer cells (Yabu M, Korekane H, Takahashi H, Ohigashi H, Ishikawa O, Miyamoto Y. 2012. Accumulation of free Neu5Ac-containing complex-type N-glycans in human pancreatic cancers. Glycoconjugate J Epub ahead of print). In the present paper, we further extend our cancer glycomic study of human prostate cancer. Specifically, we demonstrate that, in addition to the free Neu5Ac-containing N-glycans, significant amounts of free deaminoneuraminic acid (KDN)-containing N-glycans had accumulated in the prostate cancer tissues from four out of five patients. Indeed in one of the four cases, the free KDN-glycans accumulated as major components in prostate cancer tissue. The structures of the KDN-containing free oligosaccharides were analyzed by a variety of methods. Specifically we used fluorescent labeling with aminopyridine combined with two dimensional mapping, KDNase digestion and mass spectrometry to facilitate identification. The analysis also utilized newly synthesized KDN-linked oligosaccharides as standards. The prostate-specific glycans were composed of five species having the following sequence, KDN-Gal-GlcNAc-Man-Man-GlcNAc (α2,6-KDN-linked glycans being the dominant form). The most abundant free KDN-containing N-glycan was KDNα2-6Galβ1-4GlcNAcβ1-2Manα1-3Manβ1-4GlcNAc followed by KDNα2-6Galβ1-4GlcNAcβ1-2Manα1-6Manβ1-4GlcNAc. This is the first study to show unequivocal chemical evidence for the occurrence of KDN-glycoconjugates in human tissues together with their detailed structures. These oligosaccharides might be developed as tumor markers, especially for prostate cancer.
    No preview · Article · Sep 2012 · Glycobiology
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    ABSTRACT: A highly glycosylated protein, which has unique, novel features in localization, structure, and potential function, is found in pig sperm, and named WGA-gp due to its high binding property with wheat germ agglutinin (WGA). WGA-gp is localized mainly in flagella and enriched in membrane microdomains or lipid rafts. It is not detected by ordinary protein staining methods due to a high content of both N- and O-glycans consisting of neutral monosaccharides. Interestingly, WGA-gp may be involved in intracellular Ca(2+) regulation. Treatment of sperm with anti-WGA-gp antibody enhances the amplitude of Ca(2+) oscillation without changing the basal intracellular Ca(2+) concentrations. All these features of WGA-gp, except for different carbohydrate structures occupying most part of the molecules, are similar to those of flagellasialin in sea urchin sperm, which regulates the intracellular Ca(2+) concentration. Presence of carbohydrate-enriched flagellar proteins involved in intracellular Ca(2+) regulation may be a common feature among animal sperm.
    No preview · Article · Aug 2012 · Biochemical and Biophysical Research Communications
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    ABSTRACT: The sialic acid (Sia) N-acetylneuraminic acid (Neu5Ac) and its hydroxylated derivative N-glycolylneuraminic acid (Neu5Gc) differ by one oxygen atom. CMP-Neu5Gc is synthesized from CMP-Neu5Ac, with Neu5Gc representing a highly variable fraction of total Sias in various tissues and among different species. The exception may be the brain, where Neu5Ac is abundant and Neu5Gc is reported to be rare. Here, we confirm this unusual pattern and its evolutionary conservation in additional samples from various species, concluding that brain Neu5Gc expression has been maintained at extremely low levels over hundreds of millions of years of vertebrate evolution. Most explanations for this pattern do not require maintaining neural Neu5Gc at such low levels. We hypothesized that resistance of α2-8-linked Neu5Gc to vertebrate sialidases is the detrimental effect requiring the relative absence of Neu5Gc from brain. This linkage is prominent in polysialic acid (polySia), a molecule with critical roles in vertebrate neural development. We show that Neu5Gc is incorporated into neural polySia and does not cause in vitro toxicity. Synthetic polymers of Neu5Ac and Neu5Gc showed that mammalian and bacterial sialidases are much less able to hydrolyze α2-8-linked Neu5Gc at the nonreducing terminus. Notably, this difference was not seen with acid-catalyzed hydrolysis of polySias. Molecular dynamics modeling indicates that differences in the three-dimensional conformation of terminal saccharides may partly explain reduced enzymatic activity. In keeping with this, polymers of N-propionylneuraminic acid are sensitive to sialidases. Resistance of Neu5Gc-containing polySia to sialidases provides a potential explanation for the rarity of Neu5Gc in the vertebrate brain.
    Full-text · Article · Jun 2012 · Journal of Biological Chemistry
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    ABSTRACT: Modulation of levels of polysialic acid (polySia), a sialic acid polymer, predominantly associated with the neural cell adhesion molecule (NCAM), influences neural functions, including synaptic plasticity, neurite growth, and cell migration. Biosynthesis of polySia depends on two polysialyltransferases ST8SiaII and ST8SiaIV in vertebrate. However, the enzyme involved in degradation of polySia in its physiological turnover remains uncertain. In the present study, we identified and characterized a murine sialidase NEU4 that catalytically degrades polySia. Murine NEU4, dominantly expressed in the brain, was found to efficiently hydrolyze oligoSia and polySia chains as substrates in sialidase in vitro assays, and also NCAM-Fc chimera as well as endogenous NCAM in tissue homogenates of postnatal mouse brain as assessed by immunoblotting with anti-polySia antibodies. Degradation of polySia by NEU4 was also evident in neuroblastoma Neuro2a cells that were co-transfected with Neu4 and ST8SiaIV genes. Furthermore, in mouse embryonic hippocampal primary neurons, the endogenously expressed NEU4 was found to decrease during the neuronal differentiation. Interestingly, GFP- or FLAG-tagged NEU4 was partially co-localized with polySia in neurites and significantly suppressed their outgrowth, whereas silencing of NEU4 showed the acceleration together with an increase in polySia expression. These results suggest that NEU4 is involved in regulation of neuronal function by polySia degradation in mammals.
    Full-text · Article · Mar 2012 · Journal of Biological Chemistry

Publication Stats

2k Citations
257.49 Total Impact Points

Institutions

  • 1998-2015
    • Nagoya University
      • • Department of Bioengineering Sciences
      • • Department of Applied Molecular Biosciences
      • • Graduate School of Bio-Agricultural Sciences
      Nagoya, Aichi, Japan
  • 2006
    • Mie University
      • Third Department of Internal Medicine
      Tu, Mie, Japan
  • 1993-1997
    • The University of Tokyo
      • Department of Biophysics and Biochemistry
      白山, Tōkyō, Japan