Showing papers on "Sialic acid published in 2003"
TL;DR: It is found that Neu5Gc is rare in poultry and fish, common in milk products, and enriched in red meats, and normal humans have variable amounts of circulating IgA, IgM, and IgG antibodies against Neu 5Gc, with the highest levels comparable to those of the previously known anti-α-galactose xenoreactive antibodies.
Abstract: Humans are genetically unable to produce the sialic acid N-glycolylneuraminic acid (Neu5Gc), because of a mutation that occurred after our last common ancestor with great apes. Although Neu5Gc is presumed absent from normal humans, small amounts have been claimed to exist in human tumors and fetal meconium. We have generated an antibody with high specificity and avidity for Neu5Gc. Fetal tissues, normal adult tissues, and breast carcinomas from humans showed reactivity to this antibody, primarily within secretory epithelia and blood vessels. The presence of small amounts of Neu5Gc was confirmed by MS. Absent any known alternate pathway for its synthesis, we reasoned that these small amounts of Neu5Gc might originate from exogenous sources. Indeed, human cells fed with Neu5Gc incorporated it into endogenous glycoproteins. When normal human volunteers ingested Neu5Gc, a portion was absorbed and eliminated in urine, and small quantities were incorporated into newly synthesized glycoproteins. Neu5Gc has never been reported in plants or microbes to our knowledge. We found that Neu5Gc is rare in poultry and fish, common in milk products, and enriched in red meats. Furthermore, normal humans have variable amounts of circulating IgA, IgM, and IgG antibodies against Neu5Gc, with the highest levels comparable to those of the previously known anti-α-galactose xenoreactive antibodies. This finding represents an instance wherein humans absorb and metabolically incorporate a nonhuman dietary component enriched in foods of mammalian origin, even while generating xenoreactive, and potentially autoreactive, antibodies against the same molecule. Potential implications for human diseases are briefly discussed.
559 citations
TL;DR: Whether the sialic acid in human milk is a conditional nutrient and confers developmental advantages on breast-fed infants compared to those fed infant formula is critically discussed.
Abstract: Sialic acids are a family of nine-carbon acidic monosaccharides that occur naturally at the end of sugar chains attached to the surfaces of cells and soluble proteins. In the human body, the highest concentration of sialic acid (as N-acetylneuraminic acid) occurs in the brain where it participates as an integral part of ganglioside structure in synaptogenesis and neural transmission. Human milk also contains a high concentration of sialic acid attached to the terminal end of free oligosaccharides, but its metabolic fate and biological role are currently unknown. An important question is whether the sialic acid in human milk is a conditional nutrient and confers developmental advantages on breast-fed infants compared to those fed infant formula. In this review, we critically discuss the current state of knowledge of the biology and role of sialic acid in human milk and nervous tissue, and the link between sialic acid, breastfeeding and learning behaviour.
327 citations
TL;DR: In this article, the anomalous binding profile of borate in aqueous solution with N-acetylneuraminic acid (Neu5Ac, sialic acid) was revealed.
Abstract: Borates are known to interact with carbohydrate moieties expressed on the surface of biological membranes of a variety of cells, viruses, bacteria, and fungi. This study revealed the anomalous binding profile of borate in aqueous solution with N-acetylneuraminic acid (Neu5Ac, sialic acid) as a potential receptor site on the surfaces of biological membranes using 11B, 1H, 13C, and 15N nuclear magnetic resonance spectroscopies. 3-(Propionamido)phenylboronic acid (PAPBA) was chosen as the model borate compound. The equilibrium constant (K) for Neu5Ac binding to PAPBA was compared with those for glucose, mannose, and galactose, which are the major carbohydrate constituents of glycoproteins and glycolipids expressed on biological membranes. In the Neu5Ac/PAPBA system, the unusual pH dependency of the K values, a decrease in K with increasing pH, was observed, suggesting the formation of a trigonal-formed complex stabilized by the coordination of an amide group of Neu5Ac at the C-5 position to the boron atom, f...
280 citations
TL;DR: Both W2mef and 3D7 parasites lacking EBA-175 expression invaded chymotrypsin-treated erythrocytes inefficiently compared with the parental lines, suggesting a model where a minimal affinity supplied by multiple ligand–receptor interactions is required for successful invasion.
Abstract: The Plasmodium falciparum erythrocyte-binding antigen 175 (EBA-175) is a ligand for merozoite invasion into human erythrocytes that binds to glycophorin A in a sialic acid-dependent manner. P. falciparum strain W2mef depends on sialic acid for invasion of erythrocytes, whereas 3D7 is sialic acid-independent. We generated parasites that lack expression or express truncated forms of EBA-175 in W2mef and 3D7. Lack of EBA-175 expression in W2mef parasites was associated with a switch to sialic acid-independent invasion. 3D7 parasites lacking expression of EBA-175 showed no alteration in their ability to utilize sialic acid-independent pathways. Strikingly, both W2mef and 3D7 parasites lacking EBA-175 expression invaded chymotrypsin-treated erythrocytes inefficiently compared with the parental lines. This loss of function suggests that the EBA-175/glycophorin A ligand-receptor interaction is the major chymotrypsin-resistant invasion pathway. Parasite lines with truncated EBA-175 had invasion phenotypes equivalent to parasites lacking expression of EBA-175. The EBA-175 ligand is functional in erythrocyte invasion by merozoites that utilize either sialic acid-dependent or -independent invasion pathways. This finding suggests a model where a minimal affinity supplied by multiple ligand-receptor interactions is required for successful invasion and has implications for EBA-175 as a malaria vaccine candidate.
243 citations
TL;DR: Modified sialic acid substrates have been used to label Trypanosoma cruzi trans-sialidase, demonstrating that the enzyme catalyses the transfer of sIALic acid through a covalent glycosyl-enzyme intermediate, a mechanism common to most retaining glycosidases.
Abstract: Modified sialic acid substrates have been used to label Trypanosoma cruzi trans-sialidase, demonstrating that the enzyme catalyses the transfer of sialic acid through a covalent glycosyl−enzyme intermediate, a mechanism common to most retaining glycosidases. Peptic digestion of labeled protein, followed by LC-MS/MS analysis of the digest, identified Tyr342 as the catalytic nucleophile. This is the first such example of a retaining glycosidase utilizing an aryl glycoside intermediate. It is suggested that this alternative choice of nucleophile is a consequence of the chemical nature of sialic acid. A Tyr/Glu couple is invoked to relay charge from a remote glutamic acid, thereby avoiding electrostatic repulsion with the sialic acid carboxylate group.
235 citations
TL;DR: Regulation of glycoprotein sialylation may control susceptibility to cell death at specific points during T cell development and peripheral activation.
211 citations
TL;DR: It is shown that in capsule-deficient (nontypeable) strains, sialic acid, a terminal residue of the core sugars of H. influenzae lipopolysaccharide (LPS), is a critical virulence factor in the pathogenesis of experimental otitis media in chinchillas and play a key role in pathogenicity of nontypeable H. Influenzae disease.
Abstract: Otitis media, a common and often recurrent bacterial infection of childhood, is a major reason for physician visits and the prescription of antimicrobials. Haemophilus influenzae is the cause of approximately 20% of episodes of bacterial otitis media, but most strains lack the capsule, a factor known to play a critical role in the virulence of strains causing invasive H. influenzae disease. Here we show that in capsule-deficient (nontypeable) strains, sialic acid, a terminal residue of the core sugars of H. influenzae lipopolysaccharide (LPS), is a critical virulence factor in the pathogenesis of experimental otitis media in chinchillas. We used five epidemiologically distinct H. influenzae isolates, representative of the genetic diversity of strains causing otitis media, to inoculate the middle ear of chinchillas. All animals developed acute bacterial otitis media that persisted for up to 3 wk, whereas isogenic sialic acid-deficient mutants (disrupted sialyltransferase or CMP-acetylneuraminic acid synthetase genes) were profoundly attenuated. MS analysis indicated that WT bacteria used to inoculate animals lacked any sialylated LPS glycoforms. In contrast, LPS of ex vivo organisms recovered from chinchilla middle ear exudates was sialylated. We conclude that sialylated LPS glycoforms play a key role in pathogenicity of nontypeable H. influenzae and depend on scavenging the essential precursors from the host during the infection.
210 citations
TL;DR: The presence of polysialic acid is always associated with expression of ST8Sia II and/or IV, suggesting that ST8 sialic Acid II and IV are the key enzymes that control the expression ofpolysIALic acid.
209 citations
TL;DR: In this review focus is given to the metabolic turnover of ganglioside/glycosphingolipid turnover, with particular attention to the processes of de novo biosynthesis, metabolic salvage and direct glycosylation.
Abstract: In this review focus is given to the metabolic turnover of gangliosides/glycosphingolipids. The metabolism and accompanying intracellular trafficking of gangliosides/glycosphingolipids is illustrated with particular attention to the following events: (a) the de novo biosynthesis in the endoplasmic reticulum and Golgi apparatus, followed by vesicular sorting to the plasma membrane; (b) the enzyme-assisted chemical modifications occurring at the plasma membrane level; (c) the internalization via endocytosis and recycling to the plasma membrane; (d) the direct glycosylations taking place after sorting from endosomes to the Golgi apparatus; (e) the degradation at the late endosomal/lysosomal level with formation of fragments of sugar (glucose, galactose, hexosamine, sialic acid) and lipid (ceramide, sphingosine, fatty acid) nature; (f) the metabolic recycling of these fragments for biosynthetic purposes (salvage pathways); and (g) further degradation of fragments to waste products. Noteworthy, the correct course of ganglioside/glycosphingolipid metabolism requires the presence of the vimentin intracellular filament net work, likely to assist intracellular transport of sphingoid molecules. ut of the above events those that can be quantitatively evaluated with acceptable reliability are the processes of de novo biosynthesis, metabolic salvage and direct glycosylation. Depending on the cultured cells employed, the percentage of distribution of de novo biosynthesis, salvage pathways, and direct glycosylation, over total metabolism were reported to be: 35% (range: 10-90%) for de novo biosynthesis, 7% (range: 5-10%) for direct glycosylation, and 58% (range: 10-90%) for salvage pathways. The attempts made to calculate the half-life of overall ganglioside turnover provided data of unsure reliability, especially because in many studies salvage pathways were not taken into consideration. The values of half-life range from 2 to 6.5 h to 3 days depending on the cells used. Available evidence for changes of ganglioside/glycosphingolipid turnover, due to extracellular stimuli, is also considered and discussed.
204 citations
TL;DR: Recent concepts suggesting that the oligosaccharide composition of the gut constitutes a varied ecosystem for microorganisms that are susceptible to adapt there and possess the specific adhesion system and specific enzymes able to provide a carbohydrate nutrient are discussed.
202 citations
TL;DR: Higher brain ganglioside and glycoprotein sialic acid concentrations in infants fed human milk suggests increased synaptogenesis and differences in neurodevelopment.
TL;DR: The structure of the HA of an avian influenza virus, A/duck/Ukraine/63, a member of the same antigenic subtype, H3, as the virus that caused the 1968 Hong Kong influenza pandemic, and a possible progenitor of the pandemic virus is determined.
TL;DR: Sialidases are indeed closely related to malignancy and are thus potential targets for cancer diagnosis and therapy and are summarized from both a retrospective and a prospective viewpoint.
Abstract: Aberrant sialylation in cancer cells is thought to be a characteristic feature associated with malignant properties including invasiveness and metastatic potential. Sialidase which catalyzes the removal of sialic acid residues from glycoproteins and glycolipids, has been suggested to play important roles in many biological processes through regulation of cellular sialic acid contents. The altered expression of sialidase observed in cancer would, therefore, suggest its involvement in the malignant process. In mammalian cells, three types of sialidase cloned and characterized to date were found to behave in different manners during carcinogenesis. Recent progress in molecular cloning of these sialidases has facilitated elucidation of the molecular mechanisms and significance of these alterations. Herein we briefly describe our own studies on sialidase changes associated with malignant transformation and summarize the topic from both a retrospective and a prospective viewpoint. Sialidases are indeed closely related to malignancy and are thus potential targets for cancer diagnosis and therapy. Published in 2004.
TL;DR: Although a role for these natural inhibitors in the innate anti‐influenza immunity is still not clear, studies are in progress on the design of synthetic sialic acid‐containing inhibitors of receptor binding which could be used as anti‐ influenza drugs.
Abstract: SUMMARY Influenza viruses attach to susceptible cells via multivalent interactions of their haemagglutinins with sialyloligosaccharide moieties of cellular glycoconjugates. Soluble macromolecules containing sialic acid from animal sera and mucosal fluids can act as decoy receptors and competitively inhibit virus-mediated haemagglutination and infection. Although a role for these natural inhibitors in the innate anti-influenza immunity is still not clear, studies are in progress on the design of synthetic sialic acid-containing inhibitors of receptor binding which could be used as anti-influenza drugs. Copyright # 2003 John Wiley & Sons, Ltd.
TL;DR: Increasing the proportion of SAα2,3Gal linkages on the erythrocytes used, by enzymatic modification or change of species, improves the ability of ery Throcytes to bind to avian influenza strains and thereby improves the sensitivity of detection of antibody toAvian and equine HA in a range of mammalian and human sera using HI tests.
Abstract: Haemagglutination-inhibition tests (HI) are used to detect increases in influenza antibody in serum. However, they are relatively insensitive for the detection of human antibody responses to avian haemagglutinin, even in the presence of high titres of neutralising antibody after confirmed infection or vaccination. Human influenza viruses bind preferentially sialic acid containing N-acetylneuraminic acid alpha2,6-galactose (SAalpha2,6Gal) linkages while avian and equine viruses bind preferentially those containing N-acetylneuraminic acid alpha2,3-galactose (SAalpha2,3Gal) linkages. Increasing the proportion of SAalpha2,3Gal linkages on the erythrocytes used, by enzymatic modification or change of species, improves the ability of erythrocytes to bind to avian influenza strains and thereby improves the sensitivity of detection of antibody to avian and equine HA in a range of mammalian and human sera using HI tests.
TL;DR: The notion arises that these salvage pathways, leading to the formation of gangliosides and other glycosphingolipids, sphingomyelin, glycoproteins and glycosaminoglycans, represent an important saving of energy in the cell economy and constitute a relevant event in overallganglioside turnover, covering from 50% to 90% of it, depending on the cell line and stage of cell life.
TL;DR: Highly water-soluble glycopolymers with poly(alpha-L-glutamic acid) backbones carrying multivalent sialyl oligosaccharides units were chemoenzymatically synthesized as polymeric inhibitors of infection by human influenza viruses.
Abstract: Highly water-soluble glycopolymers with poly(a-L-glutamic acid) (PGA) backbones carrying multivalent sialyl oligosaccharides units were chemoenzymatically synthesized as polymeric inhibitors of infection by human influenza viruses. p-Aminophenyl disaccharide glycosides were coupled with g-carboxyl groups of PGA side chains and enzymatically converted to Neu5Aca2-3Galb1-4GlcNAcb-, Neu5Aca26Galb1-4GlcNAcb-, Neu5Aca2-3Galb1-3GalNAca-, and Neu5Aca2-3Galb1-3GalNAcb- units, respectively, by a2,3or a2,6-sialytransferases. The glycopolymers synthesized were used for neutralization of human influenza A and B virus infection as assessed by measurement of the degree of cytopathic inhibitory effect in virus-infected MDCK cells. Among the glycopolymers tested, a2,6-sialo-PGA with a high molecular weight (260 kDa) most significantly inhibited infection by an influenza A virus, strain A/Memphis/1/71 (H3N2), which predominantly binds to a2-6 Neu5Ac residue. The a2,6-sialo-PGA also inhibited infection by an influenza B virus, B/Lee/40. The binding preference of viruses to terminal sialic acids was affected by core determinants of the sugar chain, Galb1-4GlcNAcb- or Galb1-3GalNAca/b- units. Inhibition of infection by viruses was remarkably enhanced by increasing the molecular weight and sialic acid content of glycopolymers.
TL;DR: This is the first demonstration that galectin-8 binds to specific sulfated or sialylated glycosphingolipids with high affinity, indicating that this Gln47 plays important roles for binding to Neu5Acalpha2-->3Gal or SO3--->3Gal residues.
Abstract: Galectin-8 is a member of the galectin family and has two tandem repeated carbohydrate recognition domains (CRDs). We determined the binding specificities of galectin-8 and its two CRDs for oligosaccharides and glycosphingolipids using ELISA and surface plasmon resonance assays. Galectin-8 had much higher affinity for 3'-O-sulfated or 3'-O-sialylated lactose and a Lewis x-containing glycan than for oligosaccharides terminating in Galβ → 3/4GlcNAc. This specificity was mainly attributed to the N-terminal CRD (N-domain), whereas the C-terminal CRD (C-domain) had only weak affinity for a blood group A glycan. The N-domain bound not only to oligosaccharides but also to glycosphingolipids including sulfatide (SM4s), SM3, sialyl Lc4Cer, SB1a, GD1a, GM3, and sialyl nLc4Cer, suggesting that the N-domain recognizes a 3-O-sulfated or 3-O-sialylated Gal residue. The substitution of the C-3 of the Gal residue in lactose or N-acetyllactosamine with sulfate increased the degree of recognition by galectin-8 more potently than substitution with sialic acid. This is the first demonstration that galectin-8 binds to specific sulfated or sialylated glycosphingolipids with high affinity (K D ∼ 10 - 8 -10 - 9 M). When the Gln 4 7 residue of the N-domain was converted to Ala 4 7 , the specific affinity for sulfated or sialylated glycans was selectively lost, indicating that this Gln 4 7 plays important roles for binding to Neu5Acα2→3Gal or SO - 3 → 3Gal residues. The binding ability of galectin-8 to membrane-associated GM3 was confirmed using CHO cells, which predominantly express GM3. Binding of CHO cells to the mutein was significantly lower than to the N-domain.
TL;DR: Using a cell-free receptor/ligand-binding assay, it is shown that purified, desialylated α1β1 integrins have diminished collagen-binding capability, providing strong evidence that sialic acids play a causal role in regulating β1 integrin function.
Abstract: Intense investigation has centered on understanding the regulation of integrin cell adhesion receptors. In the present study, we propose that variant N-glycosylation represents an important mechanism for regulation of beta1, but not beta3 or beta5 integrins. We find that expression of oncogenic ras in HD3 colonocytes causes increased alpha2-6 sialylation of beta1 integrins, whereas expression of dominant-negative ras induces decreased alpha2-6 sialylation, relative to cells with wild-type ras. In contrast, neither beta3 nor beta5 integrins are alpha2-6 sialylated, regardless of the state of ras activation. Results from RT-PCR analyses suggest that differential integrin sialylation is due to a ras-dependent alteration in the expression of ST6Gal I, the enzyme that adds alpha2-6-linked sialic acids. Cells that express differentially sialylated beta1 integrins exhibit altered adhesion to collagen I (a beta1 ligand), but not to vitronectin (a beta3 or beta5 ligand). Similarly, the enzymatic removal of cell surface sialic acids from control cells alters binding to collagen, but not to vitronectin. Finally, using a cell-free receptor/ligand-binding assay, we show that purified, desialylated alpha1beta1 integrins have diminished collagen-binding capability, providing strong evidence that sialic acids play a causal role in regulating beta1 integrin function.
TL;DR: A new transgenic insect cell line is created, SfSWT-3, that can sialylate recombinant glycoproteins in the absence of fetal bovine serum and will be widely useful as an improved host for baculovirus-mediated recombinant Glycoprotein production.
Abstract: We have previously engineered transgenic insect cell lines to express mammalian glycosyltransferases and showed that these cells can sialylate N-glycoproteins, despite the fact that they have little intracellular sialic acid and no detectable CMP-sialic acid. In the accompanying study, we presented evidence that these cell lines can salvage sialic acids for de novo glycoprotein sialylation from extracellular sialoglycoproteins, such as fetuin, found in fetal bovine serum. This finding led us to create a new transgenic insect cell line designed to synthesize its own sialic acid and CMP-sialic acid. SfSWT-1 cells, which encode five mammalian glycosyltransferases, were transformed with two additional mammalian genes that encode sialic acid synthase and CMP-sialic acid synthetase. The resulting cell line expressed all seven mammalian genes, produced CMP-sialic acid, and sialylated a recombinant glycoprotein when cultured in a serum-free growth medium supplemented with N-acetylmannosamine. Thus the addition of mammalian genes encoding two enzymes involved in CMP-sialic acid biosynthesis yielded a new transgenic insect cell line, SfSWT-3, that can sialylate recombinant glycoproteins in the absence of fetal bovine serum. This new cell line will be widely useful as an improved host for baculovirus-mediated recombinant glycoprotein production.
TL;DR: In this paper, the potential of an N-Troc-protected sialic acid donor, equipped with phenylsulfenyl functionality as a leaving group, has been explored.
TL;DR: It is demonstrated that L-selectin binds with high affinity to the N-terminal region of PSGL-1 through cooperative interactions with three sulfated tyrosine residues and an appropriately positioned C2-O-sLex O-glycan.
TL;DR: Crystal structures of these sialosides in complex with SnD1 suggest explanations for the differences in specificity and affinity, providing further ideas for compound design of physiological and potentially therapeutic relevance.
TL;DR: The O-glycosylation of the individual mZP glycoproteins is analyzed by using ultrasensitive MS methods and it is found that the majority of the O- Glycans that are linked to mZp3 are core type 2 sequences terminated with sialic acid, lacNAc (Galβ1-4GlcNAc), lacdiNAc, Galα1-3Gal, and NeuAcα2-3[GalNAcβ1
Abstract: Murine sperm initiate fertilization by binding to the outer covering of the egg known as the murine zona pellucida (mZP). This binding is thought to require the interaction of O-glycans linked to a specific mZP glycoprotein (mZP3) with egg-binding proteins coating the sperm plasma membrane. The precise molecular basis of this interaction remains to be resolved. In this study, we analyzed the O-glycosylation of the individual mZP glycoproteins by using ultrasensitive MS methods. We found that the majority of the O-glycans that are linked to mZP3 are core type 2 sequences terminated with sialic acid, lacNAc (Galβ1-4GlcNAc), lacdiNAc (Gal-NAcβ1-4GlcNAc), Galα1-3Gal, and NeuAcα2-3[GalNAcβ1-4]Galβ1-4 (Sda antigen). Many of these terminal sequences have been implicated previously in murine sperm–egg binding. Core type 1 O-glycans are also present and are generally unmodified, although some are terminated with sialic acid, β-linked N-acetylhexosamine, or NeuAcα2-3[GalNAcβ1-4]Galβ1-4. Eggs expressing human ZP (huZP) glycoprotein huZP3, derived from transgenic mice, bind murine but not human sperm, implying that huZP3 acquires the same O-glycans as native mZP3. Sequencing of huZP3-associated O-glycans confirms that this implication is correct. The data obtained in this investigation may prove to be very useful for studies to determine the precise molecular basis of initial murine sperm–egg binding.
TL;DR: The results indicate that, unlike UDP-GlcNAc 2-epimerase, which promotes biosynthesis of sialic acid, GlcNAC 2-EPimerase can serve a catabolic role, diverting metabolic flux away from the sIALic acid pathway.
TL;DR: This report is the first description of sequences of sialic acid O‐acetyltransferase genes that have not been cloned from either other bacterial or mammalian organisms.
Abstract: Capsular polysaccharides of serogroup C, W-135 and Y meningococci were previously reported to be O-acetylated at the sialic acid residues. There is evidence that O-acetylation affects the immunogenicity of polysaccharide vaccines. We identified genes indispensable for O-acetylation of serogroup C, W-135 and Y meningococci downstream of the capsule synthesis genes siaA-D. The genes were co-transcribed with the sia operon as shown by reverse transcription polymerase chain reaction analysis. The putative capsular polysaccharide O-acetyltransferases were designated OatC and OatWY. The protein OatWY of serogroups W-135 and Y showed sequence homologies to members of the NodL-LacA-CysE family of bacterial acetyltransferases, whereas no sequence homology with any known protein in the different databases was found for the serogroup C protein OatC. In serogroup W-135 and Y meningococci, several clonal lineages either lacked OatWY or OatWY was inactivated by insertion of IS1301. For serogroup C meningococci, we observed in vitro phase variation of O-acetylation, which resulted from slipped-strand mispairing in homopolymeric tracts. This finding explains the observation of naturally occurring de-O-acetylated serogroup C meningococci. Our report is the first description of sequences of sialic acid O-acetyltransferase genes that have not been cloned from either other bacterial or mammalian organisms.
TL;DR: The results suggest that selective binding of type 1 reoviruses to M cells in vivo involves interaction of the type 1 σ1 protein with glycoconjugates containing α2-3-linked sialic acid that are accessible to viral particles only on M cell apical surfaces.
Abstract: Type 1 reoviruses invade the intestinal mucosa of mice by adhering selectively to M cells in the follicleassociated epithelium and then exploiting M cell transport activity. The purpose of this study was to identify the apical cell membrane component and viral protein that mediate the M cell adherence of these viruses. Virions and infectious subviral particles of reovirus type 1 Lang (T1L) adhered to rabbit M cells in Peyer’s patch mucosal explants and to tissue sections in an overlay assay. Viral adherence was abolished by pretreatment of sections with periodate and in the presence of excess sialic acid or lectins MAL-I and MAL-II (which recognize complex oligosaccharides containing sialic acid linked 2-3 to galactose). The binding of T1L particles to polarized human intestinal (Caco-2BBe) cell monolayers was correlated with the presence of MAL-I and MAL-II binding sites, blocked by excess MAL-I and -II, and abolished by neuraminidase treatment. Other type 1 reovirus isolates exhibited MAL-II-sensitive binding to rabbit M cells and polarized Caco-2BBe cells, but type 2 or type 3 isolates including type 3 Dearing (T3D) did not. In assays using T1L-T3D reassortants and recoated viral cores containing T1L, T3D, or no 1 protein, MAL-II-sensitive binding to rabbit M cells and polarized Caco-2BBe cells was consistently associated with the T1L 1. MAL-II-recognized oligosaccharide epitopes are not restricted to M cells in vivo, but MAL-II immobilized on virus-sized microparticles bound only to the follicle-associated epithelium and M cells. The results suggest that selective binding of type 1 reoviruses to M cells in vivo involves interaction of the type 1 1 protein with glycoconjugates containing 2-3-linked sialic acid that are accessible to viral particles only on M cell apical surfaces. Reovirus is a nonenveloped, 85-nm icosahedral pathogen that enters the mouse intestinal Peyer’s patch mucosa by adhering to M cells and then exploiting the antigen-transporting
TL;DR: This chapter summarizes the use of azido sugars for metabolic labeling of cell surface glycoconjugates in ManNAc derivatives and discusses the conversion of unnatural biosynthetic precursors to unnatural cell surface polysaccharides with altered biological function.
Abstract: Publisher Summary Cellular perceptions and responses are often initiated by binding events on the cell surface. Carbohydrates have been recognized as central players in these recognition events. Glycosylation also modulates how efficiently viruses, such as human immunodeficiency virus type 1 and influenza A, infect human cells. Glycosylation-mediated recognition events have been studied using targeted gene disruption in mice, mutant cell lines selected for specific glycosylation phenotypes, and small molecule inhibitors. Targeted disruption of glycosylation genes has provided significant insight into the function and diversity of carbohydrates. An alternative approach to studying the biology of carbohydrates, pioneered by Reutter and co-workers, utilizes the conversion of unnatural biosynthetic precursors to unnatural cell surface polysaccharides with altered biological function. This chapter summarizes the use of azido sugars for metabolic labeling of cell surface glycoconjugates. In addition to ManNAc derivatives, analogs of N-acetylglucosamine, fucose, N-acetylgalactosamine, and sialic acid have been tested for metabolic incorporation. Studies of metabolic incorporation and characterization of the cell surface products are also discussed in the chpater.
TL;DR: It is suggested that the carbohydrate-binding specificity of a virus can dramatically alter disease in the host and highlight the need for epidemiologic studies focusing on infection by sialic acid-binding reovirus strains as a possible contributor to the pathogenesis of neonatal biliary atresia.
Abstract: Infection of neonatal mice with some reovirus strains produces a disease similar to infantile biliary atresia, but previous attempts to correlate reovirus infection with this disease have yielded conflicting results. We used isogenic reovirus strains T3SA- and T3SA+, which differ solely in the capacity to bind sialic acid as a coreceptor, to define the role of sialic acid in reovirus encephalitis and biliary tract infection in mice. Growth in the intestine was equivalent for both strains following peroral inoculation. However, T3SA+ spread more rapidly from the intestine to distant sites and replicated to higher titers in spleen, liver, and brain. Strikingly, mice infected with T3SA+ but not T3SA- developed steatorrhea and bilirubinemia. Liver tissue from mice infected with T3SA+ demonstrated intense inflammation focused at intrahepatic bile ducts, pathology analogous to that found in biliary atresia in humans, and high levels of T3SA+ antigen in bile duct epithelial cells. T3SA+ bound 100-fold more efficiently than T3SA- to human cholangiocarcinoma cells. These observations suggest that the carbohydrate-binding specificity of a virus can dramatically alter disease in the host and highlight the need for epidemiologic studies focusing on infection by sialic acid-binding reovirus strains as a possible contributor to the pathogenesis of neonatal biliary atresia.
TL;DR: In mice, intestinal glycosyltransferase activities are under tissue and developmental control and microflora play a major role in their specific ontogeny but not in overall development, which may help explain the regional specificity of commensal bacteria and of enteric pathogens and may also relate age‐related changes in micro Flora to susceptibility to enteropathogens.
Abstract: SPECIFIC AIMSThe ratio of sialic acid to fucose on rodent brush-border glycoconjugates reverses from a predominance of sialic acid to fucose during postnatal development; this inversion is attributed to a reciprocal developmental change in the level of fucosyl- and sialytransferase activities. Since enteric bacteria use intestinal brush-border glycoconjugates as their target host cell receptors, we hypothesized that initial bacterial colonization of the rodent gut may help regulate those specific glycosyltransferases responsible for synthesizing brush-border glycoconjugates. To investigate this hypothesis, glycosyltransferase enzymes activities were measured in mucosal microsomal fractions from different intestinal regions of maturing conventional (CONV), germ-free (GF), and ex germ-free (XGF) mice and compared with general enzyme markers of gut development (e.g., disaccharidases).PRINCIPAL FINDINGS1. Age-dependent and tissue-specific changes in fucosyl- and sialyltransferase and disaccharidase activities...