Showing papers on "Sialic acid published in 2008"
TL;DR: Klotho participates in specific removal of α2,6-linked sialic acids and regulates cell surface retention of TRPV5 through this activity, which represents a novel mechanism for regulation of the activity of cell-surface glycoproteins and likely contributes to maintenance of calcium balance by Klotho.
Abstract: Klotho is a mammalian senescence-suppression protein that has homology with glycosidases. The extracellular domain of Klotho is secreted into urine and blood and may function as a humoral factor. Klotho-deficient mice have accelerated aging and imbalance of ion homeostasis. Klotho treatment increases cell-surface abundance of the renal epithelial Ca2+ channel TRPV5 by modifying its N-linked glycans. However, the precise sugar substrate and mechanism for regulation by Klotho is not known. Here, we report that the extracellular domain of Klotho activates plasma-membrane resident TRPV5 through removing terminal sialic acids from their glycan chains. Removal of sialic acids exposes underlying disaccharide galactose-N-acetylglucosamine, a ligand for a ubiquitous galactoside-binding lectin galectin-1. Binding to galectin-1 lattice at the extracellular surface leads to accumulation of functional TRPV5 on the plasma membrane. Knockdown of β-galactoside α2,6-sialyltransferase (ST6Gal-1) by RNA interference, but not other sialyltransferases, in a human cell line prevents the regulation by Klotho. Moreover, the regulation by Klotho is absent in a hamster cell line that lacks endogenous ST6Gal-1, but is restored by forced expression of recombinant ST6Gal-1. Thus, Klotho participates in specific removal of α2,6-linked sialic acids and regulates cell surface retention of TRPV5 through this activity. This action of Klotho represents a novel mechanism for regulation of the activity of cell-surface glycoproteins and likely contributes to maintenance of calcium balance by Klotho.
390 citations
TL;DR: It is suggested that this ongoing antigen-antibody reaction may generate chronic inflammation, possibly contributing to the high frequency of diet-related carcinomas and other diseases in humans.
Abstract: Human heterophile antibodies that agglutinate animal erythrocytes are known to detect the nonhuman sialic acid N-glycolylneuraminic acid (Neu5Gc). This monosaccharide cannot by itself fill the binding site (paratope) of an antibody and can also be modified and presented in various linkages, on diverse underlying glycans. Thus, we hypothesized that the human anti-Neu5Gc antibody response is diverse and polyclonal. Here, we use a novel set of natural and chemoenzymatically synthesized glycans to show that normal humans have an abundant and diverse spectrum of such anti-Neu5Gc antibodies, directed against a variety of Neu5Gc-containing epitopes. High sensitivity and specificity assays were achieved by using N-acetylneuraminic acid (Neu5Ac)-containing probes (differing from Neu5Gc by one less oxygen atom) as optimal background controls. The commonest anti-Neu5Gc antibodies are of the IgG class. Moreover, the range of reactivity and Ig classes of antibodies vary greatly amongst normal humans, with some individuals having remarkably large amounts, even surpassing levels of some well-known natural blood group and xenoreactive antibodies. We purified these anti-Neu5Gc antibodies from individual human sera using a newly developed affinity method and showed that they bind to wild-type but not Neu5Gc-deficient mouse tissues. Moreover, they bind back to human carcinomas that have accumulated Neu5Gc in vivo. As dietary Neu5Gc is primarily found in red meat and milk products, we suggest that this ongoing antigen-antibody reaction may generate chronic inflammation, possibly contributing to the high frequency of diet-related carcinomas and other diseases in humans.
282 citations
TL;DR: Analysis of the biosynthetic pathways in cloned EBV-immortalized IgA1-producing cells from patients with IgA nephropathy indicated a decrease in beta1,3-galactosyltransferase activity and an increase in N-acetylGalactosamine-specific alpha2,6-sialyl transferase activity, suggesting that premature sialylation likely contributes to the aberrant IgA 1 glycosylation in IgANephrop
Abstract: Aberrant glycosylation of IgA1 plays an essential role in the pathogenesis of IgA nephropathy. This abnormality is manifested by a deficiency of galactose in the hinge-region O-linked glycans of IgA1. Biosynthesis of these glycans occurs in a stepwise fashion beginning with the addition of N-acetylgalactosamine by the enzyme N-acetylgalactosaminyltransferase 2 and continuing with the addition of either galactose by beta1,3-galactosyltransferase or a terminal sialic acid by a N-acetylgalactosamine-specific alpha2,6-sialyltransferase. To identify the molecular basis for the aberrant IgA glycosylation, we established EBV-immortalized IgA1-producing cells from peripheral blood cells of patients with IgA nephropathy. The secreted IgA1 was mostly polymeric and had galactose-deficient O-linked glycans, characterized by a terminal or sialylated N-acetylgalactosamine. As controls, we showed that EBV-immortalized cells from patients with lupus nephritis and healthy individuals did not produce IgA with the defective galactosylation pattern. Analysis of the biosynthetic pathways in cloned EBV-immortalized cells from patients with IgA nephropathy indicated a decrease in beta1,3-galactosyltransferase activity and an increase in N-acetylgalactosamine-specific alpha2,6-sialyltransferase activity. Also, expression of beta1,3-galactosyltransferase was significantly lower, and that of N-acetylgalactosamine-specific alpha2,6-sialyltransferase was significantly higher than the expression of these genes in the control cells. Thus, our data suggest that premature sialylation likely contributes to the aberrant IgA1 glycosylation in IgA nephropathy and may represent a new therapeutic target.
239 citations
TL;DR: It is shown that SubB has a strong preference for glycans terminating in the sialic acid N-glycolylneuraminic acid (Neu5Gc), a monosaccharide not synthesized in humans, which confers susceptibility to the gastrointestinal and systemic toxicities of SubAB.
Abstract: AB(5) toxins comprise an A subunit that corrupts essential eukaryotic cell functions, and pentameric B subunits that direct target-cell uptake after binding surface glycans. Subtilase cytotoxin (SubAB) is an AB(5) toxin secreted by Shiga toxigenic Escherichia coli (STEC), which causes serious gastrointestinal disease in humans. SubAB causes haemolytic uraemic syndrome-like pathology in mice through SubA-mediated cleavage of BiP/GRP78, an essential endoplasmic reticulum chaperone. Here we show that SubB has a strong preference for glycans terminating in the sialic acid N-glycolylneuraminic acid (Neu5Gc), a monosaccharide not synthesized in humans. Structures of SubB-Neu5Gc complexes revealed the basis for this specificity, and mutagenesis of key SubB residues abrogated in vitro glycan recognition, cell binding and cytotoxicity. SubAB specificity for Neu5Gc was confirmed using mouse tissues with a human-like deficiency of Neu5Gc and human cell lines fed with Neu5Gc. Despite lack of Neu5Gc biosynthesis in humans, assimilation of dietary Neu5Gc creates high-affinity receptors on human gut epithelia and kidney vasculature. This, and the lack of Neu5Gc-containing body fluid competitors in humans, confers susceptibility to the gastrointestinal and systemic toxicities of SubAB. Ironically, foods rich in Neu5Gc are the most common source of STEC contamination. Thus a bacterial toxin's receptor is generated by metabolic incorporation of an exogenous factor derived from food.
215 citations
TL;DR: First in vivo evidence for a role of ST6Gal-I in tumor progression was confirmed using a novel approach, which conditionally restored St6gal1 in cell lines derived from the null tumors.
Abstract: Sialic acids on vertebrate cell surfaces mediate many biological roles. Altered expression of certain sialic acid types or their linkages can have prognostic significance in human cancer. A classic but unexplained example is enhanced alpha2-6-sialylation on N-glycans resulting from overexpression of the Golgi enzyme beta-galactoside:alpha2-6-sialyltransferase (ST6Gal-I). Previous data supporting a role for the resulting Sia alpha 2-3Gal beta 1-4GlcNAc (Sia6LacNAc) structure in tumor biology were based on in vitro studies in transfected carcinoma cells, in which increased Sia6LacNAc on beta1-integrins enhanced their binding to ligands, and stimulated cell motility. Here, we examine for the first time the in vivo role of the ST6Gal-I enzyme in the growth and differentiation of spontaneous mammary cancers in mice transgenic for a mouse mammary tumor virus promoter-driven polyomavirus middle T antigen, a tumor in which beta1-integrin function is important for tumorigenesis and in maintaining the proliferative state of tumor cells. Tumors induced in St6gal1-null animals were more differentiated compared with those in the wild-type background, both by histologic analysis and by protein expression profiles. Furthermore, we show the St6gal1-null tumors have selectively altered expression of genes associated with focal adhesion signaling and have decreased phosphorylation of focal adhesion kinase, a downstream target of beta1-integrins. This first in vivo evidence for a role of ST6Gal-I in tumor progression was confirmed using a novel approach, which conditionally restored St6gal1 in cell lines derived from the null tumors. These findings indicate a role for ST6Gal-I as a mediator of tumor progression, with its expression causing a less differentiated phenotype, via enhanced beta1-integrin function.
171 citations
TL;DR: In contrast to those of all other reported AAVs, AAV12 cell attachment and transduction do not require cell surface sialic acids or heparan sulfate proteoglycans, which makes rAAV12 an interesting candidate for gene transfer applications.
Abstract: Recombinant adeno-associated virus (rAAV) is a promising vector for gene therapy. Recent isolations of novel AAV serotypes have led to significant advances by broadening the tropism and increasing the efficiency of gene transfer to the desired target cell. However, a major concern that remains is the strong preexisting immune responses to several vectors. In this paper, we describe the isolation and characterization of AAV12, an AAV serotype with unique biological and immunological properties. In contrast to those of all other reported AAVs, AAV12 cell attachment and transduction do not require cell surface sialic acids or heparan sulfate proteoglycans. Furthermore, rAAV12 is resistant to neutralization by circulating antibodies from human serum. The feasibility of rAAV12 as a vector was demonstrated in a mouse model in which muscle and salivary glands were transduced. These characteristics make rAAV12 an interesting candidate for gene transfer applications.
168 citations
TL;DR: It is suggested that recombinant HA proteins as individual or oligomeric trimers can elicit potent neutralizing antibody responses to avian H5N1 influenza viruses.
Abstract: Although the human transmission of avian H5N1 virus remains low, the prevalence of this highly pathogenic infection in avian species underscores the need for a preventive vaccine that can be made without eggs. Here, we systematically analyze various forms of recombinant hemagglutinin (HA) protein for their potential efficacy as vaccines. Monomeric, trimeric, and oligomeric H5N1 HA proteins were expressed and purified from either insect or mammalian cells. The immunogenicity of different recombinant HA proteins was evaluated by measuring the neutralizing antibody response. Neutralizing antibodies to H5N1 HA were readily generated in mice immunized with the recombinant HA proteins, but they varied in potency depending on their multimeric nature and cell source. Among the HA proteins, a high-molecular-weight oligomer elicited the strongest antibody response, followed by the trimer; the monomer showed minimal efficacy. The coexpression of another viral surface protein, neuraminidase, did not affect the immunogenicity of the HA oligomer, as expected from the immunogenicity of trimers produced from insect cells. As anticipated, HA expressed in mammalian cells without NA retained the terminal sialic acid residues and failed to bind α2,3-linked sialic acid receptors. Taken together, these results suggest that recombinant HA proteins as individual or oligomeric trimers can elicit potent neutralizing antibody responses to avian H5N1 influenza viruses.
162 citations
TL;DR: The current knowledge about sialic acid distribution in human tissues is reviewed and extended, and viruses with ocular tropism and their preference for α2,3‐linked sIALic acid are discussed.
Abstract: Avian influenza A viruses exhibit a strong preference for using alpha2,3-linked sialic acid as a receptor. Until recently, the presumed lack of this receptor in human airways was believed to constitute an efficient barrier to avian influenza A virus infection of humans. Recent zoonotic outbreaks of avian influenza A virus have triggered researchers to analyse tissue distribution of sialic acid in further detail. Here, we review and extend the current knowledge about sialic acid distribution in human tissues, and discuss viruses with ocular tropism and their preference for alpha2,3-linked sialic acid.
128 citations
TL;DR: This is the first O-glycan analysis of MUC1 from the serum of a breast cancer patient and the results suggest that amongst the cell lines commonly used to express recombinant M UC1 the T47D cell line processes glycans that are most similar to patient-derived material.
Abstract: MUC1 is a high molecular weight glycoprotein that is overexpressed in breast cancer. Aberrant O-linked glycosylation of MUC1 in cancer has been implicated in disease progression. We investigated the O-linked glycosylation of MUC1 purified from the serum of an advanced breast cancer patient. O-Glycans were released by hydrazinolysis and analyzed by liquid chromatography-electrospray ionization-mass spectrometry and by high performance liquid chromatography coupled with sequential exoglycosidase digestions. Core 1 type glycans (83%) dominated the profile which also confirmed high levels of sialylation: 80% of the glycans were mono-, di- or trisialylated. Core 2 type structures contributed approximately 17% of the assigned glycans and the oncofoetal Thomsen-Friedenreich (TF) antigen (Galbeta1-3GalNAc) accounted for 14% of the total glycans. Interestingly, two core 1 type glycans were identified that had sialic acid alpha2-8 linked to sialylated core 1 type structures (9% of the total glycan pool). This is the first O-glycan analysis of MUC1 from the serum of a breast cancer patient; the results suggest that amongst the cell lines commonly used to express recombinant MUC1 the T47D cell line processes glycans that are most similar to patient-derived material.
128 citations
TL;DR: The distribution pattern of AIV‐Rs is partially inconsistent with the pattern of infected cells as detected in previous studies, which suggests there may be other receptors or mechanisms involved in H5N1 infection.
Abstract: Avian and human influenza viruses preferentially bind to alpha-2,3-linked and alpha-2,6-linked sialic acids, respectively. Until today, the distributions of these two receptor types had never been investigated in H5N1-infected human tissue samples. Here, the expression of avian (AIV-Rs) and human influenza receptors (HuIV-Rs) is studied in various organs (upper and lower respiratory tracts, brain, placenta, liver, kidney, heart, intestines, and spleen) of two H5N1 cases and 14 control cases. Histochemical stains using biotinylated Maackia amurensis lectin II and Sambucus nigra agglutinin were performed to localize AIV-Rs and HuIV-Rs, respectively. Immunohistochemical stainings were performed to identify the receptor-bearing cells. AIV-Rs were detected on type II pneumocytes; a limited number of epithelial cells of the upper respiratory tract; and the bronchi, bronchioli, and trachea; as well as on Kupffer cells, glomerular cells, splenic T cells, and neurons in the brain and intestines. HuIV-Rs were abundantly present in the respiratory tract and lungs. They were also detected on Hofbauer cells, glomerular cells, splenic B cells, and in the liver. Moreover, endothelial cells of all organs examined expressed both receptor types. In conclusion, the distribution pattern of AIV-Rs is partially inconsistent with the pattern of infected cells as detected in previous studies, which suggests there may be other receptors or mechanisms involved in H5N1 infection. In addition, the diffuse presence of receptors on endothelial cells may account for the multiple organ involvement in H5N1 influenza. Finally, the relative lack of AIV-Rs in the upper airway may be a one of the factors preventing efficient human-to-human transmission of H5N1 influenza.
126 citations
TL;DR: The crystal structures suggested that NanI is able to hydrate 2-deoxy-2,3-dehydro-N-acetylneuraminic acid to N-acetelneuramic acid, and this was confirmed by NMR, and a mechanism for this activity is suggested.
TL;DR: The results suggest that identification of alpha2,3-linked sialic acids on PSA potentially discriminates malignant from benign conditions, if the analysis is applied to oligosaccharides specifically attached to the N-glycosylation site of PSA in either a free or a complexed form in the serum.
Abstract: The oligosaccharide structures of prostate specific antigen (PSA) are expected to be useful in discriminating prostate cancer from benign conditions both accompanied by increased serum PSA levels A large proportion of PSA forms a covalent complex with a glycoprotein, alpha(1)-antichymotrypsin, in human blood In the present study, the glycan profiles of free and complexed forms of PSA from cancer patient serum and of seminal plasma PSA were compared by analyzing the glycopeptides obtained by lysylendopeptidase digestion of the electrophoretically separated PSA with mass spectrometry The profiles of the PSA N-glycans from the free and complexed molecules were quite similar to each other and consisted of fucosylated biantennary oligosaccharides as the major class They were mostly sialylated, and a considerable sialic acid fraction was alpha2,3-linked as determined by Streptococcus pneumoniae neuraminidase digestion of the glycopeptides In the seminal plasma PSA, high-mannose and hybrid types of oligosaccharides were predominant, and the sialic acids attached to the latter as well as to biantennary oligosaccahrides were exclusively alpha2,6-linked because they were removed by Arthrobacter ureafaciens neuraminidase but resistant to S pneumoniae neuraminidase Complex-type oligosaccharides from other sources were found in the seminal plasma sample, indicating that analysis of released glycans carries a risk of being misleading The results suggest that identification of alpha2,3-linked sialic acids on PSA potentially discriminates malignant from benign conditions, if the analysis is applied to oligosaccharides specifically attached to the N-glycosylation site of PSA in either a free or a complexed form in the serum
TL;DR: It is suggested that glycosylation has little or no impact on the pharmacokinetic behavior of these two monoclonal antibodies in mice.
TL;DR: Substrates specificity studies showed that 5-O-methyl-ManNAc, a ManNAc derivative, can be used efficiently as a substrate by PmNanA, but not efficiently by EcNAnA, for the synthesis of 8- O-methyl Neu5Ac.
Abstract: Sialic acid aldolases or N-acetylneuraminate lyases (NanAs) catalyze the reversible aldol cleavage of N-acetylneuraminic acid (Neu5Ac) to form pyruvate and N-acetyl-d-mannosamine (ManNAc). A capillary electrophoresis assay was developed to directly characterize the activities of NanAs in both Neu5Ac cleavage and Neu5Ac synthesis directions. The assay was used to obtain the pH profile and the kinetic data of a NanA cloned from Pasteurella multocida P-1059 (PmNanA) and a previously reported recombinant Escherichia coli K12 NanA (EcNanA). Both enzymes are active in a broad pH range of 6.0–9.0 in both reaction directions and have similar kinetic parameters. Substrates specificity studies showed that 5-O-methyl-ManNAc, a ManNAc derivative, can be used efficiently as a substrate by PmNanA, but not efficiently by EcNanA, for the synthesis of 8-O-methyl Neu5Ac. In addition, PmNanA (250 mg l−1 culture) has a higher expression level (2.5-fold) than EcNanA (94 mg l−1 culture). The higher expression level and a broader substrate tolerance make PmNanA a better catalyst than EcNanA for the chemoenzymatic synthesis of sialic acids and their derivatives.
TL;DR: It is concluded that (125)I-ASOR is a facilely-prepared, stable assay reagent for ASGPR expression if appropriately prepared, and that HepG2 cells, but not HepAD38 or Huh-5-2 Cells, are suitable for studies exploiting the endocytotic AsGPR.
Abstract: The asialoglycoprotein receptor (ASGPR), an endocytotic cell surface receptor expressed by hepatocytes, is triggered by triantennary binding to galactose residues of macromolecules such as asialoorosomucoid (ASOR). The capacity of this receptor to import large molecules across the cellular plasma membrane makes it an enticing target for receptor-mediated drug delivery to hepatocytes and hepatoma cells via ASGPR-mediated endocytosis. This study describes the preparation and characterization of (125)I-ASOR, and its utility in the assessment of ASGPR expression by HepG2, HepAD38 and Huh5-2 human hepatoma cell lines. ASOR was prepared from human orosomucoid, using acid hydrolysis to remove sialic acid residues, then radioiodinated using iodogen. (125)I-ASOR was purified by gel column chromatography and characterized by SDS-PAGE electrophoresis. The ASOR yield by acid hydrolysis was 75%, with approximately 87 % of the sialic acid residues removed. Electrophoresis and gel chromatography demonstrated substantial differences in (125)I-ASOR quality depending on the method of radioiodination. ASGPR densities per cell were estimated at 76,000 (HepG2), 17,000 (HepAD38) and 3,000 (Huh-5-2). (125)I-ASOR binding to ASGPR on HepG2 cells was confirmed through galactose- and EDTA- challenge studies. It is concluded that (125)I-ASOR is a facilely-prepared, stable assay reagent for ASGPR expression if appropriately prepared, and that HepG2 cells, but not HepAD38 or Huh-5-2 cells, are suitable for studies exploiting the endocytotic ASGPR.
TL;DR: This review summarizes the latest developments in the synthesis of C-5 modified sialic acid glycosyl donors and Glycosyl acceptors and their application in the synthesisation of alpha-sialosides.
TL;DR: It was proposed that B-cells in the human blood are a mixture of clones equipped with different sets and ratios of glycosyltransferases, and that each glycoform of IgG might have a different function.
TL;DR: In this article, the activated sialic acid donor (CMP-Neu5Ac) was generated from exogenous SIALIC acid, which was transported into the cells by the permease NanT.
TL;DR: NMR studies show that, like the leech sialidase, NanB acts as an intramolecular trans-sialid enzyme releasing Neu2,7-anhydro5Ac, and provide support for a possible differential role for NanB compared to NanA in pneumococcal virulence.
TL;DR: Both sialidases and sialyltransferases seem to tell us that sialic acid-handling enzymes have evolved important modifications related to the distinctive features of siali acid itself.
TL;DR: Findings suggest that experimental approaches that prevent the formation of large Gal-deficient IgA1-IgG IC may be applied ultimately in an immunologically mediated therapy.
Abstract: Studies of the properties of immune complexes (IC) in the circulation, urine, and mesangium of IgA nephropathy (IgAN) patients have provided data relevant to the pathogenesis of this disease IC contain predominantly polymeric IgA1 molecules which are deficient in galactose (Gal) residues on O-linked glycan chains in the hinge region (HR) of their heavy (H) chains As a result of this aberrancy, a novel antigenic determinant(s) involving N-acetylgalactosamine (GalNAc) and perhaps sialic acid (SA) of O-linked glycans is generated and recognized by naturally occurring GalNAc-specific antibodies Thus, IC in IgAN consist of Gal-deficient IgA1 molecules as an antigen, and GalNAc-specific IgG and/or IgA1 as an antibody IgG antibodies to Gal-deficient IgA1 are probably induced by cross-reactive microbial antigens; they are present at variable levels not only in humans with or without IgAN but also in many phylogenetically diverse vertebrate species Incubation of human mesangial cells with IC from sera of IgAN patients indicated that stimulation of cellular proliferative activity was restricted to the large (>800 kDa) complexes These findings suggest that experimental approaches that prevent the formation of large Gal-deficient IgA1-IgG IC may be applied ultimately in an immunologically mediated therapy
TL;DR: The results indicate the STs expression modulates the increased expression of surface sialylated structures during mo-DC generation, which is probably related with changes in cell mechanisms.
Abstract: Several glycoconjugates are involved in the immune response. Sialic acid is frequently the glycan terminal sugar and it may modulate immune interactions. Dendritic cells (DCs) are antigen-presenting cells with high endocytic capacity and a central role in immune regulation. On this basis, DCs derived from monocytes (mo-DC) are utilised in immunotherapy, though many features are ignored and their use is still limited. We analyzed the surface sialylated glycans expressed during human mo-DC generation. This was monitored by lectin binding and analysis of sialyltransferases (ST) at the mRNA level and by specific enzymatic assays. We showed that alpha 2-3-sialylated O-glycans and alpha 2-6- and alpha 2-3-sialylated N-glycans are present in monocytes and their expression increases during mo-DC differentiation. Three main ST genes are committed with this rearrangement: ST6Gal1 is specifically involved in the augmented alpha 2-6-sialylated N-glycans; ST3Gal1 contributes for the alpha2-3-sialylation of O-glycans, particularly T antigens; and ST3Gal4 may contribute for the increased alpha2-3-sialylated N-glycans. Upon mo-DC maturation, ST6Gal1 and ST3Gal4 are downregulated and ST3Gal1 is altered in a stimulus-dependent manner. We also observed that removing surface sialic acid of immature mo-DC by neuraminidase significantly decreased its endocytic capacity, while it increased in monocytes. Our results indicate the STs expression modulates the increased expression of surface sialylated structures during mo-DC generation, which is probably related with changes in cell mechanisms. The ST downregulation after mo-DC maturation probably results in a decreased sialylation or sialylated glycoconjugates involved in the endocytosis, contributing to the downregulation of one or more antigen-uptake mechanisms specific of mo-DC.
TL;DR: The histomorphology, the histochemistry and the distribution of glycoconjugates in the mucosa of the digestive tract of the weakfish Cynoscion guatucupa revealed that the buccopharyngeal cavity and the esophagus are lined by a stratified epithelium where the mucoso is thrown into longitudinal folds.
TL;DR: A novel amidation using acetohydrazide is developed which can completely modify both types of linkages of sialoglycans and is demonstrated MS profiling of N-linked glycans released from a bovine fetuin which is rich in alpha2,3-linked sialic acids.
Abstract: Recently, glycans have been recognized as valuable biomarkers for various disease states. In particular, sialoglycans, which have sialic acids at their terminal end, are likely to have relevance to diseases such as cancer and inflammation. Mass spectrometry (MS) has become an indispensable tool for biomarker discovery. However, matrix-assisted laser desorption ionization (MALDI) MS of sialoglycans normally causes loss of sialic acid. Methylesterification or amidation of carboxyl functionality in sialic acid has been reported to suppress the loss of sialic acids. We found that the modifications of alpha2,3-linked sialic acids proceed less efficiently than those at alpha2,6-linkages. Furthermore, the modifications of the alpha2,3-linked sialic acids are incomplete. This variability in the extent of derivatization presents a major problem in terms of glycan biomarker discovery using MALDI MS. In this study, we developed a novel amidation using acetohydrazide which can completely modify both types of linkages of sialoglycans. With the use of this method, we demonstrate MS profiling of N-linked glycans released from a bovine fetuin which is rich in alpha2,3-linked sialic acids.
TL;DR: It is demonstrated that glycan microarrays can be used for high-throughput acceptor specificity screening of various recombinant sialyltransferases and can be use towards synthesis of new carbohydrate compounds and expand the glycan array compound library.
Abstract: Here we demonstrate that glycan microarrays can be used for high-throughput acceptor specificity screening of various recombinant sialyltransferases. Cytidine-5′-monophospho-N-acetylneuraminic acid (CMP-Neu5Ac) was biotinylated at position 9 of N-acetylneuraminic acid (Neu5Ac) by chemoenzymatic synthesis generating CMP-9Biot-Neu5Ac. The activated sugar nucleotide was used as donor substrate for various mammalian sialyltranferases which transferred biotinylated sialic acids simultaneously onto glycan acceptors immobilized onto a microarray glass slide. Biotinylated glycans detected with fluorescein–streptavidin conjugate to generate a specificity profile for each enzyme both confirming previously known specificities and reveal additional specificity information. Human α2,6sialyltransferase-I (hST6Gal-I) also sialylates chitobiose structures (GlcNAcβ1-4GlcNAc)n including N-glycans, rat α2,3sialyltransferase (rST3Gal-III) tolerates fucosylated acceptors such as Lewisa, human α2,3sialyltransferase-IV (hST3Gal-IV) broadly sialylates oligosaccharides of types 1–4 and porcine α2,3sialyltransferase-I (pST3Gal-I) sialylates ganglio-oligosaccharides and core 2 O-glycans in our array system. Several of these sialyltransferases perform a substitution reaction and exchange a sialylated acceptor with a biotinylated sialic acid but are restricted to the most specific acceptor substrates. Thus, this method allows for a rapid generation of enzyme specificity information and can be used towards synthesis of new carbohydrate compounds and expand the glycan array compound library.
TL;DR: The decreased ability of H. influenzae to import sialic acid had negative effects on resistance to complement-mediated killing and viability of biofilms in vitro, confirming the importance of sIALic acid transport to the bacterium.
TL;DR: This paper deals only with glucosaminoglycans of mammalian tissues containing neuraminic acid and complexes of these compounds with proteins or peptides will be referred to as glycoproteins.
Abstract: Glycoproteins are complexes between heteropolyor oligosaccharides with polypeptides linked to each other by covalent bonds. They are widely distributed in vertebrates and present in either free form or linked with larger protein molecules. They are found in the greatest concentration in animal fluids like blood plasma and urine and also in connective tissue in which two types of glycoproteins were found, one linked to a certain type of collagen fibers and the reticulin matrix and the other present in the interfibrillary spaces of typical connective tissue. Only the latter type contains hexosamines as an essential constituent. Hexosaminoglycans in mammalian tissues which do not contain hexuronic acids in general contain two hexoses, galactose and mannose, one or two hexosamines, glucosamine and galactosamine, and two other sugars, namely fucose and a derivative of neuraminic acid. There is evidence that the two last sugars are end group constituents. Neuraminic acid can be cleaved off by mild acid hydrolysis under conditions in which other constituents of glycoproteins were shown not to be set free. The same is also true to a lesser degree of fucose which was directly shown to be an end group constituent in blood group substances? This paper deals only with glucosaminoglycans of mammalian tissues containing neuraminic acid and complexes of these compounds with proteins or peptides will be referred to as glycoproteins. It has been remarked that glycoproteins are found in those parts of the animal body which are in continuous or intermittent motion and as particularly glycoproteins were found to be the main constituents in all forms of mucus, it was suggested that they play the role of lubricants in the animal body. This concept, although it may be fundamentally correct, does not explain one very characteristic structural feature of this type of Complexes, namely the high degree of structural specificity which is shown by glycoprotehs froin various body constituents of the same species, as well as the high degree of species specificity of glycoproteins extracted from the same tissue of different species. This specificity appears particularly striking with respect to the end group constituents and in fucosialo glycoproteins manifests itself in the wide range of variations in the content of fucose and neuraminic acid when carbohydrates of glycoproteins of different origin are compared with each other with respect to their composition. In addition to this variability, a characteristic interrelation between the two end group constituents seems to prevail when different glycoproteins representing certain physiological units, for instance glycoproteins of blood plasma or urine, are compared with each other. In general, in such a series of glycoproteins, the individual components will be distinguishable by the ratio of neuraminic acid to fucose and if the ratio of these two end group constituents to one of the backbone constituents, namely hexose or hexosamine are considered, it will be found that the two ratios are in a reciprocal relation to each other in the sense that when one of the ratios is rising in the series the other will be moving in the opposite direction.
TL;DR: High-throughput screening assays performed in NeutrAvidin-coated microtiter plates show that whereas Sambucus nigra Lectin binds to alpha2,6-linked sialosides with high promiscuity, human Siglec-2 (CD22) is highly selective for a number of sialic acid structures and the underlying glycans in its sIALoside ligands.
Abstract: Although the vital roles of structures containing sialic acid in biomolecular recognition are well documented, limited information is available on how sialic acid structural modifications, sialyl linkages, and the underlying glycan structures affect the binding or the activity of sialic acid-recognizing proteins and related downstream biological processes. A novel combinatorial chemoenzymatic method has been developed for the highly efficient synthesis of biotinylated sialosides containing different sialic acid structures and different underlying glycans in 96-well plates from biotinylated sialyltransferase acceptors and sialic acid precursors. By transferring the reaction mixtures to NeutrAvidin-coated plates and assaying for the yields of enzymatic reactions using lectins recognizing sialyltransferase acceptors but not the sialylated products, the biotinylated sialoside products can be directly used, without purification, for high-throughput screening to quickly identify the ligand specificity of sialic acid-binding proteins. For a proof-of-principle experiment, 72 biotinylated alpha2,6-linked sialosides were synthesized in 96-well plates from 4 biotinylated sialyltransferase acceptors and 18 sialic acid precursors using a one-pot three-enzyme system. High-throughput screening assays performed in NeutrAvidin-coated microtiter plates show that whereas Sambucus nigra Lectin binds to alpha2,6-linked sialosides with high promiscuity, human Siglec-2 (CD22) is highly selective for a number of sialic acid structures and the underlying glycans in its sialoside ligands.
TL;DR: This first comprehensive glycoproteomic analysis of the important human plasma glycoprotein BChE did not give any indication of O‐glycosylation or any other kind of PTMs as previously postulated.
Abstract: Human butyrylcholinesterase (hBChE) is a highly glycosylated protein present in human plasma. The enzyme hydrolyses choline esters, for example benzoylcholine, butyrylthiocholine and acetylthiocholine as well as noncholine esters like heroin and aspirin. hBChE is primarily involved in neuronal transmission and is a potential bioscavenger of toxic organophosphates to protect acetylcholinesterase. A prerequisite for the therapeutic use of hBChE is a detailed characterization of this glycoprotein purified from human plasma. In this study, MS/MS could confirm most of the protein backbone, including the N- and the C-terminus. Site-specific analysis of all nine potential N-glycosylation sites revealed mainly mono- and disialylated N-glycans to be present on this glycoprotein. Sialic acids (Neu5Ac) are mainly alpha2,6-linked, however a fraction of the N-glycans contained Neu5Ac also in alpha2,3 linkage. On monosialylated N-glycans, sialic acid is exclusively located on the 3-arm and in alpha2,6 linkage, as verified by 2D-HPLC and exoglycosidase digests of 2-aminopyridine (PA)-labelled N-glycans. This first comprehensive glycoproteomic analysis of the important human plasma glycoprotein BChE did not give any indication of O-glycosylation or any other kind of PTMs as previously postulated.
TL;DR: The characterization of a truncated CstII mutant (CstIIDelta32(I53S), cloned from a synthetic gene whose codons are optimized for an Escherichia coli expression system, indicates that the enzyme is flexible in using different CMP-activated sialic acids and their analogs for the synthesis of GD3 oligosaccharides containing natural and nonnatural modifications at the terminal sIALic acid.
Abstract: CstII from bacterium Campylobacter jejuni strain OH4384 has been previously characterized as a bifunctional sialyltransferase having both alpha2,3-sialyltransferase (GM3 oligosaccharide synthase) and alpha2,8-sialyltransferase (GD3 oligosaccharide synthase) activities which catalyze the transfer of N-acetylneuraminic acid (Neu5Ac) from cytidine 5'-monophosphate (CMP)-Neu5Ac to C-3' of the galactose in lactose and to C-8 of the Neu5Ac in 3'-sialyllactose, respectively (Gilbert M, Karwaski MF, Bernatchez S, Young NM, Taboada E, Michniewicz J, Cunningham AM, Wakarchuk WW. 2002. The genetic bases for the variation in the lipo-oligosaccharide of the mucosal pathogen, Campylobacter jejuni. Biosynthesis of sialylated ganglioside mimics in the core oligosaccharide. J Biol Chem. 277:327-337). We report here the characterization of a truncated CstII mutant (CstIIDelta32(I53S)) cloned from a synthetic gene whose codons are optimized for an Escherichia coli expression system. In addition to the alpha2,3- and alpha2,8-sialyltransferase activities reported before for the synthesis of GM3- and GD3-type oligosaccharides, respectively, the CstIIDelta32(I53S) has alpha2,8-sialyltransferase (GT3 oligosaccharide synthase) activity for the synthesis of GT3 oligosaccharide. It also has alpha2,8-sialidase (GD3 oligosaccharide sialidase) activity that catalyzes the specific cleavage of the alpha2,8-sialyl linkage of GD3-type oligosaccharides and alpha2,8-trans-sialidase (GD3 oligosaccharide trans-sialidase) activity that catalyzes the transfer of a sialic acid from a GD3 oligosaccharide to a different GM3 oligosaccharide (3'-sialyllactoside). The donor substrate specificity study of the CstIIDelta32(I53S) GD3 oligosaccharide synthase activity indicates that the enzyme is flexible in using different CMP-activated sialic acids and their analogs for the synthesis of GD3 oligosaccharides containing natural and nonnatural modifications at the terminal sialic acid.