Occurrence of Sialic Acids

Phylogenetic Distribution of CMP-Neu5Ac Hydroxylase (CMAH), the Enzyme Synthetizing the Proinflammatory Human Xenoantigen Neu5Gc

The enzyme CMP-N-acetylneuraminic acid hydroxylase (CMAH) is responsible for the synthesis of N-glycolylneuraminic acid (Neu5Gc), a sialic acid present on the cell surface proteins of most deuterostomes. The CMAH gene is thought to be present in most deuterostomes, but it has been inactivated in a number of lineages, including humans. The inability of humans to synthesize Neu5Gc has had several evolutionary and biomedical implications. Remarkably, Neu5Gc is a xenoantigen for humans, and consumption of Neu5Gc-containing foods, such as red meats, may promote inflammation, arthritis, and cancer. Likewise, xenotransplantation of organs producing Neu5Gc can result in inflammation and organ rejection. Therefore, knowing what animal species contain a functional CMAH gene, and are thus capable of endogenous Neu5Gc synthesis, has potentially far-reaching implications. In addition to humans, other lineages are known, or suspected, to have lost CMAH; however, to date reports of absent and pseudogenic CMAH genes are restricted to a handful of species. Here, we analyze all available genomic data for nondeuterostomes, and 322 deuterostome genomes, to ascertain the phylogenetic distribution of CMAH. Among nondeuterostomes, we found CMAH homologs in two green algae and a few prokaryotes. Within deuterostomes, putatively functional CMAH homologs are present in 184 of the studied genomes, and a total of 31 independent gene losses/pseudogenization events were inferred. Our work produces a list of animals inferred to be free from endogenous Neu5Gc based on the absence of CMAH homologs and are thus potential candidates for human consumption, xenotransplantation research, and model organisms for investigation of human diseases.

Isolation of Unusually Composed Sialyl-Compounds from Hemofiltrate

Sialyl compounds are essential components of various biological fluids but relatively little is known about their occurrence in the extracellular fluid of patients with end-stage renal disease. As we have developed a macropreparative method for concentrating and desalting a wide range of fractions from diluted biological fluids we have been able to isolate and identify 5 sialooligosaccharides, 3 sialosugarphosphates, 2 monosialoglycopeptides and 1 disialoglycopeptide. The structures have been elucidated predominantly by one and two-dimensional NMR spectroscopy, enzymatic degradation and FAB mass spectrometry.

The accumulation of these compounds in uremic sera may be of particular interest as they may interact in the molecular biology of diseases typically associated with the uremic state, e.g., immune deficiency, neurological disorders, receptor binding abnormalities, complement system disturbances and cell membrane alterations.

Phylogenetic-Derived Insights into the Evolution of Sialylation in Eukaryotes: Comprehensive Analysis of Vertebrate β-Galactoside α2,3/6-Sialyltransferases (ST3Gal and ST6Gal)

Cell surface of eukaryotic cells is covered with a wide variety of sialylated molecules involved in diverse biological processes and taking part in cell–cell interactions. Although the physiological relevance of these sialylated glycoconjugates in vertebrates begins to be deciphered, the origin and evolution of the genetic machinery implicated in their biosynthetic pathway are poorly understood. Among the variety of actors involved in the sialylation machinery, sialyltransferases are key enzymes for the biosynthesis of sialylated molecules. This review focus on β-galactoside α2,3/6-sialyltransferases belonging to the ST3Gal and ST6Gal families. We propose here an outline of the evolutionary history of these two major ST families. Comparative genomics, molecular phylogeny and structural bioinformatics provided insights into the functional innovations in sialic acid metabolism and enabled to explore how ST-gene function evolved in vertebrates.

Antibodies against Escherichia coli O24 and O56 O-Specific Polysaccharides Recognize Epitopes in Human Glandular Epithelium and Nervous Tissue

Lipopolysaccharide (LPS), the major component of the outer membrane of Gram-negative bacteria, contains the O-polysaccharide, which is important to classify bacteria into different O-serological types within species. The O-polysaccharides of serotypes O24 and O56 of E. coli contain sialic acid in their structures, already established in our previous studies. Here, we report the isolation of specific antibodies with affinity chromatography using immobilized lipopolysaccharides. Next, we evaluated the reactivity of anti-O24 and anti-O56 antibody on human tissues histologically. The study was conducted under the assumption that the sialic acid based molecular identity of bacterial and tissue structures provides not only an understanding of the mimicry-based bacterial pathogenicity. Cross-reacting antibodies could be used to recognize specific human tissues depending on their histogenesis and differentiation, which might be useful for diagnostic purposes. The results indicate that various human tissues are recognized by anti-O24 and anti-O56 antibodies. Interestingly, only a single specific reactivity could be found in the anti-O56 antibody preparation. Several tissues studied were not reactive with either antibody, thus proving that the presence of cross-reactive antigens was tissue specific. In general, O56 antibody performed better than O24 in staining epithelial and nervous tissues. Positive staining was observed for both normal (ganglia) and tumor tissue (ganglioneuroma). Epithelial tissue showed positive staining, but an epitope recognized by O56 antibody should be considered as a marker of glandular epithelium. The reason is that malignant glandular tumor and its metastasis are stained, and also epithelium of renal tubules and glandular structures of the thyroid gland are stained. Stratified epithelium such as that of skin is definitely not stained. Therefore, the most relevant observation is that the epitope recognized by anti-O56 antibodies is a new marker specific for glandular epithelium and nervous tissue. Further studies should be performed to determine the structure of the tissue epitope recognized.

The Adhesive Glycoprotein of the Orb Web of Argiope Aurantia (Araneae, Araneidae)

A phosphorylated, glycoprotein preparation has been obtained from orb webs of the araneid spider Argiope aurantia. This preparation probably contains proteins from more than one gland type, but resolution of these proteins has not yet been achieved. Nevertheless, a major component appears to be the adhesive glycoprotein(s) from the adhesive spiral. A product of the aggregate glands, this glycoprotein(s) occurs as discrete nodules along the core fibers of the adhesive spiral, within the viscid, aqueous droplets.

The glycoprotein preparation has a high apparent molecular weight (> 200 kDa) and is polydisperse. The only monosaccharide constituent identified by gas-liquid chromatography or in lectin studies is N-acetylgalactosamine and this is at least primarily O-linked to threonine. By electron microscopy, linear, unbranched and apparently flexible filaments are observed. Phosphorylated serine and threonine residues are present in the preparation and glycine, proline and threonine together account for about 57 mole % of the preparation's amino acid content. Thus, in some, but not all, respects, this glycoprotein preparation is reminiscent of a secretory mucin.

Novel method for chase analysis of oligosaccharide metabolic error caused by xenobiotics

Saccharide primers, such as dodecyl beta-lactoside (Lac-C12), are unique artificial precursors of glycolipid synthesis. In culture media supplemented with saccharide primers, they are taken up by the cells in the culture media and glycosylated by cellular glycosyltransferases in the Golgi apparatus to form pseudo-glycolipids. In this study, we examine the effects of various xenobiotics on glycolipid synthesis by implementing a novel method to analyze pseudo-glycolipids, mainly gangliosides, produced by ONS-76 medulloblastoma cells in a culture medium containing various xenobiotics. The ganglioside group of pseudo-glycolipids was effectively purified by using strong anion-exchange cartridges. The production of pseudo-gangliosides was stimulated by N-(n-butyl)deoxygalactonojirimycin (NB-DGJ), but was inhibited by castanospermine, 2-deoxy-2-fluoro-d-galactose, tunicamycin, and brefeldin A. Because the cells in the culture medium are exposed to the saccharide primers and xenobiotics at the same time, and are secreted in the culture medium in their glycosylated form, our method can be used to effectively analyze the direct effects of xenobiotics on ganglioside synthesis.

Prophylactic treatment with sialic acid metabolites precludes the development of the myopathic phenotype in the DMRV-hIBM mouse model

Distal myopathy with rimmed vacuoles (DMRV)-hereditary inclusion body myopathy (hIBM) is an adult-onset, moderately progressive autosomal recessive myopathy; eventually, affected individuals become wheelchair bound1. It is characterized clinically by skeletal muscle atrophy and weakness, and pathologically by rimmed vacuoles, which are actually accumulations of autophagic vacuoles2, 3, 4, scattered angular fibers and intracellular accumulation of amyloid and other proteins5. To date, no therapy is available for this debilitating myopathy, primarily because the disease pathomechanism has been enigmatic. It is known that the disease gene underlying DMRV-hIBM is GNE, encoding glucosamine (UDP-N-acetyl)-2-epimerase and N-acetylmannosamine kinase6, 7, 8--two essential enzymes in sialic acid biosynthesis9. It is still unclear, however, whether decreased sialic acid production causes muscle degeneration, as GNE has been proposed to have roles other than for sialic acid biosynthesis10, 11, 12. By showing that muscle atrophy and weakness are completely prevented in a mouse model of DMRV-hIBM after treatment with sialic acid metabolites orally, we provide evidence that hyposialylation is indeed one of the key factors in the pathomechanism of DMRV-hIBM. These results support the notion that DMRV-hIBM can potentially be treated simply by giving sialic acids, a strategy that could be applied in clinical trials in the near future.

Low incidence of N-glycolylneuraminic acid in birds and reptiles and its absence in the platypus

The sialic acids of the platypus, birds, and reptiles were investigated with regard to the occurrence of N-glycolylneuraminic (Neu5Gc) acid. They were released from tissues, eggs, or salivary mucin samples by acid hydrolysis, and purified and analyzed by thin-layer chromatography, high-performance liquid chromatography, and mass spectrometry. In muscle and liver of the platypus only N-acetylneuraminic (Neu5Ac) acid was found. The nine bird species studied also did not express N-glycolylneuraminic acid with the exception of an egg, but not tissues, from the budgerigar and traces in poultry. Among nine reptiles, including one turtle, N-glycolylneuraminic acid was only found in the egg and an adult basilisk, but not in a freshly hatched animal. BLAST analysis of the genomes of the platypus, the chicken, and zebra finch against the CMP-N-acetylneuraminic acid hydroxylase did not reveal the existence of a similar protein structure. Apparently monotremes (platypus) and sauropsids (birds and reptiles) cannot synthesize Neu5Gc. The few animals where Neu5Gc was found, especially in eggs, may have acquired this from the diet or by an alternative pathway. Since Neu5Gc is antigenic to man, the observation that this monosaccharide does not or at least only rarely occur in birds and reptiles, may be of nutritional and clinical significance.

Biochemical characterization of human and murine isoforms of UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE)

The bifunctional enzyme UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) is the key enzyme for the biosynthesis of sialic acids, terminal components of glycoconjugates associated with a variety of physiological and pathological processes. Different protein isoforms of human and mouse GNE, deriving from splice variants, were predicted recently: GNE1 represents the GNE protein described in several studies before, GNE2 and GNE3 are proteins with extended and deleted N-termini, respectively. hGNE2, recombinantly expressed in insect and mamalian cells, displayed selective reduction of UDP-GlcNAc 2-epimerase activity by the loss of its tetrameric state, which is essential for full enzyme activity. hGNE3, which had to be expressed in Escherichia coli, only possessed kinase activity, whereas mGNE1 and mGNE2 showed no significant differences. Our data therefore suggest a role of GNE1 in basic supply of cells with sialic acids, whereas GNE2 and GNE3 may have a function in fine-tuning of the sialic acid pathway.

Prediction of three different isoforms of the human UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase

The bifunctional enzyme UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE) is the key enzyme of the biosynthesis of sialic acids, terminal components of glycoconjugates associated with a variety of cellular processes. Two novel isoforms of human GNE, namely GNE2 and GNE3, which possess extended and deleted N-termini, respectively, were characterized. GNE2 was also found in other species like apes, rodents, chicken or fish, whereas GNE3 seems to be restricted to primates. Both, GNE2 and GNE3, displayed tissue specific expression patterns, therefore may contribute to the complex regulation of sialic acid metabolism.

Genetic basis for the lack of N-glycolylneuraminic acid expression in human tissues and its implication to human evolution

Sialic acid is a family of acidic monosaccharides and consists of over 30 derivatives. Two major derivatives are N-acetylneuraminic acid (NeuAc) and N-glycolylneuraminic acid (NeuGc), and the hydroxylation of CMP-NeuAc is the rate limiting reaction for the production of NeuGc. The hydroxylation was carried out by a complex formed with hydroxylase, cytochrome b5, and NADH-cytochrome b5 reductase. Mouse hydroxylase was purified from the cytosolic fraction of the liver and its cDNA was cloned. Normal human tissues do not contain NeuGc. Human hydroxylase cDNA was also cloned and the sequence revealed that human hydroxylase has 92 bp deletion. The deletion is the cause of defective expression of NeuGc in human. Chimpanzee has intact hydroxylase gene and the 92 bp deletion occurred after the divergence of human ancestor from chimpanzee ancestor. Biochemical and molecular biological studies on the biosynthesis of NeuGc and biological functions of NeuGc are reviewed.

Clinical evidences of GM3 (NeuGc) ganglioside expression in human breast cancer using the 14F7 monoclonal antibody labelled with (99m)Tc

The relevance of certain gangliosides in tumour growth and metastatic dissemination has been well documented, reasons for considering these molecules as potential targets for cancer immunotherapy and diagnosis. GM3(NeuGc) ganglioside is particularly interesting due to its restrictive expression in normal human tissues according to immunohistochemical studies, using either polyclonal or monoclonal antibodies. But both immunohistochemical and biochemical methods have strongly suggested its over-expression in human breast tumours. Nevertheless, the lack of a direct evidence of this antigenic display in human breast cancer has kept the subject controversial. For the first time, we described herein the "in vivo" detection of GM3(NeuGc) ganglioside in human breast primary tumours using a radioimmunoscintigraphic technique with 14F7, a highly specific anti-GM3(NeuGc) ganglioside monoclonal antibody, labelled with (99m)Tc. In an open, prospective Phase I/II clinical trial, including women diagnosed in stage II breast cancer, the 14F7 monoclonal antibody accumulation in tumours at doses of 0.3 (n=5), 1 (n=5) and 3 mg (n=4) was evaluated. Noteworthy, the immunoscintigraphic study showed antibody accumulation in 100% of patients' tumours for the 1 mg dose group. In turn, the radioimmunoconjugate injected at doses of 0.3 mg or 3 mg of the antibody, was uptaken by 60 and 33.3% of breast tumours, respectively. "In vivo" immune recognition of GM3(NeuGc) in breast tumours reinforces the value of this peculiar target for cancer immunotherapy.

Domain-specific characteristics of the bifunctional key enzyme of sialic acid biosynthesis, UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase

UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase is a bifunctional enzyme, which initiates and regulates sialic acid biosynthesis. Sialic acids are important compounds of mammalian glycoconjugates, mediating several biological processes, such as cell-cell or cell-matrix interactions. In order to characterize the function of UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase, a number of deletion mutants were generated, lacking either parts of the N-terminal epimerase or the C-terminal kinase domain. N-terminal deletion of only 39 amino acids results in a complete loss of epimerase activity. Deletions in the C-terminal part result in a reduction or complete loss of kinase activity, depending on the size of the deletion. Deletions at either the N- or the C-terminus also result in a reduction of the other enzyme activity. These results indicate that a separate expression of both domains is possible, but that a strong intramolecular dependency of the two domains has arisen during evolution of the enzyme. N-terminal, as well as C-terminal, mutants tend to form trimers, in addition to the hexameric structure of the native enzyme. These results and yeast two-hybrid experiments show that structures required for dimerization are localized within the kinase domain, and a potential trimerization site is possibly located in a region between the two domains. In conclusion, our results reveal that the activities, as well as the oligomeric structure, of this bifunctional enzyme seem to be organized and regulated in a complex manner.

NAN fusions: a synthetic sialidase reporter gene as a sensitive and versatile partner for GUS

GUS continues to be the reporter of choice for many gene fusion applications, due to the unparalleled sensitivity of the encoded enzyme and the ease with which it can be quantified in cell-free extracts and visualized histochemically in cells and tissues. A compatible and functionally equivalent reporter gene would facilitate dual promoter studies and internal standardization of expression analyses in the same plant. A search for a candidate enzyme activity not found in plants, which might form the basis of a novel GUS-compatible reporter system, led us to investigate nanH, a Clostridium perfringens gene which encodes the so-called 'small' cytoplasmic sialidase. Expression of the native, AT-rich nanH gene in transgenic plants did not, however, result in detectable sialidase activity. For this reason, a codon-optimized derivative, NAN, was synthesized which possesses a GC content similar to that found in highly expressed plant genes. NAN enzyme activity was expressed at high levels in both stably and transiently transformed cells, possessed kinetic and stability properties similar to those of GUS, and showed optimal activity in GUS buffer. Moreover, NAN and GUS activity could be visualized simultaneously in polyacrylamide gels using the corresponding methylumbelliferone-based substrates, and in whole seedlings and tissue sections using the histochemical substrates 5-bromo-4-chloro-3-indolyl alpha-d-N-acetylneuraminic acid (X-NeuNAc) and 5-bromo-6-chloro-3-indolyl beta-d-glucuronide (X-GlucM), respectively.

Cloning and expression of a membrane-bound CMP-N-acetylneuraminic acid hydroxylase from the starfish Asterias rubens

The sialic acid N-glycolylneuraminic acid (Neu5Gc) is synthesized by the action of CMP-Neu5Ac hydroxylase. The enzyme from various mammals has been purified, characterized and sequenced by cDNA cloning. Although functional sequence motifs can be postulated from comparisons with several enzymes, no global homologies to any other proteins have been found. The unusual characteristics of this hydroxylase raise questions about its evolution. As echinoderms are phylogenetically the oldest organisms possessing Neu5Gc, they represent a starting point for investigations on the origin of this enzyme. Despite many similarities with its mammalian counterpart, CMP-Neu5Ac hydroxylase from the starfish A. rubens exhibits fundamental differences, most notably its association with a membrane and a requirement for high ionic strength. In order to shed light on the structural basis for these differences, the primary structure of CMP-Neu5Ac hydroxylase from A. rubens has been determined by PCR and cDNA-cloning techniques, using initial sequence information from the mouse enzyme. The complete assembled cDNA contained an ORF coding for a protein of 653 amino acids with a molecular mass of 75 kDa. The deduced amino-acid sequence exhibited a high degree of homology with the mammalian enzyme, although the C-terminus was some 60 residues longer. This extension consists of a terminal hydrophobic region, which may mediate membrane-binding, and a preceding hydrophilic sequence which probably serves as a hinge or linker. The identity of the ORF was confirmed by expression of active CMP-Neu5Ac hydroxylase in E. coli at low temperatures.

Purification and identification of N-glycolylneuraminic acid (Neu5Gc) from the holothuroidea Gumi, Cucumaria echinata

N-Glycolylneuraminic acid (Neu5Gc), precious sialic acid which could not be synthesized by a chemical method, occurrs in the body of holothuroidea, Gumi Cucumaria echinata. Gumi contains 85% of total sialic acid, as Neu5Gc, in the body. Neu5Gc was purified from dry powder of the body using Dowex 1-x8 (HCOO* form) anion exchange chromatography after mild acid hydrolysis with 0.1 N trifluoroacetic acid. Using GC-MS and 1H-NMR spectroscopy, the purified Neu5Gc was correctly identified to be Neu5Gc. The purity of Neu5Gc was more than 99%. This is the first report of purification and identification of Neu5Gc from holothuroidea by using anion exchange chromatography, GC-MS, and 1H-NMR.

Chemoenzymatic synthesis of sialyl oligosaccharides with sialidases employing transglycosylation methodology

A series of sialyloligosaccharides was synthesized using the transglycolytic activity of the sialidases from Vibrio cholerae, Clostridium perfringens, Salmonella typhimurium, and Newcastle disease virus. According to their hydrolytic activities the sialidases from V. cholerae and C. perfringens catalyze preferentially the formation of sialyl alpha(2-6)-linkages whereas the sialidases from S.typhimurium and Newcastle disease virus show a distinct preference for alpha(2-3) directed sialylations. Using combined chemical and enzymatic methodologies structures such as T-(Thomsen-Friedenreich) antigen [beta-D-Gal-(1-3)-alpha-D-GalNAc-OThr], Tn-(Thomsen nouveau) antigen (alpha-D-GalNAc-OThr) and beta-D-Gal-(1-4)-alpha-D-2-deoxy-Gal-OMe were sialylated in alpha(2-3)- and alpha(2-6)-positions regioselectively or in high regioisomeric excess and purified by simple isolation procedures. Depending on the enzyme source and acceptor structure yields for transsialylation varied between 10 and 30%.

A mouse IgG1 monoclonal antibody specific for N-glycolyl GM3 ganglioside recognized breast and melanoma tumors

14F7 murine monoclonal antibody (MAb) is an IgG1 immunoglobulin that is generated by immunizing Balb/c mice with GM3(NeuGc) ganglioside hydrophobically conjugated with human very-low-density lipoproteins and in the presence of Freund's adjuvants. 14F7 MAb binds specifically to GM3(NeuGc), whereas neither N-glycolyl or N-acetyl gangliosides, nor a sulfated glycolipid, are recognized as assessed by enzyme-linked immunosorbent assay or immunostaining on thin layer chromatograms. Immunohistochemical studies in fresh tumor tissues showed that 14F7 MAb strongly recognized in antigen expressed in human breast and melanoma tumors.

Delineation of the epitope recognized by an antibody specific for N-glycolylneuraminic acid-containing gangliosides

P3 is a mouse monoclonal antibody (mAb) that binds to several NeuGc-containing gangliosides. It also reacts with antigens expressed in human breast tumors (Vázquez et al. (1995) Hybridoma , 14, 551-556). In this work, the binding specificity of P3 has been characterized in more detail using a panel of glycolipids that included several disialylated gangliosides and several chemical derivatives of NeuGc-GM3. The carboxyl group and the nitrogen function of sialic acid were found to play important roles in the antibody binding, whereas the glycerol tail appears to be nonrelevant. Molecular modeling was used to analyze the binding data, including the finding that P3 selectively recognizes the internal NeuGc in GD3. For this purpose, conformational studies of GD3 were performed using molecular dynamics. It was concluded that sialic acid binds the P3 antibody through its upper face (the one on which the carboxyl group is exposed) and the C4-C5 side of the sugar ring, whereas none or very little contact between the galactose residue and the protein is evident. Conformational analysis of GD3 revealed that, despite the large flexibility of the NeuGcalpha8NeuGc linkage, the P3 binding epitope on the external sialic acid is not well exposed for any of the possible conformations this linkage can adopt, whereas the internal sialic acid presents the epitope in a proper way for several of these conformations. As a final result, a coherent picture of the epitope that fits the wide binding data was obtained.

Cytidine monophosphate-N-acetylneuraminate hydroxylase in the starfish Asterias rubens and other echinoderms

The sialic acid N-glycolylneuraminic acid (Neu5Gc) is synthesised by an NADH-dependent hydroxylase which acts on CMP-N-acetylneuraminic acid (CMP-Neu5Ac). Although Neu5Gc is the predominant sialic acid in many echinoderms, little is known about the hydroxylase from organisms of this phylum. We show here that in contrast to the mammalian enzyme, the hydroxylase from various echinoderms is predominantly membrane-bound and exhibits optimal activity in the presence of 100 mM NaCl. A detailed characterisation of the hydroxylase from echinoderms was performed using fractionated gonads of the starfish Asterias rubens. Solubilisation using detergents led to an inactivation of the hydroxylase. However, the solubilised enzyme was reactivated by the addition of cytochrome b5 reductase together with the amphiphilic or soluble form of cytochrome b5. Although these latter proteins were only available from a mammalian source, the high affinity of the hydroxylase for cytochrome b5 suggests that, as with the mammalian enzyme, these electron carriers participate in the catalytic cycle of the hydroxylase from A. rubens in vivo. The relevance of these results to the interaction between cytochrome b5 and the hydroxylase is discussed.

Isolation and characterization of sialate lyase from pig kidney

Sialate lyase (sialate aldolase; systematic name N-acetylneuraminate pyruvate-lyase, EC 4.1.3.3) was isolated as soluble enzyme from pig kidney and purified 630-fold using a heating step, gel filtration, and chromatography on immobilized neuraminic acid beta-methyl glycoside in 14% yield to apparent homogeneity as tested by SDS-gel electrophoresis. The molecular mass is 58 kDa and the pH-optimum is at pH 7.2. Kinetic parameters were determined with N-acetyl-neuraminic acid as substrate: Km 3.7 mM and Vmax 37.1 mU. The lyase cleaves only free sialic acids with relative rates of 100% for N-acetylneuraminic acid, 55% for N-glycolylneuraminic acid and 32% for N-acetyl-9-O-acetylneuraminic acid, whereas N-acetyl-4-O-acetylneuraminic acid or 2-deoxy-2,3-didehydro-N-acetylneuraminic acid are not substrates. Enzyme activity was inhibited with p-chloromercuribenzoate, o-phenanthroline, cyanide, 5-diazonium-1-H-tetrazole, 5,5'-dithiobis(2-nitrobenzoic acid), diethylpyro-carbonate, and Rose Bengal in the presence of light and O2. Reduction with sodium borohydride in the presence of N-acetylneuraminic acid or pyruvate resulted in irreversible inhibition of enzyme activity. The inhibition experiments suggest the involvement of histidine, lysine and SH-residues in enzyme catalysis. Thus, this mammalian lyase most probably belongs to the Class I aldolases, and has properties similar to the same enzyme from Clostridium perfringens and is active with the alpha-form of N-acetylneuraminic acid.

Structural and immunochemical characterization of the type VIII group B Streptococcus capsular polysaccharide

The type VIII capsular polysaccharide has been isolated and purified from a newly described strain of group B Streptococcus which is a leading cause of sepsis and neonatal meningitis in Japan. The polysaccharide contains D-glucose, D-galactose, L-rhamnose, and sialic acid in the molar ratio 1:1:1:1. By means of high resolution 1H nuclear magnetic resonance (1H NMR), 13C NMR, and homo- and heterocorrelated NMR, the repeating unit structure of the type VIII polysaccharide was delineated as the following, [formula: see text] Enzymatic studies established this polysaccharide as the first from which sialic acid, linked to a branched beta-D-galactopyranosyl residue, is known to be removed by bacterial neuraminidase.

Inhibitory effects of milk gangliosides on the adhesion of Escherichia coli to human intestinal carcinoma cells

The effects of milk gangliosides and their derivatives on the adhesion of enterotoxigenic and enteropathogenic Escherichia coli to Caco-2 cells, a human intestinal carcinoma cell line, were investigated. Human milk gangliosides inhibited the adhesion of enterotoxigenic E. coli to Caco-2 cells in the same proportion, regardless of the lactational stage, but bovine milk gangliosides were less effective. The most effective inhibitor was monosialoganglioside 1 (GM1); the adhesion rate of enterotoxigenic E. coli in the presence of GM1 was less than 20% of the positive control. The adhesion of E. coli was also depressed to 31.4% by monosialoganglioside 3 (GM3). However, the inhibitory effect of disialoganglioside 3 (GD3) was less than that of GM3. GD3 lactone, ceramide lactoside, and N-acetylneuraminic acid did not inhibit E. coli adhesion to Caco-2 cells. GM3 also inhibited the adhesion of enteropathogenic E. coli to Caco-2 cells. Thus, these results suggest that GM3 possibly behaves as a physiological component in the intestinal tract of infants to protect them against enteric infections.

Structure of the Escherichia coli O24 and O56 O-specific sialic-acid-containing polysaccharides and linkage of these structures to the core region in lipopolysaccharides

The lipopolysaccharides from Escherichia coli O24 and O56 could be separated into higher-molecular-mass and lower-molecular-mass fractions. Mild acid hydrolysis of lipopolysaccharides of both serotypes released an O-specific polysaccharide and a tetrasaccharide repeating unit. Oligomers of the repeating unit, the core and the oligosaccharide that contains a fragment of the repeating unit linked to the core region were also obtained according to hydrolysis conditions. On the basis of sugar and methylation analyses, Smith degradation, fast-atom-bombardment mass spectrometry and NMR spectroscopy of the hydrolysis products, the biological repeating units of the O-specific polysaccharides were shown to be the following tetrasaccharides: [formula: see text] The structures differ from the structures proposed previously by Kogan et al. [Kogan, G., Shashkov, A. S., Jann, B. & Jann, K. (1993) Carbohydr. Res. 238, 261-270; Kogan, G., Jann, B. & Jann, K. (1993) Carbohydr. Res. 238, 335-338]. The O-specific repeating unit in E. coli O24 lipopolysaccharide is linked to O6 of the terminal D-galactose in the core region, whereas in O56 LPS the repeating unit is linked to O4 of a subterminal D-glucose residue in an R2 type core.

The sialic acid-containing lipopolysaccharides of Salmonella djakarta and Salmonella isaszeg (serogroup O: 48): chemical characterization and reactivity with a sialic acid-binding lectin from Cepaea hortensis

Lipopolysaccharides (LPS) of Salmonella djakarta and Salmonella isaszeg, as well as of a spontaneous R-mutant of S. djakarta were investigated as to their content in neuraminic acid (Neu) and its individual linkage. The two Salmonella serovars both belong to the O:48 serogroup of Salmonella, but to two different subgroups. LPS of both S-forms contained high amounts of Neu, although in different quantities, whereas the R-form was completely devoid of it. Methylation analysis indicated that Neu is exclusively terminally linked in S. djakarta whereas both terminal and 4-linked Neu were recognized in S. isaszeg. Although terminally linked, a sialidase from Arthrobacter ureafaciens was unable to split Neu even after prolonged incubation from both S-type LPSs. When LPS was first treated by mild alkali, however, the total amount of Neu from S. djakarta LPS and about 50% from that of LPS of S.isaszeg could be removed. In contrast, alkali-treated LPS, but also the non-treated one, proved to be effective inhibitors for a sialic acid-binding lectin from Cepaea hortensis. The resistance of terminal Neu towards sialidase may be due to the presence of an O-acetyl group which would be removed during the methylation analysis but would, especially when linked to C-4, not interfere with the reactivity of the lectin.

Purification, characterization and reconstitution of CMP-N-acetylneuraminate hydroxylase from mouse liver

CMP-N-acetylneuraminate hydroxylase was isolated from mouse liver high speed supernatant with a yield of 0.4% and an apparent 1000-fold purification. The enzyme is a monomeric protein with a molecular weight of 66 kDa, as determined by gel filtration and SDS-PAGE. The hydroxylase system was reconstituted with Triton X-100-solubilized mouse liver microsomes and purified soluble or microsomal forms of cytochrome b5 reductase and cytochrome b5. The systems were characterized in detail and kinetic parameters for each system were determined.

CMP-N-acetylneuraminic acid hydroxylase from mouse liver and pig submandibular glands. Interaction with membrane-bound and soluble cytochrome b5-dependent electron transport chains

In this report, the nature of the protein components involved in the functioning of cytidine-5'-monophosphate-N-acetylneuraminic acid (CMP-Neu5 Ac) hydroxylase in high-speed supernatants of mouse liver has been investigated. Fractionation and reconstitution experiments showed that this enzyme system consists of NADH-cytochrome b5 reductase, cytochrome b5 and a 56-kDa terminal electron acceptor having the CMP-Neu5 Ac hydroxylase activity. This enzyme system is extracted in a soluble protein fraction; however, the amphipathic, usually membrane-associated, forms of cytochrome b5 and the reductase were found to predominate and are presumably the forms which support the turnover of the hydroxylase in vivo. Although the majority of cellular cytochrome b5 and cytochrome b5 reductase is membrane-bound, the addition of intact microsomes elicited no significant increase in the hydroxylase activity of supernatants. Detergent-solubilised microsomes, however, potently activated the hydroxylase, probably due to the greater accessibility of the cytochrome b5. Accordingly, in reconstitution experiments, pure hydrophilic cytochrome b5 interacts more effectively with the hydroxylase than isolated amphipathic cytochrome b5. Studies on the CMP-Neu5 Ac hydroxylase system in fractionated porcine submandibular glands and bovine liver suggest that the composition of this enzyme system is conserved in all mammals possessing sialoglycoconjugates containing N-glycolylneuraminic acid.

The sialidase superfamily and its spread by horizontal gene transfer

Sialidases (neuraminidases, EC 3.2.1.18) belong to a class of glycosyl hydrolases that release terminal N-acylneuraminate (sialic acid) residues from glycoproteins, glycolipids, and polysaccharides. These enzymes are common in animals of the deuterostomate lineage (Echinodermata through Mammalia) and also in diverse microorganisms that mostly exist as animal commensals or pathogens. Sialidases, and their sialyl substrates, appear to be absent from plants and most other metazoans. Even among bacteria, sialidase is found irregularly so that related species or even strains of one species differ in this property. This unusual phylogenetic distribution makes sialidases interesting for evolutionary studies. The biochemical diversity among bacterial sialidases does not indicate close relationships. However, at the molecular level, homologies are detectable, supporting the hypothesis of a common sialidase origin and thus of a sialidase superfamily. Some findings indicate that sialidase genes were recently transferred via phages among bacteria. The proposal of a sialidase origin in higher animals is suggested by the presence of apparently homologous enzymes in this kingdom, supporting the idea that some microbes may have acquired the genetic information during association with their animal hosts.

Lactational changes in the N-glycoloylneuraminic acid content of bovine milk gangliosides

The N-glycoloylneuraminic acid (Neu5Gc) contents of milk and milk gangliosides from bovines were investigated during the different stages of lactation. The Neu5Gc content of milk is high in the colostrum (32% of the total sialic acid content of milk) and decreases thereafter until the end of the period considered (6% on day 30). When the Neu5Gc content of gangliosides was evaluated a similar profile to that of Neu5Gc in total sialic acids was found. Gangliosides from colostrum showed the highest Neu5Gc content (21-22% of the total sialic acid content of milk gangliosides). This content dropped towards the end of the period studied (8% on day 90). Our results indicate that a significant supply of Neu5Gc by the milk could be important for the newborn during the first days after parturition.

High resolution proton NMR investigations of rat blood plasma. Assignment of resonances for the molecularly mobile carbohydrate side-chains of 'acute-phase' glycoproteins

An intense broad resonance at 2.14 ppm present in high field (400, 500 and 600 MHz) Hahn spin-echo 1H-NMR spectra of rat blood plasma, but absent from those of human blood plasma is attributable to the presence of terminal O-acetylsialate sugars in the molecularly mobile carbohydrate side-chains of 'acute-phase' glycoproteins (predominantly alpha 1-acid glycoprotein). The presence of such alternative acetylsugars in the carbohydrate side-chains of rat plasma glycoproteins are of much physiological and experimental significance in view of the regular use of these animals in model systems of human inflammatory conditions.

Isolation and properties of the natural and the recombinant sialidase from Clostridium septicum NC 0054714

The natural sialidase of Clostridium septicum was purified and characterized in parallel with the recombinant enzyme expressed by Escherichia coli. The two enzymes exhibit almost identical properties. The maximum hydrolytic activity was measured at 37 degrees C in 60 mM sodium acetate buffer, pH 5.3. Glycoproteins like fetuin and saponified bovine submandibular gland mucin, most of them having alpha(2-6) linked sialic acids, are preferred substrates, while sialic acids from gangliosides, sialyllactoses, or the alpha(2-8) linked sialic acid polymer (colominic acid) are hydrolysed at lower rates. alpha(2-3) Linkages are more rapidly hydrolysed than alpha(2-6) bonds of sialyllactoses. The cleavage rate is markedly reduced by O-acetylation of the sialic acid moiety. These properties are similar to those of other secreted clostridial sialidases. The enzyme exists in mono-, di- and trimeric forms, the monomer exhibiting a molecular mass of 125 kDa, which is close to the protein mass of 111 kDa deduced from the nucleotide sequence of the cloned gene.

Action of rat liver Gal beta 1-4GlcNAc alpha(2-6)-sialyltransferase on Man beta 1-4GlcNAc beta-OMe, GalNAc beta 1-4GlcNAc beta-OMe, Glc beta 1-4GlcNAc beta-OMe and GlcNAc beta 1-4GlcNAc beta-OMe as synthetic substrates

Incubation of synthetic Man beta 1-4GlcNAc beta-OMe, GalNAc beta 1-4GlcNAc beta-OMe, Glc beta 1-4GlcNAc beta-OMe, and GlcNAc beta 1-4GlcNAc beta-OMe with CMP-Neu5Ac and rat liver Gal beta 1-4GlcNAc alpha(2-6)-sialyltransferase resulted in the formation of Neu5Ac alpha 2-6Man beta 1-4GlcNAc beta-OMe, Neu5Ac alpha 2-6GalNAc beta 1-4GlcNAc beta-OMe, Neu5Ac alpha 2-6Glc beta 1-4GlcNAc beta-OMe and Neu5Ac alpha 2-6GlcNAc beta 1-4GlcNAc beta-OMe, respectively. Under conditions which led to quantitative conversion of Gal beta 1-4GlcNAc beta-OEt into Neu5Ac alpha 2-6Gal beta 1-4GlcNAc beta-OEt, the aforementioned products were obtained in yields of 4%, 48%, 16% and 8%, respectively. HPLC on Partisil 10 SAX was used to isolate the various sialyltrisaccharides, and identification was carried out using 1- and 2-dimensional 500-MHz 1H-NMR spectroscopy.

The structure of the sialic acid-containing Escherichia coli O104 O-specific polysaccharide and its linkage to the core region in lipopolysaccharide

Mild acid hydrolysis of Escherichia coli O104 lipopolysaccharide released an O-specific polysaccharide, a tetrasaccharide repeating unit, the corresponding dimer, and a disaccharide fragment of the repeating unit. Complete and incomplete cores, and oligosaccharides comprising fragments of the repeating unit and the core region, were also obtained. On the basis of sugar and methylation analysis, FAB-mass spectrometry and NMR spectroscopy of the hydrolysis products, the repeating unit of the O-specific polysaccharide was shown to be the tetrasaccharide:-->4)-alpha-D-Galp-(1-->4)-alpha-Neup5,7,9Ac3++ +-(2-->3)-beta-D- Galp-(1-->3)-beta-D-GalpNAc (1-->. The linkage between the O-specific polysaccharide chain and the core region, which appeared to be of the R2 type, was established. These results indicate that N-acetylneuraminic acid, located in the O-specific polysaccharide, is an inherent lipopolysaccharide component.