NMR Spectroscopy of Sialic Acids

Enzymatic Sialylation of Synthetic Multivalent Scaffolds: From 3'-Sialyllactose Glycomacromolecules to Novel Neoglycosides

Sialoglycans play a key role in many biological recognition processes and sialylated conjugates of various types have successfully been applied, e.g., as antivirals or in antitumor therapy. A key feature for high affinity binding of such conjugates is the multivalent presentation of sialoglycans which often possess synthetic challenges. Here, the combination is described of solid phase polymer synthesis and enzymatic sialylation yielding 3'-sialyllactose-presenting precision glycomacromolecules. CMP-Neu5Ac synthetase from Neisseria meningitidis (NmCSS) and sialyltransferase from Pasteurella multocida (PmST1) are combined in a one-pot reaction giving access to sequence-defined sialylated macromolecules. Surprisingly, when employing Tris(hydroxymethyl)aminomethane (Tris) as a buffer, formation of significant amounts of α-linked Tris-sialoside is observed as a side reaction. Further exploring and exploiting this unusual sialylation reaction, different neoglycosidic structures are synthesized showing that PmST1 can be used to derive both, sialylation on natural carbohydrates as well as on synthetic hydroxylated scaffolds.

Novel pH-sensitive polysialic acid based polymeric micelles for triggered intracellular release of hydrophobic drug

Polysialic acid (PSA), a non-immunogenic and biodegradable natural polymer, is prone to hydrolysis under endo-lysosomal pH conditions. Here, we synthesized an intracellular pH-sensitive polysialic acid-ursolic acid conjugate by a condensation reaction. To further test the drug loading capability, we prepared paclitaxel-loaded polysialic acid-based amphiphilic copolymer micelle (PTX-loaded-PSAU) by a nanoprecipitation method. Results showed PTX-loaded-PSAU exhibited well-defined spherical shape and homogeneous distribution. The drug-loading was 4.5% with an entrapment efficiency of 67.5%. PTX released from PTX-loaded-PSAU was 15% and 42% in 72 h under simulated physiological condition (pH 7.4) and mild acidic conditions (pH 5.0), respectively. In addition, In vitro cytotoxicity assay showed that PTX-loaded-PSAU retained anti-tumor (SGC-7901) activity with a cell viability of 53.8% following 72 h incubation, indicating PTX-loaded-PSAU could efficiently release PTX into the tumor cells. These results indicated that the pH-responsive biodegradable PTX-loaded-PSAU possess superior extracellular stability and intracellular drug release ability.

Conserved glycolipid termini in capsular polysaccharides synthesized by ATP-binding cassette transporter-dependent pathways in Gram-negative pathogens

Bacterial capsules are surface layers made of long-chain polysaccharides. They are anchored to the outer membrane of many Gram-negative bacteria, including pathogens such as Escherichia coli, Neisseria meningitidis, Haemophilus influenzae, and Pasteurella multocida. Capsules protect pathogens from host defenses including complement-mediated killing and phagocytosis and therefore represent a major virulence factor. Capsular polysaccharides are synthesized by enzymes located in the inner (cytoplasmic) membrane and are then translocated to the cell surface. Whereas the enzymes that synthesize the polysaccharides have been studied in detail, the structure and biosynthesis of the anchoring elements have not been definitively resolved. Here we determine the structure of the glycolipid attached to the reducing terminus of the polysialic acid capsular polysaccharides from E. coli K1 and N. meningitidis group B and the heparosan-like capsular polysaccharide from E. coli K5. All possess the same unique glycolipid terminus consisting of a lyso-phosphatidylglycerol moiety with a β-linked poly-(3-deoxy-d-manno-oct-2-ulosonic acid) (poly-Kdo) linker attached to the reducing terminus of the capsular polysaccharide.

Conformational free energy surface of alpha-N-acetylneuraminic acid: an interplay between hydrogen bonding and solvation

The conformational free energy surface of alpha-N-acetylneuraminic acid (Neu5Ac, sialic acid) in the space of ring-puckering coordinates was calculated using the metadynamics method. Free energy surfaces in vacuum and with an explicit solvent were calculated in GLYCAM 06 force field. In vacuum three structures are almost equivalently populated, namely, the (2)C(5) chair and the B(3,6)/(2)S(6) and (O)S(3) boat/skew-boat conformations. The B(3,6)/(2)S(6) structure is stabilized by an ionic hydrogen bond between the amide N-H bond and the carboxylic group. However, this structure is unfavorable in a water environment in which the experimentally observed (2)C(5) chair conformation is predicted to be more stable than the other structures. These results indicate that environment significantly influences conformation of Neu5Ac and that Neu5Ac-processing enzymes might modify a conformation of their substrates solely by a changing polarity of the environment. The structure of Neu5Ac bound in influenza neuraminidase ((4)S(2)/B(2,5)) belongs to conformations preferred in a water environment. The free energy penalty of this conformational change was calculated (relative to (2)C(5)) as 10.2 +/- 2.0 and 17.3 +/- 2.0 kJ/mol for (4,O)B/(O)S(3) and (4)S(2), respectively. This result indicates that mimicking of the enzyme-bound conformation is likely to be a viable strategy for the design of neuraminidase inhibitors.

Extracellular structure of polysialic acid explored by on cell solution NMR

The capsular polysaccharide of the pathogens Neisseria meningitidis serogroup B and of Escherichia coli K1, alpha(2 --> 8) polysialic acid (PSA), is unusual, because when injected into adult humans, it generates little or no antibody. In contrast, people infected with these pathogens generate specific serum antibodies. A structural study on cells is used to address this anomaly by characterizing antigen structures in vivo. We introduce on cell multidimensional solution NMR spectroscopy for direct observation of PSA on E. coli bacteria. Using 13C,15N-labeled PSA, we applied a combination of heteronuclear NMR methods, such as heteronuclear single quantum coherence, HNCA, and HNCO, in vivo. Analysis reveals that free and cell-bound PSA are structurally similar, indicating that the poor immunogenicity of PSA is not due to major structural differences between cells and purified PSA. The 13C linewidths of PSA on cells are 2 to 3 times larger than the corresponding ones in free PSA. The possible implications of the differences between free and on cell PSA are discussed. In addition, we demonstrate the suitability of the method for in vivo kinetic studies.

Targeted metabolomics analysis of Campylobacter coli VC167 reveals legionaminic acid derivatives as novel flagellar glycans

Glycosylation of Campylobacter flagellin is required for the biogenesis of a functional flagella filament. Recently, we used a targeted metabolomics approach using mass spectrometry and NMR to identify changes in the metabolic profile of wild type and mutants in the flagellar glycosylation locus, characterize novel metabolites, and assign function to genes to define the pseudaminic acid biosynthetic pathway in Campylobacter jejuni 81-176 (McNally, D. J., Hui, J. P., Aubry, A. J., Mui, K. K., Guerry, P., Brisson, J. R., Logan, S. M., and Soo, E. C. (2006) J. Biol. Chem. 281, 18489-18498). In this study, we use a similar approach to further define the glycome and metabolomic complement of nucleotide-activated sugars in Campylobacter coli VC167. Herein we demonstrate that, in addition to CMP-pseudaminic acid, C. coli VC167 also produces two structurally distinct nucleotide-activated nonulosonate sugars that were observed as negative ions at m/z 637 and m/z 651 (CMP-315 and CMP-329). Hydrophilic interaction liquid chromatography-mass spectrometry yielded suitable amounts of the pure sugar nucleotides for NMR spectroscopy using a cold probe. Structural analysis in conjunction with molecular modeling identified the sugar moieties as acetamidino and N-methylacetimidoyl derivatives of legionaminic acid (Leg5Am7Ac and Leg5AmNMe7Ac). Targeted metabolomic analyses of isogenic mutants established a role for the ptmA-F genes and defined two new ptm genes in this locus as legionaminic acid biosynthetic enzymes. This is the first report of legionaminic acid in Campylobacter sp. and the first report of legionaminic acid derivatives as modifications on a protein.

High affinity binding of long-chain polysialic acid to antibody, and modulation by divalent cations and polyamines

Long-chain polysialic acid (PSA) is expressed on the vertebrate neural cell adhesion molecule (NCAM) during neuronal plasticity. Its structural similarity to the capsular PSAs of some pathogenic bacteria has hampered the development of polysaccharide vaccines against meningitis. The antibodies formed during immunization require a long epitope for binding, and cross-react with host tissue PSA. The nature of the epitope and possible external effectors involved are still unclear. We have evaluated the interaction of PSA with its antibody mAb735 by surface plasmon resonance. The influences of PSA chain length, pH, temperature, ionic environment, and polyamines were also determined. The antibody binding affinity was found to dramatically increase with PSA chain length. A sub-nanomolar dissociation constant (K(D)=8.5 x 10(-10)M) was obtained for the binding of very long chain native MenB polysaccharides (approximately 200 Neu5Ac-residues). Colominic acid from Escherichia coli K1 (approximately 100 residues) and shorter polymers exhibited progressively weaker affinities. The antibody also bound tightly (K(D) approximately 5 x 10(-9)M) to polysialylated glycopeptides from human embryonal brain. The effects of pH and ionic strength suggested that the interaction is largely electrostatic. Ca2+ and Mn2+ ions promoted the observed surface plasmon resonance response in a concentration dependent fashion. Spermine increased the response in a similar way. Our results suggest that divalent cations and polyamines may play significant role in the regulation of the PSA epitope presentation in vivo.

Investigation of the stability of thiosialosides toward hydrolysis by sialidases using NMR spectroscopy

[formula: see text] 1H NMR spectroscopy has been used to investigate whether the alpha(2-->6)-linked thiosialoside 3 and the alpha(2-->3)-linked thiosialoside 9 are hydrolyzed in the presence of Vibrio cholerae sialidase. Similarly, the hydrolysis of the O-ketosides Neu5Ac-2-O-alpha-(2-->3)-Gal beta Me (4) and the alpha-(2-->6)-sialyllactoside 7, representing natural alpha(2-->3)- and alpha(2-->6)-linked sialosides, respectively, was investigated. The results of the 1H NMR experiments clearly demonstrate that the thiosialosides are not hydrolyzed by Vibrio cholerae sialidase. As expected, the O-sialosides are hydrolyzed to give N-acetyl-alpha-D-neuraminic acid as the first product of substrate cleavage.

Synthesis of a novel sialic acid derivative (sialylphospholipid) as an antirotaviral agent

A novel sialylphospholipid (SPL) was synthesized from N-acetylneuraminic acid (NeuAc) and phosphatidylcholine (PC) by a chemical and enzymatic method and evaluated as an inhibitor of rotavirus. PC and 1,8-octanediol were conjugated by transesterification reaction of Streptomyces phospholipase D (PLD) under a water-chloroform biphasic system to afford phosphatidyloctanol, which was condensed with a protected 2-chloro-2-deoxyneuraminic acid derivative by using silver trifluoromethanesulfonate as an activator in chloroform and converted, after deprotection, to SPL. Rhesus monkey kidney cells (MA-104) were incubated with simian (SA-11 strain) and human (MO strain) rotaviruses in the presence of SPL, and the cells infected were detected indirectly with anti-rotavirus antibody. SPL showed dose dependent inhibition against both virus strains. The concentrations required for 50% inhibition (IC50) against SA-11 and MO were 4.35 and 16.1 microM, respectively, corresponding to 10(3)- and 10(4)-fold increases in inhibition as compared to monomeric NeuAc.

Chemical synthesis of 4-trifluoromethylumbelliferyl-alpha-D-N-acetylneuraminic acid glycoside and its use for the fluorometric detection of poorly expressed natural and recombinant sialidases

When compared to bacterial or viral sialidases, eukaryotic sialidases are expressed at lower levels and frequently show poor specific activities. The identification and characterization of sialidases from eukaryotes have been slowed down due to the limited sensitivity of available sialidase substrates. Therefore, we chemically synthesized a fluorogenic compound, 4-trifluoromethylumbelliferyl-alpha-D-N-acetylneuraminic acid (CF3MU-Neu5Ac), and tested its use as a substrate for eight different sialidases, including enzymes from viral, bacterial, and eukaryotic sources. Kinetic analysis revealed CF3MU-Neu5Ac to be a very sensitive sialidase substrate. Furthermore, this substance proves to be perfectly suitable for the in vivo examination of sialidases and for the detection of recombinant sialidase by means of expression cloning.

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.

Sequence-specific 1H-NMR assignments and folding topology of human CD59

CD59 is a recently discovered cell-surface glycoprotein that restricts lysis by homologous complement and has limited sequence similarity to snake venom neurotoxins. This paper describes the first results of a two-dimensional NMR study of CD59 prepared from human urine. Nearly complete 1H-NMR assignments were obtained for the 77 amino acid residues and partial assignments for the N-glycan and the glycosylphosphatidylinositol (GPI) anchor. These results together confirm that the C-terminal residue of the mature protein is Asn 77 and that the urine-derived form retains the nonlipid part of the GPI anchor. The data further indicate that the GPI anchor and possibly the N-glycan are structurally inhomogeneous and suggest that the phospholipid present in the intact GPI anchor was removed by phosphatidylinositol-specific phospholipase-D. The folding topology of the protein was determined from NOE enhancements and slowly exchanging backbone amide protons and consists primarily of five extended strands (denoted beta 1-beta 5 in sequence order), arranged into separate two-stranded (beta 1 and beta 2) and three-stranded (beta 3-beta 5) antiparallel beta-sheets. The same folding topology is found in all of the snake venom neurotoxins whose structures have been determined. The region between the beta 4 and beta 5 strands has helical character, a feature that is not present in the neurotoxins but that is seen in the topologically similar wheat germ agglutinin.

Calcium binding to sialic acids and its effect on the conformation of ependymins

Soluble ependymins from the predominant protein constituents in the cerebrospinal fluid from many orders of teleost fish. Furthermore, these glycoproteins also exist in a bound form associated with the extracellular matrix. Ependymins are synthesized in meningeal fibroblasts. In goldfish, their synthesis is increased during the regeneration of the optic nerve and they share several characteristics with molecules involved in cell contact phenomena. In this study, we show by a calcium overlay technique that ependymins from goldfish and rainbow trout are able to bind 45Ca2+. However, nearly all of this Ca(2+)-binding capacity is lost after digestion with sialidase. Furthermore, circular-dichroism spectra from FPLC-purified rainbow trout ependymins have been recorded in the presence and absence of Ca2+. Below 250 nm, the CD spectrum showed a characteristic minimum of ellipticity at 217 nm typical of beta structures. This signal is independent of the Ca2+ concentration. In contrast, the complex signal at 250-310 nm mainly decreased with increasing Ca2+ concentration indicating changes in the environment of aromatic side chains.

The structure of the O-antigenic polysaccharide from lipopolysaccharide of Vibrio cholerae strain H11 (non-O1)

After acid degradation of the lipopolysaccharide (LPS) of Vibrio cholerae strain H11 (non-O1), a tetrasaccharide was obtained, the structure of which was determined by quantitative and methylation analyses, periodate oxidation, one- and two-dimensional NMR spectroscopy, and fast-atom-bombardment and four-sector tandem mass spectrometry as beta-D-GalANGro-(1-3)-beta-D-QuiNAc-(1-4)-alpha-D-GalANGr o-(1-4)-NeuAc, in which GalANGro is N-galacturonoyl-2-aminoglycerol and QuiN 2-amino-2,6-dideoxy-glucopyranose. In addition, the trisaccharide beta-D-GalANGro-(1-3)-beta-D-QuiNAc-(1-4)-D-altro-hept ulose and the disaccharide alpha-D-GalANGro-(1-4)-NeuAc were isolated from acid-degraded lipopolysaccharide; the occurrence of sedoheptulose in lipopolysaccharide has not been described before. Based on the result of methylation analysis showing that galacturonic acid was the terminal sugar of the polysaccharide chain, and on the assumption that the tri- and the disaccharide represented the reducing and the non-reducing ends of the polysaccharide, respectively, the chemical structure of the O-specific chain of V. cholerae H11 is proposed as alpha-D-GalANGro-(1-4)-alpha-NeuAc-(2-3)-beta-D-GalANGro-(1- 3)-beta-D-QuiNAc- (1-[4)-alpha-D-GalANGro-(1-4)-alpha-NeuAc-(2-3)-beta-D-GalANGro -(1-3)-beta-D- QuiNAc-(1-]n-(1-4)-D-altro-heptulose. However, other possible structures can not be ruled out since the tri- and the disaccharide could be localised at different positions.

Structural analysis of a novel sialic-acid-containing trisaccharide from Rhodobacter capsulatus 37b4 lipopolysaccharide

Sialic-acid-containing lipopolysaccharides from Rhodobacter capsulatus 37b4 (S-form lipopolysaccharide), KB-1 (R-type lipopolysaccharide) and Sp 18 (deep R-type lipopolysaccharide) were investigated for the linkage and substitution of sialic acids. Methylation analysis and behaviour towards acid and enzymic hydrolysis indicated a non-reducing terminal location of sialic acids in the R-type lipopolysaccharide of strain Sp 18, whereas an internal, chain-linked location of sialic acids was found in the lipopolysaccharides of strains 37b4 and KB-1. For these latter strains, methylation analysis revealed a substitution of sialic acids by other sugars at position 7 for strain 37b4 and positions 4 and 7 for strain KB-1. In accordance with the chain-linked position of sialic acids, mild hydrolysis of R. capsulatus 37b4 lipopolysaccharide with acetic acid released a trisaccharide with sialic acid at the reducing terminus. Structural investigation of this trisaccharide by methylation analysis, 1H- and 13C-NMR spectroscopy revealed the presence of the disaccharide Gal1-6Glc at the non-reducing end, probably with an alpha-anomeric configuration of the galactose residue, i.e. melibiose, beta-glycosidically linked to position 7 of sialic acid. Therefore the structure Gal alpha 1-6Glc beta 1-7Neu5Ac is proposed for this core oligosaccharide from R. capsulatus 37b4 lipopolysaccharide.

Structural characterization of sialylated tetrasaccharides and pentasaccharides with blood group H and Le(x) activity isolated from bovine submaxillary mucin

In this study we have investigated the structures of a sialylated tetrasaccharide and two sialylated pentasaccharides released from bovine submaxillary mucin by alkaline borohydride treatment and isolated by high-performance liquid chromatography. The tetrasaccharide contained NeuGc, while one of the pentasaccharides contained NeuAc and the other contained NeuGc. All three oligosaccharides contained the core type-3 structure (GlcNAc beta 1----3GalNAcol). The structures, determined by a combination of one- and two-dimensional 1H-NMR spectroscopy at 270 MHz and methylation analysis involving gas-liquid chromatography/mass spectrometry, were as follows: [formula: see text]. The oligosaccharides occurred in the approximate molar ratios, 1.0:0.6:0.3. This is the first report of these oligosaccharides in bovine submaxillary mucin. 1H-NMR data for structures A1/2c and A1/2e, which are novel structures, are presented for the first time. Oligosaccharide A1/2e contains the blood-group-H type-2 antigenic determinant while oligosaccharide A1/2d contains the Lewis(x) determinant.

Structure determination of five sialylated trisaccharides with core types 1, 3 or 5 isolated from bovine submaxillary mucin

In this study we have investigated the structures of five sialylated trisaccharides released from bovine submaxillary mucin by alkaline borohydride treatment and isolated by high-performance liquid chromatography. Three of the trisaccharides contained NeuAc while two contained NeuGc. One oligosaccharide contained core-type 1, two contained core-type 3 and two contained core-type 5. The structures, determined by a combination of one- and two-dimensional 1H-NMR spectroscopy at 270 MHz and methylation analysis involving gas-liquid chromatography/mass spectrometry, were as follows: A4b, GalNAc alpha(1----3) [NeuAc alpha(2----6)]GalNAcol; A4c, GlcNAc beta(1----3)[NeuAc alpha(2----6)]GalNAcol; A4d, Gal beta(1----3)[NeuAc alpha(2----6)]GalNAcol; A4e, GalNAc alpha(1----3)-[NeuGc alpha(2----6)]GalNAcol; A4f, GlcNAc beta(1----3)[NeuGc alpha (2----6)]GalNAcol. The oligosaccharides occurred in the approximate molar ratios 1.0:12.0:0.3:0.2:2.0. This is the first report of oligosaccharides containing core-type 5 and of the occurrence of oligosaccharides A4b, A4e, and A4f in bovine submaxillary mucin. 1H-NMR data for structure A4e, which is a novel structure, are presented for the first time.

Structures of O-glycosidically linked oligosaccharides isolated from human meconium glycoproteins

The structure of the major O-glycosidically linked neutral and acidic oligosaccharides isolated from human meconium glycoproteins were established. Neutral and acidic oligosaccharides were released by alkaline borohydride treatment, purified by Biogel P-6 and fractionated by high-performance liquid chromatography. This approach resulted in 50 neutral and 30 acidic oligosaccharides. The present study reports the primary structural analysis of five neutral oligosaccharides, ten monosialylated oligosaccharides, one monosialylated monosulfated oligosaccharide and three disialylated oligosaccharides, by permethylation, fast-atom-bombardment mass spectrometry analysis and 400-MHz 1H-NMR spectroscopy. The following structure have not been described previously: (formula; see text) The intestinal glycoproteins of human meconium are characterized as high molecular mass compounds with numerous carbohydrate chains of the mucin type. These mucins are a rich source of carbohydrate structures which express multiple blood group activities and occur as membrane-associated antigens, recognized by hybridoma antibodies [1-4]. A previous study [5] described the structure of fifteen free oligosaccharides derived from catabolism of O- and N-glycans accumulating in new born meconium. In the same group [6] the research has been extended to glycoasparagines with the description of thirteen of them by high resolution 1H-NMR spectroscopy analysis. From O-glycosidically linked glycoproteins, further studies [7] established the structures of nine major monosaccharides to tetrasaccharides obtained after mild acid hydrolysis and base-borohydride degradation from meconium samples of group O secretors. These oligosaccharides were derived from meconium glycopeptides which had been depleted of I- and i-antigen activities. Recently [8], neutral and acidic oligosaccharide-alditols obtained by alkaline borohydride degradation of human meconium glycoproteins have been separated by HPLC on an anion-exchange column. The neutral fraction was further purified by normal-phase and reversed-phase chromatography while acidic fractions were fractionated only by normal-phase chromatography. Thus, we have isolated several low molecular mass oligosaccharides of different size and composition and also isomers which vary in linkage position or anomer configuration. Using methylation analysis, 1H-NMR spectroscopy and fast-atom-bombardment mass spectrometry (FAB-MS), we propose the primary structure for 19 major oligosaccharides.

Analysis of N-acetyl-4-O-acetylneuraminic-acid-containing N-linked carbohydrate chains released by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F. Application to the structure determination of the carbohydrate chains of equine fibrinogen

The carbohydrate chains of equine fibrinogen were enzymatically released by peptide-N4-(N-acetyl-beta-glucosaminyl)asparagine amidase F. The oligosaccharides obtained were fractionated by a combination of FPLC and HPLC and analyzed by 500-MHz 1H-NMR spectroscopy. Four monosialo and four disialo diantennary N-acetyllactosamine type of carbohydrate chains occur: (formula; see text)

[Chemical characterization of Escherichia coli K 1 capsular polysaccharide]

The exact chemical characterization of the prepared Escherichia coli K 1 capsule polysaccharide is necessary and a prerequisite for using this antigen as a screening antigen in the production of monoclonal anti-K 1-antibodies. The K 1-antigen, prepared by phenol-water-extraction, was analyzed by protein, RNA, and neuraminic acid determination. An addition, the antigen was subjected to elementary analysis, infrared- and 13C-NMR-spectroscopy, and gelchromatography. After testing the serological specificity, the K 1-antigen was identified as a high molecular polyneuraminic acid.

Use of the inhibition of enzymatic antioxidant systems in order to evaluate their physiological importance

Chemical inhibitors of the different antioxidant enzymes were systematically testet either on purified enzymes of after incubation with human fibroblasts in culture. Inhibition values were obtained for catalase with aminotriazole, for superoxide dismutase with diethyldithiocarbamate, for glutathione peroxidase with mercaptosuccinate, for glutathione reductase with bischloroethylnitrosourea and for glutathione synthesis with buthionine sulfoximine. Viability of cells incubated with these inhibitors was then tested under normal conditions and under high oxygen pressure; the data were correlated with the above-mentioned inhibitory values. Cell viability was particularly affected when the glutathione-related enzymes, especially glutathione peroxidase, were inhibited.

Primary structure of neutral oligosaccharides derived from respiratory-mucus glycoproteins of a patient suffering from bronchiectasis, determined by combination of 500-MHz 1H-NMR spectroscopy and quantitative sugar analysis. 1. Structure of 16 oligosaccharides having the Gal beta(1----3)GalNAc-ol core (type 1) or the Gal beta(1----3)[GlcNAc beta(1----6)]GalNac-ol core (type 2)

Carbohydrate chains of respiratory-mucus glycopeptides from a patient (blood group O) suffering from bronchiectasis with a Kartagener's syndrome have been released by alkaline borohydride treatment. Application of high-performance liquid chromatography using subsequently two silica columns, one bonded with aminopropyl groups and the other with octadecyl groups, afforded 39 neutral fractions; 35 oligosaccharide-alditol structures have been characterized by employing 500-MHz 1H-NMR spectroscopy in conjunction with sugar analysis. Here, 16 oligosaccharide structures, possessing a core consisting of Gal beta(1----3)GalNAc-ol branching through a GlcNAc residue linked beta(1----6) to the GalNAc residue (core type 2 or core type 1, respectively), are described. Ten oligosaccharide-alditols with these types of cores (2, 3, 10a, 14, 7, 11a, 15a, 16a, 12 and 16c) have been identified previously in human bronchial mucins of patients suffering from cystic fibrosis [Lamblin, G., Boersma, A., Lhermitte, M., Roussel, P., Mutsaers, J.H.G.M., Van Halbeek, H. and Vliegenthart, J.F.G. (1984) Eur. J. Biochem. 143, 227-236]. Of the remaining six compounds, one is a partial structure of oligosaccharides previously described: (Formula: see text). The structures 17a and 20 contain the Y determinant, i.e., Fuc alpha(1----2)Gal beta(1----4)[Fuc alpha(1----3)]GlcNAc beta(1----). High-resolution 1H-NMR spectroscopy is able to distinguish whether the Y determinant is beta(1----3) or beta(1----6) linked in such oligosaccharide-alditols.

Activation and transfer of novel synthetic 9-substituted sialic acids

In this report several NeuAc analogues differently modified at position C-9 were tested as substrates for CMP sialic acid synthase from bovine brain: the hydroxy group at C-9 was replaced by an amino, acetamido, benzamido, hexanoylamido and azido group. The synthase was partially purified by chromatography on CDP-hexanolamine--Sepharose. CMP-glycosides synthesized were measured by analytical HPLC at 275 nm. Each NeuAc analogue was activated to the respective CMP-glycoside: Km-values varied from 0.8 mM to 4.6 mM, the Km for NeuAc was 1.4 mM. Thus affinity of the enzyme was influenced only moderately by chemical modification at C-9. CMP-glycosides were synthesized on a preparative scale with good yield and characterized by analytical HPLC. In addition, 500-MHz 1H-NMR data of CMP-9-amino-NeuAc and CMP-9-acetamido-NeuAc were obtained. Each CMP-activated NeuAc analogue was a suitable donor substrate for Gal beta 1-4GlcNAc alpha 2,6-sialyltransferase from rat liver. Transfer was determined by the thiobarbituric acid method and by analytical HPLC at 200 nm. The results demonstrate that synthetic, not naturally occurring, non-labelled NeuAc analogues can be incorporated into glycoprotein with high yield.

Structure of sialyl-oligosaccharides isolated from bronchial mucus glycoproteins of patients (blood group O) suffering from cystic fibrosis

The carbohydrate chains of the bronchial-mucus glycoproteins of six cystic fibrosis patients with blood group O were released by alkaline borohydride treatment. Low-molecular-mass, monosialyl oligosaccharide-alditols were isolated by anion-exchange chromatography and fractionated by high-performance liquid chromatography. Structural characterization was performed by 500-MHz 1H-NMR spectroscopy in combination with quantitative sugar analysis. The established structures range in size from tetra- up to heptasaccharides. They are all sialyl analogs of neutral oligosaccharides that were characterized previously [Lamblin G., Boersma A., Lhermitte M., Roussel P., Mutsaers J. H. G. M., Van Halbeek H. & Vliegenthart J. F. G. (1984) Eur. J. Biochem. 143, 227-236]. The NeuAc residue was found to occur either in alpha (2----3)-linkage to Gal, or in alpha (2----6)-linkage to GalNAc-ol or Gal.

Primary structure of O- and N-glycosylic carbohydrate chains derived from murine submandibular mucin (MSM)

The carbohydrate moiety of mouse submandibular mucin (MSM) contains mainly D-mannose and 2-acetamido-2-deoxy-D-glucose together with sialic acid, D-galactose, and 2-acetamido-2-deoxy-D-galactose. O-Glycosylically bound saccharides, obtained by treatment of MSM with alkaline borohydride, were shown by methylation analysis to have the structure: alpha-NeuAc-(2----3)-beta-Gal-(1----3)-GalNAc-ol. N-Glycosylically bound saccharides obtained from MSM by hydrazinolysis, and analysed by 500-MHz 1H-n.m.r. spectroscopy, were shown to have the following comprehensive structures. (Formula: see text).

Somatic antigens of Pseudomonas aeruginosa. The structure of the O-specific polysaccharide chain of the lipopolysaccharide from P. aeruginosa O13 (Lányi)

The O-specific polysaccharide, obtained on mild acid degradation of lipopolysaccharide of Pseudomonas aeruginosa O13 (Lányi classification), is built up of trisaccharide repeating units involving 2-acetamidino-2,6-dideoxy-D-glucose (N-acetyl-D-quinovosamine, D-QuiNAc), 2-acetamidino-2,6-dideoxy-L-galactose (L-fucosacetamidine, L-FucAm), and a new sialic-acid-like sugar, 5,7-diacetamido-3,5,7,9-tetradeoxy-D-glycero-L-galacto-nonuloso n ic acid (Sug), and thus contains simultaneously both acidic and basic functions. Cleavage of the polysaccharide with hydrogen fluoride in methanol revealed the high stability of the glycosidic linkage of the ulosonic acid and afforded methyl glycosides of a disaccharide and a trisaccharide. The structures of the new ulosonic acid and acetamidino group were established by analysing the oligosaccharide fragments by 1H, 13C nuclear magnetic resonance spectrometry, as well as on the basis of their chemical conversions: alkaline hydrolysis of the acetamidino group into acetamido group, reductive deamination with lithium borohydride into the ethylamino group and acetylation with acetic anhydride in pyridine accompanied by intramolecular acylation of the acetamidino function by the ulosonic acid to form a six-membered lactam ring. Identification of the oligosaccharide fragments and comparative analysis of the 13C nuclear magnetic resonance spectra of the oligosaccharides and polysaccharide revealed the following structure of the repeating unit: ----3)D-QuiNAcp(alpha 1----3)Sugp(alpha 2----3)L-FucAmp(alpha 1----.

Porcine submaxillary mucin contains alpha 2----3- and alpha 2----6-linked N-acetyl- and N-glycolylneuraminic acid

Four acidic trisaccharides have been obtained by alkaline borohydride reductive cleavage (beta-elimination) of a fraction of porcine submaxillary mucin precipitating at 60-75% ethanol. Their structures have been investigated using the techniques of methylation analysis involving gas-liquid chromatography/mass spectrometry along with high-resolution 1H-NMR analysis. Two of the four oligosaccharides, B1-B4, contain N-acetylneuraminic acid (NeuAc) while two contain N-glycolylneuraminic acid (NeuGc). The following structures are proposed for the acidic trisaccharide fraction: (B1) NeuAc alpha(2----3)Gal beta(1----3)GalNAcol, (B2) NeuGc alpha(2----3)Gal beta(1----3)GalNAcol, (B3) Gal beta(1----3)[NeuAc alpha(2----6)]GalNAcol and (B4) Gal beta(1----3)[NeuGc alpha(2----6)]GalNAcol, (GalNAcol = reduced N-acetylgalactosamine. These oligosaccharides were present in a molar ratio of 69:22:4:5. Although oligosaccharide B4 has previously been found in porcine submaxillary mucin B1, B2 and B3 have not. Furthermore, oligosaccharide B2 is a novel structure.

A 500-MHz 1H-n.m.r. study of oligosaccharides derived from gangliosides by ozonolysis-alkaline fragmentation

The structural-reporter-group resonances in the 1H-n.m.r. spectra of a series of ganglioside-derived oligosaccharides are completely assigned. The three different types of sialic acid residues which may occur in these compounds could be adequately characterized. They are distinguishable on the basis of the set of chemical shifts of their H-3a and H-3e atoms. The mutual influence of GalNAc beta-(1----4) and Neu5Ac alpha-(2----3), both linked to the same Gal residue, on the 1H-n.m.r. parameters of each other, reflects a well-defined solution conformation, which is held to be responsible for the resistance of this "internal" sialic acid towards various sialidases.

Typing of core and backbone domains of mucin-type oligosaccharides from human ovarian-cyst glycoproteins by 500-MHz 1H-NMR spectroscopy

Human blood-group A active glycoproteins from ovarian-cyst fluid were subjected to Smith degradation and subsequent beta-elimination. The resulting oligosaccharide-alditols represent the core and backbone domains of the O-linked carbohydrate chains. Nine of these, ranging in size from disaccharides to hexasaccharides, were investigated by 1H-NMR spectroscopy. Their primary structures could be adequately characterized. In particular, the core types, i.e. the substitution patterns of N-acetylgalactosaminitol (GalNAc-ol) as well as the types of backbone, i.e. the linkage types of alternating Gal-GlcNAc sequences, were unambiguously identified. The core type GlcNAc beta(1-3)GalNAc-ol is described for the first time as occurring in ovarian-cyst glycoprotein.

Primary structure of two major glycans of bovine fibrinogen

After pronase digestion of bovine fibrinogen, the asparagine-linked glycans were released from the resulting glycopeptides by hydrazinolysis, and subsequently re-N-acetylated. Two sialylated glycans were isolated by ion-exchange chromatography. Their primary structure has been determined by methylation analysis and 360-MHz 1H-NMR spectroscopy. The structures proposed to be present in the native glycoprotein are as follows: (formula: see text).

Structure determination of oligosaccharides isolated from Cad erythrocyte membranes by permethylation analysis and 500-MHz 1H-NMR spectroscopy

Alkaline borohydride reductive cleavage (beta-elimination) of glycophorin A isolated from one individual of the rare blood group Cad, resulted in the release of six acidic oligosaccharide-alditols which were separated by high-performance liquid chromatography (HPLC) on an alkyl amine silicagel column. The structure of four of them has been determined by the application of methanolysis, methylation analysis and 1H-NMR spectroscopy at 500 MHz. The structures and relative amounts were as follows: oligosaccharide 1: NeuAc(alpha 2-3)Gal(beta 1-3)GalNAc-ol (3.5%); oligosaccharide 3: GalNAc(beta 1-4)[NeuAc(alpha 2-3)]Gal(beta 1-3)GalNAc-ol (10.5%); oligosaccharide 5: NeuAc(alpha 2-3)Gal(beta 1-3)[NeuAc(alpha 2-6)]GalNAc-ol (10.4%); oligosaccharide 6: GalNAc(beta 1-4)[NeuAc(alpha 2-3)]Gal(beta 1-3)[NeuAc(alpha 2-6)]GalNAc-ol (71.2%). The two other oligosaccharides (2 and 4) were obtained in very low amount. The major pentasaccharide (oligosaccharide 6) carries the blood group Cad determinant and is a potent inhibitor of human anti-Sda antibody.

Further characterization, by a combined high-performance liquid chromatography/1H-NMR approach, of the heterogeneity displayed by the neutral carbohydrate chains of human bronchial mucins

From bronchial mucins of cystic fibrosis patients with blood group O, the carbohydrate chains were released in the form of oligosaccharide-alditols by alkaline borohydride treatment. Application of high-performance liquid chromatography directly on the pool of neutral oligosaccharides afforded 23 fractions. Twenty oligosaccharide structures were characterized by employing 500-MHz 1H-NMR spectroscopy in conjunction with sugar analysis. Thirteen among these had been revealed before to occur in human bronchial mucins [Van Halbeek, H., Dorland, L., Vliegenthart, J. F. G., Hull, W. E., Lamblin, G., Lhermitte, M., Boersma, A., and Roussel, P. (1982) Eur. J. Biochem. 127, 7-20], when paper-chromatographic fractionation of this pool of neutral oligosaccharides was employed. High-performance liquid chromatography enabled to obtain another seven pentasaccharide and hexasaccharide alditols; the largest-size representatives are: (Formula see text). Thereby, this approach afforded deeper insight into the structural heterogeneity displayed by the carbohydrate chains of bronchial mucins.