Herman Van Halbeek

Double dioxygenation of arachidonic acid by soybean lipoxygenase-1 kinetics and regio-stereo specificities of the reaction steps

The kinetic parameters of the first and second oxygenation of arachidonic acid by soybean lipoxygenase-1 were determined and found to be for the first step at pH 10.0, Km (arachidonic acid) = 8.5 +/- 0.5 microM; kcat = 225 +/- 7 s-1 and for the second step at pH 8.7 Km (15-HPETE) = 440 +/- microM; kcat = 25 +/- 1 s-1. In the second oxygenation for which 15-Ls-hydroperoxy 5-cis, 8-cis, 11-cis 13-trans-eicosatetraenoic acid is a substrate, two isomeric dihydroperoxy fatty acids are formed. After separation of the corresponding dihydroxy esters by high-performance liquid chromatography, they were identified by mass-spectrometry, 1H- and 13C-NMR spectroscopy as 8-DS, 15-LS-dihydroperoxy 5-cis, 9-trans, 11-cis, 13-trans-eicosatetraenoic acid and 5-DS, 15-LS-dihydroperoxy 6-trans, 8-cis, 11-cis, 13-trans-eicosatetraenoic acid. Independent evidence for the absolute configurations was obtained by capillary gas-liquid chromatography of diastereomeric R-(-)-2-butyl esters of the acetylated 2-hydroxy carboxylic acids produced by oxidative ozonolysis of the acetylated dihydroxy fatty acids. It is concluded that soybean lipoxygenase-1 produces hydroperoxides with predominantly the S-configuration irrespective of the position in the fatty acid which is oxygenated.

Heterogeneity of bovine lactotransferrin glycans. Characterization of α-D-Galp-(1→3)-β-D-Gal- and α-NeuAc-(2→6)-β-D-GalpNAc-(1→4)-β-D-GlcNAc-substituted N-linked glycans

Abstract Lactotransferrin isolated from a pool of mature bovine milk has been shown to contain N-glycosidically-linked glycans possessing N-acetylneuraminic acid, galactose, mannose, fucose, N-acetylglucosamine and N-acetylgalactosamine. The glycopeptides obtained by Pronase digestion were fractionated by concanavalin A-Sepharose affinity chromatography into three fractions: slightly retained (A), retained (B), and strongly retained (C). The structure of the glycans of the three fractions has been determined by application of methanolysis, methylation analysis, fast atom bombardment-mass spectrometry, and 1H NMR spectroscopy. Diantennary structures without GalNAc were present as partially sialylated and partially (1 → 6)-α- l -fucosylated structures in Fractions A and B. Sequences containing α- d -Galp-(1 → 3)-β- d -Gal on the α- d -Man-(1 → 6) antenna, and β- d -GalpNAc-(1 → 4)-β- d -GlcNAc and α-NeuAc-(2 → 6)-β- d -GalpNAc-(1 → 4)-β- d -GlcNAc on the α- d -Man-(1 → 3) antenna were characterized in the oligosaccharide-alditols obtained by reductive cleavage of Fraction B. A series of Man4 − 9-GlcNAc structures were identified in Fraction C after endo-N-acetyl-β- d -glucosaminidase digestion. These results show that the structures of bovine lactotransferrin glycans are more heterogeneous than those of previously characterized transferrin glycans.

Primary structure of two sialylated triantennary glycans from human serotransferrin

Transferrin NMR analysis Glycan structure Glycoprotein heterogeneity

Identification and structural analysis of the tetrasaccharide NeuAc.alpha.(2.fwdarw.6)Gal.beta.(1.fwdarw.4)GlcNAc.beta.(1.fwdarw.3)Fuc.alpha.1.fwdarw.O-linked to serine 61 of human factor IX

O-Linked fucose has been found attached to Thr/Ser residues within the sequence Cys-X-X-Gly-Gly-Thr/Ser-Cys in the N-terminal EGF domains of several coagulation/fibrinolytic proteins. Carbohydrate composition and mass spectrometric analyses of tryptic and thermolytic peptides containing the corresponding site (Ser-61) in the first EGF domain of human factor IX indicated the presence of a tetrasaccharide containing one residue each of sialic acid, galactose, N-acetylglucosamine, and fucose. The Ser-61 tetrasaccharide was not susceptible to alpha-fucosidase digestion. Fragments generated during mass spectrometric analysis indicated that fucose was the attachment sugar residue. The involvement of fucose in the carbohydrate-peptide linkage was confirmed by two-dimensional 1H NMR spectroscopic analysis of the glycopeptide containing factor IX residues 57-65. The complete structure of the tetrasaccharide was obtained by methylation analysis and two-dimensional 1H TOCSY and ROESY experiments as NeuAc alpha(2-->6)Gal beta(1-->4)GlcNAc beta(1-->3)Fuc alpha 1-->O-Ser61.

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

A pool of neutral carbohydrate chains was prepared from respiratory mucins of a patient suffering from bronchiectasis. Fractionation by HPLC led to 35 smaller-size oligosaccharide-alditols; the structure of 16 oligosaccharide-alditols with core type 1 or type 2 has been established (Klein, A., Lamblin, G., Lhermitte, M., Roussel, P., Breg, J., Van Halbeek, H. & Vliegenthart, J.F.G., preceding paper in this journal). In this second part, we identified 19 oligosaccharide-alditols possessing core types 3 and 4. Nine of the structures (1, 5, 9, 6, 10b, 13, 19, 15b and 18.1) have been described previously to be present in cystic fibrosis mucins [Lamblin, G., Boersma, A., Lhermitte, M., Roussel, P., Mutsaers, J.G.H. M., Van Halbeek, H. & Vliegenthart, J.F.G. (1984) Eur. J. Biochem. 143, 227-234]. The remaining ten are new structures isolated from bronchial mucins; they are all extensions of the above-mentioned nine oligosaccharides. These compounds are octassaccharide-alditols containing the Y determinant together with the H determinant of either backbone-type 1 or 2, and partial structures thereof: (Formula: see text) and 21b, which is 23c without Fuc alpha(1----3), 18.2, which is 23c without any Fuc in the 6-branch, and 22b, which is 23c without Fuc in the 3-branch.

Structural studies of 4-O-acetyl-α-N-acetylneuraminyl-(2→3)-lactose, the main oligosaccharide in echidna milk

The main oligosaccharide (50%) in the milk of the Australian echidna (Tachyglossus aculeatus) has been identified unequivocally as 4-O-acetyl-α-N-acetylneur-aminyl-(2→3)-lactose. The 4-O-acetyl substituent of the sialic acid residue was characterised by g.l.c.-m.s. of the isolated (after mild, acid hydrolysis) and trimethyl-silylated/esterified sialic acid, and by m.s. (after derivatisation) and 500-MHz, 1H-n.m.r. spectroscopy of the intact oligosaccharide. Information about the glycosidic bonds was obtained by methylation analysis and 500-MHz, 1H-n.m.r. spectroscopy. This animal species is the third one known to produce 4-O-acetylated sialic acid.

The identification of terminal α(1→3)-linked galactose in N-acetyllactosamine type of glycopeptides by means of 500-MHz 1H-NMR spectroscopy

500-MHz 1H-NMR spectroscopy was employed to study two N-acetyllactosamine-type glycopeptide fractions which were derived from a bovine thyroglobulin preparation (Cummings, R.D., and Kornfeld, S. (1982) J. Biol. Chem. 257, 11230-11234). By this method, their branches were found to be terminated either by NeuAc in alpha (2----6)-linkage or by Gal in alpha (1----3)-linkage. For the first time, the Gal alpha (1----3) Gal beta (1----4) GlcNAc beta (1----.) sequence is characterized by 1H-NMR to occur in N-glycosidic carbohydrate chains of glycoproteins. Moreover, this approach made possible the branch localization of such a unit. Microheterogeneity with respect to the presence of alpha-linked Gal or NeuAc in terminal position of a certain branch in one of the preparations, could be adequately assessed in terms of structures by 1H-NMR.

α-D-Galactosyltransferase activity in calf thymus: A high-resolution 1H-NMR study

In calf thymus an alpha-D-galactosyltransferase activity has been detected that transfers galactosyl residues from UDP-galactose to suitable acceptors having galactose at the non-reducing terminus. For example, incubation of UDP-[14C]galactose and Gal beta(1 leads to 4) GlcNAc (N-acetyllactosamine) in the presence of a calf thymus cell-free suspension containing this galactosyltransferase activity resulted in the enzymic synthesis of a 14C-labelled trisaccharide. 500-MHz 1H-NMR spectroscopic analysis revealed the structure of the trisaccharide to be: Gal alpha (1 leads to 3) Gal beta (1 leads to 4) GlcNAc. This study illustrates the suitability of the 1H-NMR method for the analysis of enzymic conversions of carbohydrate chains.

Occurrence of the Y determinant on the N-glycosidic carbohydrate units of human gamma-seminoprotein

Abstract 500-MHz 1 H-NMR spectroscopy of the oligosaccharides derived from γ-seminoprotein, a human seminal plasma glycoprotein, revealed considerable microheterogeneity both with respect to the degree of branching and with regard to the peripheral sugars. Although the protein possesses only one N-glycosylation site, di-, tri- and tetra-antennary glycans in a ratio of 40:15:45 were found to be present. Moreover, certain branches of the tri- and tetra-antennas contain one or two Fuc residues which form part of the SSEA-1 and Y determinants. It should be noted that this is the first report that describes the occurrence and localization of the Y determinant, i.e. Fucα(1→2)Galβ(1→4)[Fucα(1→3)]GlcNAcβ(1→·), in an N-glycan of a glycoprotein.

Terminal α(1→4)-linked N-acetylglucosamine: A characteristic constituent of duodenal-gland mucous glycoproteins in rat and pig. A high-resolution 1H-NMR study

Abstract The structure of the carbohydrate chains of mucous glycoproteins from the gastro-intestinal tract was examined for species- and tissue-specificity. To this purpose, oligosaccharides were released from purified glycoprotein preparations of rat and pig gastric, duodenal-gland and small-intestinal mucus, by alkaline borohydride reductive cleavage. Based on the results of 500-MHz 1 H-NMR spectroscopy and of sugar analysis of the total oligosaccharide fractions, terminal GlcNAc, α(1→4)-linked to galactose, appears to be a characteristic constituent of duodenal-gland oligosaccharides. Similarly, NeuAc in α(2→3)-linkage to galactose turns out to be a typical constituent of small-intestinal mucous glycoproteins. In general, glycoproteins from gastric mucus possess larger and more-branched carbohydrate chains than those from duodenal-gland and small-intestinal mucus. Comparing rat and pig, oligosaccharide structures for corresponding tissues are less complex for the former. After fractionation, the rat duodenal-gland oligosaccharides could be characterized by application of 1 H-NMR spectroscopy as being branched tetra- up to hexa-saccharide chains, all sharing the italicized trisaccharide element. The chains exhibit microheterogeneity as to the termination by fucose in α(1→2)- or by GlcNAc in α(1→4)-linkage to galactose. The following structures can be proposed for the most abundant rat duodenal-gland oligosaccharides: