alpha-D-galactosyltransferase activity in calf thymus. A high-resolution 1H-NMR study

Use of Wisteria floribunda agglutinin affinity chromatography in the structural analysis of the bovine lactoferrin N-linked glycosylation

BACKGROUND

Over the years, the N-glycosylation of both human and bovine lactoferrin (LF) has been studied extensively, however not all aspects have been studied in as much detail. Typically, the bovine LF complex-type N-glycans include certain epitopes, not found in human LF N-glycans, i.e. Gal(α1-3)Gal(β1-4)GlcNAc (αGal), GalNAc(β1-4)GlcNAc (LacdiNAc), and N-glycolylneuraminic acid (Neu5Gc). The combined presence of complex-type N-glycans, with αGal, LacdiNAc, LacNAc [Gal(β1-4)GlcNAc], Neu5Ac (N-acetylneuraminic acid), and Neu5Gc epitopes, and oligomannose-type N-glycans complicates the high-throughput analysis of such N-glycoprofiles highly.

METHODS

For the structural analysis of enzymatically released N-glycan pools, containing both LacNAc and LacdiNAc epitopes, a prefractionation protocol based on Wisteria floribunda agglutinin affinity chromatography was developed. The sub pools were analysed by MALDI-TOF-MS and HPLC-FD profiling, including sequential exoglycosidase treatments.

RESULTS

This protocol separates the N-glycan pool into three sub pools, with (1) free of LacdiNAc epitopes, (2) containing LacdiNAc epitopes, partially shielded by sialic acid, and (3) containing LacdiNAc epitopes, without shielding by sialic acid. Structural analysis by MALDI-TOF-MS and HPLC-FD showed a complex pattern of oligomannose-, hybrid-, and complex-type di-antennary structures, both with, and without LacdiNAc, αGal and sialic acid.

CONCLUSIONS

Applying the approach to bovine LF has led to a more detailed N-glycome pattern, including LacdiNAc, αGal, and Neu5Gc epitopes, than was shown in previous studies.

GENERAL SIGNIFICANCE

Bovine milk proteins contain glycosylation patterns that are absent in human milk proteins; particularly, the LacdiNAc epitope is abundant. Analysis of bovine milk serum proteins is therefore excessively complicated. The presented sub fractionation protocol allows a thorough analysis of the full scope of bovine milk protein glycosylation. This article is part of a Special Issue entitled Glycoproteomics.

Synthesis of linear-B saccharopeptides via enzymatic galactosylation of non-natural glucosamide acceptors

A series of D- and L-glycopyranuronic acids are coupled to glucosamines to give saccharopeptides. These 'disaccharides', in which the acetyl moiety of the natural N-acetyl-glucosamine is replaced by various sugar acids, turned out to be surprisingly good substrates for beta(1-4)-galactosyl-transferase and alpha(1-3)-galactosyl-transferase. The enzymes transfer successively two galactose units from the donor UDP-galactose onto these acceptor substrates, despite the far reaching alterations, regio- and stereospecifically in the expected manner to give linear-B saccharopeptides.

N-linked oligosaccharides of cobra venom factor contain novel alpha(1-3)galactosylated Le(x) structures

Cobra venom factor (CVF), a nontoxic, complement-activating glycoprotein in cobra venom, is a functional analog of mammalian complement component C3b. The carbohydrate moiety of CVF consists exclusively of N-linked oligosaccharides with terminal alpha1-3-linked galactosyl residues, which are antigenic in human. CVF has potential for several medical applications, including targeted cell killing and complement depletion. Here, we report a detailed structural analysis of the oligosaccharides of CVF. The structures of the oligosaccharides were determined by lectin affinity chromatography, antibody affinity blotting, compositional and methylation analyses, and high-resolution (1)H-NMR spectroscopy. Approximately 80% of the oligosaccharides are diantennary complex-type, approximately 12% are tri- and tetra-antennary complex-type, and approximately 8% are oligomannose type structures. The majority of the complex-type oligosaccharides terminate in Galalpha1-3Galbeta1-4(Fucalpha1-3)GlcNAcbeta1, a unique carbohydrate structural feature abundantly present in the glycoproteins of cobra venom.

The glycosylation of the influenza A virus hemagglutinin by mammalian cells. A site-specific study

We have characterized the glycans at individual sites on the hemagglutinin of three influenza A variants to obtain information on the role of cell-specific glycosylation in determining the receptor binding properties of this virus. The variants differ in whether they have a glycosylation site at residue 129 on the tip of the hemagglutinin and whether amino acid 184 (near to the receptor binding site) is His or Asn. We found that all sites on each variant are glycosylated in Madin-Darby bovine kidney cells, that the glycosylation is site-specific, and that the glycans at the same site in each variant are highly similar. One site that is buried in the hemagglutinin trimer contains only oligomannose glycans. The remaining sites carry complex glycans of increasing size as the distance of the site from the viral membrane decreases. Most of these complex glycans are terminated with alpha-galactose residues, a consequence in bovine cells of the removal of terminal sialic acids by the viral neuraminidase. Although the glycans at residue 129 are among the smallest on the molecule, they are large enough to reach the receptor binding pocket on their own and adjacent monomers. The results suggest that the reduction in receptor binding observed with Madin-Darby bovine kidney cell-grown virus is due to the combined effect of large complex glycans at the tip of the hemagglutinin and a His to Asn substitution close to the receptor binding pocket.

One-pot enzymatic synthesis of the Gal alpha 1-->3Gal beta 1-->4GlcNAc sequence with in situ UDP-Gal regeneration

The trisaccharide Gal alpha 1-->3Gal beta 1-->4GlcNAc beta 1-->O-(CH2)8COOCH3 was enzymatically synthesized, with in situ UDP-Gal regeneration. By combination in one pot of only four enzymes, namely, sucrose synthase, UDP-Glc 4'-epimerase, UDP-Gal:GlcNAc beta 4-galactosyltransferase and UDP-Gal:Gal beta 1-->4GlcNAc alpha 3-galactosyltransferase, Gal alpha 1-->3Gal beta 1-->4GlcNAc beta 1-->O-(CH2)8COOCH3 was formed in a 2.2 mumol ml-1 yield starting from the acceptor GlcNAc beta 1-->O-(CH2)8COOCH3. This is an efficient and convenient method for the synthesis of the Gal alpha 1-->3Gal beta 1-->4GlcNAc epitope which pays an important role in various biological and immunological processes.

Enzyme-assisted synthesis of a bivalent high-affinity dodecasaccharide inhibitor of mouse gamete adhesion. The length of the chains carrying distal alpha 1,3-bonded galactose residues is critical

Proposing to study the molecular mechanisms of mouse gamete adhesion with the aid of high affinity adhesion inhibitors of saccharide nature, we report here the enzymatic synthesis of a bivalent oligosaccharide Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-3(Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4GlcNAc beta 1-6)Gal beta 1-4GlcNAc (4), consisting of two long arms that link together two distal alpha 1,3-galactose residues. Binding data reported elsewhere (E. Litscher et al., Biochemistry, 1995, 34, 4662-4669) show that 4 is a high affinity inhibitor of mouse gamete adhesion in vitro (IC50 = 9 microM), while a related octasaccharide Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-3(Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-6)Gal beta 1-4GlcNAc, consisting of two short arms is of very low inhibitory activity. The data highlight the importance of the two alpha-galactose residues of 4, and the length of the sugar chains joining them.

Stepwise transfer of alpha-D-Galp-(1-->3)-beta-D-Galp-(1-->4)-beta-D-GlcpNAc sequences to 3-OH and 6-OH of distal galactose residues in bi-, tri-, and tetra-antennary asialo-glycans of N-linked complex type

The hydroxyl groups 3 and 6 of distal galactose units in bi-, tri-, and tetra-antennary asialo-glycans of N-linked complex type were substituted stepwise by transferase reactions with the sequence alpha-D-Galp-(1-->3)-beta-D-Galp-(1-->4)-beta-D-GlcpNAc. The products of each transferase reaction were purified chromatographically and the structures were confirmed by 1H NMR spectroscopy. Molecular weights of the final products were determined by matrix-assisted laser-desorption mass spectrometry (MALDI-MS).

Bi-antennary oligo-(N-acetyllactosamino)glycans of I-type are galactosylated preferentially at the GlcNAc beta 1-6Gal linked arms by alpha 1,3-galactosyltransferase of bovine thymus

alpha 1,3-Galactosylation of radiolabelled bi-antennary acceptors Gal beta 1-4GlcNAc beta 1-3(Gal beta 1-4GlcNAc beta 1-6)Gal-R (R = 1-OH, beta 1-4GlcNAc or beta 1-4Glc) with bovine thymus alpha 1,3-galactosyltransferase was studied. At all stages of the reactions the three acceptors reacted faster at the 1-->6 linked arm than at the 1-->3 linked branch. Hence, in addition to the doubly alpha 1,3-galactosylated products, practically pure Gal beta 1-4GlcNAc beta 1-3(Gal alpha 1-3Gal beta 1-4GlcNAc beta 1-6)Gal-R could be obtained from the three acceptors in reactions that had proceeded to near completion. The isomeric mono-alpha 1,3-galactosylated products were identified by using exoglycosidases to remove the branches unprotected by alpha 1,3-galactoses and by subsequently identifying the resulting linear glycans chromatographically.

alpha-D-galactose-bearing glycoproteins on the surface of stimulated murine peritoneal macrophages. Biochemical and immunochemical characterization of purified glycoproteins

Two glycoproteins were isolated from lysates of thioglycollate-stimulated, murine peritoneal macrophages by affinity chromatography on immobilized Griffonia simplicifolia I lectin and by preparative SDS/PAGE. The glycoproteins were readily labeled on the surface of intact macrophages with 3H and 125I. The labeled glycoproteins migrated as broad bands of molecular mass 92-109 kDa and 115-125 kDa. The mobility of the glycoproteins decreased only slightly after reduction with dithiothreitol, indicating the absence of intersubunit disulfide bridges. The 92-kDa and 115-kDa glycoproteins had pI 5.2-5.4 and pI less than or equal to 4, respectively. Digestion of both glycoproteins with alpha-galactosidase released 23% of their 3H content and abolished their ability to bind to the G. simplicifolia I lectin, showing that they contain terminal alpha-D-galactosyl groups. After reduction with 2-mercaptoethanol, each glycoprotein fraction was sensitive to N-glycanase; the 115-kDa glycoproteins produced a smear with the front at approximately 67 kDa, whereas the 92-kDa glycoprotein gave two bands of 61 kDa and 75 kDa. Unreduced glycoproteins were insensitive to N-glycanase, suggesting the presence of intramolecular disulfide bonds. Although each glycoprotein fraction was sensitive to endoglycosidase H, this enzyme produced only slight changes in molecular mass when compared with N-glycanase. From these results as well as from the specificity of the enzymes involved, it is concluded that each glycoprotein fraction contains complex-type oligosaccharides and a small amount of high-mannose and/or hybrid-type oligosaccharides. While each glycoprotein fraction was bound to Datura stramonium lectin, they failed to react with anti-[i-(Den)] serum and their digestion with endo-beta-galactosidase did not cause a band shift in SDS/PAGE. Taken together, these results suggest the presence of N-acetyllactosamine units which are not arrayed in linear form but occur as single units, bound either to C2 and C6, or to C2 and C4, or both, of outer mannosyl residues on complex-type oligosaccharides. The glycoprotein(s) fraction precipitated with anti-[I (Step)] serum, suggesting the presence of branched lactosaminoglycans. Digestion of both glycoprotein fractions with a mixture of sialidase and O-glycanase did not alter their mobility in SDS/PAGE, suggesting a lack or low content of O-linked trisaccharides and tetrasaccharides. Each glycoprotein fraction was bound specifically to Sambucus nigra and Maackia amurensis immobilized lectins, indicating the presence of sialic acid linked alpha 2,6 to subterminal D-galactose or N-acetylgalactosamine residues, and alpha 2,3 to N-acetyllactosamine residues, respectively.

The glycopeptides of the mouse immunoglobulin A T15

Cleavage of mouse IgA T15 with papain yielded (a) a glycosylated Fab fragment, (b) a non-glycosylated Fc fragment and (c) a glycosylated C-terminal peptide. The cleavage sites at the hinge and at the end of the C alpha 3 domain were located by sequencing. The two glycopeptides were prepared from the Fab and C-terminal fragments by pronase digestion. The C alpha 1 glycopeptide at Asn 155 was complex type with alpha (1-3)galactose terminal groups, and closely resembled the Asn 171 glycopeptide of mouse IgM (Anderson et al. (1985) Arch. Biochem. Biophys. 243, 605-618). In contrast, the C-terminal glycopeptide at Asn 446 was entirely different from the corresponding IgM glycopeptide, being complex rather than high-mannose type.

Alpha 1----3-galactosyltransferase: the use of recombinant enzyme for the synthesis of alpha-galactosylated glycoconjugates

We have reported the isolation and characterization of a bovine cDNA clone containing the complete coding sequence for UDP-Gal:Gal beta 1----4GlcNAc alpha 1----3-galactosyltransferase [Joziasse, D. H., Shaper, J. H., Van den Eijnden, D. H., Van Tunen, A. J. & Shaper, N. L. (1989) J. Biol. Chem. 264, 14290-14297]. Insertion of this cDNA clone into the genome of Autographa californica nuclear polyhedrosis virus (AcNPV) and subsequent infection of Spodoptera frugiperda (Sf9) insect cells with recombinant virus, resulted in high-level expression of enzymatically active alpha 1----3-galactosyltransferase. The expressed enzyme accounted for about 2% of the cellular protein; the corresponding specific enzyme activity was 1000-fold higher than observed in calf thymus, the tissue with the highest specific enzyme activity reported to date. The recombinant alpha 1----3-galactosyltransferase could be readily detergent-solubilized and subsequently purified by affinity chromatography on UDP-hexanolamine-Sepharose. The recombinant alpha 1----3-galactosyltransferase showed the expected preference for the acceptor substrate N-acetyllactosamine (Gal beta 1----4GlcNAc), and demonstrated enzyme kinetics identical to those previously reported for affinity-purified calf thymus alpha 1----3-galactosyltransferase [Blanken, W. M. & Van den Eijnden, D. H. (1985) J. Biol. Chem. 260, 12927-12934]. In pilot studies, the recombinant enzyme was examined for the ability to synthesize alpha 1----3-galactosylated oligosaccharides, glycolipids and glycoproteins. By a combination of 1H-NMR, methylation analysis, HPLC, and exoglycosidase digestion it was established that, for each of the model compounds, the product of galactose transfer had the anticipated terminal structure, Gal alpha 1----3Gal beta 1----4-R. Our results demonstrate that catalysis by recombinant alpha 1----3-galactosyltransferase can be used to obtain preparative quantities of various alpha 1----3-galactosylated glycoconjugates. Therefore, enzymatic synthesis using the recombinant enzyme is an effective alternative to the chemical synthesis of these biologically relevant compounds.

O-specific polysaccharides of Hafnia alvei lipopolysaccharides isolated from two serologically related strains: ATCC 13337 and 1187. A serological and structural study using chemical methods, gas chromatography/mass spectrometry and NMR spectroscopy at 500 MHz

The O-specific polysaccharides of Hafnia alvei ATCC 13337 standard strain and 1187 strain have been isolated and characterized. By means of 1H-NMR spectroscopy, methylation analysis and periodate oxidation, the repeating unit of the polysaccharides could be allocated the respective structures. (formula; see text) where Acyl = D-3-hydroxybutyryl, and 3-O-acetylation was to about 66%. The structural similarity of the polysaccharides was confirmed in the serological study; their epitopes were determined and the importance of various structural elements for the serological specificity was discussed.

Abnormal expression of alpha-galactosyl epitopes in man. A trigger for autoimmune processes?

1% of circulating IgG in man is anti-Gal antibody, which interacts specifically with the carbohydrate structure Gal alpha 1----3Gal beta 1----4GlcNAc-R on mammalian glycoconjugates (described throughout as the alpha-galactosyl epitope). This epitope is abundant on cell surface glycoconjugates of non-primate mammals, prosimians, and New World monkeys. It is not found on cells of Old World monkeys, apes, and man because of diminished alpha 1----3 galactosyltransferase enzyme activity. However, the alpha 1----3 galactosyltransferase gene seems to be present within the human genome. A mechanism that increases alpha 1----3 galactosyltransferase activity in human cells could trigger an autoimmune process mediated by anti-Gal binding to the newly synthesised alpha-galactosyl epitopes.

A novel sialylhexasaccharide from human milk: purification by affinity chromatography on immobilized wheat germ agglutinin

A sialylhexasaccharide fraction (S-5) of human milk was obtained as described by A. Kobata and V. Ginsburg [(1972) Arch. Biochem. Biophys. 150, 273-281] and labeled by reduction with NaB[3H]4. When subjected to affinity chromatography on immobilized wheat germ agglutinin (WGA), a single component representing 60% of the S-5 fraction was retarded by the column. The asialo derivative of the WGA-retarded oligosaccharide had a higher affinity for the WGA column than the native sialyloligosaccharide. The neutral hexaose was identified as lacto-N-neohexaose by sequential exoglycosidase digestions in combination with gel filtration analyses of digestion products. Enzymatic removal of the nonsialylated branch of the intact sialyloligosaccharide by jack bean beta-galactosidase and beta-N-acetylhexosaminidase resulted in a single sialyl[3H]tetraose which was identified as sialyltetrasaccharide c (NeuAc alpha 2-6Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4GlcO[3H]) by cochromatography with authentic standard and specific antibody binding. Independent evidence for the structure of the sialylhexasaccharide was obtained by 500-MHz1H NMR spectroscopy of the WGA-purified oligosaccharide before and after neuraminidase digestion. The structural data are consistent with the following, previously undescribed, sialylhexaose in human milk: (formula; see text).

Interaction between human natural anti-alpha-galactosyl immunoglobulin G and bacteria of the human flora

Anti-alpha-galactosyl immunoglobulin G (anti-Gal) is a natural antibody present in unusually high amounts in human sera. It constitutes as much as 1% of circulating immunoglobulin G in humans and displays a distinct specificity for the carbohydrate epitope galactosyl alpha(1----3) galactosyl (Gal alpha 1----3Gal). Recently, it has been suggested by various investigators that anti-Gal may be related to some autoimmune phenomena, since marked elevation of its titer was found in sera of patients with autoimmune thyroid disorders, rheumatoid arthritis, glomerulonephritis, and Chagas' disease. In view of the ubiquitous presence of anti-Gal in high titers in humans, throughout life, we hypothesized that, analogous with synthesis of anti-blood group antibodies against bacterial antigens, bacteria within normal intestinal flora may provide constant antigenic stimulation for the synthesis of anti-Gal. This hypothesis would imply that anti-Gal may bind to a variety of bacterial strains of human flora. In the present study, the interaction between affinity chromatography-purified anti-Gal and various bacterial strains was studied. By the use of a direct immunostaining assay and an enzyme-linked immunosorbent assay, anti-Gal was found to interact with a variety of Escherichia coli, Klebsiella, and Salmonella strains, some of which were isolates from normal stool. Furthermore, the anti-Gal-binding sites in some strains were found to be present on the carbohydrate portion of bacterial lipopolysaccharides. It is thus suggested that Gal alpha 1----3Gal epitopes in the outer membranes of normal flora enterobacteria may provide a continuous source for antigenic stimulation. Since there is no immune tolerance to the Gal alpha 1----3Gal carbohydrate structure in humans, anti-Gal seems to be constantly produced in response to these enterobacteria. In addition, bacteria which express Gal alpha----3Gal epitopes and which may adhere to various cells mediated binding of anti-Gal to human cell lines. These findings raise the possibility that anti-Gal may damage normal human tissues via inflammatory processes facilitated by bacterial Gal alpha 1----3Gal epitopes.

Evolutionary relationship between the natural anti-Gal antibody and the Gal alpha 1----3Gal epitope in primates

Anti-Gal is a natural antibody, which constitutes as much as 1% of circulating IgG in humans and displays a distinct specificity for the structure Gal alpha 1----3Gal. This glycosidic structure has been found on various tissues of many nonprimate mammals. A comparative study of the occurrence of anti-Gal versus the expression of the Gal alpha 1----3Gal epitope was performed in primates, and a distinct evolutionary pattern was observed. Whereas anti-Gal was found to be present in Old World monkeys and apes in titers comparable to those in humans, its corresponding antigenic epitope is abundantly expressed on erythrocytes of New World monkeys. Immunostaining with anti-Gal of glycolipids from New World monkey erythrocytes indicated that the molecules to which anti-Gal binds are similar to those found in rabbit and bovine erythrocytes. These findings indicate that there is an evolutionary reciprocity between New World and Old World primates in the production of the Gal alpha 1----3Gal structure and the antibody that recognizes it. The expression of the Gal alpha 1----3Gal epitope was evolutionarily conserved in New World monkeys, but it was suppressed in ancestral lineages of Old World primates. The suppression of this epitope was accompanied by the production of anti-Gal. The observed in vivo binding of anti-Gal to human normal senescent and some pathologic erythrocytes implies that the Gal alpha 1----3Gal epitope is present in man in a cryptic form.

Major carbohydrate structures at five glycosylation sites on murine IgM determined by high resolution 1H-NMR spectroscopy

Mouse myeloma immunoglobulin IgM heavy chains were cleaved with cyanogen bromide into nine peptide fragments, four of which contain asparagine-linked glycosylation. Three glycopeptides contain a single site, including Asn 171, 402, and 563 in the intact heavy chain. Another glycopeptide contains two sites at Asn 332 and 364. The carbohydrate containing fragments were treated with Pronase and fractionated by elution through Bio-Gel P-6. The major glycopeptides from each site were analyzed by 500 MHz 1H-NMR and the carbohydrate compositions determined by gas-liquid chromatography. The oligosaccharide located at Asn 171 is a biantennary complex and is highly sialylated. The amount of sialic acid varies, and some oligosaccharides contain alpha 1,3-galactose linked to the terminal beta 1,4-galactose. The oligosaccharides at Asn 332, Asn 364, an Asn 402 are all triantennary and are nearly completely sialylated on two branches and partially sialylated on the triantennary branch linked beta 1,4 to the core mannose. The latter is sialylated about 40% of the time for all three glycosylation sites. The major oligosaccharide located at Asn 563 is of the high mannose type. The 1H-NMR determination of structures at Asn 563 suggests that the high mannose oligosaccharide contains only three mannose residues.

High-pressure liquid chromatography of neutral oligosaccharides: effects of structural parameters

Sixty-five neutral oligosaccharides were analyzed by high-pressure liquid chromatography on an amine-modified silica column (Lichrosorb-NH2). By systematic comparison of the retention times, it was possible to attribute chromatographic behavior to specific structural features. It appeared that retention times increase with the number of sugar residues. The presence of a fucose or an N-acetylglucosamine residue results in a decreased retention time, in particular when the latter sugar is at the reducing end. A dramatic increase in retention time is shown by oligosaccharides having a 1----6 linkage, regardless of whether this linkage is involved in a branch. Less important features are the nature of the component sugars other than N-acetylglucosamine and fucose, the anomeric configuration of the sugars, and the presence of a reduced terminal sugar.

Major oligosaccharides in the glycoprotein of Friend murine leukemia virus: structure elucidation by one- and two-dimensional proton nuclear magnetic resonance and methylation analysis

The highly microheterogeneous, N-glycosidically linked oligosaccharides in the glycoproteins of Friend murine leukemia virus (as produced by Eveline cells) were liberated with endo-beta-N-acetylglucosaminidase H and by alkaline hydrolysis. They were fractionated (as desialylated oligosaccharitols) by gel filtration and by concanavalin A affinity chromatography, and the major fractions were analyzed by methylation-gas chromatography-mass spectrometry, by digestion with exoglycosidases, and, especially, by one- and two-dimensional proton nuclear magnetic resonance spectroscopy. Guidelines for qualitative and quantitative analysis of complex oligosaccharide mixtures by NMR were worked out and the results compared with those obtained by methylation analysis. It was found that these major fractions consist of bi-, tri-, and tetraantennary oligosaccharitols of the "complex" type (comprising a minority of species with N-acetyllactosamine repeating units), which are, in part, substituted by nonreducing terminal Gal alpha (1----3) and/or bisecting GlcNAc beta (1----4) residues.

The identification of terminal alpha (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.

The structure of sialyl-glycopeptides of the O-glycosidic type, isolated from sialidosis (mucolipidosis I) urine

Sialyl-glycopeptides containing an O-glycosidically linked tetrasaccharide chain were obtained from the urine of a patient suffering from mucolipidosis I. Isolation of these compounds was achieved by gel filtration, ion-exchange chromatography and preparative paper chromatography. Their structures were determined by a combination of carbohydrate and amino acid analysis, dansylation, periodate oxidation, methylation studies, enzymatic hydrolysis and 1H-NMR spectroscopy, to be as follows: (formula; see text) wherein R = peptide linked through -Thr-, -Ser-Thr- or -Thr-Ser-. The finding of these glycopeptides in urine shows that mucolipidosis I is characterized by a general "glycoprotein-specific" sialidase deficiency. The possibility of the existence of a human endo-alpha-N-acetylgalactosaminidase is discussed.

Primary structure of N-glycosidically linked asialoglycans of secretory immunoglobulins A from human milk

The asialoglycopeptides obtained from secretory immunoglobulins A from human milk have been separated by gel filtration and affinity chromatography on Concanavalin A-Sepharose and Lens culinaris agglutinin-Sepharose columns. Their structures have been determined by sugar analysis, methylation studies including mass spectrometry and 500-MHz 1H-NMR spectroscopy. The glycans are of the biantennary N-acetyllactosamine type differing in their degree of extension by fucosyl-N-acetyllactosamine residues. The overall structures of the glycopeptides are as follows: (Formula: see text) Most of the asialoglycopeptide structures possess an intersecting GlcNAc residue; they are suggested to be located on the alpha chain of the secretory immunoglobulins A of human milk. The non-intersected structures probably occur on the secretory piece. The methodology applied to the structural analysis adequately coped with the extremely high degree of heterogeneity shown by the structures.

Characterization of the neutral glycopeptides containing the structure alpha-L-fucopyranosyl-(1 leads to 3)-2-acetamido-2-deoxy-D-glucose from human neuroblastoma cells

Human tumor cells of neurectoderm origin contain a high proportion of alpha-L-fucosyl linkages were determined by high-resolution, 500-MHz, 1H-n.m.r. spectroscopy which gave signals characteristic for alpha-L-Fucp-(1 leads to 3)-D-GlcNAc residues these L-fucosyl residues. This was shown by use of a specific alpha-L-fucosidase from almond emulsin and a broad-spectrum alpha-L-fucosidase from rat testes. The exact alpha-L-fucosyl linkages were determined by high-resolution, 500-MHz, 1H-n.m.r. spectroscopy which gave signals characteristic for alpha-L-Fucp-(1 leads to 3)-D-GlcNAc residues linked to branches and for alpha-L-Fucp-(1 leads to 6)-D-GlcNAc residues linked to the core. More than 95% of the asparagine-linked GlcNAc residues were substituted with (1 leads to 6)-alpha-L-fucosyl groups. Further definition of the range of neutral glycopeptides was obtained with immobilized lectins. Binding to E-PHA-agarose suggested the presence of a beta-D-mannopyranosyl residue substituted at O-4 by a 2-acetamido-2-deoxy-D-glucopyranosyl group. alpha-L-Fucp-(1 leads to 3)-GlcNAc interfered with this binding since removal of alpha-L-fucosyl groups by almond emulsin alpha-L-fucosidase increased the binding by 100%. These studies demonstrate the ability of a combination of high-resolution 1H-n.m.r., enzyme degradation, and lectin-binding affinities to delineate structural elements of small amounts of oligosaccharide residues.

Identification and characterization of an UDP-Gal: N-acetyllactosaminide alpha-1,3-D-galactosyltransferase in calf thymus

Calf thymus was found to contain a high activity of a galactosyltransferase, which transfers galactose from UDP-galactose to asialo-alpha 1-acid glycoprotein and N-acetyllactosamine. By means of competition and acceptor-specificity studies the enzyme could be distinguished from an N-acetylglucosaminide beta-1,4-galactosyltransferase and an N-acetylgalactosamine-protein beta-1,3-galactosyltransferase, which in addition occur in calf thymus, as well as from the blood-group-B-associated alpha-galactosyltransferase. Identification of the products revealed that the enzyme accomplishes an alpha 1 leads to 3 linkage resulting in a terminal Gal(alpha 1 leads to 3)Gal(beta 1 leads to 4)GlcNAc sequence. The enzyme is membrane-bound and is activated by Triton X-100. It shows optimal activity over a broad pH range (5.5-7.0) and has a pronounced requirement for Mn2+ ions (Km = 6.1 mM) for its action. It is suggested that the alpha-1,3-galactosyltransferase functions in the biosynthesis of calf thymocyte cell-surface glycoconjugates including glycoproteins.