Isolation and characterization of oligosaccharides from rat colonic mucus glycoprotein

D-galactosyltransferase and its endogenous substrates in chick embryo fibroblasts transformed by Rous sarcoma virus

UDP-D-galactose: 2-acetamido-2-deoxy-beta-D-glucopyranosyl 4-beta-D-galactosyltransferase (GalTase) activity was purified, from primary chick embryo fibroblast (CEF) transformed by a temperature-sensitive, Rous sarcoma virus mutant (CEF-RSV), by chromatography on an affinity resin prepared with monoclonal antibodies to GalTase. Cellular glycopeptides from CEF, as well as CEF-RSV, maintained at permissive (37 degrees) [CEF-RSF (37 degrees)] and nonpermissive temperatures (41 degrees) [CEF-RSV (41 degrees)], were solubilized and galactosylated in vitro by incubation with purified GalTase substrates, composed of at least six discrete complex glycopeptides having bi- to tetra-antennary structures. The glycopeptides isolated from transformed cells, CEF-RSV (37 degrees), included the six types observed in nontransformed cells, but demonstrated alterations in their relative amounts, including an increase in the content of a glycopeptide containing 3 mannose and 4 glucosamine residues. Furthermore, two additional complex-type glycopeptides were isolated from CEF- but demonstrated alterations in their relative amounts, including an increase in the content of a glycopeptide containing 3 mannose and 4 glucosamine residues. Furthermore, two additional complex type glycopeptides were isolated from CEF-RSV (37 degrees). These malignant transformation-related glycopeptides were partially characterized and found to represent tri- and tetra-antennary complex glycopeptides. Endogenous galactosylation appeared to have occurred in a branched, nonspecific manner in these transformed cell-derived glycopeptides. These findings indicate that transformed cells may contain a greater preponderance of more highly branched, complex oligosaccharides which are randomly galactosylated at nonreducing termini by cellular GalTase.

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.

Structural analysis of the O-glycosidically linked core-region oligosaccharides of human meconium glycoproteins which express oncofoetal antigens

Glycoproteins were extracted from meconium samples of group O neonates of secretor type by pronase digestion followed by precipitation in 67% aqueous ethanol and separated into Ii antigen enriched and depleted fractions by affinity chromatography. The latter fraction strongly expressed the oncofoetal antigens recognised by natural antibodies in mouse sera and the hybridoma antibody FC 10.2, and this activity was enhanced after mild acid hydrolysis to remove sialic acid and fucose residues. Oligosaccharides were released from the mild-acid-treated fraction by base-borohydride degradation and purified by gel permeation chromatography on Bio-Gel P4 and high performance liquid chromatography on octadecylsilyl and aminopropylsilyl columns. The major oligosaccharides were characterised by fast atom bombardment and electron impact mass spectrometry, combined gas-liquid chromatography/mass spectrometry and 500-MHz proton NMR spectroscopy. Their structures, in order of abundance, were: (Formula: see text).

Mucin synthesis. UDP-GlcNAc:GalNAc-R beta 3-N-acetylglucosaminyltransferase and UDP-GlcNAc:GlcNAc beta 1-3GalNAc-R (GlcNAc to GalNAc) beta 6-N-acetylglucosaminyltransferase from pig and rat colon mucosa

Pig and rat colon mucosal membrane preparations catalyze the in vitro transfer of N-acetyl-D-glucosamine (GlcNAc) from UDP-GlcNAc to GalNAc-ovine submaxillary mucin to form GlcNAc beta 1-3GalNAc-mucin. Rat colon also catalyzes the in vitro transfer of GlcNAc from UDP-GlcNAc to GlcNAc beta 1-3GalNAc-mucin to form GlcNAc beta 1-3(GlcNAc beta 1-6) GalNAc-mucin. This is the first demonstration of in vitro synthesis of the GlcNAc beta 1-3GalNAc disaccharide and of the GlcNAc beta 1-3-(GlcNAc beta 1-6)GalNAc trisaccharide, two of the four major core types found in mammalian glycoproteins of the mucin type, i.e., those containing oligosaccharides with GalNAc-alpha-serine (threonine) linkages. The activity catalyzing synthesis of the disaccharide has been named UDP-GlcNAc:GalNAc-R beta 3-N-acetylglucosaminyltransferase (mucin core 3 beta 3-GlcNAc-transferase), while the activity responsible for synthesizing the trisaccharide has been named UDP-GlcNAc:GlcNAc beta 1-3GalNAc-R (GlcNAc to GalNAc) beta 6-N-acetylglucosaminyltransferase (mucin core 4 beta 6-GlcNAc-transferase). The beta 3-GlcNAc-transferase from pig colon is activated by Triton X-100, has an absolute requirement for Mn2+, and transfers GlcNAc to GalNAc-alpha-phenyl, GalNAc-alpha-benzyl, and GalNAc-ovine submaxillary mucin with apparent Km values of 5, 2, and 3 mM and Vmax values of 59, 62, and 37 nmol h-1 (mg of protein)-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Galactosyl transferases of baby hamster kidney (BHK) cells. Characterization of two oligosaccharide products synthesised using bovine asialo submaxillary-gland mucin as acceptor

Extracts of BHK (baby hamster kidney) cells catalyse incorporation of galactose from UDP-galactose into asialo bovine submaxillary gland mucin. The galactosylated oligosaccharide products were released by alkaline-borohydride treatment and purified by Bio-Gel P2 chromatography and high-performance liquid chromatography. The structures of the oligosaccharide sequences synthesised have been identified unequivocally by high resolution 500 MHz 1H-NMR as galactosyl-(beta 1----3) N-acetylgalactosamine and galactosyl (beta 1----4) N-acetylglucosaminyl (beta 1----3)-N-acetylgalactosamine. Characterization of the latter sequence shows the presence in bovine mucin of the type III core sequence N-acetylglucosamine-(beta 1----3) N-acetylgalactosamine. Fractionation of BHK cell extracts on alpha-lactalbumin-Agarose has shown that the (beta 1----4)-galactosyl transferase responsible for synthesis of the trisaccharide binds to alpha-lactalbumin, a modulator of the (beta 1----4)-galactosyl transferase involved in N-glycan assembly. The evidence that the same transferase activity may be responsible for galactose transfer to both O-glycans and N-glycans is discussed.

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

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 1H-NMR spectroscopy and of sugar analysis of the total oligosaccharide fractions, terminal GlcNAc, alpha (1 leads to 4)-linked to galactose, appears to be a characteristic constituent of duodenal-gland oligosaccharides. Similarly, NeuAc in alpha (2 leads to 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 1H-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 alpha (1 leads to 2)- or by GlcNAc in alpha (1 leads to 4)-linkage to galactose. The following structures can be proposed for the most abundant rat duodenal-gland oligosaccharides: (table; see text).

The separation by liquid chromatography (under elevated pressure) of phenyl, benzyl, and O-nitrophenyl glycosides of oligosaccharides. Analysis of substrates and products for four N-acetyl-D-glucosaminyl-transferases involved in mucin synthesis

Liquid chromatography under elevated pressure (h.p.l.c.) has been applied to the separation of the phenyl, benzyl, and O-nitrophenyl glycosides of 2-acetamido-2-deoxy-D-galactopyranose and of various mucin-type, di-, tri-, and tetra-saccharides. The separations were carried out with a Whatman Partisil PXS 5/25 PAC column and various proportions of acetonitrile and water in the mobile phase. These methods were subsequently used to separate the substrates and products of the following N-acetylglucosaminyltransferase reactions: UDP-GlcNAc + beta-Gal-(1 leads to 3)-GalNAc-R leads to beta-Gal-(1 leads to 3)-[beta-GlcNAc-(1 leads to 6)]-GalNAc-R + UDP (1); UDP-GlcNAc + beta-Gal-(1 leads to 3)-[beta-GlcNAc-(1 leads to 6)]-GalNAc-R leads to beta-GlcNAc-(1 leads to 3)-beta-Gal-(1 leads to 3)-[beta-GlcNAc-(1 leads to 6)]-GalNAc-R + UDP (2); UDP-GlcNAc + GalNAc-R' leads to beta-GlcNAc-(1 leads to 3)-GalNAc-R' + UDP (3); and UDP-GlcNAc + beta-GlcNAc-(1 leads to 3)-GalNAc-R' leads to beta-GlcNAc-(1 leads to 6)-[beta-GlcNAc-(1 leads to 3)]-GalNAc-R' + UDP (4), where R is = benzyl or o-nitrophenyl, and R' = benzyl or phenyl alpha-D-glycoside. Reaction 1 is catalyzed by a transferase in canine submaxillary glands and porcine gastric mucosa, and reaction 2 by an enzyme in porcine gastric mucosa. Enzyme activities catalyzing reactions 3 and 4 have recently been demonstrated in rat colonic mucosa. Liquid chromatography can be used at the preparative level for the purification and identification of the transferase products, and at the analytical level in the assay of glycosyltransferases.

Lipids associated with rat small-intestinal mucus glycoprotein

The lipid content and composition of rat small-intestinal mucus, and the purified mucus glycoprotein before and after Pronase digestion were investigated. The mucus, obtained by the instillation of intestine with 2M NaCl, was fractionated on Bio-Gel A-50 in the presence of 6M urea and the mucus glycoprotein free of noncovalently bound protein was isolated. A portion of the purified glycoprotein was subjected to Pronase digestion to yield glycopeptides. The native mucus, and the purified glycoprotein and glycopeptides were extracted with chloroform-methanol, and the lipids contained in the extracts were analyzed. The lipids accounted for 17.6 of the dry weight of mucus, 26.4 of the mucus glycoprotein, and 25.3% of the glycopeptides. In comparison to mucus, the lipids associated with mucus glycoprotein contained 1.9 times more phospholipids and 2.1 times more glycolipids, showed a 26% increase in neutral lipids, and were virtually free of glycosphingolipids. Treatment of the purified glycoprotein with Pronase led to a moderate (22.3%) loss in neutral lipids, 4.3-fold decrease in phospholipids, and 52.3% increase in glyceroglucolipids. The results indicate that while the interaction of mucus glycoprotein with phospholipids involves its Pronase-susceptible region, the interaction with glyceroglucolipids occurs in the glycosylated region of the glycoprotein that is resistant to proteolysis.

Structure of intestinal-mucus glycoprotein from human post-mortem or surgical tissue: inferences from correlation analyses of sugar and sulfate composition of individual mucins

The carbohydrate composition of 14 human, small-intestine mucins, obtained at surgery or post-mortem, varied greatly from specimen to specimen with respect to individual sugars and average chain-length (ratio of total carbohydrate to N-acetylgalactosamine). Three monosaccharides, galactose, N-acetylglucosamine, and fucose gave good correlations with each other, and to total carbohydrate content, when expressed as a ratio to the chain-terminal N-acetylgalactosamine residue. In contrast, sialic acid gave a good correlation only with N-acetylgalactosamine. In eight specimens the molar sulfate to N-acetylgalactosamine ratios gave good correlation with the ratios of galactose to N-acetylgalactosamine, N-acetylglucosamine to N-acetylgalactosamine, and total carbohydrate to N-acetylgalactosamine. These results indicate that the intraspecies variability of intestinal-mucin carbohydrates arises from the interdependent addition of galactose, N-acetylglucosamine, fucose, and sulfate residues. Partial correlation-analysis indicated that proportions of N-acetylglucosamine and fucose were correlated only through a mutual dependence on galactose, suggesting that the key elongating-factors involve the addition of galactose residues. The number of sialic acid residues per oligosaccharide chain remained relatively unchanged from mucin to mucin, and this, coupled with the close correlation between the proportions of sialic acid and N-acetylgalactosamine, suggests that almost all sialic acid residues are bound to the core N-acetylgalactosamine residues in intestinal mucin. High fucose-to-sialic acid and high sulfate-to-sialic acid ratios reported in some disease states are explained as the consequence of chain elongation.

Specific detection of N-acetylglucosamine-containing oligosaccharide chains on ovine submaxillary asialomucin

Human milk beta-N-acetylglucosaminide beta 1 leads to 4-galactosyltransferase (EC 2.4.1.38) was used to galactosylate ovine submaxillary asialomucin to saturation. The major [14C]galactosylated product chain was obtained as a reduced oligosaccharide by beta-elimination under reducing conditions. Analysis by Bio-Gel filtration and gas-liquid chromatography indicated that this compound was a tetrasaccharide composed of galactose, N-acetylglucosamine and reduced N-acetylgalactosamine in a molar ratio of 2:0.9:0.8. Periodate oxidation studies before and after mild acid hydrolysis in addition to thin-layer chromatography revealed that the most probable structure of the tetrasaccharide is Gal beta 1 leads to 3([14C]Gal beta 1 leads to 4GlcNAc beta 1 leads to 6)GalNAcol. Thus it appears that Gal beta 1 leads to 3(GlcNAc beta 1 leads to 6)GalNAc units occur as minor chains on the asialomucin. The potential interference of these chains in the assay of alpha-N-acetylgalactosaminylprotein beta 1 leads to 3-galactosyltransferase activity using ovine submaxillary asialomucin as an acceptor can be counteracted by the addition of N-acetylglucosamine.

Primary-structure determination of fourteen neutral oligosaccharides derived from bronchial-mucus glycoproteins of patients suffering from cystic fibrosis, employing 500-MHz 1H-NMR spectroscopy

The structure of carbohydrate units of bronchial-mucus glycoproteins obtained from cystic fibrosis patients was investigated by 500-MHz 1H-NMR spectroscopy and methylation analysis. To that purpose, the mucin was subjected to alkaline borohydride degradation. Neutral oligosaccharide-alditols, ranging in size from disaccharides to pentasaccharides, were isolated. Eight compounds could be purified to homogeneity; furthermore, three fractions were obtained consisting mainly of two components. For all 14 compounds the primary structure could be elucidated. 500-MHz 1H-NMR spectroscopy was found to be effective in detecting heterogeneity and to be invaluable for the determination of structures in mixtures of oligosaccharide-alditols. The structures can be divided into two groups depending on the core disaccharide. One group contains Gal(beta 1 leads to 3)GalNAc-ol as common structural element, the other GlcNAc(beta 1 leads to 3)GalNAc-ol. Both disaccharides were identified as such; the other compounds can be conceived as extensions thereof. The most complex representatives of the two groups are: (formula; see text) The italicized structural elements, comprising the SSEA-1 determinant and the type-1 blood-group-H determinant, are novel sequences in oligosaccharide chains of mucin-type glycoproteins.

Clinical aspects of gastrointestinal mucus

In such a bird's eye view of a very complicated and complex literature it is inevitable that significant contributions, particularly from earlier investigators, will have been overlooked. We have tried, however, to provide a reasonable framework for the many presentations and discussions which will take place at this conference. As in the past, it is evident that much needs to be done to reconcile the excellent histochemical studies of gastrointestinal mucus in many diseases with the increasing knowledge of mucin structure and composition. This will only be achieved by extraction of highly pure mucin from diseased bowel. In this regard, post mortem material provides an opportunity for mucin researchers which is not available to workers in other fields because of relative freedom from decomposition. The wedding of mucin technology with immunology is also a major priority. Immunoassay techniques provide the answer to quick and accurate product identification in secretion studies. Specific monoclonal antibodies will provide the route to structural differentiation of antigens in complex mixtures. It is also evident that we must seek to develop a variety of controllable models for the study of functional parameters of mucus in physiological conditions, parasite rejection, neoplasia and inflammatory states. Promising initiatives have been touched upon in this review, but these must only be the beginning. One must conclude, however, by recognizing that advances in knowledge have been truly remarkable since the last conference in 1976. One senses that some of the keys which will one day unlock the gates of this "ill-defined" kingdom are already in hand, while the remainder are at least within reach.