Further investigations into the structure of human gastric mucin: the structural configuration of the oligosaccharide chains

Quantifying diffusion in mucosal systems by pulsed-gradient spin-echo NMR

Mucus, a thick and slimy secretion produced by submucosal cells, covers many epithelial surfaces in mammalian organs and prevents foreign particles that enter the body from accessing cells. However, the mucus layer also represents a potential barrier to the efficient delivery of nano-sized drug delivery systems (polyplexes, lipoplexes, particles) to the underlying mucosal epithelium. Many studies have considered the ability of nano-sized particles and polymers to diffuse within the mucosal network using a range of different techniques, including multiple-particle tracking (MPT), diffusion chamber studies and fluorescence recovery after photobleaching (FRAP). This review highlights the current understanding of the interaction of the diffusion of nano-sized structures within mucosal networks. Moreover, this article presents an introduction to pulsed-gradient spin-echo NMR (PGSE-NMR), a potential new tool to investigate the mobility of molecular species through mucosal networks and related biological gels.

Glycodynamics of Mucin Biosynthesis in Gastrointestinal Tumor Cells

Glycoproteins found in the secretions and on the surfaces of cancer cells include mucins and mucin-like glycoproteins. These molecules have been shown to carry antigens that are characteristically expressed on cancer cells, including Tn and T antigens and Lewis epitopes. The structures of O-glycans are often abnormal in gastrointestinal tumors, or else are present in abnormal amounts, and these structures greatly contribute to the phenotype and biology of cancer cells. It has been shown that glycans of cancer cells have functional importance in cell adhesion, invasion and metastasis. The possible mechanisms leading to these cancer-specific changes in carbohydrate structures (termed glycodynamics) involve altered mRNA expression and catalytic activities of glycosyltransferases and sulfotransferases found in tissues and cells of gastrointestinal tumors. In a number of cases it has been possible to correlate enzyme changes with oligosaccharide structures. Different mechanisms have been suggested leading to the synthesis of cancer-specific Lewis, T and Tn antigens, but the regulation of cancer mucin antigens generally appears to be very complex and is poorly understood. The expression levels of specific mucin antigens and enzymes in gastro-intestinal tumors have diagnostic as well as prognostic value. These antigens also have potential for cancer immunotherapy. However, we first need to unravel the complexity of the control of glycosylation in cancer cells. Most importantly, studies of the functional implications of the glycodynamics in cancer cells, as related to cell adhesion and impact on the immune system will provide promising directions for future research.

Measuring H type 1 and H type 2 antigens in human saliva by immunoassay using artificial antigens as standard substances

A time-resolved fluorometric immunoassay for water-soluble H antigens of ABH blood group substances has been developed. Introducing artificial antigens (trisaccharide-albumin complexes for H type 1 and H type 2) as reference substances, H blood group substances in human saliva were measured. The monoclonal antibody, anti-H 1E3, reacted with both H type 1 and type 2 chains, and the commercially available anti-H reacted with H type 2 chain. Using these two antibodies we found 10-20-fold higher concentration of H type 1 compared with that of H type 2 in human saliva. The H type 2 was not found in the saliva samples from nonsecretors, irrespective of ABO phenotypes. The results suggest that approximately 90% of A and B blood group substances in human saliva are built on type 1 chains.

Structure-retention index relationships for derivatized monosaccharides on non-polar gas chromatography columns

A gas chromatographic method for predicting the retention index of a derivatized monosaccharide is presented. The procedures are especially useful to detect and predict minute quantities of sugars in biological or chemical samples. Monosaccharides are first converted to the alditols and then derivatized by acetylation, permethylation or silylation. The derivatized monosaccharide structure-retention index relationship that has been developed is useful in the identification of unknown monosaccharides that can be readily confirmed by gas chromatography-mass spectrometry.

Isolation and characterization of mucin from the serum of cystic fibrosis patients

Using monoclonal antibody 19-9, elevated levels of the sialyl Lea antigen (NeuAc alpha 2-3Gal beta 1-3[Fuc alpha 1-4]GlcNac beta 1-3R) are detected in serum from most cystic fibrosis patients. We now report further characterization of the serum antigen and evidence that it is on a mucin glycoprotein and not on glycolipids. The antigen has an apparent molecular weight greater than 2 X 10(6) by gel filtration on Sephacryl S-400. On density gradient centrifugation, the antigen has a density of 1.54 g/ml in cesium chloride and 1.42 g/ml in cesium chloride/4 M guanidine HCl. Immunostaining with monoclonal antibody 19-9 of lipid extracts from cystic fibrosis patient serum and erythrocytes does not detect any antigen on glycolipids. The antigen was purified by gel filtration and density gradient centrifugation. After tritium labeling of the sialic acid residues, sodium dodecyl sulfate gel electrophoresis separates two subunits with apparent molecular weights of 200,000 and 400,000. All of the labeled sialic acid is released as low molecular weight oligosaccharides after mild alkaline borohydride degradation. The purified antigen contains fucose, galactosamine, glucosamine, and galactose but no mannose and is enriched in the amino acids threonine, serine, glycine, proline, and alanine. The purified antigen binds several antibodies recognizing epitopes common to many mucins. Thus, the physical, biochemical, and immunochemical properties of the purified antigen indicate that the sialyl Lea antigen is present on mucins in the serum of cystic fibrosis patients.

Evaluation of the liquid chromatographic separation of monosaccharides, disaccharides, trisaccharides, tetrasaccharides, deoxysaccharides and sugar alcohols with stable cyclodextrin bonded phase columns

Both alpha- and beta-cyclodextrin (CD) bonded phase columns were evaluated for their ability to separate carbohydrates and related molecules. Chromatographic data on approximately 50 solutes are reported. Mobile phases consisting of acetonitrile-water or acetone-water produce the best separations. Separations could be run in isocratic or gradient modes. The alpha-CD column produced slightly more efficient separations than the beta-CD column. Both cyclodextrin columns seemed to be more efficient and selective than alkylamine and ion-exchange columns. The stability and reproducibility of the CD columns were excellent and showed little deterioration after several thousand injections. The retention of saccharides on CD bonded phases seems to be related to the number of available hydroxy groups per solute and to the size of the solute. Analysis times and detection sensitivity are discussed.

Radiolysis of human gastric glycopolypeptides in aqueous solution

The degradation of human gastric glycopolypeptides by hydroxyl radicals formed in irradiated N2O-saturated aqueous solution has been investigated. Gel exclusion chromatography shows the formation of lower molecular weight degradation products after irradiation and the appearance of unsaturated carbonyl-containing products which absorb in the ultra-violet. The radiation-induced destruction of individual monosaccharides in three human glycopolypeptides having different oligosaccharide chains has been measured. The results indicate that the structure of the oligosaccharide chain determines the extent of destruction of each type of monosaccharide present.

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).

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.

13C-N.M.R.-spectral study of the binding of Gd3+ to glycophorin

Natural-abundance, 13C-n.m.r. spectroscopy was used to study the binding of Gd3+ to glycophorin, and also to the tetrasaccharides isolated from glycophorin after treatment of the glycoprotein with NaOH-NaBH4. Gd3+ binds to the tetrasaccharide (both in the isolated, reduced form and when still attached to the native glycoprotein), and, especially, to the alpha-NeuAc residues. In order to cause severe line-broadening of the 13C resonances of alpha-NeuAc, the ratios of the alpha-NeuAc residues of glycophorin, and of the isolated, reduced tetrasaccharide, to Gd3+ were much higher than that needed for causing similar broadening for 2-O-methyl-alpha-NeuAc-Gd3+ solutions. These results indicate that the other carbohydrate residues of the tetrasaccharide may be involved in the binding of Gd3+, producing a stronger metal-ion-binding effect.

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.

Immunocytochemical studies of blood group A, H, I, and i antigens in gastric mucosae of infants with normal gastric histology and of patients with gastric carcinoma and chronic benign peptic ulceration

Indirect immunofluorescence studies of blood group A, H, I, and i antigens were performed on the gastric mucosae and tumor tissues of patients with gastric carcinoma, on the mucosae of patients with chronic benign gastric ulceration, and on the mucosae of infants who had died of causes other than gastrointestinal disease. The following findings were of particular interest: (1) Normal 'secretor' type mucosae were distinguishable from 'non-secretor' type mucosae by the uniform staining of the A or H antigens at the surface and in the pits. Normal 'non-secretor' type mucosae showed little staining of the H or A antigens but, instead, there was staining with anti-I(Ma) antibody. Staining with anti-I(Step) and anti-i(Den) did not show a clear correlation with the 'secretor'/'non-secretor' status of the normal mucosae. (2) Apparently normal areas of gastric mucosae of patients with gastric carcinoma or the normal part of gastric mucosae of patients with benign gastric ulcer frequently showed focal areas of loss or gain of the blood group antigens as is often seen in gastric carcinoma tissues. (3) In the mucosae of patients with intestinal metaplasia there was marked loss of A/H antigens in 'secretors' and I(Ma) antigen in 'non-secretors'. (4) Staining characteristics of tissues from gastric carcinoma were:(a) Focal loss of the expected A/H or I antigens was observed with much variation in staining from area to area, but only a minority showed complete loss of the expected staining. (b) A majority of the carcinomas from 'secretors' showed foci of substantial staining with anti-I(Ma) in contrast to normal 'secretor' mucosae. This is probably due to incomplete biosynthesis of A/H determinants. (c) Incompatible A-like staining by a rabbit anti-A serum was observed in one out of nine adenocarcinomas from blood group B or O persons. (d) A few cases showed substantial i antigen staining. The aberrant expression of blood group A, H, I, and i antigens in neoplastic as well as in some areas of morphologically normal mucosa of patients with benign and malignant diseases of the stomach is discussed in the context of current biochemical knowledge.

Sugar residues on proteins

Glycoproteins have become increasingly important in the structure and function of many different mammalian systems; for example, membrane glycoproteins and glycoprotein hormones. It is, therefore, important to understand their chemistry, which would include an understanding of both the carbohydrate and protein parts of the molecule. Since the chemical characterization of the protein moiety has been extensively examined and the techniques for its characterization are well worked out, only the carbohydrate portion of glycoproteins will be reviewed in this article. The chemical nature of the carbohydrate moiety of glycoproteins will be examined. First, the types of monosaccharides present in animal systems, especially those in the mammalian systems, will be described. Next, various types of simple and complex carbohydrate chains will be discussed to establish the diversity, size, and number of chains present in the carbohydrate units in different glycoproteins. Then, the type of linkages of the carbohydrate to the protein will be examined to determine if the primary sequence of protein is important in determining the size and type of carbohydrate chains present in glycoproteins. Finally, the current methods of structural elucidation such as monosaccharide sequence, intersugar bonds, and anomeric linkages in the carbohydrate moiety of glycoproteins will be reviewed. These methods include the techniques of periodate oxidation, methylation, partial acid hydrolysis, and specific glycosidase digestion of glycoproteins, as well as the latest techniques using micromethods of carbohydrate quantitation and characterization involving gas chromatography and mass spectrometry. The function of the carbohydrate in glycoproteins will also be considered. First, hormone glycoproteins will be discussed in their relationship to the immunological and biological function of the glycoprotein when the carbohydrate is sequentially removed. Next, the function of the carbohydrate in the turnover of glycoproteins will be discussed. These topics will be considered in order to develop an understanding of a specific function(s) of the carbohydrate in glycoproteins.

Structure of the asialyl oligosaccharide chains of kappa-casein isolated from ovine colostrum

Three oligosaccharide alditols, a di (44-63%), tetra (32-46%), and a pentasacchariditol (5-10%) have been isolated from desialylated caseinomacropeptide obtained from kappa-casein of ewe colostrum. The disacchariditol is 2-acetamido-2-deoxy-3-O-(beta-D-galactopyranosyl)galactitol; in the tetrasaccharide this unit is substituted in position 6 of the galactosaminitol moiety by 2-acetamido-2-deoxy-4-O-(beta-D-galactopyranosyl)-beta-D-glucopyranose, while the pentasacchariditol is derived from the tetrasaccharide by addition of a D-galactopyranosyl unit to position 3 of the galactopyranose unit substituting the glucosamine unit.