Carbon-13 NMR studies of native and modified ovine submaxillary mucin

Natural abundance 13C NMR spectroscopy has been used to study the solution structure and dynamics of the ovine submaxillary mucin (OSM). Results at both 45.3 and 67.9 MHz show the extremely viscous mucin to possess sufficient internal segmental flexibility to allow high-resolution 13C NMR studies. Essentially all of the resonances in the spectra have been assigned to individual carbons of the carbohydrate disaccharide side chain alpha- NeuNAc2 ----6 alpha-Gal-NAc-Ser/Thr and to the protonated carbons of the major peptide residues. Spin-lattice relaxation times and nuclear Overhauser enhancements reveal that the internal mobility of the mucin is unaffected by large changes in molecular weight and hence bulk viscosity. On the basis of the relaxation measurements the peptide and carbohydrate side chain mobilities increase stepwise from the glycosylated peptide residue alpha-carbons to the terminal sialic acid (NeuNAc) side-chain C9 carbon. Removal of the terminal sialic acid C8 and C9 side-chain carbons as well as the complete removal of the NeuNAc residue does not alter the dynamics of the peptide core. However, the removal of carbons C8 and C9 from the NeuNAc residue produces an increase in its ring mobility or conformational flexibility. Complete removal of sialic acid produces an increase in the mobility or flexibility of the GalNAc ring and reduces the chemical shift sensitivity of the GalNAc ring carbons to the different serine and threonine linkages. The pKa value for the sialic acid carboxyl group in the intact mucin is 2.0, while it increases to 2.4 after the removal of the NeuNAc C8 and C9 side-chain carbons. This change in pKa confirms the intramolecular hydrogen bond interaction of the C8 hydroxyl with the C2 carboxyl group in the alpha-NeuNAc residue as previously suggested by Jennings and Bhattacharjee [ Jennings , H.J., & Bhattacharjee , A.K. (1977) Carbohydr . Res. 55, 105-112]. The relaxation time values and temperature dependence of the chemical shift of the NeuNAc C7 carbon suggest that this group is also involved in an intramolecular interaction. Overall the 13C NMR results indicate that the relatively simple mucous glycoprotein, OSM, is a highly extended and internally flexible molecule which in solution possesses little secondary structure.

Characterisation of glycoproteins in the sweat of the horse (Equus caballus)

The two major polypeptides H (Mr 49,000) and L (Mr 33,000) of equine sweat have been purified by gel filtration and characterised by gel electrophoresis and compositional analysis. Both H and L are glycoproteins containing sialic acid, neutral sugars, N-acetylglucosamine and N-acetylgalactosamine, but the two polypeptides differ considerably in the extent of glycosylation. H and L also differ in amino acid composition, but both contain only low levels of sulphur containing amino acids and histidine. These glycoproteins may behave as surfactants.

Analysis of sialic acids in bovine intestinal mucins

Molecular species of sialic acids released by mild acid hydrolysis from mucins of bovine small and large intestine were characterized by two dimensional thin-layer chromatography and gas chromatography-mass spectrometry. The small and large intestinal mucins contained both N-acetyl- and N-glycolylneuraminic acid. Although O-acetylated derivatives were not detectable in the small intestinal mucin, 9-O-acetyl-N-glycolylneuraminic acid was demonstrated in the large intestinal mucin by thin-layer chromatography and its structure was confirmed by mass spectrometry. Moreover, the presence of three kinds of O-acetyl-N-acetylneuraminic acid and five kinds of O-acetyl-N-glycolylneuraminic acid in the large intestinal mucin was suggested by thin-layer chromatography and mass chromatography. The limited distribution of O-acetylated neuraminic acids suggests that their derivatives are only produced in the mucous glands of the large intestine.

Chemical and histochemical studies of normal and diseased human gastrointestinal tract. I. A comparison between histologically normal colon, colonic tumours, ulcerative colitis and diverticular disease of the colon

Chemical and histochemical methods were used to compare the epithelial glycoproteins from formalin-fixed surgical specimens of normal human large intestine, colonic tumours, ulcerative colitis and diverticular disease. All the epithelial glycoproteins contained fucose, galactose, glucosamine, galactosamine and, in addition, sialic acids both with and without O-acyl substituents in the side chain and/or at position C4. The glycoproteins of the normal ascending and descending colons differed significantly with respect to the percentage of the sialic acids released following digestion of the de-O-acylated glycoprotein with Vibrio cholera neuraminidase and to the molar fucose-sialic acid ratio. Statistical analysis of the chemical data showed that (a) compared to normal, the sialic acids of the tumour and ulcerative colitis glycoproteins from the descending colon were significantly less substituted in the side chain and at position C4; (b) the O-acetyl substitution pattern of the sialic acids of the ulcerative colitis glycoproteins from the ascending colon and the quantitative composition of the carbohydrate prosthetic groups of the ulcerative colitis glycoproteins from both ascending and descending colons differed from normal; (c) it was not always possible to distinguish between the ulcerative colitis and tumour glycoproteins on the basis of the O-acetyl substitution pattern of their sialic acids; and (d), there were minor differences between normal glycoproteins and those from cases of diverticular disease.

Chemical and histochemical studies of normal and diseased human gastrointestinal tract. II. A comparison between histologically normal small intestine and Crohn's disease of the small intestine

Comparative chemical and histochemical studies were performed on formalin-fixed, surgical specimens of human small intestine from cases of Crohn's disease and normal controls. The sialic acids of the crude glycoproteins isolated from normal ileum were significantly less neuraminidase-susceptible and more C4 substituted (P less than 0.01) than those of the glycoproteins isolated either from normal upper small intestine (duodenum and jejunum) or from cases of Crohn's disease of the ileum. Fractionation yielded two major sialic acid-containing fractions, eluting from DEAE-cellulose with 0.2 M or 0.3 M sodium chloride. Both fractions contained fucose, galactose, glucosamine and galactosamine in addition to sialic acids both with and without O-acyl substituents at position C4 and/or in the side-chain (side-chain O-acylated sialic acids were also detected by histochemical procedures). The fractions differed significantly from one another with respect to the neuraminidase susceptibility of their sialic acids (P less than 0.01), the percentage of C4 (P less than 0.01) and side-chain substituted sialic acids (P less than 0.05), and the molar fucose-sialic acid ratio (P less than 0.05). The O-acyl substitution patterns of the sialic acids of both the 0.2 M and 0.3 M fractions of the upper small intestine glycoproteins differed significantly from those of the corresponding fractions from normal ileum, while the sialic acids of the 0.2 M fractions from Crohn's disease of the ileum differed significantly from normal with respect to neuraminidase susceptibility (P less than 0.01) and percentage C4 substitution (P less than 0.01); the 0.3 M fractions differed only in the percentage of sialic acids substituted at C4. The differences between the sialic acids from the normal and Crohn's disease specimens were shown to be independent of either the anatomical origin of the specimen or the histopathological sub-group of the Crohn's disease specimens; no significant differences were noted between the sub-groups but all the sub-groups differed from normal.

Sugar constituents of the seromucoid in insulin-dependent diabetes

Seromucoid glycoproteins reveal different carbohydrate composition in diabetic patients as compared with normal subjects. An increased glucose content is the most characteristic feature of seromucoid found in diabetic patients. The amounts of proteins, neutral sugars, amino-sugars and sialic acids in seromucoid correlate with diabetic microangiopathy.

In vitro labeling of the sialic acid moiety of glycoconjugates with carbon-14

Labeling of sialoglycoproteins with carbon-14 in vitro was performed by reacting the aldehyde groups, generated by mild periodate oxidation of the terminal sialyl groups, with 14C-labeled sodium cyanide to produce the labeled cyanohydrin derivatives (Kiliani reaction). Labeling with tritium was carried out by reduction of the aldehyde groups generated on the sialyl residues with 3H-labeled sodium borohydride following standard procedures. The behavior of both types of labeled specimens of fetuin and ovine submaxillary mucin, individually and in mixtures, was investigated by gel-filtration chromatography, gel electrophoresis, and cesium bromide gradient ultracentrifugation. The labeled sialyl residues were subjected to partial characterization: color yield with the resorcinol and thiobarbituric acid reagents, behavior on ion-exchange chromatography, and susceptibility to mild acid and enzymatic hydrolyses. In addition to these model glycoproteins, this procedure was also utilized to label the sialoglycoproteins present in human tracheobronchial secretions collected from normal subjects and patients with chronic bronchitis. The potential uses of this approach for comparative studies of normal and pathological sialoglycoconjugates available in minute amounts is described. The extension of this approach to the labeling of the galactosyl and N-acetylgalactosaminyl moieties of glycoconjugates following treatment with galactose oxidase is outlined.

A clinical and histopathological study of gastric polyps in familial polyposis coli

Fundic gland area gastric polyps in familial polyposis coli (FPC) were compared with those in non-familial polyposis coli clinicopathologically to elucidate their histogenetic and biological characteristics. Some differences were observed in age, sex, and radiological and endoscopical features. Although the polyps were similar histologically, they showed an apparent histochemical difference between the two groups in periodic borohydride technique/potassium hydroxide/periodic acid-Schiff stain which demonstrates O-acylated sialic acid. The superficial and foveolar epithelium of the polyps was positive in 10 of 12 familial polyposis coli cases, while the epithelium was positive in only one of 13 non-familial polyposis coli cases with the same staining. These results suggest differences between the two groups in the degree of epithelial intestinal metaplasia. The presence of gastric polyps with O-acylated sialic acid therefore indicates the necessity of examination of the colorectum.

Genetic and molecular analyses of Escherichia coli K1 antigen genes

The plasmid pSR23, composed of a 34-kilobase E. coli chromosomal fragment inserted into the BamHI site of the pHC79 cosmid cloning vector, contains genes encoding biosynthesis of the K1 capsular polysaccharide. Deletions, subclones, and Tn5 insertion mutants were used to localize the K1 genes on pSR23. The only deletion derivative of pSR23 that retained the K1 phenotype lacked a 2.7-kilobase EcoRI fragment. Subclones containing HindIII and EcoRI fragments of pSR23 did not produce K1. Cells harboring pSR27, a subclone containing a 23-kilobase BamHI fragment, synthesized K1 that was not detectable extracellularly. Six acapsular Tn5 insertion mutants of three phenotypic classes were observed. Class I mutants synthesized K1 only when N-acetylneuraminic acid (NANA) was provided in the medium. Reduced amounts of K1 were detectable in cell extracts of class II mutants. Class III mutants did not produce detectable K1 in either extracts or when cells were provided exogenous NANA. All mutants had sialyltransferase activity. Analysis in the E. coli minicell system of proteins expressed by derivatives of pSR23 identified a minimum of 12 polypeptides, ranging in size from 18,000 to 80,000 daltons, involved in K1 biosynthesis. The 16-kilobase coding capacity required for the proteins was located in three gene clusters designated A, B, and C. We propose that the A cluster contains a NANA operon of two genes that code for proteins with apparent molecular weights of 45,000 and 50,000. The A region also includes a 2-kilobase segment involved in regulation of K1 synthesis. The B region encoding five protein species appears responsible for the translocation of the polymer from its site of synthesis on the cytoplasmic membrane to the cell surface. The C region encodes four protein species. Since the three gene clusters appear to be coordinately regulated. we propose that they constitute a kps regulon.

[Dissociation of human serum low density lipoproteins in several immunologically distinct subunits. Isolation and characterization of a B-III subunit]

Low density lipoproteins (d = 1.030-1.055) were partially delipidated with ethyl-ether (LDLe). These LDLe exhibit a spontaneous dissociation several days after delipidation. Four different immunoprecipitation complexes (B-I to B-IV) are observed when using two dimensional immunoelectrophoresis against anti LDLe immunserum. The various subunits of LDLe have different behaviour upon electrophoresis. On disc gel electrophoresis containing urea three bands can be seen; all are phospholipoproteins. The apolipoprotein moiety of LDL and LDLe have the same apparent molecular weight around 550 000. With time several subunits appear in LDLe, the majority of them have a molecular weight around 370 000, 260 000 and 125 000. One of the components from dissociated LDLe containing the immunodeterminant B-III, has been separated by chromatography on heparin-agarose. This LDLe-B-III has the same phospholipid/protein ratio as total LDLe and a protein moiety with an apparent molecular weight of 110 000. This part of apolipoprotein B has no affinity for heparin. Immunocompetition studies by the ELISA technique indicated that sialic acid, one of terminal residues of LDL glycoprotein, is involved in the immunological recognition of LDL and of its derivatives by anti LDL and anti LDLe antisera.

Alpha 1- and beta 2-adrenergic receptors co-expressed on cloned MDCK cells are distinct glycoproteins

We have explored the molecular differences between alpha 1- and beta 2-adrenergic receptors that are co-expressed by a clonally-derived cell line, Madin-Darby canine kidney clone D (MDCK-D). MDCK-D membranes were pre-labeled with selective alpha 1- and beta-adrenergic radioligands and were then solubilized with the non-ionic detergent digitonin. Solubilized alpha 1- and beta 2-adrenergic receptors were retained by immobilized wheat germ agglutinin and were eluted following addition of N-acetyl-D-glucosamine or sialic acid. Both receptors were also retained by immobilized Limax flavus lectin, a sialic acid-binding lectin. Lectins that were specific for N-acetyl-D-glucosamine residues did not bind to these receptors. These results indicate that both alpha 1 and beta 2 receptors are sialylated glycoproteins. The solubilized alpha 1- and beta 2-adrenergic receptors migrated with different elution profiles from an Ultragel AcA 34 column. The apparent molecular sizes of the digitonin-receptor complexes were 68A for the alpha 1 receptor and 55A for the beta 2 receptor. These results show that alpha 1- and beta 2-adrenergic receptors can be present on the same cell as distinct sialic acid-containing glycoproteins.

Structure analysis of glycosphingolipids using fast atom bombardment (FAB) techniques

The results presented show, that with the aid of negative ion FAB MS native glycosphingolipids and especially gangliosides are amenable to sequence analysis. The preferred formation of pseudomolecular ions M-1 and of sialic acid containing fragments gives conclusive information on the number of sialic acids present and the sites of their attachment to the oligosaccharide backbone. Positive ion FAB MS of branched permethylated glycosphingolipids with up to 25 sugar units yielded pseudomolecular ions [M+Na]+ in excess of 6000 daltons, that allowed an exact calculation of carbohydrate constituents. Furthermore highly (Formula: see text) specific fragmentation patterns furnished information on number and positions of branching points as well as on the ceramide moiety. It can be anticipated, that FAB MS will be very useful in the analysis of more complex gangliosides carrying additional fucose or acyl residues and of even larger molecules with molecular weights up to 15,000 daltons.

Sulfur dioxide-induced chronic bronchitis in beagle dogs

This study was done to produce a model of chronic bronchitis. Twelve beagle dogs were exposed to 500 ppm sulfur dioxide (SO2) for 2 h/d, 5 d/wk for 21 wk and 4 dogs were sham-exposed to filtered ambient air for the same period. Exposure effects were evaluated by periodically examining the dogs using chest radiographs, pulmonary function, tracheal mucous clearance; and the cellular and soluble components of bronchopulmonary lavage fluids. Dogs were serially sacrificed after 13 and 21 wk of exposure and after 6 and 14 wk of recovery. Clinical signs produced in the SO2-exposed dogs included mucoid nasal discharge, productive cough, moist rales on auscultation, tonsilitis, and conjunctivitis. Chest radiographs revealed mild peribronchiolar thickening. Histopathology, tracheal mucous clearance measurements, and lavage cytology were consistent with a diagnosis of chronic bronchitis. It is concluded that repeated exposure to 500 ppm SO2 for 21 wk produced chronic bronchitis in the beagle dog. Complete recovery occurred within 5 wk following cessation of SO2 exposure.

Erythrocyte membrane sialic acid in new-born infants

Erythrocyte surface sialic acid was measured in 94 full-term new-born infants and in 20 premature infants of different ages, varying from 1 to 16 post-natal days. After the first 3 days of life, the amount of sialic acid, both per cell and per gramme of haemoglobin, was rapidly reduced to 70-80% of the initial value; these lower levels were maintained on the following days. The decrease observed on the 4th day may represent an expression of the mechanism by which a large amount of fetal red blood cells is eliminated from the circulation during the same period. Therefore, the relationship between sialic acid decrement and red cell sequestration exists also in fetal erythrocytes, and this may contribute to clarify the exact role of sialic acid in red cell survival time.

Identification of a sialic acid containing glycocalyx on the surface of Schistosoma mansoni

Ruthenium red fixation of adult Schistosoma mansoni revealed the existence of a negatively charged layer external to the outer bilayer, which was morphologically similar to the glycocalyx of other cell types. Regional and sexual differences were found in the extent and organisation of the surface coat, which can be correlated with interfacial free energy, adhesiveness and protection from immune effectors. Neuraminidase treatment confirmed the presence of surface sialic acid. Mechanical or skin penetrated schistosomula, maintained in vitro for 24 h were found not to have a glycocalyx and this may relate to their increased susceptibility to immune killing. Lung stage schistosomula however, did bind ruthenium red to their surface.

Studies on Perivitelline Fluid of Horseshoe Crab Embryo. II. Purification of Agglutinin-Binding Substance from the Perivitelline Fluid of Tachypleus gigas Embryo12

Three glycoproteins with potent agglutinin-binding activity have been isolated from the perivitelline fluid of Tachypleus gigas, horseshoe crab, embryo. In the native form, these agglutinin-binding substances were highly aggregated. After being dissociated in 10 M urea, these proteins were fractionated by gel-filtration on a Fractogel TSK (Toyopearl) HW-60 in Tris-NaCl-CaCl2 (0.05 M Tris-HCl, pH 7.5, containing 0.5 M NaCl and 0.1 M CaCl2) containing 10 M urea. The proteins thus obtained were designated as ABS-I, -II, and -III in the order of elution and have apparent molecular weights of 25,000 (ABS-II) and 10,000 (ABS-III) as judged by both gel-filtration on Fractogel TSK (Toyopearl) HW-60 in 10 M urea and sodium dodecyl sulfate-gel electrophoresis; the molecular weight of ABS-I could not be estimated in the two systems since it was too high. ABS-I, -II, and -III, of which only ABS-I is water-soluble, inhibit one hemagglutination unit of activity with minimum quantities of 0.5 micrograms/ml, 7.8 micrograms/ml, and 1.0 micrograms/ml, respectively. They were found to be glycoproteins in which 6.6% of the dry weight (ABS-I), 4.2% of the dry weight (ABS-II), and 7.5% of the dry weight (ABS-III) were carbohydrate. The dry weight ratio of hexosamines in these substances is 3:1:2 (ABS-I: ABS-II: ABS-III), and that of sialic acid is also 3:1:2. Amino acid analyses of these proteins indicated that they have high contents of aspartic acid, glutamic acid, and glycine in common.

Diurnal variation of sialomucin concentration in female mouse submandibular glands measured by radioimmunoassay

The validity of a radioimmunoassay (RIA) for the predominant sialomucin from female mouse submandibular glands was confirmed by immunological and non-immunological approaches. The maximum sensitivity was in the low nanogramme range. The RIA did not cross-react with parotid, sublingual, trachea, stomach or colon tissues, but showed incomplete cross-reactivity with duodenal tissue. An analysis of protein, sialic acid and mucin contents of submandibular glands obtained during diurnal samplings, indicated that mean sialic acid and mucin concentrations, relative to protein in sample groups, decreased overnight approx. 30 per cent and showed a net increase during the day. Sialic acid per gland showed a 3-fold variation among individuals in the population; mucin showed greater than 20-fold variation. An analysis of variation indicated that influence by time of day was the greatest factor affecting sialic-acid concentrations and was statistically significant but, variation in mucin concentration was not. Variation between individuals accounted for more than 90 per cent of the total population variation in mucin concentrations and in sialic acid to mucin ratios. Regression analyses of the sialic acid to mucin ratios at different times of day suggested that the rates of replenishment of sialic acid and mucin may be co-ordinated.

Effects of fasting on mucus glycoprotein in rat stomach

Quantitative changes and chemical composition of gastric mucus glycoproteins in rats after fasting for 24 and 72 hr were studied. The amount of glycoproteins increased in the corpus mucosa during these periods (220% in control for 72 hr), but remained the same in the antrum. The acidity of corpus glycoproteins decreased during the fasting.

Characterization of low- and high-metastatic clones isolated from a Lewis lung carcinoma

Cloned cell lines with low and high metastatic potentials were established from a Lewis lung carcinoma. Those with a high metastatic potential, LM12 -3-II cells, grew slower than those with a low potential, P-29 cells, both in vivo and in vitro. No significant difference between these cell lines was found in their susceptibility to natural killer cell-mediated lysis in vitro. Both LM12 -3-II and P-29 cells showed poor organization of microfilament bundles containing actin. LM-12-3-II cells showed lower cloning efficiency in semisolid 0.3% and 0.6% agar medium, lower lysosomal enzyme activities and lower homotypic aggregation than P-29 cells. LM12 -3-II cells adhered to monolayers of endothelial cells more slowly than P-29 cells, although they adhered to a subendothelial matrix a little more rapidly than P-29 cells. On the other hand, LM12 -3-II cells adhered to the surface of plastic culture dishes more firmly than P-29 cells. The neuraminidase-accessible sialic acid of LM12 -3-II cells was less than that of P-29 cells. Thus, the firmness of adhesion was positively correlated with the metastatic potential in these cells.

New techniques for the investigation of structure and metabolism of sialic acids

Sialic acid analysis in biological material including gangliosides is often confronted with the necessity to determine trace amounts of various N,O-substituted species. Therefore, techniques of high sensitivity and resolution are required, such as capillary gas-liquid chromatography (GLC) and high performance liquid chromatography (HPLC). Both methods in combination with mass spectrometry allow structural analysis of the different neuraminic acid derivatives. Thus, the number of natural sialic acids known so far has increased to more than 30, including non only saturated, but also 2,3-unsaturated and 2,7-anhydro-sialic acids. Furthermore, HPLC has proved to be especially useful for the study of enzyme reactions, as the sialic acids of enzyme assay mixtures in most cases can be analyzed without prior extensive purification or derivatization.

Canine GM2-gangliosidosis: chemical and enzymatic features

The chemical and enzymatic features in tissues of GM2-gangliosidosis are characterized by the analysis of glycolipids and FD-MS, and also by enzymatic analysis with DEAE-Sepharose column chromatography. The results suggest that canine GM2-gangliosidosis is equivalent to human juvenile GM2-gangliosidosis.