A mouse submandibular sialomucin containing both N- and O-glycosylic linkages

Isolation, structures and biological activities of medicinal glycoproteins from natural resources: A review

In recent years, natural resources have proven to be tremendous sources of glycoproteins. As biological macromolecules, glycoproteins are essential to the growth and development of organisms, and have attracted increasing attention around the world. This review summarized and discussed the development of glycoproteins from natural resources, including isolation methods, purification processes, structural features and biological activities. Generally, the vast majority of glycoproteins can be isolated by hot water extraction followed by purification through gel filtration chromatography. Combined with component analysis, the physicochemical properties of glycoproteins are studied by using several spectroscopic techniques such as ultraviolet-visible (UV-Visible), Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR). Moreover, natural glycoproteins possess various remarkable biological activities, including anti-tumor, anti-oxidant, anti-coagulant and anti-microbial activities. The content of this review will provide a theoretical basis for the research on related glycoproteins and give a perspective on the use of these medical resources.

Glycomic mapping of O- and N-linked glycans from major rat sublingual mucin

Carbohydrate moieties of salivary mucins play various roles in life processes, especially as a microbial trapping agent. While structural details of the salivary O-glycans from several mammalian sources are well studied, very little information is currently available for the corresponding N-glycans. The existence of N-glycans alongside O-glycans on mucin isolated from rat sublingual gland has previously been implicated by total glycosyl compositional analysis but the respective structural data are both lacking. The advent of facile glycomic mapping and sequencing methods by mass spectrometry (MS) has enabled a structural reinvestigation into many previously unsolved issues. For the first time, high energy collision induced dissociation (CID) MALDI-MS/MS as implemented on a TOF/TOF instrument was applied to permethyl derivatives of mucin type O-glycans and N-glycans, from which the linkage specific fragmentation pattern could be established. The predominant O-glycans carried on the rat sublingual mucin were defined as sialylated core 3 and 4 types whereas the N-glycans were determined to be non-bisected hybrid types similarly carrying a sialylated type II chain. The masking effect of terminal sialylation on the tight binding of rat sublingual mucin to Galbeta1-->4GlcNAc specific lectins and three oligomannose specific lectins were clearly demonstrated in this study.

Low-molecular-mass human salivary mucin, MG2: structure and binding of Pseudomonas aeruginosa

Low-molecular-mass human salivary mucin, MG2, was isolated from human submandibular-sublingual saliva (HSMSL) employing citraconylation, gel filtration, and ion-exchange chromatography. Following proteolysis with trypsin, two glycopeptides were purified. The higher molecular weight glycopeptide was highly glycosylated with O-linked units. The lower molecular weight glycopeptide was less glycosylated and contained most of the N-linked units. Interaction between components of HSMSL and pili of Pseudomonas aeruginosa was examined by an overlay binding assay. Pili were found to bind to MG2. Preliminary studies indicated that the binding may involve a protein to protein interaction.

Glycoconjugate composition of mammalian parotid glands elucidated in situ by lectins and glycosidases

Sugar specific lectins (PNA, RCA I, LPA, SBA, DBA, GSA IB4, GSA II, WGA, LTA, UEA I, Con A, LCA) with and without prior selective glycosidase digestion (sialidase, alpha-fucosidase, alpha-mannosidase, beta-N-acetylglucosaminidase, alpha- and beta-galactosidase, beta-glucosidase) were used in order to investigate the distribution of native accessible carbohydrates and obtain information dealing with the composition of terminal disaccharides within glycoconjugates present in acinar compartments and ductal segments of mammalian (mouse, rat, hare, and rabbit) parotid glands. Glycoconjugates containing variable amounts of mannose, glucose, N-acetylgalactosamine and N-acetylglucosamine were present in the parotid glands of all species. However, these carbohydrate chains exhibited a different composition of terminal sequences within each type of gland. For example, sialylated components having the terminal dimers sialic acid-galactose and sialic acid-N-acetylgalactosamine were found in all acinar cells, whereas fucoglycoconjugates with terminal disaccharide fucose-galactose were localized in the rat striated ducts and hare acinar cells. The terminal sequence alpha-galactose-beta-galactose was demonstrated in the mouse acinar cells. Finally, glycoconjugates characterized by the terminal dimer beta-galactose-N-acetylgalactosamine were demonstrated in the mouse acinar and ductal cells and the rat ductal ones. Thus, present findings outlined and further confirmed the possibility to elucidate the oligosaccharide structure in situ using lectin histochemistry combined with enzymatic degradation.

Comparative analysis of lysosomal hydrolases and natural glycoprotein substrates in the rat major salivary glands

1. The activities of some lysosomal hydrolases and the concentrations of their natural substrates were studied in the submandibular and sublingual glands of male and female rats using biochemical procedures. 2. In sublingual gland enzyme activities and substrate concentrations show the highest values. 3. The enzyme activities appear, in general, lower and the natural substrate concentrations higher in the females with respect to males. 4. In both glands beta-galactosidase shows the highest activity and beta-glucosidase the lowest. 5. These findings suggest that metabolic turnover of glycoproteins is slower in females than in males, probably because the oestrogens control the activity of lysosomal hydrolases.

The effect of ageing on mucin contents in mouse submandibular glands

There may be deleterious effects if there is an age-dependent reduction in mucin composition or content in salivary glands. To assess whether there was an effect of age in submandibular glands from male mice aged 3 months, 10 and 20 months and 27, 29 and 30 months, mucin, protein and sialic acid were quantitated. Changes in wet weight per gland and protein per gland were highly significant (p less than 0.001), as tested by analysis of variance, and the means for both were highest in middle aged glands. While sialic acid per gland showed no significant change from middle aged to old glands, mucin per gland showed an age-related decrease (p less than 0.01) when comparing either young or middle aged glands with old glands.

Purification and characterization of subunits of a high molecular weight human salivary mucin

A high molecular-weight mucin was purified from human submandibular-sublingual saliva. The purity of the mucin preparation was demonstrated by the absence of other salivary proteins, by antibody reactivity and by gel electrophoresis. After reduction with mercaptoethanol a putative link component with approximate Mr 150,000 and a glycoprotein component of higher Mr could be detected by gel electrophoresis. These subunits were subsequently purified and they showed distinct differences in their amino acid compositions, demonstrating that the mucin consisted of two different subunits. The link had a number of similarities with the link component of intestinal mucin and a parotid agglutinin and has previously been shown to cross-react with antiserum to link component from intestinal mucin. Salivary and intestinal mucins may therefore have similar subunit structure.

Studies on the isolation and composition of human ocular mucin

A method for the isolation and purification of human ocular mucin from the brief saline extract of human ocular mucus is reported. Initial purification of ocular mucin was achieved by sequential chromatography of the saline-soluble mucus extract from an individual donor's mucus pool on columns of Sephadex G-50 and Sepharose CL-4B. A portion of such mucin isolate was subjected to quantitative analysis of the O-seryl (threonyl)-N-acetylgalactosaminyl linkage, characteristic of mucins, by alkaline beta-elimination and tritiated borohydride reduction. Following Bio-Gel P-2 filtration, the mucin isolate whose cleaved oligosaccharides contained tritiated galactosaminitol greater than 0.5 microCi mg-1, a value that represents at least 64% of that observed for bovine and ovine submaxillary reference mucins, was considered to be mucin-rich. These isolates were subjected to further purification on Sephacryl S-500 and DEAE-Trisacryl M column chromatographies. The purified mucin had a minimum molecular weight of 120 kDa. It consisted of 25-30% protein and 54-55% carbohydrate. Its amino acid and carbohydrate compositions are characteristic of a mucin structure. The purity of the mucin was verified by SDS-gradient PAGE. Upon isoelectric focusing, polydispersity/microheterogeneity were exhibited in the pI range 5.0-6.6.

Biochemistry and lectin binding properties of mammalian salivary mucous glycoproteins

The molecules responsible for the highly viscous properties of mucus are secretory glycoproteins referred to as mucins. Salivary mucins are characterized by a high sugar to protein ratio and are of a broad range of molecular weight from 7 x 10(4) to millions. With a few exceptions, they contain up to 30% of hexosamine (galactosamine and glucosamine), 8-33% of sialic acid, trace to 15% of galactose or fucose and little or no mannose. The size of carbohydrate side chains of these glycoproteins ranges from one to about fifteen units of sugar. These carbohydrate side chains are usually O-glycosidically linked through N-acetylgalactosamine to a peptidyl serine or threonine. In some instances, ester sulfate groups, mainly on N-acetylglucosamine, are also a structural feature. In many of these glycoproteins, the saccharide sequence is the same as that which determines the specificity of blood groups. Carbohydrate sequence analysis shows that salivary mucins exhibit considerable polydispersity, great diversity and remarkable structural flexibility not only among animal species but also within the same mucin molecule. Based on their lectin-binding ability, they can be used for purification of lectins, and lectins coupled to resin may be useful for the isolation of mucin-type glycoproteins. The epithelial mucous secretions modulate oral microbial flora; many secretory components serve as lectin-receptors for the attachment of microbes. The judicious use of lectins with widely differing binding characteristics has already been valuable in the in situ localization of salivary glycoproteins, in elucidating structural details, recording sugar density within a given tissue section, and defining host-parasite interactions. It is hoped that their use, together with monoclonal antibody (158) and tissue culture techniques (159, 160) will further clarify the roles of individual secretory mucous glycoproteins in health and disease.

Primary structure of O- and N-glycosylic carbohydrate chains derived from murine submandibular mucin (MSM)

The carbohydrate moiety of mouse submandibular mucin (MSM) contains mainly D-mannose and 2-acetamido-2-deoxy-D-glucose together with sialic acid, D-galactose, and 2-acetamido-2-deoxy-D-galactose. O-Glycosylically bound saccharides, obtained by treatment of MSM with alkaline borohydride, were shown by methylation analysis to have the structure: alpha-NeuAc-(2----3)-beta-Gal-(1----3)-GalNAc-ol. N-Glycosylically bound saccharides obtained from MSM by hydrazinolysis, and analysed by 500-MHz 1H-n.m.r. spectroscopy, were shown to have the following comprehensive structures. (Formula: see text).

Simultaneous determination of N-acetylglucosamine, N-acetylgalactosamine, N-acetylglucosaminitol and N-acetylgalactosaminitol by gas-liquid chromatography

A gas-liquid chromatographic procedure is described which will concomitantly separate and quantitate N-acetylglucosamine, N-acetylgalactosamine, N-acetylglucosaminitol and N-acetylgalactosaminitol in a single analytical run. The hexosamines, as their O-methyloximes, and the hexosaminitols can be separated as either their per-O-acetylated or per-O-trimethylsilylated derivatives. This method is particularly useful with samples that possess both N-acetylhexosaminitols and N-acetylhexosamines as are seen with N-linked oligosaccharides that are cleaved from glycoproteins by alkaline borohydride treatment. This procedure demonstrates a range of acceptable linearity of 1-1000 nmoles for each type of amino sugar.

Isolation and characterization of a mucin-glycoprotein from rat submandibular glands

A blood group A+ mucin-glycoprotein was purified from aqueous extracts of rat submandibular glands by sequential chromatography on columns of Sepharose CL-6B and Sephacryl S-300 in urea-containing buffers. Final purification was facilitated by reductive methylation which appeared to release contaminating (hydrophobic) peptides. Homogeneity of the purified mucin was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis at varying concentrations of acrylamide, lectin affinity chromatography, and Western blot analysis. In contrast to previously described preparations, the purified mucin contained only trace amounts of N-acetylglucosamine and aromatic amino acids. In addition, only low levels of basic amino acids were present.

Ca 125 and Ca 19-9: two cancer-associated sialylsaccharide antigens on a mucus glycoprotein from human milk

The cancer-associated antigens Ca 125 and Ca 19-9 were demonstrated by radioimmunoassay to form structural units of a mucus glycoprotein in human milk taken from healthy women four days after parturition. The glycoprotein precipitated with the casein fraction at pH 4.6 and was completely absent in the whey as judged from Ca 19-9 assay. It could be effectively enriched by phenol-saline extraction from soluble milk proteins and further purified by gel filtration on Sephacryl S300 and Sephacryl S400. The active component with a bouyant density of 1.41 g/ml in isopycnic density gradient centrifugation (CsCl) shared common physico-chemical and chemical characteristics of mucus glycoproteins. Carbohydrates representing about 68% by weight were conjugated to protein by alkali-labile linkages, exclusively and were essentially free of D-mannose. Activities of Ca 125 and Ca 19-9 were both destroyed by treatment with periodate, mild alkali or neuraminidase suggesting the antigens are sialylated saccharides bound to protein by alkali-labile linkages. The fraction of monosialylated saccharide alditols isolated after reductive beta-elimination from the mucus glycoprotein was shown to inhibit monoclonal antibodies anti-(Ca 125) and anti-(Ca 19-9) in radioimmunoassay.

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.

Specificity of submaxillary gland sialyltransferases

A method has been developed to determine the activities of specific sialyltransferases by analysis of the products of the reaction. This method, which utilizes high performance liquid chromatography, distinguishes addition of sialic acid to the N-acetylgalactosamine vs. galactose residues of the mucin disaccharide Gal beta(1 leads to 3)GalNac, and can be used to distinguish formation of the 3'- and 6'-isomers of sialyllactose. For the bovine, ovine, and porcine submaxillary extracts, more than 95% of the activity with asialo ovine submaxillary mucin is due to formation of NeuAc alpha(2 leads to 6)GalNAc. With lactose as the acceptor, more than 95% of the alpha(2 leads to 3) isomer is produced. Activity with asialofetuin is due solely to the O-linked chain, with relative activity toward the galactose vs. GalNAc residues of 0.32, 1.5, and 0.10 for bovine, ovine, and porcine, respectively. The rat submaxillary gland extract showed equal formation of 3'- and 6'-sialyllactose, and very low activity with asialo ovine submaxillary mucin. However, at least 40% of the activity toward the Gal beta(1 leads to 3)GalNAc disaccharide of asialofetuin was directed toward the GalNAc residue. The relative preference of the N-acetylgalactosaminide alpha(2 leads to 6) sialyltransferase for a monosaccharide vs. a substituted GalNAc may play a role in regulation of chain length during mucin synthesis.