Isolation and structural characterization of alkali-labile oligosaccharides from bovine milk-fat-globule membrane

N- and o-glycosylation of a commercial bovine whey protein product

Bovine whey protein products are used as a base ingredient in infant formulas to optimize the amino acid pattern to a more human-like composition. Although the protein composition of bovine milk has been studied in detail, glycosylation details of commercial whey protein products are missing. To this end, both the N- and O-glycans of such a protein concentrate were sequentially released, the N-glycans enzymatically and the O-glycans chemically (reducing and nonreducing conditions). For the structural analysis of the N- and O-glycans a combination of MALDI-TOF-MS, one-dimensional (1)H NMR spectroscopy, Wisteria floribunda agglutinin affinity chromatography, HPAEC-PAD profiling, and HPLC-FD profiling (2-aminobenzamide derivatives), together with exoglycosidase treatments, were used. A mixture of over 60 N-glycans and 10 O-glycans was characterized, giving a detailed insight into the glycosylation of a bovine whey protein product, Deminal 90, which is applied as an ingredient for infant formulas.

A new hexasaccharide chain isolated from bovine colostrum kappa-casein taken at the time of parturition

The carbohydrate units linked to caseinoglycopeptide from colostrum taken 30 min after parturition were released as reduced oligosaccharides by alkaline borohydride treatment, and separated into four acidic oligosacchariditols (a hexa- (11.0%), penta- (38.5%), tetra- (35.5%) and a trisacchariditol (15.0%)). Structural studies showed that the hexasacchariditol was a new structure and had the chemical structure: NeuNAc-alpha-2-3-Gal-beta-1-3-[NeuNAc-alpha-2-3-Gal- beta-1-4-GlcNAc-beta-1-6-]-N-acetylgalactosaminitol(GalNAcItol). The other three oligosacchariditols were shown to be NeuNAc-alpha-2-3-Gal-beta-1-3-[Gal-beta-1-4-GlcNAc-beta-1-6-]-GalNAcItol, NeuNAc-alpha-2-3-Gal-beta-1-3-[NeuNAc-alpha-2-6-]-GalNAcItol and NeuNAc-alpha-2-3-Gal-beta-1-3-GalNAcItol, which were identical with those found previously in colostrum kappa-casein taken 6 h after parturition.

Isolation and characterization of two individual glycoprotein components from human milk-fat-globule membranes

Two individual glycoprotein components from human milk-fat-globule membranes (MFGM) has been purified by selectively extracting the membrane glycoproteins followed by lectin affinity chromatography and gel filtration on Sephadex G-200 in the presence of protein-disaggregating agents. The purified glycoprotein components, termed 'epithelial-membrane glycoprotein' (EMGP-155 and EMGP-39) have estimated molecular weights of 155 000 and 39 000 respectively, and yield a single band under reducing conditions on sodium dodecyl sulphate/polyacrylamide gel. EMGP-155 and EMGP-39 contain 21.0% and 7.0% carbohydrate by weight, with fucose (13.5%, 12.4%), mannose (3.7%, 6.2%), galactose (28.5%, 22.6%), N-acetylglucosamine (17.8%, 7.4%) and sialic acid (36.4%, 51.4%) of the carbohydrate moiety respectively. For both the glycoprotein components, aspartic and glutamic acid and serine are the major amino acid residues.

Isolation and characterization of the major oligosaccharide of human platelet membrane glycoprotein GPIb

Treatment of intact human platelets with chymotrypsin released a glycopolypeptide that was shown to be derived from the major membrane glycoprotein, GPIb. The glycopolypeptide contained 59% carbohydrate on a molar basis and was rich in serine, threonine and proline. Almost all the carbohydrate could be released from the glycopolypeptide by treatment with alkali in the presence of NaBH4. The major component (comprising 80% of the released sugar) was purified and shown to be a hexasaccharide containing sialic acid, galactose, N-acetylglucosamine and N-acetylgalactosaminitol in the molar ratios 2:2:1:1. Two possible structures for this hexasaccharide are proposed on the basis of the known biosynthetic pathways of mucus-type glycoproteins. Our data is consistent with the occurrence of an O-glycosidically linked oligosaccharide on one amino acid in four of the glycopolypeptide. These results suggest that glycoprotein Ib can best be described as a membrane-bound mucus-type glycoproteins. Our data are consistent with the occurrence of an O- in the process by which platelets adhere to the exposed subendothelium of damaged blood-vessel walls. The possible role of the glycopolypeptide portion of GPIb in this process was investigated. Neither the major oligosaccharide nor the glycopolypeptide itself inhibited ristocetin-induced platelet agglutination at the concentrations tested. It is suggested that the carbohydrate moieties of GPIb molecules at the cell surface interact to form a barrier to macromolecules. Such a barrier could play a major role in modulating platelet function.

Immunochemical studies of infectious mononucleosis--X. Characterization of a glycoprotein from horse erythrocytes which reacts with Paul-Bunnell antibody

A highly purified preparation of horse erythrocyte glycoprotein was prepared from an aqueous ethanolic extract of hemoglobin-free membranes. The subunit apparent mol. wt was 30,000. In aqueous solution the glycoprotein formed globular aggregates of 93 +/- 16 A diameter. The glycoprotein had a receptor for the Paul-Bunnell antibody of infectious mononucleosis which was associated with an O-glycosidically linked oligosaccharide and dependent on the presence of N-glycolylneuraminic acid. In addition the glycoprotein had a neuraminidase-sensitive receptor for human peripheral blood lymphocytes. Fifty per cent inhibition of the rosetting of sheep red cells by 4 x 10(5) lymphocytes was caused by 30 microgram of glycoprotein.

The chemical structure of a tetrasaccharide containing N-acetylglucosamine obtained from bovine colostrum kappa-casein

A tetrasaccharide consisting of D-galactose, N-acetylneuraminic acid, N-acetylglucosamine and N-acetylgalactosaminitol (1 : 1 : 1: 1) was obtained from bovine colostrum kappa-casein. It is the main carbohydrate portion of a caseinoglycopeptide formed by alkaline borohydride treatment. The carbohydrate sequence was analyzed by enzymatic and chemical methods and by mass spectrometry, and was shown to be N-acetylglucosaminyl-beta-1-3-galactosyl-beta-1-3[N-acetylneuraminyl-alpha-2-6- ]-N-acetylgalactosaminitol.

Isolation and characterization of a major glycoprotein from milk-fat-globule membrane of human breast milk

A major periodate--Schiff-positive component from milk-fat-globule membrane of human breast milk has been purified by selectively extracting the membrane glycoproteins, followed by lectin affinity chromatography and gel filtration on Sephadex G-200 in the presence of protein-dissociating agents. The purified glycoprotein, termed epithelial membrane glycoprotein (EMGP-70), has an estimated mol.wt. of 70 000 and yields a single band under reducing conditions on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. The glycoprotein contains 13.5% carbohydrate by weight, with fucose, mannose, galactose, N-acetylglucosamine and sialic acid 17.2, 17.0, 21.1, 7.9 and 36.6% respectively of the carbohydrate moiety. Aspartic and glutamic acid and serine are the major amino acid residues.

Comparison of isolated peanut agglutinin receptor glycoproteins from human, bovine and porcine erythrocyte membranes

Affinity chromtography has been used to isolate and compare the peanut agglutinin receptors from neuraminidase-treated human, bovine and porcine erythrocyte membranes. Passage of Triton X-100-solubilised membrane material through either Sepharose- or acrylamide-based affinity columns resulted in the reversible binding of receptor molecules to the immobilised lectin. Elution with 0.2 M galactose released specifically bound glycoprotein fractions, the composition and molecular weights of which were determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. Carbohydrate analysis by gas chromatography identified these bound glycoprotein fractions as the major sources of the O-glycosidic-linked disaccharide galactosyl-beta-(1 leads to 3)-N-acetylgalactosamine in these membranes. It is suggested that these isolated fractions represent a discrete population of glycoproteins within the membranes studied, which possess both O-glycosidic- and N-glycosidic-linked carbohydrates.

The carbohydrate portions of milk glycoproteins

kappa-Casein is the main glycoprotein of cow's milk. Its polysaccharide part is O-glycosidically linked to threonine residue 133. It contains only 3 different sugars (Gal, GalNAc, NeuNAc), but a microheterogeneity has been detected at the sugar level. Two main polysaccharides have so far been characterized. The structure of the trisaccharide is NeuNAc alpha 2 leads to 3 Gal beta 1 leads to GalNAc; the tetrasaccharide contains one additional sialic acid. The polysaccharide part of ovine kappa-casein resembles that of bovine kappa-casein, but contains also N-glycolyl neuraminic acid. Human kappa-casein contains 3 times more carbohydrate than bovine kappa-casein with 2 additional sugars, GlcNAc and Fuc. The various polysaccharide parts isolated from bovine colostrum kappa-caseinoglycopeptide are much more complex than those obtained from the normal glycopeptide, indicating an evolution of the sugar part as a function of time after parturition. Some aspects of the secondary structure of kappa-casein and the role of the sugar part are discussed. The carbohydrate moiety of another milk protein, human lactotransferrin, is also discussed briefly. it is comprised of 2 identical glycan groups, N-glycosidically linked to the protein, and quite different from the kappa-casein carbohydrate moiety.