Biosynthesis of lipid-linked oligosaccharides. Isolation and structure of a second lipid-linked oligosaccharide in Chinese hamster ovary cells

Previous work has shown that vesicular stomatitis virus-infected Chinese hamster ovary cells contain a major high molecular weight lipid-linked oligosaccharide which is transferred en bloc to protein during the formation of the asparagine-linked complex-type oligosaccharides of the vesicular stomatitis virus G protein (Tabas, I., Schlesinger, S., and Kornfeld, S. (1978) J. Biol. Chem. 253, 716-722). We now report the characterization of a second, lower molecular weight lipid-linked oligosaccharide. The oligosaccharide portion of this molecule was isolated and its structure was determined by methylation analysis, digestion with exoglycosidases, acetolysis and Smith periodate degradation to be: (formula: see text). Several lines of evidence are presented which indicate that this lipid-linked oligosaccharide is primarily involved in the assembly of the major lipid-linked oligosaccharide rather than in the direct glycosylation of proteins.

Structural studies of the major high mannose oligosaccharide units from Chinese hamster ovary cell glycoproteins

The major high mannose-type glycopeptides present in Chinese hamster ovary cells have the compositions (Man)9(GlcNAc)2-Asn, (Man)8(GlcNAc)2-Asn, and (Man)6(GlcNAc)2-Asn. The structures of these glycopeptides were determined by the combination of methylation analysis, acetolysis, Smith periodate degradation, and alpha- and beta-mannosidase digestion. Their complete structures are: manalpha1 leads to 2Manaalpha1 leads to 6(Manalpha1 leads to 2Manalpha1 leads to 3)Manalpha1 leads to 6(Manalpha1 leads to 2Manalpha1 leads to 2Manalpha1 leads to 3)Manbeta1 leads to 4GlcNAcbeta1 leads to 4GlcNAc-Asn, Manalpha1 leads to 2Manalpha1 leads to 6(Manalpha1 leads to 3)Manalpha1 leads to 6(Manalpha1 leads to 2Manalpha1 leads to 2Manalpha1 leads to 3)Manbeta1 leads to 4GlcNAcbeta1 leads to 4GlcNAc-Asn, and Manalpha1 leads to 6(Manalpha1 leads to 3)Manalpha1 leads to 6(Manalpha1 leads to 2Manalpha1 leads to 3)Manbeta1 leads to 4GlcNAcbeta1 leads to 4GlcNAc-Asn. These structures are compared with the structures of the peptide-bound oligosaccharide intermediates that are processed to form complex-type oligosaccharides. From these results, it is proposed that the high mannose-type oligosaccharides are a product of "incomplete" processing of the protein-bound oligosaccharide along the same pathway which leads ultimately to the formation of a complex-type oligosaccharide.

The synthesis of complex-type oligosaccharides. I. Structure of the lipid-linked oligosaccharide precursor of the complex-type oligosaccharides of the vesicular stomatitis virus G protein

The synthesis of the complex-type oligosaccharide unit of the vesicular stomatitis virus G protein is initiated by the en bloc transfer of a high molecular weight oligosaccharide from a lipid carrier to the nascent polypeptide. Following transfer the oligosaccharide is "processed" by removal of glucose and mannose residues and the sugars that constitute the outer branches of the complex-type oligosaccharide are added. The structure of the oligosaccharide moiety of the lipid-linked precursor has been elucidated in order to further define the steps involved in processing. Since it was not feasible to obtain adequate amounts of material for standard structural studies, most of the structural studies were performed on radiolabeled material, with radioactivity incorporated differentially into glucose, mannose, and N-acetylglucosamine. Based on endo-beta-N-acetylglucosaminidase CII digestion, alpha-mannosidase digestion, acetolysis, Smith periodate degradation, methylation analysis, and periodate oxidation, we propose the following structure for the oligosaccharide moiety of the lipid-linked oligosaccharide.

Structure of the altered oligosaccharide present in glycoproteins from a clone of Chinese hamster ovary cells deficient in N-acetylglucosaminyltransferase activity

Clone 15B cells, derived from Chinese hamster ovary cells and deficient in a specific UDP-N-acetylglucosamine:glycoprotein N-acetylglucosaminyltransferase activity, synthesize glycoproteins with altered oligosaccharide units. Glycopeptides prepared from these glycoproteins contain large quantities of a glycopeptide with the composition (Man)5(GlcNAc)2-Asn whereas parent cells have only small amounts of this glycopeptide. The structure of the glycopeptide was determined by the combination of methylation analysis, acetolysis, Smith periodate degradation, and alpha- and beta-mannosidase digestion. Its complete structure is Manalpha 1 leads to 6[Manalpha1 leads to 3]-Manalpha1 leads to 6[Manalpha 1 leads to 3]-Manbeta1 leads to 4 GlcNAcbeta1 leads to 4 GlcNAc leads to Asn-peptide. The structures of two other glycopeptides found in smaller quantities in clone 15B but not detected in the parent cells were determined and are Manalpha 1 leads to 6 [Manalpha 1 leads to 3]-Manalpha1 leads to 6Manbeta 1 leads to 4 GlcNAcbeta 1 leads to 4GlcNAc-Asn-peptide and Manalpha 1 leads to 3 Manalpha 1 leads to 6[Manalpha 1 leads to 3] Manbeta 1 leads to 4GlcNAcbeta 1 leads to 4GlcNAc-Asn-peptide. It is proposed that the (Man)5(GlcNAc)2-Asn unit is the physiologic acceptor for the particular N-acetylglucosaminyltransferase which is deficient in clone 15B cells and that this reaction is necessary for complex oligosacchari-e biosynthesis.

Effects of wheat germ agglutinin on membrane transport

(1) Low concentrations of wheat germ agglutinin are cytotoxic toward several tissue culture lines, including Chinese hamster ovary cells, Swiss 3T3 cells, mouse L cells and baby hamster kidney cells. The LD50 ranged from 1 to 5 microgram wheat germ agglutinin per ml. Similar concentrations of the lectin inhibited the transport of the non-utilizable amino acids alpha-aminoisobutyric acid and cycloleucine and inhibited the uptake of thymidine. In contrast, 2-deoxy-D-glucose uptake was not altered and colchicine uptake was enhanced. (2) The inhibition of alpha-aminoisobutyric acid uptake occurred within minutes after lectin addition and was maximal by 1 h. Maximal inhibition ranged from 50 to 70% of control values. Studies of the kinetics of the uptake demonstrated that wheat germ agglutinin decreased the V of the uptake by 70% without affecting the apparent Km. Ovomucoid, a haptene inhibitor of wheat germ agglutinin-binding to cell surface receptors, prevented the wheat germ agglutinin-induced inhibition of alpha-aminoisobutyric acid transport. Three other lectins (Concanavalin A, Phaseolus vulgaris E-phytohemagglutinin and L-phytohemagglutinin) inhibited the uptake by 20% or less at doses up to 50 microgram/ml. (3) We propose that the cytotoxicity of wheat germ agglutinin probably results in part, if not totally, from membrane alterations which impair multiple membrane transport systems.

Isolation of wheat germ agglutinin-resistant clones of Chinese hamster ovary cells deficient in membrane sialic acid and galactose

Several clones of Chinese hamster ovary cells have been selected for their resistance to the toxic effects of wheat germ agglutinin. The clones do not bind wheat germ agglutinin as well as parent cells and are 5- to 250-fold more resistant to the toxic effects of the lectin. Of three clones studied in detail, all exhibit a decrease in wheat germ agglutinin binding affinity. Two have normal numbers of wheat germ agglutinin binding sites, while one (Clone 13) has a 65% decrease in binding sites. Crude membrane preparations of the clones have a decrease in sialic acid content relative to parent cells, and Clone 13 membranes are also deficient in galactose, while the mannose and hexosamine contents of all three clones are normal. The membrane sugar deficiencies affect both glycoproteins and glycolipids. Sialyl-lactosylceramide is the major glycolipid in parent cells, while Clones 1 and 1021 have lactosylceramide and Clone 13 has glucosylceramide as the predominant glycolipid. Labeling experiments with N-[G-3H]acetylmannosamine suggest that Clone 1021 cells have a block in the transfer of sialic acid from CMP-sialic acid to glycoprotein and glycolipid acceptors. Yet CMP-sialic acid:glycoprotein sialyl-transferase activity in cell lysates of Clone 1021 cells is 80% of normal. While CMP-sialic acid:lactosylceramide sialyl-transferase activity is only 25% of normal, it can be restored to normal or elevated levels by sodium butyrate induction without an associated increase in cellular sialyl-lactosylceramide content. Similarly, the galactose-deficient Clone 13 can synthesize UDP-galactose and has normal levels of UDP-galactose:glycoprotein galactosyltransferase and UDP-galactose:glucosylceramide galactosyltransferase when assayed in vitro. The glycosyltransferases of both these clones can utilize their own glycoproteins as sugar acceptors in in vitro assays. These data suggest that the variant cells fail to carry out specific glycosyltransferase reactions in vivo despite the fact that they possess the appropriate nucleotide sugars, glycoprotein and glycolipid acceptors, and glycosyltransferases.

Metalloprotease from Bacillus thuringiensis

Bacillus thuringiensis var. kurstaki was shown to produce an extracellular, metal chelator-sensitive protease during the early stages of sporulation. Protease production in nutrient broth was dependent upon supplementation with Mn2+ or Ca2. The addition of Ca24 was required for enzyme stabilization...

Cellular binding sites for insulin in rat liver

A study of the sites of insulin binding in subcellular fractions of rat liver is reported. A method for the isolation of liver plasma membranes, which permits one to follow quantitatively the distribution of all the parameters of interest, was modified and applied to the study of the cellular topography of insulin binding. The insulin binding capacity did not follow closely the enzyme marker (5'-nucleotidase) for plasma membranes when differential centrifugation schemes were used, and the divergence from this marker was more prominent when separations were performed on discontinous sucrose gradients. A significant amount of insulin binding capacity was always present in fractions with higher density than those containing the majority of 5'-nycleotidase. Results of studies on linear sucrose gradients have disclosed in some of the purified membrane fractions small but consistent differences in density of the insulin binding, and plasma membrane particles. It is suggested that there may be several types of intracellular membranes to which insulin can bind besides the plasma membranes.