Genetic and biochemical studies of asparagine-linked oligosaccharide assembly.
The formation of N-glycosidic linkages of eukaryotic glycoproteins involves the assembly of a specific lipid-linked precursor oligosaccharide in the endoplasmic reticulum. This oligosaccharide is transferred from the lipid carrier to appropriate asparagine residues during protein synthesis. The protein-linked oligosaccharide then undergoes processing reactions that include both removal and addition of carbohydrate residues. In this paper we report recent studies from our laboratory on the synthesis of asparagine-linked oligosaccharides. In the first part we describe the isolation and characterization of temperature-sensitive mutants of yeast blocked at specific stages in the assembly of the lipid-linked oligosaccharide. In addition, we are using these mutants to clone the genes for the enzymes in this pathway by complementation of the temperature-sensitive phenotype. The second part deals with the topography of asparagine-linked oligosaccharide assembly. Our studies on the transmembrane movement of sugar residues during the assembly of secreted glycoproteins from cytoplasmic precursors are presented. Finally, experiments on the control of protein-linked oligosaccharide processing are described. Recent data are presented on the problem of how specific oligosaccharides are assembled from the common precursors at individual sites on glycoproteins.
D001216:Asparagine; D002451:Cell Compartmentation; D004288:Dolichol Phosphates / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006023:Glycoproteins / Q000096:biosynthesis* / Q000235:genetics; D008358:Mannose / Q000378:metabolism; D008715:Methionine / Q000378:metabolism; D009844:Oligosaccharides / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics
D004288:Dolichol Phosphates; D006023:Glycoproteins; D009844:Oligosaccharides; D001216:Asparagine; D008715:Methionine; D008358:Mannose