Yeast oligosaccharyltransferase: glycosylation of peptide substrates and chemical characterization of the glycopeptide product
作者:Richard S. Clark、Shyamal Banerjee、James K. Coward
DOI:10.1021/jo00313a013
日期:1990.12
The product of the reaction catalyzed by yeast oligosaccharyltransferase was examined in order to determine the nature of the chemical linkage between the sugar and peptide. Biosynthetic donor lipid [H-3]oligosaccharide was prepared and used as a substrate for yeast oligosaccharyltransferase together with a chemically synthesized peptide acceptor, N-benzoyl-Asn-Leu-Thr-NH2. the glycosylated peptide product of the in vitro reaction was isolated and hydrolyzed with endo-beta-N-acetylglucosaminidase-H to yield a large oligosaccharide and the glycotripeptide, N-benzoyl-Asn(GlcNAc)-Leu-Thr-Nh2. This glycopeptide was purified using gel filtration, affinity binding, and reverse-phase high-performance liquid chromatography. The biosynthetic glycopeptide was compared with chemically synthesized glycopeptides in which a 1-amino-GlcNAc moiety was linked to either the alpha- or beta-carboxyl of aspartate. It was determined that the sole biosynthetic product has the structure in which the carbohydrate is linked to the peptide through the beta-carbonyl of asparagine, i.e., a normal alpha-peptide. These experiments provide an unambiguous structural proof of the protein-carbohydrate linkage in the glycoprotein product of the oligosaccharyltransferase-catalyzed reaction.