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Updated: Jun 1, 2026

Pulse-chase Analysis of N-linked Sugar Chains from Glycoproteins in Mammalian Cells
Published on: April 27, 2010
Oligosaccharyltransferase: the central enzyme of N-linked protein glycosylation
Elisabeth Mohorko1, Rudi Glockshuber, Markus Aebi
1Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zürich, Schafmatt 20, CH, 8093, Zürich, Switzerland.
Abstract:
N-linked glycosylation is one of the most abundant modifications of proteins in eukaryotic organisms. In the central reaction of the pathway, oligosaccharyltransferase (OST), a multimeric complex located at the membrane of the endoplasmic reticulum, transfers a preassembled oligosaccharide to selected asparagine residues within the consensus sequence asparagine-X-serine/threonine. Due to the high substrate specificity of OST, alterations in the biosynthesis of the oligosaccharide substrate result in the hypoglycosylation of many different proteins and a multitude of symptoms observed in the family of congenital disorders of glycosylation (CDG) type I. This review covers our knowledge of human OST and describes enzyme composition. The Stt3 subunit of OST harbors the catalytic center of the enzyme, but the function of the other, highly conserved, subunits are less well defined. Some components seem to be involved in the recognition and utilization of glycosylation sites in specific glycoproteins. Indeed, mutations in the subunit paralogs N33/Tusc3 and IAP do not yield the pleiotropic phenotypes typical for CDG type I but specifically result in nonsyndromic mental retardation, suggesting that the oxidoreductase activity of these subunits is required for glycosylation of a subset of proteins essential for brain development.
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