Research Article

Structure of the yeast oligosaccharyltransferase complex gives insight into eukaryotic N-glycosylation

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Science  04 Jan 2018:
eaar5140
DOI: 10.1126/science.aar5140

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Abstract

Oligosaccharyltransferase (OST) is an essential membrane protein complex in the Endoplasmic Reticulum, where it transfers an oligosaccharide from a dolichol-pyrophosphate-activated donor to glycosylation sites of secretory proteins. We here describe the atomic structure of yeast OST determined by cryo-EM, revealing a conserved subunit arrangement. The active site of the catalytic STT3 subunit points away from the center of the complex, allowing unhindered access to substrates. The dolichol-pyrophosphate moiety binds to a lipid-exposed groove of STT3, while two non-catalytic subunits and an ordered N-glycan form a membrane-proximal pocket for the oligosaccharide. The acceptor polypeptide site faces an oxidoreductase domain in standalone OST complexes or is immediately adjacent to the translocon, suggesting how eukaryotic OSTs efficiently glycosylate a large number of polypeptides prior to their folding.

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