Cryo-EM is uncovering the mechanism of eukaryotic protein N-glycosylation.

N-glycosylation is one of the predominant modifications of eukaryotic proteins. It is catalyzed by oligosaccharyl transferase (OST), an eight-subunit protein complex in the endoplasmic reticulum membrane. OST transfers the oligosaccharide from a lipid-linked donor (LLO) to the Asn-Xaa-Ser/Thr sequon of nascent polypeptide, usually cotranslationally by partnering with the ribosome and the translocon. We and two other groups have recently determined high-resolution cryo-EM structures of the yeast and mammalian OST complexes. In this Structural Snapshot, we describe the molecular mechanism of eukaryotic OST and its interaction with the translocon.