The oligosaccharyltransferase complexes (OST) are multi-span ER membrane protein complexes that catalyzes the addition of glycans to selected secretory and membrane protein polypeptides in the ER lumnen. They transfers the dolicholphosphate-linked core oligosaccharide to selected Asn residues within the motif Asn-X-Ser/Thr in a process termed N-glycosylation. Mammalian cells have been shown to possess two distinct OST complexes that contain STT3A or STT3B as the catalytic subunit and several accessory proteins: six common subunits, two STT3A-OST-specific subunits and two STT3B-OST-specific subunits. The two OST complexes are known to have distinct, but partially overlapping roles. (Adapted from
PMID:31810196.)
