Dolichyl-diphosphooligosaccharide--protein glycosyltransferase subunit STT3B (Stt3b)

Catalytic component of oligosaccharyltransferase (OST) complex which catalyzes the transfer of a high mannose oligosaccharide from a lipid-linked oligosaccharide donor to an asparagine residue within an Asn-X-Ser/Thr consensus motif in nascent polypeptide chains. N-glycosylation occurs cotranslationally and the complex associates with the Sec61 complex at the channel-forming translocon complex that mediates protein translocation across the endoplasmic reticulum (ER).

STT3B is present in a small subset of OST complexes and mediates both cotranslational and post-translational N-glycosylation of target proteins: STT3B-containing complexes are required for efficient post-translational glycosylation and while they are less capable than STT3A-containing complexes for cotranslational glycosylation, they have the capacity to mediate glycosylation of some nascent sites that are not accessible for STT3A. STT3B-containing complexes also behave post-translationally and mediate modification of skipped glycosylation sites in unfolded proteins.