Catalytic subunit of the oligosaccharyl transferase (OST) complex that catalyzes the initial transfer of a defined glycan (Glc(3)Man(9)GlcNAc(2) in eukaryotes) from the lipid carrier dolichol-pyrophosphate to an asparagine residue within an Asn-X-Ser/Thr consensus motif in nascent polypeptide chains, the first step in protein N-glycosylation. 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). All subunits are required for a maximal enzyme activity. This subunit contains the active site and the acceptor peptide and donor lipid-linked oligosaccharide (LLO) binding pockets (By similarity). 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 competent than STT3A-containing complexes for cotranslational glycosylation, they have the ability to mediate glycosylation of some nascent sites that are not accessible for STT3A. STT3B-containing complexes also act post-translationally and mediate modification of skipped glycosylation sites in unfolded proteins. Plays a role in ER-associated degradation (ERAD) pathway that mediates ubiquitin-dependent degradation of misfolded endoplasmic reticulum proteins by mediating N-glycosylation of unfolded proteins, which are then recognized by the ERAD pathway and targeted for degradation. Mediates glycosylation of the disease variant AMYL-TTR 'Asp-38' of TTR at 'Asn-118', leading to its degradation.
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Protein Aliases: B6dom1 antigen; dolichyl-diphosphooligosaccharide protein glycotransferase; Dolichyl-diphosphooligosaccharide--protein glycosyltransferase subunit STT3B; homolog of yeast STT3; Oligosaccharyl transferase subunit STT3B; Source of immunodominant MHC-associated peptides; Source of immunodominant MHC-associated peptides homolog; STT3, subunit of the oligosaccharyltransferase complex, homolog B; STT3-B; STT3B, subunit of the oligosaccharyltransferase complex (catalytic)
Gene Aliases: 1300006C19Rik; CDG1X; RGD1311563; SIMP; STT3-B; STT3B