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Dolichyl-diphosphooligosaccharide--protein glycosyltransferase subunit STT3A

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^1,2,3,4,5,6. 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)^{7,8,9,10,11,12}. All subunits are required for a maximal enzyme activity^13,14,15. This subunit contains the active site and the acceptor peptide and donor lipid-linked oligosaccharide (LLO) binding pockets¹⁶. STT3A is present in the majority of OST complexes and mediates cotranslational N-glycosylation of most sites on target proteins, while STT3B-containing complexes are required for efficient post-translational glycosylation and mediate glycosylation of sites that have been skipped by STT3A^17,18,19. STT3A-containing OST-A complex is also required to prevent hyperglycosylation of some target proteins by preventing glycosylation of facultative sites before folding of target proteins is completed²⁰.

AlphaFold DB , UniProt , Accession P46977, Species HUMAN (Homo sapiens, Human), Gene STT3A, Length 705 aa.