Dolichyl-diphosphooligosaccharide--protein glycosyltransferase subunit STT3A (STT3A)

Catalytic subunit of the oligosaccharyl transferase (OST) complex that catalyzes the first move of a specified glycan (Glc(3)Man(9)GlcNAc(2) in eukaryotes) in 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 maximum enzyme activity. This subunit contains the active site and the acceptor peptide and donor lipid- linked oligosaccharide (LLO) binding pockets (By similarity).