FEATURES

FAMILY

DESCRIPTION

Also known as STT3A_HUMAN, STT3A, ITM1, TMC. 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). 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 (PubMed:19167329). Component of the oligosaccharyltransferase (OST) complex. OST exists in two different complex forms which contain common core subunits RPN1, RPN2, OST48, OST4, DAD1 and TMEM258, either STT3A or STT3B as catalytic subunits, and form-specific accessory subunits (PubMed:23606741, PubMed:25135935). STT3A complex assembly occurs through the formation of 3 subcomplexes. Subcomplex 1 contains RPN1 and TMEM258, subcomplex 2 contains the STT3A-specific subunits STT3A, DC2/OSTC, and KCP2 as well as the core subunit OST4, and subcomplex 3 contains RPN2, DAD1, and OST48. The STT3A complex can form stable complexes with the Sec61 complex or with both the Sec61 and TRAP complexes (By similarity).

EXTERNAL LINKS

STT3A

Dolichyl-diphosphooligosaccharide--protein glycosyltransferase subunit STT3A

STT3A

Molecular Synopsis