STT3A
STT3A is the catalytic subunit of the oligosaccharyltransferase (OST) complex in the endoplasmic reticulum, where it starts protein N-glycosylation. It is also known as STT3-A, TMC, ITM1 and MGC9042, and was previously named integral membrane protein 1. Browse Assay Genie's current range of STT3A research reagents below, or read on for the biology behind the target.
STT3A is the catalytic subunit of the oligosaccharyl transferase (OST) complex. It catalyses the first step of protein N-glycosylation: 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 subunit contains the active site and the binding pockets for the acceptor peptide and the donor lipid-linked oligosaccharide (LLO). All subunits of the complex are required for maximal enzyme activity.
N-glycosylation occurs cotranslationally, and the OST complex associates with the Sec61 complex at the channel-forming translocon that mediates protein translocation across the endoplasmic reticulum (ER). STT3A is present in the majority of OST complexes and mediates cotranslational N-glycosylation of most sites on target proteins. Complexes containing the paralogous subunit STT3B are required for efficient post-translational glycosylation, and they glycosylate sites that STT3A has skipped. The STT3A-containing OST-A complex also helps prevent hyperglycosylation of some targets by blocking glycosylation of facultative sites before folding is complete.
The STT3A gene belongs to the STT3 family and sits in the HGNC groups for STT3 oligosaccharyltransferase catalytic subunits and oligosaccharyltransferase complex subunits. The protein is assigned EC 2.4.99.18 and localises to the ER and ER membrane. According to RefSeq, multiple transcript variants encoding different isoforms have been described. Earlier literature refers to it as integral membrane protein 1 or as the S. cerevisiae STT3 homolog A; mouse has an ortholog, Stt3a.
STT3A catalyses the initial glycan transfer to Asn-X-Ser/Thr motifs, making it central to studies of how nascent proteins are glycosylated in the ER.
The OST complex associates with the Sec61 translocon, so STT3A is relevant to work on cotranslational modification during protein translocation across the ER.
STT3A and STT3B complexes glycosylate different sites, cotranslationally and post-translationally, which allows site-specific glycosylation mechanisms to be dissected.
STT3A-containing OST-A prevents hyperglycosylation of facultative sites before folding is complete, linking glycosylation timing to glycoprotein folding.
STT3A is the catalytic subunit of the oligosaccharyltransferase complex. It transfers a Glc(3)Man(9)GlcNAc(2) glycan from dolichol-pyrophosphate to asparagine in Asn-X-Ser/Thr motifs of nascent polypeptides, the first step of N-glycosylation, mostly cotranslationally at the ER translocon.
Aliases include STT3-A, TMC, ITM1 and MGC9042. Previous names are integral membrane protein 1 and STT3, subunit of the oligosaccharyltransferase complex, homolog A (S. cerevisiae). The UniProt name is dolichyl-diphosphooligosaccharide--protein glycosyltransferase subunit STT3A. Multiple transcript variants encoding different isoforms are reported.
Both are catalytic OST subunits with overlapping function. STT3A is in most OST complexes and glycosylates most sites cotranslationally. STT3B complexes mediate efficient post-translational glycosylation of sites STT3A has skipped. Mouse has an Stt3a ortholog; check the datasheet of any product for its validated reactivity.
Other oligosaccharyltransferase subunits, translocon components and N-glycosylation pathway targets.
Gene and protein annotations from HGNC, NCBI Gene and UniProt P46977; product specifications from Assay Genie datasheets.