STT3A Gene: Function, Associated Diseases, and Clinical Significance

STT3A encodes the catalytic subunit A of the oligosaccharyltransferase (OST) complex, which is responsible for the transfer of a high-mannose oligosaccharide from dolichol to asparagine residues of nascent polypeptides in the endoplasmic reticulum (ER). This process is essential for proper protein folding, stability, and function. STT3A is one of two catalytic isoforms (STT3A and STT3B) that define distinct OST complexes with different substrate specificities. STT3A is involved in co-translational glycosylation, while STT3B mediates post-translocational glycosylation. Mutations in STT3A cause a congenital disorder of glycosylation (CDG) known as STT3A-CDG, characterized by severe neurological and developmental defects. Additionally, altered STT3A expression has been implicated in various cancers and immune regulation.

Tissue Expression

Cell Line Expression

Hotspot Mutations

Mutation functional classification

• N-glycan biosynthesis

• Protein processing in endoplasmic reticulum

• Metabolism of proteins

• Asparagine N-linked glycosylation

STT3A is a 705-amino acid, multi-pass transmembrane protein localized to the endoplasmic reticulum. It is the catalytic subunit of the OST complex, which transfers oligosaccharides to asparagine residues in the consensus sequence N-X-S/T. STT3A contains a conserved C-terminal catalytic domain and is essential for co-translational glycosylation. The protein interacts with other OST subunits (e.g., ribophorin I, OST48) to form a functional complex. STT3A deficiency leads to hypoglycosylation of proteins, triggering ER stress and unfolded protein response, which underlies the pathophysiology of STT3A-CDG.