Oligosaccharyltransferase complex subunit 4, non-catalytic (OST4)

OST4 is a very small, approximately 30-amino-acid, integral membrane protein that functions as a non-catalytic subunit of the oligosaccharyltransferase (OST) complex. The OST complex mediates the transfer of a pre-assembled oligosaccharide from dolichyl-pyrophosphate to specific asparagine residues on nascent polypeptides within the lumen of the endoplasmic reticulum, constituting the primary step in N-linked protein glycosylation. OST4 is essential for the stability and assembly of the OST complex, particularly complexes that contain the catalytic STT3A subunit, and its absence leads to defective N-glycosylation and destabilization of OST complexes. OST4 is evolutionarily conserved across eukaryotes and, while it lacks enzymatic or receptor activity itself, proper function is vital for glycoprotein biosynthesis and cellular protein quality control[1][2][3][5][7].

Other names

Dolichyl-diphosphooligosaccharide–protein glycosyltransferase subunit 4Oligosaccharyltransferase 4 homologOligosaccharyltransferase complex subunit 4 (non-catalytic)OST4 homolog (S. cerevisiae)