Oligosaccharyltransferase Complex Subunit (OSTC)

The enzyme that catalyzes this process is a heteromeric, multisubunit membrane complex, called oligosaccharyltransferase (OST) . Purification of OST from yeast and genetic methods identified nine proteins. Five of them, Wbp1, Swp1, Stt3, Ost1, and Ost2, are essential for viability of the cell, whereas Ost4, Ost5, Ost3, and Ost6 are not essential but are required for maximal OST activity. The specific function of the various subunits and the organization in the complex is largely enigmatic. Subunits Ost3 and Ost6 are alternatively present in the yeast OST complex; they modify the transfer specificity toward protein to be glycosylated and they specify the interaction with different translocation complexes. In mammals, two OST complexes exist that contain either one of two isoforms of Stt3, which display tissue-specific expression.