Yeast Wbp1p and Swp1p form a protein complex essential for oligosaccharyl transferase activity.

Asparagine‐linked N‐glycosylation is an essential protein modification occurring in all eukaryotic cells. The central step is the co‐translational transfer of the core oligosaccharide assembled on the lipid carrier dolichol phosphate to selected Asn‐X‐Ser/Thr residues of nascent polypeptide chains in the endoplasmic reticulum. This reaction is catalyzed by the enzyme N‐oligosaccharyl transferase. In yeast, Wbp1p is an essential component of this enzyme. Using a high copy number suppression approach, the SWP1 gene was isolated as an allele specific suppressor of a wbp1 mutation. Swp1p is a 30 kDa type I transmembrane protein and essential for cell viability. Similar to Wbp1p, depletion of Swp1p results in reduced N‐oligosaccharyl transferase activity in vivo and in vitro. Wbp1p and Swp1p can be chemically cross‐linked, suggesting that both proteins are essential constituents of the N‐oligosaccharyl transferase complex.