Cryo-EM Reveals the Structure of the Yeast Oligosaccharyltransferase Complex
The pathway of N-linked protein glycosylation is conserved among most of the eukaryotic organisms. N-linked protein glycosylation initiates with the assembly of an oligosaccharide on a lipid-carrier, first on the cytoplasmic side of the endoplasmic reticulum (ER) membrane, catalyzed by a series of specific glycosyltransferases. The resulting intermediate is flipped into the ER lumen where more hexose residues are added by a distinct set of glycosyltransferases. The oligosaccharide is finally transferred en bloc from the lipid to selected asparagine residues of secretory proteins by the key enzyme of the pathway, the oligosaccharyltransferase (OST).
A high-resolution 3D structure of the yeast OST complex has been determined using single-particle cryo-Electron Microscopy. It reveals the architecture of eukaryotic OSTs and provides an understanding of how these transmembrane proteins recognize and process a number of acceptor proteins.