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This is a 3D printed protein model of Oligosaccharyltransferase Complex. Each chain is colored to match the illustrations from the academic paper published by ETH Zurich, Structure of the yeast oligosaccharyltransferase complex gives insight into eukaryotic N-glycosylation.
Of particular interest to ETH's research are the active sites (dark green) of OST, found in the green chain F, STT3. The active sites (next to the red chain) are orientated away from the core center of the protein positioned to interact with emerging proteins from the endoplasmic reticulum. Colored by atom type are the monosaccharide glycans.
Protein DescriptionWhenever cells physically interact or exchange chemical signals, proteins with specific 3-dimensional structure find stable contact with each other. Only until recently, a new and important component of this molecular handshake is the ability of proteins to maintain this connection. Chains of sugar molecules (oligosaccharides) are attached to proteins. Sugar is extremely reactive, finding binding residues throughout the genome. When proteins come into contact, sugar chains attach one protein to another prolonging its the cellular communications signal. If protein-to-protein interactions are a molecular handshake, then oligosaccharides are protein handcuffs binding proteins to each other. The Oligosaccharyltransferase Complex (OST) is the protein that arms newly synthesized proteins from the nucleus with sugar chains.
Oligosaccharyltransferase (OST) is an essential membrane protein complex in the Endoplasmic Reticulum, where it transfers an oligosaccharide from a dolichol-pyrophosphate-activated donor to glycosylation sites of secretory proteins. We here describe the atomic structure of yeast OST determined by cryo-EM, revealing a conserved subunit arrangement. The active site of the catalytic STT3 subunit points away from the center of the complex, allowing unhindered access to substrates. The dolichol-pyrophosphate moiety binds to a lipid-exposed groove of STT3, while two non-catalytic subunits and an ordered N-glycan form a membrane-proximal pocket for the oligosaccharide. The acceptor polypeptide site faces an oxidoreductase domain in standalone OST complexes or is immediately adjacent to the translocon, suggesting how eukaryotic OSTs efficiently glycosylate a large number of polypeptides prior to their folding.