Journal Article

Structural basis for coupling protein transport and N-glycosylation at the mammalian endoplasmic reticulum

Mandon, Elisabet C., Berninghausen, Otto, Pfeffer, Stefan, Shrimal, Shiteshu, Beckmann, Roland, Gilmore, Reid, Becker, Thomas, Förster, Friedrich, Braunger, Katharina

2018

Overview

Many secretory and membrane proteins are modified through the attachment of sugar chains by N-glycosylation. Such modification is required for correct protein folding, targeting, and functionality. In mammalian cells, N-glycosylation is catalyzed by the oligosaccharyltransferase (OST) complex via its STT3 subunit. OST forms a complex with the ribosome and the Sec61 protein translocation channel. Braunger et al. combined cryo–electron microscopy approaches to visualize mammalian ribosome-Sec61-OST complexes in order to build an initial molecular model for mammalian OST. Science , this issue p. 215 Cryo–electron microscopy reveals how cotranslational protein transport and N-glycosylation are coupled in mammals. Protein synthesis, transport, and N-glycosylation are coupled at the mammalian endoplasmic reticulum by complex formation of a ribosome, the Sec61 protein-conducting channel, and oligosaccharyltransferase (OST). Here we used different cryo–electron microscopy approaches to determine structures of native and solubilized ribosome-Sec61-OST complexes. A molecular model for the catalytic OST subunit STT3A (staurosporine and temperature sensitive 3A) revealed how it is integrated into the OST and how STT3-paralog specificity for translocon-associated OST is achieved. The OST subunit DC2 was placed at the interface between Sec61 and STT3A, where it acts as a versatile module for recruitment of STT3A-containing OST to the ribosome-Sec61 complex. This detailed structural view on the molecular architecture of the cotranslational machinery for N-glycosylation provides the basis for a mechanistic understanding of glycoprotein biogenesis at the endoplasmic reticulum.

• Publisher: The American Association for the Advancement of Science
• Subject: Catalysis / Chemical synthesis / Complex formation / Coupling (molecular) / Cryoelectron Microscopy / Electron microscopy / Endoplasmic reticulum / Endoplasmic Reticulum - metabolism / Glycoproteins / Glycosylation / HEK293 Cells / Hexosyltransferases - chemistry / Hexosyltransferases - ultrastructure / Humans / Machinery and equipment / Mammalian cells / Mammals / Membrane proteins / Membrane Proteins - chemistry / Membrane Proteins - ultrastructure / Microscopy / Models, Molecular / Oligosaccharyltransferase / Protein biosynthesis / Protein Conformation / Protein folding / Protein synthesis / Protein Transport / Proteins / Ribosomes - chemistry / Ribosomes - ultrastructure / SEC Translocation Channels - chemistry / SEC Translocation Channels - ultrastructure / Staurosporine / Sugar / Translocation