Molecular snapshots of translation and protein translocation at the ER membrane

ABSTRACT: The dynamic ribosome-translocon complex, which resides at the endoplasmic reticulum (ER) membrane, produces a major fraction of the human proteome . It governs the synthesis, translocation, membrane insertion, N-glycosylation, folding and disulfide-bond formation of nascent proteins. While individual components of this machine have been studied at high resolution in isolation, insights into their interplay in the native membrane remain limited. Here, we use electron cryo-tomography (cryo-ET), extensive classification and molecular modeling to capture molecular resolution snapshots of mRNA translation and protein maturation at the ER membrane. Comprehensively recapitulating the translational elongation cycle, we identify a highly abundant classical pre-translocation (PRE) intermediate with eEF1a in an extended conformation following the decoding state, which indicates that eEF1a remains ribosome-associated after GTP-hydrolysis during proofreading. The complete atomic structure of the most abundant ER translocon variant comprising the protein-conducting channel Sec61, the translocon-associated protein complex (TRAP) and the oligosaccharyltransferase complex A (OSTA) reveals the molecular framework for signal peptide (SP) membrane insertion and protein N-glycosylation. Associated with OSTA we observe stoichiometric and sub-stoichiometric cofactors, likely including protein isomerases. Collectively, comprehensive analysis of ER-associated protein biogenesis ex vivo reveals numerous mechanistic insights advancing beyond the study of isolated components.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Cell Culture

SUBMITTER: Richard Scheltema  

LAB HEAD: Richard Scheltema

PROVIDER: PXD035475 | Pride | 2023-02-03

REPOSITORIES: Pride