title: Structure of ratcheted ribosomes with tRNAs in hybrid states.
abstract: During protein synthesis, tRNAs and mRNA move through the ribosome between aminoacyl (A), peptidyl (P), and exit (E) sites of the ribosome in a process called translocation. Translocation is accompanied by the displacement of the tRNAs on the large ribosomal subunit toward the hybrid A/P and P/E states and by a rotational movement (ratchet) of the ribosomal subunits relative to one another. So far, the structure of the ratcheted state has been observed only when translation factors were bound to the ribosome. Using cryo-electron microscopy and classification, we show here that ribosomes can spontaneously adopt a ratcheted conformation with tRNAs in their hybrid states. The peptidyl-tRNA molecule in the A/P state, which is visualized here, is not distorted compared with the A/A state except for slight adjustments of its acceptor end, suggesting that the displacement of the A-site tRNA on the 50S subunit is passive and is induced by the 30S subunit rotation. Simultaneous subunit ratchet and formation of the tRNA hybrid states precede and may promote the subsequent rapid and coordinated tRNA translocation on the 30S subunit catalyzed by elongation factor G.
authors.affiliation: Structural Biology Unit, Center for Cooperative Research in Biosciences bioGUNE, 48160 Derio, Spain.
authors.forename: Patricia
authors.initials: P
authors.lastname: Julián
authors.forename: Andrey L
authors.initials: AL
authors.lastname: Konevega
authors.forename: Sjors H W
authors.initials: SH
authors.lastname: Scheres
authors.forename: Melisa
authors.initials: M
authors.lastname: Lázaro
authors.forename: David
authors.initials: D
authors.lastname: Gil
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wintermeyer
authors.forename: Marina V
authors.initials: MV
authors.lastname: Rodnina
authors.forename: Mikel
authors.initials: M
authors.lastname: Valle
mesh_terms: D020285:Cryoelectron Microscopy; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D020653:Peptide Elongation Factor G / Q000737:chemistry / Q000378:metabolism; D012343:RNA, Transfer / Q000737:chemistry* / Q000378:metabolism; D012346:RNA, Transfer, Amino Acyl / Q000737:chemistry / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry* / Q000378:metabolism
chemical_list: D020653:Peptide Elongation Factor G; D012346:RNA, Transfer, Amino Acyl; C019037:tRNA, peptidyl-; D012343:RNA, Transfer