4v6t | pdb_00004v6t
Structure of the bacterial ribosome complexed by tmRNA-SmpB and EF-G during translocation and MLD-loading
Structural highlights
FunctionRS9_ECOLI The C-terminal tail plays a role in the affinity of the 30S P site for different tRNAs. Mutations that decrease this affinity are suppressed in the 70S ribosome.[1] Publication Abstract from PubMedBacterial ribosomes stalled at the 3' end of malfunctioning messenger RNAs can be rescued by transfer-messenger RNA (tmRNA)-mediated trans-translation. The SmpB protein forms a complex with the tmRNA, and the transfer-RNA-like domain (TLD) of the tmRNA then enters the A site of the ribosome. Subsequently, the TLD-SmpB module is translocated to the P site, a process that is facilitated by the elongation factor EF-G, and translation is switched to the mRNA-like domain (MLD) of the tmRNA. Accurate loading of the MLD into the mRNA path is an unusual initiation mechanism. Despite various snapshots of different ribosome-tmRNA complexes at low to intermediate resolution, it is unclear how the large, highly structured tmRNA is translocated and how the MLD is loaded. Here we present a cryo-electron microscopy reconstruction of a fusidic-acid-stalled ribosomal 70S-tmRNA-SmpB-EF-G complex (carrying both of the large ligands, that is, EF-G and tmRNA) at 8.3 A resolution. This post-translocational intermediate (TI(POST)) presents the TLD-SmpB module in an intrasubunit ap/P hybrid site and a tRNA(fMet) in an intrasubunit pe/E hybrid site. Conformational changes in the ribosome and tmRNA occur in the intersubunit space and on the solvent side. The key underlying event is a unique extra-large swivel movement of the 30S head, which is crucial for both tmRNA-SmpB translocation and MLD loading, thereby coupling translocation to MLD loading. This mechanism exemplifies the versatile, dynamic nature of the ribosome, and it shows that the conformational modes of the ribosome that normally drive canonical translation can also be used in a modified form to facilitate more complex tasks in specialized non-canonical pathways. The complex of tmRNA-SmpB and EF-G on translocating ribosomes.,Ramrath DJ, Yamamoto H, Rother K, Wittek D, Pech M, Mielke T, Loerke J, Scheerer P, Ivanov P, Teraoka Y, Shpanchenko O, Nierhaus KH, Spahn CM Nature. 2012 May 6;485(7399):526-9. doi: 10.1038/nature11006. PMID:22622583[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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