Yun Chen1, Shu Feng1, Veerendra Kumar1, Rya Ero1, and Yong-Gui Gao1,2,*
1 - School of Biological Sciences, Nanyang Technological University, Singapore.
2 - Institute of Molecular and Cell Biology, A*Star, Singapore.
* - To whom correspondence should be addressed. E-mail: email@example.com
Published in Nature Structural & Molecular Biology, 2013, 20:1077–1084 (online on 4 August 2013, doi:10.1038/nsmb.2645). Also highlighted under News and Views by Achenbach and Nierhaus in the same issue.
In protein synthesis, elongation factor G (EF-G) facilitates movement of tRNA-mRNA by one codon, which is coupled to the ratchet-like rotation of the ribosome complex and is triggered by EF-G-mediated GTP hydrolysis. Here we report the structure of a pretranslocational ribosome bound to Thermus thermophilus EF-G trapped with a GTP analog. The positioning of the catalytic His87 into the active site coupled to hydrophobic-gate opening involves the 23S rRNA sarcin-ricin loop and domain III of EF-G and provides a structural basis for the GTPase activation of EF-G. Interactions of the hybrid peptidyl-site-exit-site tRNA with ribosomal elements, including the entire L1 stalk and proteins S13 and S19, shed light on how formation and stabilization of the hybrid tRNA is coupled to head swiveling and body rotation of the 30S as well as to closure of the L1 stalk.
Figure legend: Structure of EF-G bound to the 70S ribosome in the pretranslocation state. (A) Overall view of the complex. EF-G, hybrid P/E tRNA, and mRNA are shown as surfaces. 50S and 30S subunits are shown as cartoons. (B) Rotation of 16S rRNA in the 30S subunit relative to the 50S subunit in the EF-G complex. In our pre-translocation complex, 16S rRNA (cyan) shows a counter-clockwise rotation by 7.4° of the 30S body and an orthogonal swiveling by 9.0° of the 30S head toward the L1 stalk (viewed from the solvent side of the 30S subunit), compared with 16S rRNA (gray) in the post-translocation complex with EF-G trapped by fusidic acid. The two structures are aligned on 23S rRNA. (C) Unbiased difference Fourier electron density map with refined GTP analogue GDPCP, Mg2+ ion, and EF-G. GDPCP shown in sticks, with carbon, oxygen, nitrogen, and phosphate atoms colored green, red, blue ,and orange, respectively. Mg2+ ion is shown as violet sphere. Switch loops I and II in EF-G are shown in yellow and green, respectively; G1, G4 and G5 motifs involved in nucleotide binding are shown in blue.
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