Gagnon Matthieu G, Lin Jinzhong, Steitz Thomas A
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114; Howard Hughes Medical Institute, Yale University, New Haven, CT 06520-8114;
Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114; Howard Hughes Medical Institute, Yale University, New Haven, CT 06520-8114; Department of Chemistry, Yale University, New Haven, CT 06520-8107
Proc Natl Acad Sci U S A. 2016 May 3;113(18):4994-9. doi: 10.1073/pnas.1522932113. Epub 2016 Apr 18.
During translation, a plethora of protein factors bind to the ribosome and regulate protein synthesis. Many of those factors are guanosine triphosphatases (GTPases), proteins that catalyze the hydrolysis of guanosine 5'-triphosphate (GTP) to promote conformational changes. Despite numerous studies, the function of elongation factor 4 (EF-4/LepA), a highly conserved translational GTPase, has remained elusive. Here, we present the crystal structure at 2.6-Å resolution of the Thermus thermophilus 70S ribosome bound to EF-4 with a nonhydrolyzable GTP analog and A-, P-, and E-site tRNAs. The structure reveals the interactions of EF-4 with the A-site tRNA, including contacts between the C-terminal domain (CTD) of EF-4 and the acceptor helical stem of the tRNA. Remarkably, EF-4 induces a distortion of the A-site tRNA, allowing it to interact simultaneously with EF-4 and the decoding center of the ribosome. The structure provides insights into the tRNA-remodeling function of EF-4 on the ribosome and suggests that the displacement of the CCA-end of the A-site tRNA away from the peptidyl transferase center (PTC) is functionally significant.
在翻译过程中，大量蛋白质因子与核糖体结合并调节蛋白质合成。其中许多因子是鸟苷三磷酸酶（GTPases），这类蛋白质催化鸟苷5'-三磷酸（GTP）水解以促进构象变化。尽管有大量研究，但高度保守的翻译GTPase延伸因子4（EF-4/LepA）的功能仍不清楚。在此，我们展示了嗜热栖热菌70S核糖体与结合有不可水解GTP类似物以及A、P和E位点tRNA的EF-4复合物在2.6埃分辨率下的晶体结构。该结构揭示了EF-4与A位点tRNA的相互作用，包括EF-4的C末端结构域（CTD）与tRNA的受体螺旋茎之间的接触。值得注意的是，EF-4诱导A位点tRNA发生扭曲，使其能够同时与EF-4和核糖体的解码中心相互作用。该结构为EF-4在核糖体上的tRNA重塑功能提供了见解，并表明A位点tRNA的CCA末端从肽基转移酶中心（PTC）移位在功能上具有重要意义。
