Agrawal R K, Penczek P, Grassucci R A, Frank J
Wadsworth Center, New York State Department of Health, Empire State Plaza, Albany, NY 12201-0509, USA.
Proc Natl Acad Sci U S A. 1998 May 26;95(11):6134-8. doi: 10.1073/pnas.95.11.6134.
During protein synthesis, elongation factor G (EF-G) binds to the ribosome and promotes the step of translocation, a process in which tRNA moves from the A to the P site of the ribosome and the mRNA is advanced by one codon. By using three-dimensional cryo-electron microscopy, we have visualized EF-G in a ribosome-EF-G-GDP-fusidic acid complex. Fitting the crystal structure of EF-G-GDP into the cryo density map reveals a large conformational change mainly associated with domain IV, the domain that mimics the shape of the anticodon arm of the tRNA in the structurally homologous ternary complex of Phe-tRNAPhe, EF-Tu, and a GTP analog. The tip portion of this domain is found in a position that overlaps the anticodon arm of the A-site tRNA, whose position in the ribosome is known from a study of the pretranslocational complex, implying that EF-G displaces the A-site tRNA to the P site by physical interaction with the anticodon arm.
在蛋白质合成过程中,延伸因子G(EF-G)与核糖体结合并促进转位步骤,在此过程中,tRNA从核糖体的A位点移动到P位点,mRNA前进一个密码子。通过使用三维冷冻电子显微镜,我们观察到了核糖体-EF-G-GDP-夫西地酸复合物中的EF-G。将EF-G-GDP的晶体结构拟合到冷冻密度图中,发现主要与结构域IV相关的大的构象变化,该结构域在苯丙氨酸-tRNA苯丙氨酸、EF-Tu和GTP类似物的结构同源三元复合物中模拟tRNA反密码子臂的形状。该结构域的尖端部分位于与A位点tRNA的反密码子臂重叠的位置,从转位前复合物的研究中已知其在核糖体中的位置,这意味着EF-G通过与反密码子臂的物理相互作用将A位点tRNA置换到P位点。