在翻譯過程中,，轉(zhuǎn)移RNA (tRNA)進(jìn)入核糖體,，然后在其將它們所攜帶的氨基酸轉(zhuǎn)移到增長(zhǎng)中的肽鏈上時(shí),，順序通過被稱為A、P和E的三個(gè)點(diǎn),。然而,，核糖體是怎樣幫助tRNA在這些點(diǎn)之間的轉(zhuǎn)位的在很大程度上卻不清楚,。Christian Spahn及其同事利用結(jié)合到“翻譯伸長(zhǎng)因子”EF-G上的一個(gè)核糖體的“多粒子冷電子顯微鏡”圖像來獲取關(guān)于tRNA運(yùn)動(dòng)的信息,。他們識(shí)別出兩個(gè)新的亞狀態(tài)， 并且得出這樣的結(jié)論：在亞單元之間自發(fā)的“棘輪作用”之后，轉(zhuǎn)位是30S核糖體亞單元的頭部轉(zhuǎn)動(dòng)和“去棘輪作用”的直接結(jié)果,。（生物谷Bioon.com）
生物谷推薦原文出處：
Nature doi:10.1038/nature09547
Head swivel on the ribosome facilitates translocation by means of intra-subunit tRNA hybrid sites
Andreas H. Ratje,Justus Loerke,Aleksandra Mikolajka,Matthias Brünner,Peter W. Hildebrand,Agata L. Starosta,Alexandra D?nh?fer,Sean R. Connell,Paola Fucini,Thorsten Mielke,Paul C. Whitford,José N. Onuchic,Yanan Yu,Karissa Y. Sanbonmatsu,Roland K. Hartmann,Pawel A. Penczek,Daniel N. [email protected]& Christian M. T. [email protected]
The elongation cycle of protein synthesis involves the delivery of aminoacyl-transfer RNAs to the aminoacyl-tRNA-binding site (A?site) of the ribosome, followed by peptide-bond formation and translocation of the tRNAs through the ribosome to reopen the A?site1, 2. The translocation reaction is catalysed by elongation factor G (EF-G) in a GTP-dependent manner3. Despite the availability of structures of various EF-G–ribosome complexes, the precise mechanism by which tRNAs move through the ribosome still remains unclear. Here we use multiparticle cryoelectron microscopy analysis to resolve two previously unseen subpopulations within Thermus thermophilus EF-G–ribosome complexes at subnanometre resolution, one of them with a partly translocated tRNA. Comparison of these substates reveals that translocation of tRNA on the 30S subunit parallels the swivelling of the 30S head and is coupled to unratcheting of the 30S body. Because the tRNA maintains contact with the peptidyl-tRNA-binding site (P?site) on the 30S head and simultaneously establishes interaction with the exit site (E?site) on the 30S platform, a novel intra-subunit ‘pe/E’ hybrid state is formed. This state is stabilized by domain?IV of EF-G, which interacts with the swivelled 30S-head conformation. These findings provide direct structural and mechanistic insight into the ‘missing link’ in terms of tRNA intermediates involved in the universally conserved translocation process.
