美国哥伦比亚大学Joachim Frank和Ruben L. Gonzalez Jr研究团队的论文，用时间分辨冷冻电镜技术解析了细菌翻译起始过程中的晚期步骤。 相关成果于2019年6月20日发表在《自然》杂志上。

利用时间分辨低温电子显微镜，研究人员解析出形成70S延长复合物过程中近原子分辨率的结构，在时间顺序的构象变化序列中如何驱动和调节亚单位连接，启动因子解离和fMet-tRNAfMet定位。研究结果证明了时间分辨低温电子显微镜的强大功能，它可以确定一系列时间顺序的构象变化如何促进生物学基础过程的调控机制。

研究人员表示，细菌的起始翻译受到精密的调控，由50 s核糖体亚基及包含30 s核糖体翻译起始复合物的tRNA(fMet-tRNAfMet)，形成一个70s的翻译起始复合物,进而变为成熟的70s延长复合物。70s的快速、准确形成，依赖于翻译起始因子从30s起始复合物分离，进而产生成熟的70s延长复合物以启动翻译。虽然比较30S和70S起始复合物的结构已经揭示核糖体，起始因子和fMet-tRNAfMet可以在这些复合物中获得不同的构象，在70S起始复合物形成过程中构象变化的时间，在这些重排期间形成的任何中间体，以及这些动力学可能对启动机制和调节作出的贡献仍然未知。此外，通过缺乏起始因子催化反应形成的70S伸长能力复合物的结构，无法理解对70S起始复合物成熟期间的核糖体，起始因子和fMet-tRNAfMet的重排。

附：英文原文

Title: Late steps in bacterial translation initiation visualized using time-resolved cryo-EM

Author: Sandip Kaledhonkar, Ziao Fu, Kelvin Caban, Wen Li, Bo Chen, Ming Sun, Ruben L. Gonzalez, Joachim Frank

Issue&Volume: Volume 570 Issue 7761, 20 June 2019

Abstract: The initiation of bacterial translation involves the tightly regulated joining of the 50S ribosomal subunit to an initiator transfer RNA (fMet-tRNAfMet)-containing 30S ribosomal initiation complex to form a 70S initiation complex, which subsequently matures into a 70S elongation-competent complex. Rapid and accurate formation of the 70S initiation complex is promoted by initiation factors, which must dissociate from the 30S initiation complex before the resulting 70S elongation-competent complex can begin the elongation of translation. Although comparisons of the structures of the 30S and 70S initiation complexes have revealed that the ribosome, initiation factors and fMet-tRNAfMet can acquire different conformations in these complexes, the timing of conformational changes during formation of the 70S initiation complex, the structures of any intermediates formed during these rearrangements, and the contributions that these dynamics might make to the mechanism and regulation of initiation remain unknown. Moreover, the absence of a structure of the 70S elongation-competent complex formed via an initiation-factor-catalysed reaction has precluded an understanding of the rearrangements to the ribosome, initiation factors and fMet-tRNAfMet that occur during maturation of a 70S initiation complex into a 70S elongation-competent complex. Here, using time-resolved cryogenic electron microscopy, we report the near-atomic-resolution view of how a time-ordered series of conformational changes drive and regulate subunit joining, initiation factor dissociation and fMet-tRNAfMet positioning during formation of the 70S elongation-competent complex. Our results demonstrate the power of time-resolved cryogenic electron microscopy to determine how a time-ordered series of conformational changes contribute to the mechanism and regulation of one of the most fundamental processes in biology.

DOI: 10.1038/s41586-019-1249-5

Source:https://www.nature.com/articles/s41586-019-1249-5