【题目】 活化的GTP酶在RNA框架上的移动,驱动共转录蛋白靶向作用

【译文】约三分之一蛋白质组最初运往真核内质网或细菌质膜的。这些蛋白适当的定位是由一种普遍保守的丹巴靶向机关信号识别蛋白(SRP)介导的,SRP可以识别携带信号序列识别核糖体,并通过与SRP受体的相互作用将其传送到目标膜上的蛋白转位装置。SRP是一种古老的核蛋白微粒,它含有一种重要的、延展的SRP RNA,但其准确的功能还不清楚。本研究利用单分子荧光显微技术表明大肠杆菌SRP–SRP受体GTP酶复合物在SRP RNA四环末端的初步组装后,转移到距离该RNA远侧末端100 Å处,在此处发生快速GTP水解作用。 这种移动受到翻译的核糖体的负调控,在后期受到SecYEG转位子的正调控,这为保证在核糖体出口具有高度空间和短暂精确度的寻靶和转位装置的有效交换提供了一种机制。我们的结果表明大RNA可以发挥分子支架的作用,以促使复杂细胞过程中不同因子的容易交换以及分子事件的精确计时;这一概念可能被延伸到其他核糖核蛋白复合物中的类似现象。


[Title]: Activated GTPase movement on an RNA scaffold drives co-translational protein targeting

[Authors]:Kuang Shen,1 Sinan Arslan,2 David Akopian,1 Taekjip Ha2, 3 & Shu-ou Shan1

[Abstract]Approximately one-third of the proteome is initially destined for the eukaryotic endoplasmic reticulum or the bacterial plasma membrane. The proper localization of these proteins is mediated by a universally conserved protein-targeting machinery, the signal recognition particle (SRP), which recognizes ribosomes carrying signal sequences and, through interactions with the SRP receptor, delivers them to the protein-translocation machinery on the target membrane. The SRP is an ancient ribonucleoprotein particle containing an essential, elongated SRP RNA for which precise functions have remained elusive. Here we used single-molecule fluorescence microscopy to show that the Escherichia coli SRP–SRP receptor GTPase complex, after initial assembly at the tetraloop end of SRP RNA, travels over 100 Å to the distal end of this RNA, where rapid GTP hydrolysis occurs. This movement is negatively regulated by the translating ribosome and, at a later stage, positively regulated by the SecYEG translocon, providing an attractive mechanism for ensuring the productive exchange of the targeting and translocation machineries at the ribosome exit site with high spatial and temporal accuracy. Our results show that large RNAs can act as molecular scaffolds that enable the easy exchange of distinct factors and precise timing of molecular events in a complex cellular process; this concept may be extended to similar phenomena in other ribonucleoprotein complexes.



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