The pathway to GTPase activation of elongation factor SelB on the ribosome
The pathway to GTPase activation of elongation factor SelB on the ribosome
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DOI：
10.1038/nature20560
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发表时间：
2016-12-01
期刊：
影响因子：
64.8
通讯作者：
Stark, Holger
中科院分区：
文献类型：
--
作者：
Fischer, Niels;Neumann, Piotr;Stark, Holger
在生命的所有领域中，硒代半胱氨酸（Sec）通过硒代半胱氨酸特异性tRNA（tRNA(Sec)）在细菌中特殊翻译因子SelB的帮助下传递给核糖体。Sec- trna （Sec）编码靠近下游mRNA茎环的UGA停止密码子。本文利用单粒子低温电子显微镜研究了大肠杆菌中UGA编码途径中6个中间体的结构。这些结构解释了Sec- trna （Sec）与SelB结合的特异性，并显示了Sec- trna （Sec）的大规模重排。当SelB-Sec-tRNA（Sec）初始结合核糖体并读取密码子后，30S亚基呈开放构象，Sec- trna （Sec）覆盖50S亚基上的sarcin-ricin环（SRL）。随后的密码子识别导致解码位点的局部关闭，使Sec- trna （Sec）远离SRL，并触发30S亚基肩域的全局关闭。结果，SelB停靠在SRL上，激活SelB的GTPase。这些结果揭示了密码子识别如何在翻译GTPase中触发GTPase激活。
In all domains of life, selenocysteine (Sec) is delivered to the ribosome by selenocysteine-specific tRNA (tRNA(Sec)) with the help of a specialized translation factor, SelB in bacteria. Sec-tRNA(Sec) recodes a UGA stop codon next to a downstream mRNA stem-loop. Here we present the structures of six intermediates on the pathway of UGA recoding in Escherichia coli by single-particle cryo-electron microscopy. The structures explain the specificity of Sec-tRNA(Sec) binding by SelB and show large-scale rearrangements of Sec-tRNA(Sec). Upon initial binding of SelB-Sec-tRNA(Sec) to the ribosome and codon reading, the 30S subunit adopts an open conformation with Sec-tRNA(Sec) covering the sarcin-ricin loop (SRL) on the 50S subunit. Subsequent codon recognition results in a local closure of the decoding site, which moves Sec-tRNA(Sec) away from the SRL and triggers a global closure of the 30S subunit shoulder domain. As a consequence, SelB docks on the SRL, activating the GTPase of SelB. These results reveal how codon recognition triggers GTPase activation in translational GTPases.