Quality Control of Protein Translation

基因信息从DNA到RNA再到蛋白质的准确流动对所有生物来说都是必不可少的 有机体。一系列惊人的质量保证机制已经发展起来，以确保 在这一过程的每个阶段都保持了高度的保真度。其中最令人着迷的 质量控制机制涉及tmRNA，也称为SsrA或10Sa RNA。TmRNA是一种 多功能和高度保守的细菌分子，具有组合的结构和 TRNA和信使核糖核酸的功能特性。我们之前的研究表明，所有的 已知的tmRNA活性需要SmpB，SmpB是一种小蛋白，能与tmRNA特异性结合，并 具有高亲和力以促进其与停滞的核糖体的结合。SmpB-tmRNA系统 协调三个关键的生物学功能：1)识别和拯救停滞不前的核糖体 异常的mRNAs，2)处理引起缺陷的mRNAs，以及3)添加 降解标签到不完全的蛋白质片段，用于定向蛋白质降解。虽然不是 在大肠杆菌中必不可少的tmna活性对于细菌在不利条件下的生存是必不可少的。 以及部分甚至全部致病细菌的致病力。最近的证据来自我们的 实验室表明，除了其质量控制功能外，tmna系统还可能 在某些生理途径中起着关键的调节作用。此外，因为SmpB和 Tmrna仅在原核生物中发现，涉及新的rna和蛋白质因子，是必需的。 对于病原菌的生存，对这一系统有更深的机理认识 可能会设计出高度特异的新型抗菌剂。 SmpB-tmRNA复合体形成及随后形成的分子基础 对停滞不前的核糖体的识别还不是很清楚。这项研究计划的目标是 是利用分子遗传学、蛋白质生物化学、生物信息学和 SmpB-tmRNA质控作用机制的结构研究 系统。重点是SmpB-tmRNA复合体的分子特征 识别停滞不前的核糖体并促进对致病因子的检测和选择性衰退 3‘-5’外切酶RNaseR导致的有缺陷的mRNA。具体地说，通过这些研究，我们希望 了解SmpB和RNase R相互作用的生化和结构基础 与tmrna和核糖体；即涉及哪些氨基酸残基，哪些碱基特异 进行接触，哪些结构特征有助于tmRNA相关的形成 SmpB和RNaseR复合体及其与停滞核糖体的相互作用。

The accurate flow of genetic information from DNA to RNA to protein is essential for all living organisms. An astonishing array of quality-assurance mechanisms have evolved to ensure that high degree of fidelity is maintained at every stage of this process. One of the most fascinating quality control mechanisms involves tmRNA, also known as SsrA or 10Sa RNA. tmRNA is a versatile and highly conserved bacterial molecule endowed with the combined structural and functional properties of both a tRNA and an mRNA. Our previous studies have shown that all known activities of tmRNA require SmpB, a small protein that binds tmRNA specifically and with high affinity to promote its association with stalled ribosomes. The SmpB-tmRNA system orchestrates three key biological functions: 1) recognition and rescue of ribosomes stalled on aberrant mRNAs, 2) disposal of the causative defective mRNAs, and 3) addition of a degradation tag to the incomplete protein fragments for directed proteolysis. Although not essential in E. coli, tmRNA activity is essential for bacterial survival under adverse conditions and for virulence in some, and perhaps all, pathogenic bacteria. Recent evidence from our laboratory suggests that in addition to its quality control function the tmRNA system might also play a key regulatory role in certain physiological pathways. Moreover, because the SmpB and tmRNA are found only in prokaryotes, involves novel RNA and protein factors, and is essential for the survival of pathogenic bacteria, a deeper mechanistic understanding of this system might allow the design of highly specific new anti-bacterial agents. The molecular basis for the formation of the SmpB-tmRNA complex and the subsequent recognition of stalled ribosomes are not well understood. The objective of this research program is to use a combination of molecular genetics, protein biochemistry, bioinformatics, and structural approaches to elucidate the mechanism of action of the SmpB-tmRNA quality control system. The emphasis is on the molecular characterization of how SmpB-tmRNA complex recognizes stalled ribosomes and promotes the detection and selective decay of the causative defective mRNA by the 3¿-5¿ exonuclease RNase R. Specifically, through these studies we wish to understand the biochemical and structural basis for the interactions of SmpB and RNase R with tmRNA and the ribosome; i.e. what amino acid residues are involved, what base specific contacts are made, what structural features contribute to the formation of the tmRNAassociated SmpB and RNase R complexes and their interaction with stalled ribosome.