Liu Ziwei, Vargas-Rodriguez Oscar, Goto Yuki, Novoa Eva Maria, Ribas de Pouplana Lluís, Suga Hiroaki, Musier-Forsyth Karin
Department of Chemistry and Biochemistry and Center for RNA Biology, The Ohio State University, Columbus, OH 43210;
Department of Chemistry, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan;
Proc Natl Acad Sci U S A. 2015 May 12;112(19):6027-32. doi: 10.1073/pnas.1423664112. Epub 2015 Apr 27.
Aminoacyl-tRNA synthetases (ARSs) establish the rules of the genetic code, whereby each amino acid is attached to a cognate tRNA. Errors in this process lead to mistranslation, which can be toxic to cells. The selective forces exerted by species-specific requirements and environmental conditions potentially shape quality-control mechanisms that serve to prevent mistranslation. A family of editing factors that are homologous to the editing domain of bacterial prolyl-tRNA synthetase includes the previously characterized trans-editing factors ProXp-ala and YbaK, which clear Ala-tRNA(Pro) and Cys-tRNA(Pro), respectively, and three additional homologs of unknown function, ProXp-x, ProXp-y, and ProXp-z. We performed an in vivo screen of 230 conditions in which an Escherichia coli proXp-y deletion strain was grown in the presence of elevated levels of amino acids and specific ARSs. This screen, together with the results of in vitro deacylation assays, revealed Ser- and Thr-tRNA deacylase function for this homolog. A similar activity was demonstrated for Bordetella parapertussis ProXp-z in vitro. These proteins, now renamed "ProXp-ST1" and "ProXp-ST2," respectively, recognize multiple tRNAs as substrates. Taken together, our data suggest that these free-standing editing domains have the ability to prevent mistranslation errors caused by a number of ARSs, including lysyl-tRNA synthetase, threonyl-tRNA synthetase, seryl-tRNA synthetase, and alanyl-tRNA synthetase. The expression of these multifunctional enzymes is likely to provide a selective growth advantage to organisms subjected to environmental stresses and other conditions that alter the amino acid pool.
氨酰-tRNA合成酶（ARSs）确立了遗传密码规则，据此每种氨基酸都与相应的tRNA相连。这一过程中的错误会导致错译，而错译对细胞可能有毒性。物种特异性需求和环境条件施加的选择压力可能塑造了用于防止错译的质量控制机制。一类与细菌脯氨酰-tRNA合成酶的编辑结构域同源的编辑因子包括先前已表征的反式编辑因子ProXp-ala和YbaK，它们分别清除丙氨酰-tRNA（Pro）和半胱氨酰-tRNA（Pro），以及另外三个功能未知的同源物ProXp-x、ProXp-y和ProXp-z。我们对230种条件进行了体内筛选，在这些条件下，一株大肠杆菌proXp-y缺失菌株在氨基酸和特定ARSs水平升高的情况下生长。该筛选以及体外脱酰基测定结果揭示了该同源物的丝氨酰-tRNA和苏氨酰-tRNA脱酰酶功能。体外实验证明百日咳博德特氏菌的ProXp-z也有类似活性。这些蛋白质现在分别重新命名为“ProXp-ST1”和“ProXp-ST2”，它们将多种tRNA识别为底物。综合来看，我们的数据表明这些独立的编辑结构域有能力防止由多种ARSs引起的错译错误，包括赖氨酰-tRNA合成酶、苏氨酰-tRNA合成酶、丝氨酰-tRNA合成酶和丙氨酰-tRNA合成酶。这些多功能酶的表达可能为遭受环境压力和其他改变氨基酸库的条件的生物体提供选择性生长优势。
