Quality control despite mistranslation caused by an ambiguous genetic code
Quality control despite mistranslation caused by an ambiguous genetic code
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DOI：
10.1073/pnas.0809179105
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发表时间：
2008-10-28
影响因子：
11.1
通讯作者：
Soell, Dieter
中科院分区：
文献类型：
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作者：
Ruan, Benfang;Palioura, Sotiria;Soell, Dieter
蛋白质合成过程中的高水平准确性被认为是生命所必需的。氨酰-tRNA合成酶（aaRS）通过确保氨基酸与其同源tRNA的正确配对来翻译遗传密码。由于一些aaRS在体内也产生错酰化氨酰-tRNA（aa-tRNA），我们在Cys-tRNA（Pro）、Ser-tRNA（Thr）、Glu-tRNA（Gln）和Asp-tRNA（Asn）的错义抑制背景下解决了蛋白质质量的问题。活性位点错义突变的抑制导致无活性突变蛋白（来自与正确酰化的aa-tRNA的翻译）和与野生型蛋白（来自与错酰化的aa-tRNA的翻译）不可区分的活性酶的混合物。在这里，我们提供了遗传和生化证据，在选择压力下，大肠杆菌不仅容忍存在的错酰化的aa-tRNA，但甚至可以需要它的生长。此外，通过使用质谱的报告蛋白不受选择，我们表明，E。大肠杆菌可以耐受由错酰化的aa-tRNA施加的模糊遗传密码，耐受高达10%的错构蛋白。aaRSs水解错酰化aa-tRNA的编辑功能对于存活不是必需的，并且针对错酰化aa-tRNA的EF-Tu屏障不是绝对的。相反，E。大肠杆菌通过触发热休克反应来处理错误翻译，热休克反应刺激非优化的多肽实现天然构象或被降解。这样，E。大肠杆菌确保了足够的功能蛋白的存在，尽管是以相当大的能量成本。
A high level of accuracy during protein synthesis is considered essential for life. Aminoacyl-tRNA synthetases (aaRSs) translate the genetic code by ensuring the correct pairing of amino acids with their cognate tRNAs. Because some aaRSs also produce misacylated aminoacyl-tRNA (aa-tRNA) in vivo, we addressed the question of protein quality within the context of missense suppression by Cys-tRNA(Pro), Ser-tRNA(Thr), Glu-tRNA(Gln), and Asp-tRNA(Asn). Suppression of an active-site missense mutation leads to a mixture of inactive mutant protein (from translation with correctly acylated aa-tRNA) and active enzyme indistinguishable from the wild-type protein (from translation with misacylated aa-tRNA). Here, we provide genetic and biochemical evidence that under selective pressure, Escherichia coli not only tolerates the presence of misacylated aa-tRNA, but can even require it for growth. Furthermore, by using mass spectrometry of a reporter protein not subject to selection, we show that E. coli can survive the ambiguous genetic code imposed by misacylated aa-tRNA tolerating up to 10% of mismade protein. The editing function of aaRSs to hydrolyze misacylated aa-tRNA is not essential for survival, and the EF-Tu barrier against misacylated aa-tRNA is not absolute. Rather, E. coli copes with mistranslation by triggering the heat shock response that stimulates nonoptimized polypeptides to achieve a native conformation or to be degraded. In this way, E. coli ensures the presence of sufficient functional protein albeit at a considerable energetic cost.