Oxidation of cellular amino acid pools leads to cytotoxic mistranslation of the genetic code.
Oxidation of cellular amino acid pools leads to cytotoxic mistranslation of the genetic code.
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Bullwinkle TJ;Reynolds NM;Raina M;Moghal A;Matsa E;Rajkovic A;Kayadibi H;Fazlollahi F;Ryan C;Howitz N;Faull KF;Lazazzera BA;Ibba M
氨基酰基- trna合成酶使用多种机制来确保遗传密码的保真度，并最终选择正确的氨基酸用于蛋白质合成。这些质量控制机制在不同环境下的生理必要性尚不清楚，因为精确蛋白质合成的成本与收益难以预测。我们发现，在大肠杆菌中，通过氧化损伤产生的非编码氨基酸对蛋白质合成的准确性有重大威胁，必须通过苯丙氨酸- trna合成酶清除，以防止错误合成的蛋白质引起的细胞毒性。这些发现证明了压力如何导致非规范氨基酸的积累，这些非规范氨基酸必须从蛋白质组中排除，以维持细胞活力。DOI: http://dx.doi.org/10.7554/eLife.02501.001蛋白质是由称为氨基酸的分子构成的。构成特定蛋白质的氨基酸及其出现的顺序，是由编码该蛋白质的基因决定的。首先，基因被转录成信使RNA分子，然后被称为核糖体的分子机器翻译。这涉及到其他RNA分子，称为转移RNA (trna)，将正确的氨基酸带到核糖体中，核糖体将氨基酸连接在一起构建蛋白质。氨基酸通过一种叫做tRNA合成酶的酶装载到相应的tRNA分子上。然而，偶尔会有错误的氨基酸被装载到tRNA上。如果这种氨基酸最终出现在蛋白质中，蛋白质可能无法正常工作，甚至可能对细胞有毒，所以细胞需要能够解决这个问题。一些tRNA合成酶可以检查错误的氨基酸是否被装载到tRNA上，并在它造成伤害之前将其移除。然而，这些“编辑”活动对活细胞的重要性尚不清楚。在这里，Bullwinkle， Reynolds等人表明，在大肠杆菌中，tRNA合成酶可以阻止不正确的氨基酸（在暴露于有害化学物质的细胞中积累）被构建成蛋白质。没有这种酶的编辑活性，这种氨基酸的积累就会减缓细菌的生长。然而，当大肠杆菌在实验室的正常条件下生长时，它可以在没有这种编辑活性的情况下茁壮成长。当暴露于应激产生的氨基酸时，酵母从这种编辑活动中略微受益。但是，与大肠杆菌不同的是，当酵母在另一种氨基酸过量的情况下生长时，它强烈依赖于这种活性，这种氨基酸用于构建蛋白质，但却不是这种tRNA合成酶所需的氨基酸。Bullwinkle、Reynolds等人的发现将有助于我们更好地理解细胞中哪些活动最受蛋白质合成错误的影响，以及这些错误与疾病的关系。DOI: http://dx.doi.org/10.7554/eLife.02501.002
Aminoacyl-tRNA synthetases use a variety of mechanisms to ensure fidelity of the genetic code and ultimately select the correct amino acids to be used in protein synthesis. The physiological necessity of these quality control mechanisms in different environments remains unclear, as the cost vs benefit of accurate protein synthesis is difficult to predict. We show that in Escherichia coli, a non-coded amino acid produced through oxidative damage is a significant threat to the accuracy of protein synthesis and must be cleared by phenylalanine-tRNA synthetase in order to prevent cellular toxicity caused by mis-synthesized proteins. These findings demonstrate how stress can lead to the accumulation of non-canonical amino acids that must be excluded from the proteome in order to maintain cellular viability. DOI: http://dx.doi.org/10.7554/eLife.02501.001 Proteins are built from molecules called amino acids. The amino acids that make up a particular protein, and the order they appear in, are determined by the gene that encodes that protein. First, the gene is transcribed to produce a molecule of messenger RNA, which is then translated by a molecular machine called a ribosome. This involves other RNA molecules, called transfer RNAs (tRNAs), bringing the correct amino acids to the ribosome, which then joins the amino acids together to build the protein. Amino acids are loaded onto their corresponding tRNA molecules by enzymes called tRNA synthetases. Occasionally, however, the wrong amino acid can be loaded onto a tRNA. If this amino acid ends up in a protein, the protein might not be able to function properly, or it might even be toxic to the cell, so cells need to be able to fix this problem. Some tRNA synthetases can check if a wrong amino acid has been loaded onto a tRNA, and remove it before it can cause harm. However, the importance of these ‘editing’ activities to living cells is unclear. Here, Bullwinkle, Reynolds et al. show that, in the bacterium E. coli, a tRNA synthetase works to stop an incorrect amino acid—which accumulates in cells that are exposed to harmful chemicals—from being built into proteins. Without the enzyme’s editing activity, the build-up of this amino acid slows the growth of the bacteria. However, E. coli can thrive without this editing activity when it is grown under normal conditions in a laboratory. Yeast benefit slightly from this editing activity when exposed to the stress-produced amino acid. But, unlike E. coli, yeast strongly rely on this activity when grown in an excess of another amino acid, which is used to build proteins but is the wrong amino acid for this tRNA synthetase. The findings of Bullwinkle, Reynolds et al. will help to improve our understanding of which activities in a cell are most affected by mistakes in protein synthesis, and how these mistakes may relate to disease. DOI: http://dx.doi.org/10.7554/eLife.02501.002