Misacylation of specific nonmethionyl tRNAs by a bacterial methionyl-tRNA synthetase
Misacylation of specific nonmethionyl tRNAs by a bacterial methionyl-tRNA synthetase
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DOI：
10.1073/pnas.1019033108
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发表时间：
2011-04-26
影响因子：
11.1
通讯作者：
Pan, Tao
中科院分区：
文献类型：
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作者：
Jones, Thomas E.;Alexander, Rebecca W.;Pan, Tao
氨酰-tRNA合成酶通过氨酰化tRNA及其同源氨基酸来执行翻译中的关键步骤。虽然氨酰-tRNA合成酶的高保真度通常被认为是细胞生物学所必需的，但最近的研究表明，在某些条件下，细胞耐受甚至可能受益于tRNA的错酰化。例如，哺乳动物细胞选择性地诱导非甲硫氨酰tRNA的错甲硫氨酰化，并且这种类型的错酰化有助于细胞对氧化应激的反应。然而，负责tRNA错甲硫氨酸化的酶和特定tRNA被错甲硫氨酸化的机制尚未阐明。在这里，我们通过tRNA微阵列和过滤器保留表明，来自大肠杆菌的甲硫氨酰-tRNA合成酶（EcMRS）足以使两种tRNA物质，tRNA（CCU）（Arg）和tRNA（CGU）（Thr）发生错误甲硫氨酰化，这表明tRNA错误甲硫氨酰化也存在于细菌的生命领域中。我们证明了这些错酰化的tRNA的反密码子核苷酸在赋予错误甲硫氨酸化身份中起着关键作用。我们还表明，这些tRNA保持一定的低水平的甲硫氨酸化，这表明甲硫氨酸化水平可能已经演变为赋予细胞益处，同时仍然保持足够的翻译保真度，以确保细胞活力。EcMRS突变体表现出不同的影响蛋氨酸错，这表明在这种合成酶的许多地区的影响蛋氨酸错。我们的研究结果表明，tRNA的错甲硫氨酸化可以由一个单一的蛋白酶进行，错甲硫氨酸化也需要在tRNA的身份元素，和EcMRS有一个明确的结构-功能关系的tRNA错甲硫氨酸化。
Aminoacyl-tRNA synthetases perform a critical step in translation by aminoacylating tRNAs with their cognate amino acids. Although high fidelity of aminoacyl-tRNA synthetases is often thought to be essential for cell biology, recent studies indicate that cells tolerate and may even benefit from tRNA misacylation under certain conditions. For example, mammalian cells selectively induce mismethionylation of nonmethionyl tRNAs, and this type of misacylation contributes to a cell's response to oxidative stress. However, the enzyme responsible for tRNA mismethionylation and the mechanism by which specific tRNAs are mismethionylated have not been elucidated. Here we show by tRNA microarrays and filter retention that the methionyl-tRNA synthetase enzyme from Escherichia coli (EcMRS) is sufficient to mismethionylate two tRNA species, tRNA(CCU)(Arg) and tRNA(CGU)(Thr), indicating that tRNA mismethionylation is also present in the bacterial domain of life. We demonstrate that the anticodon nucleotides of these misacylated tRNAs play a critical role in conferring mismethionylation identity. We also show that a certain low level of mismethionylation is maintained for these tRNAs, suggesting that mismethionylation levels may have evolved to confer benefits to the cell while still preserving sufficient translational fidelity to ensure cell viability. EcMRS mutants show distinct effects on mismethionylation, indicating that many regions in this synthetase enzyme influence mismethionylation. Our results show that tRNA mismethionylation can be carried out by a single protein enzyme, mismethionylation also requires identity elements in the tRNA, and EcMRS has a defined structure-function relationship for tRNA mismethionylation.