Department of Molecular Biology, University Medical Centre Göttingen, Humboldtallee 23, 37073, Göttingen, Germany.
Institute of Organic Chemistry, Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
Nat Commun. 2022 Jan 11;13(1):209. doi: 10.1038/s41467-021-27905-1.
Modified nucleotides in tRNAs are important determinants of folding, structure and function. Here we identify METTL8 as a mitochondrial matrix protein and active RNA methyltransferase responsible for installing mC in the human mitochondrial (mt-)tRNA and mt-tRNA. METTL8 crosslinks to the anticodon stem loop (ASL) of many mt-tRNAs in cells, raising the question of how methylation target specificity is achieved. Dissection of mt-tRNA recognition elements revealed UG and tA/(ms)iA, present concomitantly only in the ASLs of the two substrate mt-tRNAs, as key determinants for METTL8-mediated methylation of C. Several lines of evidence demonstrate the influence of U, G, and the mC and tA/(ms)iA modifications in mt-tRNA on the structure of these mt-tRNAs. Although mt-tRNA lacking METTL8-mediated mC are efficiently aminoacylated and associate with mitochondrial ribosomes, mitochondrial translation is mildly impaired by lack of METTL8. Together these results define the cellular targets of METTL8 and shed new light on the role of mC within mt-tRNAs.
tRNA 中的修饰核苷酸是折叠、结构和功能的重要决定因素。在这里，我们鉴定出 METTL8 是一种线粒体基质蛋白和活性 RNA 甲基转移酶，负责在人类线粒体（mt-）tRNA 和 mt-tRNA 中安装 mC。METTL8 在细胞中与许多 mt-tRNA 的反密码子茎环（ASL）交联，这引发了一个问题，即如何实现甲基化靶标特异性。对 mt-tRNA 识别元件的剖析揭示了 UG 和 tA/(ms)iA，它们仅同时存在于两个底物 mt-tRNA 的 ASL 中，是 METTL8 介导的 C 甲基化的关键决定因素。有几条证据表明 mt-tRNA 中的 U、G 以及 mC 和 tA/(ms)iA 修饰影响这些 mt-tRNA 的结构。尽管缺乏 METTL8 介导的 mC 的 mt-tRNA 能够有效地被氨酰化并与线粒体核糖体结合，但缺乏 METTL8 会轻微损害线粒体翻译。这些结果共同定义了 METTL8 的细胞靶标，并为 mt-tRNA 中的 mC 作用提供了新的见解。
