TRMT1是N2-甲基鸟苷(m2G)和N2,N2-甲基鸟苷(m22G)甲基转移酶,其靶向细胞质和线粒体tRNA的G26。在高等真核生物中,大多数带有G26的细胞质tRNA携带m22G26,尽管大多数含线粒体G26的tRNA携带m2G26或G26,这表明TRMT1催化这些tRNA修饰的机制存在差异。人TRMT1的功能缺失突变导致神经系统疾病,并完全消除了tRNA:m22G26的形成。然而,人TRMT1的独立催化活性及其特定底物的身份的机制仍然难以捉摸,阻碍了对TRMT1突变引起的神经系统疾病发病机制的全面了解。这里,我们表明,人TRMT1独立催化tRNA的形成:m2G26或m22G26修饰以底物依赖的方式,这解释了m2G26和m22G26在细胞质和线粒体tRNA上的不同分布。对于人TRMT1介导的tRNA:m22G26形成,半保守的C11:G24作为决定因素,U10:A25或G10:C25碱基对也是必需的,而变量循环的大小没有影响。我们将这种识别机制的要求定义为“m22G26标准”。我们发现m22G26修饰发生在几乎所有符合这些标准的高级真核tRNA中,这表明“m22G26标准”适用于其他高等真核tRNA。
TRMT1 is an N2-methylguanosine (m2G) and N2,N2-methylguanosine (m22G) methyltransferase that targets G26 of both cytoplasmic and mitochondrial tRNAs. In higher eukaryotes, most cytoplasmic tRNAs with G26 carry m22G26, although the majority of mitochondrial G26-containing tRNAs carry m2G26 or G26, suggesting differences in the mechanisms by which
TRMT1 catalyzes modification of these tRNAs. Loss-of-function mutations of human
TRMT1 result in neurological disorders and completely abrogate tRNA:m22G26 formation. However, the mechanism underlying the independent catalytic activity of human
TRMT1 and identity of its specific substrate remain elusive, hindering a comprehensive understanding of the pathogenesis of neurological disorders caused by TRMT1 mutations. Here, we showed that human TRMT1 independently catalyzes formation of the tRNA:m2G26 or m22G26 modification in a substrate-dependent manner, which explains the distinct distribution of m2G26 and m22G26 on cytoplasmic and mitochondrial tRNAs. For human
TRMT1-mediated tRNA:m22G26 formation, the semi-conserved C11:G24 serves as the determinant, and the U10:A25 or G10:C25 base pair is also required, while the size of the variable loop has no effect. We defined the requirements of this recognition mechanism as the \"m22G26 criteria\". We found that the m22G26 modification occurred in almost all the higher eukaryotic tRNAs conforming to these criteria, suggesting the \"m22G26 criteria\" are applicable to other higher eukaryotic tRNAs.