转移核糖核酸（transfer RNA, tRNA）是细胞中参与蛋白质合成的重要分子之一。tRNA上的核苷酸存在广泛修饰，这些修饰对于稳定tRNA的三级结构以及tRNA在细胞内发挥功能起着重要作用。 tRNA的第34位是反密码子上的第一位,为摇摆位点，该位核苷酸上存在众多修饰， 这些修饰对tRNA上反密码子与mRNA上密码子的精确识别很重要, 其修饰缺陷通常能引起细胞功能受损。TrmL是2010年被鉴定出来的催化两种亮氨酸tRNA等受体上第34位核苷酸2'-O-甲基化的修饰酶。TrmL属于SPOUT核酸甲基转移酶家族，然而与该家族其它成员不同，TrmL仅具有催化结构域却不具备专门的tRNA结合结构域。本项目拟通过酶学和结构生物学等方法研究TrmL的催化机理以及其与亮氨酸tRNA复合物的晶体结构， 试图阐明这种特殊的tRNA修饰酶的催化机制以及其与tRNA相互识别的新方式。

tRNAs play central roles in protein synthesis by transfer amino acids. Nucleotides in tRNA are often post-transcriptionally modified, which generally reinforces the tertiary structure of tRNA and accelerates its cellular function. Position 34 is the first wobble site in the anti-codon of tRNA, which is usually highly modified.Modifications at wobble nucleotide are essential to the precise recognition of anti-codon on tRNA to codon on mRNA, and lack of these modifications can cause some severe cellular deficiency in vivo. TrmL is one of the latest identified tRNA modification enzymes reported in 2010, which is responsible for the 2'-O-methylation at position 34 in two Leucine tRNA isoacceptors (CAA and UAA). TrmL belongs to the SAM-dependent SPOUT methyltransferase family. However, unlike the other SPOUT family members, TrmL is only comprised of a catalytic domain but lack of tRNA binding domain. In this proposal, we plan to study the mechanism of this special tRNA methyltransferase and try to solve the crystal structure of the complex of TrmL and tRNA. The mechanism study will illustrate the new catalytic mode of tRNA modification; In the meantime the structural study will uncover the unconventional inter-recognition mode between tRNA and its modification enzyme.