Structural and functional analysis of the tRNA-modifying enzymes DNMT2 and tRNA-guanine-transglycosylase

在trna中已经鉴定出至少93种转录后修饰的核苷。tRNA修饰酶必须识别其同源tRNA(s)和在tRNA内的修饰位点。对于许多这些酶的结构要求导致它们的高特异性尚不清楚。真核甲基转移酶DNMT2引入了C38的重要功能修饰，其特异性的结构基础将通过DNMT2- trna复合物的晶体结构分析来揭示。这也将为反密码子第34位超修饰tRNA核苷队列苷刺激甲基转移酶活性的机制提供见解。在这方面，我们还将研究真核trna -鸟嘌呤-转糖基酶（TGT），它通过取代鸟嘌呤引入trna中的排队。我们刚刚确定了人类TGT的晶体结构，并揭示了与细菌TGT在四级结构上的意想不到的差异。我们将分析与tRNA结合有关的结果。特别开放的问题，关于拟议的调节TGT的磷酸化将被解决。

At least 93 post-transcriptionally modified nucleosides have been identified in tRNAs. tRNA-modifying enzymes have to identify their cognate tRNA(s) and within the tRNA the site of modification. For many of these enzymes the structural requirements leading to their high specificity are yet unknown. The structural basis for the specificity of the eukaryotic methyltransferase DNMT2, which introduces a functionally important modification of C38, will be unraveled by the crystal structure analysis of a DNMT2-tRNA complex. This will also provide insights into the mechanism of stimulation of the methyltransferase activity by the hypermodified tRNA nucleoside queuosine at position 34 in the anticodon. With that respect, we will also study the eukaryotic tRNA-guanine-transglycosylase (TGT), which introduces queuine in tRNAs by replacing the guanine. The crystal structure of human TGT was just determined by us, and revealed unexpected differences in the quaternary structure with regard to the bacterial TGT. The resulting consequences concerning tRNA binding will be analyzed. Particularly open questions regarding the proposed regulation of TGT by phosphorylation will be addressed.