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

至少有93个转录后修饰的核苷已被确定在tRNA。tRNA修饰酶必须识别它们的同源tRNA和tRNA内的修饰位点。对于这些酶中的许多酶，导致其高特异性的结构要求尚不清楚。真核甲基转移酶DNMT 2的特异性的结构基础，它引入了一个功能上重要的修改C38，将被解开的DNMT 2-tRNA复合物的晶体结构分析。这也将提供洞察甲基转移酶活性的刺激机制的超修饰的tRNA核苷腺苷在反密码子的位置34。在这方面，我们还将研究真核生物的tRNA-鸟嘌呤转糖基酶（TGT），它通过取代鸟嘌呤将鸟嘌呤引入tRNA。我们刚刚确定了人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。将分析关于tRNA结合的结果。特别是开放的问题，提出的TGT的磷酸化调节将得到解决。

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.