Bork P, Holm L, Koonin E V, Sander C
EMBL, Heidelberg, Germany.
Proteins. 1995 Jul;22(3):259-66. doi: 10.1002/prot.340220306.
The crystal structure of glycerol-3-phosphate cytidylyltransferase from B. subtilis (TagD) is about to be solved. Here, we report a testable structure prediction based on the identification by sequence analysis of a superfamily of functionally diverse but structurally similar nucleotide-binding enzymes. We predict that TagD is a member of this family. The most conserved region in this superfamily resembles the ATP-binding HiGH motif of class I aminoacyl-tRNA synthetases. The predicted secondary structure of cytidylyltransferase and its homologues is compatible with the alpha/beta topography of the class I aminoacyl-tRNA synthetases. The hypothesis of similarity of fold is strengthened by sequence-structure alignment and 3D model building using the known structure of tyrosyl tRNA synthetase as template. The proposed 3D model of TagD is plausible both structurally, with a well packed hydrophobic core, and functionally, as the most conserved residues cluster around the putative nucleotide binding site. If correct, the model would imply a very ancient evolutionary link between class I tRNA synthetases and the novel cytidylyltransferase superfamily.
枯草芽孢杆菌甘油-3-磷酸胞苷酰转移酶（TagD）的晶体结构即将被解析。在此，我们基于通过序列分析鉴定出的一个功能多样但结构相似的核苷酸结合酶超家族，报告了一个可验证的结构预测。我们预测TagD是这个家族的成员。该超家族中最保守的区域类似于I类氨酰-tRNA合成酶的ATP结合HiGH基序。胞苷酰转移酶及其同源物的预测二级结构与I类氨酰-tRNA合成酶的α/β拓扑结构相符。通过序列-结构比对以及以酪氨酰tRNA合成酶的已知结构为模板进行三维模型构建，折叠相似性的假设得到了加强。所提出的TagD三维模型在结构上是合理的，具有紧密堆积的疏水核心，在功能上也是合理的，因为最保守的残基聚集在假定的核苷酸结合位点周围。如果正确，该模型将意味着I类tRNA合成酶与新的胞苷酰转移酶超家族之间存在非常古老的进化联系。
