Liu H, Kessler J, Peterson R, Musier-Forsyth K
Department of Chemistry, University of Minnesota, Minneapolis 55455, USA.
Biochemistry. 1995 Aug 1;34(30):9795-800. doi: 10.1021/bi00030a017.
Aminoacyl-tRNA synthetases have been divided into two classes based on the existence of two structurally distinct active sites. To date, few class-specific tRNA recognition features have been elucidated. High-resolution X-ray structures of representative class I and class II synthetases complexed to cognate tRNA substrates have been solved. In these structures, the class I enzyme approaches the end of the tRNA acceptor stem from the minor-groove side, while the class II synthetase approaches its cognate tRNA from the major-groove side. This distinction is reflected in the different initial sites (2'- or 3'-OH) of amino acid attachment. The role that the semiconserved G1.C72 terminal base pair plays in the aminoacylation of Escherichia coli tRNAs is probed in this in vitro study. We show here that class II alanyl-, prolyl-, and histidyl-tRNA synthetases are sensitive to changes at position 1 x 72. Previous work on class I synthetases and new data presented here with the valine-specific enzyme indicate that class I enzymes show little sensitivity to replacements of G1.C72. This work provides new evidence for class-specific differences in tRNA acceptor stem interactions that appear to be reflected not only in the initial site of aminoacylation but also in the mode of synthetase interaction with the semiconserved G1.C72 base pair proximal to the amino acid attachment site.
基于两个结构不同的活性位点的存在，氨酰 - tRNA合成酶已被分为两类。迄今为止，很少有特定类别的tRNA识别特征被阐明。已解析出与同源tRNA底物复合的代表性I类和II类合成酶的高分辨率X射线结构。在这些结构中，I类酶从小沟侧接近tRNA受体茎的末端，而II类合成酶从大沟侧接近其同源tRNA。这种差异反映在氨基酸连接的不同起始位点（2'-或3'-OH）上。在这项体外研究中，探讨了半保守的G1.C72末端碱基对在大肠杆菌tRNA氨酰化中的作用。我们在此表明，II类丙氨酰 -、脯氨酰 - 和组氨酰 - tRNA合成酶对1×72位的变化敏感。先前关于I类合成酶的工作以及此处给出的缬氨酸特异性酶的新数据表明，I类酶对G1.C72的替换几乎不敏感。这项工作为tRNA受体茎相互作用中特定类别的差异提供了新证据，这种差异似乎不仅反映在氨酰化的起始位点，还反映在合成酶与氨基酸连接位点近端的半保守G1.C72碱基对的相互作用模式中。
