Liu Yunqing, Liao Jing, Zhu Bin, Wang En-Duo, Ding Jianping
Key Laboratory of Proteomics, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue-Yang Road, Shanghai 200031, China.
Biochem J. 2006 Mar 1;394(Pt 2):399-407. doi: 10.1042/BJ20051249.
aaRSs (aminoacyl-tRNA synthetases) are responsible for the covalent linking of amino acids to their cognate tRNAs via the aminoacylation reaction and play a vital role in maintaining the fidelity of protein synthesis. LeuRS (leucyl-tRNA synthetase) can link not only the cognate leucine but also the nearly cognate residues Ile and Met to tRNA(Leu). The editing domain of LeuRS deacylates the mischarged Ile-tRNA(Leu) and Met-tRNA(Leu). We report here the crystal structures of ecLeuRS-ED (the editing domain of Escherichia coli LeuRS) in both the apo form and in complexes with Met and Ile at 2.0 A, 2.4 A, and 3.2 A resolution respectively. The editing active site consists of a number of conserved amino acids, which are involved in the precise recognition and binding of the noncognate amino acids. The substrate-binding pocket has a rigid structure which has an optimal stereochemical fit for Ile and Met, but has steric hindrance for leucine. Based on our structural results and previously available biochemical data, we propose that ecLeuRS-ED uses a lock-and-key mechanism to recognize and discriminate between the amino acids. Structural comparison also reveals that all subclass Ia aaRSs share a conserved structure core consisting of the editing domain and conserved residues at the editing active site, suggesting that these enzymes may use a common mechanism for the editing function.
氨酰-tRNA合成酶（aaRSs）负责通过氨酰化反应将氨基酸与其对应的tRNA共价连接，在维持蛋白质合成的保真度方面发挥着至关重要的作用。亮氨酰-tRNA合成酶（LeuRS）不仅可以将对应的亮氨酸连接到tRNA(Leu)上，还可以将几乎对应的异亮氨酸和甲硫氨酸连接到tRNA(Leu)上。LeuRS的编辑结构域可使错误负载的异亮氨酰-tRNA(Leu)和甲硫氨酰-tRNA(Leu)脱酰基。我们在此报告了大肠杆菌LeuRS的编辑结构域（ecLeuRS-ED）分别以apo形式以及与甲硫氨酸和异亮氨酸形成复合物时的晶体结构，分辨率分别为2.0 Å、2.4 Å和3.2 Å。编辑活性位点由许多保守氨基酸组成，这些氨基酸参与对非对应氨基酸的精确识别和结合。底物结合口袋具有刚性结构，对异亮氨酸和甲硫氨酸具有最佳的立体化学契合度，但对亮氨酸存在空间位阻。基于我们的结构结果和先前可得的生化数据，我们提出ecLeuRS-ED使用锁钥机制来识别和区分氨基酸。结构比较还表明，所有Ia亚类aaRSs都共享一个由编辑结构域和编辑活性位点的保守残基组成的保守结构核心，这表明这些酶可能使用共同的机制来实现编辑功能。
