Human cytosolic leucyl-tRNA synthetase (hcLRS) is an essential and multifunctional enzyme. Its canonical function is to catalyze the covalent ligation of leucine to tRNALeu, and it may also hydrolyze mischarged tRNAs through an editing mechanism. Together with eight other aminoacyl-tRNA synthetases (AaRSs) and three auxiliary proteins, it forms a large multi-synthetase complex (MSC). Beyond its role in translation, hcLRS has an important moonlight function as a leucine sensor in the rapamycin complex 1 (mTORC1) pathway. Since this pathway is active in cancer development, hcLRS is a potential target for anti-tumor drug development. Moreover, LRS from pathogenic microbes are proven drug targets for developing antibiotics, which however should not inhibit hcLRS. Here we present the crystal structure of hcLRS at a 2.5 Å resolution, the first complete structure of a eukaryotic LRS, and analyze the binding of various compounds that target different sites of hcLRS. We also deduce the assembly mechanism of hcLRS into the MSC through reconstitution of the entire mega complex in vitro. Overall, our study provides the molecular basis for understanding both the multifaceted functions of hcLRS and for drug development targeting these functions.

中文翻译：

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人类亮氨酰tRNA合成酶在蛋白质合成及其他方面的多方面功能的分子基础。

人胞质亮氨酰tRNA合成酶（hcLRS）是必不可少的多功能酶。它的规范功能是催化亮氨酸与tRNALeu的共价连接，并且它还可以通过编辑机制水解带错电荷的tRNA。它与其他八种氨酰基-tRNA合成酶（AaRSs）和三种辅助蛋白一起，形成了一个大型的多合成酶复合物（MSC）。hcLRS除了在翻译中的作用外，还具有重要的月光功能，可作为雷帕霉素复合物1（mTORC1）途径中的亮氨酸传感器。由于该途径在癌症发展中很活跃，因此hcLRS是抗肿瘤药物发展的潜在目标。此外，来自病原微生物的LRS已被证明是开发抗生素的药物靶标，但不应抑制hcLRS。在这里，我们介绍了hcLRS的晶体结构，分辨率为2.5Å，真核LRS的第一个完整结构，并分析靶向hcLRS不同位点的各种化合物的结合。我们还通过在体外重建整个大型复合体，推导了hcLRS进入MSC的组装机制。总体而言，我们的研究为理解hcLRS的多方面功能以及针对这些功能的药物开发提供了分子基础。