Leucyl-tRNA synthetase (LeuRS) catalyzes the esterification of leucine (Leu) to its cognate tRNALeu in a two-step reaction, supplying the building blocks, aminoacyl-tRNAs (aa-tRNAs) for protein biosynthesis. During evolution, LeuRS, together with other two aminoacyl-tRNA synthetases (AARSs), gradually fused CP1 domain as their editing domain. They could perform their pre-transfer editing and post-transfer editing activities by hydrolyzing mis-activated product (aa-AMP) or mis-aminoacylated product (aa-tRNA) and guarantee aminoacylation accuracy.
Usually LeuRSs use the CP1 domain to exclude tRNA mis-charging with non-cognate amino acids; and in some species which have no requirement for high translational fidelity, LeuRSs’ CP1 domain are evolutionarily truncated or lost. Intriguingly, human mitochondrial LeuRS (hmtLeuRS) contains a full-length but degenerate CP1 domain, which has mutations in some residues important for post-transfer editing. Why hmtLeuRS still keeps this defunct CP1 domain and how hmtLeuRS achieves the translational accuracy remain unclear.
Recently, graduate students YE Qing et al, under the supervision of Prof. WANG Enduo and Dr. ZHOU Xiaolong, at the Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, CAS, identified the essential role of evolutionarily divergent CP1 domain in facilitating hmtLeuRS’s catalytic efficiency and endowing enzyme with resistance to AN2690, broad-spectrum drug acting on LeuRSs. In addition, they found hmtLeuRS could mis-activate non-cognate norvaline (Nva) and valine (Val). HmtLeuRS has neither post-transfer editing nor tRNA-dependent pre-transfer editing; it only exhibits a very weak tRNA-independent pre-transfer editing activity for Nva, which is insufficient to remove mis-activated Nva. HmtLeuRS could catalyze the formation of a considerable amount of Nva-tRNALeu and a trace amount of Val-tRNALeu in vitro. Besides, hmtLeuRS chimeras fused with a functional CP1 domain from LeuRSs of other species, regardless of origin, showed restored post-transfer editing activity, and acquired fidelity during aminoacylation. Taken together, their present work shows that the degenerate CP1 domain, which contributes to enzyme’s aminoacylation efficiency, is not redundant in hmtLeuRS and facilitates our understanding towards quality control of protein synthesis in mitochondrial system.
This work, entitled “Degenerate CP1 Domain from Human Mitochondrial Leucyl-tRNA Synthetase”, was published online in Journal of Biological Chemistry on August 13, 2015 and was supported by grants from the National Natural Science Foundation of China, the Ministry of Science and Technology of China, the Chinese Academy of Sciences and the Science and Technology Commission of Shanghai Municipality.
AUTHOR CONTACT:
WANG Enduo
Shanghai Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences,
Shanghai, China
Phone: 86-21-54921241;
E-mail: edwang@sibcb.ac.cn
Figure. Alignment of active sites in CP1 domain from various LeuRSs
(Image provided by Prof. WANG Enduo’s group)
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