Researchers Identified a Novel Component of Mammalian Multiple tRNA Synthetase Complex
On July 9,《Nucleic Acids Research》online published a new joint work from Prof. ZHOU Xiaolong’s group and Prof. WANG Enduo’s group in Shanghai Institute of Biochemistry and Cell Biology entitled “Newly acquired N-terminal extension targets threonyl-tRNA synthetase-like protein into the multiple tRNA synthetase complex”.
In mammalian cytoplasm, nine aminoacyl-tRNA synthetases (aaRSs) (ArgRS, AspRS, GlnRS, GluProRS, IleRS, LeuRS, MetRS, LysRS, respectively) with three auxiliary scaffold protein co-factors (AIMP1/p43, AMIP2/p38 and AIMP3/p18) form a multiple tRNA synthetase complex (MSC). Little is known about the structure and significance of the MSC. It is previously believed that there are 37 aaRS genes in human cells, encoding full sets of aaRSs for both cytoplasmic and mitochondrial protein synthesis. However, an aaRS-duplicated gene, TARSL2 was identified in 2013 for the first time in Prof. Wang’s lab, which encodes a threonyl-tRNA synthetase (ThrRS)-like protein (ThrRS-L) (Nucleic Acids Res., 2013). ThrRS-L shares high similarity with canonical ThrRS in the N1, N2, aminoacylation and C-terminal tRNA binding domains; however, it has evolved a quite different N-terminal extension (N-extension) from that of ThrRS. Recently, they further revealed that the mRNA of mouse Tarsl2 is present at significantly lower levels than that of Tars in various mouse tissues and mouse cell lines with most enriched proteins in the muscle and heart. Interestingly, mThrRS-L is able to locate to the nucleus and, in vitro, can catalyze aminoacylation with similar efficiency despite having decreased editing activity and a distinct cross-species tRNA recognition capability compared with those of mouse ThrRS (mThrRS) (Nucleic Acids Res., 2018).
In this new work, they found the first half of the N-extension of human ThrRS-L (hThrRS-L) is homologous to that of human ArgRS. Using the N-extension as a probe in a yeast two-hybrid screening, p43 was identified as an interactor with hThrRS-L. They showed that ThrRS-L is a novel component of the MSC, and is reliant on two leucine zippers in the N-extension for MSC-incorporation in humans, and mouse cell lines and muscle tissue. The N-extension was sufficient to target a foreign protein into the MSC. The results from a Tarsl2-deleted cell line showed that it does not mediate MSC integrity. The effect of phosphorylation at various sites of hThrRS-L on its MSC-targeting is also explored. In summary, they revealed that ThrRS-L is a bona fide component of the MSC, which is mediated by a newly evolved N-extension domain.
Overall, this work identified a novel component of the MSC complex and clarified its incorporation mechanism into the MSC. It provides new insights into MSC formation and new basis for further studies of potential non-canonical functions of ThrRS-L.
This work was supported by grants from the National Key Research and Development Program of China; National Natural Science Foundation of China; Strategic Priority Research Program of the Chinese Academy of Sciences; Youth Innovation Promotion Association, CAS; and Shanghai Rising-Star Program.