tRNA-dependent Pre-transfer Editing by Prokaryotic Leucyl-tRNA Synthetase

On January 29, 2010, the lab of Professor En-Duo Wang in the Institute of Biochemistry and Cell Biology published a paper entitled “tRNA-dependent pre-transfer editing by prokaryotic leucyl-tRNA synthetase” in The Journal of Biological Chemistry (Vol. 285, pp 3235-3244).

 

Aminoacyl-tRNA synthetase (aaRS) catalyzes the ligation between cognate amino acid and tRNA to form cognate aminoacyl-tRNA for protein biosynthesis on the ribosome. The correct recognition of aaRS to its cognate amino acid and tRNA ensure the accuracy from mRNA translation to protein; otherwise, it will synthesize non-cognate aminoacyl-tRNA, leading to the mutation of newly-synthesized protein and then abnormal cells. Some aaRSs misactivate and mischarge noncognate amino acid and have proofreading (editing) activity to remove the incorrect products to maintain the fidelity of protein biosynthesis. The lab of Professor En-Duo Wang has identified the post-transfer editing and tRNA-independent pre-transfer editing of leucy-tRNA synthetase (LeuRS) in 2000 and 2009, respectively.

 

In the present paper, Min Tan, Bin Zhu, and Xiao-Long Zhou showed that LeuRS from Escharicha coli and Aquifex aeolicus possess tRNA-dependent pre-transfer editing and analyzed the contribution of different editing pathways in the whole editing process, by using point mutagenesis and an inhibitor LeuRS, AN2690 targeted post-transfer editing active site. The study emphasizes the crucial importance of tRNA for the pre- and post-transfer editing catalysis. Both reactions have comparable efficiencies in prokaryotic Aquifex aeolicus and Escherichia coli LeuRSs, although the E. coli enzyme favors post-transfer editing, whereas the A. aeolicus enzyme favors pre-transfer editing. The results also indicate that the entry of the CCA-acceptor end of tRNA in the editing domain is strictly required for tRNA-dependent pre-transfer editing.

 

Surprisingly, this editing reaction was resistant to AN2690, which inactivates the enzyme by forming a covalent adduct with tRNA(Leu) in the post-transfer editing site. Taken together, these data suggest that the binding of tRNA in the post-transfer editing conformation confers to the enzyme the capacity for pre-transfer editing catalysis, regardless of its capacity to catalyze post-transfer editing. The systematic studies in the lab of Professor En-Duo Wang show that check point for quality control is present at every reaction step of aminoacylation catalyzed by aaRS to remove noncognate amino acid and ensure high fidelity of protein biosynthesis.

 

The research work was fund by the Chinese Academy of Sciences, Natural Science Foundation of China, National Key Basic Research Foundation of China, and Committee of Science and Technology in Shanghai.