Leucyl-tRNA synthetase from the ancestral bacterium Aquifex aeolicus contains relics of synthetase evolution

摘要

The editing reactions catalyzed by aminoacyl-tRNA synthetases are critical for the faithful protein synthesis by correcting misactivated amino acids and misaminoacylated tRNAs. We report that the isolated editing domain of leucyl-tRNA synthetase from the deep-rooted bacterium Aquifex aeolicus (αβ-LeuRS) catalyzes the hydrolytic editing of both mischarged tRNA^Leu and minihelix^Leu. Within the domain, we have identified a crucial 20-amino-acid peptide that confers editing capacity when transplanted into the inactive Escherichia coli LeuRS editing domain. Likewise, fusion of the β-subunit of αβ-LeuRS to the E. coli editing domain activates its editing function. These results suggest that αβ-LeuRS still carries the basic features from a primitive synthetase molecule. It has a remarkable capacity to transfer autonomous active modules, which is consistent with the idea that modern synthetases arose after exchange of small idiosyncratic domains. It also has a unique αβ-heterodimeric structure with separated catalytic and tRNA-binding sites. Such an organization supports the tRNA/synthetase coevolution theory that predicts sequential addition of tRNA and synthetase domains.