Coordination of tRNA synthetase active sites for chemical fidelity.

Statistical proteomes that are naturally occurring can result from mechanisms involving aminoacyl-tRNA synthetases (aaRSs) with inactivated hydrolytic editing active sites. In one case, Mycoplasma mobile leucyl-tRNA synthetase (LeuRS) is uniquely missing its entire amino acid editing domain, called CP1, which is otherwise present in all known LeuRSs and also isoleucyl- and valyl-tRNA synthetases. This hydrolytic CP1 domain was fused to a synthetic core composed of a Rossmann ATP-binding fold. The fusion event splits the primary structure of the Rossmann fold into two halves. Hybrid LeuRS chimeras using M. mobile LeuRS as a scaffold were constructed to investigate the evolutionary protein:protein fusion of the CP1 editing domain to the Rossmann fold domain that is ubiquitously found in kinases and dehydrogenases, in addition to class I aaRSs. Significantly, these results determined that the modular construction of aaRSs and their adaptation to accommodate more stringent amino acid specificities included CP1-dependent distal effects on amino acid discrimination in the synthetic core. As increasingly sophisticated protein synthesis machinery evolved, the addition of the CP1 domain increased specificity in the synthetic site, as well as provided a hydrolytic editing site.