Species-specific differences in amino acid editing by class II prolyl-tRNAsynthetase

Aminoacyl-tRNA synthetases are a family of enzymes responsible for ensuring the accuracy of the genetic code by specifically attaching a particular am ino acid to their cognate tRNA substrates. Through primary sequence alignme nts, prolyl-tRNA synthetases (ProRSs) have been divided into two phylogenet ically divergent groups. We have been interested in understanding whether t he unusual evolutionary pattern of ProRSs corresponds to functional differe nces as well. Previously, we showed that some features of tRNA recognition and aminoacylation are indeed group-specific. Here, we examine the species- specific differences in another enzymatic activity, namely amino acid editi ng. Proofreading or editing provides a mechanism by which incorrectly activ ated amino acids are hydrolyzed and thus prevented from misincorporation in to proteins. "Prokaryotic-like" Escherichia coli ProRS has recently been sh own to be capable of misactivating alanine and possesses both pretransfer a nd post-transfer hydrolytic editing activity against this noncognate amino acid. We now find that two ProRSs belonging to the "eukaryotic-like" group exhibit differences in their hydrolytic editing activity. Whereas ProRS fro m Methanococcus jannaschii is similar to E. coli in its ability to hydrolyz e misactivated alanine via both pretransfer and post-transfer editing pathw ays, human ProRS lacks these activities. These results have implications fo r the selection or design of antibiotics that specifically target the editi ng active site of the prokaryotic-like group of ProRSs.