title: Retracing the evolution of amino acid specificity in glutaminyl-tRNA synthetase.
abstract: Molecular phylogenetic studies of glutaminyl-tRNA synthetase suggest that it has relatively recently evolved from the closely related enzyme glutamyl-tRNA synthetase. We have now attempted to retrace one of the key steps in this process by selecting glutaminyl-tRNA synthetase mutants displaying enhanced glutamic acid recognition. Mutagenesis of two residues proximal to the active site, Phe-90 and Tyr-240, was found to improve glutamic acid recognition 3-5-fold in vitro and resulted in the misacylation of tRNA(Gln) with glutamic acid. In vivo expression of the genes encoding these misacylating variants of glutaminyl-tRNA synthetase reduced cellular growth rates by 40%, probably as a result of an increase in translational error rates. These results provide the first biochemical evidence that glutaminyl-tRNA synthetase originated through duplication and consequent diversification of an ancestral glutamyl-tRNA synthetase-encoding gene.
authors.affiliation: Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114, USA.
authors.forename: K W
authors.initials: KW
authors.lastname: Hong
authors.forename: M
authors.initials: M
authors.lastname: Ibba
authors.forename: D
authors.initials: D
authors.lastname: Söll
mesh_terms: D000595:Amino Acid Sequence; D000604:Amino Acyl-tRNA Synthetases / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D019143:Evolution, Molecular; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D016415:Sequence Alignment
chemical_list: D018698:Glutamic Acid; D000604:Amino Acyl-tRNA Synthetases; C020659:glutaminyl-tRNA synthetase