title: Anticodon recognition in evolution: switching tRNA specificity of an aminoacyl-tRNA synthetase by site-directed peptide transplantation.
abstract: The highly conserved aspartyl-, asparaginyl-, and lysyl-tRNA synthetases compose one subclass of aminoacyl-tRNA synthetases, called IIb. The three enzymes possess an OB-folded extension at their N terminus. The function of this extension is to specifically recognize the anticodon triplet of the tRNA. Three-dimensional models of bacterial aspartyl- and lysyl-tRNA synthetases complexed to tRNA indicate that a rigid scaffold of amino acid residues along the five beta-strands of the OB-fold accommodates the base U at the center of the anticodon. The binding of the adjacent anticodon bases occurs through interactions with a flexible loop joining strands 4 and 5 (L45). As a result, a switching of the specificity of lysyl-tRNA synthetase from tRNALys (anticodon UUU) toward tRNAAsp (GUC) could be attempted by transplanting the small loop L45 of aspartyl-tRNA synthetase inside lysyl-tRNA synthetase. Upon this transplantation, lysyl-tRNA synthetase loses its capacity to aminoacylate tRNALys. In exchange, the chimeric enzyme acquires the capacity to charge tRNAAsp with lysine. Upon giving the tRNAAsp substrate the discriminator base of tRNALys, the specificity shift is improved. The change of specificity was also established in vivo. Indeed, the transplanted lysyl-tRNA synthetase succeeds in suppressing a missense Lys --> Asp mutation inserted into the beta-lactamase gene. These results functionally establish that sequence variation in a small peptide region of subclass IIb aminoacyl-tRNA synthetases contributes to specification of nucleic acid recognition. Because this peptide element is not part of the core catalytic structure, it may have evolved independently of the active sites of these synthetases.
authors.affiliation: Laboratoire de Biochimie, Unité Mixte de Recherche 7654, CNRS-Ecole Polytechnique, 91128 Palaiseau Cedex, France.
authors.forename: Annie
authors.initials: A
authors.lastname: Brevet
authors.forename: Josiane
authors.initials: J
authors.lastname: Chen
authors.forename: Stéphane
authors.initials: S
authors.lastname: Commans
authors.forename: Christine
authors.initials: C
authors.lastname: Lazennec
authors.forename: Sylvain
authors.initials: S
authors.lastname: Blanquet
authors.forename: Pierre
authors.initials: P
authors.lastname: Plateau
mesh_terms: D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000926:Anticodon / Q000235:genetics*; D001224:Aspartic Acid / Q000235:genetics; D020134:Catalytic Domain; D017124:Conserved Sequence; D004926:Escherichia coli / Q000235:genetics*; D019143:Evolution, Molecular; D008239:Lysine / Q000235:genetics; D020125:Mutation, Missense; D009690:Nucleic Acid Conformation; D012343:RNA, Transfer / Q000737:chemistry / Q000235:genetics*; D013379:Substrate Specificity
chemical_list: D000926:Anticodon; D001224:Aspartic Acid; D012343:RNA, Transfer; D000604:Amino Acyl-tRNA Synthetases; D008239:Lysine