Conformational Activation of Aminoacyl-tRNA Synthetases upon Binding of tRNA. A Facet of a Multi-Step Adaptation Process Leading to the Optimal Biological Activity

Abstract

The activation of the catalytic center of aminoacyl-tRNA synthetases upon binding of the tRNA, previously reported in the case of yeast phenylalanyl-tRNA and valyl-tRNA synthetases was investigated in other systems. This property is encountered not only in cognate systems (phenylalanyl, valyl and arginyl) but also in the non-cognate systems which are particularly efficient in misaminoacylation reactions. The arginyl system, the peculiarity of which is to form the aminoacyladenylate only in the presence of the cognate tRNA, is a border-line case of this general process of catalytic center activation. In the phenylalanyl system, the crucial role of the wybutine residue (adjacent to the anticodon) in the activation of phenylalanyl-tRNA synthetase by the tRNA core was analyzed by comparison with native or modified non-cognate tRNAs (tRNATyr, tRNAArg). Upon complex formation between a tRNA and its cognate aminoacyl-tRNA synthetase, a multistep adaptation process may take place in order to promote the optimal rate for the aminoacylation reaction, thus contributing to the specificity of this reaction.