Aminoacylation of tRNA Induces a Conformational Switch on the 3’-Terminal Ribose

Abstract

The 3’-terminal adenosine-76 in tRNA is an important recognition element for the interaction of tRNA or aminoacyl-tRNA with proteins and nucleic acids. The aromatic adenine-76 is usually located in a lipophilic binding pocket of the tRNA binding proteins. The ribofuranose ring of nucleosides is not planar and can adopt a C3’-endo-C2’-exo (north sugar, N) or C2’-endo-C3’-exo (south sugar, S) conformation. This sugar pucker defines the position of the nucleobase attached to Cl’ either in the axial or equatorial position. The conformation of the ribose residues in the RNA is determined by the electronic nature of the sugar ring and its substituents as well as by the chemical nature and stacking interactions of the nucleobase. Using a fluorescent analogue of tRNA, tRNA-CCF, we demonstrate, that the aminoacylation of the tRNA results in a conformational change of the 3’-terminal nucleobase. The increase of the fluorescence intensity of formycin in tRNA-CCF¹ upon aminoacylation is explained by partial destacking of the 3’-terminal base moiety. Several analogues of anminoacyl-tRNA which were modified on 3’-terminal ribose were tested in their ability to interact with elongation factor Tu.GTP complex. The results indicate that the aminoacylation of the ribose in the tRNA triggers a conformational N⇋S ribose switch which determines the position of adenine-76 for recognition by the elongation factor Tu.