Modeling the reactive properties of tandemly activated tRNAs

Tandemly activated tRNAs, bearing amino acid moieties at both the 2'- and 3'-positions of the 3'-terminal adenosine moiety (A(76)), have been shown to participate efficiently in protein synthesis [B. Wang, J. Zhou, M. Lodder, R. D. Anderson, III and S. M. Hecht, J. Biol. Chem., 2006, 281, 13865]. The mechanism by which such activated tRNAs are able to donate both amino acids to the growing polypeptide chain is not well understood. Here we report the chemical behavior and participation in protein synthesis of new bisaminoacyl derivatives of pdCpA and tRNA. Both amino moieties of the aminoacyl groups are shown to be important to enable participation in protein synthesis; paradoxically, they also confer an unanticipated chemical stability toward different nucleophiles. The results obtained suggest a model for participation of bisaminoacylated tRNAs in protein synthesis.