Biochemistry and Biology of Aminoacyl-tRNA-Protein Transferases

Abstract

The critical role played by aminoacyl-tRNA in protein biosynthesis has tended to obscure its participation as an aminoacyl donor in a number of other biological processes. The enzymes that catalyze these reactions have been termed aminoacyl-tRNA transferases (Soffer 1974). The reactions differ fundamentally from protein synthesis in that the reactive moiety of the aminoacyl residue is its carboxyl group and there is no requirement for ribosomes, GTP, or template nucleic acids. These transfer reactions can be classified on the basis of the acceptor molecule to which the aminoacyl residue is transferred from tRNA (Soffer 1974). Lennarz (1972) is largely responsible for the discovery that certain bacteria contain particulate activities that transfer lysine and/or alanine from tRNA into an ester linkage with the 3′-OH group of phosphatidylglycerol to yield aminoacyl phosphatidylglycerol. Strominger (1970) provided most of the evidence that similar enzymes account for the biosynthesis of interpeptide bridges in various bacterial mureins. These latter reactions are initiated by aminoacylation of the ε-amino group in a lysine residue of one peptide chain and can be extended by sequential enzymatic aminoacylation of primary α-amino groups until ultimate peptide bond formation with a D-alanine residue of a different peptide chain in the complex peptidoglycan molecule. Details concerning donor and substrate specificity in these reactions and appropriate original author citations have been presented previously (Soffer 1974). The third category of aminoacyl transfer reactions is those catalyzed by aminoacyl-tRNA-protein transferases. The discovery of these enzymes emerged as a consequence of the unexpected observations by H. Kaji...