Recognition of Human Mitochondrial tRNA Leu(UUR) by its Cognate Leucyl-tRNA Synthetase

Abstract

Accuracy of protein synthesis depends on specific recognition and aminoacylation of tRNAs by their cognate aminoacyl-tRNA synthetases. Rules governing these processes have been established for numerous prokaryotic and eukaryotic cytoplasmic systems, but only limited information is available for human mitochondrial systems. It has been shown that the in vitro transcribed human mitochondrial tRNA Leu(UUR) does not fold into the expected cloverleaf, but is however aminoacylated by the human mitochondrial leucyl-tRNA synthetase. Here, the role of the structure of the amino acid acceptor branch and the anticodon branch of tRNA Leu(UUR) in recognition by leucyl-tRNA synthetase was investigated. The kinetic parameters for aminoacylation of wild-type and mutant tRNA Leu(UUR) transcripts and of native tRNA Leu(UUR) were determined. Solution structure probing was performed in the presence or in the absence of leucyl-tRNA synthetase and correlated with the aminoacylation kinetics for each tRNA. Replacement of mismatches in either the anticodon-stem or D-stem that are present in the wild-type tRNA Leu(UUR) by G-C base-pairs is sufficient to induce (i) cloverleaf folding, (ii) improved aminoacylation efficiency, and (iii) interactions with the synthetase that are similar to those with the native tRNA Leu(UUR). Leucyl-tRNA synthetase contacts tRNA Leu(UUR) in the amino acid acceptor stem, the anticodon stem, and the D-loop, which is unprecedented for a leucine aminoacylation system.