Solution Nuclear Magnetic Resonance Analyses of the Anticodon Arms of Proteinogenic and Nonproteinogenic tRNAGly
journal contributionposted on 01.05.2012, 00:00 by Andrew T. Chang, Edward P. Nikonowicz
Although the fate of most tRNA molecules in the cell is aminoacylation and delivery to the ribosome, some tRNAs are destined to fulfill other functional roles. In addition to their central role in translation, tRNA molecules participate in processes such as regulation of gene expression, bacterial cell wall biosynthesis, viral replication, antibiotic biosynthesis, and suppression of alternative splicing. In bacteria, glycyl-tRNA molecules with anticodon sequences GCC and UCC exhibit multiple extratranslational functions, including transcriptional regulation and cell wall biosynthesis. We have determined the high-resolution structures of three glycyl-tRNA anticodon arms with anticodon sequences GCC and UCC. Two of the tRNA molecules are proteinogenic (tRNAGly,GCC and tRNAGly,UCC), and the third is nonproteinogenic (np-tRNAGly,UCC) and participates in cell wall biosynthesis. The UV-monitored thermal melting curves show that the anticodon arm of tRNAGly,UCC with a loop-closing C-A+ base pair melts at a temperature 10 °C lower than those of tRNAGly,GCC and np-tRNAGly,UCC. U-A and C-G pairs close the loops of the latter two molecules and enhance stem stability. Mg2+ stabilizes the tRNAGly,UCC anticodon arm and reduces the Tm differential. The structures of the three tRNAGly anticodon arms exhibit small differences among one another, but none of them form the classical U-turn motif. The anticodon loop of tRNAGly,GCC becomes more dynamic and disordered in the presence of multivalent cations, whereas metal ion coordination in the anticodon loops of tRNAGly,UCC and np-tRNAGly,UCC establishes conformational homogeneity. The conformational similarity of the molecules is greater than their functional differences might suggest. Because aminoacylation of full-length tRNA molecules is accomplished by one tRNA synthetase, the similar structural context of the loop may facilitate efficient recognition of each of the anticodon sequences.