Search

Abstract: The millisecond conformational flexibility is functionally important for nucleic acids and can be studied through probing the base pair open–close kinetics by proton exchange nuclear magnetic resonance (NMR) spectroscopy. Here, the traditional imino proton exchange NMR experiments were modified with transverse relaxation optimized spectroscopy and were applied to accurately measure imino proton exchange rates of all base pairs in Escherichia coli tRNALeu (CAG), and their dependence on magnesium ion concentration. Finally, we correlated millisecond conformational flexibility with aminoacylation of tRNALeu and proposed that the flexibility of the acceptor stem and the core region might contribute to aminoacylation of tRNALeu. [ABSTRACT FROM AUTHOR]

Abstract: The mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes syndrome (MELAS) is a rare congenital disorder of mitochondrial DNA. Five single nucleotide substitutions within the human mitochondrial tRNALeu(UUR) gene have been reported to be associated with MELAS. Here, we provide in vitro evidence that the aminoacylation capacities of these five hmtRNALeu(UUR) transcripts are reduced to different extents relative to the wild-type hmtRNALeu(UUR) transcript. A thermal denaturation experiment showed that the A3243G and T3291C mutants, which were the least charged by LeuRS, have fragile structures. In addition, the T3291C mutant can inhibit aminoacylation of the wild-type hmtRNALeu(UUR), indicating that it may act as an inhibitor in the mitochondrial heteroplasmic environment. [Copyright &y& Elsevier]

The 19F nuclear magnetic resonance (NMR) spectra of 4-fluorotryptophan (4-F-Trp)-labeled Escherichia coli arginyl–tRNA synthetase (ArgRS) show that there are distinct conformational changes in the catalytic core and tRNA anticodon stem and loop-binding domain of the enzyme, when arginine and tRNAArg are added to the unliganded enzyme. We have assigned five fluorine resonances of 4-F-Trp residues (162, 172, 228, 349 and 446) in the spectrum of the fluorinated enzyme by site-directed mutagenesis. The local conformational changes of E. coli ArgRS induced by its substrates observed herein by 19F NMR are similar to those of crystalline yeast homologous enzyme. [Copyright &y& Elsevier]