Pyrazinamide resistance and mutations L19R,R140H,and E144K in Pyrazinamidase of Mycobacterium tuberculosis

Pyrazinamide (PZA) is an important component of first-line antituberculosis drugs activated by Mycobacterium tuberculosis pyrazinamidase (PZase) into its active form pyrazinoic acid. Mutations in the pncA gene have been recognized as the major cause of PZA resistance. We detected some novel mutations, Leucine19Arginine (L19R), Arginine140Histidine (R140H), and Glutamic acid144 Lysine (E144K), in the pncA gene of PZA-resistant isolates in our wet lab PZA drug susceptibility testing and sequencing. As the molecular mechanism of resistance of these variants has not been reported earlier, we have performed multiple analyses to unveil different mechanisms of resistance because of PZase mutations L19R, R140H, and E144K. The mutants and native PZase structures were subjected to comprehensive computational molecular dynamics (MD) simulations at 100 nanoseconds in apo and drug-bound form. Mutants and native PZase binding pocket were compared to observe the consequence of mutations on the binding pocket size. Hydrogen bonding, Gibbs free energy, and natural ligand Fe ⁺² effect were also analyzed between native and mutants. A significant variation between native and mutant PZase structure activity was observed. The native PZase protein docking score was found to be the maximum, showing strong binding affinity in comparison with mutants. MD simulations explored the effect of the variants on the biological function of PZase. Hydrogen bonding, metal ion Fe ⁺² deviation, and fluctuation also seemed to be affected because of the mutations L19R, R140H, and E144K. The variants L19R, R140H, and E144K play a significant role in PZA resistance, altering the overall activity of native PZase, including metal ion Fe ⁺² displacement and free energy. This study offers valuable evidence for better management of drug-resistant tuberculosis.     

The interaction of an I-like R factor and transfer-deficient mutants of Flac in E. coli K 12

Summary Strains carrying an I-like R factor, R64, or its derepressed derivative, R64-11, together with an Flac episome mutant in one of ten cistrons determining transfer-proficiency, transferred the Flac mutant at a frequency equivalent to about 1% of the level of R factor transfer. Similarly, R64, R64-11 and transfer-deficient mutants of R64-11, were transferred at increased frequencies in the presence of wild-type Flac. Experiments using RecA^– strains showed that mobilisation by recA ⁺-promoted recombination was not involved, and others using strains carrying transfer-deficient mutants of both R64-11 and Flac suggested that even inefficient complementation between R64-11 and Flac transfer mutants did not occur. The transfer systems of the two plasmids seemed, therefore, to be unrelated, and plasmid-specific, although at a low frequency the entire transfer system of one, not just the pilus, could transfer a transfer-deficient mutant of the other.     

Structures of the lamin A/C R335W and E347K mutants: implications for dilated cardiolaminopathies

Dilated cardiomyopathy (DCM) is a condition whereby the normal muscular function of the myocardium is altered by specific or multiple aetiologies. About 25-35% of DCM patients show familial forms of the disease, with most mutations affecting genes encoding cytoskeletal proteins. Most of the DCM-related mutations fall in the Lamin AC gene, in particular in the Coil2B domain of the encoded protein. In this context, we focussed our studies on the crystal structures of two lamin Coil2B domain mutants (R335W and E347K). Both R335 and E347 are higly conserved residues whose substitution has little effects on the Coil2B domain three-dimensional structure; we can thus hypothesize that the mutations may interfere with the binding of components within the nuclear lamina, or of nuclear factors, that have been proposed to interact/associate with lamin A/C.