Computational approach to understanding the mechanism of action of isoniazid, an anti-TB drug

Tuberculosis [TB] is an ancient disease caused by Mycobacterium tuberculosis [MTB], which remains a major cause for morbidity and mortality in several developing countries. Most drug-resistant MTB clinical strains are resistant to isoniazid [INH], a first-line anti-TB drug. Mutation in KatG, a catalase-peroxidase, of MTB is reported to be a major cause of INH resistance. Normally upon activation by KatG, INH is converted to an active intermediate which has antimycobacterial action in MTB. This INH intermediate in the presence of NADH forms INH-NAD adduct which inhibits inhA [2-trans-enoyl-acyl carrier protein reductase] of MTB, thus blocking the synthesis of mycolic acid, a major lipid of the myco-bacterial cell wall. In this docking study, the high binding affinity of INH-NAD adduct towards InhA was observed in comparison with INH alone. In this study, two resistant mutants of KatG [S315Tand S315N] were modeled using Modeller9vlO and docking analysis with INH was performed using AutoDock4.2 and the docking results of these mutants were compared with the wild type KatG. Docking results revealed the formation of a single hydrogen [H] bond between the secondary amine nitrogen [-NH] of INH with Thr or Asn residues in place of Serine at 315 position of KatG mutant strains respectively, whereas in the case of the wild type, there was no H-bond formation observed between INH and Ser315. The H-bond formation may prevent free radical formation by KatG in mutant strains thus the development of resistance to the drug. This in silico evidence may implicate the basis of INH resistance in KatG mutant strains

Comparative proteomic analysis of Mycobacterium tuberculosis strain H[37]Rv versus H[37]Ra

Mycobacterium tuberculosis [MTB] H[37]Ra is an attenuated tubercle bacillus closely related to the virulent type strain MTB H[37]Rv. In spite of extensive study, variation in virulence between the MTB H[37]Rv and MTB H[37]Ra strains is still to be understood. The difference in protein expression or structure due to mutation may probably be an important factor for the virulence property of MTB H[37]Rv strain. In this study, a whole proteome comparison between these two strains was carried out using bioinformatics approaches to elucidate differences in their protein sequences. On comparison of whole proteome using NCBI standalone BLAST program between these two strains, 3759 identical proteins in both the strains out of 4003 proteins were revealed in MTB H[37]Rv and 4034 proteins were revealed in MTB H[37]Ra; 244 proteins of MTB H[37]Rv and 260 proteins of MTB H[37]Ra were found to be non-identical. A total of 172 proteins were identified with mutations [Insertions/deletions/substitutions] in MTB H[37]Ra while 53 proteins of MTB H[37]Rv and 85 proteins of MTB H[37]Ra were found to be distinct. Among 244 non-identical proteins, 19 proteins were reported to have an important biological function; In this study, mutation was shown in these proteins of MTB H[37]Ra. This study reports the protein differences with mutations between MTB H[37]Rv and H[37]Ra, which may help in better understanding the pathogenesis and virulence properties of MTB H[37]Rv