Computational Approach in Understanding Mechanism of Action of Isoniazidand Drug Resistance

Most Multi Drug Resistance and Extremely Drug Resistance clinical strains of Mycobacterium tuberculosis are found to be resistant to the anti-tuberculousis drugs such as Isoniazid and Rifampicin. The mechanism of action and drug resistance due to Isoniazid has been the subject of extensive study. According to Tuberculosis drug resistance mutation database, 22 genes/proteins are associated with Isoniazid resistance such as katG, nat, inhA, ahpc, ndh, kasA etc. Mutation in the gene seems to affect the formation of Isoniazid to its active form or enhancing the catabolism thus making it ineffective. Studies in different laboratories have shown usefulness of computational approach in elucidating the mechanism of action of Isoniazid and development of drug resistance. Computational studies in our laboratory showed that a mutation in KatG (S315T/S315N) prevents free radical formation, thus the development of resistance to the drug. Further, we observed through molecular dynamics simulation approach that mutation (G67R/G207E) in NAT enzyme increases the stability and catalytic ability of the mutant enzyme, thus making the drug ineffective.