Characterization of isoniazid-resistant mutant (S315R) of catalase-peroxidase, KatG, from Mycobacterium tuberculosis.

Unissa, A.N.; Selvakumar, N.; Narayanan, S.

International Journal of Medical Sciences and Technology; 2011; 4; 13-22.     

Abstract : Catalase-peroxidase, KatG, plays a key role in activating the prodrug isoniazid - an important drug in the anti-tuberculosis therapy. Mutation in katG gene is a major mechanism of INH resistance in Mycobacterium tuberculosis . In this study, the characterization of KatG mutant S315R and wild type (WT) was performed using rDNA technology. The catalytic turnover ( k cat/ K m ) in the mutant was decreased by 20% for catalase activity whereas the peroxidase activity was found to decrease by 62% and 61% with ABTS and INH compared to WT KatG respectively. The kinetic data indicates that the mutant activity towards INH was reduced considerably compared to WT. The results suggest that lesser activity in the mutant (S315R) could be due to the steric hindrance mediated by the bulkier guanido group present in the Arg residue instead of simpler hydroxyl group in the Ser residue. This could have induced conformational change in the mutant protein and leads to altered binding of Heme, eventually affects the binding of INH causing resistance.

Keywords: Mycobacterium tuberculosis; INH resistance; KatG; Mutant; Cloning, expression, characterization

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