ahpC, a gene involved in isoniazid resistance of the Mycobacterium tuberculosis complex

Abstract

A gene conferring low-level isoniazid (INH) resistance on Mycobacterium smegmatis was isolated from a cosmid library of the genome of an INH-resistant Mycobacterium bovis strain. The gene had good homology with ahpC, the product of which is a subunit of alkyl hydroperoxide reductase, and also with a family of thiol-specific antioxidant enzymes. A mutation was found in the promoter upon comparison with the equivalent DNA sequence from the INH-sensitive parent strain. Promoter sequences from other INH-sensitive and INH-resistant M. bovis and Mycobacterium tuberculosis strains were sequenced and the mutation was found only in the INH-resistant strains. An INH-resistant M. tuberculosis strain also had an additional mutation in the promoter region. The wild-type promoter and promoters with one and two mutations were ligated into a reporter plasmid containing the lacZ gene. The presence of the first mutation resulted in a sixfold induction of beta-galactosidase activity, and the presence of both mutations caused a 10-fold induction. Increased expression of AhpC may account for some of the INH resistance of strains of the M. tuberculosis complex.

Tuberculose resistente: revisão molecular

“…A resistência para INH (INH R ) parece estar associada a uma variedade de mutações que afetam um ou mais genes (Tabela), como os que codificam para catalase-peroxidase (katG) 44 a enzima enoyl-ACP redutase, envolvida na biossíntese do ácido micólico (inhA) 2 , a alkyl hidroperóxido redutase, envolvida na resposta celular ao estresse oxidativo (ahpC) 42 e a enzima β-ketoacyl ACP syntase (kasA). 21 A partir da análise de regiões do DNA de isolados de M. tuberculosis resistentes à INH, diversos pesquisadores têm relatado a ocorrência de mutações associadas a esse tipo de resistência, sendo que as mutações nos genes katG e inhA são encontradas em 75-85% dos isolados de M. tuberculosis resistentes a esse fármaco.…”

A Novel Mechanism of Growth Phase-dependent Tolerance to Isoniazid in Mycobacteria

“…In addition to mutations in katG and inhA, ahpC (coding for alkyl hydroperoxide) (11) and ndh (coding for NADH dehydrogenase) (12) have also been reported to be associated with INH resistance. Mutations in kasA, which encodes ketoacyl acyl carrier protein synthase, are involved in INH resistance (13).…”

Mycobacterial catalases, peroxidases, and superoxide dismutases and their effects on virulence and isoniazid-susceptibility in mycobacteria - a review

“…As was described by several authors (Deretic et al, 1995;Sherman et al, 1996;Wilson and Collins, 1996) the presence of AhpC is associated with resistance to isoniazid in strains of E. coli and M. smegmatis. Also several Inh R isolates of M. tuberculosis have been described that carry ahpC promoter mutations resulting in AhpC overexpression and have reduced KatG catalase-peroxidase activity (Heym et al, 1997;Sherman et al, 1999).…”

“…KatG -deletion mutants of M. tuberculosis had lower levels of survival in spleens of mice and guinea pigs (Wilson and Collins, 1996;Li et al, 1998). Introduction of a cloned katG catalaseperoxidase gene into the katG -deletion strain led to persistence in spleens of mice and guinea pigs (Li et al, 1998).…”