THE KATE GENE, WHICH ENCODES THE CATALASE HPII OF MYCOBACTERIUM-AVIUM

Disseminated Mycobacterium avium-Mycobacterium intracellulare disease is a prevalent opportunistic infection in patients with acquired immun e deficiency syndrome (AIDS). These pathogens are generally resistant to isoniazid (INH), a powerful antituberculosis drug. It is now genera lly accepted that the INH susceptibility of Mycobacterium tuberculosis results from the transformation of the drug into a toxic derivative, as a result of the action of the enzyme catalase-peroxidase (HPI), enc oded by the katG gene. It has been speculated that the presence of a s econd catalase (HPII) in some mycobacterial species, but lacking in M. tuberculosis, may impair the action of INH. In this report, the nucle otide sequence of the M. avium katE gene, encoding catalase HPII, is d escribed. This enzyme shows strong similarity to Escherichia coil cata lase HPII and eukaryotic catalases. All amino acids previously postula ted as participating directly in catalysis by liver catalase and most of the amino acids binding the prosthetic group are conserved in M. av ium catalase HPII. The enzyme is expressed in E. coli and is inhibited by 3 amino-1 ,2,4-triazole (AT). Furthermore, Southern blot hybridiza tions and polymerase chain reaction experiments demonstrate the distri bution of katE gene in several mycobacterial species. To evaluate the potentially antagonistic effect of HPII catalase on INH susceptibility , the katE gene was transformed into M. tuberculosis H37Rv and the min imum inhibitory concentration (MIC) for INH was determined. Despite st rong expression of the katE gene, no change in MIC was observed, thus ruling out a possible contribution of this enzyme to the natural resis tance of M. avium to the drug. The availability of the gene probe, enc oding the second mycobacterial catalase HPII, should open the way for the development of new drugs and diagnostic tests to combat drug-resis tant pathogen strains.