Involvement of the N- and C-terminal domains of Mycobacterium tuberculosisKatG in the protection of mutant Escherichia coli against DNA-damaging agents

The Mycobacterium tuberculosis KatG enzyme, like most hydroperoxidase I (HP I)-type catalases, consists of two related domains, each with strong simila rity to the yeast cytochrome c peroxidase. The catalase-peroxidase activity is associated with the amino-terminal domain but currently no definite fun ction has been assigned to the carboxy-terminal domain, although it may pla y a role in substrate binding. This paper reports another possible function of the KatG protein involving protection of the host cell against DNA-dama ging agents. The M, tuberculosis katG gene, the 5' domain and the 3' domain were cloned separately, in-frame with the maltose-binding protein, into th e vector pMAL-c2, These constructs were introduced into four DNA-repair mut ants of Escherichia coli, DK1 (recA), AB1884 (uvrC), AB1885 (uvrB) and AB18 86 (uvrA), which were then tested for their ability to survive treatment wi th UV light (254 nm), hydrogen peroxide (1.6 mg ml(-1)) and mitomycin C (6 mu g ml(-1)). All three constructs conferred resistance to UV upon the recA E. coli cells, whereas resistance to mitomycin C was found in all repair m utants tested. Protection against hydrogen peroxide damage was less pronoun ced and predominantly found in the recA host. These results indicated that the M, tuberculosis katG gene can enhance DNA repair in E, coli, and that t he 5' and 3' domains can function separately. UV sensitivity tests on Mycob acterium intracellulare and M. tuberculosis strains mutant in katG revealed that the katG gene product does not play an additive role in the survival of mycobacterial cells after exposure to short-wavelength UV irradiation, i n repair-competent cells.