Mycobacterium tuberculosis cells contain two apurinic/apyrimidinic (AP) endonucleases, endonuclease IV (MtbEnd) and exonuclease III (MtbXthA), the former playing a dominant role in protecting mycobacterial DNA from oxidative stress. Mycobacterial endonuclease IV substantially differs from its homologs found in Escherichia coli and other proteobacteria in a number of conserved positions important for DNA binding and AP site recognition. The M. tuberculosis end gene was cloned, and recombinant MtbEnd purified and characterized. The protein efficiently hydrolyzed DNA at the natural AP site and its 1'-deoxy analog in the presence of divalent cations, of which Ca^(2+), Mn^(2+), and Co^(2+) supported the highest activity. Exonuclease activity was not detected in MtbEnt preparations. The pH optimum was estimated at 7.0-8.0; the ionic strength optimum, at ~50 mM NaCl. Enzymatic activity of MtbEnd was suppressed in the presence of methoxyamine, a chemotherapeutic agent that modifies AP sites. Based on the results, MtbEnd was assumed to provide a possible target for new anti-tuberculosis drugs.
Keywords: AP endonuclease; DNA repair; Mycobacterium tuberculosis; methoxyamine.