Resonance Raman spectroscopy of Compound II and its decay in Mycobacterium tuberculosis catalase-peroxidase KatG and its isoniazid resistant mutant S315T

The reaction of Mycobacterium tuberculosis KatG and the mutant KatG(S315T) with two different organic peroxides is studied using resonance Raman spectroscopy. For the first time, an intermediate is observed in a catalase-peroxidase with vibrations that are characteristic of Compound II. The observation of this intermediate is consistent with photoreduction of Compound I and is in agreement with the formation of Compound I during the catalytic cycle of KatG. The same intermediate is detected in KatG(S315T), a mutant associated with resistance to isoniazid (INH), but with a lower yield, indicating that the organic peroxides cannot react with the heme iron in KatG(S315T) as efficiently as in wild-type KatG. Our results are consistent with catalytic competence of the S315T mutant and support the model that the S315T mutation confers antibiotic resistance by modifying the interaction between the enzyme and the drug.