Mycobacterium tuberculosis KatG(S315T) Catalase−Peroxidase Retains All Active Site Properties for Proper Catalytic Function†

Mycobacterium tuberculosis (Mtb) KatG is a catalase−peroxidase that is thought to activate the antituberculosis drug isoniazid (INH). The local environment of Mtb KatG and its most prevalent INH-resistant mutant, KatG(S315T), is investigated with the exogenous ligands CO and NO in the absence and presence of INH by using resonance Raman, FTIR, and transient absorption spectroscopy. The Fe−His stretching vibration is detected at 244 cm-1 in the ferrous forms of both the wild-type enzyme and KatG(S315T). The ferrous−CO complex of both enzymes exhibits ν(CO), ν(Fe−CO), and δ(Fe−C−O) vibrations at 1925, 525, and 586 cm-1, respectively, indicating a positive electrostatic environment for the CO complex, which is probably weakly hydrogen-bonded to a distal residue. The CO geometry is nonlinear as indicated by the unusually high intensity of the Fe−C−O bending vibration. The ν(FeIII−NO) and δ(FeIII−N−O) vibrations are detected at 596 and 571 cm-1, respectively, in the ferric forms of wild-type and mutant enzyme ...