Crystal structure of <i>Mycobacterium tuberculosis</i> mycothione reductase in complex with a specific inhibitor reveals competition with <scp>NADP</scp> (H) binding

Tuberculosis (TB) remains a major health threat, while the increasing occurrence of drug-resistant strains underscores the need for new antitubercular drugs. A promising strategy to combat TB is based on disrupting the mycobacterial redox homeostasis by inhibiting an NADPH-dependent oxidoreductase, mycothione reductase (Mtr). Using high-throughput screening, we recently identified potent and selective Mtr inhibitors. Here we report high-resolution X-ray structures of Mtr from Mycobacterium tuberculosis and Mycobacterium xenopi, including the M. tuberculosis enzyme complexed with a novel inhibitor, Respiri-1093. Our findings demonstrate that Respiri-1093 competes with the NADP(H) binding rather than mycothione binding. Analysis of the binding site explains the observed selectivity of the inhibitor towards the M. tuberculosis enzyme. These results provide a structural basis for rational drug design.