Mycobacterium tuberculosis Type-II NADH dehydrogenase (NDH-2) Catalytic Mechanism and Mode of Action of NDH-2 Inhibitors

poster · 7 years ago
by Takahiro Yano, Miriam Rahimian, Kawalpreet K. Aneja, Norman Schechter, Charles P. Scott, Harvey Rubin (University of Pennsylvania)
MarvinSketch Instant JChem
Type-II NADH-quinone (Q) oxidoreductase (NDH-2) catalyzes electron transfer from NADH to the Q-pool and plays an essential role in the oxidative phosphorylation system (OxPhos) of Mycobacterium tuberculosis (Mtb). The absence of NDH-2 in the mammalian mitochondrial OxPhos makes this enzyme an attractive target for antibiotic development. In this study, the catalytic mechanism of Mtb NDH-2 was investigated in detail by comparing the kinetics of the NADH-Q reductase reaction to those of the NADH-thio-NAD+ transhydrogenase reaction catalyzed by NDH-2, which follows a one-site ping-pong mechanism. We obtained evidence that the Mtb NDH-2 catalyzes electron transfer from NADH to Q by a non-classical two-site ping-pong mechanism where the substrate Q binds to a site distinct from the NADH-binding site. Furthermore, a study of effects of quinols on Mtb NDH-2 catalytic activity strongly suggested the presence of two Q-binding sites, one binds to oxidized Q and the other preferably binds to reduced Q. Based on the catalytic mechanism determined in this study, the mode of action of NDH-2 specific inhibitors that had been identified through a high throughput screening was investigated. We indentified two classes of inhibitors that interact with the Q-binding sites by different inhibition modes. One class of inhibitors compete with substrate Q and the other class shows a uncompetitive inhibition pattern with Q. The results suggest that the two-quinone sites in NDH-2 may constitute a unique target for the development of selective antibiotics. Download poster here