Re-Understanding the Mechanisms of Action of the Anti-Mycobacterial Drug Bedaquiline

Bedaquiline (BDQ) inhibits ATP generation in Mycobacterium tuberculosis by interfering with the F-ATP synthase activity. Two mechanisms of action of BDQ are broadly accepted. A direct mechanism involves BDQ binding to the enzyme's c-ring to block its rotation, thus inhibiting ATP synthesis in the enzyme's catalytic alpha(3)beta(3)-headpiece. An indirect mechanism involves BDQ uncoupling electron transport in the electron transport chain from ATP synthesis at the F-ATP synthase. In a recently uncovered second direct mechanism, BDQ binds to the enzyme's epsilon-subunit to disrupt its ability to link c-ring rotation to ATP synthesis at the alpha(3)beta(3)-headpiece. However, this mechanism is controversial as the drug's binding affinity for the isolated epsilon-subunit protein is moderate and spontaneous resistance mutants in the epsilon-subunit cannot be isolated. Recently, the new, structurally distinct BDQ analogue TBAJ-876 was utilized as a chemical probe to revisit BDQ's mechanisms of action. In this review, we first summarize discoveries on BDQ's mechanisms of action and then describe the new insights derived from the studies of TBAJ-876. The TBAJ-876 investigations confirm the c-ring as a target, while also supporting a functional role for targeting the epsilon-subunit. Surprisingly, the new findings suggest that the uncoupler mechanism does not play a key role in BDQ's anti-mycobacterial activity.