Abstract
A broad chemical genetic screen in Mycobacterium tuberculosis (Mtb) identified compounds (BRD-8000.3 and BRD-9327) that inhibit the essential efflux pump EfpA. To understand the mechanisms of inhibition, we determined the structures of EfpA with these inhibitors bound at 2.7-3.4 Å resolution. Our structures reveal different mechanisms of inhibition by the two inhibitors. BRD-8000.3 binds in a tunnel contacting the lipid bilayer and extending toward the central cavity to displace the fatty acid chain of a lipid molecule bound in the apo structure, suggesting its blocking of an access route for a natural lipidic substrate. Meanwhile, BRD-9327 binds in the outer vestibule without complete blockade of the substrate path to the outside, suggesting its possible inhibition of the movement necessary for alternate access of the transporter. Our results show EfpA as a potential lipid transporter, explain the basis of the synergy of these inhibitors and their potential for combination anti-tuberculosis therapy.