Assembly and inhibition of transferable TMexCD1-TOprJ1 efflux pump.

Recent emergence and dissemination of plasmid-borne tmexCD1-toprJ1 tigecycline resistance threatens the efficacy of tigecycline as a "last-resort" defense against bacterial infections. Here, we report two cryo-EM structures of TMexCD1-TOprJ1 alone and in complex with its NMP inhibitor, and both are determined at the resolutions of 2.97 Å and 3.0 Å, respectively. The symmetry of overall architecture explains how the tripartite organization adopts a 3:6:3 protomer stoichiometry (TOprJ1: TMexC1: TMexD1) to assemble an elongated, rod-like pump spanning bacterial double membranes. The periplasmic TMexC1 adaptor bind the trimeric TOprJ1 funnel via a universal "tip-to-tip" contact, and bridges the bottom TMexD1 engine by extensive interactions. A unique form of resting (R) states is observed for TMexD1 trimer. Besides two binding-interfaces of TMexC1 with TOprJ1 and TMexD1, we characterize a substrate/inhibitor-loading cavity. Collectively, these findings constitute molecular bases for assembly and inhibition of transferable TMexCD1-TOprJ1 machinery, and benefit developing next-generation of antimicrobials targeting functional efflux pump.