Assembly and operation of bacterial tripartite multidrug efflux pumps

•Multidrug efflux pumps in Gram-negative bacteria can be assembled in tripartite structures to enable transport across the cell envelope.•The structure of a full tripartite assembly illuminates the drug transport mechanism.

Microorganisms encode several classes of transmembrane pumps that can expel an enormous range of toxic substances, thereby improving their fitness in harsh environments and contributing to resistance against antimicrobial agents. In Gram-negative bacteria these pumps can take the form of tripartite assemblies that actively efflux drugs and other harmful compounds across the cell envelope. We describe recent structural and functional data that have provided insights into the transport mechanisms of these intricate molecular machines.