(A) Schematic of an efflux pump removing harmful substances. The pump comprises an IMC protein from the RND, ABC, or MFS superfamilies, a PAP, and an OMF family component, like TolC [1]. (B) Ribbon diagram of TolC (PDB: 1EK9). Sizes of each structural domain are indicated to the right [7]. One of the 3 monomers is coloured pink for clarity. (C) Structural map of one TolC monomer (without its signal peptide), based on its crystal structure (PDB: 1EK9) over residues 1–428 and as predicted using PSIPRED 4.0 [8] over residues 429–471. The characteristic OEP regions are indicated. Cylinders represent α-helices; arrows represent β-strands. IMC, inner membrane channel; OEP, outer membrane efflux protein; OMF, outer membrane factor; PAP, periplasmic adaptor protein; PGN, peptidoglycan.