Outer membrane channel, which is required for the function of several efflux systems such as AcrAB-TolC, AcrEF-TolC, EmrAB-TolC and MacAB-TolC. These systems are involved in export of antibiotics and other toxic compounds from the cell. TolC is also involved in import of colicin E1 into the cells. In vitro, inhibited by hexaamminecobalt(3+). Homotrimer. Part of tripartite efflux systems, which are composed of an inner membrane transporter, a periplasmic membrane fusion protein, and an outer membrane component, TolC. The complexes form a large protein conduit and can translocate molecules across both the inner and outer membranes. TolC interacts with the membrane fusion proteins AcrA, EmrA and MacA. Forms a continuous, solvent-accessible conduit: a 'channel-tunnel' over 140 Angstroms long that spans both the outer membrane and periplasmic space. The periplasmic or proximal end of the tunnel is sealed by sets of coiled helices. Cannot grow on efflux substrates novobiocin or fusidic acid. Belongs to the outer membrane factor (OMF) (TC 1.B.17) family. Extended N-terminus. Extended N-terminus. Extended N-terminus.