Outer membrane channel, which is required for the function of several efflux systems (By similarity). Required to export RtxA cytotoxin. 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 (By similarity). Increased sensitivity to bile salts and other detergents, erythromycin and novobiocin, but not to chloramphenicol, nalidixic acid, or tetracycline. Highly attenuated in mouse in vivo growth competition assays. Belongs to the outer membrane factor (OMF) (TC 1.B.17) family.