AcrA-AcrB-AcrZ-TolC is a drug efflux protein complex with broad substrate specificity that uses the proton motive force to export substrates. This subunit may act as an adapter protein that links AcrB and TolC stably together. It is elongated in shape, being long enough to span the periplasm. Monomeric in solution. Homotrimeric; interacts independently with AcrB and TolC as well as AcrZ. Part of the AcrA-AcrB-TolC efflux pump. Complex assembly is independent of an efflux substrate and appears to be constitutive. An unlipidated version of this protein (directed to the periplasm by the OmpA signal sequence) functions normally. Cannot grow on efflux substrates novobiocin or fusidic acid. Belongs to the membrane fusion protein (MFP) (TC 8.A.1) family.