The Escherichia coli Acriflavine resistance (acrA and acrB genes) encode a multi-drug efflux system that is believed to protect the bacterium against hydrophobic inhibitors.

[1] The E. coli AcrB protein is a transporter that is energized by proton-motive force and that shows the widest substrate specificity among all known multidrug pumps, ranging from most of the currently used antibiotics, disinfectants, dyes, and detergents to simple solvents.

X-ray analysis of the overexpressed AcrB protein demonstrated that the three periplasmic domains form, in the centre, a funnel-like structure and a connected narrow (or closed) pore.

These vestibules were proposed to allow direct access of drugs from the periplasm as well as the outer leaflet of the cytoplasmic membrane.

The three transmembrane domains of AcrB protomers form a large, 30A-wide central cavity that spans the cytoplasmic membrane and extends to the cytoplasm X-ray crystallographic structures of the trimeric AcrB pump from E. coli with four structurally diverse ligands demonstrated that three molecules of ligand bind simultaneously to the extremely large central cavity of 5000 cubic angstroms, primarily by hydrophobic, aromatic stacking and van der Waals interactions.