Figure 3.

AcrB undergoes a conformational cycle that functionally connects the movement of protons through the protein to drug extrusion. (a) Porter domains of AcrB viewed from the periplasm, showing the different conformational changes that correspond to drug access, binding and extrusion. The Access state is coloured pink, the Binding state is coloured yellow, and the Extrusion state is coloured in blue. Adapted from Matsunaga et al. (2018). (b) Drugs are thought to move through the proximal binding pocket (purple) in the Access state, bind to the distal pocket (dark blue) in the Binding state, and leave through the exit gate (cyan) in the Extrusion state. A drug (minocycline), is shown moving through these different regions. The drug was placed manually in the Access and Extrusion states for illustrative purposes, but the position of the drug in the binding state comes from PDB ID:4DX5 (Eicher et al., 2012). The definition of the different regions comes from Vargiu and Nikaido (2012).