Figure 1.

Superfamilies and families of solute transporters. Shown are the outer and inner bacterial membranes with graphic representations of solute transporter superfamilies and families. MFS denotes the major facilitator superfamily; SMR, small multi-drug resistant family; ABC, ATP-binding cassette transporter superfamily; MOP (referred to previously as MATE), multidrug/ oligosaccharidyl-lipid/polysaccharide flippase superfamily; RND, resistance-nodulation-cell division superfamily. H⁺ and Na⁺ denote protons and sodium ions, respectively. Courtesy of Ann Varela.