FIG. 1.

Lateral capture model of RND family pump function. This model is slightly modified from that of the original publication (15) and shows specific components of the AcrAB-TolC complex of E. coli. Abbreviations: OM, outer membrane; IM, inner membrane. The substrates, which are usually amphiphilic (the lipophilic portions of the substrates are drawn as black rectangles), are thought to partition spontaneously into the outer leaflet of IM and then are hypothesized to be captured laterally by the AcrB pump. The outer leaflet of OM is composed of lipopolysaccharides (LPS), which produce a strong diffusion barrier, presumably because of their less fluid interior.