FIGURE 4. Substrate translocation pathway.
From the following article:
Structure of a bacterial multidrug ABC transporter
Roger J. P. Dawson and Kaspar P. Locher
Nature 443, 180-185(14 September 2006)
doi:10.1038/nature05155
a, Backbone traces of the Sav1866 subunits (green and yellow) in two orientations, rotated by 90° around a vertical axis. The molecular surface of the central cavity is coloured according to its calculated electrostatic potential (blue, positively charged; red, negatively charged), whereas that of the rest of the transporter is in transparent light grey. Lines indicate the approximate position of the two leaflets of the lipid bilayer. Access from the cavity to the outer leaflet of the lipid bilayer is visible in the right panel from the front and back, between the 'wings' formed by the TMDs. b, Cavity at the level of the inner leaflet viewed from the extracellular side. The transmembrane helices are numbered and the cavity is shown as a grey surface. c, Same as b but at the level of the outer leaflet. Note that owing to helix bending, different subsets of helices line the cavity when compared with b.
