Proton Oligopeptide Symporters Comprise Four Inverted-Topology Repeat Units
(A) Each inverted-topology repeat unit (labeled A–D) is made up of three transmembrane α helices (labeled 1–12) (Radestock and Forrest, 2011).
(B) The inward-occluded structure of PepTSo rendered using curved cylinders (Dahl et al., 2012) to illustrate their intrinsic kinks and bends and colored according to the same scheme as in (A).