A side view of a three-dimensional model of BCRP in the nucleotide-free closed apo inward-facing form is presented. The TM helices are labeled with roman numerals, I, II, III, IV, V and VI. The residues Pro392, Pro480 and Pro485 are shown in magenta, green and green, respectively, and pointed by arrows. Also shown on the right is an expanded view of TM3 and neighboring helices indicating a potential hinge (shown in green) introduced by Pro485. The C-terminal half of TM3 is kinked between TM1 and TM6 in the hinged conformation and rotated closer to the interior of the drug-binding cavity of BCRP. The undistorted TM3 in the original BCRP model is shown in grey.