(A) Model of SUR1 with the various domains colored as in Figure 1, with each TM helix labeled. On the left, TMD1/NBD1 (green) is toward the front and TMD2/NBD2 (tan) is toward the back. (B) Cross-section of the SUR1 model, showing relative orientation of each of the 17 TM helices and a helix in L0. (C) Comparison of inward-facing ABC transporter structures: From left, C elegans Pgp (PDB code 4 F4C); mouse Pgp (4 M1M); hamSUR1. For each model, TMD2/NBD2 is colored tan. Lines on the side of the SUR1 NBDs denote the relative orientation of the NBD dimerization interface, demonstrating the observed twisting relative to other inward-facing structures.