Fig. 3

Large change in the chamber volume. a, b The inside anterior views of inward- (a) and outward-facing (b) conformations of QTA CmABCB1. For clarity, TM4, TM5, TM4*, and TM5* shown in Fig. 1a, c are omitted here. Residues forming close inter-subunit contacts on the cytosolic side in the outward-facing conformation are shown as spheres. The inner chamber in the inward-facing conformation is shown as a green mesh (a). One subunit is shown in color, and the other is shown in gray. Horizontal black and gray bars represent the expected positions of the hydrophilic and hydrophobic surfaces of the lipid membrane, respectively. In b, bound Mg²⁺•AMP-PNP molecules at NBDs are shown as spheres. c, d Close-up of TM6* and TM3 in inward- (a) and outward-facing (b) conformations viewed parallel to the membrane. Intra-helical interactions within the main chains of TM6 are shown as dashed lines. In c, the internal large cavity facing the intracellular side in the inward-facing conformation is outlined in green. In d, TM3 and the side chains of residues interacting with Gln398 are shown as ribbon and sticks, respectively. Polar and van der Waals interactions are shown as black and orange dashed lines, respectively. Non-α-helical hydrogen bonds in TM6 are indicated by red arrowheads. The stretching directions of TM6 from the inward- to outward-facing conformations are shown as thick black arrows in the schematic. e Bar graph, overlaid with the actual data points, shows IC₅₀ for growth inhibition in a rhodamine 6G susceptibility assay using S. cerevisiae AD1-8u⁻ cells. Error bars indicate standard deviation (n = 3). Cells expressing the ATPase-deficient mutant E610A served as controls. Inset shows the amounts of mutant and WT CmABCB1 expressed in AD1-8u⁻ cells, as determined by western blotting. Uncropped images of the blots are shown in Supplementary Fig. 6