CFTR homology model with three pairs of interacting residues labeled in both closed and open states. Top view of the homology model (McCarty laboratory model; Rahman et al., 2013) with salt bridge residues shown as spheres: R117-E1126, red; E116-R104, green; and D110-K892E, magenta. (left) Closed state (equivalent to the state where the NBDs are fully dedimerized). (right) Open state. TM1-6 is indicated in brown shades, and TM7-12 is indicated in blue shades.