Fig. 5

AMP-PMP-dependent structural transitions from the open state (O1) to the locked-open (O*) state of CFTR Cl⁻ channel. Left A hypothetical drawing depicts the solute-accessible interior of a highly asymmetric pore with narrower extracellular (the radius of R1 = 0.70 nm) and wider intracellular (R2 = 1.19 nm) entrances in the presence of ATP and in the absence of AMP-PNP. The size of the narrowest constriction inside the pore (smallest filled circle, R5 = 0.27 nm) is based on the permeability data reported by Linsdell et al. [66]. Right A hypothetical drawing illustrates AMP-PNP-induced dilatation of the extracellular entrance (R3 = 0.93 nm) but not of the intracellular entrance (R4 = 1.15 nm) of the CFTR Cl⁻ channel pore. Smaller hatched circle in the middle corresponds to an AMP-PNP-dependent widening of the narrowest constriction which may represent the selectivity filter. For the radius of the narrowest constriction in the presence of AMP-PNP, the value of R6 = 0.69 nm reported by Linsdell and Hanrahan [43] is adopted, and its localization in the proximity to the extracellular entrance of the channel is based on the present PEG partition study. NBD1 and NBD2 denote two nucleotide-binding domains of CFTR channel protein. The transmembrane and regulatory domains are not depicted for the simplicity