A cartoon depicting possible mechanisms for the independent gating modulation by NO₃⁻ and VX-770. Because our intention is to elaborate the experimental results shown in Fig. 8 with ΔNBD2- and G551D-CFTR, in this simplified scheme, a closed state (left) and an open state (right) are portrayed as in equilibrium. The hydrophobic VX-770, by partitioning into the lipid bilayer, acts on CFTR’s TMDs at the interface between the channel protein and membrane lipids. In contrast, nitrate ions interact with the channel at the water–protein interface. By acting through different interfaces, NO₃⁻ and VX-770 can perturb the free energy levels of both open and closed states independently. As a result, the free energy changes by NO₃⁻ plus VX-770 on gating will be the sum of the free energy alterations by individual molecules.