(A) Normal CFTR function permits conductance of chloride anions. (B) Class II mutations (e.g., F508del) cause misfolded CFTR and impair trafficking to the apical cell membrane. Class III mutations (e.g., G551D) impair opening (gating) of the CFTR chloride channel. (C) CFTR correctors (e.g., elexacaftor, tezacaftor) promote proper protein folding and trafficking. CFTR potentiators (e.g., ivacaftor) enhance channel opening to promote proper channel gating.