External Zn(2+) binding to cysteine-substituted cystic fibrosis transmembrane conductance regulator constructs regulates channel gating and curcumin potentiation.

The cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel is activated by ATP binding-induced dimerization of nucleotide-binding domains, the interaction between the phosphorylated regulatory (R) domain and the curcumin-sensitive interface between intracellular loop (ICL) 1 and ICL4, and the resultant inward-to-'outward' reorientation of transmembrane domains. Although transmembrane helices (TM) 2 and TM11 link the ICL1-ICL4 interface with the interface between extracellular loop (ECL) 1 and ECL6, it is unknown whether both interfaces are gating-coupled during the reorientation. Herein, R334C and T1122C mutations were used to engineer two Zn(2+) bridges near and at the ECL1-ECL6 interface, respectively, and the gating effects of a Zn(2+) disturbance at the ECL1-ECL6 interface on the stimulatory ICL1/ICL4-R interaction were determined.