Demonstration That CFTR Is a Chloride Channel by Alteration of Its Anion Selectivity

TLDR

Expression of CFTR generates cAMP‑regulated chloride channels, indicating it may be a chloride channel or a regulator. The study aims to determine whether CFTR functions as a chloride channel or a regulator by mutating basic amino acids in its transmembrane domains. The authors mutated basic amino acids in the putative transmembrane domains to assess their role in channel function. The anion selectivity sequence of cAMP‑regulated CFTR channels was bromide > chloride > iodide > fluoride, and mutating lysines 95 or 335 to acidic residues reversed the sequence to iodide > bromide > chloride > fluoride, confirming CFTR as a chloride channel with lysines 95 and 335 determining selectivity.

Abstract

Expression of the cystic fibrosis transmembrane conductance regulator (CFTR) generates adenosine 3′,5′-monophosphate (cAMP)-regulated chloride channels, indicating that CFTR is either a chloride channel or a chloride channel regulator. To distinguish between these possibilities, basic amino acids in the putative transmembrane domains were mutated. The sequence of anion selectivity of cAMP-regulated channels in cells containing either endogenous or recombinant CFTR was bromide > chloride > iodide > fluoride. Mutation of the lysines at positions 95 or 335 to acidic amino acids converted the selectivity sequence to iodide > bromide > chloride > fluoride. These data indicate that CFTR is a cAMP-regulated chloride channel and that lysines 95 and 335 determine anion selectivity.