Identification of an Ion Channel-Forming Motif in the Primary Structure of CFTR, the Cystic Fibrosis Chloride Channel

Synthetic peptides with sequences representing putative transmembrane (M) segments of CFTR (the cystic fibrosis transmembrane conductance regulator) were used as tools to identify the involvement of such segments in forming the ionic pore of the CFTR Cl-channel. Peptides with sequences corresponding to M2 and M6 form anion-selective channels after reconstitution in lipid bilayers. In contrast, peptides with the sequences of M1, M3, M4, and M5, or peptides of the same amino acid composition as M2 and M6 but with scrambled sequences, do not form channels. Conductive heterooligomers of M2 and M6 exhibit a single channel conductance of 8 pS (in 0.15 M KCl) and a 95% selectivity for anions over cations, properties that emulate both the conductance and the selectivity of the authentic CFTR channel. The identification of sequence-specific motifs that account for key functional attributes of the CFTR channel suggests that such modules may represent fundamental units of function and are plausible constituents of the pore-forming structure of the CFTR Cl-channel.