Distinct structural elements that direct solution aggregation and membrane assembly in the channel-forming peptide M2GlyR

Restoration of chloride conductance via the introduction of an anion selective pore, formed by a channel-forming peptide, has been hypothesized as a novel treatment modality for patients with cystic fibrosis (CF). Delivery of these peptide sequences to airway cells from an aqueous environment in the absence of organic solvents is paramount. New highly soluble COOH- and NH2-terininal truncated peptides, derived from the second transmembrane segment of the glycine receptor alpha-subunit (M2GlyR), were generated, with decreasing numbers of amino acid residues. NH2-terminal lysyl-adducted truncated peptides with lengths of 22, 25, and 27 amino acid residues are equally able to stimulate short circuit current (I-SC). Peptides with as few as 16 amino acid residues are able to stimulate I-SC, although to a lesser degree. In contrast, COOH-terminal truncated peptides show greatly reduced induced I-SC values for all peptides fewer than 27 residues in length and show no measurable activity for peptides fewer than 21 residues in length. CD spectra for both the NH2- and COOH-truncated peptides have random structure in aqueous solution, and those sequences that stimulated the highest maximal I-SC are predominantly helical in 40% trifluoroethanol. Peptides with a decreased propensity to form helical structures in TFE also failed to stimulate I-SC. Palindromic peptide sequences based on both the NH2- and COOH-terminal halves of M2GlyR were synthesized to test roles of the COOH- and NH2-terminal halves of the molecule in solution aggregation and channel forming ability. On the basis of the study presented here, there are distinct, nonoverlapping regions of the M2GlyR sequence that define solution aggregation and membrane channel assembly. Peptides that eliminate solution aggregation with complete retention of channel forming activity were generated.