Ion-channel formation assisted by electrostatic interhelical interactions in covalently dimerized amphiphilic helical...

An ultimate goal of synthetic ion-channel peptide design is to construct stable and functional ion-conducting pores. It is expected that specific interhelical interactions would facilitate the association of helices in phospholipid membranes and the successive helix-bundle formation. In the present study, we rationally designed helix-bundle ion channels using the synthetic hybrid peptide K20E20, a disulfide dimer of cationic- and anionic-amphiphilic helices Ac-CGG-(BKBA) 5-NH 2 and Ac-CGG-(BEBA) 5-NH 2. Circular dichroism (CD) measurements in aqueous media implied helix stabilization in the peptide caused by the interhelical electrostatic interactions. In addition, CD spectra recorded in the presence of DPPC liposomes and dye-leakage measurements suggested a high degree of association of peptide monomers in phospholipid membranes as well as high affinities between peptide and lipid bilayers. These features allowed ion-channel formation at extremely low peptide concentrations (as low as 1 nM). According to electrophysiological analyses, stable helix bundles were constructed of six peptide helices by association of three K20E20 molecules. Helix-helix association in lipid membranes, peptide-membrane interactions, and ion-channel formation of K20E20 peptides were all facilitated by intramolecular electrostatic interactions between the helices of the hybrid peptide and were pH-dependent. Conductance through K20E20 ion channels decreased under acidic conditions because of the interruption of the salt bridges.