A HELICAL-DIPOLE MODEL DESCRIBES THE SINGLE-CHANNEL CURRENT RECTIFICATION OF AN UNCHARGED PEPTIDE ION-CHANNEL

We are designing simple peptide ion channels as model systems for the study of the physical principles controlling conduction through ion-ch annel proteins. Here we report on an uncharged peptide, Ac-(Leu-Ser-Se r-Leu-Leu-Ser-Leu)(3)-CONH2, designed to form an aggregate of parallel , amphiphilic, membrane-spanning alpha-helices around a central water- filled pore. This peptide in planar lipid bilayers forms ion channels that show single-channel current rectification in symmetric 1 M KCl. T he current at a given holding membrane potential is larger than the cu rrent measured through the same channel when the potential is reversed . Based on our hypothesized gating mechanism, the larger currents flow from the peptide carboxyl terminus toward the amino terminus. We pres ent an ionic electrodiffusion model based on the helical-dipole potent ial and the dielectric interfacial polarization energy, which with rea sonable values for dipole magnitude and dielectric constants, accurate ly replicates the current-voltage data.