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-channel proteins. Here we report on an uncharged peptide, Ac-(Leu-Ser-Ser-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. The current at a given holding membrane potential is larger than the current 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 present an ionic electrodiffusion model based on the helical-dipole potential and the dielectric interfacial polarization energy, which with reasonable values for dipole magnitude and dielectric constants, accurately replicates the current-voltage data.