Directional Potassium Transport through a Unimolecular Peptide Channel.

Three unimolecular peptide channels have been designed and prepared by using the β-helical conformation of gramicidin A (gA). The new peptides bear one to three NH3+ groups at the N-end and one to three CO2- groups at the C-end. These zwitterionic peptides were inserted into lipid bilayers in an orientation-selective manner. Conductance experiments on planar lipid bilayers showed that this orientation bias could lead to observable directional K+ transport under multi-channel conditions. This directional transport behavior can further cause the generation of a current across a planar bilayer without applying a voltage. More importantly, in vesicles with identical external and internal KCl concentrations, the channels can pump K+ across the lipid bilayer and cause a membrane potential.