We have designed a four-helix protein that is expected to tetramerize in the membrane to form an ion channel with a structurally well-defined pore. This should serve as a model system to study the structural requirements of voltage-sensitive, ion-selective transmembrane channels. We have synthesized the peptide corresponding to the channel-lining helix. Circular dichroism (CD) spectroscopy shows that this peptide is helical in the membrane. Fluorescence resonance energy transfer (FRET) shows that this peptide, at low concentrations, forms aggregates in 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) liposomes and facilitates ion transport across liposomal membranes. Our data indicate that a component of the designed four-helix protein, i.e., the channel-lining helix, behaves as per design.