Interactions of membrane active peptides with planar supported bilayers: an impedance spectroscopy study

Membrane active peptides exert their biological effects by interacting directly with a cell's lipid bilayer membrane. These therapeutically promising peptides have demonstrated a variety of activities including antimicrobial, cytolytic, membrane translocating, and cell penetrating activities. Here, we use electrochemical impedance spectroscopy (EIS) on polymer-cushioned supported lipid bilayers constructed on single crystal silicon to study two pairs of closely related membrane active peptides selected from rationally designed, combinatorial libraries to have different activities in lipid bilayers: translocation, permeabilization, or no activity. Using EIS, we observed that binding of a membrane translocating peptide to the lipid bilayer resulted in a small decrease in membrane resistance followed by a recovery back to the original value. The recovery may be directly attributable to peptide translocation. A nontranslocating peptide did not decrease the resistance. The other pair, two membrane permeabilizing peptides, caused an exponential decrease of membrane resistance in a concentration-dependent manner. This permeabilization of the supported bilayer occurs at peptide to lipid ratios as much as 1000-fold lower than that needed to observe effects in vesicle leakage assays and gives new insights into the fundamental peptide-bilayer interactions involved in membrane permeabilization.