Redistribution of Cholesterol in Model Lipid Membranes in Response to Alamethicin

Abstract

Cell membranes are complex mixtures of lipids, proteins and other molecules that serve as active, semipermeable barriers between cells and their internal organelles and the surrounding medium. Cell membrane molecular and macromolecular compositions are tightly regulated to ensure proper function. Cholesterol is a key component in mammalian cellular membranes, where it serves to maintain membrane fluidity and permeability. Here, the interaction of alamethicin, a 20 amino acid residue peptide that creates transmembrane pores in lipid bilayer membranes in a concentration-dependent manner, with cholesterol (Chol) containing dimyristoyl phosphatidylcholine (DMPC) membranes. Small-angle neutron scattering (SANS) data demonstrate that a low concentration of alamethicin (lipid to peptide ratio of 200:1) disrupts the lateral inhomogeneity seen in peptide-free DMPC:Chol vesicles, which is a coexistence of different phases. The resulting laterally heterogeneous bilayers are thinner than the peptide-free Lo phase, and possess a stronger asymmetry in the Chol content of the inner and outer bilayer leaflets. The results point to an alternative to the well-understood cytotoxic membrane permeabilization mechanism of action, specifically that membrane-active peptides are capable of disrupting lipid rafts and other functional structures in cell membranes.