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Abstract
The peptide melittin, a 26 amino acid, cationic peptide from honey bee (Apis mellifera)
venom, disrupts lipid bilayer membranes in a concentration-dependent manner. Rather
than interacting with a specific receptor, the peptide interacts directly with the
lipid matrix of the membrane in a manner dependent on the lipid composition. Here,
a small-angle neutron scattering study of the interaction of melittin with lipid bilayers
made of mixtures of dimyristoylphosphatidylcholine (DMPC) and cholesterol (Chol) is
presented. Through the use of deuterium-labeled DMPC, changes in the distribution
of the lipid and cholesterol in unilamellar vesicles were observed for peptide concentrations
below those that cause pores to form. In addition to disrupting the in-plane organization
of Chol, melittin produces vesicles having inner and outer leaflet compositions that
depend on the lipid-Chol molar ratio and on the peptide concentration. The changes
seen at high cholesterol and low peptide concentration are similar to those produced
by alamethicin (Qian, S. et al., J. Phys. Chem. B 2014, 118, 11200-11208), which points
to an underlying physical mechanism driving the redistribution of Chol, but melittin
displays an additional effect not seen with alamethicin. A model for how the peptide
drives the redistribution of Chol is proposed. The results suggest that redistribution
of the lipids in a target cell membrane by membrane active peptides takes places as
a prelude to the lysis of the cell.