Membrane Disruption by Antimicrobial Peptide Protegrin-1 is Tuned by Incorporation of Cholesterol and Phosphoethanolamine Lipids

Abstract

Antimicrobial peptides (AMPs) are a class of small (less than 100 amino acid residues) host defense peptides that induce selective membrane lytic activity against microbial pathogens. To understand the mechanism of membrane disruption by AMPs, we investigated, via atomic force microscopy, topological changes induced by protegrin-1 (PG-1), an 18-residue, cationic, β-sheet AMP isolated from pig leukocytes, in supported phospholipid bilayers (SPBs). Lipid mixtures of dioleoylphosphatidylserine (DOPS), dioleoylphosphatidylcholine (DOPC), and cholesterol were used to mimic eukaryotic cell membranes while bacterial cell membranes were emulated by substitution of cholesterol for dioleoylphosphatidylethanolamine (DOPE). We have previously shown that AMP disruption of zwitterionic dimyristoylphosphatidylcholine (DMPC) SPBs induce concentration dependent structural transformations that progress from fingerlike instabilities at bilayer edges, to the formation of sievelike nanoporous structures, and finally to a network of wormlike micellar structures. The observed transformations suggest that the peptides act to lower the interfacial energy of the bilayer in a manner similar to detergents. Detergent solubilization of membranes encompass processes such as pore formation, blebbing, budding, and vesiculation that share common saddle-splay (“negative Gaussian”) curved topologies. We pose that membranes rich in negative curvature lipids such as those with phosphoethanolamine (PE) headgroups enhance the efficacy of AMP disruption while those membranes containing cholesterol retard disruption. Results have shown that cholesterol incorporation shifts the disruption susceptibility of a bilayer to a higher peptide dosage regime while an opposite effect is observed in the presence of PE. The observed trend sheds light on a lingering debate as to how nature has evolved AMPs to discriminate between host and pathogen.