Electrostatic Interactions of Peptides with Lipid Membranes: Competitive Binding between Cationic Peptides and Divalent Counterions

In this thesis, we investigate a variety of problems involving the interaction of cationic peptides with lipid membranes. To this end we adopt Poisson-Boltzmann (PB) theory and coarse-grained models of these molecules. We first examine the electrostatic interaction of a positively-charged peptide with a negatively charged membrane immersed in a salty solution. In particular, we study how this interaction is influenced by peptides geometry, valence of salt ions, and lipid demixibility. Also we develop a more analytically tractable approach to peptide-membrane association, and then compare it with our PB approach. Finally, we study the interactions of cationic antimicrobial peptides with the outer leaflet of the outer membrane of Gram-negative bacteria. In particular, we incorporate charge discreteness and thus transverse charge correlations on the membrane surface. The main effect of charge discreteness is to enhance the affinity of counterions, especially multivalent ones, for the membrane. This effort enables us to study the competitive binding between cationic peptides and divalent counterions. Our results offer a physical explanation for the observed preferred binding of cationic antimicrobial peptides onto the outer leaflet of Gram-negative bacteria over divalent counterions.