Adsorption of the antimicrobial peptide arenicin and its linear derivative to model membranes--a maximum insertion pressure study.

Antimicrobial peptides (AMPs) are widely distributed in nature representing an ancient tool of host defence against bacterial invasion. The ability of the cyclic cationic antimicrobial peptide arenicin, Ar-1, and its novel and highly efficient linear derivative, C/S-Ar-1, to interact with 2D model membranes (POPC, DPPC, POPG, and DPPG) has been studied. Different phospholipid monolayers at the air-buffer interface, as simple and easy to manipulate models of the membrane surface, were used for these studies. The equilibrium adsorption pressure of both peptides depends on the charge of the lipid head group as well as on the lipid packing density (the largest value is observed for POPG). Only in the case of DPPG, the original Ar-1 penetrates much faster into the DPPG monolayer compared to the linear derivative C/S-Ar-1. Additionally, C/S-Ar-1 has been injected under lipid layers compressed to different starting pressures. In this way, the maximum insertion pressure (MIP) has been determined. Only for the negatively charged POPG, the MIP is clearly above the commonly accepted membrane pressure values, whereas they are between 30 and 34 mN/m for the zwitterionic lipids and the condensed DPPG. The results point to the importance of the membrane charge and fluidity. Electrostatic interactions can be clearly enhanced by hydrophobic ones.