New Insights into the Mechanism of Action of the Antimicrobial Peptide Aurein 1.2. Isothermal Titration Calorimetry and Confocal Microscopy Studies

Abstract

Aurein 1.2 is a short (13 residue) cationic antimicrobial peptide (AMP) from the glandular skin secretions of Australian anurans of the Litoria genus. It has been suggested that this peptide disrupts membranes in a detergent-like manner. This peptide is considered too short to span the membrane and may possibly lie on the membrane surface without pore formation. Here, we use isothermal titration calorimetric (ITC) and phase-contrast microscopy to study the interaction of AU with membrane mimetic composed of SOPC/SOPG (95:5) and SOPC/SOPG (50:50). The hypothesis is that different membrane composition may lead to different peptide membrane interaction and to different mechanisms of action. ITC data showed an exothermic event at low lipid/peptide ratio, which is stronger for large unilamellar vesicles (LUVs) composed of SOPC/SOPG (50:50). These results showed that the affinity of AU is higher for the most charged vesicles. Phase contrast microscopy studies showed that AU solubilizes giant unilamellar vesicles (GUVs) containing SOPC/SOPG (50:50), but form pores on SOPC/SOPG (95:5) GUVs. These results showed that the mechanism of action of AU dependent on the membrane composition, making pores on low charged membranes but solubilizing the highest. It is according with the proposed in literature that the detergent mechanism can be considered and extreme of the toroidal pore mechanism.