Liptin interactions with phospholipid membranes as shown by differential scanning calorimetry and fluorescence efflux studies

Abstract

This thesis describes the work done with various liptins on lipid membranes. The liptins are organic molecules designed to interact with bacteria in hopes of reducing the antimicrobial resistance threat. The hypothesis is that the liptins will have a pocket which can interact with phosphatidylglycerol, PG, on the phospholipid membrane. With this interaction, the liptins binds to the membrane and causes membrane destabilization. Various lipids vesicles were prepared and liptins were introduced to examine the effect. By the use of differential scanning calorimetry (DSC), and fluorescence efflux studies, details about the liptin interactions can be investigated. The DSC studies reveal that the liptins affect the membrane bilayer by reducing the enthalpy of the transition from gel ordered phase to liquid disordered phase, while keeping the transition temperature constant. As for the fluorescence efflux studies, they reveal information on possible pore formation induced in the membrane by the liptins with the use of carboxyfluorescein. Carboxyfluorescein are encapsulated within the lipid vesicles, where it will self-quench. As carboxyfluorescein is released from leakage of the vesicles, it no longer self-quenches and the solution will have a higher fluorescence intensity. The resulting intensity will be used in calculations to determine the percent efflux. The fluorescence efflux studies shows an increase in efflux or leakage due to interaction of the liptins with the lipid vesicles.