Determining how antimicrobial peptides affect the transversal diffusion rate of Cardiolipin, a central component in the bacterial membrane.

Antimicrobial peptides (AMPs) are promising alternatives to conventional antibiotics, as they can evade much of the bacterial resistance mechanisms as they do not block specific biochemical pathways, but rather act physically on the cytoplasmic membrane itself. AMPs have been shown to accelerate the transversal lipid diffusion, (lipid flip-flop) in phospholipid bilayers, which is normally very slow and controlled process in bacteria. The resulting lipid scrambling is believed to be fatal for the bacteria and could be central to the AMPs mode of action. Cardiolipin (CL) which is a larger, four tailed lipid is found to be localized at specific domains in the bacterial membrane, and with it’s large size the rate of lipid flip-flop is likely very slow. We propose to use the novel, floating asymmetric membranes developed by Dr. Clifton and coworkers, to systematically characterize the lipid flip-flop of CL-containing membranes, at several temperatures and with the addition of the natural AMPs Indolicidin and LL-37, using Neutron Reflectometry (NR). Having already successfully performed an initial NR experiment, demonstrating the ability to reliably make and characterise asymmetric membranes, we propose to further investigate the system using higher fraction of CL. This will enhance the contrast, and enable us to more reliably track the membrane asymmetry over time and to determine how the AMPs affect the rate of CL flip-flop.