Quantification of Aminophospholipid Asymmetry in Supported Lipid Bilayers by Neutron Reflectometry

• Applicant: Dr. Ilya Reviakine, Ph.D.
• Subject Area: Biophysics
• Term: from 2014 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 264479891

Cell membranes are based on lipid bilayers that exhibit complex composition and organization. In healthy cells, the distribution of lipids between the two leaflets of the bilayer is asymmetric: phosphatidyl serine (PS) is restricted to the inner leaflet of the membrane, while the outer leaflet is predominantly composed of phosphatidyl choline and sphingomyelin. Lipids are also organized laterally, with heterogeneities on the lengthscale of tens of nm. How these arise is not clear, because the canonical high-melting, low-melting, cholesterol mixtures of phosphatidylcholines commonly used to model cell membranes exhibit macroscopic phase separation with um-size domains. Model systems that can capture both the lateral and the transverse aspects of lipid organization are scarce, and for that reason, studying how the two aspects of lipid organization in cell membranes couple to each other has been difficult. We developed a model system that captures both these features. It is based on supported lipid bilayers (SLBs) on TiO2 that contain the high-melting, low-melting, cholesterol mixture of phosphatidyl cholines, and PS, that is distributed asymmetrically. The goal of the current work is to quantify lipid distribution in these asymmetric cell membrane mimics by neutron reflectometry (NR) so that further studies of phase behavior and lipid diffusion in these systems could be carried out.

• DFG Programme: Research Grants