Interaction between inclusions mediated by lipid membranes – MEMINT

We will probe the interaction induced by lipid membranes between included molecules (and other nano-objects). This study presents both a fundamental interest, from the point of view of soft matter physics, and a relevance to understanding the activity of important biological molecules, such as native membrane proteins and antimicrobial peptides. In particular, the cytotoxic activity of the latter is directly related to the composition of the membrane (charge, thickness, presence of cholesterol) rather than to specific chemical recognition. It has long been posited that highly simplified descriptions (e.g. in terms of ‘hydrophobic matching’) capture the essence of the process, but the extensive body of theoretical and numerical work cannot be validated and refined due to the lack of experimental results. We intend to measure accurately the interaction between membrane inclusions. Highly aligned lipid multilayers, doped with antimicrobial peptides and fully hydrated (in excess water) will be studied using small-angle X-ray scattering. The resulting two-dimensional structure factor of the fluid formed by the inclusions will yield the interaction potential in the plane of the membrane. We will perform systematic studies of this potential as a function of the relevant parameters and compare the results to existing theoretical models. The next step will be to use as ‘membrane probes’ monodisperse and hydrophobic inorganic particles (contained within the bilayer), in order to extend the investigation to a wider range of parameters (especially to lower concentrations of inclusions). From the results of this wide investigation will emerge a clearer picture of the lipid membrane as a complex two-dimensional fluid and of the way it influences the interaction between included objects, in particular antimicrobial peptides and membrane proteins.