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Fluctuating Lipid Bilayer Membranes with Diffusing Protein Inclusions : A Hybrid Continuum-Particle Approach

Lipid bilayer membranes appearing in biology and related experimental systems are often heterogeneous mixtures of lipid molecules and proteins. Many proteins through their geometry and specific interactions with lipids are thought to induce changes in the membrane material properties, which manifest in local stiffness variations and curvature. Consequently, as proteins diffuse within a bilayer, large-scale membrane features track with protein location. These interactions play an important role in the heterogeneous membrane mechanics and in the kinetics of membrane associated processes. To capture such effects, we have developed a hybrid continuum-particle description for the membrane-protein system that incorporates hydrodynamic coupling and thermal fluctuations. As an initial study we have investigated how protein curvature and membrane stiffness influence protein diffusion. We are also investigating how the area fraction of proteins influences membrane mechanical properties such as the elastic stiffness of the bilayer. Below are some recent simulation results.

First is a single curved protein diffusing within a membrane. The protein induces a local curvature that creates a membrane deformation that tracks with the protein location and influences significantly the protein diffusion. In the middle is shown a collection of flat proteins embedded within a lipid bilayer and how this influences the fluctuations of a membrane. Observation of the fluctuations along with spectral analysis can be used as a passive experimental measure of the effective membrane elasticity. Last is a collection of proteins that induce significant local curvature in the membrane. This is seen to drive significant deformations in the shape of the membrane and alter the fluctuation spectrum. This work is being carried out in collaboration with my advisor Paul J. Atzberger and Frank L. Brown.