Diffusion in complex membranes: bridging experiment and theory through simulation

Abstract

Cell membranes are highly complex, heterogeneous systems. This makes interpreting experimental measurements of interesting physical phenomena in terms of theoretical descriptions challenging, since there may be several different microscopic mechanisms affecting the observed diffusion. ☐ We use simulation to address this issue first in the context of diffusion in two membrane phases, where simultaneous measurements of single particle trajectories and fluorescence correlation spectroscopy (FCS) report two different diffusive behaviors. A technique was developed which allows simulation of FCS measurements from single particle trajectories, connecting the two experimental techniques. This technique finds no dependence of diffusion on spot width, indicative of simple homogeneous diffusion, and in contradiction with analysis of the single particle trajectories. ☐ We also measure dependence of diffusion on protein concentration in the membrane, where current theoretical treatments and other simulation results are limited. Using a simulation method that is explicitly designed to capture the peculiar hydrodynamics of membranes, we find no significant dependence of the diffusion constant on membrane protein concentration.