From a hydrodynamic perspective, a lipid membrane is considered to be a quasi-2D viscous liquid, with molecular motion confined to 2D, while momentum is also exchanged with the 3D surrounding solvent. The hydrodynamic picture, classically analyzed by Saffman and Delbrück, was recently proposed to lead to correlated motion of membrane-embedded biomolecules separated by distances much larger than their size. Here, we present the first experimental measurements of correlated Brownian motion in lipid bilayers. We study pairs of lipid tracers using dual-color single particle tracking techniques. Employing a novel laser modulation scheme that allows us to obtain sub-millisecond temporal resolution, we measure coupling diffusion coefficients (correlation functions) and find them to decay over a distance as large as ~100 nm. To interpret the experimental results, we apply the “regularized Stokeslets” method, generalized to a two leaflet membrane. The correlated diffusion measured here provides a powerful means to probe membrane hydrodynamics. It has the potential to expose important differences between the dynamics of freely floating membranes and of supported bilayers, such as those attached to the cytoskeleton in cells or placed on a solid surface.

Brownian motion within lipid bilayers is correlated over large distances

2019 Fall National Meeting

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