Fluctuation Spectrum and Electrical Stresses in Biomembranes Probed by Molecular Dynamics Simulations

Abstract

We simulate a large patch of membrane (130x10x20 nm) using the Martini coarse grained force field for lipids. The large size of the membrane enables access to long wavelength fluctuations, which allows us to compute a fluctuation spectrum (fluctuation amplitude at different wavelengths). The spectrum contains both a tension dominated and a bending rigidity dominated regime on wavelengths well above the protrusion regime [1] or molecular tilt regime [2]. The fluctuation spectrum can then be fitted to the prediction of to the standard Helfrich effective Hamiltonian [3], like in flickering experiments. The tension used in the fit of the fluctuation spectrum is calculated directly from the lateral stresses, and our only fit parameter is then the bending rigidity. We establish an overall consistency of the bending rigidity obtained from fits of the fluctuation spectrum for membranes with different tensions. We have also applied an electric field on the membrane. The electric field will change the lateral stress profile of the membrane and the change of the fluctuation spectrum is studied in detail. In particular, the response of the membrane stress profile to the applied electric field is compared to our recent theory [4].[1] G. Brannigan and F. L. H. Brown, Biophys J. 90, 1501 (2006)[2] M. C. Watson E. G. Brandt P. M. Welch and F. L. H. Brown, Phys. Rev. Lett. 109, 028102 (2012)[3] U. Seifert, Adv. Phys., 46, 13-137 (1997)[4] M. A. Lomholt, B. Loubet and J. H. Ipsen, Phys. Rev. E 83, 011913 (2011)