Abstract
Stabilization of protein charges due to their interaction with membrane fluctuations is a subject of growing interest, especially because of its possible implications for voltage gating. Two complementary mechanisms governing charge-fluctuation interactions are considered: (1) the electroelastic mechanism (EM) [Partenskii, et al., Israel J. Chem. 47, 385 (2007)], where the membrane is treated as an elastic slab (smectic bilayer model); (2) the hydrophobic mechanism (HM), which accounts for water penetration into the membrane's hydrophobic core with a corresponding interfacial tension contribution. In both cases the linear Poisson-Boltzmann equation is solved using a multi-dielectric continuum model with arbitrarily shaped membrane-water interfaces and a point charge surrounded by a “Born sphere” of low dielectric constant. The EM often leads to large membrane thickness perturbations, far larger than are consistent with elastic model descriptions. We demonstrate that switching from EM to HM becomes energetically advantageous at intermediate perturbation amplitudes. We apply kinetic Monte Carlo Reaction Path Following [Miloshevsky & Jordan. J. Chem. Phys. 122, 214901 (2005)] using the water dimple's amplitude or the z-coordinate of the charge as the reaction coordinate for determining the shape of the solvation cavity. The resulting picture confirms that of recent MD studies.