Membrane Diffusion of Tethered Dimer and Trimer Systems

Abstract

We have used molecular dynamics simulations to investigate the diffusion of tethered dimer and trimer systems in lipid bilayers. Coarse-grained (CG) models of DPPC dimers were simulated in a DPPC bilayer with the MARTINI model, and single-lipid diffusion constants compared to those obtained for dimmers and trimers at various tether lengths. The ratio of diffusion constants matches well with theoretical predictions of a simple bead model. A full theoretical model of the translational and rotational diffusion of tethered dimers and trimers was developed at the Saffman-Delbruck level, and results were compared to the simple bead model. The ratios of diffusion constants from the theoretical and CG models were then compared to experimental diffusion constants of pleckstrin homology (PH) domains bound to lipids with a PIP3 (phosphatidylinositol (3,4,5)-trisphosphate) head group. Excellent agreement between all systems was found, indicating that the frictional contributions of multiple, coupled but well-separated lipids are additive, analogous to the free-draining limit for isotropic fluids.