The Effect of Ions on Membrane Elasticity - Implications for Vesicle Fusion

Abstract

Ions and charged peptides can have dramatic effects on the properties of membranes. A case in point is calcium and its crucial role in vesicle fusion.[1] Using all-atom molecular dynamics, we simulated calcium mediated vesicle fusion.[2] Aided by a new, local approach to determining membrane elastic properties,[3] we are able to quantify the effect of ions on lipid spontaneous curvature, bending rigidity, and tilt. We probe the effect of ions on membranes of different composition. Our simulations indicate that calcium specifically induces negative spontaneous curvature in those anionic lipid membranes which are susceptible to calcium mediated fusion, concomitantly strongly affecting the Gaussian bending modulus. We further determine the mechanism of membrane curvature induction through ion-headgroup interactions, giving special attention to lipid clustering. In addition to membrane elasticity, we discuss electrostatic effects on osmotic pressures and the hydration force. This systematic approach allows us to fill crucial gaps in our understanding of the mechanism of membrane fusion. Finally, we point out possible implications for synaptic vesicle fusion and endocytosis. [1] E. Neher, R. Schneggenburger, Nature 406, 889-893 (2000) [2] C. Allolio, A. Magarkar, P. Jurkiewicz, K. Baxova, M. Javanainen, R. Šachl, M. Hof, D. Horinek, V. Heinz, R. Rachel, C. Ziegler, M. Cebecauer, A. Schrofel, P. Jungwirth, resubmitted to PNAS (2018) [3] C. Allolio, A. Haluts, D. Harries,Chem. Phys, in press (2018)