Kinetics, Statistics, and Energetics of Lipid Membrane Electroporation Studied by Molecular Dynamics Simulations
Rainer A Böckmann 1*, Bert L de Groot 2, Sergej Kakorin 3, Eberhard Neumann 3 and Helmut Grubmüller 2
1 Theoretical & Computational Membrane Biology, Saarland University
2 Max Planck Institute for Biophys. Chemistry
3 Bielefeld University, Department of Chemistry, Biophysical Chemistry (PC III)
* To whom correspondence should be addressed. E-mail: rainer{at}bioinformatik.uni-saarland.de.
Submitted on January 14, 2008
Revised on February 18, 2008
Accepted on 31 March 2008
 |
Abstract |
|---|
Membrane electroporation is the method to directly transfer bioactive substances such as drugs and genes into living cells, as well as preceding electrofusion. Although much information on the microscopic mechanism has been obtained both from experiment and simulation, the existence and nature of possible intermediates is still unclear. To elucidate intermediates of electropore formation by direct comparison with measured prepore formation kinetics, we have carried out 49 atomistic electroporation simulations on a POPC bilayer for electric field strengths between 0.04 and 0.7 V/nm. A statistical theory is developed to facilitate direct comparison of experimental (macroscopic) prepore formation kinetics with the (single event) preporation times derived from the simulations, which also allows to extract an effective number of lipids involved in each pore formation event. A linear dependency of the activation energy for prepore formation on the applied field is seen, with quantitative agreement between experiment and simulation. The distribution of preporation times suggests a four state pore formation model. The model involves a first intermediate characterized by a differential tilt of the polar lipid head groups on both leaflets, and a second intermediate ('prepore'), where a polar chain across the bilayer is formed by 3-4 lipid head groups and several water molecules, thereby providing a microscopic explanation for the polarizable volume derived previously from the measured kinetics. An average pore radius of 0.47 ± 0.15 nm is seen, in favourable agreement with conductance measurements and electrooptical experiments of lipid vesicles.
Key Words:
lipid bilayer, membrane electroporation, membrane electropores, molecular dynamics simulation, pore formation
