The basic structural component of biological cell membranes are bilayer-forming lipids. In these amphiphilic molecules a hydrophilic group is connected to one or two hydrophobic hydrocarbon chains. When dissolved into water they spontaneously assemble into a variety of structures. In Nature lipid bilayers form the outer plasma membrane of cells as well as the walls of the different cellular compartments and organelles, such as the endoplasmic reticulum, the Golgi apparatus, and the nucleus [1]. 






1. 1. H. Lodish, A. Berk, L. Zirpursky, P. Matsurada, D. Baltimore, and J. Darnell, Molecular Cell Biology, (Freemen and Company, New York, 2000).

2. 2. I.R. Cooke and M. Deserno, J. Chem. Phys.  123, 224710 (2005).

3. 3. V.A. Harmandaris and M. Deserno, J. Chem. Phys. 125, 204905, 2006.

4. 4. V.A. Harmandaris and M. Deserno,  in preparation.

5. 5. B. Reynolds, G. Illya, V.A. Harmandaris, M.M. Müller, K. Kremer, M. Deserno,  Nature 447, 461-464, 2007.

We have developed [3] a new method for calculating the bending rigidity of lipid membranes in simulations.  It involves the simulation of cylindrical membrane tethers, spanned across the periodic boundary conditions of the simulation box, and measuring their equilibrium radius as well as the tensile force they exercise on the box.  In contrast to fluctuation based schemes, which monitor thermally excited shape deformations, our approach actively imposes a deformation on the system and measures the restoring force and is thus not limited to the regime of deformations accessible by thermal energy. Our method is very efficient, also applicable to stiff membranes which show very small undulations to begin with, and does not crucially depend on the relaxation of very slow long wavelength modes.


Recently the method has been extended to biphasic cylindrical tethers [4]. The study of the interface allows us to get direct information about the difference between the two Gaussian rigidities of the two phases.

Curvature-mediated interactions between inclusion in cell lipid membranes is an open question. Recently we used coarse-grained membrane simulations to show that curvature-inducing model proteins adsorbed on lipid bilayer membranes can experience attractive interactions that arise purely as a result of membrane curvature [5]. We find that once a minimal local bending is realized, the effect robustly drives protein cluster formation and subsequent transformation into vesicles with radii that correlate with the local curvature imprint. Owing to its universal nature, curvature-mediated attraction can operate even between proteins lacking any specific interactions, such as newly synthesized and still immature membrane proteins in the endoplasmic reticulum.

Modeling of Biological Membranes