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Journal Article

Exploiting lipid permutation symmetry to compute membrane remodeling free energies.

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Bubnis,  G.
Department of Theoretical and Computational Biophysics, MPI for biophysical chemistry, Max Planck Society;

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Risselada,  H. J.
Department of Theoretical and Computational Biophysics, MPI for biophysical chemistry, Max Planck Society;

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Grubmüller,  H.
Department of Theoretical and Computational Biophysics, MPI for biophysical chemistry, Max Planck Society;

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Fulltext (public)

2382931.pdf
(Publisher version), 606KB

Supplementary Material (public)

2382931_Suppl.pdf
(Supplementary material), 6MB

Citation

Bubnis, G., Risselada, H. J., & Grubmüller, H. (2016). Exploiting lipid permutation symmetry to compute membrane remodeling free energies. Physical Review Letters, 117(18): 188102. doi:10.1103/PhysRevLett.117.188102.


Cite as: http://hdl.handle.net/11858/00-001M-0000-002C-4072-2
Abstract
A complete physical description of membrane remodeling processes, such as fusion or fission, requires knowledge of the underlying free energy landscapes, particularly in barrier regions involving collective shape changes, topological transitions, and high curvature, where Canham-Helfrich (CH) continuum descriptions may fail. To calculate these free energies using atomistic simulations, one must address not only the sampling problem due to high free energy barriers, but also an orthogonal sampling problem of combinatorial complexity stemming from the permutation symmetry of identical lipids. Here, we solve the combinatorial problem with a permutation reduction scheme to map a structural ensemble into a compact, nondegenerate subregion of configuration space, thereby permitting straightforward free energy calculations via umbrella sampling. We applied this approach, using a coarse-grained lipid model, to test the CH description of bending and found sharp increases in the bending modulus for curvature radii below 10 nm. These deviations suggest that an anharmonic bending term may be required for CH models to give quantitative energetics of highly curved states.