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The shape and free energy of a lipid bilayer surrounding a membrane inclusion
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Biological Physics.
KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Biological Physics.ORCID iD: 0000-0002-7448-4664
2013 (English)In: Chemistry and Physics of Lipids, ISSN 0009-3084, E-ISSN 1873-2941, Vol. 169, 2-8 p.Article in journal (Refereed) Published
Abstract [en]

Membrane inclusion interactions are studied within the scope of continuum theory. We show that the free energy functional for the membrane thickness can be rewritten as a constant times a dimensionless integral. For cylindrical inclusions, the resulting differential equation gives a thickness profile that depends on the radius of the cylinder and one single lipid property, a correlation length that is determined by the ratio of the thickness compressibility and bending moduli. The solutions decay in a non-monotonic fashion with one single observable minimum. A solution for planar geometry may either be explicitly constructed or obtained by letting the radius of the cylinder go to infinity. In dimensionless units the initial derivative of the thickness profile is universal and equal to -1/root 2 In physical units, the derivative depends on the size of the hydrophobic mismatch as well as the membrane correlation length and will usually be fairly small but clearly non-zero. The line tension between the protein inclusion and a fluid phase membrane will depend on the hydrophobic mismatch and be of the order of 10 pN (larger for the gel phase). This results in free energy costs for the inclusion that will be up to tens of kJ/mol (in the fluid phase).

Place, publisher, year, edition, pages
2013. Vol. 169, 2-8 p.
Keyword [en]
Membrane protein interactions, Continuum theory, Line tension, Kelvin functions, Coarse graining, Molecular dynamics
National Category
Physical Chemistry
URN: urn:nbn:se:kth:diva-124470DOI: 10.1016/j.chemphyslip.2012.12.005ISI: 000319310800002ScopusID: 2-s2.0-84876420080OAI: diva2:636081

QC 20130708

Available from: 2013-07-08 Created: 2013-07-05 Last updated: 2014-09-19Bibliographically approved
In thesis
1. Classical and Quantum Descriptions of Proteins, Lipids and Membranes
Open this publication in new window or tab >>Classical and Quantum Descriptions of Proteins, Lipids and Membranes
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis the properties of proteins and membranes are studied by molecular dynamics simulations. The subject is decomposed into parts addressing free energy calculations in proteins, mechanical inclusion models for lipid bilayers, phase transitions and structural correlations in lipid bilayers and atomistic lipid bilayer models. The work is based on results from large scale computer simulations, quantum mechanical and continuum models. Efficient statistical sampling and the coarseness of the models needed to describe the ordered and disordered states are of central concern.

Classical free energy calculations of zinc binding, in metalloproteins, require a quantum mechanical correction in order to obtain realistic binding energies. Classical electrostatic polarisation will influence the binding energy in a large region surrounding the ion and produce reasonable equilibrium structures in the bound state, when compared to experimental evidence.

The free energy for inserting a protein into a membrane is calculated with continuum theory. The free energy is assumed quadratic in the mismatch and depend on two elastic constants of the membrane. Under these circumstances, the free energy can then be written as a line tension multiplied by the circumference of the membrane inclusion. The inclusion model and coarse grained particle simulations of the membranes show that the thickness profile around the protein will be an exponentially damped oscillation.

Coarse-grained particle simulations of model membranes containing mixtures of phospholipid and cholesterol molecules at different conditions were performed. The gel-to-liquid crystalline phase transition is successively weakened with increasing amounts of cholesterol without disappearing even at a concentration of cholesterol as high as 60%.

A united atom parameterization of diacyl lipids was constructed. The aim was to construct a new force field that retains and improves the good agreement for the fluid phase and at the same time produces a gel phase at low temperatures, with properties coherent with experimental findings. The global bilayer tilt obtains an azimuthal value of 31and is aligned between lattice vectors in the bilayer plane. It is also shown that the model yield a correct heat of melting as well as heat capacities in the fluid and gel phase of DPPC.


Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2014. xiv, 73 p.
TRITA-FYS, ISSN 0280-316X ; 2014:55
Quantum corrections, Coordination structure, Polarisation, Phase transitions, Kelvin differential equation, Line tension, Elastic membrane models, Molecular particle models, Zinc binding, Cholesterol and Phospholipids
National Category
Physical Sciences
Research subject
Biological Physics
urn:nbn:se:kth:diva-151396 (URN)978-91-7595-253-6 (ISBN)
Public defence
2014-10-03, Sal FA32, AlbaNova Universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Swedish Research Council

QC 20140919

Available from: 2014-09-19 Created: 2014-09-19 Last updated: 2014-10-07Bibliographically approved

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Tjörnhammar, RichardEdholm, Olle
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