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Computer simulation study of intermolecular voids in unsaturated phosphatidylcholine lipid bilayers
A L Rabinovich1, N K Balabaev, M G Alinchenko
1Institute of Biology, Karelian Research Centre, Russian Academy of Sciences, Pushkinskaya 11, R-185910 Petrozavodsk, Russia.
The Journal of Chemical Physics
|April 20, 2005
Summary
Computer simulations reveal how lipid bilayer free volume changes with unsaturation. Increased unsaturation in lipid tails enhances membrane flexibility and free volume, facilitating water permeation through existing channels.
Area of Science:
- Biophysics
- Computational Chemistry
- Materials Science
Background:
- Phosphatidylcholine (PC) lipid bilayers are fundamental components of cell membranes.
- Understanding the free volume within these bilayers is crucial for predicting membrane properties and function.
- Lipid unsaturation significantly impacts membrane fluidity and permeability.
Purpose of the Study:
- To investigate the free volume characteristics of hydrated unsaturated phosphadidylcholine (PC) lipid bilayers using computer simulations.
- To analyze how varying degrees of unsaturation in the lipid tails affect the free volume distribution within the membrane.
- To compare the free volume profiles of unsaturated PC bilayers with a saturated reference system.
Main Methods:
- Performed isothermal-isobaric ensemble (NPT) simulations at 1 atm and 303 K for five different unsaturated PC lipid bilayers and one saturated PC bilayer.
- Utilized a generalized Voronoi-Delaunay method to analyze the characteristics and distribution of free volume within the simulated lipid bilayers.
- Interpreted the free volume profiles by dividing the membrane into distinct aqueous, polar, and apolar zones, and further into five subzones.
Main Results:
- The fraction of free volume across the membrane exhibits a complex, structured pattern, divisible into three major zones and five subzones.
- Free volume in the central region of the membrane increases with greater unsaturation in the sn-2 lipid chain.
- Increased methylene-interrupted double bonds lead to more flexible lipid tails, reducing their extension into the membrane's middle.
Conclusions:
- The study elucidates the intricate relationship between lipid unsaturation and free volume distribution in PC bilayers.
- While no broad pre-existing channels for water permeation were identified, existing free volume channels significantly facilitate the passage of small molecules like water.
- The findings provide valuable insights into membrane transport mechanisms and the role of lipid composition.