The Effects of Calcium on the Structure of Zwitterionic Lipid Bilayers

Calcium is one of many different ions found in the extracellular fluid and in the cytosol of the cells of the body. Calcium has a major effect on the cellular environment and especially the lipid bilayer that encases it. Calcium also has major implications when discussing the structure of the bilayer and the fusion of cells to various other vesicles. Molecular simulation using the CHARMM (ver. 36) force field parameters and the molecular dynamics simulation engine NAMD (ver. 2.9) were performed  on lipid bilayers composed of the zwitterionic lipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in the presence of various ions to demonstrate what effects these ions have on bilayer structure. Systems of sodium ions, calcium ions, and systems without ions were simulated under isobaric and isothermal conditions. Results show that both ions decrease the area per lipid and increase the order parameter of the lipid tails. This data directly shows the effects of calcium on the lipid bilayer structure and its implications for the cell as a whole.