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Structural Effects of Cation Binding to DPPC Monolayers

preprint
submitted on 30.08.2020 and posted on 31.08.2020 by Matti Javanainen, Wei Hua, Ondrej Tichacek, Pauline Delcroix, Lukasz Cwiklik, Heather Allen
Ions at the two sides of the plasma membrane maintain the transmembrane potential, participate in signaling, and affect the properties of the membrane itself. The extracellular leaflet is particularly enriched in phosphatidylcholine lipids an under the influence of Na+, Ca2+, and Cl− ions. In this work, we combined molecular dynamics simulations performed using state-of-the-art models with vibrational sum frequency generation (VSFG) spectroscopy to study the effects of these key ions on the structure of dipalmitoylphosphatidylcholine. We used lipid monolayers as a proxy for membranes, as this approach enabled a direct comparison between simulation and experiment. We find that the effects of Na+ are minor. Ca2+, on the other hand, strongly affects the lipid head group conformations and induces a tighter packing of lipids, thus promoting the liquid condensed phase. It does so by binding to both the phosphate and carbonyl oxygens via direct and water-mediated binding modes, the ratios of which depend on the monolayer packing. Clustering analysis performed on simulation data revealed that changes in area per lipid or CaCl2 concentration both affect the head group conformations, yet their effects are anti-correlated. Cations at the monolayer surface also attract Cl−, which at large CaCl2 concentrations penetrates deep to the monolayer. This phenomenon coincides with a radical change in the VSFG spectra of the phosphate group, thus indicating the emergence of a new binding mode.

Funding

Czech Science Foundation, EXPRO grant 19-26854X

Emil Aaltonen Foundation

NSF, grant CHE-1111762

NSF Center for Aerosol Impacts on Chemistry on the Environment, grant CHE-1305427

Czech Science Foundation, grant 17-06792S

History

Email Address of Submitting Author

matti.javanainen@gmail.com

Institution

Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences

Country

Czech Republic

ORCID For Submitting Author

0000-0003-4858-364X

Declaration of Conflict of Interest

no conflict of interest

Version Notes

Initial submission

Exports