Molecular dynamics simulation study of water at the model biomembranes interfaces

Hock-Seng Nguan^1*, Jer-Lai Kuo¹

¹Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan

* Presenter:Hock-Seng Nguan, email:nguanhs@gmail.com

The biological processes happen at the cell membranes require the presence of water. Intriguingly, as the important medium of the biological process, the water at the interface with the biomolecule is structurally and dynamically different from that of the bulk [1, 2]. Although these hydration water has been studied by many researchers [1,3,4,5,6], there are still lacking of understanding especially on their dynamics, structural heterogeneity and spatial extent of the hydration layer. In this work, using the molecular dynamics (MD) simulation, we aim to provide more understanding of the dynamics and the thermodynamics of these hydration layer of water at the biomembranes interfaces. Here, we simulated three different hydrated biomembranes bilayers; each bilayer consisted of lipid molecules 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamin (POPE) and digalactosyldiacylglycerols (DGDG), respectively. From the MD simulations, we analyzed the normal mode vibrational density of states (VDOS) of the water at the lipid-water interfaces, as well as that some of the headgroups atoms of the lipids. With the analysis, we are also able to calculate the contributions of rotational and vibrational motions towards the entropy of the interfacial water. Our results reveal the influence of the lipid head group vibration towards those interfacial water and the extent of the influence in terms of distances. Furthermore, we found the interfacial water has logarithmic dependent of the reorientational power spectrum at low frequency region, which resemble that of the supercooled and glassy water.

References
[1] Ball P., Chemical Reviews. 2008, 108, 74-108.
[2] Laage D., T. Elsaesser, and J.T. Hynes, Chemical Reviews, 2017. 117(16): p. 10694-10725.
[3] Berkowitz, M.L. and R. Vacha, Accounts of Chemical Research, 2012. 45(1): p. 74-82.
[4] Yamamoto, E., et al., Scientific Reports, 2014. 4.
[5] von Hansen, Y., S. Gekle, and R.R. Netz, Physical Review Letters, 2013. 111(11).
[6] Kanduč, M. et al., Nature Communications 8, 14899, (2017).

Keywords: Molecular dynamics, lipid bilayers, interfacial water, vibrational density of states, supercooled and glassy