Mosaic of Water Orientation Structures at a Neutral Zwitterionic Lipid/Water Interface Revealed by Molecular Dynamics Simulations

Abstract

Ordering of water structures near the surface of biological membranes has been recently extensively studied using interface-selective techniques like vibrational sum frequency generation (VSFG) spectroscopy. The detailed structures of interface water have emerged for charged lipids, but those for neutral zwitterionic lipids remain obscure. We analyze an all-atom molecular dynamics (MD) trajectory of a hydrated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine bilayer to characterize the orientation of interface waters in different chemical environments. The structure and dynamics of interfacial waters strongly depend on both their vertical position along the bilayer normal as well as vicinal lipid charged groups. Water orientation in the vicinity of phosphate groups is opposite to that around choline groups. The results are consistent with observed VSFG spectra and demonstrate that a mosaic of water orientation structures exists on the surface of a neutral zwitterionic phospholipid bilayer, reflecting rapid water exchange and the influence of local chemical environments.

Insights into the behavioral difference of water in the presence of GM1

“…S1 in Supporting information. We have found orientation of H-atoms of waters towards the PO 4 À group and reverse orientation for the choline group which is in accordance with the recent molecular dynamics simulation study [38]. Same type of orientation was also recognized near Cholesterol and GM1 head groups which concur well with the previous findings that the orientation of water molecules depends upon their local environment [31,61,62].…”

“…Theory of solvation of small and large apolar species in water was also developed [36]. The detailed structure of interfacial water for charged lipids has been extensively studied using vibrational sum frequency generation spectroscopy [37], and it was revealed very recently using molecular dynamics simulation study that a mosaic of water orientation exists on the surface of neutral zwitterionic phospholipid bilayers [38]. Though there exist a large amount of data on the structure and dynamics of interfacial water in lipid bilayer with different lipids, the works mostly emphasize on the properties of water near the surface of biomolecules [39][40][41][42][43] and there is a lack of evidences about the behavior of water near a comparatively rough surface containing molecule with bulky head group like GM1 (Monosialotetrahexosylganglioside) which is an important glycosphingolipid, present in the outer layer of the cell membrane [44] and it plays significant role to promote the toxicity of amyloid proteins present in raft membranes [45].…”

Molecular Modeling of Water Interfaces: From Molecular Spectroscopy to Thermodynamics

“…For instance, (1) the ~3100 cm -1 O-H stretch band of water in the imaginary part of the vibrational SFG response for the water-air interface 22,25,[30][31][32] and its assignments 23,27,33,34 are still under debate; (2) the surface tension of water at the waterair interface has been simulated only very recently with AIMD techniques, 15 In addition, simulations can be used for predicting the molecular mechanism of the physical phenomena at interfaces. For instance, MD simulations at the water-air interface have been used for predicting the molecular mechanism behind water evaporation at the water-air interface [35][36][37] and the behavior of the water droplet at the surface, [38][39][40] as well as understanding the molecular mechanism of the surface phenomena such as the fusion mechanism of the lipid bilayer 41,42 and ion transport mechanism in membranes.…”

Exploring fast proton transfer events associated with lateral proton diffusion on the surface of membranes

“…Proton diffusion (PD) along a membrane surface is more complicated than bulk PD since the structure of the lipid molecule, the distance between adjacent lipid molecules, and the water molecules in and around the lipid membrane all affect PD. Due to advances in fast spectroscopy experiments and molecular dynamics (MD) simulations, significant progress in our understanding of this type of PD has been made in the past decade (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23).…”