Molecular dynamics simulations of ether- and ester-linked phospholipids

Differences in bilayer structure between ether- and ester-linked phospholipids are well documented. However, the specific atomistic mechanisms underlying these structural differences remain unclear. Ester-linked lipids like dipalmitoylphosphatidylcholine (DPPC) are common in eukaryotes, while ether-linked lipids like dihexadecylphosphatidylcholine (DHPC) are found in archaea and certain mammalian membranes. These differences raise questions about their functional implications. Prior research has shown that ether-linked lipids can alter membrane permeability and stability. Yet, the exact molecular interactions that cause these effects are not fully understood. This gap motivated the use of molecular dynamics simulations to explore the atomistic behavior of these lipid bilayers. The goal is to clarify whether structural or dynamic properties of water in the headgroup region contribute to the observed differences in bilayer permeability. This study builds on prior work by investigating the dipole potential and water dynamics in ether- and ester-linked membranes.

The aim of this study is to investigate the atomistic interactions that distinguish ether-linked from ester-linked phospholipid bilayers. The researchers focus on two specific lipids: DPPC, an ester-linked phospholipid, and DHPC, an ether-linked counterpart. The study seeks to clarify whether differences in bilayer permeability arise from variations in compressibility, dipole potential, or water dynamics in the headgroup region. The motivation stems from the need to understand why ether-linked lipids, such as plasmalogens, are enriched in certain human membranes. The authors also aim to address a prior unresolved question about whether permeability differences are due to area per lipid or water diffusion coefficients. By simulating these bilayers, the researchers hope to provide insights into the molecular mechanisms underlying membrane stability and function.

The researchers employed molecular dynamics simulations to model two lipid bilayers: DPPC and DHPC. Simulations were performed using established computational protocols to capture structural and dynamic properties. The study focused on analyzing compressibility, dipole potential, and water order in the headgroup region. Structural parameters such as bilayer thickness and area per lipid were calculated to compare the two systems. Dipole potential was measured to assess electrostatic interactions at the bilayer surface. Water dynamics were evaluated by tracking hydrogen bonding and diffusion coefficients in the headgroup region. The simulations provided atomistic resolution of lipid-water interactions and bilayer stability. These methods allowed the researchers to distinguish between structural and dynamic contributions to bilayer permeability.

The simulations revealed that DPPC bilayers are more compressible than DHPC bilayers. This suggests that ether-linkage may confer greater structural rigidity. The dipole potential of DHPC was found to be lower than that of DPPC, but DHPC exhibited a higher potential barrier at the bilayer surface. This indicates that DHPC may resist ion permeation more effectively. Water in the headgroup region of DHPC was more ordered and less mobile compared to DPPC. The hydrogen bonding network in DHPC was more stable, reducing water diffusion. These findings suggest that water dynamics in the headgroup region play a key role in determining bilayer permeability. The results align with prior studies showing that DHPC bilayers have lower permeability than DPPC. The data support the hypothesis that water order and mobility, rather than area per lipid, are the primary factors affecting permeability differences.

The authors conclude that ether-linked DHPC bilayers exhibit distinct structural and dynamic properties compared to ester-linked DPPC bilayers. The higher compressibility of DPPC suggests that ether-linkage provides greater stability. The dipole potential measurements indicate that DHPC has a higher surface barrier, which may reduce ion permeability. The more ordered and less mobile water layer in DHPC supports the idea that water dynamics are central to permeability differences. These findings help clarify the molecular basis for the functional differences between ether- and ester-linked lipids. The study resolves a prior uncertainty about whether permeability differences stem from area per lipid or water diffusion coefficients. The results suggest that water order and mobility are the primary contributors to the observed effects. The authors propose that these findings could inform future studies on membrane stability and lipid function in different biological contexts.