Phase behavior of supported lipid bilayers: A systematic study by coarse-grained molecular dynamics simulations

Area of Science:

• Membrane biophysics
• Computational biophysics
• Materials science

Background:

• Solid-supported lipid bilayers (SSLBs) are widely used models for biological membranes due to their enhanced stability.
• The proximity to the solid substrate can influence the phase behavior of SSLBs, a phenomenon that remains poorly understood.
• Limited computational studies exist on the phase behavior of SSLBs, especially concerning lipid-substrate interactions.

Purpose of the Study:

• To investigate the effect of varying lipid-substrate interactions on the phase behavior of solid-supported lipid bilayers.
• To understand how substrate proximity and attractive forces influence lipid distribution and membrane properties.
• To provide insights into the computational modeling of SSLBs.

Main Methods:

• Molecular dynamics simulations were employed using an implicit-solvent model.
• The study systematically varied the attractive interactions between the lipid head groups and the substrate.
• Simulations focused on analyzing lipid translocation, transbilayer density, order parameters, and phase behavior.

Main Results:

• Attractive lipid-substrate interactions promote lipid translocation to the leaflet closest to the substrate, creating a transbilayer lipid density imbalance.
• The proximal leaflet exhibits a higher lipid density and order parameter compared to the distal leaflet, with effects intensifying with stronger lipid-substrate interactions.
• The proximal leaflet shows distinct gel and fluid phases with an abrupt melting transition, while the distal leaflet displays inhomogeneous gel and fluid domains, particularly at lower temperatures.

Conclusions:

• Lipid-substrate interactions significantly alter the phase behavior and lipid distribution in solid-supported lipid bilayers.
• The observed transbilayer imbalance and distinct phase transitions in SSLBs are direct consequences of attractive forces with the underlying substrate.
• Computational modeling provides valuable insights into the complex behavior of SSLBs, aiding in their application as biomembrane models.