Roles of Interleaflet Coupling and Hydrophobic Mismatch in Lipid Membrane Phase-Separation Kinetics

Area of Science:

• Biophysics
• Materials Science
• Computational Biology

Background:

• Understanding nanoscale organization in lipid bilayers is crucial for cell membrane function.
• Lipid phase separation and leaflet communication influence membrane properties.
• Hydrophobic mismatch is a key factor in lipid bilayer behavior.

Purpose of the Study:

• To investigate phase separation and inter-leaflet communication in ternary lipid bilayers.
• To explore the role of hydrophobic mismatch in lipid bilayer organization.
• To understand the kinetics and thermodynamics of lipid domain formation.

Main Methods:

• Coarse-grained molecular dynamics simulations of lipid bilayers with varying saturated lipid tail lengths.
• Analysis of phase separation kinetics and equilibrium states.
• Development of a semimicroscopic model to describe inter-leaflet couplings.

Main Results:

• A novel two-step kinetic process was observed, involving initial anti-registration followed by registration.
• Anti-registration becomes thermodynamically favored below a critical domain size of approximately 20 nm.
• Hydrophobic mismatch drives phase purification and influences lipid immiscibility at the molecular level.

Conclusions:

• Competing inter-leaflet couplings, including direct and indirect (hydrophobic mismatch) interactions, govern phase behavior.
• The identified length scale influences both lateral and transverse organization within cell membranes.
• Findings have implications for the symmetry and composition of membrane rafts and nanoclusters.