Percolation properties of two-component, two-phase phospholipid bilayers

Area of Science:

• Biophysics
• Materials Science
• Physical Chemistry

Background:

• Binary lipid mixtures commonly exhibit component immiscibility, particularly in the solid phase, but also in the fluid phase.
• Understanding phase behavior and diffusion barriers in lipid bilayers is crucial for various biological and material applications.

Purpose of the Study:

• To investigate the long-range translational diffusion of fluid-phase lipids in coexisting solid and fluid lipid bilayer phases.
• To characterize the nature of diffusion barriers presented by solid-phase domains using fluorescence recovery after photobleaching (FRAP).

Main Methods:

• Utilized the fluorescence recovery after photobleaching (FRAP) technique to measure lipid diffusion over micrometers.
• Examined lipid bilayers composed of binary lipid mixtures at varying temperatures and compositions, including coexisting solid and fluid phases.
• Analyzed diffusion behavior in relation to the percolation threshold between fluid and solid phase domains.

Main Results:

• Solid-phase domains act as impenetrable barriers to fluid-phase lipid diffusion.
• FRAP experiments distinguished between non-percolating (island) and percolating (sea) solid domains based on diffusion coefficients and fluorescence recovery.
• The position of the percolation threshold allowed estimation of phase mass fractions and solid domain symmetry.

Conclusions:

• Component immiscibility is prevalent in binary lipid mixtures, forming distinct solid and fluid domains.
• Solid domains significantly restrict lipid diffusion, with the nature of these barriers (percolating vs. non-percolating) detectable by FRAP.
• FRAP analysis of diffusion and percolation thresholds provides insights into lipid phase behavior and domain structure.