A correlation between lipid domain shape and binary phospholipid mixture composition in free standing bilayers: A...

Area of Science:

• Biophysics
• Materials Science
• Physical Chemistry

Background:

• Giant unilamellar vesicles (GUVs) are crucial model systems for studying lipid membrane behavior.
• Understanding lipid phase behavior is essential for cell membrane function and drug delivery.

Purpose of the Study:

• To investigate the phase behavior of binary phospholipid mixtures within GUVs.
• To characterize the formation, morphology, and dynamics of fluid and solid lipid domains.
• To correlate lipid domain properties with the hydrophobic chain length mismatch between components.

Main Methods:

• Utilized two-photon excitation fluorescence microscopy for high-resolution imaging of GUVs.
• Employed the fluorescent probe Laurdan to differentiate lipid phases based on generalized polarization (GP).
• Analyzed GUVs composed of various phospholipid binary mixtures at different temperatures.

Main Results:

• Observed distinct fluid and solid lipid domains in GUVs at phase coexistence, irrespective of the specific lipid mixture.
• Demonstrated that solid domains expand and migrate upon cooling, with domain morphology influenced by chain length differences.
• Established a linear relationship between GP values and hydrophobic chain length mismatch, indicating domain composition changes.

Conclusions:

• Hydrophobic mismatch significantly impacts lipid domain formation and composition in GUVs.
• Solid domains span both leaflets of the GUV membrane, suggesting strong inter-leaflet coupling.
• Lipid miscibility in the solid phase varies, with some mixtures showing complete disappearance of solid domains.