Lateral organization and domain formation in a two-component lipid membrane system

Area of Science:

• Membrane biophysics
• Lipidomics
• Thermodynamics

Background:

• Understanding lipid membrane organization is crucial for biological processes.
• Mixtures of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2 distearoyl-sn-glycero-3-phosphocholine (DSPC) form complex phase behaviors.
• Lipid domains influence membrane fluidity and function.

Purpose of the Study:

• To investigate the thermodynamic phase behavior and lateral organization of DMPC/DSPC lipid mixtures.
• To characterize the formation and dynamics of lipid domains within unilamellar vesicles.
• To correlate probe segregation with phase transitions in binary lipid systems.

Main Methods:

• Utilized fluorescence resonance energy transfer (FRET) with headgroup-labeled lipid probes (NBD-DPPE and N-Rh-DPPE).
• Analyzed lipid mixtures across varying temperatures and compositions.
• Validated phase boundaries using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC).

Main Results:

• Observed two distinct increases in FRET efficiency near the phase lines of the DMPC/DSPC phase diagram.
• Attributed increased energy transfer to differential probe partitioning in dynamic, coexisting gel/fluid phases.
• Confirmed probe segregation correlates with phase diagram boundaries measured by FTIR and DSC.

Conclusions:

• Proposed the existence of DMPC-rich and DSPC-rich domains forming dynamic gel/fluid phases at two temperatures.
• Demonstrated that these domains are compositionally distinct, not pure lipid phases.
• Highlighted probe segregation as a sensitive indicator of lipid domain formation and membrane phase transitions.