Fast diffusion along defects and corrugations in phospholipid P beta, liquid crystals

Area of Science:

• Lipid bilayer dynamics
• Liquid crystal phases
• Membrane biophysics

Background:

• The P beta' phase of dimyristoylphosphatidylcholine (DMPC) exhibits anisotropic liquid crystalline properties.
• Lipid diffusion in such phases is crucial for understanding membrane function and integrity.
• Structural defects can significantly influence molecular mobility within lipid bilayers.

Purpose of the Study:

• To investigate the diffusion pathways of a fluorescent lipid analogue in the DMPC P beta' phase.
• To quantify diffusion coefficients and identify factors contributing to variability.
• To correlate diffusion behavior with structural features like defects and corrugations.

Main Methods:

• Fluorescence photobleaching recovery (FPR) experiments were employed to measure lipid diffusion.
• Anisotropic liquid crystalline phases of DMPC were utilized.
• Microscopic observations were used to identify structural features like mosaic patches and oily streaks.

Main Results:

• Two distinct diffusion pathways were identified, with coefficients differing by over 100-fold.
• Fast diffusion (D ~ 4 X 10(-11) cm2/s at 16°C) was observed along disordered "defect" bands and oily streaks.
• Slow diffusion (D ≤ 2 X 10(-16) cm2/s at 22°C) occurred in the ordered regions of the bilayer corrugations.

Conclusions:

• Structural defects, specifically disordered bands and oily streaks, act as fast diffusion pathways in DMPC P beta' phase.
• Lipid diffusion is highly heterogeneous, influenced by phase structure and defects.
• Understanding these diffusion dynamics is key to comprehending lipid packing and membrane phase behavior.