Cholesterol enhances surface water diffusion of phospholipid bilayers

Area of Science:

• Membrane biophysics
• Biochemistry
• Physical chemistry

Background:

• Cholesterol's role in cell membrane structure and function is crucial but not fully understood.
• The influence of hydration water on cholesterol-rich lipid membranes remains an area of active research.
• Direct experimental data on water dynamics in cholesterol-lipid systems are limited.

Purpose of the Study:

• To investigate the effect of cholesterol on water diffusion dynamics within lipid bilayers.
• To elucidate the role of hydration water in cholesterol-modulated membrane properties.
• To correlate water dynamics with lipid packing changes induced by cholesterol.

Main Methods:

• Utilized (1)H Overhauser dynamic nuclear polarization (ODNP) NMR relaxometry for site-specific water diffusion measurements.
• Employed Electron Paramagnetic Resonance (EPR) lineshape analysis to assess lipid packing.
• Prepared cholesterol-rich and depleted lipid bilayer systems using specific phospholipids.

Main Results:

• Cholesterol significantly alters water translational diffusion: acceleration at the membrane surface and deceleration within the bilayer interior.
• Increasing cholesterol content leads to looser lipid headgroup packing and tighter packing in the bilayer core.
• These effects are most pronounced in lipid compositions known to form liquid-ordered, raft-like domains.

Conclusions:

• Cholesterol modulates membrane hydration dynamics and lipid packing, influencing membrane structure and function.
• Faster surface water diffusion may facilitate biological interactions by weakening repulsive forces.
• Tighter core packing reduces passive diffusion of water and ions across the bilayer.