Intrinsic molecules in fluid phospholipid bilayers. Fluorescence probe studies

Area of Science:

• Biophysics
• Membrane Biophysics
• Fluorescence Spectroscopy

Background:

• Lipid bilayers are essential cellular structures.
• Intrinsic molecules like proteins and cholesterol modulate membrane properties.
• Fluorescence probes are valuable tools for studying membrane dynamics.

Purpose of the Study:

• To investigate the effect of intrinsic molecule concentration on lipid bilayer dynamics using fluorescence probe data.
• To develop a theoretical model explaining the observed changes in probe behavior.
• To reconcile fluorescence probe findings with other biophysical techniques.

Main Methods:

• Utilized 1,6-diphenyl-1,3,5-hexatriene (DPH) as a fluorescence probe.
• Examined DPH polarization in fluid lipid bilayers with varying concentrations of cholesterol, gramicidin A, and cytochrome oxidase.
• Performed empirical curve-fitting of polarization data against intrinsic molecule concentration.
• Developed a theoretical model based on the probability of probe-molecule proximity.

Main Results:

• Polarization values increased with intrinsic molecule concentration, approaching a plateau.
• Experimental data were well-fitted by exponential curves.
• A theoretical model accurately predicted probe motion changes based on proximity probability (p).
• Increased intrinsic protein concentration correlated with increased protein-protein contacts.

Conclusions:

• Fluorescence probe data suggest increased protein-protein interactions in lipid bilayers with higher intrinsic protein content.
• The theoretical model provides a framework for understanding probe response to molecular crowding.
• Discrepancies with deuterium magnetic resonance can be attributed to different sensitivities to molecular motion and disorder.