Can di-4-ANEPPDHQ reveal the structural differences between nanodiscs and liposomes?

Area of Science:

• Biophysics
• Membrane biophysics
• Fluorescence spectroscopy

Background:

• The potential-sensitive di-4-ANEPPDHQ dye is popular for lipid bilayer structural studies.
• Dye sensitivity is typically linked to solvent relaxation, but this is insufficient for complex systems.
• Comparing neutral and charged lipid bilayers in nanodiscs and liposomes requires advanced methods.

Purpose of the Study:

• To compare the structure of neutral and negatively charged lipid bilayers in nanodiscs and liposomes.
• To investigate the limitations of steady-state fluorescence spectroscopy for di-4-ANEPPDHQ.
• To develop a more sensitive approach for analyzing di-4-ANEPPDHQ fluorescence in lipid bilayers.

Main Methods:

• Time-resolved fluorescence decay and emission spectra analysis.
• Solvatochromic shift measurements (steady-state).
• Molecular dynamics simulations.

Main Results:

• Distinguished two (liposomes) and three (nanodiscs) emissive di-4-ANEPPDHQ species, attributed to dual emission, not solvent relaxation.
• Identified an additional long-lived component in nanodiscs, suggesting a highly ordered domain.
• Confirmed structural alterations in nanodiscs and lipid composition-dependent probe distribution via simulations.

Conclusions:

• Steady-state fluorescence of di-4-ANEPPDHQ requires cautious interpretation.
• Time-resolved fluorescence enhances sensitivity for studying lipid bilayer structure.
• Nanodisc structure is altered and probe distribution is sensitive to lipid composition.