Laurdan Adopts Distinct, Phase-Specific Orientations in Lipid Membranes.

Area of Science:

• Biophysics
• Membrane Biophysics
• Fluorescence Spectroscopy

Background:

• Laurdan is a widely used fluorescent probe for lipid membrane studies.
• Molecular dynamics simulations suggest Laurdan's orientation varies within lipid bilayers.
• Experimental validation of Laurdan's orientation-dependent properties is lacking.

Purpose of the Study:

• To experimentally investigate Laurdan's molecular orientation in phase-separated lipid bilayers.
• To correlate Laurdan's spatial orientation with its emission spectra in different lipid phases.
• To provide quantitative validation for simulation-based findings on Laurdan's behavior.

Main Methods:

• Utilized supported lipid bilayers with distinct liquid-ordered (L_o) and liquid-disordered (L_d) phases.
• Employed azimuthally and radially polarized excitation beams for orientation-sensitive measurements.
• Analyzed Laurdan's emission spectra in relation to its molecular orientation within the lipid bilayer.

Main Results:

• Laurdan exhibits distinct orientations in L_o and L_d phases.
• Molecules align more parallel to the membrane normal in the L_o phase.
• A more planar orientation was observed in the L_d phase, with altered emission spectra.

Conclusions:

• Molecular orientation significantly impacts Laurdan's fluorescence properties in lipid membranes.
• Orientation-sensitive analysis is crucial for accurate biophysical investigations using Laurdan.
• This study refines understanding of Laurdan's behavior and its application in membrane research.