Hexagonal phase forming propensity detected in phospholipid bilayers with fluorescent probes

Area of Science:

• Biophysics
• Membrane Biophysics
• Fluorescence Spectroscopy

Background:

• Phospholipid bilayers are fundamental to cell membranes.
• Understanding membrane phase transitions is crucial for cell function.
• Fluorescent probes can report on membrane microenvironment properties.

Purpose of the Study:

• To investigate the utility of N epsilon-dansyl-L-Lysine and Laurdan as fluorescent probes for membrane phase transitions.
• To characterize the spectral changes of these probes in different phospholipid environments.
• To correlate probe behavior with lipid phase behavior.

Main Methods:

• Incorporation of N epsilon-dansyl-L-Lysine into dipalmitoleoylphosphatidylcholine (DPPC) and dipalmitoleoylphosphatidylethanolamine (DPPE) bilayers.
• Measurement of fluorescence emission spectra and temperature dependence.
• Utilizing Laurdan to assess membrane surface hydrophobicity via generalized polarization.
• Comparing probe responses in DPPC and DPPE membranes, particularly near the bilayer to hexagonal phase transition.

Main Results:

• N epsilon-dansyl-L-Lysine showed a blue shift in phospholipid bilayers, more pronounced in DPPC than DPPE.
• Dansyl-lysine fluorescence was temperature-dependent in DPPE bilayers, especially near the phase transition.
• Laurdan exhibited significant changes in generalized polarization and emission intensity below the DPPE phase transition.
• DPPC bilayers did not show similar probe responses near the phase transition.

Conclusions:

• Both dansyl-L-lysine and Laurdan are effective fluorescent probes for detecting physical property changes in membranes.
• These probes are sensitive to lipid packing and hydration changes occurring near the bilayer to hexagonal phase transition.
• The differential response of probes in DPPC versus DPPE highlights the influence of lipid headgroup on membrane properties and probe behavior.