Stabilization of non-bilayer structures by the etherlipid ethanolamine plasmalogen

Area of Science:

• Lipid bilayer and non-bilayer structures
• Thermotropic phase behavior of lipids
• Membrane biophysics

Background:

• Diradylphosphatidylethanolamines and diacylphosphatidylcholine are key membrane components.
• Understanding lipid phase transitions is crucial for membrane function.
• Ether lipids, like ethanolamine plasmalogen, exhibit unique structural properties.

Purpose of the Study:

• To investigate the thermotropic phase behavior of mixtures between diradylphosphatidylethanolamines and diacylphosphatidylcholine.
• To compare the phase transition properties of alkenylacylphosphatidylethanolamine (ethanolamine plasmalogen) with its alkylacyl- and diacyl-analogs.
• To determine the influence of palmitoyloleoylphosphatidylcholine on the phase behavior of ethanolamine plasmalogen.

Main Methods:

• Polarized light microscopy
• 31P-NMR spectroscopy
• Synchrotron X-ray diffraction
• 2H-NMR spectroscopy

Main Results:

• Ethanolamine plasmalogen undergoes a lamellar to inverse hexagonal phase transition at 30°C, lower than its analogs.
• Ether lipids show a higher affinity for non-bilayer structures.
• Palmitoyloleoylphosphatidylcholine shifts the transition to higher temperatures but maintains structural integrity.
• Ethanolamine plasmalogen strongly stabilizes the inverted hexagonal phase, even with high concentrations of palmitoyloleoylphosphatidylcholine.
• 2H-NMR suggests optimized hydrocarbon chain packing in ethanolamine plasmalogen's hexagonal phase.

Conclusions:

• Ethanolamine plasmalogen exhibits a pronounced tendency to form non-bilayer structures, particularly the inverse hexagonal phase.
• The unique conformation of the sn-2 chain in ethanolamine plasmalogen contributes to its enhanced stabilization of the hexagonal phase.
• These findings highlight the distinct biophysical properties of ether lipids in membrane structures.