NMR studies on phospholipid bilayers. Some factors affecting lipid distribution

Area of Science:

• Biochemistry
• Physical Chemistry
• Chemical Physics

Background:

• Understanding phospholipid distribution in vesicles is crucial for membrane biophysics.
• Nuclear Magnetic Resonance (NMR) spectroscopy offers non-invasive methods to probe molecular arrangements.

Purpose of the Study:

• To quantify the outside/inside distribution of phospholipids in mixed vesicles.
• To investigate the influence of lipid properties and environmental factors on phospholipid asymmetry.

Main Methods:

• Utilized proton Nuclear Magnetic Resonance (1H-NMR) and phosphorus-31 Nuclear Magnetic Resonance (31P-NMR) spectroscopy.
• Employed ferricyanide as a shift reagent for 1H-NMR analysis.
• Analyzed chemical shift differences and linewidths in 31P-NMR spectra.

Main Results:

• Demonstrated that 31P-NMR can resolve and quantify the distribution of various phospholipids in mixed vesicles.
• Observed preferential incorporation of phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, and phosphatidic acid into the inner leaflet of lecithin vesicles.
• Found that lecithin preferentially resides in the inner leaflet of lecithin-sphingomyelin mixtures.
• Showed that decreasing pH enhances the preference of phosphatidylserine for the inner leaflet.

Conclusions:

• Phospholipid distribution in mixed vesicles is governed by both electrostatic charge and head group packing properties.
• NMR parameters like chemical shift differences provide insights into vesicle packing density and size.