Lipid Microdomain Formation: Characterization by Infrared Spectroscopy and Ultrasonic Velocimetry
Zachary D. Schultz 1 and Ira W. Levin 1*
1 National Institutes of Health
* To whom correspondence should be addressed. E-mail: iwl{at}helix.nih.gov.
Submitted on August 15, 2007
Revised on October 7, 2007
Accepted on 11 December 2007
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Abstract |
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Results are presented that demonstrate the use of vibrational infrared spectroscopy applied toward characterizing lipid microdomain sizes derived from a model raft-like system consisting of non-hydroxy galactocerebroside, cholesterol, and dipalmitoylphosphatidylcholine components. The resulting spectroscopic correlation field components of the lipid acyl chain CH2 methylene deformation modes, observed when lipid multilamellar assemblies are rapidly frozen from the liquid crystalline state to the gel phase, indicate the existence of lipid microdomains at the several nanometer scale. The addition of cholesterol disrupts the glycosphingolipid selectively, in contrast to perturbing the disaturated chain phospholipid matrix. Complementary acoustic velocimetry measurements indicate that the microdomain formation decreases the total volume adiabatic compressibilities of the multilamellar vesicle assemblies. Addition of cholesterol, however, disrupts the galactocerebroside domains, resulting in a slight increase in the lipid assemblies' total adiabatic compressibility. The combination of these two physical approaches offers new insights into microdomain formation and their properties in model bilayer systems.
Key Words:
cholesterol, compressibility, galactocerebroside, lipid rafts, sphingolipid, vibrational spectroscopy
