SPECTROSCOPY, IMAGING, OTHER TECHNIQUES |
Distinguishing Individual Lipid Headgroup Mobility and Phase Transitions in Raft Forming Lipid Mixtures with 31P MAS NMR
Greg P Holland 1, Sarah K. Mcintyre 1 and Todd M Alam 1*
1 Sandia National Labs
* To whom correspondence should be addressed. E-mail: tmalam{at}sandia.gov.
Submitted on November 7, 2005
Revised on January 19, 2006
Accepted on 22 February 2006
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Abstract |
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A model membrane system composed of egg sphingomyelin (SM), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), and cholesterol was studied with static and magic angle spinning (MAS) 31P nuclear magnetic resonance (NMR) spectroscopy. This model membrane system is of significant biological relevance since it is known to form lipid rafts. 31P NMR under MAS conditions resolves the SM and DOPC headgroup resonances allowing for extraction of the 31P NMR parameters for the individual lipid components. The isotropic chemical shift, chemical shift anisotropy (CSA), and asymmetry parameter can be extracted from the spinning side band manifold of the individual components that form liquid ordered and liquid disordered domains. The magnitude of the 31P CSA and the line width is used to determine headgroup mobility and monitor the gel to gel and gel to liquid crystalline phase transitions of SM as a function of temperature in these mixtures. Spin-spin (T2) relaxation measurements are in agreement with the line width results reflecting mobility differences and some heterogeneities. It will be shown that the presence of DOPC and/or cholesterol greatly impacts the headgroup mobility of SM both above and below the liquid crystalline phase transition temperature (Tm), while DOPC displays only minor variations in these lipid mixtures.
Key Words:
31P, Lipids, MAS, Membranes, NMR, Raft
