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Biophys. J. BioFAST: First Published December 30, 2005. doi:10.1529/biophysj.105.070441
© 2005 by the Biophysical Society.

A more recent version of this article appeared on March 15, 2006.
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MEMBRANES

Characterization of the Liquid-Ordered State by Proton MAS NMR

Ivan V. Polozov 1 and Klaus Gawrisch 2*

1 NICHD, NIH
2 NIAAA, NIH

* To whom correspondence should be addressed. E-mail: gawrisch{at}helix.nih.gov.

Submitted on July 10, 2005
Revised on August 18, 2005
Accepted on 23 November 2005


  Abstract
We investigated if 1H MAS NMR can be used as a tool for detection of liquid ordered domains (rafts) in membranes. In experiments with the lipids SOPC, DOPC, DPPC, and cholesterol we demonstrated that 1H MAS NMR spectra of liquid ordered domains (lo) are distinctly different from liquid disordered (ld) and solid ordered (so) membrane regions. At a MAS spinning frequency of 10 kHz the methylene proton resonance of hydrocarbon chains in the ld phase has a linewidth of ~ 50Hz. The corresponding linewidth is ~1 kHz for the lo phase, and several kHz for the so phase. According to results of 1H NMR dipolar echo spectroscopy, the broadening of MAS resonances in the lo phase results from an increase in effective strength of intramolecular proton dipolar interactions between adjacent methylene groups, most likely because of lower probability of gauche/trans isomerization in lo. In spectra recorded as a function of temperature, the onset of lo domain (raft) formation is seen as a sudden onset of line broadening. Formation of small domains yielded homogenously broadened resonance lines, while large lo domains (diameter >0.3 µm) in an ld environment resulted in superposition of the narrow resonances of the ld phase and the much broader resonances of lo. 1H MAS NMR may be applied to detection of rafts in cell membranes.

Key Words: MAS, NMR, cholesterol, liquid ordered phase, membrane, raft




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Copyright © 2005 by the Biophysical Society.