Optimization of bicelle lipid composition and temperature for EPR spectroscopy of aligned membranes

[Display omitted] •Conventional DMPC-only lipid bicelles align at 318K for EPR spectroscopy.•Addition of 1:1 POPC:DMPC to bicelle reduces alignment temperature to 298K.•POPC:DMPC bicelles align homogeneously just as DMPC-only bicelles do.•Spectral simulation was used to quantify aligned and unaligne...

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Bibliographic Details
Published in:Journal of magnetic resonance (1997) 2015-01, Vol.250, p.71-75
Main Authors: McCaffrey, Jesse E., James, Zachary M., Thomas, David D.
Format: Article
Language:English
Subjects:
Alignment
Bicelle
Dimyristoylphosphatidylcholine - chemistry
Electron Spin Resonance Spectroscopy - methods
EPR
Lipid Bilayers - chemistry
Lipid composition
Lipids
Magnetic resonance
Magnetic Resonance Spectroscopy
Membranes
Phosphatidylcholines - chemistry
Phospholipids
Phospholipids - chemistry
Spectra
Spectral simulation
Spectrometers
Spectroscopy
Temperature
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Summary:[Display omitted] •Conventional DMPC-only lipid bicelles align at 318K for EPR spectroscopy.•Addition of 1:1 POPC:DMPC to bicelle reduces alignment temperature to 298K.•POPC:DMPC bicelles align homogeneously just as DMPC-only bicelles do.•Spectral simulation was used to quantify aligned and unaligned populations.•Alignment was measured using 5-DOXYL stearic acid lipid spin label. We have optimized the magnetic alignment of phospholipid bilayered micelles (bicelles) for EPR spectroscopy, by varying lipid composition and temperature. Bicelles have been extensively used in NMR spectroscopy for several decades, in order to obtain aligned samples in a near-native membrane environment and take advantage of the intrinsic sensitivity of magnetic resonance to molecular orientation. Recently, bicelles have also seen increasing use in EPR, which offers superior sensitivity and orientational resolution. However, the low magnetic field strength (less than 1T) of most conventional EPR spectrometers results in homogeneously oriented bicelles only at a temperature well above physiological. To optimize bicelle composition for magnetic alignment at reduced temperature, we prepared bicelles containing varying ratios of saturated (DMPC) and unsaturated (POPC) phospholipids, using EPR spectra of a spin-labeled fatty acid to assess alignment as a function of lipid composition and temperature. Spectral analysis showed that bicelles containing an equimolar mixture of DMPC and POPC homogeneously align at 298K, 20K lower than conventional DMPC-only bicelles. It is now possible to perform EPR studies of membrane protein structure and dynamics in well-aligned bicelles at physiological temperatures and below.
ISSN:1090-7807
1096-0856
DOI:10.1016/j.jmr.2014.09.026