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Skew projection of echo-detected EPR spectra for increased sensitivity and resolution.

ABSTRACT: The measurement of EPR spectra during pulsed EPR experiments is commonly accomplished by recording the integral of the electron spin echo as the applied magnetic field is stepped through the spectrum. This approach to echo-detected EPR spectral measurement (ED-EPR) limits sensitivity and spectral resolution and can cause gross distortions in the resulting spectra because some of the information present in the electron spin echo is discarded in such measurements. However, Fourier transformation of echo shapes measured at a series of magnetic field values followed by skew projection onto either a magnetic field or resonance frequency axis can increase both spectral resolution and sensitivity without the need to trade one against the other. Examples of skew-projected spectra with single crystals, glasses and powders show resolution improvements as large as a factor of seven with sensitivity increases of as much as a factor of five.

SUBMITTER: Bowman MK

PROVIDER: S-EPMC3691685 | biostudies-literature | 2013 Jun

REPOSITORIES: biostudies-literature

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Skew projection of echo-detected EPR spectra for increased sensitivity and resolution.

Bowman Michael K MK Krzyaniak Matthew D MD Cruce Alex A AA Weber Ralph T RT

Journal of magnetic resonance (San Diego, Calif. : 1997) 20130412

The measurement of EPR spectra during pulsed EPR experiments is commonly accomplished by recording the integral of the electron spin echo as the applied magnetic field is stepped through the spectrum. This approach to echo-detected EPR spectral measurement (ED-EPR) limits sensitivity and spectral resolution and can cause gross distortions in the resulting spectra because some of the information present in the electron spin echo is discarded in such measurements. However, Fourier transformation o ...[more]

PMID: 23644351

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Project description:Solid-state NMR spectroscopy has emerged as an excellent tool to study the structure and dynamics of membrane proteins under native-like conditions in lipid bilayers. One of the key considerations in experimental design is the uniaxial rotational diffusion of the protein that can affect the NMR spectral observables. In this regard, temperature plays a fundamental role in modulating the phase properties of the lipids, which directly influences the rotational diffusion rate of the protein in the bilayer. In fact, it is well established that below the main phase transition temperature of the lipid bilayer the protein's motion is significantly slowed while above this critical temperature the rate is increased. In this article, we carried out a systematic comparison of the signal intensity and spectral resolution as a function of temperature using magic-angle-spinning (MAS) solid-state NMR spectroscopy. These observables were directly correlated with the relative fluidity of the lipid bilayer as inferred from differential scanning calorimetry (DSC). We applied our hybrid biophysical approach to two polytopic membrane proteins from the small multidrug resistance family (EmrE and SugE) reconstituted into model membrane lipid bilayers (DMPC-14:0 and DPPC-16:0). From these experiments, we conclude that the rotational diffusion giving optimal spectral resolution occurs at a bilayer fluidity of ~5%, which corresponds to the percentage of lipids in the fluid or liquid-crystalline fraction. At the temperature corresponding to this critical value of fluidity, there is sufficient mobility to reduce inhomogeneous line broadening that occurs at lower temperatures. A greater extent of fluidity leads to faster uniaxial rotational diffusion and a sigmoidal-type reduction in the NMR signal intensity, which stems from intermediate-exchange dynamics where the motion has a similar frequency as the NMR observables (i.e., dipolar couplings and chemical shift anisotropy). These experiments provide insight into the optimal temperature range and corresponding bilayer fluidity to study membrane proteins by solid-state NMR spectroscopy.

Dataset Information

Skew projection of echo-detected EPR spectra for increased sensitivity and resolution.

Publications

Skew projection of echo-detected EPR spectra for increased sensitivity and resolution.

Similar Datasets

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