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nmrlearner 02-28-2013 07:57 PM

Dynamic nuclear polarization-enhanced 13C NMR spectroscopy of static biological solids
 
Dynamic nuclear polarization-enhanced 13C NMR spectroscopy of static biological solids


Available online 27 February 2013
Publication year: 2013
Source:Journal of Magnetic Resonance</br>
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We explore the possibility of using dynamic nuclear polarization (DNP) to enhance signals in structural studies of biological solids by solid state NMR without sample spinning. Specifically, we use 2D 13C-13C exchange spectroscopy to probe the peptide backbone torsion angles (?,?) in a series of selectively 13C-labeled 40-residue ?-amyloid (A ?1-40) samples, in both fibrillar and non-fibrillar states. Experiments are carried out at 9.39 T and 8 K, using a static double-resonance NMR probe and low-power microwave irradiation at 264 GHz. In frozen solutions of A ?1-40 fibrils doped with DOTOPA-TEMPO, we observe DNP signal enhancement factors of 16-21. We show that the orientation- and frequency-dependent spin polarization exchange between sequential backbone carbonyl 13C labels can be simulated accurately using a simple expression for the exchange rate, after experimentally determined homogeneous 13C lineshapes are incorporated in the simulations. The experimental 2D 13C-13C exchange spectra place constraints on the ? and ? angles between the two carbonyl labels. Although the data are not sufficient to determine ? and ? uniquely, the data do provide non-trivial constraints that could be included in structure calculations. With DNP at low temperatures, 2D 13C-13C exchange spectra can be obtained from a 3.5 mg sample of A ?1-40 fibrils in 4 hr or less, despite the broad 13C chemical shift anisotropy line shapes that are observed in static samples.
Graphical abstract

http://origin-ars.els-cdn.com/conten...000517-fx1.jpg Highlights

? DNP allows for rapid accumulation of 2D exchange spectra. ? Samples with varying labeling and structure show distinct 2D patterns. ? 2D exchange orientation dependence can be included into simulation. ? Comparison with simulations reveals allowed ranges of backbone torsion angles.</br>
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Source: Journal of Magnetic Resonance


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