Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 131, Issue 5, Pages 1915-1926Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja807796a
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- Canadian Institutes of Health Research (CIHR)
- Canada Research Chair in Biochemistry
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Carr-Purcell-Meiboom-Gill relaxation dispersion NMR spectroscopy can provide detailed information about low populated, invisible states of protein molecules, including backbone chemical shifts of the invisible conformer and bond vector orientations that can be used as structural constraints. Notably, the measurement of H-1(alpha) chemical shifts in excited protein states has not been possible to date because, in the absence of suitable labeling, the homonuclear proton scalar coupling network in side chains of proteins leads to a significant degradation in the performance of proton-based relaxation dispersion experiments. Here we have overcome this problem through a labeling scheme in which proteins are prepared with U-H-2 glucose and 50% D2O/50% H2O that results in deuteration levels of between 50-88% at the C-beta carbon. Effects from residual H-1(alpha)-H-1(beta) scalar couplings can be suppressed through a new NMR experiment that is presented here. The utility of the methodology is demonstrated on a ligand binding exchanging system and it is shown that H-1(alpha) chemical shifts extracted from dispersion profiles are, on average, accurate to 0.03 ppm, an order of magnitude better than they can be predicted from structure using a database approach. The ability to measure H-1(alpha) chemical shifts of invisible conformers is particularly important because such shifts are sensitive to both secondary and tertiary structure. Thus, the methodology presented is a valuable addition to a growing list of experiments for characterizing excited protein states that are difficult to study using the traditional techniques of structural biology.
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