| Abstract
| - High-level deuteration is a prerequisite for the study of high molecular weight systems usingliquid-state NMR. Here, we present new experiments for the measurement of proton−proton dipolarcouplings in CH2D methyl groups of 13C labeled, highly deuterated (70−80%) proteins. 1H−1H residualdipolar couplings (RDCs) have been measured in two alignment media for 57 out of 70 possible methylcontaining residues in the 167-residue flavodoxin-like domain of the E. coli sulfite reductase. These datayield information on the orientation of the methyl symmetry axis with respect to the molecular alignmentframe. The alignment tensor characteristics were obtained very accurately from a set of backbone RDCsmeasured on the same protein sample. To demonstrate that accurate structural information is obtainedfrom these data, the measured methyl RDCs for Valine residues are analyzed in terms of χ1 torsion anglesand stereospecific assignment of the prochiral methyl groups. On the basis of the previously determinedbackbone solution structure of this protein, the methyl RDC data proved sufficient to determine the χ1torsion angles in seven out of nine valines, assuming a single-rotamer model. Methyl RDCs arecomplementary to other NMR data, for example, methyl−methyl NOE, to determine side chain conformationin high molecular weight systems.
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