Targeted 13C-13C distance measurements in a microcrystalline protein via J-decoupled rotational resonance width measurements.

Rotational resonance width (R(2)W) magic-angle spinning (MAS) NMR experiments are performed to measure (13)C-(13)C distances in the hydrophobic core of the microcrystalline model protein G(Beta1). Such inter-residue distances are of particular value in NMR structure determinations. The experiments are done at a Larmor frequency of 750 MHz (1)H where the contribution of (13)C chemical shift anisotropy (CSA) to the R(2) transfer mechanism is significant. To minimize line broadening in the 2D spectra, we employ a combination of even/odd isotopic labeling with [1,3-(13)C] glycerol, and J-decoupling in the indirect dimension. This results in high-precision distance measurements between aromatic side chains of three tyrosine residues and distant methyl groups in the hydrophobic core of the protein. Even in the absence of information on the relative orientation of the shift tensors, we obtain relatively high precision data, which can be further improved by additional constraints on the tensor orientations.