In this Communication,
we introduce a 3D magic-angle spinning recoupling experiment that correlates chemical shift anisotropy (CSA) po
wder line shapes
with t
wo dimensions of site-resolved isotropic chemical shifts. The principal tensor elements from 127 ROCSA line shapes are reported, constraining 102 unique backbone and side-chain
13C sites in a microcrystalline protein (the 56 residue
1 immunoglobulin binding domain of protein G). The tensor elements, determined by fitting to numerical simulations, agree
well
with quantum chemical predictions. The experiments, therefore, validate calculations of CSAs in a protein of kno
wn structure. The data
will be useful for the development of side-chain CSA quantum calculations and
will aid in the design and interpretation of solution NMR experiments that utilize CSA-dipole cross-correlation to constrain torsion angles or to enhance resolution and sensitivity (such as in TROSY). Furthermore, the methodology described here
will enable databases of CSA data to be generated
with higher efficiency, for purposes of direct protein structure refinement.