Relative orientation of peptide planes in proteins is reflected in carbonyl-carbonyl chemical shift anisotropy cross-correlated spin relaxation

Experiments for measuring chemical shift anisotropy (CSA) cross-correlated spin relaxation between pairs of carbonyl spins in (15)N,(13)C-labeled proteins based on differences in relaxation rates of double- and zero-quantum carbonyl coherences are presented. In the case where the carbonyl spins reside on successive residues, information about the intervening (phi,phi) backbone dihedral angles is obtained. A good correlation between predicted and measured cross-correlation rates is observed in experiments recorded on an SH3 domain from spectrin. Cross-correlated spin relaxation between carbonyl spins residing on two peptide planes linked via hydrogen bonding can also be measured for small proteins in concentrated samples, providing information about the relative orientation of these planes, as demonstrated for the spectrin SH3 domain.