Measurement of two-bond JCOH alpha coupling constants in proteins uniformly enriched with 13C.

A simple E.COSY type technique is described for measurement of two-bond JCOH alpha coupling constants in proteins that are uniformly enriched with 13C. The method has been used to measure 2JCOH alpha for 132 residues in the proteins calmodulin and staphylococcal nuclease having non-overlapping H alpha-C alpha correlations. Measured 2JCOH alpha coupling constants fall in the 0 to -9.5 Hz range. A separate experiment, measuring the accuracy of these values, indicates a root-mean-square error of 1 Hz. Comparison of the J couplings with the dihedral backbone angles from crystallographic studies confirms a weak but statistically significant correlation between the dihedral angle psi and the magnitude of 2JCOH alpha, but also indicates that parameters other than psi have a significant effect on the value of the coupling.