Correlated motions of successive amide N-H bonds in proteins

New NMR (NMR) methods are described for the measurement of cross-correlation rates of zero- and double-quantum coherences involving two nitrogen nuclei belonging to successive amino acids in proteins and peptides. Rates due to the concerted fluctuations of two NHN dipole-dipole interactions and to the correlated modulations of two nitrogen chem. shift anisotropies have been obtained in a sample of doubly labeled Ubiquitin. Ambiguities in the detn. of dihedral angles can be lifted by comparison of different rates. By defining a heuristic order parameter, exptl. rates can be compared with those expected for a rigid mol. The cross-correlation order parameter that can be derived from a model-free approach can be sepd. into structural and dynamic contributions. [on SciFinder (R)]