Internal consistency of NMR data obtained in partially aligned biomacromolecules.
A method of testing structure-related NMR data prior to structure calculations is presented. The test is applicable to second rank tensor interactions (dipolar coupling, anisotropic chemical shielding, and quadrupolar interaction) observed in partially aligned samples of biomacromolecules. The method utilizes the fact that only limited number of frequencies corresponding to the mentioned interactions can be measured independently in a rigid fragment of the macromolecule. Additional values can be predicted as linear combinations of the set of independent frequencies. Internal consistency of sufficiently large sets of frequencies measured in individual molecular fragments is tested by comparing the experimental data with their predicted values. The method requires only knowledge of local geometry (i.e., definition of the interaction tensors in the local coordinate frames of the fragments). No information about the alignment or shape of the molecule is required. The test is best suited for planar fragments. Application to peptide bonds and nucleic acid bases is demonstrated.