Recognition of protein folds via dipolar couplings

Alignment of proteins in dilute liquid crystalline medium gives rise to res idual dipolar couplings which provide orientational information of vectors connecting the interacting nuclei. Considering that proteins are mainly com posed of regular secondary structures in a finite number of different mutua l orientations, main chain dipolar couplings appear sufficient to reveal st ructural resemblance. Similarity between dipolar couplings measured from a protein and corresponding values computed from a known structure imply homo logous structures. For dissimilar structures the agreement between experime ntal and calculated dipolar couplings remains poor. In this way protein fol ds can be readily recognized prior to a comprehensive structure determinati on. This approach has been demonstrated by showing the similarity in fold b etween the hitherto unknown structure of calerythrin and sarcoplasmic calci um-binding proteins from Nereis diversicolor and Branchiostoma lanceolatum with known crystal structures.