The direct determination of protein structure by NMR without assignment

Assignment of the resonances in nuclear magnetic resonance spectra is considered a pre-requisite for the interpretation of spectra that yield structural information. The determination of the three-dimensional structure of a biological macromolecule may, however, be achieved directly without spectral assignment, using the same set of heteronuclear scalar and dipolar coupling experiments as normally used. A cross-peak in any of the spectra may be interpreted as a distance between atoms, yielding a set of distances between unassigned atoms that serves to define the tertiary structure of the molecule. The principle is illustrated using the 76 amino acid protein ubiquitin.