Unambiguous assignment of NMR protein backbone signals with a time-shared triple-resonance experiment

An experiment that provides a simple procedure to assign backbone nuclei in proteins is presented. The method relies on time-shared evolution of the coherences present in the (HN)NCAHA and (HA)CANNH experiments. By exploiting the fact that some of the coherences are common to both experiments the alpha and amide protons that are simultaneously detected are correlated with each other and with nitrogen and carbon nuclei. Thus, simultaneous assignment of H-alpha, H-N, C-alpha and N signals is achieved in a single 3D spectrum. The experiment was tested on the streptococcal protein G B1 domain (GB1) which was easily assigned using a "stairway" procedure and on an 11 kDa domain of the yeast transcriptional co-activator Gal11.