A general method for assigning NMR spectra of denatured proteins using 3D HC(CO)NH-TOCSY triple resonance experiments.

A general approach for assigning the resonances of uniformly 15N- and 13C-labeled proteins in their unfolded state is presented. The assignment approach takes advantage of the spectral dispersion of the amide nitrogen chemical shifts in denatured proteins by correlating side chain and backbone carbon and proton frequencies with the amide resonances of the same and adjacent residues. The 1H resonances of the individual amino acid spin systems are correlated with their intraresidue amide in a 3D 15N-edited 1H,1H-TOCSY-HSQC experiment, which allows the spin systems to be assigned to amino acid type. The spin systems are then linked to the adjacent i-1 spin system using the 3D H(C)(CO)NH-TOCSY experiment. Complete 13C assignments are obtained from the 3D (H)C(CO)NH-TOCSY experiment. Unlike other methods for assigning denatured proteins, this approach does not require previous knowledge of the native state assignments or specific interconversion rates between the native and denatured forms. The strategy is demonstrated by assigning the 1H, 13C, and 15N resonances of the FK506 binding protein denatured in 6.3 M urea.