4D Non-uniformly sampled HCBCACON and 1 J(NCα)-selective HCBCANCO experiments for the sequential assignment and chemical shift analysis of intrinsically disordered proteins

A pair of 4D NMR experiments for the backbone assignment of disordered proteins is presented. The experiments exploit C-13 direct detection and non-uniform sampling of the indirectly detected dimensions, and provide correlations of the aliphatic proton (H-alpha, and H-beta) and carbon (C-alpha, C-beta) resonance frequencies to the protein backbone. Thus, all the chemical shifts regularly used to map the transient secondary structure motifs in the intrinsically disordered proteins (H-alpha, C-alpha, C-beta, C', and N) can be extracted from each spectrum. Compared to the commonly used assignment strategy based on matching the C-alpha and C-beta chemical shifts, inclusion of the H-alpha and H-beta provides up to three extra resonance frequencies that decrease the chance of ambiguous assignment. The experiments were successfully applied to the original assignment of a 12.8 kDa intrinsically disordered protein having a high content of proline residues (26 %) in the sequence.