4D non-uniformly sampled HCBCACON and ¹J(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 (13)C direct detection and non-uniform sampling of the indirectly detected dimensions, and provide correlations of the aliphatic proton (H(α), and H(β)) and carbon (C(α), C(β)) 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(α), C(α), C(β), C', and N) can be extracted from each spectrum. Compared to the commonly used assignment strategy based on matching the C(α) and C(β) chemical shifts, inclusion of the H(α) and H(β) 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.