HACANCOi: a new H^α-detected experiment for backbone resonance assignment of intrinsically disordered proteins

Unidirectional coherence transfer is highly efficient in intrinsically disordered proteins (IDPs). Their elevated ps-ns timescale dynamics ensures long transverse (T₂) relaxation times allowing sophisticated coherence transfer pathway selection in comparison to folded proteins. ¹H^α-detection ensures non-susceptibility to chemical exchange with the solvent and enables chemical shift assignment of consecutive proline residues, typically abundant in IDPs. However, many IDPs undergo a disorder-to-order transition upon interaction with their target protein, which leads to the loss of the favorable relaxation properties. Long coherence transfer routes now result in prohibitively large decrease in sensitivity. We introduce a novel 4D ¹H^α-detected experiment HACANCOi, together with its 3D implementation, which warrant high sensitivity for the assignment of proline-rich regions in IDPs in complex with a globular protein. The experiment correlates ¹H^α_i, ¹³C^α_i, ¹⁵N_i and [Formula: see text] spins by transferring the magnetization concomitantly from ¹³C^α_i to ¹⁵N_i and [Formula: see text]. The B1 domain of protein G (GB1), and the enteropathogenic E. coli EspF in complex with human SNX9 SH3, serve as model systems to demonstrate the attainable sensitivity and successful sequential assignment.