Triple‐Resonance NMR Experiments for Assignment of Asparagine and Glutamine Side‐Chain NH ₂ Groups in Intrinsically Disordered Proteins

Complete degeneracy of aliphatic ¹³C chemical shifts of the same type of amino-acid residues precludes unambiguous NMR assignments of asparagine (Asn) and glutamine (Gln) carboxamide NH₂ groups in intrinsically disordered proteins with conventional techniques. Here, a pair of triple-resonance NMR experiments is described that correlate the ¹H/¹⁵N chemical shifts of Asn and Gln carboxamide NH₂ groups with the backbone amide ¹⁵N chemical shifts of the same and the next residue. These experiments exploit a by far superior dispersion of backbone amide ¹⁵N chemical shifts, and permit unambiguous assignments of all Asn/Gln side-chain NH₂ groups in the intrinsically disordered protein α-synuclein and the majority of Gln NH₂ groups in the disordered huntington exon-1 protein with a 7-residue glutamine repeat, htt^ex1Q₇.