Sensitive and simplified: a combinatorial acquisition of five distinct 2D constant-time ¹³C-¹H NMR protein...

A procedure is presented for the substantial simplification of 2D constant-time ¹³C-¹H heteronuclear single-quantum correlation (HSQC) spectra of ¹³C-enriched proteins. In this approach, a single pulse sequence simultaneously records eight sub-spectra wherein the phases of the NMR signals depend on spin topology. Signals from different chemical groups are then stratified into different sub-spectra through linear combination based on Hadamard encoding of ¹³CH_n multiplicity (n = 1, 2, and 3) and the chemical nature of neighboring ¹³C nuclei (aliphatic, carbonyl/carboxyl, aromatic). This results in five sets of 2D NMR spectra containing mutually exclusive signals from: (i) ¹³C^β-¹H^β correlations of asparagine and aspartic acid, ¹³C^γ-¹H^γ correlations of glutamine and glutamic acid, and ¹³C^α-¹H^α correlations of glycine, (ii) ¹³C^α-¹H^α correlations of all residues but glycine, and (iii) ¹³C^β-¹H^β correlations of phenylalanine, tyrosine, histidine, and tryptophan, and the remaining (iv) aliphatic ¹³CH₂ and (v) aliphatic ¹³CH/¹³CH₃ resonances. As HSQC is a common element of many NMR experiments, the spectral simplification proposed in this article can be straightforwardly implemented in experiments for resonance assignment and structure determination and should be of widespread utility.