Significantly improved resolution for noe correlations from valine and isoleucine (C(y)²) methyl groups in ¹⁵N, ¹³C- and ¹⁵N, ¹³C, ²H-labeled proteins

A new NMR experiment is described for recording NOEs from Val and Ile methyl groups in ¹⁵N, ¹³C-labeled or methyl-protonated, ¹⁵N, ¹³C, ²H-labeled proteins that offers far superior resolution than conventional 3D ¹³C-edited NOESY data sets. Resolution is achieved by recording both the C(β) and C(γ) (Val) or C(γ²) (Ile) chemical shifts as well as the chemical shift of the destination proton, and a strategy is introduced for refocusing homonuclear carbon couplings during the constant-time evolution of C(β) carbon magnetization. The utility of the method is demonstrated with applications on a 160- residue fully proton areal ¹⁵N, ¹³C-labeled, dNumb PTB domain- peptide complex and a methyl protonated, highly deuterated ¹⁵N, ¹³C-labeled complex of maltose binding protein and β-cyclodextrin (42 kDa).