High-resolution methyl edited GFT NMR experiments for protein resonance assignments and structure determination.

Three-dimensional (3D) structure determination of proteins is benefitted by long-range distance constraints comprising the methyl groups, which constitute the hydrophobic core of proteins. However, in methyl groups (of Ala, Ile, Leu, Met, Thr and Val) there is a significant overlap of ¹³C and ¹H chemical shifts. Such overlap can be resolved using the recently proposed (3,2)D HCCH-COSY, a G-matrix Fourier transform (GFT) NMR based experiment, which facilitates editing of methyl groups into distinct spectral regions by combining their ¹³C chemical shifts with that of the neighboring, directly attached, ¹³C nucleus. Using this principle, we present three GFT experiments: (a) (4,3)D NOESY-HCCH, (b) (4,3)D ¹H-TOCSY-HCCH and (c) (4,3)D ¹³C-TOCSY-HCCH. These experiments provide unique 4D spectral information rapidly with high sensitivity and resolution for side-chain resonance assignments and NOE analysis of methyl groups. This is exemplified by (4,3)D NOESY-HCCH data acquired for 17.9 kDa non-deuterated cytosolic human J-protein co-chaperone, which provided crucial long-range distance constraints for its 3D structure determination.