Improved 3D gd-HCACO and gd-(H)CACO-TOCSY experiments for isotopically enriched proteins dissolved in H2O

Summary Pulsed field gradients were incorporated into the HCACO experiment for acquiring spectra on isotopically enriched protein samples dissolved in H₂O. Excellent water suppression and spectral quality were achieved using the modified pulse sequence (gd-HCACO), as demonstrated for a ¹³C-/¹⁵N-labeled sample of the SH2 domain from the hematopoietic cellular kinase dissolved in 90% H₂O/10% D₂O. Strong correlations for all residues were observed in the gd-HCACO spectrum, even for residues having -protons resonating exactly at the H₂O frequency. The HCACO-TOCSY experiment was modified to correlate intraresidue ¹³C (rather than ¹H), carbonyl (¹³C), and aliphatic side-chain protons (H)CACO-TOCSY]. Pulsed field gradients were also incorporated into the (H)CACO-TOCSY experiment for water suppression.