Dipolar filtered H-1-C-13 heteronuclear correlation spectroscopy for resonance assignment of proteins

Resonance assignment is necessary for the comprehensive structure determina tion of insoluble proteins by solid-state NMR spectroscopy. While various 2 D and 3D correlation techniques involving C-13 and N-15 spins have been dev eloped for this purpose, H-1 chemical shift has not been exploited sufficie ntly. We demonstrate the combination of the regular H-1-C-13 heteronuclear correlation (HETCOR) experiment and a dipolar filtered HETCOR technique to obtain better resolved H-1 chemical shift spectra. The dipolar filtered exp eriment, MELODI-HETCOR, simplifies the H-1 spectra by suppressing the direc tly bonded C-H correlation peaks and retaining only the medium- and long-ra nge cross peaks. We apply this MELODI-HETCOR technique to several amino aci ds and proteins with various isotopic labeling patterns. The enhanced H-1 c hemical shift resolution allows the assignment of overlapping H alpha and H beta resonances in Ser, identifies the H-1 chemical shift differences betw een neutral and cationic imidazole rings of His, and permits the assignment of residues with side chain nitrogen atoms in ubiquitin. The potential uti lity of this dipolar filtered HETCOR technique to resonance assignment of e xtensively labeled proteins is discussed.