Assignment of the nonexchanging protons of the alpha-spectrin SH3 domain by two- and three-dimensional H-1-C-13 solid-state magic-angle spinning NMR and comparison of solution and solid-state proton chemical shifts

The assignment of nonexchanging protons of a small microcrystalline protein , the a-spectrin SH3 domain (7.2 kDa, 62 residues), was achieved by means o f three-dimensional (3D) heteronuclear (H-1-C-13-C-13) magic-angle spinning (MAS) NMR dipolar correlation spectroscopy. With the favorable combination of a high B-0-field, a moderately high spinning frequency, and frequency-s witched Lee-Goldburg irradiation applied during H-1 evolution, a proton lin ewidth less than or equal to 0.5 ppm at 17.6 Tesla was achieved for the par ticular protein preparation used. A comparison of the solid-state H-1 chemi cal shifts with the shifts found in solution shows a remarkable similarity, which reflects the identical protein structures in solution and in the sol id. Significant differences between the MAS solid- and liquid-state H-1 che mical shifts are only observed for residues that ore located at the surface of the protein and that exhibit contacts between different SH3 molecules. In two cases, aromatic residues of neighboring SH3 molecules induce pronoun ced upfield ring-current shifts for protons in the contact area.