High Resolution 1H-Detected Solid-State NMR Spectroscopy of Protein Aliphatic Resonances: Access to Tertiary Structure Information

Biological magic angle spinning (MAS) solid-state nuclear magnetic resonance spectroscopy has developed rapidly over the past two decades. For the structure determination of a protein by solid-state NMR, routinely C-13,C-13 distance restraints as well as dihedral restraints are employed. In protonated samples, this is achieved by growing the bacterium on a medium which contains [1,3]-C-13 glycerol or [2]-C-13 glycerol to dilute the C-13 spin system. Labeling schemes, which rely on heteronuclei, are insensitive both for detection and in terms of quantification of distances, since they are relying on low-gamma nuclei. Proton detection can in principle provide a gain in sensitivity by a factor of 8 and 31, compared to the C-13 or N-15 detected version of the experiment. We report here a new labeling scheme, which enables H-1-detection of aliphatic resonances with high resolution in MAS solid-state NMR spectroscopy. We prepared microcrystals of the SH3 domain of chicken a-spectrin with 5% protonation at nonexchangeable sites and obtained line widths on the order of 25 Hz for aliphatic H-1 resonances. We show further that C-13 resolved 3D-H-1,H-1 correlation experiments yield access to long-range proton-proton distances in the protein.