Sensitivity enhancement in (13)C solid-state NMR of protein microcrystals by use of paramagnetic metal ions for optimizing (1)H T(1) relaxation.

We discuss a simple approach to enhance sensitivity for (13)C high-resolution solid-state NMR for proteins in microcrystals by reducing (1)H T(1) relaxation times with paramagnetic relaxation reagents. It was shown that (1)H T(1) values can be reduced from 0.4-0.8s to 60-70 ms for ubiquitin and lysozyme in D(2)O in the presence of 10 mM Cu(II)Na(2)EDTA without substantial degradation of the resolution in (13)C CPMAS spectra. Faster signal accumulation using the shorter (1)H T(1) attained by paramagnetic doping provided sensitivity enhancements of 1.4-2.9 for these proteins, reducing the experimental time for a given signal-to-noise ratio by a factor of 2.0-8.4. This approach presented here is likely to be applicable to various other proteins in order to enhance sensitivity in (13)C high-resolution solid-state NMR spectroscopy.