H detection of heteronuclear dipolar oscillations with water suppression in single crystal peptide and oriented protein samples.

Oriented sample solid-state NMR is a complementary approach to protein structure determination with the distinct advantage that it can be applied to supramolecular assemblies, such as viruses and membrane proteins, under near-native conditions, which generally include high levels of hydration as found in living systems. Thus, in order to perform H detected versions of multi-dimensional experiments water suppression techniques must be integrated into the pulse sequences. For example, H-windowed detection of H-N dipolar couplings enable multi-dimensional NMR experiments to be performed. Here we show that the addition of a solvent suppression pulse during the z-filter interval greatly improves the sensitivity of the experiments by suppressing the H signals from water present. This is demonstrated here with a crystal sample submerged in water and then extended to proteins. The combination of solvent-suppressed H detected PISEMO and the use of a strip shield-solenoid coil probe configuration provides a two-fold sensitivity enhancement in both the crystal sample and Pf1 coat protein sample compared to the N direct detection method. Here we also examine protein NMR line-widths and sensitivity enhancements in the context of window detected separated local field experiments for protein samples.