Residue-Specific High-Resolution 17O Solid-State Nuclear Magnetic Resonance of Peptides: Multidimensional Indirect 1H Detection and Magic-Angle Spinning

Oxygen is an integral component of proteins but remains sparsely studied because its only NMR active isotope, O-17, has low sensitivity, low resolution, and large quadrupolar couplings. These issues are addressed here with efficient isotopic labeling, high magnetic fields, fast sample spinning, and H-1 detection in conjunction with multidimensional experiments to observe oxygen sites specific to each amino acid residue. Notably, cross-polarization at high sample spinning frequencies provides efficient C-13 <-> O-17 polarization transfer. The use of O-17 for initial polarization is found to provide better sensitivity per unit time compared to H-1. Sharp isotropic O-17 peaks are obtained by using a low-power multiple-quantum sequence, which in turn allows extraction of quadrupolar parameters for each oxygen site. Finally, the potential to determine sequential assignments and long-range distance restraints is demonstrated by using 3D H-1/C-13/O-17 experiments, suggesting that such methods can become an essential tool for biomolecular structure determination.

Automated summary

This study addresses the challenges of low sensitivity, low resolution, and large quadrupolar couplings in the NMR study of oxygen by employing efficient isotopic labeling, high magnetic fields, fast sample spinning, and H-1 detection. Oxygen sites specific to each amino acid residue are observed through multidimensional experiments. The use of cross-polarization at high sample spinning frequencies enables efficient C-13<->O-17 polarization transfer. Results show that using O-17 for initial polarization provides better sensitivity per unit time compared to H-1.