¹H‑Detected REDOR with Fast Magic-Angle Spinning of a Deuterated Protein

Rotational echo double resonance (REDOR) is a highly successful method for heteronuclear distance determination in biological solid-state NMR, and ¹H detection methods have emerged in recent years as a powerful approach to improving sensitivity and resolution for small sample quantities by utilizing fast magic-angle spinning (>30 kHz) and deuteration strategies. In theory, involving ¹H as one of the spins for measuring REDOR effects can greatly increase the distance measurement range, but few experiments of this type have been reported. Here we introduce a pulse sequence that combines frequency-selective REDOR (FSR) with ¹H detection. We demonstrate this method with applications to samples of uniformly ¹³C,¹⁵N,²H-labeled alanine and uniformly ¹³C,²H,¹⁵N-labeled GB1 protein, back-exchanged with 30% H₂O and 70% D₂O, employing a variety of frequency-selective ¹³C pulses to highlight unique spectral features. The resulting, robust REDOR effects provide (1) tools for resonance assignment, (2) restraints of secondary structure, (3) probes of tertiary structure, and (4) approaches to determine the preferred orientation of aromatic rings in the protein core.