H-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 H 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 H 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 H detection. We demonstrate this method with applications to samples of uniformly C,N,H-labeled alanine and uniformly C,H,N-labeled GB1 protein, back-exchanged with 30% HO and 70% DO, employing a variety of frequency-selective C 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.