Conformation-selective detection of residues in solid proteins under magic-angle-spinning

We demonstrate here a pulse sequence based on rotational-echo double resonance (REDOR) that can help distinguish resonances based on the ψ-torsion angle, which allows it to distinguish α-helical and β-sheet regions in solid proteins under magic-angle-spinning. The method relies on conformation-dependent differences in distances between an amide [Formula: see text]H and amide [Formula: see text]N nuclei not covalently attached to it. Dephasing from this remote [Formula: see text]N nucleus is obtained in presence of the much stronger one-bond dipole-dipole coupling by using the [Formula: see text]-REDOR sequence. Experiments are demonstrated on perdeuterated (and 70% backexchanged) sample of uniformly [Formula: see text]C, [Formula: see text]N labeled model protein GB1 at the magic-angle spinning frequency of 41.67 kHz. This method will be useful in simplifying chemical-shift assignments in proteins where the structure is already known, and we anticipate a direct application in determining secondary structures without relying on [Formula: see text]C chemical-shifts.