Conformational constraints in solid-state NMR of uniformly labeled polypeptides from double single-quantum-filtered rotational echo double resonance.

A solid-state nuclear magnetic resonance (NMR) technique is described for obtaining constraints on the backbone conformation of a protein or peptide that is prepared with uniform (15)N,(13)C labeling of consecutive pairs of amino acids or of longer segments. The technique, called double single-quantum-filtered rotational echo double resonance (DSQ-REDOR), uses frequency-selective REDOR to prepare DSQ coherences involving directly bonded backbone (13)CO and (15)NH sites, to dephase these coherences under longer-range (15)NH-(13)CO dipole-dipole couplings in a conformationally dependent manner, and to convert the remaining DSQ coherences to detectable transverse (13)C-spin polarization. The efficacy of DSQ-REDOR is demonstrated in experiments on two isotopically labeled samples, the helical peptide MB(i + 4)EK and the amyloid-forming peptide Abeta(11-25).