Solid-state NMR measurement of Ψ in peptides: a NCCN 2Q-heteronuclear local field experiment

A solid-state NMR experiment is presented for measuring Ψ torsion angles in (15N–13Cα–13CO–15N)-labeled peptides. Creation of 13Cα–13CO double-quantum coherence (DQC) is followed by selective evolution under 15N–13C dipolar interactions. The time-course of 13Cα–13CO DQC dephasing is sensitive to the Ψ torsion angle, particularly for values associated with β-sheet secondary structure (120–180°). We apply the technique to glycylglycine⋅HCl and extract a value for Ψ that matches the diffraction-determined value (Ψ=162.1°C) with a precision of ±5°.