NH-NH vector correlation in peptides by solid-state NMR.

We present a novel solid-state magic angle-spinning NMR method for measuring the NH(i)-NH(i+1) projection angle θ(i,i+1) in peptides. The experiment is applicable to uniformly (15)N-labeled peptides and is demonstrated on the chemotactic tripeptide N-formyl-l-Met-l-Leu-l-Phe. The projection angle θ(i,i+1) is directly related to the peptide backbone torsion angles φ(i) and psi(i). The method utilizes the T-MREV recoupling scheme to restore (15)N-(1)H interactions, and proton-mediated spin diffusion to establish (15)N-(15)N correlations. T-MREV has recently been shown to increase the dynamic range of the (15)N-(1)H recoupling by gamma-encoding, and permits an accurate determination of the recoupled NH dipolar interaction. The results are interpreted in a quasi-analytical fashion that permits efficient extraction of the structural parameters.