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

We present a novel solid-state magic angle-spinning NMR method for measurin g the NHi-NHi+1 projection angle theta(l,i+1) in peptides. The experiment i s applicable to uniformly N-15-labeled peptides and is demonstrated on the chemotactic tripeptide N-formyl-L-Met-L-Leu-L-Phe. The projection angle the ta(i,i+1),is directly related to the peptide backbone torsion angles phi(i) and psi(i). The method utilizes the T-MREV recoupling scheme to restore N- 15-H-1 interactions, and proton-mediated spin diffusion to establish N-15-N -15 correlations. T-MREV has recently been shown to increase the dynamic ra nge of the N-15-H-1 recoupling by gamma-encoding, and permits an accurate d etermination of the recoupled NH dipolar interaction. The results are inter preted in a quasi-analytical fashion that permits efficient extraction of t he structural parameters. (C) 2000 Academic Press.