Solid-state NMR spin diffusion for measurement of membrane-bound peptide structure: Gramicidin A

A recently developed solid-state NMR method for measurement of depths in membrane systems is applied to gramicidin A, a membrane-bound peptide of known structure, to investigate the potential of this method. 1 5 N-detected, 1 H spin diffusion experiments demonstrate the resolution of the technique by measuring the 4-5 A depth differences between three 1 5 N-labeled backbone sites (Trpl3, Val7, Gly2) in gramicidin A. We also show that 1 3 C-detected, 'H spin diffusion experiments on unlabeled gramicidin A are sufficient to discriminate between the end-to-end dimer and double-helix structures of gramicidin A. Thus, spin diffusion solid-state NMR experiments can provide a simple approach, which does not require labeled samples, for testing structural models of membrane-bound peptides.