Determination of an 8-Å Interatomic Distance in a Helical Peptide by Solid-State NMR Spectroscopy

The combination of transferred-echo double resonance (TEDOR) with rotational-echo double resonance (REDOR) has been used to measure an 8-Å fluorine-carbon internuclear distance in a nine-residue fragment of the peptide antibiotic emerimicin. The fragment is ¹⁹FCH₂CO-Phe-MeA-MeA-[1-¹³C]MeA-[¹⁵N]Val-Gly-Leu-MeA-MeA-OBzl (MeA = α-methylalanine or aminoisobutyric acid). The TEDOR part of this magic-angle-spinning, solid-state NMR experiment selects the ¹³C label by its dipolar coupling to ¹⁵N and suppresses the natural-abundance carbon background. The REDOR part of the experiment measures dipolar coupling of the selected carbon to ¹⁹F. The TEDOR-REDOR combined experiment works with a variety of spin 1/2 nuclei and can be used to characterize internuclear distances and geometry in macromolecular aggregates that do not crystallize.