Structural Investigations of a Human Calcitonin-Derived Carrier Peptide in a Membrane Environment by Solid-State NMR †

Previous studies have shown that human calcitonin (hCT) and its C-terminal fragment hCT(9−32) translocate in nasal epithelium. Moreover, hCT(9−32) was used as a carrier to internalize efficiently the green fluorescent protein, drugs, and plasmid DNA. To understand the mechanism of the membrane crossing process, we determined structural parameters of the carrier peptide hCT(9−32) in a membrane environment using solid-state NMR. For that purpose, we synthesized a multiply labeled hCT(9−32) peptide comprising four positions with fully 15N- and 13C-labeled amino acids. Multilamellar vesicle samples containing varying mixing ratios of hCT(9−32) and phospholipids found in the plasma membrane of nasal epithelium were prepared. The typical axially symmetric powder patterns of 31P NMR spectra confirmed the presence of lamellar bilayers in our samples. The chemical shift anisotropy of the 31P NMR spectra of the samples in the presence of hCT(9−32) is slightly reduced, revealing weak interaction of the peptide with ...