Solid-state NMR structure determination of melittin in a lipid environment

Solid-state C-13 NMR spectroscopy was used to investigate the three-dimensi onal structure of melittin as lyophilized powder and in ditetradecylphospha tidylcholine (DTPC) membranes. The distance between specifically labeled ca rbons in analogs [1-C-13]Gly3-[2-C-13]Ala4, [1-C-13]Gly3-[2-C-13]Leu6, [1-C -13]Leu13-[2-C-13]Ala15, [2-C-13]Leu13-[1-C-13]Ala15, and [1-C-13]Leu13-[2- C-13]Leu16 was measured by rotational resonance. As expected, the internucl ear distances measured in [1-C-13]Gly3-[2-C-13]Ala4 and [1-C-13]Gly3-[2-C-1 3]Leu6 were consistent with alpha -helical structure in the N-terminus irre spective of environment. The Internuclear distances measured in [1-C-13]Leu 13-[2-C-13]Ala15, [2-C-13]Leu13-[1-C-13]Ala15, and [1-C-13]Leu13-[2-C-13]Le u16 revealed, via molecular modeling, some dependence upon environment for conformation in the region of the bend in helical structure induced by Pro1 4. A slightly larger interhelical angle between the N- and C-terminal helic es was indicated for peptide in dry or hydrated gel state DTPC (139 degrees -145 degrees) than in lyophilized powder (121 degrees -139 degrees) or cry stals (129 degrees). The angle, however, is not as great as deduced for mel ittin in aligned bilayers of DTPC in the liquid-crystalline state (similar to 160 degrees) (R. Smith, F. Separovic, T. J. Milne, A. Whittaker, F. M. B ennett, B. A. Cornell, and A. Makriyannis, 1994, J. Mol, Biol 241:456-466). The study illustrates the utility of rotational resonance in determining l ocal structure within peptide-lipid complexes.