Fluorescence, CD, Attenuated Total Reflectance (ATR) FTIR, and 13C NMR Characterization of the Structure and Dynamics of Synthetic Melittin and Melittin Analogues in Lipid Environments

The structure and dynamics of synthetic melittin (MLT) and MLT analogues bound to monomyristoylphosphatidylcholine micelles, dimyristoylphosphatidylcholine vesicles, and diacyl-phosphatidylcholine films have been investigated by fluorescence, CD, attenuated total reflectance (ATR) FTIR, and ¹³C NMR spectroscopy. All of these methods provide information about peptide secondary structure and/or about the environment of the single tryptophan side chain in these lipid environments. ATR-FTIR data provide additional information about the orientation of helical peptide segments with respect to the bilayer plane. Steady-state fluorescence anisotropy, fluorescence lifetime, and ¹³C NMR relaxation data are used in concert to provide quantitative information about the dynamics of a single ¹³C-labeled tryptophan side chain at position 19 in lipid-bound MLT, and at positions 17, 11, and 9, respectively, in lipid-bound MLT analogues. Peptide chain dynamics are probed by NMR relaxation studies of ¹³Cα-labeled glycine incorporated into each of the MLT peptides at position 12. The cumulative structural and dynamic data are consistent with a model wherein the N-terminal a-helical segment of these peptides is oriented perpendicular to the bilayer plane. Correlation times for the lysolipid-peptide complexes provide evidence for binding of a single peptide monomer per micelle. A model for the membranolytic action of MLT and MLT-like peptides is proposed.