magainin-2-peptide--xenopus and dodecylphosphocholine

The role played by noncovalent interactions in inducing a stable secondary structure onto the sodium dodecyl sulfate (SDS) and dodecylphosphocholine (DPC) micelle-bound conformations of (Ala(8,13,18))magainin 2 amide and the DPC micelle bound conformation of magainin 1 were determined. Two-dimensional NMR and molecular modeling investigations indicated that (Ala(8,13,18))magainin 2 amide bound to DPC micelles adopts a alpha-helical secondary structure involving residues 2-16. The four C-terminal residues converge to a lose beta-turn structure. (Ala(8,13,18))magainin 2 amide bound to SDS miscelles adopts a alpha-helical secondary structure involving residues 7-18. The C- and N-terminal residues exhibited a great deal of conformational flexibility. Magainin 1 bound to DPC micelles adopts a alpha-helical secondary structure involving residues 4-19. The C-terminal residues converge to a lose beta-turn structure. The results of this investigation indicate hydrophobic interactions are the major contributors to stabilizing the induced helical structure of the micelle-bound peptides. Electrostatic interactions between the polar head groups of the micelle and the cationic side chains of the peptides define the positions along the peptide backbone where the helical structures begin and end.

Topics: Amino Acid Sequence; Animals; Antimicrobial Cationic Peptides; Binding Sites; Magainins; Magnetic Resonance Spectroscopy; Micelles; Models, Molecular; Phosphorylcholine; Protein Conformation; Sodium Dodecyl Sulfate; Static Electricity; Surface Properties; Xenopus laevis; Xenopus Proteins

Magainin2 is a 23-residue antibiotic peptide that disrupts the ionic gradient across certain cell membranes. Two-dimensional 1H NMR spectroscopy was used to investigate the structure of the peptide in three of the membrane environments most commonly employed in biophysical studies. Sequence-specific resonance assignments were determined for the peptide in perdeuterated dodecylphosphocholine (DPC) and sodium dodecylsulfate micelles and confirmed for the peptide in 2,2,2-trifluoroethanol solution. The secondary structure is shown to be helical in all of the solvent systems. The NMR data were used as a set of restraints for a simulated annealing protocol that generated a family of three-dimensional structures of the peptide in DPC micelles, which superimposed best between residues 4 and 20. For these residues, the mean pairwise rms difference for the backbone atoms is 0.47 +/- 0.10 A from the average structure. The calculated peptide structures appear to be curved, with the bend centered at residues Phe12 and Gly13.

Topics: Amino Acid Sequence; Anti-Infective Agents; Antimicrobial Cationic Peptides; Deuterium; Hydrogen; Magainins; Magnetic Resonance Spectroscopy; Micelles; Models, Molecular; Molecular Sequence Data; Peptides; Phosphorylcholine; Protein Structure, Secondary; Sodium Dodecyl Sulfate; Solutions; Trifluoroethanol; Water; Xenopus Proteins