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Mastoparan is a small peptide composed of 14 amino acid residues found in wasp venom. It penetrates into cytoplasm through the cell membranes and then binds to a G protein to stimulate the release of histamine. Conformation and its thermal stability of mastoparan from Vespula lewisi (MP) in methanol are investigated by using proton nuclear magnetic resonance (NMR) spectroscopy. On the basis of data on NOESY cross peaks, spin-spin coupling constants between an amide proton (NH) and an α-proton, NH chemical shift analyses, and temperature dependence of integrated intensity of NH resonance lines, we found that MP forms the helix between the 5th and 12th residues at low temperatures and the helix segment is maintained even at 54°C. This conformation is similar to that of MP bound to detergent micelles, and hence, methanol is considered to be appropriate as a membrane mimetic for MP. In connection with the function of the venom peptide, significance of high stability of the helical conformation is discussed.

Thermal stability of the α-helix conformation of melittin in pure ethanol and ethanol–water mixture solvents has been investigated by using NMR spectroscopy. With increase in water concentration of the mixture solvents (from 0 wt% to ~71.5 wt%) as well as temperature (from room temperature to 60 °C), the intramolecular hydrogen bonds formed in melittin are destabilized and the α-helix is partially uncoiled. Further, the hydrogen bonds are found to be more thermally stable in pure ethanol than in pure methanol, suggesting that their stability is enhanced with increase in the size of the alkyl groups of alcohol molecules. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.