Temperature dependence of the α-helix conformation of bee venom melittin in methanol-water mixed solvents has been examined by NMR, in order to elucidate conformation stability and a phase diagram. At high methanol concentration of 100 – ca. 80 wt.%, melittin forms a full α-helix conformation in the temperature range from 25 °C to 60 °C. At intermediate methanol concentration of ca. 80 – ca. 25 wt.%, it undergoes a thermal transformation from a full α-helix to a partial α-helix. In solutions of low methanol concentrations of ca. 25 – 0 wt.%, partial α-helix monomers and their selfaggregated conformers coexist at low temperatures, and the relative number of the monomers increases with increase in temperature. The monomers turn to a random coil state at high temperatures only below ca. 10 wt. % methanol concentrations. The thermal transitions are discussed from the viewpoint of stability of intra-molecular hydrogen bonds and intermolecular hydrophobic interactions.
Keywords: α-helix, hydrogen bond, hydrophobic interaction, melittin, methanol-water mixed solvent, NMR, phase diagramα-helix, hydrogen bond, hydrophobic interaction, melittin, methanol-water mixed solvent, NMR, phase diagram