Structure and solvation of melittin in 1,1,1,3,3,3-hexafluoro-2-propanol/water

Fluorinated alcohols can induce peptides and proteins to take up helical conformations. Nuclear Overhauser effect (NOE) spectroscopy experiments and analysis of C(alpha)H proton chemical shifts show that the conformation of melittin in 35% hexafluoro-2-propanol/water is alpha-helical from residues Ile-2 to Val-8 and from Leu-13 to Gln-25. As has been found in other solvent systems, the two helical regions are not colinear; the interhelix angle (73 +/- 15 degrees ) in 35% 1,1,1,3,3,3-hexafluoro-2-propanol/water is smaller than the angle found in other fluoroalcohol-water mixtures or in the crystal. Intermolecular (1)H(19)F and (1)H(1)H nuclear Overhauser effects were used to explore interaction of solvent components with melittin dissolved in this solvent mixture. The NOEs observed indicate that fluoroalcohol and water molecules are both tightly bound to the peptide in the vicinity of the interhelix bend. For the remainder of the molecule, solute-solvent NOEs are consistent with preferential solvation of the peptide by the fluoroalcohol component of the solvent mixture.