Conformational studies of a melittin-inhibitor complex

The conformation of a melittin-inhibitor complex was studied by solution NMR, solid-state NMR, and circular dichroism. In solution, binding was studied by titrating inhibitor against melittin in dimethyl sulfoxide, methanol, aqueous buffer, and dodecylphosphocholine micelles. The change in chemical shift of Trp19 resonances and the formation of a precipitate at 1:1 molar ratio indicated that the inhibitor was bound to melittin. Solid-state NMR also showed a change in chemical shift of two labeled carbons of melittin near Pro14 and a change in 1HT1 relaxation times when complexed with inhibitor. Rotational resonance experiments of melittin labeled in the proline region indicated a change in conformation for melittin complexed with inhibitor. This observation was also supported by circular dichroism measurements, indicating a reduction in alpha-helical structure for increasing ratios of inhibitor bound to melittin.