Folding and dynamics of melittin in reversed micelles

The main structural characteristics and the dynamic properties of melittin bound to the internal surface of reversed micelles, formed by sodium bis(2-ethyl-1-exyl)sulfosuccinate (AOT) in isooctane, were investigated by several spectroscopic techniques. Melittin has been found associated to reversed AOT micelles in a single state, thus indicating that this system behaves differently with respect to phospholipid vesicles where at least two forms of lipid associated melittin are observed. The dynamic properties of melittin in reversed AOT micelles at different water contents were examined by frequency domain fluorometry. The whole emission decay was analyzed in terms of lifetime distribution having a Lorentzian shape. The results indicated that the binding of melittin to inverted micelles determines an increase of emission heterogeneity compared to that observed for the fully extended helical monomer. This was explained in terms of a larger variety of microenvironmental conditions that the tryptophan residue experiences during its excited state. However, the conformation freedom of the peptide can be modulated by varying the micellar size.