A study of melittin, motilin and galanin in reversed micellar environments, using circular dichroism spectroscopy

Circular dichroism spectroscopy has been used to study the behaviour of the cytolytic peptide melittin, the intestinal peptide hormone motilin (porcine) and the neuropeptide galanin (porcine) in various reversed micellar systems. The micellar systems used contained sodium dodecyl sulphate, bis(2-ethylhexyl) sulfosuccinate, n-dodecyltrimethylammonium chloride or polyoxyethylene(7) lauryl ether. Various structural changes of the peptides, induced either by varying the water content or the surface charge of the reversed micelles, could be monitored. Melittin has in all micellar systems a large amount of alpha-helix, and is almost unaffected by both water content and the surface charge of the reversed micelles. Motilin on the other hand attains an alpha-helical structure at low water content only. The surface charges seem to be of importance for the association between motilin and the hydrated reversed micellar surface. Galanin has the most complicated behaviour with a large dependence on surface charge and with a water content dependence which varies with the surfactant used. Stabilization of alpha-helical secondary structures was only seen in negatively charged reversed micelles. These observations indicate a specific interaction between galanin and surfactant, probably of electrostatic nature.