TUNING MICELLES OF A BIOACTIVE HEPTAPEPTIDE BIOSURFACTANT VIA EXTRINSICALLY INDUCED CONFORMATIONAL TRANSITION OF SURFACTIN ASSEMBLY

We have studied the effects of extrinsic environmental conditions on t he conformation of surfactin, a heptapeptide biosurfactant from Bacill us subtilis, in aqueous solutions. It has been made clear that tempera ture, pH, Ca2+ ions and the synthetic nonionic surfactant hepta-ethyle ne glycol (C12E7) affect the conformation of surfactin in aqueous solu tions. The beta-sheet formation reached a maximum at 40 degrees C both in presence and absence of (C12E7) and the nonionic surfactant enhanc es the beta-sheet formation even at 25 degrees C. Ca2+ induced the for mation of a-helices and caused this transition at 0.3 mM with surfacti n monomers or at 0.5 mM with surfactin micelles, but above these trans ition concentrations of Ca2+ beta-sheets were observed. In micellar so lution the beta-sheet structure was stabilized at pH values below 7 or upon addition of Ca2+ in concentrations above 0.5 mM. Our results ind icated that the bioactive conformation of surfactin is most likely the beta-sheets when the molecules are assembled in micelles. The beta-sh eet structure in micelles could be retained by tuning the micelles. Su rfactin micelles could be tuned in the bioactive conformation by manip ulating pH, temperature, Ca2+ or (C12E7) concentrations in surfactin s olutions. Our results strongly indicated that Ca2+ and other molecules (such as C12E7) may function as directing templates in the assembly a nd conformation of surfactin in micelles. Thus, we suggest environment al manipulation and template-aided micellation (TAM) as a new approach for preparing predesigned micelles, microemulsions or micro-spheres f or specific application purposes. (C) 1998 European Peptide Society an d John Wiley gr Sons, Ltd.