Tuning micelles of a bioactive heptapeptide biosurfactant via extrinsically induced conformational transition of surfactin assembly

Abstract

We have studied the effects of extrinsic environmental conditions on the conformation of surfactin, a heptapeptide biosurfactant from Bacillus subtilis, in aqueous solutions. It has been made clear that temperature, pH, Ca2+ ions and the synthetic nonionic surfactant hepta-ethylene glycol (C12E7) affect the conformation of surfactin in aqueous solutions. The beta-sheet formation reached a maximum at 40 degrees C both in presence and absence of (C12E7) and the nonionic surfactant enhances the beta-sheet formation even at 25 degrees C. Ca2 + induced the formation of alpha-helices and caused this transition at 0.3 mM with surfactin monomers or at 0.5 mM with surfactin micelles, but above these transition concentrations of Ca2+ beta-sheets were observed. In micellar solution the beta-sheet structure was stabilized at pH values below 7 or upon addition of Ca2+ in concentrations above 0.5 mM. Our results indicated that the bioactive conformation of surfactin is most likely the beta-sheets when the molecules are assembled in micelles. The beta-sheet structure in micelles could be retained by tuning the micelles. Surfactin micelles could be tuned in the bioactive conformation by manipulating pH, temperature, Ca2+ or (C12E7) concentrations in surfactin solutions. Our results strongly indicated that Ca2+ and other molecules (such as C12E7) may function as directing templates in the assembly and conformation of surfactin in micelles. Thus, we suggest environmental manipulation and template-aided micellation (TAM) as a new approach for preparing predesigned micelles, microemulsions or micro-spheres for specific application purposes.

Review of surfactin chemical properties and the potential biomedical applications

“…The two acidic residues Glu-1 and Asp-5 form a well-suited "claw", which can easily stabilize a surfactin-Ca 2+ 1:1 complex via an intramolecular bridge [29]. This effect of Ca 2+ ions on the surfactin conformation promotes the deeper insertion of the lipopeptide into the membrane [27,30].…”

Liquid membrane extraction of bio-active amphiphilic substances: Recovery of surfactin

“…In aqueous media various surfactin conformations, with gradual shifting from one to another, have been reported [9]. At neutral zone of pH (6.5-7.5), surfactin molecules are organized mainly in ␤-sheet micelles.…”

“…In literature, there has been considerable interest on the microbiological productivities [1][2][3][4][5][6][7], properties [1,[8][9][10][11][12] and applications [12][13][14][15][16][17] of biosurfactants, including heptapeptide surfactin, which is one of the most powerful ones [18]. However, few reports have been mentioned concerning surfactin separation, purification and concentration [19][20][21][22].…”

Molecular and Crystal Structure of Spiculisporic Acid and Correlation with the Surface Activity

“…Otherwise, Microbially produced surfactin, a lipopeptidetype biosurfactant, is a kind of macrocyclic-lactone derivative, and formed rod-shaped micelles organized in β-sheet conformation from α-helix monomers despite of macrocyclic-and linear-type ones 13,14 . Microbially produced biosur-from ethanol.…”