Modulation of fibrillogenesis of amyloid beta(1-40) peptide with cationic gemini surfactant.

Modulation of the fibrillogenesis of amyloid peptide Abeta(1-40) with the cationic gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (C(12)C(6)C(12)Br(2)) has been studied. Both UV-vis and AFM results show that C(12)C(6)C(12)Br(2) monomers can promote the fibrillogenesis of Abeta(1-40) while its micelles inhibit this process. The electrostatic/hydrophobic force balance plays important roles in determining the Abeta(1-40) aggregation style and the secondary structures. When the surfactant positive charges are close to the Abeta(1-40) negative charges in number, the hydrophobic interaction is highly enhanced in the system. Both the nucleation rate and the lateral association between fibrils are greatly promoted. However, when the surfactant positive charges are in excess of the Abeta(1-40) negative charges, the electrostatic interaction is strengthened. In this case, the lateral association is inhibited and the alpha-helix to beta-sheet transition in the secondary structure is prevented. Simultaneously, another assembly pathway is induced to give the amorphous aggregates. Moreover, the size and surface roughness of the Abeta(1-40) aggregates also vary upon increasing C(12)C(6)C(12)Br(2) concentration.