Self-Assembly of Aβ-Based Peptide Amphiphiles with Double Hydrophobic Chains

Two peptide-amphiphiles (PAs), 2C(12)-Lys-A beta(12-17) and C-12-A beta(11-17)-C-12, were constructed with two alkyl chains attached to a key fragment of amyloid beta-peptide (A beta(11-17)) at different positions. The two alkyl chains of 2C(12)-Lys-A beta(12-17) were attached to the same terminus of A beta(12-17), while the two alkyl chains of C-12-A beta(11-17)-C-12 were separately attached to each terminus of A beta(11-17). The self-assembly behavior of both the PAs in aqueous solutions was studied at 25 degrees C and at pHs 3.0, 4.5, 8.5, and 11.0, focusing on the effects of the attached positions of hydrophobic chains to A beta(11-17) and the net charge quantity of the A beta(11-17) headgroup. Cryogenic transmission electron microscopy and atomic force microscopy show that 2C(12)-Lys-A beta(12-17) self-assembles into long stable fibrils over the entire pH range, while C-12-A beta(11-17)-C-12 forms short twisted ribbons and lamellae by adjusting pHs. The above fibrils, ribbons, and lamellae are generated by the lateral association of nanofibrils. Circular dichroism spectroscopy suggests the formation of beta-sheet structure with twist and disorder to different extents in the aggregates of both the PM. Some of the C-12-A beta(11-17)-C-12 molecules adopt turn conformation with the weakly charged peptide sequence, and the Fourier transform infrared spectroscopy indicates that the turn content increases with the pH increase. This work provides additional basis for the manipulations of the PA's nanostructures and will lead to the development of tunable nanostructure materials.