Ethanol induced the formation of β-sheet and amyloid-like fibrils by surfactant-like peptide A6K.

Self-assembly of natural or designed peptides into fibrillar structures based on β-sheet conformation is a ubiquitous and important phenomenon. Recently, organic solvents have been reported to play inductive roles in the process of conformational change and fibrillization of some proteins and peptides. In this study, we report the change of secondary structure and self-assembling behavior of the surfactant-like peptide A6K at different ethanol concentrations in water. Circular dichroism indicated that ethanol could induce a gradual conformational change of A6K from unordered secondary structure to β-sheet depending upon the ethanol concentration. Dynamic light scattering and atomic force microscopy revealed that with an increase of ethanol concentration the nanostructure formed by A6K was transformed from nanosphere/string-of-beads to long and smooth fibrils. Furthermore, Congo red staining/binding and thioflavin-T binding experiments showed that with increased ethanol concentration, the fibrils formed by A6K exhibited stronger amyloid fibril features. These results reveal the ability of ethanol to promote β-sheet conformation and fibrillization of the surfactant-like peptide, a fact that may be useful for both designing self-assembling peptide nanomaterials and clarifying the molecular mechanism behind the formation of amyloid fibrils.