Probing the role of aromatic residues in the self-assembly of Aβ(16-22) in fluorinated alcohols and their aqueous mixtures.

The Aβ(16-22) sequence KLVFFAE spans the hydrophobic core of the Aβ peptide and plays an important role in its self-assembly. Apart from forming amyloid fibrils, Aβ(16-22) can self-associate into highly ordered nanotubes and ribbon-like structures depending on the composition of solvent used for dissolution. The Aβ(16-22) sequence which has FF at the 19th and 20th positions would be a good model to investigate peptide self-assembly in the context of aromatic interactions. In this study, self-assembly of Aβ(16-22) and its aromatic analogs obtained by replacement of F19, F20 or both by Y or W was examined after dissolution in fluorinated alcohols and their aqueous mixtures in solvent cluster forming conditions. The results indicate that the presence of aromatic residues Y and W and their position in the sequence plays an important role in self-assembly. We observe the formation of amyloid fibrils and other self-assembled structures such as spheres, rings and beads. Our results indicate that 20% HFIP is more favourable for amyloid fibril formation as compared to 20% TFE, when F is replaced with Y or W. The dissolution of peptides in DMSO followed by evaporation of solvent and dissolution in water appears to greatly influence peptide conformation, morphology and cross-β content of self-assembled structures. Our study shows that positioning of aromatic residues F, Y and W have an important role in directing self-assembly of the peptides.