Tripeptide-based amyloid hydrogels: phenylalanine mutation outcomes on self-assembly, hydrogelation and their cytotoxicity assays

A tripeptide segment Leu-Val-Phe (Aβ17-19) has been judiciously selected from the core β-amyloid (Aβ1-42) peptide sequence. Seven tripeptides with the general sequence Boc-Leu-Val-X-COOH (Boc-LVX-OH), where X = L-phenylalanine, L-4-nitro-phenylalanine, L-tyrosine, L-3-nitro-tyrosine, L-tryptophan, L-valine, and γ-amino butyric acid for AP1 to AP7, respectively, have been synthesized to study their aggregation behavior, hydrogel forming abilities and corresponding cytotoxicity. Stable hydrogelation for Boc-LVF-OH (AP1) and Boc-LV(4-nF)-OH (AP2), weak hydrogelation for Boc-LVY-OH (AP3), transient hydrogelation for Boc-LV(4-nY)-OH (AP4) and no hydrogelation for Boc-LVW-OH (AP5), Boc-LV-GABA-OH (AP6 and GABA = γ-amino butyric acid) and Boc-LVV-OH (AP7) have been observed in phosphate buffer. A well-defined nanofibrillar network structure and vesicular morphologies have been observed for all of the hydrogelators and non-hydrogelators, respectively. A CD spectroscopic study suggests the presence of β-sheet structures in their hydrogel states. MTT assays suggest that the nonaromatic mutations on phenylalanine do not change the toxicity; however, other natural and unnatural aromatic amino acid mutations lead to higher toxicity. Interestingly, AP6 and AP7 lead to the formation of a non-toxic fibril-free environment, suggesting anti-amyloidogenic behaviour. This study aims to elucidate the fibrillization process and the mechanisms of the primary hydrophobic core sequence in amyloid peptides and their cytotoxicity.