Blocking Oligomeric Insulin Amyloid Fibrillation via Perylenebisimides Containing Dipeptide Tentacles

Molecular motifs that could interfere with amyloid fibrillation via non-covalent interactions are vital for aberrant protein aggregation and related human diseases. Mutual aggregation ensues in the presence of these structural motifs, and nucleation on the particle surface leads to inhibition of the fibrillization process. This modular process generates a new generation of inhibitory reagents. Oligomers are the primary toxic species that initiate pathogenic aggregation, leading to toxic β-sheet-rich structures. To inhibit these toxic oligomers, two dipeptide-linked perylenebisimide isomers (PAPAP and APPPA) are developed as selective modulators for insulin fibrillization. Early insulin aggregates are adsorbed onto the modulator surface and stabilize soluble oligomeric aggregates. Fibrillation and inhibition are examined by thioflavin T (ThT) assay in the presence and the absence of both inhibitors PAPAP and APPPA. Conformational modulation using far-UV circular dichroism studies also highlights their role as aggregation inhibitors via reduction of α-helix into β-sheet along with increased random coil contents. Moreover, the inhibitory effects were more pronounced due to the ability of these isomers to undergo varying multiple non-covalent interactions, a performance well beyond all known modulators with respect to selectivity and efficiency, with the more-aggregation-prone derivative due to higher probability of a hydrophobic encounter between the protein and the molecular modulator. These results also lead to the elucidation of an insulin fibril regulating mechanism via selective non-covalent binding and provide fundamental insights into the chemistry of peptide-based probes as tools for developing next-generation therapeutics.