Heptameric Peptide Interferes with Amyloid-β Aggregation by Structural Reorganization of the Toxic Oligomers

Pathogenesis of Alzheimer's disease (AD), the most common type of dementia, involves misfolding and aggregation of the extracellular amyloid-β (Aβ) protein where the intermediate oligomers, formed during the aggregation progression cascade, are considered the prime toxic species. Here, we identify an active peptide fragment from a medicinal plant-derived (Aristolochia indica) fibrinolytic enzyme having anti-amyloidogenic effects against Aβ fibrillation and toxicity. Liquid chromatography with tandem mass spectrometry (LC-MS/MS), followed by computational analysis of the peptide pool generated by proteolytic digestion of the enzyme, identifies two peptide sequences with predictive high-propensity binding to Aβ₄₂. Microscopic visualizations in conjunction with biochemical and biophysical assessments suggest that the synthetic version of one of the peptides (termed here P_active, GFLLHQK) arrests Aβ molecules in off-pathway oligomers that can no longer participate in the cytotoxic fibrillation pathway. In contrast, the other peptide (termed P₁) aggravates the fibrillation process. Further investigations confirm the strong binding affinity of P_active with both Aβ₄₂ monomers and toxic oligomers by biolayer interferometric assays. We have also shown that, mechanistically, P_active binding induces conformational alterations in the Aβ molecule along with modification of Aβ hydrophobicity, one of the key players in aggregation. Importantly, the biostability of P_active in human blood serum and its nontoxic nature make it a promising therapeutic candidate against Alzheimer's, for which no disease-modifying treatments are available to date.