Insights into the baicalein-induced destabilization of LS-shaped Aβ₄₂ protofibrils using computer simulations

Amyloid-β (Aβ) peptides aggregate spontaneously into various aggregating species comprising oligomers, protofibrils, and mature fibrils in Alzheimer's disease (AD). Disrupting β-sheet rich neurotoxic smaller soluble Aβ₄₂ oligomers formed at early stages is considered a potent strategy to interfere with AD pathology. Previous experiments have demonstrated the inhibition of the early stages of Aβ aggregation by baicalein; however, the molecular mechanism behind inhibition remains largely unknown. Thus, in this work, molecular dynamics (MD) simulations have been employed to illuminate the molecular mechanism of baicalein-induced destabilization of preformed Aβ₄₂ protofibrils. Baicalein binds to chain A of the Aβ₄₂ protofibril through hydrogen bonds, π-π interactions, and hydrophobic contacts with the central hydrophobic core (CHC) residues of the Aβ₄₂ protofibril. The binding of baicalein to the CHC region of the Aβ₄₂ protofibril resulted in the elongation of the kink angle and disruption of K28-A42 salt bridges, which resulted in the distortion of the protofibril structure. Importantly, the β-sheet content was notably reduced in Aβ₄₂ protofibrils upon incorporation of baicalein with a concomitant increase in the coil content, which is consistent with ThT fluorescence and AFM images depicting disaggregation of pre-existing Aβ₄₂ fibrils on the incorporation of baicalein. Remarkably, the interchain binding affinity in Aβ₄₂ protofibrils was notably reduced in the presence of baicalein leading to distortion in the overall structure, which agrees with the structural stability analyses and conformational snapshots. This work sheds light on the molecular mechanism of baicalein in disrupting the Aβ₄₂ protofibril structure, which will be beneficial to the design of therapeutic candidates against disrupting β-sheet rich neurotoxic Aβ₄₂ oligomers in AD.