Resolution of localized small molecule–Aβ interactions by deep-ultraviolet resonance Raman spectroscopy Original Research Article

The mechanism by which flavonoids prevent formation of amyloid-β (Aβ) fibrils, as well as how they associate with non-fibrillar Aβ is still unclear. Fresh, un-oxidized myricetin exhibited excitation and emission fluorescence maxima at 481 and 531 nm, respectively. Introduction of either Aβ(1–42) or Aβ(25–40) resulted in a fluorescence decrease, when measured at 481 nm, suggesting formation of a myricetin–Aβ complex. Circular dichroism (CD) and ultraviolet resonance Raman (UVRR) studies indicate that the association of myricetin with the Aβ peptide or its hydrophobic fragment, Aβ(25–40), leads to subtle changes in each peptideʹs conformation. Aβ(25–40) formed amyloid fibrils at a similar rate, when compared to the full-length peptide, Aβ(1–42), using thioflavin T (ThT) fluorescence. Studies also indicated that myricetin was equally effective at preventing the formation of both Aβ(1–42) and Aβ(25–40) fibrils. Although ThT assays indicated that Aβ(1–16) did not form amyloid fibrils, CD studies of the hydrophilic fragment, Aβ(1–16), suggest possible interactions between myricetin and aromatic side chains. UVRR studies of the full-length peptide and Aβ(1–16) showed increases in the intensity of the aromatic modes upon introduction of myricetin. Our findings suggest that myricetin interacts with soluble Aβ via two mechanisms, association with the hydrophobic C-terminal region and interactions with the aromatic side chains.