Differentiating the Aβ42 aggregation states via intrinsic tyrosine fluorescence spectrum

Aggregation of amyloid β-peptide (Aβ) into β-sheet-rich fibrils is central to the development of Alzheimer's disease, with Aβ42 more prone to aggregation over Aβ40. Using the intrinsic tyrosine fluorescence spectrum, we show that Aβ42 exhibits a biphasic fluorescence pattern featuring a broad band and a narrow one, distinct from Aβ40 and dissolved tyrosine. Molecular dynamics simulations highlighted the differences in tyrosine's rotamer populations and dynamics between dissolved and aggregated amyloids. Fibrillar Aβ42 shows slower, more uniform tyrosine rotations, corresponding to the narrower fluorescence band. This approach offers a rapid means to differentiate Aβ42 aggregates, benefiting Aβ-related research.