Resolution of Oligomeric Species during the Aggregation of Aβ_1–40 Using ¹⁹F NMR

In the commonly used nucleation-dependent model of protein aggregation, aggregation proceeds only after a lag phase in which the concentration of energetically unfavorable nuclei reaches a critical value. The formation of oligomeric species prior to aggregation can be difficult to detect by current spectroscopic techniques. By using real-time ¹⁹F NMR along with other techniques, we are able to show that multiple oligomeric species can be detected during the lag phase of Aβ_1–40 fiber formation, consistent with a complex mechanism of aggregation. At least six types of oligomers can be detected by ¹⁹F NMR. These include the reversible formation of large β-sheet oligomer immediately after solubilization at high peptide concentration, a small oligomer that forms transiently during the early stages of the lag phase, and four spectroscopically distinct forms of oligomers with molecular weights between ∼30 and 100 kDa that appear during the later stages of aggregation. The ability to resolve individual oligomers and track their formation in real-time should prove fruitful in understanding the aggregation of amyloidogenic proteins and in isolating potentially toxic nonamyloid oligomers

Reactivity of Diphenylpropynone Derivatives Toward Metal-Associated Amyloid‑β Species

In Alzheimer’s disease (AD), metal-associated amyloid-β (metal–Aβ) species have been suggested to be involved in neurotoxicity; however, their role in disease development is still unclear. To elucidate this aspect, chemical reagents have been developed as valuable tools for targeting metal–Aβ species, modulating the interaction between the metal and Aβ, and subsequently altering metal–Aβ reactivity. Herein, we report the design, preparation, characterization, and reactivity of two diphenylpropynone derivatives (<b>DPP1</b> and <b>DPP2</b>) composed of structural moieties for metal chelation and Aβ interaction (bifunctionality). The interactions of these compounds with metal ions and Aβ species were confirmed by UV–vis, NMR, mass spectrometry, and docking studies. The effects of these bifunctional molecules on the control of in vitro metal-free and metal-induced Aβ aggregation were investigated and monitored by gel electrophoresis and transmission electron microscopy (TEM). Both <b>DPP1</b> and <b>DPP2</b> showed reactivity toward metal–Aβ species over metal-free Aβ species to different extents. In particular, <b>DPP2</b>, which contains a dimethylamino group, exhibited greater reactivity with metal–Aβ species than <b>DPP1</b>, suggesting a structure-reactivity relationship. Overall, our studies present a new bifunctional scaffold that could be utilized to develop chemical reagents for investigating metal–Aβ species in AD