The process of amyloid-β (Aβ) amyloid formation is pathologically linked to Alzheimer’s disease (AD). The identification of Aβ amyloids and intermediates that are crucial players in the pathology of AD is critical for exploring the underlying mechanism of Aβ aggregation and the diagnosis of the disease. Herein, we performed a gold nanoparticle (AuNP)-based study to detect the formation of Aβ amyloid fibrils and oligomers. Our results demonstrate that the intensity of the surface plasmon resonance (SPR) absorption band of the AuNPs is sensitive to the quantity of Aβ40 amyloids. This allows the SPR assay to be used for detection and semi-quantification of Aβ40 amyloids, and characterization of the kinetics of Aβ amyloid formation. Furthermore, our study demonstrates that the SPR band intensity of the AuNPs is sensitive to the presence of oligomers of both Aβ40 and an Aβ40 mutant, which forms more stable oligomers. The kinetics of the stable oligomer formation of the Aβ40 mutant can also be monitored following the SPR band intensity change of AuNPs. Our results indicate that this nanoparticle based method can be used for mechanistic studies of early protein self-assembly and fibrillogenesis.

Elucidating local dynamics of protein aggregation is crucial for understanding the mechanistic details of protein amyloidogenesis. Herein, we studied the residue-specific dynamics and local environmental changes of Ab40 along the course of aggregation by using para-cyanophenylalanine (PheCN) as a fluorescent and vibrational probe. Our results show that the PheCN residues introduced at various positions all exhibited an immediate decay of fluorescence intensity, indicating a relatively synergistic process in early oligomer formation. The fast decreases in the fluorescence intensities of residues 19 and 20 in the central hydrophobic core region and residue 10 in the N-terminal region suggest that they play crucial roles in the formation of the oligomeric core. The PheCN4 residue exhibits a remarkably slower decrease in fluorescence intensity, implicating its dynamic conformational characteristics in oligomer and fibril formation. Our results also suggest that the N-terminal residues in fibrils are surrounded by a relatively hydrophobic local environment, as opposed to being solvated.

Interactions of amyloid-β (Aβ) peptides and cellular membranes are proposed to be closely related with Aβ neurotoxicity in Alzheimer’s disease. In this study, we systematically investigated the effect of the N-terminal hydrophilic region of Aβ40 on its amyloidogenesis and interaction with supported phospholipid bilayer. Our results show that modulation of the charge properties of the dynamic N-terminal region dramatically influences the aggregation properties of Aβ. Furthermore, our results demonstrate that the N-terminal charged residues play a crucial role in driving the early adsorption and latter remobilization of the peptide on membrane bilayer, and mediating the rigidity and viscoelasticity properties of the bound Aβ40 at the membrane interface. The results provide new mechanistic insight into the early Aβ-membrane interactions and binding, which may be critical for elucidating membrane-mediated Aβ amyloidogenesis in a physiological environment and unravelling the origin of Aβ neurotoxicity.

Understanding of the mechanistic progess of Amyloid-β peptide (Aβ) aggregation is critical for elucidating the underlying pathogenesis of Alzheimer’s disease (AD). Herein, we report for the first time the effects of two cholesterol derivatives, negatively charged cholesterol sulfate (cholesterol-SO4) and positively charged 3β-[N-(dimethylaminoethane)carbamoyl]-cholesterol (DC-cholesterol), on the fibrillization of Aβ40. Our results demonstrate that both of the nonvesicle forms of cholesterol-SO4 and DC-cholesterol moderately accelerate the aggregation rate of Aβ40. This effect is similar to that observed for unmodified cholesterol, indicating the importance of hydrophobic interactions in binding of Aβ40 to these steroid molecules. Furthermore, we show that the vesicles formed at higher concentrations of anionic cholesterol-SO4 facilitate Aβ40 aggregation rate markedly. In contrast, the cationic DC-cholesterol vesicles show the ability to inhibit Aβ40 fibril formation under appropriate experimental conditions. The results suggest that the electrostatic interactions between Aβ40 and the charged vesicles can be of great importance in regulating Aβ40-vesicle interaction. Our results also indicate that the structural properties of the aggregates of the cholesterol derivatives, including the surface charge and the size of the vesicles, are critical in regulating the effects of these vesicles on Aβ40 aggregation kinetics.

Elucidating local dynamics of protein aggregation is crucial for understanding the mechanistic details of protein amyloidogenesis. Herein, we studied the residue‐specific dynamics and local environmental changes of Aβ40 along the course of aggregation by using para‐cyanophenylalanine (PheCN) as a fluorescent and vibrational probe. Our results show that the PheCN residues introduced at various positions all exhibited an immediate decay of fluorescence intensity, indicating a relatively synergistic process in early oligomer formation. The fast decreases in the fluorescence intensities of residues 19 and 20 in the central hydrophobic core region and residue 10 in the N‐terminal region suggest that they play crucial roles in the formation of the oligomeric core. The PheCN4 residue exhibits a remarkably slower decrease in fluorescence intensity, implicating its dynamic conformational characteristics in oligomer and fibril formation. Our results also suggest that the N‐terminal residues in fibrils are surrounded by a relatively hydrophobic local environment, as opposed to being solvated.