Simultaneous analysis of oligomer and fibril assembly kinetics reveals inhibitory effects of metastable oligomers on amyloid fibril formation.

Amyloidogenic proteins share a propensity to convert to the β-structure-rich amyloid state that is associated with the progression of several protein-misfolding disorders. Here we show that a single engineered β-hairpin-binding protein, the β-wrapin AS10, binds monomers of three different amyloidogenic proteins, that is, amyloid-β peptide, α-synuclein, and islet amyloid polypeptide, with sub-micromolar affinity. AS10 binding inhibits the aggregation and toxicity of all three proteins. The results demonstrate common conformational preferences and related binding sites in a subset of the amyloidogenic proteins. These commonalities enable the generation of multispecific monomer-binding agents.

Background: Protofibrils of the amyloid-␤ peptide (A␤) are neurotoxic oligomers implicated in development and progression of Alzheimer disease. Results: The dissociation of A␤ protofibrils into their monomeric subunits is a slow process, occurring on the time scale of hours. Conclusion: A␤ protofibrils possess a high kinetic stability toward dissociation into monomers. Significance: The longevity of A␤ protofibrils permits sustained toxic effects.

Conversion of the intrinsically disordered protein α-synuclein (α-syn) into amyloid aggregates is a key process in Parkinson's disease. The sequence region 35-59 contains β-strand segments β1 and β2 of α-syn amyloid fibril models and most disease-related mutations. β1 and β2 frequently engage in transient interactions in monomeric α-syn. The consequences of β1-β2 contacts are evaluated by disulfide engineering, biophysical techniques, and cell viability assays. The double-cysteine mutant α-synCC, with a disulfide linking β1 and β2, is aggregation-incompetent and inhibits aggregation and toxicity of wild-type α-syn. We show that α-syn delays the aggregation of amyloid-β peptide and islet amyloid polypeptide involved in Alzheimer's disease and type 2 diabetes, an effect enhanced in the α-synCC mutant. Tertiary interactions in the β1-β2 region of α-syn interfere with the nucleation of amyloid formation, suggesting promotion of such interactions as a potential therapeutic approach.

Background:Aggregates of the protein Tau are associated with Alzheimer disease and other neurodegenerative diseases. Results: The engineered binding protein TP4, targeting the Tau repeat domain, was obtained from a novel ␤-wrapin protein library. Conclusion: TP4 interacts with two alternative conformations of Tau, thereby inhibiting Tau aggregation. Significance: Binding of aggregation-prone sequence stretches is an approach to interfere with Tau aggregation.