The cleavage of the amyloid precursor protein by β- and γ-secretases is a key event in Alzheimer's disease. A fusion protein was constructed to investigate the cleavage rate and aggregation kinetics of amyloid-beta (1–40) (Aβ(1–40)) peptides. The peptide was expressed with a Small Ubiquitin-Like Modifier (SUMO) on the N-terminus and cleaved by a SUMO protease Ulp1. The time course of the cleavage reaction was monitored by SDS-PAGE gel with 100:1 or 1000:1 SUMO-Aβ(1–40) to Ulp1 molar ratio and in the presence of brain total lipid extract unilamellar vesicles. Similarly, the aggregation of Aβ(1–40) peptides upon cleavage was monitored by thioflavin T fluorescence assays and by circular dichroism. The cleavage reaction was modulated by the concentration of Ulp1, with fast release of Aβ(1–40) peptides producing shorter lag time before fibril formation, but with similar elongation rate. The presence of lipids significantly reduced the cleavage completion at 1000:1, but reduced the lag time before fibril formation, while at 100:1 similar cleavage and aggregation kinetics were observed compared to the lipid-free condition. Overall, the results showed that the fusion protein SUMO-Aβ(1–40) is a means to study the cleavage and aggregation of amyloid peptides and that the presence of lipids and the fast release rate accelerated the aggregation of Aβ(1–40) peptides.
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