Catalytic Activity of Amyloids of α-Synuclein Variants with Pathological Mutations

Abstract

Parkinson’s disease is a progressive neurogenerative disorder which is characterized by the presence of Lewy bodies, which consist of insoluble α-Synuclein amyloid aggregates. While amyloids have been considered to be inert end-products, recent studies show that some amyloids exhibit catalytic properties. This master’s thesis focuses on the catalytic activity of α-Synuclein, including the wild-type and three pathological mutations: E46K, H50Q and A53T. In this thesis, the monomers of each variant were over-expressed in Escherichia coli, purified, aggregated as well as quality controlled through circular dichroism, Thioflavin T fluorescence and atomic force microscopy. The catalytic activity of these four amyloid fibril variants were studied in relation of their control group consisting either monomers or buffer background. Substrate paranitrophenyl acetate was used to study esterase activity, while paranitrophenyl phosphate and adenosine 5’-triphosphate were used for dephosphorylation assays. Results show that all variants exhibit strong esterase activity, while phosphatase activity varies between the variants and individual experiments, suggesting sensitivity on how amyloid fibrils are prepared. The dephosphorylation results are discussed in terms of how fibril polymorphism may influences the catalytic activity. While esterase activity was high, the differences between the variants were not statistically significant enough to draw firm conclusions.