Catalytic Activity of α-Synuclein Amyloid Fibers

Abstract

Amyloid fibers play a significant role in neurodegenerative diseases such as Alzheimer’s Disease (AD) and Parkinson’s Disease (PD). They have for long been considered nonreactive dead-end products of protein aggregation. Recent research show that amyloid fibers, but not monomers, exhibit enzymatic catalytic activity in vitro. This project investigates the catalytic activity of α-Synuclein (aS) amyloid fibers. First, homogeneous aS amyloid fibers were made in a two-step seeding process and amyloids confirmed through ThT-fluorescence, far UV circular dichroism (CD) and atomic force microscopy (AFM). Then, an already established esterase activity assay, in vitro, was used to study ester bond cleavage of WT and A53T (disease-causing mutant) aS amyloid fibers. Another in vitro enzymatic assay was developed to study ATPase activity of WT, A53T and H50A (model of disease-causing mutants with altered residue 50) aS amyloid fibers. Results indicate that there is catalytic activity when aS amyloid fibers are incubated with both ester-bond and ATP substrates. However, the results are only qualitatively interpreted due to large variability in obtained kinetic parameters. To draw firm conclusions regarding the difference between the investigated aS mutants, additional experiments are needed.