Abstract
Aggregation of proteins into amyloid deposits is the hallmark of several neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease. The suggestion that intermediate oligomeric species may be cytotoxic has led to intensified investigations of pre-fibrillar oligomers, which are complicated by their transient nature and low population. Here we investigate alpha-synuclein oligomers, enriched by a 2-pyridone molecule (FN075), and the conversion of oligomers into fibrils. As probed by leakage assays, the FN075 induced oligomers potently disrupt vesicles in vitro, suggesting a potential link to disease related degenerative activity. Fibrils formed in the presence and absence of FN075 are indistinguishable on microscopic and macroscopic levels. Using small angle X-ray scattering, we reveal that FN075 induced oligomers are similar, but not identical, to oligomers previously observed during alpha-synuclein fibrillation. Since the levels of FN075 induced oligomers correlate with the amounts of fibrils among different FN075:protein ratios, the oligomers appear to be on-pathway and modeling supports an ‘oligomer stacking model’ for alpha-synuclein fibril elongation.
Highlights
Amyloid deposits of protein fibrils are the hallmarks of several grave diseases, one example being Lewy bodies in Parkinson’s disease[1]
We show how the levels of oligomers are correlated with the levels of fibrils at different FN075 concentrations, which suggests that the FN075 oligomers are embedded within the final fibrils
Far-UV Circular Dichroism (CD) was recorded for native aSN and for samples with different aSN:FN075 ratios with a maximum of 1:9 (Fig. 1a)
Summary
FN075 is an on-pathway oligomer, and its concentration is dependent on the presence of native monomer and aSN fibrils, and regulated by the overall concentration of FN075 This is in contrast to other oligomers reported[9,10,11,16], which highlights the highly sensitive nature of the aggregation prone, transient species and how different methods/protocols will potentially reveal different aspects of the oligomerisation processes happening during fibrillation[25]. For rod-like structures, it is possible to calculate the p(r)-function of the cross-section We have done this for fibrils produced in the presence and absence of FN075 (blue and red, respectively), and it is clear that the cross-sectional dimensions are comparable for the two species. We suggest that the FN075 induced oligomer is a modulated form of the native oligomer, where binding of the small-molecule induces only subtle structural changes but the principal architecture of the two oligomers is the same
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