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theses

Alpha-synuclein (αS) and beta-synuclein (βS) are small pre-synaptic, neuronal proteins, which have high sequence similarity, co-localize and very likely play a similar function in cells. However, αS and βS differ significantly in terms of their involvement in Parkinson's disease: while αS aggregation is believed to be a centerpiece and main hallmark of the disease, non-fibrillar βS is held to be a negative regulator of αS toxicity. In my research I focused on uncovering the basis for the non-aggregating properties of βS and understanding the basis of inhibition of αS aggregation by βS. In my research I used integrated biophysical approach primarily focusing on NMR with compliments from CD, DLS, ESI-MS, aggregation assays, cell toxicity assays, chromatography and TEM. Using paramagnetic relaxation enhancement (PRE) I was able to obtain the first ever contact maps for alpha synuclein transient dimers. A similar approach enabled me to discriminate between interactions of alpha synuclein homo-dimers and alpha/beta hetero-dimers which shed light on the interactivity profiles of alpha and beta synuclein. PRE titrations further revealed additional differences in the interactive propensities of these two proteins, that possibly give rise to the differences in aggregation rates. Thus, I was able to provide an initial answer to the first question: beta synuclein can inhibit alpha synuclein aggregation through specific weak interactions that can slow down formation of the aggregation prone complexes. I also sought to extend the knowledge about the inhibition of αS aggregation by βS by characterizing inhibition events at the later stages of aggregation that involve higher order species such as oligomers. I further investigated the molecular determinants of P123H, a beta synuclein mutant that switches beta synuclein from being a non-toxic to a toxic species. I discovered that the mutation in the C-terminus induces a conformational change in the P123H ensemble that leads to a collapse of the C-terminus. It is especially interesting that this one mutation can exacerbate the effect of alpha synuclein aggregation, suggesting again that the extension of the synuclein C-terminus plays an important regulatory role in aggregation and inhibition. Coupled together these facts suggest that beta-synuclein’s conformational characteristics make it particularly well-suited to inhibit alpha synuclein aggregation, which in turn provides a good candidate platform for developing inhibitors of alpha synuclein aggregation.

ETD_6663

Ph.D.

Includes bibliographical references

by Maria K. Janowska

doi:10.7282/T3F76FHX

ETD doctoral

The author owns the copyright to this work.