Nanobodies raised against monomeric α-synuclein inhibit fibril formation and destabilize toxic oligomeric species

Background: The aggregation of the protein alpha-synuclein (alpha S) underlies a range of increasingly common neurodegenerative disorders including Parkinson's disease. One widely explored therapeutic strategy for these conditions is the use of antibodies to target aggregated alpha S, although a detailed molecular-level mechanism of the action of such species remains elusive. Here, we characterize alpha S aggregation in vitro in the presence of two alpha S-specific single-domain antibodies (nanobodies), NbSyn2 and NbSyn87, which bind to the highly accessible C-terminal region of alpha S. Results: We show that both nanobodies inhibit the formation of alpha S fibrils. Furthermore, using single-molecule fluorescence techniques, we demonstrate that nanobody binding promotes a rapid conformational conversion from more stable oligomers to less stable oligomers of alpha S, leading to a dramatic reduction in oligomer-induced cellular toxicity. Conclusions: The results indicate a novel mechanism by which diseases associated with protein aggregation can be inhibited, and suggest that NbSyn2 and NbSyn87 could have significant therapeutic potential.