α-Synuclein Misfolding Assessed with Single Molecule AFM Force Spectroscopy: Effect of Pathogenic Mutations

Misfolding and subsequent aggregation of alpha-synuclein (alpha-Syn) protein are critically involved in the development of several neurodegenerative diseases, including Parkinson's disease (PD). Three familial single point mutations, A30P, E46K, and A53T, correlate with early onset PD; however, the molecular mechanism of the effects of these mutations on the structural properties of alpha-Syn and its propensity to misfold remains unclear. Here, we address this issue utilizing a single molecule AFM force spectroscopy approach in which structural details of dimers formed by all four variants of alpha-Syn are characterized. Analysis of the force spectroscopy data reflecting contour length distribution for alpha-Syn dimer dissociation suggests that multiple segments are involved in the assembly of the dimer. The interactions are not limited to the central nonamyloid-beta component (NAC) of the protein but rather expand beyond this segment. All three mutations alter the protein's folding and interaction patterns affecting interactions far beyond their immediate locations. Implementation of these findings to our understanding of alpha-Syn aggregation pathways is discussed.