Familial Parkinson disease-associated mutations alter the site-specific microenvironment and dynamics of α-synuclein.

Human α-synuclein (α-Syn) is a natively unstructured protein whose aggregation into amyloid fibrils is associated with Parkinson disease (PD) pathogenesis. Mutations of α-Syn, E46K, A53T, and A30P, have been linked to the familial form of PD. In vitro aggregation studies suggest that increased propensity to form non-fibrillar oligomers is the shared property of these familial PD-associated mutants. However, the structural basis of the altered aggregation propensities of these PD-associated mutants is not yet clear. To understand this, we studied the site-specific structural dynamics of wild type (WT) α-Syn and its three PD mutants (A53T, E46K, and A30P). Tryptophan (Trp) was substituted at the N terminus, central hydrophobic region, and C terminus of all α-Syns. Using various biophysical techniques including time-resolved fluorescence studies, we show that irrespective of similar secondary structure and early oligomerization propensities, familial PD-associated mutations alter the site-specific microenvironment, solvent exposure, and conformational flexibility of the protein. Our results further show that the common structural feature of the three PD-associated mutants is more compact and rigid sites at their N and C termini compared with WT α-Syn that may facilitate the formation of a partially folded intermediate that eventually leads to their increased oligomerization propensities.