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α-Synuclein (α-Syn) aggregation and amyloid formation are associated with loss of dopaminergic neurons in Parkinson's disease (PD). In addition, familial mutations in α-Syn are shown to be one of the definite causes of PD. Here we have extensively studied familial PD associated α-Syn G51D, H50Q, and E46K mutations using Drosophila model system. Our data showed that flies expressing α-Syn familial mutants have a shorter lifespan and exhibit more climbing defects compared to wild-type (WT) flies in an age-dependent manner. The immunofluorescence studies of the brain from the old flies showed more dopaminergic neuronal cell death in all mutants compared to WT. This adverse effect of α-Syn familial mutations is highly correlated with the sustained population of oligomer production and retention in mutant flies. Furthermore, this was supported by our in vitro studies, where significantly higher amount of oligomer was observed in mutants compared to WT. The data suggest that the sustained population of oligomer formation and retention could be a major cause of cell death in α-Syn familial mutants.

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., (© 2015 by The American Society for Biochemistry and Molecular Biology, Inc.)

α-Synuclein (α-Syn) oligomerization and amyloid formation are associated with Parkinson's disease (PD) pathogenesis. Studying familial α-Syn mutants associated with early onset PD has therapeutic importance. Here we report the aggregation kinetics and other biophysical properties of a newly discovered PD associated Finnish mutation (A53E). Our in vitro study demonstrated that A53E attenuated α-Syn aggregation and amyloid formation without altering the major secondary structure and initial oligomerization tendency. Further, A53E showed reduced membrane binding affinity compared to A53T and WT. The present study would help to delineate the role of A53E mutation in early onset PD pathogenesis.