Effect of Familial Parkinson's Disease Point Mutations A30P and A53T on the Structural Properties, Aggregation, and Fibrillation of Human α-Synuclein

Parkinson's disease involves the loss of dopaminergic neurons in the substantia nigra, leading to movement disorders. The pathological hallmark of Parkinson's disease is the presence of Lewy bodies and Lewy neurites, which are intracellular inclusions consisting primarily of α-synuclein. Although essentially all cases of sporadic and early-onset Parkinson's disease are of unknown etiology, two point mutations (A53T and A30P) in the α-synuclein gene have been identified in familial early-onset Parkinson's disease. Previous reports have shown that mutant α-synuclein may form fibrils more rapidly than wild-type protein. To determine the underlying molecular basis for the enhanced fibrillation of the mutants, the structural properties, responses to changes in the environment, and propensity to aggregate of wild-type, A30P, and A53T α-synucleins were systematically investigated. A variety of biophysical methods, including far-UV circular dichroism, FTIR, small-angle X-ray scattering, and light scattering, were employed. Neither the natively unfolded nor the partially folded intermediate conformations are affected by the familial Parkinson's disease point mutations. However, both mutants underwent self-association more readily than the wild type (i.e., at much lower protein concentration and more rapidly). We attribute this effect to the increased propensity of their partially folded intermediates to aggregate, rather than to any changes in the monomeric natively unfolded species. This increased propensity of these mutants to aggregate, relative to wild-type α-synuclein, would account for the correlation of these mutations with Parkinson's disease.