Post-translational modifications of alpha-synuclein protein by oxidative and nitrative stress mechanisms and their effects on the pathogenesis of synucleinopathies

α-Synuclein (α-syn) is a small, soluble protein found primarily in neurons and is the major component of proteinaceous inclusions that characterize many neurodegenerative disorders, collectively termed synucleinopathies. Since these pathological lesions contain aggregated α-syn that is nitrated and oxidized, it is important to understand how oxidative and nitrative stress modifies α-syn in vitro and in vivo. To better define the consequences of α-syn oxidation and nitration, the roles of specific amino acid residues within α-syn were examined. Results showed that nitrating and oxidizing agents induce the formation of stable o,o′-dityrosine oligomers through distinct mechanisms. Tyrosine residues were not required for protein cross-linking or filament stabilization resulting from transition metal-mediated oxidation, but they were necessary for cross-linking and stabilization resulting from exposure to nitrating agents. We next examined the role of dopamine, another cellular oxidant, in modulating α-syn fibril formation since a recent report suggests that dopamine inhibits the conversion of α-syn oligomers into mature fibrils. Biochemical, molecular biological, and analytical techniques were conducted to define the structure and conformation of α-syn after its modification by dopamine and also to identify the specific dopamine-syn interaction site. Our results suggest that the inhibitory effect of dopamine is not mediated through the oxidation of Tyr, Met, or His residues. Instead, it appears that the interaction requires residues 125–127 of α-syn for this inhibition to occur. Our data suggest a novel mechanism of dopamine inhibition of α-syn fibrillization, and this may have implications on our understanding of the pathogenesis of Parkinson\u27s disease. Additionally, oxidative and nitrative challenges may arise from exposure to environmental and industrial chemicals, which have been implicated in the pathogenesis of synucleinopathies. A mouse model of synucleinopathy that overexpresses human A53T α-syn was exposed to chronic levels of pesticides. Significantly, these environmental oxidants disrupted the normal distribution of α-syn in mice and exacerbated their pathology and phenotype, thereby confirming a role for oxidative and nitrative stress in the pathogenesis of synucleinopathies in an in vivo model. Collectively, these results suggest that nitrative and oxidative challenges produce distinct mechanisms of α-syn protein modifications that influence the formation of different species of α-syn protein, the degree of α-syn filament formation, and the stability of α-syn fibrils, which provides extensive evidence for the implication of oxidative and nitrative modifications of α-syn in the pathogenesis of human disease