Identification of rotenone-induced modifications in α-synuclein using affinity pull-down and tandem mass spectrometry

Parkinson's disease is a movement disorder that results from a loss of dopaminergic neurons in the substantia nigra. The disease is characterized by mitochondrial dysfunction, oxidative stress, and the presence of Lewy body inclusions enriched with aggregated forms of alpha-synuclein, a presynaptic protein. Although alpha-synuclein is modified at various sites in Lewy bodies, it is unclear how sequence-specific posttranslational modifications modulate the aggregation of the protein in oxidatively stressed neurons. To begin to address this problem, we developed an affinity pull-down/mass spectrometry method to characterize the primary structure of histidine-tagged alpha-synuclein isolated from catecholaminergic neurons. Using this method, we mapped postitranslational modifications of alpha-synuclein from untreated neurons and neurons exposed to rotenone, an inhibitor of mitochondrial complex I. Various posttranslational modifications suggestive of oxidative damage or repair were identified in a region comprising a 20-residue stretch in the C-terminal part of the protein. The results indicate that a-synuclein is subject to discrete posttranslational modifications in neurons with impaired mitochondrial function. Our affinity pull-down/ mass spectrometry method is a useful tool to examine how specific modifications of alpha-synuclein contribute to neurologic disorders such as Parkinson's disease.