Tyrosine 125 of alpha-synuclein plays a critical role for dimerization following nitrative stress.

alpha-Synuclein is a major component of Lewy bodies in Parkinson's disease, dementia with Lewy bodies, and glial cytoplasmic inclusions in multiple system atrophy. Increasing evidence suggests that the nitration of tyrosine residues in alpha-synuclein induced by oxidative injury is involved in the formation of inclusions characteristic to these synucleinopathies. Exposure of alpha-synuclein to peroxynitrite induces nitration of tyrosine residues, thereby forming alpha-synuclein oligomers. However, the contribution of tyrosine residues to either the nitration or the oligomerization is currently unknown. The present study used recombinant wild-type and mutant alpha-synuclein proteins to investigate the role of each alpha-synuclein tyrosine residue in the in vitro formation of alpha-synuclein oligomers under nitrative stress. Confocal microscopic analysis revealed that wild-type alpha-synuclein protein was able to accumulate and form an inclusion-like structure in the cytoplasm of living cells upon introduction by streptolysin O. Authentic peroxynitrite induced nitration of tyrosine residues in alpha-synuclein protein, as well as dimerization of alpha-synuclein. The formation of both SDS- and heat-stable dimers suggests cross-linking between nitrated tyrosine residues. Nonetheless, dimerization of alpha-synuclein proteins lacking tyrosine 125 was significantly decreased compared with alpha-synuclein proteins lacking tyrosine residues at positions 39, 133, or 136. Presumably, tyrosine 125 plays a critical role for alpha-synuclein dimerization under nitrative stress.