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

Abstract

α-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 α-synuclein induced by oxidative injury is involved in the formation of inclusions characteristic to these synucleinopathies. Exposure of α-synuclein to peroxynitrite induces nitration of tyrosine residues, thereby forming α-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 α-synuclein proteins to investigate the role of each α-synuclein tyrosine residue in the in vitro formation of α-synuclein oligomers under nitrative stress. Confocal microscopic analysis revealed that wild-type α-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 α-synuclein protein, as well as dimerization of α-synuclein. The formation of both SDS- and heat-stable dimers suggests cross-linking between nitrated tyrosine residues. Nonetheless, dimerization of α-synuclein proteins lacking tyrosine 125 was significantly decreased compared with α-synuclein proteins lacking tyrosine residues at positions 39, 133, or 136. Presumably, tyrosine 125 plays a critical role for α-synuclein dimerization under nitrative stress.