Functional Consequences of α-Synuclein Tyrosine Nitration

Abstract

Previous studies have shown the presence of nitrated α-synuclein (α-syn) in human Lewy bodies and other α-syn inclusions. Herein, the effects of tyrosine nitration on α-syn fibril formation, lipid binding, chaperone-like function, and proteolytic degradation were systematically examined by employing chromatographically isolated nitrated monomeric, dimeric, and oligomeric α-syn. Nitrated α-syn monomers and dimers but not oligomers accelerated the rate of fibril formation of unmodified α-syn when present at low concentrations. Immunoelectron microscopy revealed that nitrated monomers and dimers are incorporated into the fibrils. However, the purified nitrated α-syn monomer by itself was unable to form fibrils. Nitration of the tyrosine residue at position 39 was largely responsible for decreased binding of nitrated monomeric α-syn to synthetic vesicles, which correlated with an impairment of the nitrated protein to adopt α-helical conformation in the presence of liposomes. The chaperone-like activity of α-syn was not inhibited by nitration or oxidation. Furthermore, the 20 S proteasome and calpain I degraded nitrated monomeric α-syn, although at a slower rate compared with control α-syn. Collectively, these data suggest that post-translational modification of α-syn by nitration can promote the formation of intracytoplasmic inclusions that constitute the hallmark of Parkinson disease and other synucleinopathies.