Dopamine‐Induced Post‐Translational Modifications of a ‐Synuclein

Abstract

a-Synuclein (SYN) comprises the major component of aggregates present in Parkinson's disease (PD). Moreover, dopamine (DA) mediated SYN post-translational modifications (PTM) play an important role in the etiology of the disease. There is a paucity of information on DA-induced SYN PTMs, and of the consequences of such modifications, we examined the effects of DA and of some of its thioether metabolites on SYN aggregation. MALDI-TOF and Western blot analysis of DA-modified SYN revealed an addition of 4.5 kDa to the SYN monomer, and up to 9 kDa to the SYN dimer, suggesting poly-DA interactions with SYN, crosslinking of protein, and aggregation of SYN. Acetylation of SYN at lysine (K) residues by acetylsalicylic acid or acetic anhydride prevented DA-induced SYN aggregation, indicating an interaction between K and DA. Free K failed to inhibit SYN aggregation. However peptides containing K with lower pKa, inhibited DA-induced SYN aggregation. To overcome the complexity of protein crosslinking, N-acetylcysteine (NAC) and glutathione (GSH) were utilized for synthesis of DA conjugates. Mono-DA conjugates oxidize and generate SYN adducts in a pH-dependent manner similar to DA, but fail to crosslink and/or cause SYN aggregation. MALDI-TOF and Western blot analysis of DA conjugates with SYN reveal addition of up to 5 kDa to SYN monomer, with very low levels of SYN dimer formation. The findings reveal that scavenging of DA quinone by cysteine and/or GSH has profound effects on the interaction of DA with SYN, and on subsequent aggregation reactions. Redox modulation of SYN PTMs and of SYN aggregation suggests potential interventions to alleviate SYN-dependent cytotoxicity. (P30ES006694 & T32-ES006694)