Site-Specific Copper-Catalyzed Oxidation of α-Synuclein: Tightening the Link between Metal Binding and Protein Oxidative Damage in Parkinson’s Disease

Abstract

The amyloid aggregation of alpha-synuclein (AS) has been linked to the pathological effects associated to Parkinson´s disease (PD). Cu(II) binds specifically at the N-terminus of AS and triggers its aggregation. Site-specific Cu(I)-catalyzed oxidation of AS has been proposed as a plausible mechanism for metal-enhanced AS amyloid formation. In this study, Cu(I) binding to AS was probed by NMR spectroscopy, in combination with synthetic peptide models, site- directed and C-terminal truncated protein variants. Our results demonstrate that both Met residues in the motif 1MDVFM5 constitute key structural determinants for the high-affinity binding of Cu(I) to the N-terminal region of AS. Replacement of one Met residue by Ile causes a dramatic decrease in binding affinity for Cu(I), whereas removal of both Met residues results in complete lack of binding. Moreover, these Met residues can be oxidized rapidly after air exposure of the AS-Cu(I) complex, whereas Met-116 and Met-127 in the C-terminal region remain unaffected. Met-1 displays higher susceptibility to oxidative damage compared to Met-5, as it is directly involved in both Cu(II) and Cu(I) coordination, resulting in a closer exposure to the reactive oxygen species that may be generated by the redox cycling of copper. Our findings support a mechanism where the interaction of AS with copper ions leads to site-specific metal catalyzed oxidation in the protein under physiologically relevant conditions. In light of recent biological findings, these results support a role for AS-copper interactions in neurodegeneration in PD.