Bioinorganic Chemistry of Parkinson's Disease: Affinity and Structural Features of Cu(I) Binding to the Full-Length beta-Synuclein Protein

摘要

Alterations in the levels of copper in brain tissue and formation of alpha-synuclein (alpha S)-copper complexes might play a key role in the amyloid aggregation of alpha S and the onset of Parkinson's disease (PD). Recently, we demonstrated that formation of the high-affinity Cu(I) complex with the N-terminally acetylated form of the protein alpha S substantially increases and stabilizes local conformations with alpha-helical secondary structure and restricted motility. In this work, we performed a detailed NMR-based structural characterization of the Cu(I) complexes with the full-length acetylated form of its homologue beta-synuclein (beta S), which is colocalized with alpha S in vivo and can bind copper ions. Our results show that, similarly to alpha S, the N-terminal region of beta S constitutes the preferential binding interface for Cu(I) ions, encompassing two independent and noninteractive Cu(I) binding sites. According to these results, beta S binds the metal ion with higher affinity than alpha S, in a coordination environment that involves the participation of Met-1, Met-5, and Met-10 residues (site 1). Compared to alpha S, the shift of His from position 50 to 65 in the N-terminal region of beta S does not change the Cu(I) affinity features at that site (site 2). Interestingly, the formation of the high-affinity beta S-Cu(I) complex at site 1 in the N-terminus promotes a short alpha-helix conformation that is restricted to the 1-5 segment of the Ac beta S sequence, which differs with the substantial increase in alpha-helix conformations seen for N-terminally acetylated alpha S upon Cu(I) complexation. Our NMR data demonstrate conclusively that the differences observed in the conformational transitions triggered by Cu(I) binding to Ac alpha S and Ac beta S find a correlation at the level of their backbone dynamic properties; added to the potential biological implications of these findings, this fact opens new avenues of investigations into the bioinorganic chemistry of PD.