Copper(I)-α-Synuclein Interaction: Structural Description of Two Independent and Competing Metal Binding Sites.

The aggregation of α-synuclein (αS) is a critical step in the etiology of Parkinson's disease. Metal ions such as copper and iron have been shown to bind αS, enhancing its fibrillation rate in vitro. αS is also susceptible to copper-catalyzed oxidation that involves the reduction of CuII to CuI and the conversion of O2 into reactive oxygen species. The mechanism of the reaction is highly selective and site-specific and involves interactions of the protein with both oxidation states of the copper ion. The reaction can induce oxidative modification of the protein, which generally leads to extensive protein oligomerization and precipitation. CuII binding to αS has been extensively characterized, indicating the N terminus and His-50 as binding donor residues. In this study, we have investigated αS–CuI interaction by means of NMR and circular dichroism analysis on the full-length protein (αS1-140) and on two, designed ad hoc, model peptides: αS1-15 and αS113-130. In order to identify and characterize the metal binding environment in full-length αS, in addition to CuI, we have also used AgI as a probe for CuI binding. Two distinct CuI/AgI binding domains with comparable affinities have been identified. The structural rearrangements induced by the metal ions and the metal coordination spheres of both sites have been extensively characterized. [ABSTRACT FROM AUTHOR]