Differential copper binding to alpha-synuclein and its disease-associated mutants affect the aggregation and amyloid formation

Background: Copper is an essential trace element required for the proper functioning of various enzymes present in the central nervous system. An imbalance in the copper homeostasis results in the pathology of various neurodegenerative disorders including Parkinson's Disease. Hence, residue specific interaction of Cu2+ to alpha-Syn along with the familial mutants H50Q and G51D needs to be studied in detail. Methods: We investigated the residue specific mapping of Cu2+ binding sites and binding strength using solution-state NMR and ITC respectively. The aggregation kinetics, secondary structural changes, and morphology of the formed fibrils in the presence and absence of Cu2+ were studied using fluorescence, CD, and AFM respectively. Results: Copper binding to alpha-Syn takes place at three different sites with a higher affinity for the region 48-53. While one of the sites got abolished in the case of H50Q the mutant G51D showed a binding pattern similar to WT. The aggregation kinetics of these proteins in the presence of Cu2+ showed an enhanced rate of fibril formation with a pronounced effect for G51D. Conclusion: Cu2+ binding results in the destabilization of long-range tertiary interactions in alpha-Syn leading to the exposure of highly amyloidogenic NAC region which results in the increased rate of fibril formation. Although the residues 48-53 have a stronger affinity for Cu2+ in case of WT and G51D, the binding is not responsible for enhancing the rate of fibril formation in case of H50Q. General Significance: These findings will help in the better understanding of Cu2+ catalyzed aggregation of synucleins. (C) 2016 Elsevier B.V. All rights reserved