Affinity of Cu⁺ for the Copper-Binding Domain of the Amyloid-β Peptide of Alzheimer’s Disease

Abstract

The role of metal ions in Alzheimer's disease etiology is unresolved. For the redox-active metal ions iron and copper, the formation of reactive oxygen species by metal amyloid complexes has been proposed to contribute to Alzheimer's disease neurodegeneration. For copper, reactive oxygen species are generated by copper redox cycling between its 1+ and 2+ oxidation states. Thus, the AβCu(I) complex is potentially a critical reactant associated with Alzheimer's disease etiology. Through competitive chelation, we have measured the affinity of the soluble copper-binding domain of the amyloid-β peptide for Cu(I). The dissociation constants are in the femtomolar range for both wild-type and histidine-to-alanine mutants. These results indicate that Cu(I) binds more tightly to monomeric amyloid-β than Cu(II) does, which leads us to propose that Cu(I) is a relevant in vivo oxidation state.

Capturing a Reactive State of Amyloid Aggregates

“…-specific indicator that forms a Cu ϩ -BCS complex, which shows a new absorption at 483 nm. The assay was performed as described previously (67). For analysis of the supernatant, the A␤ aggregate was pelleted by centrifugation at 16,000 ϫ g for 10 min, and the resulting supernatant was analyzed for A␤ aggregates by ThT fluorescence measurements (55).…”

Copper in Alzheimer’s disease: Implications in amyloid aggregation and neurotoxicity

“…70 The concentration of ascorbate present in extracellular fluid is sufficient to generate Cu(I); thus, competition between Human Serum Albumin (HSA) and Aβ for copper is expected not to be important because the strong square-planar geometry of the ATCUN motif in HSA does not support the (lower coordination number) tetrahedral coordination geometry typical for Cu(I). 70 Alies et al proposed that the three-fold stronger affinity of Aβ 42 for Cu(I) compared with Aβ 16 may originate from contributions of oligomeric species in the Aβ 42 -peptide sample, in contrast to the monomeric form present in the Aβ 16 -peptide sample. XAS-based observations support this idea and a possible involvement of the methionine residue Met35 is discarded.…”

“…72 Using Aβ 16 , the corresponding Cu(I)-Aβ complex dissociates less readily than the Cu(II)-Aβ one. 70 Based on these results, Nakamura et al have proposed that the His6, His13, and His14 residues of Aβ 42 control the redox activity of transition metals present in senile plaques. 73 Other recent studies suggest that apart from His13 and His14, Asp1 is the other main ligand in the most redox-active site that efficiently allow the oxidation of copper by H 2 O 2 and its reduction by ascorbate.…”

“…Cu(I) is the thermodynamically preferred oxidation state of copper within Aβ monomers. 70 Galeazzi et al have established the susceptibility of Aβ 42 to undergo dityrosine formation via peroxidase-catalyzed tyrosine cross-linking. This reaction generates stable dimers, 77 the formation of cross-links being favoured for the fibrillar form of the protein (in contrast to the soluble form); fibrils are also more resistant to destructive overoxidation than soluble Aβ.…”

Chelation therapy for the management of diabetic complications: a hypothesis and a proposal for clinical laboratory assessment of metal ion homeostasis in plasma

“…Eaton, Monnier, and colleagues [52,53] as outlined in Figure 1. Analogous to the binding of copper to AGEs in the vascular wall and extracellular matrix in diabetes and atherosclerosis, copper also binds strongly to β-amyloid proteins in neuronal plaques and in a redoxactive, catalytically active, ROS-generating form [51,54]. The catalytic role of copper explains the effect of copper chelators alone in treatment of diabetes, atherosclerosis, and neurodegenerative disease and also the enrichment of iron in atherosclerotic and neurodegenerative plaque.…”