Characterization of Copper Interactions with Alzheimer Amyloid β Peptides

Abstract: Cu and Zn have been shown to accumulate in the brains of Alzheimer's disease patients. We have previously reported that Cu 2+ and Zn 2+ bind amyloid β (Aβ), explaining their enrichment in plaque pathology. Here we detail the stoichiometries and binding affinities of multiple cooperative Cu 2+ ‐binding sites on synthetic Aβ1‐40 and Aβ1‐42. We have developed a ligand displacement technique (competitive metal capture analysis) that uses metal‐chelator complexes to evaluate metal ion binding to Aβ, a notoriously self‐aggregating peptide. This analysis indicated that there is a very‐high‐affinity Cu 2+ ‐binding site on Aβ1‐42 (log K app = 17.2) that mediates peptide precipitation and that the tendency of this peptide to self‐aggregate in aqueous solutions is due to the presence of trace Cu 2+ contamination (customarily ∼0.1 μ M ). In contrast, Aβ1‐40 has much lower affinity for Cu 2+ at this site (estimated log K app = 10.3), explaining why this peptide is less self‐aggregating. The greater Cu 2+ ‐binding affinity of Aβ1‐42 compared with Aβ1‐40 is associated with significantly diminished negative cooperativity. The role of trace metal contamination in inducing Aβ precipitation was confirmed by the demonstration that Aβ peptide (10 μ M ) remained soluble for 5 days only in the presence of high‐affinity Cu 2+ ‐selective chelators.