Characterization of copper interactions with alzheimer amyloid beta peptides: identification of an attomolar-affinity copper binding site on amyloid beta1-42.
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 beta (Abeta), explaining their enrichment in plaque pathology. Here we detail the stoichiometries and binding affinities of multiple cooperative Cu(2+)-binding sites on synthetic Abeta1-40 and Abeta1-42. We have developed a ligand displacement technique (competitive metal capture analysis) that uses metal-chelator complexes to evaluate metal ion binding to Abeta, a notoriously self-aggregating peptide. This analysis indicated that there is a very-high-affinity Cu(2+)-binding site on Abeta1-42 (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 approximately 0.1 microM). In contrast, Abeta1-40 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 Abeta1-42 compared with Abeta1-40 is associated with significantly diminished negative cooperativity. The role of trace metal contamination in inducing Abeta precipitation was confirmed by the demonstration that Abeta peptide (10 microM) remained soluble for 5 days only in the presence of high-affinity Cu(2+)-selective chelators.
Laboratory for Oxidation Biology, Massachusetts General Hospital and Harvard Medical School, Boston 02129-9142, USA.
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CS
Atwood
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Scarpa
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Huang
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Moir
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Jones
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Fairlie
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Tanzi
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Bush
D016229:Amyloid beta-Peptides / Q000737:chemistry* / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002614:Chelating Agents / Q000494:pharmacology; D003300:Copper / Q000737:chemistry / Q000378:metabolism*; D004285:Dogs; D006801:Humans; D007700:Kinetics; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism*; D012044:Regression Analysis; D012709:Serum Albumin / Q000737:chemistry / Q000378:metabolism; D015032:Zinc / Q000378:metabolism
D016229:Amyloid beta-Peptides; D002614:Chelating Agents; D010446:Peptide Fragments; D012709:Serum Albumin; C078592:amyloid beta-protein (1-40); C075222:amyloid beta-protein (1-42); D003300:Copper; D015032:Zinc