Amyloid-beta binds Cu2+ in a mononuclear metal ion binding site

Abstract

Amyloid-beta (Abeta) peptide is the principal constituent of plaques associated with Alzheimer's disease and is thought to be responsible for the neurotoxicity associated with the disease. Metal ions have been hypothesized to play a role in the formation and neurotoxicity of aggregates associated with Alzheimer's disease (Bush, A. I.; et al. Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 11934). Elucidation of the chemistry through which transition-metal ions participate in the assembly and toxicity of Abeta oligomers is important to drug design efforts if inhibition of Abeta containing bound metal ions becomes a treatment for Alzheimer's disease. In this paper, we report electron paramagnetic resonance (EPR) spectroscopic characterization of Cu(2+) bound to soluble and fibrillar Abeta. Addition of stoichiometric amounts of Cu(2+) to soluble Abeta produces an EPR signal at 10 K with observable Cu(2+) hyperfine lines. A nearly identical spectrum is observed for Abetafibrils assembled in the presence of Cu(2+). The EPR parameters are consistent with a Type 2 Cu(2+) center with three nitrogen donor atoms and one oxygen donor atom in the coordination sphere of Cu(2+): g( parallel) = 2.26 and A( parallel) = 174 +/- 4 G for soluble Abeta with Cu(2+), and g( parallel) = 2.26 and A( parallel) = 175 +/- 1 G for Abeta fibrils assembled with Cu(2+). Investigation of the temperature dependence of the EPR signal for Cu(2+) bound to soluble Abetaor Cu(2+) in fibrillar Abeta shows that the Cu(2+) center displays normal Curie behavior, indicating that the site is a mononuclear Cu(2+) site. Fibrils assembled in the presence of Cu(2+) contain one Cu(2+) ion per peptide. These results show that the ligand donor atom set to Cu(2+) does not change during organization of Abetamonomers into fibrils and that neither soluble nor fibrillar forms of Abeta(1-40) with Cu(2+) contain antiferromagnetically exchange-coupled binuclear Cu(2+) sites in which two Cu(2+) ions are bridged by an intervening ligand.