Abstract
Amyloid‐β peptide (Aβ) is the principal constituent of plaques associated with Alzheimer's disease (AD) and is thought to be responsible for the neurotoxicity associated with the disease. Copper binding to Aβ has been hypothesized to play an important role in the neruotoxicity of Aβ and free radical damage, and Cu^2+^ chelators represent a possible therapy for AD. However, many properties of copper binding to Aβ have not been elucidated clearly, and the location of copper binding sites on Aβ is also in controversy. Here we have used a range of spectroscopic techniques to characterize the coordination of Cu^2+^ to Aβ(1–16) in solution. Electrospray ionization mass spectrometry shows that copper binds to Aβ(1–16) at pH 6.0 and 7.0. The mode of copper binding is highly pH dependent. Circular dichroism results indicate that copper chelation causes a structural transition of Aβ(1–16). UV‐visible absorption spectra suggest that three nitrogen donor ligands and one oxygen donor ligand (3N1O) in Aβ(1–16) may form a type II square‐planar coordination geometry with Cu^2+^. By means of fluorescence spectroscopy, competition studies with glycine and L‐histidine show that copper binds to Aβ(1–16) with an affinity of K~a~ ∼ 10^7^M^–1^ at pH 7.8. Besides His6, His13, and His14, Tyr10 is also involved in the coordination of Aβ(1–16) with Cu^2+^, which is supported by ^1^H NMR and UV‐visible absorption spectra. Evidence for the link between Cu^2+^ and AD is growing, and this work has made a significant contribution to understanding the mode of copper binding to Aβ(1–16) in solution. © 2006 Wiley Periodicals, Inc. Biopolymers 83: 20–31, 2006
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