Characterization of copper binding to the peptide amyloid-β(1-16) associated with Alzheimer's disease

Amyloid-beta peptide (A beta) 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 A beta has been hypothesized to play an important role in the neruotoxicity of A P and free radical damage, and Cu2+ chelators represent a possible therapy for AD. However, many properties of copper binding to A beta have not been elucidated clearly, and the location of copper binding sites on A beta is also in controversy. Here we have used a range of spectroscopic techniques to characterize the coordination of Cu2+ to A beta(1-16) in solution. Electrospray ionization mass spectrometry shows that copper binds to A beta(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 A beta(1-16). UV-visible absorption spectra suggest that three nitrogen donor ligands and one oxygen donor ligand (3N10) in A beta(1-16) may form a type II square-planar coordination geometry with Cu2+. By means of fluorescence spectroscopy, competition studies with glycine and L-histidine show that copper binds to A beta(1-16) with an affinity of K-a similar to 10(7) M-1 at pH 7.8. Besides His6, His13, and His14, Tyr10 is also involved in the coordination of A beta(1-16) with Cu2+ which is supported by H-1 NMR and UV-visible absorption spectra. Evidence for the link between Cu2+ and AD is growing, and this work has made a significant contribution to understanding the mode of copper binding to A beta(1-16) in solution. (c) 2006 Wiley Periodicals, Inc.