Abstract

Abstract

Abstract

Abstract

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 Cu²⁺ 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 Cu²⁺ 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 Cu²⁺. 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 ∼ 10⁷M^–1 at pH 7.8. Besides His6, His13, and His14, Tyr10 is also involved in the coordination of Aβ(1–16) with Cu²⁺, which is supported by ¹H 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 Aβ(1–16) in solution. © 2006 Wiley Periodicals, Inc. Biopolymers 83: 20–31, 2006

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com

The tau protein plays an important role in some neurodegenerative diseases including Alzheimer's disease (AD). Neurofibrillary tangles (NFTs), a biological marker for AD, are aggregates of bundles of paired helical filaments (PHFs). In general, the α-sheet structure favors aberrant protein aggregates. However, some reports have shown that the α-helix structure is capable of triggering the formation of aberrant tau protein aggregates and PHFs have a high α-helix content. In addition, the third repeat fragment in the four-repeat microtubule-binding domain of the tau protein (residues 306–336: VQIVYKPVDLSKVTSKCGSLGNIHHKPGGGQ, according to the longest tau protein) adopts a helical structure in trifluoroethanol (TFE) and may be a self-assembly model in the tau protein. In the human brain, there is a very small quantity of copper, which performs an important function. In our study, by means of matrix assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS), circular dichroism (CD), and nuclear magnetic resonance (NMR) spectroscopy, the binding properties of copper (II) ion to the R3 peptide derived from the third repeat fragment (residues 318–335: VTSKCGSLGNIHHKPGGG) have been investigated. The results show that copper ions bind to the R3 peptide. CD spectra, ultraviolet (UV)-visible absorption spectra, and MALDI-TOF MS show pH dependence and stoichiometry of Cu²⁺ binding. Furthermore, CD spectra and NMR spectroscopy elucidate the copper binding sites located in the R3 peptide. Finally, CD spectra reveal that the R3 peptide adopts a mixture structure of random structures, α-helices, and β-turns in aqueous solutions at physiological pH. At pH 7.5, the addition of 0.25 mol eq of Cu²⁺ induces the conformational change from the mixture mentioned above to a monomeric helical structure, and a β-sheet structure forms in the presence of 1 mol eq of Cu²⁺. As α-helix and β-sheet structures are responsible for the formation of PHFs, it is hypothesized that Cu²⁺ is an inducer of self-assembly of the R3 peptide and makes the R3 peptide form a structure like PHF. Hence, it is postulated that Cu²⁺ plays an important role in the aggregation of the R3 peptide and tau protein and that copper (II) binding may be another possible involvement in AD. © 2005 Wiley Periodicals, Inc. Biopolymers 79: 74–85, 2005

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com