Local Structure and Global Patterning of Cu2+ Binding in Fibrillar Amyloid-β [Aβ(1-40)] Protein

The amyloid-beta (A beta) protein forms fibrils and higher-order plaque aggegrates in Alzheimer's disease (AD) brain. The copper ion, Cu2+, is found at high concentrations in plaques, but its role in AD etiology is unclear. We use high-resolution pulsed electron paramagnetic resonance spectroscopy to characterize the coordination structure of Cu2+ in the fibrillar form of full-length A beta(1-40). The results reveal a bis-cis-histidine (His) equatorial Cu2+ coordination geometry and participation of all three N-terminal His residues in Cu2+ binding. A model is proposed in which Cu2+-His6/His13 and Cu2+-His6/His14 sites alternate along the fibril axis on opposite sides of the beta-sheet fibril structure. The local intra-beta-strand coordination structure is not conducive to Cu2+/Cu+ redox-linked coordination changes, and the global arrangement of Cu sites precludes facile multielectron and bridged-metal site reactivity. This indicates that the fibrillar form of A beta suppresses Cu redox cycling and reactive oxygen species production. The configuration suggests application of Cu2+-A beta fibrils as an amyloid architecture for switchable electron charge/spin coupling and redox reactivity.