Copper-Dependent Inhibition of Human CytochromecOxidase by a Dimeric Conformer of Amyloid-β1-42

Abstract

In studies of Alzheimer's disease pathogenesis there is an increasing focus on mechanisms of intracellular amyloid-β (Aβ) generation and toxicity. Here we investigated the inhibitory potential of the 42 amino acid Aβ peptide (Aβ_1-42) on activity of electron transport chain enzyme complexes in human mitochondria. We found that synthetic Aβ_1-42specifically inhibited the terminal complex cytochromecoxidase (COX) in a dose-dependent manner that was dependent on the presence of Cu²⁺and specific “aging” of the Aβ_1-42solution. Maximal COX inhibition occurred when using Aβ_1-42solutions aged for 3-6 h at 30°C. The level of Aβ_1-42-mediated COX inhibition increased with aging time up to ∼6 h and then declined progressively with continued aging to 48 h. Photo-induced cross-linking of unmodified proteins followed by SDS-PAGE analysis revealed dimeric Aβ as the only Aβ species to provide significant temporal correlation with the observed COX inhibition. Analysis of brain and liver from an Alzheimer's model mouse (Tg2576) revealed abundant Aβ immunoreactivity within the brain mitochondria fraction. Our data indicate that endogenous Aβ is associated with brain mitochondria and that Aβ_1-42, possibly in its dimeric conformation, is a potent inhibitor of COX, but only when in the presence of Cu²⁺. We conclude that Cu²⁺-dependent Aβ-mediated inhibition of COX may be an important contributor to the neurodegeneration process in Alzheimer's disease.