Stable Complexes Involving Acetylcholinesterase and Amyloid-β Peptide Change the Biochemical Properties of the Enzyme and Increase the Neurotoxicity of Alzheimer’s Fibrils

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Abstract
Brain acetylcholinesterase (AChE) forms stable complexes with amyloid-β peptide (Aβ) during its assembly into filaments, in agreement with its colocalization with the Aβ deposits of Alzheimer’s brain. The association of the enzyme with nascent Aβ aggregates occurs as early as after 30 min of incubation. Analysis of the catalytic activity of the AChE incorporated into these complexes shows an anomalous behavior reminiscent of the AChE associated with senile plaques, which includes a resistance to low pH, high substrate concentrations, and lower sensitivity to AChE inhibitors. Furthermore, the toxicity of the AChE–amyloid complexes is higher than that of the Aβ aggregates alone. Thus, in addition to its possible role as a heterogeneous nucleator during amyloid formation, AChE, by forming such stable complexes, may increase the neurotoxicity of Aβ fibrils and thus may determine the selective neuronal loss observed in Alzheimer’s brain.