Photochemical Identification of Molecular Binding Sites on the Surface of Amyloid-β Fibrillar Aggregates

Abstract

Summary The aggregation of amyloid-β (Aβ) into insoluble fibrils has been associated with the development of Alzheimer's disease. The study of Aβ aggregation with [Re(CO) 3 (dppz)(Py)] + (dppz = dipyrido[3,2-a:2′,3′-c]phenazine; Py = pyridine) has led to the observation of an irradiation-induced light-switching response accompanied by the oxidation of the Aβ fibril. Here, we used the photophysical and photochemical properties of this complex, as well as spectroscopic and computational methods, to elucidate molecular binding sites on Aβ fibrils. [Re(CO) 3 (dppz)(Py)] + binds to Aβ fibrils with a dissociation constant of 4.2 μM and a binding stoichiometry 2.8:1 (Aβ/complex). Molecular dynamics (MD) simulations predicted binding of [Re(CO) 3 (dppz)(Py)] + through a hydrophobic cleft on the fibril axis between Val18 and Phe20. Tandem mass spectrometry analysis indicated that oxidation occurred at Met35, footprinting the place of binding, which is close to the site predicted by the MD simulations. Finding binding sites in Aβ is of great importance for the design of Aβ-binding drugs.