Characterization of the ZnII Binding to the Peptide Amyloid-β¹⁻¹⁶ linked to Alzheimer's Disease

Aggregation of the human peptide amyloid-β (Aβ) is a key event in Alzheimer's disease (AD). Zinc ions play an important role in AD and in Aβ aggregation. In vitro, ZnII binds to Aβ and accelerates its aggregation. In this work we have investigated ZnII binding to the synthetic peptide Aβ¹⁻¹⁶, which contains the metal-binding domain of Aβ. CdII was used to probe the ZnII site. Aβ¹⁻¹⁶ bound one equivalent of ZnII with an apparent dissociation constant (Kd) of 10⁻⁴ M. This Kd value is in the same range as the Zn concentration needed to precipitate Aβ. Circular dichroism and NMR indicated predominantly random-coil secondary structures of apo-Aβ¹⁻¹⁶, ZnII-Aβ¹⁻¹⁶ and CdII-Aβ¹⁻¹⁶, which were all highly dynamic and flexible. The three histidines at positions 6, 13 and 14 were suggested to be ligands to ZnII and CdII. Evidence that the aspartate at position 1 served as a fourth ligand to ZnII and CdII was found at pH 8.7. ¹¹¹CdII NMR showed a resonance at 84 ppm, in line with a mixed oxygen-/nitrogen-ligand environment. The tyrosine at position 10 could be excluded as a ligand.