Copper and zinc binding modulates the aggregation and neurotoxic properties of the prion peptide PrP106-126

The abnormal form of the prion protein (PrP) is believed to be responsible for the transmissible spongiform encephalopathies, A peptide encompassing residues 106-126 of human PrP (PrP106-126) is neurotoxic in vitro due its adoption of an amyloidogenic fibril structure. The Alzheimer's disease amyloid beta peptide (A beta) also undergoes fibrillogenesis to become neurotoxic. A beta aggregation and toxicity is highly sensitive to copper, zinc, or iron ions. We show that PrP106-126 aggregation, as assessed by turbidometry, is abolished in Chelex-100-treated buffer, ICP-MS analysis showed that the Chelex-100 treatment had reduced Cu2+ and Zn2+ levels approximately 3-fold. Restoring Cu2+ and Zn2+ to their original levels restored aggregation. Circular dichroism showed that the Chelex-100 treatment reduced the aggregated beta -sheet content of the peptide. Electron paramagnetic resonance spectroscopy identified a 2N1S1O coordination to the Cu2+ atom, suggesting histidine 111 and methionine 109 or 112 are involved. Nuclear magnetic resonance confirmed Cu2+ and Zn2+ binding to His-111 and weaker binding to Met-112, An N-terminally acetylated PrP106-126 peptide did not bind Cu2+ implicating the free amino group in metal binding. Mutagenesis of either His-111, Met-109, or Met-111 abolished PrP106-126 neurotoxicity and its ability to form fibrils. Therefore, Cu2+ and/or Zn2+ binding is critical for PrP106-126 aggregation and neurotoxicity.