Gielnik, M. | bioRxiv Science

bioRxiv2021

The Prion Protein Octarepeat Domain Forms Transient β-sheet Structures Upon Residue-Specific Cu(II) and Zn(II) Binding

Misfolding of the cellular prion protein (PrPC) is associated with the development of fatal neurodegenerative diseases called transmissible spongiform encephalopathies (TSEs). Metal ions appear to play a crucial role in the protein misfolding, and metal imbalance may be part of TSE pathologies. PrPC is a combined Cu(II) and Zn(II) metal binding protein, where the main metal binding site is located in the octarepeat (OR) region. Here, we used biophysical methods to characterize Cu(II) and Zn(II) binding to the isolated OR region. Circular dichroism (CD) spectroscopy data suggest that the OR domain binds up to four Cu(II) ions or two Zn(II) ions. Upon metal binding, the OR region seems to adopt a transient antiparallel {beta}-sheet hairpin structure. Fluorescence spectroscopy data indicates that under neutral conditions, the OR region can bind both Cu(II) and Zn(II) ions, whereas under acidic conditions it binds only Cu(II) ions. Molecular dynamics simulations suggest that binding of both metal ions to the OR region results in formation of {beta}-hairpin structures. As formation of {beta}-sheet structures is a first step towards amyloid formation, we propose that high concentrations of either Cu(II) or Zn(II) ions may have a pro-amyloid effect in TSEs.

biophysics↗

bioRxiv2021

The engineered peptide construct NCAM1-Aβ inhibits aggregation of the human prion protein (PrP)

In prion diseases, the prion protein (PrP) becomes misfolded and forms fibrillar aggregates, which are resistant to proteinase degradation and become responsible for prion infectivity and pathology. So far, no drug or treatment procedures have been approved for prion disease treatment. We have previously shown that engineered cell-penetrating peptide constructs can reduce the amount of prion aggregates in infected cells. The molecular mechanisms underlying this effect are however unknown. Here, we use atomic force microscopy (AFM) imaging to show that the aggregation of the human PrP protein can be inhibited by equimolar amounts of the 25 residues long engineered peptide construct NCAM1-A{beta}.

biochemistry↗