Department of Macromolecular Physics, Faculty of Physics, Adam Mickiewicz University, PL 61-614 Poznań, Poland.
Department of Biomedical Chemistry, Faculty of Chemistry, Gdańsk University, PL 80-308 Gdańsk, Poland.
Biochemistry. 2023 Jun 6;62(11):1689-1705. doi: 10.1021/acs.biochem.3c00129. Epub 2023 May 10.
Misfolding of the cellular prion protein (PrP) is associated with the development of fatal neurodegenerative diseases called transmissible spongiform encephalopathies (TSEs). Metal ions appear to play a crucial role in PrP misfolding. PrP is a combined Cu(II) and Zn(II) metal-binding protein, where the main metal-binding site is located in the octarepeat (OR) region. Thus, the biological function of PrP may involve the transport of divalent metal ions across membranes or buffering concentrations of divalent metal ions in the synaptic cleft. Recent studies have shown that an excess of Cu(II) ions can result in PrP instability, oligomerization, and/or neuroinflammation. Here, we have used biophysical methods to characterize Cu(II) and Zn(II) binding to the isolated OR region of PrP. Circular dichroism (CD) spectroscopy data suggest that the OR domain binds up to four Cu(II) ions or two Zn(II) ions. Binding of the first metal ion results in a structural transition from the polyproline II helix to the β-turn structure, while the binding of additional metal ions induces the formation of β-sheet structures. Fluorescence spectroscopy data indicate that the OR region can bind both Cu(II) and Zn(II) ions at neutral pH, but under acidic conditions, it binds only Cu(II) ions. Molecular dynamics simulations suggest that binding of either metal ion to the OR region results in the formation of β-hairpin structures. As the formation of β-sheet structures can be a first step toward amyloid formation, we propose that high concentrations of either Cu(II) or Zn(II) ions may have a pro-amyloid effect in TSE diseases.
细胞朊蛋白（PrP）的错误折叠与被称为传染性海绵状脑病（TSEs）的致命神经退行性疾病的发展有关。金属离子似乎在 PrP 错误折叠中起着至关重要的作用。PrP 是一种结合 Cu（II）和 Zn（II）的金属结合蛋白，其主要金属结合位点位于八重复（OR）区域。因此，PrP 的生物学功能可能涉及跨膜运输二价金属离子或缓冲突触间隙中二价金属离子的浓度。最近的研究表明，过量的 Cu（II）离子会导致 PrP 不稳定、寡聚化和/或神经炎症。在这里，我们使用生物物理方法来表征 Cu（II）和 Zn（II）与 PrP 分离的 OR 区域的结合。圆二色性（CD）光谱数据表明，OR 结构域可结合多达四个 Cu（II）离子或两个 Zn（II）离子。第一个金属离子的结合导致从多脯氨酸 II 螺旋到 β-转角结构的结构转变，而额外金属离子的结合诱导 β-折叠结构的形成。荧光光谱数据表明，OR 区域可以在中性 pH 值下结合 Cu（II）和 Zn（II）离子，但在酸性条件下，它仅结合 Cu（II）离子。分子动力学模拟表明，OR 区域与任何一种金属离子的结合都会导致β-发夹结构的形成。由于β-折叠结构的形成可能是淀粉样蛋白形成的第一步，因此我们提出 TSE 疾病中高浓度的 Cu（II）或 Zn（II）离子可能具有促淀粉样蛋白效应。
