Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, TN.
Department of Biomedical Sciences, Quillen College of Medicine, East Tennessee State University, Johnson City, TN
J Immunol. 2022 Sep 15;209(6):1180-1188. doi: 10.4049/jimmunol.2200148. Epub 2022 Aug 17.
The structure of wild-type pentameric C-reactive protein (CRP) is stabilized by two calcium ions that are required for the binding of CRP to its ligand phosphocholine. CRP in its structurally altered pentameric conformations also binds to proteins that are denatured and aggregated by immobilization on microtiter plates; however, the identity of the ligand on immobilized proteins remains unknown. We tested the hypotheses that immobilization of proteins generated an amyloid-like structure and that amyloid-like structure was the ligand for structurally altered pentameric CRP. We found that the Abs to amyloid-β peptide 1-42 (Aβ) reacted with immobilized proteins, indicating that some immobilized proteins express an Aβ epitope. Accordingly, four different CRP mutants capable of binding to immobilized proteins were constructed, and their binding to fluid-phase Aβ was determined. All CRP mutants bound to fluid-phase Aβ, suggesting that Aβ is a ligand for structurally altered pentameric CRP. In addition, the interaction between CRP mutants and Aβ prevented the formation of Aβ fibrils. The growth of Aβ fibrils was also halted when CRP mutants were added to growing fibrils. Biochemical analyses of CRP mutants revealed altered topology of the Ca-binding site, suggesting a role of this region of CRP in binding to Aβ. Combined with previous reports that structurally altered pentameric CRP is generated in vivo, we conclude that CRP is a dual pattern recognition molecule and an antiamyloidogenic protein. These findings have implications for Alzheimer's and other neurodegenerative diseases caused by amyloidosis and for the diseases caused by the deposition of otherwise fluid-phase proteins.
天然五聚体 C 反应蛋白（CRP）的结构由两个钙离子稳定，这两个钙离子对于 CRP 与其配体磷酸胆碱的结合是必需的。其结构发生改变的五聚体构象中的 CRP 也与通过固定在微量滴定板上而变性和聚集的蛋白质结合；然而，固定化蛋白质上的配体仍然未知。我们检验了以下两个假说，即蛋白质的固定化产生了类似淀粉样的结构，并且类似淀粉样的结构是结构改变的五聚体 CRP 的配体。我们发现，抗淀粉样β肽 1-42（Aβ）的抗体与固定化的蛋白质反应，表明一些固定化的蛋白质表达 Aβ 表位。因此，构建了四个能够与固定化蛋白质结合的不同 CRP 突变体，并测定了它们与液相处 Aβ 的结合情况。所有 CRP 突变体都与液相处 Aβ结合，表明 Aβ是结构改变的五聚体 CRP 的配体。此外，CRP 突变体与 Aβ 的相互作用阻止了 Aβ 纤维的形成。当 CRP 突变体添加到正在生长的纤维中时，Aβ 纤维的生长也被阻止。CRP 突变体的生化分析显示 Ca 结合位点的拓扑结构发生了改变，表明 CRP 此区域在与 Aβ 结合中起作用。结合先前关于体内产生结构改变的五聚体 CRP 的报告，我们得出结论，CRP 是一种双重模式识别分子和抗淀粉样蛋白的蛋白质。这些发现对由淀粉样变性引起的阿尔茨海默病和其他神经退行性疾病以及由其他液相处蛋白质沉积引起的疾病具有重要意义。
