探討血液循環中轉糖鏈球菌引發交互作用抗雙股去氧核糖核酸抗體生成之機制

Abstract

感染通過各類型的機制在多種自身免疫性疾病中參與自體抗原免疫耐受性的破壞。我們先前的研究結果表明，轉糖鏈球菌(S. mutans)感染可以在小鼠模型中誘導抗雙股去氧核醣核酸抗體的產生。並且，鑑於這些感染誘導的抗雙股去氧核醣核酸抗體能夠交叉辨認自轉糖鏈球菌細胞壁萃取之萄糖基轉移酶B (GtfB)蛋白，轉糖鏈球菌表面蛋白GtfB在抗雙股去氧核醣核酸抗體的感染誘導中扮演重要角色。我們提出了假說假定GtfB可能透過與去氧核醣核酸結合形成蛋白質-去氧核醣核酸複合物來誘發這些交叉反應性抗雙股去氧核醣核酸抗體的產生。在本篇研究中，我們首先預測GtfB蛋白的部分結構，並由此發現GtfB與具去氧核醣核酸結合功能之膽鹼結合蛋白之間的結構相似性。大面積的表面正電荷氨基酸暴露也支持GtfB蛋白的去氧核醣核酸結合潛力。此外，我們亦使用重組GtfB蛋白來確認交叉反應性抗雙股去氧核醣核酸抗體與GtfB交叉作用的直接性。最後，我們使用GtfB-去氧核醣核酸結合鑑定探討了GtfB蛋白的去氧核醣核酸結合能力。未切割的質粒去氧核醣核酸在提供二價離子的條件下與重組GtfB蛋白作用後能夠在膠上表現出去氧核醣核酸之條帶移動，然而已切割的質粒去氧核醣核酸則無法。這意味著GtfB可能以具去氧核醣核酸構象偏好的方式與去氧核醣核酸進行二價離子依賴性結合。總結而論，GtfB在二價離子存在下表現出具去氧核醣核酸構象偏好的去氧核醣核酸結合潛力。通過與體內之核酸相互作用，GtfB可能有助於交叉反應性抗雙股去氧核醣核酸抗體之誘導。

Infection, through a diverse range of mechanisms, contributes to the breakdown of immunological tolerance to self-antigen in a variety of autoimmune diseases. Our previous data demonstrated that Streptococcus mutans (S. mutans) infection can induce anti-dsDNA antibody production in murine models. Furthermore, the surface protein Glucosyltransferase B (GtfB) of S. mutans plays an important role in the induction of anti-dsDNA antibodies as these induced anti-dsDNA antibodies can cross-react with GtfB protein extract from the S. mutans cell wall. We hypothesized that GtfB might induce the production of these cross-reactive anti-dsDNA antibodies by interacting with DNA to form protein-DNA complexes. Here, we first predict the structure of partial length GtfB protein and discover structure similarities between GtfB and DNA-binding choline-binding proteins. Large surface areas with exposed positively charged amino acids also support the potential DNA binding ability of GtfB protein. In addition, recombinant GtfB protein was used to confirm the direct interaction of cross-reactive anti-dsDNA antibodies with GtfB. Finally, the DNA-binding capacity of GtfB protein was investigated using the GtfB-DNA binding assay. Non-cleaved plasmid DNA undergoes band shifting on gels after incubation with recombinant GtfB supplied with divalent ion, but not cleaved plasmid DNA, implying that GtfB may divalent ion dependently bind to DNA with a DNA conformational preference. Taken together, GtfB exhibits DNA binding potential with DNA conformational preference in the presence of divalent ions. By interacting with nucleic acid in vivo, GtfB may contribute to the induction of cross-reactive anti-dsDNA antibodies.