Molecular basis of viral DNA sensing through the cGAS-STING pathway

通过cGAS-STING途径的病毒DNA传感的分子基础 先天免疫反应是抵抗入侵病原体的第一道防线。病毒核酸，如 作为危险信号，在受感染的细胞中诱导强有力的免疫反应。的 病毒核酸的检测是宿主感知感染并启动保护性的核心策略， 免疫反应。环GMP-AMP合酶（cGAS）是先天免疫中的胞质dsDNA传感器。是 被病毒DNA激活，催化非典型环状二核苷酸2 ′，3 ′ cGAMP的合成（参见 作为cGAMP）。作为第二信使，cGAMP刺激I型干扰素（IFN）的诱导，通过 适配器STING位于ER膜上。STING参与cGAMP导致招募 和蛋白激酶TBK 1的活化。转录因子IRF-3然后被募集到信号传导中。 通过磷酸化STING复合。诱导的IRF-3和TBK 1的接近导致IRF-3磷酸化 和激活。磷酸化IRF-3寡聚化，易位到细胞核，并诱导表达 I型IFN，赋予宿主抗病毒活性并激活获得性免疫应答。到 为了了解通过cGAS-STING途径进行病毒DNA传感的分子基础，PI确定了 cGAS在分离和与dsDNA复合时的晶体结构; STING在分离和与dsDNA复合时的结构。 与cGAMP的复合物;与两种抑制剂结合的小鼠TBK 1的结构;磷酸化的TBK 1的结构。 与IRF-3结合的STING C-末端肽;以及IRF-3的磷酸模拟二聚体的结构。这些 全面的结构和功能研究大大推进了我们对先天性 免疫系统在分子水平上对病毒DNA作出反应。然而，仍不清楚cGAMP如何结合 激活STING并介导TBK 1和IRF-3在信号传导复合物处的募集和激活。在 此外，磷酸化如何诱导IRF-3活化并促进其表达的确切机制尚不清楚。 与IFN-β启动子的关联仍有待确定。基于我们强大的初步研究， 拟议的研究将阐明cGAS-STING途径几个关键步骤的分子基础， 以下目标：1）。通过STING确定TBK 1募集的结构基础; 2）.阐明 通过cGAMP激活STING的分子基础; 3）。阐明TBK 1激活IRF-3的机制。的 提出的研究代表了对胞质DNA的机制的严格和全面的调查， 这将极大地促进我们对先天免疫的分子基础的理解， 感染此外，它们为治疗病毒性疾病的创新方法提供了结构框架， 自身免疫性疾病和癌症通过操纵先天免疫反应。

The Molecular Basis of Viral DNA Sensing through the cGAS-STING Pathway The innate immune response is the first line of defense against invading pathogens. Viral nucleic acids, such as DNA and RNA, serve as danger signals that induce potent immune responses in infected cells. The detection of viral nucleic acids is a central strategy by which the hosts sense infection and launch protective immune responses. Cyclic GMP-AMP synthase (cGAS) is a cytosolic dsDNA sensor in innate immunity. It is activated by viral DNA and catalyzes the synthesis of a noncanonical cyclic dinucleotide 2ʹ, 3ʹ cGAMP (referred to as cGAMP). As a second messenger, cGAMP stimulates the induction of type I interferons (IFNs) via the adaptor STING located on the ER membrane. The engagement of cGAMP by STING leads to the recruitment and activation of the protein kinase TBK1. The transcriptional factor IRF-3 is then recruited to the signaling complex by phosphorylated STING. The induced proximity of IRF-3 and TBK1 leads to IRF-3 phosphorylation and activation. Phosphorylated IRF-3 oligomerizes, translocates to the nucleus, and induces the expression of type I IFNs, conferring antiviral activity to the host and activating the acquired immune responses. To understand the molecular basis of viral DNA sensing through the cGAS-STING pathway, the PI determined the crystal structures of cGAS in isolation and in complex with dsDNA; the structures of STING in isolation and in complex with cGAMP; the structures of mouse TBK1 bound to two inhibitors; the structure of phosphorylated STING C-terminal peptide bound to IRF-3; and the structure of a phosphomimetic dimer of IRF-3. These comprehensive structural and functional studies significantly advanced our understanding about how the innate immune system responds to viral DNA at molecular level. However, it remains unknown how cGAMP binding activates STING and mediates the recruitment and activation of TBK1 and IRF-3 at the signaling complex. In addition, the exact mechanism of how phosphorylation induces the activation of IRF-3 and facilitates its association with the IFN-β promoter remains to be determined. Built-upon our strong preliminary studies, the proposed research will elucidate the molecular bases of several key steps of the cGAS-STING pathway with the following aims: 1). Determine the structural basis of TBK1 recruitment by STING; 2). Elucidate the molecular basis of STING activation by cGAMP; 3). Delineate the mechanism of IRF-3 activation by TBK1. The proposed studies represent a rigorous and comprehensive investigation into the mechanisms of cytosolic DNA sensing and will dramatically advance our understanding of the molecular basis of innate immunity against viral infection. In addition, they provide a structural framework for innovative approaches to treat viral diseases, autoimmune disorders, and cancer by manipulating the innate immune response.