Cyclic GMP-AMP synthase (cGAS) is a key DNA sensor that detects aberrant cytosolic DNA arising from pathogen invasions or genotoxic stresses. Upon binding to DNA, cGAS is activated and catalyzes the synthesis of cyclic GMP-AMP (cGAMP), which induces potent antimicrobial and antitumor responses. Kaposi sarcoma-associated herpesvirus (KSHV) is a human DNA tumor virus that causes Kaposi sarcoma and several other malignancies. We previously reported that KSHV inhibitor of cGAS (KicGAS) encoded by ORF52, inhibits cGAS enzymatic activity, but the underlying mechanisms remained unclear. To define the inhibitory mechanisms, here we performed in-depth biochemical and functional characterizations of KicGAS, and mapped its functional domains. We found KicGAS self-oligomerizes and binds to double stranded DNA cooperatively. This self-oligomerization is essential for its DNA binding and cGAS inhibition. Interestingly, KicGAS forms liquid droplets upon binding to DNA, which requires collective multivalent interactions with DNA mediated by both structured and disordered domains coordinated through the self-oligomerization of KicGAS. We also observed that KicGAS inhibits the DNA-induced phase separation and activation of cGAS. Our findings reveal a novel mechanism by which DNA viruses target the host protein phase separation for suppression of the host sensing of viral nucleic acids.

中文翻译：

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KicGAS/ORF52 寡聚介导的协同 DNA 结合可抑制 DNA 诱导的相分离和 cGAS 激活

环 GMP-AMP 合酶 (cGAS) 是一种关键的 DNA 传感器，可检测病原体入侵或基因毒性应激引起的异常胞质 DNA。与 DNA 结合后，cGAS 被激活并催化环 GMP-AMP (cGAMP) 的合成，从而诱导有效的抗菌和抗肿瘤反应。卡波西肉瘤相关疱疹病毒 (KSHV) 是一种人类 DNA 肿瘤病毒，可引起卡波西肉瘤和其他几种恶性肿瘤。我们之前报道过 ORF52 编码的 KSHV cGAS 抑制剂 (KicGAS) 可抑制 cGAS 酶活性，但其潜在机制仍不清楚。为了定义抑制机制，我们对 KicGAS 进行了深入的生化和功能表征，并绘制了其功能域图。我们发现 KicGAS 自我寡聚并协同结合双链 DNA。这种自寡聚对其 DNA 结合和 cGAS 抑制至关重要。有趣的是，KicGAS 在与 DNA 结合后形成液滴，这需要通过 KicGAS 的自寡聚化协调的结构化和无序域介导的与 DNA 的集体多价相互作用。我们还观察到 KicGAS 抑制 DNA 诱导的相分离和 cGAS 的激活。我们的研究结果揭示了一种新的机制，DNA病毒通过这种机制靶向宿主蛋白相分离，从而抑制宿主对病毒核酸的感知。