The allosteric activation of cGAS underpins its dynamic signaling landscape.
The allosteric activation of cGAS underpins its dynamic signaling landscape.
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作者：
Hooy RM;Sohn J
环G/AMP合成酶(CGAS)启动针对胞质双链DNA的1型干扰素反应，其范围从抗病毒基因表达到细胞凋亡。CGAs塑造这种不同的信号格局的机制仍然没有得到很好的定义。我们发现底物结合和dsDNA长度依赖的结合与cGAS的固有二聚平衡相耦合，其N-末端结构域增强了二聚作用。值得注意的是，通过增加cGAS和底物浓度来增加二聚体比例会减少依赖于双链长度的激活，但并不会否定对dsDNA的要求。这些结果表明，反应背景决定了双链长度的依赖关系，这与关于dsDNA长度在cGAS激活中的作用的说法相一致。总体而言，我们的研究揭示了配体介导的变构如何将cGAs定位在待命状态，准备以开关的方式调整其信号通路。人类的免疫系统保护身体免受各种威胁，如受损的细胞或入侵的微生物。这些威胁中的许多都可以将DNA分子移动到周围的区域，即细胞质。DNA分子通常只存在于细胞的中央隔间，称为细胞核。一种名为cGAS的酶在人类细胞的细胞质中寻找DNA。当DNA与cGAS结合时，它会激活酶，将某些分子(称为“底物”)转化为另一个分子(“信号”)，从而触发各种免疫反应，以保护身体免受威胁。为了产生信号，两种cGAS酶需要作为一个单一的单位一起工作，称为二聚体。细胞质中DNA分子的长度可能会有很大的差异。最初人们认为，与cGAS结合的任何长度的DNA分子都可以以类似的程度激活该酶，但后来的研究表明情况并非如此。然而，目前还不清楚DNA的长度如何影响酶的活性，也不清楚为什么早期的一些研究报告了不同的结果。Hooy和Sohn使用生化方法研究了人类cGAS酶。实验表明，即使在没有DNA存在的情况下，cGAS也可以形成二聚体。然而，当DNA与cGAS结合时，酶更有可能形成二聚体。较长的DNA分子比较短的DNA分子更能促进cGAS二聚体的形成。底物与cGAS的结合也使酶更有可能形成二聚体。这些发现表明，在细胞内，当cGAS检测到细胞质中的DNA时，它已经准备好触发类似开关的反应。Hooy和Sohn的工作建立了一套简单的规则来预测cGAS在给定情况下可能会如何反应。这些信息可能有助于设计和定制调节人类患者免疫反应的努力，并可能提供洞察为什么人体以不同的方式对生物威胁做出反应。
Cyclic G/AMP synthase (cGAS) initiates type-1 interferon responses against cytosolic double-stranded (ds)DNA, which range from antiviral gene expression to apoptosis. The mechanism by which cGAS shapes this diverse signaling landscape remains poorly defined. We find that substrate-binding and dsDNA length-dependent binding are coupled to the intrinsic dimerization equilibrium of cGAS, with its N-terminal domain potentiating dimerization. Notably, increasing the dimeric fraction by raising cGAS and substrate concentrations diminishes duplex length-dependent activation, but does not negate the requirement for dsDNA. These results demonstrate that reaction context dictates the duplex length dependence, reconciling competing claims on the role of dsDNA length in cGAS activation. Overall, our study reveals how ligand-mediated allostery positions cGAS in standby, ready to tune its signaling pathway in a switch-like fashion. The human immune system protects the body from various threats such as damaged cells or invading microbes. Many of these threats can move molecules of DNA, which are usually only found within a central compartment in the cell known as the nucleus, to the surrounding area, the cytoplasm. An enzyme called cGAS searches for DNA in the cytoplasm of human cells. When DNA binds to cGAS it activates the enzyme to convert certain molecules (referred to as ‘substrates’) into another molecule (the ‘signal’) that triggers various immune responses to protect the body against the threat. To produce the signal, two cGAS enzymes need to work together as a single unit called a dimer. The length of DNA molecules in the cytoplasm of cells can vary widely. It was initially thought that DNA molecules of any length binding to cGAS could activate the enzyme to a similar degree, but later studies demonstrated that this is not the case. However, it remains unclear how the length of the DNA could affect the activity of the enzyme, or why some of the earlier studies reported different findings. Hooy and Sohn used biochemical approaches to study the human cGAS enzyme. The experiments show that cGAS can form dimers even when no DNA is present. However, when DNA bound to cGAS, the enzyme was more likely to form dimers. Longer DNA molecules were better at promoting cGAS dimers to form than shorter DNA molecules. The binding of substrates to cGAS also made it more likely that the enzyme would form dimers. These findings suggest that inside cells cGAS is primed to trigger a switch-like response when it detects DNA in the cytoplasm. The work of Hooy and Sohn establishes a simple set of rules to predict how cGAS might respond in a given situation. Such information may aid in designing and tailoring efforts to regulate immune responses in human patients, and may provide insight into why the body responds to biological threats in different ways.