Structural basis for sequestration and autoinhibition of cGAS by chromatin
Structural basis for sequestration and autoinhibition of cGAS by chromatin
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DOI：
10.1038/s41586-020-2748-0
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发表时间：
2020-09-10
期刊：
影响因子：
64.8
通讯作者：
Hopfner, Karl-Peter
中科院分区：
文献类型：
--
作者：
Michalski, Sebastian;de Oliveira Mann, Carina C.;Hopfner, Karl-Peter
环GMP-AMP合酶（cGAS）是细胞溶质微生物DNA的先天免疫传感器（1）。在结合DNA后，cGAS合成信使2 ' 3 '-环GMP-AMP（cGAMP）（2-4），其通过STING的活化触发细胞自主防御和I型干扰素和促炎细胞因子的产生（5）。除了对细胞溶质微生物DNA作出反应外，cGAS还识别错误定位的细胞溶质自身DNA，并与自身免疫和无菌性炎症有关（6，7）。对病原体或损伤相关DNA的特异性被认为是由胞质限制引起的。然而，最近的发现将cGAS稳固地置于细胞核中（8-10），其中染色质的紧密束缚对于防止自身DNA的自身反应性很重要（8）。在这里，我们展示了cGAS如何被染色质隔离和抑制。我们提供了与核小体结合的cGAS催化结构域的冷冻电子显微镜结构，其显示cGAS不与核小体DNA相互作用，而是与组蛋白2A-组蛋白2B相互作用，并且紧密锚定到“酸性补丁”。该相互作用掩埋cGAS DNA结合位点B，并阻断活性cGAS二聚体的形成。酸性补丁强有力地胜过激动性DNA与CGAS的结合，这表明核小体螯合可以有效地抑制CGAS，即使当可接近的DNA在附近时，例如在活跃转录的基因组区域中。我们的研究结果显示了核cGAS是如何被染色质隔离的，并提供了一种防止核自身DNA自身反应的机制。生化和结构分析显示了核苷酸转移酶cGAS与染色质的拴系如何防止核DNA的自身免疫识别。
Cyclic GMP-AMP synthase (cGAS) is an innate immune sensor for cytosolic microbial DNA(1). After binding DNA, cGAS synthesizes the messenger 2 ' 3 '-cyclic GMP-AMP (cGAMP)(2-4), which triggers cell-autonomous defence and the production of type I interferons and pro-inflammatory cytokines via the activation of STING(5). In addition to responding to cytosolic microbial DNA, cGAS also recognizes mislocalized cytosolic self-DNA and has been implicated in autoimmunity and sterile inflammation(6,7). Specificity towards pathogen- or damage-associated DNA was thought to be caused by cytosolic confinement. However, recent findings place cGAS robustly in the nucleus(8-10), where tight tethering of chromatin is important to prevent autoreactivity to self-DNA(8). Here we show how cGAS is sequestered and inhibited by chromatin. We provide a cryo-electron microscopy structure of the cGAS catalytic domain bound to a nucleosome, which shows that cGAS does not interact with the nucleosomal DNA, but instead interacts with histone 2A-histone 2B, and is tightly anchored to the 'acidic patch'. The interaction buries the cGAS DNA-binding site B, and blocks the formation of active cGAS dimers. The acidic patch robustly outcompetes agonistic DNA for binding to cGAS, which suggests that nucleosome sequestration can efficiently inhibit cGAS, even when accessible DNA is nearby, such as in actively transcribed genomic regions. Our results show how nuclear cGAS is sequestered by chromatin and provides a mechanism for preventing autoreactivity to nuclear self-DNA.Biochemical and structural analyses show how tethering of the nucleotidyltransferase cGAS to chromatin prevents autoimmune recognition of nuclear DNA.