cGAS senses long and HMGB/TFAM-bound U-turn DNA by forming protein-DNA ladders
cGAS senses long and HMGB/TFAM-bound U-turn DNA by forming protein-DNA ladders
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DOI：
10.1038/nature23890
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发表时间：
2017-09-21
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：
Andreeva, Liudmila;Hiller, Bjoern;Hopfner, Karl-Peter
胞内病原体产生的胞质DNA触发了强大的先天免疫反应（1,2）。它被环GMP-AMP合成酶（cGAS）感知，通过产生第二信使2' 3'-环GMP-AMP （cGAMP）诱导I型干扰素的产生（3-5）。内源性核或线粒体DNA在一定条件下也可以被cGAS感知，导致无菌性炎症。cGAS二聚体结合两个短于20个碱基对的DNA配体（6-9），但20个碱基对的DNA在体内不能激活cGAS，在体外也是一个很差的激活剂。在这里，我们表明cGAS在体外和人类细胞中都以强烈的DNA长度依赖的方式被激活。我们还发现，cGAS二聚体与DNA形成阶梯状网络，导致DNA长度的协同感知：两个DNA分子之间开创性的cGAS二聚体的组装是无效的；但是，一旦形成，它会预先安排侧翼DNA以促进随后的cGAS二聚体的结合。值得注意的是，细菌和线粒体类核蛋白HU和线粒体转录因子A （TFAM）以及高迁移率组盒1蛋白（HMGB1）可以强烈刺激cGAS的长DNA传感。这些蛋白质诱导DNA发生u型转弯和弯曲，使DNA预先结构成核cGAS二聚体。我们的研究结果表明，基于核合作的机制可以灵敏地检测线粒体DNA（10）和病原体基因组（11），并鉴定HMGB/TFAM蛋白作为DNA结构宿主因子。他们为奇特的cGAS二聚体结构提供了解释，并表明cGAS优先结合不完整的核样结构或弯曲的DNA。
Cytosolic DNA arising from intracellular pathogens triggers a powerful innate immune response(1,2). It is sensed by cyclic GMP-AMP synthase (cGAS), which elicits the production of type I interferons by generating the second messenger 2' 3'-cyclic-GMP-AMP (cGAMP)(3-5). Endogenous nuclear or mitochondrial DNA can also be sensed by cGAS under certain conditions, resulting in sterile inflammation. The cGAS dimer binds two DNA ligands shorter than 20 base pairs side-by-side(6-9), but 20-base-pair DNA fails to activate cGAS in vivo and is a poor activator in vitro. Here we show that cGAS is activated in a strongly DNA length-dependent manner both in vitro and in human cells. We also show that cGAS dimers form ladder-like networks with DNA, leading to cooperative sensing of DNA length: assembly of the pioneering cGAS dimer between two DNA molecules is ineffective; but, once formed, it prearranges the flanking DNA to promote binding of subsequent cGAS dimers. Remarkably, bacterial and mitochondrial nucleoid proteins HU and mitochondrial transcription factor A (TFAM), as well as high-mobility group box 1 protein (HMGB1), can strongly stimulate long DNA sensing by cGAS. U-turns and bends in DNA induced by these proteins pre-structure DNA to nucleate cGAS dimers. Our results suggest a nucleation-cooperativity-based mechanism for sensitive detection of mitochondrial DNA(10) and pathogen genomes(11), and identify HMGB/TFAM proteins as DNA-structuring host factors. They provide an explanation for the peculiar cGAS dimer structure and suggest that cGAS preferentially binds incomplete nucleoid-like structures or bent DNA.