Structural biology of vertebrate cGAS/Mab21 proteins and their ligand complexes

环状GMP-AMP合成酶(CGAS)是胞浆DNA的天然免疫模式识别受体，可检测细胞内细菌、逆转录病毒或DNA病毒的感染。CGAS和Mab21蛋白一起属于最近发现的核苷酸转移酶家族(Mab21/cGAS家族)，它们似乎在早期细胞命运决定中发挥作用。虽然其他Mab21蛋白的活性和细胞功能尚不清楚，但cGAS通过与干扰素基因的接头和环二核苷酸传感器刺激物结合来产生第二信使环GMP AMP(CGAMP)，从而触发I型干扰素反应。现有的结构和功能数据无法解释cGAS是如何被生理免疫刺激配体激活的，例如&gt；45碱基对DNA。在拟议的研究中，我们将使用结构、生化和基于细胞的分析来1)揭示免疫刺激配体是如何激活cGAS的；2)揭示与序列相关的Mab21蛋白的细胞配体和酶活性。预期的结果将提供一个结构和机制框架，以了解一个新的核苷酸转移酶家族的生物学、病理学和进化，这些酶家族是决定先天性免疫和发育细胞命运的关键角色。

Cyclic GMP AMP synthase (cGAS) is an innate immune pattern recognition receptor for cytosolic DNA, detecting e.g. infections by intracellular bacteria, retroviruses, or DNA-viruses. cGAS belongs together with Mab21 proteins to a recently identified family of nucleotidyl transferases (Mab21/cGAS family) that seem to play a role in early cell fate decisions. While, the activity and cellular function of other Mab21 proteins is unknown, cGAS produces the second messenger cyclic GMP AMP (cGAMP) that triggers the type I interferon response by binding to the adaptor and cyclic dinucleotide sensor stimulator of interferon genes STING. Available structural and functional data fail to explain how cGAS is activated by physiologically immune-stimulatory ligands such as >45 base pair DNA. In the proposed research, we will use structural, biochemical and cell based assays to 1) reveal how cGAS is activated by immune-stimulatory ligands and 2) reveal the cellular ligands and enzymatic activity of the sequence related Mab21 proteins. The anticipated results will provide a structural and mechanistic framework to understand the biology, pathology and evolution of a new enzyme family of nucleotidyl-transferases that are key players in innate immune and developmental cell fate decisions.