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

环GMP AMP合酶（cGAS）是细胞溶质DNA的先天免疫模式识别受体，检测例如细胞内细菌、逆转录病毒或DNA病毒的感染。cGAS与Mab 21蛋白一起属于最近鉴定的核苷酸转移酶家族（Mab 21/cGAS家族），其似乎在早期细胞命运决定中起作用。虽然其他Mab 21蛋白的活性和细胞功能是未知的，但cGAS产生第二信使环GMP AMP（cGAMP），其通过结合干扰素基因STING的衔接子和环二核苷酸传感器刺激物来触发I型干扰素应答。可用的结构和功能数据未能解释cGAS如何被生理学免疫刺激配体（例如>45个碱基对的DNA）激活。在拟议的研究中，我们将使用基于结构、生物化学和细胞的测定来1）揭示cGAS如何被免疫刺激配体激活，2）揭示序列相关Mab 21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，以了解生物学，病理学和进化的一个新的酶家族的核苷酸转移酶，是先天免疫和发育细胞命运的决定的关键球员。

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.