Elucidating the Structural Mechanisms of NAIP Receptors in Bacterial Detection and Inflammasome Activation

项目摘要 炎症体是启动炎症反应并发挥重要作用的巨型道尔顿蛋白复合体 在先天免疫系统中的作用。在激活时，炎症体招募并激活效应蛋白 Caspase-1。Caspase-1反过来裂解Gasdermin D(GSDMD)蛋白，释放其N-末端结构域，该结构域 插入细胞膜，在细胞表面打孔。结果，宿主细胞会发生焦性反应。 细胞死亡(下垂)，并将细胞内容物释放到细胞外环境中。促炎因子 Caspase-1激活的细胞因子IL-1和IL-18也将被释放，以激活下游 炎症反应。 NAIP是一个胞浆免疫受体家族，激活NAIP/NLRC4炎症体。 对革兰氏阴性细菌感染的反应。在小鼠体内有七种NAIP蛋白，每种蛋白都有一种特定的感觉 III型分泌系统中的配体，如鞭毛蛋白、针状蛋白或内杆蛋白。在之前的研究中， 我们证明了活性NAIPS通过成核聚合机制激活了NLRC4。然而，它是 对于NAIPS如何在静息细胞中保持不活跃，以及配体的特异性是如何，仍在很大程度上未知 在不同的NAIPS中确定。与老鼠不同，人类只有一个NAIP，而且它被证明是 被所有三种细菌配体激活。这导致了许多问题，包括 人类NAIP对细菌配体的广泛检测及其对人类炎症性瘤的启示 细菌检测机制？为了解决这些问题，我们建议将电子冷冻显微镜 (CryoEM)通过生化和功能研究阐明信号的结构机制 NAIP蛋白的转导作用。NAIP/NLRC4炎性小体调节失调导致巨噬细胞激活 综合征(MAS)和自身炎症，NAIP蛋白突变与脊肌高度相关 萎缩症(SMA)。这项工作的成功实施将广泛地推动有效疗法的发展 通过针对炎症小体治疗传染病、自体炎症性疾病、SMA和癌症 路径。

Project Summary Inflammasomes are mega-Dalton protein complexes that initiate inflammation responses and play important roles in the innate immune system. Upon activation, inflammasomes recruit and activate the effector protein caspase-1. Caspase-1 in turn cleaves the Gasdermin D (GSDMD) protein to release its N-terminal domain, which inserts into the cell membrane to punch holes on the cell surface. As a result, the host cell will undergo pyroptotic cell death (pyroptosis) and release the cell contents into the extracellular environment. Pro-inflammatory cytokines IL-1 and IL-18, both activated by caspase-1, will also be released to activate the downstream inflammation reactions. NAIP is a family of cytosolic immunological receptors that activate the NAIP/NLRC4 inflammasomes in response to Gram-negative bacterial infections. There are seven NAIP proteins in mouse, each sense a specific ligand such as Flagellin, Needle protein or Inner Rod protein in the type III secretion system. In previous studies, we have shown active NAIPs activate NLRC4 through the nucleated polymerization mechanism. However, it is still largely unknown about how NAIPs remain inactive in the resting cells, and how is the ligand specificity is determined among different NAIPs. Unlike in mouse, humans only have one NAIP and it was shown to be activated by all three bacterial ligands. This leads to many questions including what is the structural basis of the broad detection of bacterial ligands by human NAIP and what does it tell us about the human inflammasomal bacterial detection mechanism? To address these questions, we propose to combine electron cryo-microscopy (cryoEM) with biochemical and functional studies to elucidate the structural mechanisms underlying the signal transduction by NAIP proteins. Dysregulation of NAIP/NLRC4 inflammasomes causes macrophage activation syndrome (MAS) and autoinflammation, and mutations of NAIP protein are highly correlated with spinal muscular atrophy (SMA). The successful execution of this work will broadly advance the development of effective therapies to treat infectious diseases, autoinflammatory diseases, SMA, and cancer through targeting the inflammasome pathway.