Molecular mechanisms by which the large GTPase hGBP1 inhibits actin-based bacterial dissemination

包括人类适应的肠道病原体志贺氏菌在内的几种侵入性细菌通过内吞作用或吞噬作用进入宿主细胞，随后从细胞内空泡逃逸到宿主细胞胞质溶胶中。胞质环境中的生存推动了特定生态位适应的进化。在胞质内细菌病原体如志贺氏菌中常见的一种适应是劫持宿主的肌动蛋白聚合机制以产生胞质内运动和侵入邻近宿主细胞的力的能力。这种基于肌动蛋白的运动性使志贺氏菌能够在结肠上皮内传播，同时避免细胞外免疫机制，如抗菌肽或中性粒细胞。因此，宿主对志贺氏菌的防御严重依赖于受感染细胞本身执行的免疫防御程序。一种针对志贺氏菌的细胞自主防御程序是由动力相关的GTPase人鸟苷酸结合蛋白1（hGBP1）执行的。两项独立的研究报道，hGBP1结合志贺氏菌，并阻止细菌利用宿主肌动蛋白聚合机制进行胞内运动和细胞间传播。这种有效的hGBP1介导的防御程序的机制目前尚不清楚，代表了知识的关键差距。我的建议旨在定义的分子机制（1）hGBP1识别和结合志贺氏菌，以及（2）hGBP1阻止肌动蛋白为基础的运动志贺氏菌。多学科研究建议建立在我和同事在我的主机实验室进行的先前工作的基础上。这个建议整合了我的生物化学和生物物理学专业知识，在医学相关病原体和人类宿主之间的“肌动蛋白之战”中开辟了一个新的领域。

Several species of invasive bacteria including the human-adapted, enteric pathogen Shigella enter host cells via endocytosis or phagocytosis and subsequently escape from an intracellular vacuole into the host cell cytosol. Survival within the cytosolic milieu drove the evolution of specific niche adaptations. One adaptation commonly found amongst intracytosolic bacterial pathogens such as Shigella is the ability to hijack the host’s actin polymerization machinery in order to generate force for intracytosolic movement and the invasion of neighboring host cells. This actin-based motility enables Shigella to spread within the colonic epithelium while simultaneously avoiding extracellular immune mechanisms such as antimicrobial peptides or neutrophils. Host defense against Shigella is therefore critically dependent on immune defense programs executed by the infected cell itself. One such cell-autonomous defense program directed at Shigella is executed by the dynamin-related GTPase human guanylate-binding protein 1 (hGBP1). Two independent studies reported that hGBP1 binds to Shigella and blocks bacteria from utilizing the host actin polymerization machinery for intracytosolic motility and cell-to-cell spread. The mechanisms underlying this potent hGBP1-mediated defense program is currently unknown and represents a critical gap in knowledge. My proposal aims to define the molecular mechanisms (1) by which hGBP1 recognizes and binds to Shigella as well as (2) by which hGBP1 prevents actin-based motility of Shigella. The multidisciplinary research proposal builds on prior work I and co-workers conducted in my host lab. The proposal integrates my biochemical and biophysical expertise to break a new frontier in "the battle over actin" between a medically relevant pathogen and the human host.