Characterization of Legionella virulence mechanisms

我们调查了嗜肺军团菌如何利用人类细胞并导致一种被称为军团病的严重肺炎。嗜肺性乳杆菌通常在含有淡水的栖息地中发现，在那里它作为单细胞生物体(如阿米巴)的自然寄生虫而蓬勃发展。当被人类吸入时，嗜肺乳杆菌可以感染肺泡巨噬细胞，并导致呼吸道感染，高达30%的感染者是致命的。这种机会性病原体在感染细胞内建立复制空泡的能力是其毒力的关键。细菌将几种蛋白质，即所谓的效应器，输送到宿主细胞质中，在那里它们改变宿主信号事件，以创造一个支持细菌复制周期的环境。在过去的资助期间，我们已经证明了一些效应蛋白改变了内质网和高尔基体之间的宿主膜运输。嗜肺性乳杆菌劫持运输小泡的确切机制才刚刚开始揭开，仍然是这项研究的主要焦点。特别是，我们分析了控制小鸟嘌呤三磷酸酶(GTPase)Rab1活性的嗜肺乳杆菌效应蛋白，Rab1是这一囊泡运输途径的关键调节因子之一。其中一些嗜肺乳杆菌效应物似乎是人类蛋白的分子模拟物，通过GDP/GTP交换催化Rab1激活，通过GTP水解酶使Rab1失活。此外，我们发现了嗜肺乳杆菌特有的第二个调节电路，在该电路中，细菌效应蛋白结合或移除Rab1的翻译后修饰，以稳定其激活状态。这一新颖的概念在任何其他毒力系统中都没有描述过，也是我们正在进行的研究的重点。本研究的结果将为研究嗜肺乳杆菌的致病策略提供重要的见解，并为开发更好的治疗退伍军人病症及相关疾病的治疗方法奠定基础。

We investigate how the bacterium Legionella pneumophila can exploit human cells and cause a severe pneumonia known as Legionnaires disease. L. pneumophila is commonly found in habitats containing freshwater where it thrives as a natural parasite of unicellular organisms such as amoeba. When inhaled by humans, L. pneumophila can infect alveolar macrophages and cause a respiratory infection that is fatal for up to 30 percent of infected individuals. The ability of this opportunistic pathogen to establish a replication vacuole within infected cells is key to its virulence. The bacterium delivers several proteins, so called effectors, into the host cytosol where they alter host signaling events in order to create an environment supportive for the bacteriums replication cycle. Over the past funding period we have shown that some of the effector proteins alter host membrane transport between the endoplasmic reticulum and the Golgi compartment. The precise mechanism of how transport vesicles are hijacked by L. pneumophila is just beginning to unfold and remains the main focus of this research study. In particular, we analyze L. pneumophila effector proteins that manipulate the activity of the small guanine triphosphatase (GTPase) Rab1, one of the key regulators of this vesicle transport route. Some of these L. pneumophila effectors appear to be molecular mimics of human proteins that catalyze Rab1 activation through GDP/GTP exchange and Rab1 deactivation through hydrolysis of GTP. In addition, we discovered a second regulator circuit unique to L. pneumophila in which bacterial effector proteins attach or remove a post-translational modification to Rab1 in order to stabilize its activation state. This novel concept has not been described in any other virulence system and is the focus of our ongoing studies. The results obtained here will provide important insight into the virulence strategies of L. pneumophila and create the foundation for the development of better therapeutic approaches to treat Legionnaires disease and related illnesses.