PDF(Pubmed)
Abstract：
Legionella pneumophila is a facultative intracellular pathogen that causes legionellosis. The key to its virulence is the delivery of hundreds of effector proteins into host cells via the defective in organelle trafficking/intracellular multiplication type IV secretion system. These effectors modulate numerous host signaling pathways to create a niche called the Legionella-containing vacuole (LCV) permissive for its intracellular replication. Previous investigation revealed that exploitation of the host ubiquitin system is among the most important strategies used by L. pneumophila to coopt host processes for its benefit. Here, we show that the effector Legionella ubiquitin ligase gene 15 (Lug15) (Lpg2327), which has no detectable homology with any enzyme involved in ubiquitin signaling, is an E3 ligase. In L. pneumophila-infected cells, Lug15 is localized on the LCV and impacts its association with polyubiquitinated proteins. We also demonstrate that Sec22b is ubiquitinated and recruited to the LCV by Lug15. Thus, our results establish Lug15 as a novel E3 ligase that functions to recruit a SNARE protein to remodel the L. pneumophila phagosome.IMPORTANCEProtein ubiquitination is one of the most important post-translational modifications that plays critical roles in the regulation of a wide range of eukaryotic signaling pathways. Many successful intracellular bacterial pathogens can hijack host ubiquitination machinery through the action of effector proteins that are injected into host cells by secretion systems. Legionella pneumophila is the etiological agent of legionellosis that is able to survive and replicate in various host cells. The defective in organelle trafficking (Dot)/intracellular multiplication (Icm) type IV secretion system of L. pneumophila injects over 330 effectors into infected cells to create an optimal environment permissive for its intracellular proliferation. To date, at least 26 Dot/Icm substrates have been shown to manipulate ubiquitin signaling via diverse mechanisms. Among these, 14 are E3 ligases that either cooperate with host E1 and E2 enzymes or adopt E1/E2-independent catalytic mechanisms. In the present study, we demonstrate that the L. pneumophila effector Legionella ubiquitin ligase gene 15 (Lug15) is a novel ubiquitin E3 ligase. Lug15 is involved in the remodeling of LCV with polyubiquitinated species. Moreover, Lug15 catalyzes the ubiquitination of host SNARE protein Sec22b and mediates its recruitment to the LCV. Ubiquitination of Sec22b by Lug15 promotes its noncanonical pairing with plasma membrane-derived syntaxins (e.g., Stx3). Our study further reveals the complexity of strategies utilized by L. pneumophila to interfere with host functions by hijacking host ubiquitin signaling.
摘要：
嗜肺军团菌是引起军团菌病的兼性细胞内病原体。其毒力的关键是通过细胞器运输/细胞内增殖IV型分泌系统的缺陷将数百种效应蛋白递送到宿主细胞中。这些效应子调节许多宿主信号传导途径，以创建允许其细胞内复制的称为含军团菌的液泡（LCV）的小生境。先前的调查表明，利用宿主泛素系统是嗜肺乳杆菌为其利益而选择宿主过程的最重要策略之一。这里,我们表明，效应军团菌泛素连接酶基因15（Lug15）（LPG2327），与任何参与泛素信号传导的酶都没有检测到的同源性，是E3连接酶。在嗜肺乳杆菌感染的细胞中，Lug15位于LCV上并影响其与多泛素化蛋白的关联。我们还证明Sec22b被Lug15泛素化并募集到LCV。因此，我们的结果证实Lug15是一种新型的E3连接酶,其功能是募集一种SNARE蛋白来重塑嗜肺乳杆菌吞噬体.IMPORTANCE蛋白泛素化是最重要的翻译后修饰之一，在调节多种真核信号通路中起着关键作用。许多成功的细胞内细菌病原体可以通过通过分泌系统注射到宿主细胞中的效应蛋白的作用来劫持宿主泛素化机制。嗜肺军团菌是军团菌病的病原体，能够在各种宿主细胞中存活和复制。嗜肺乳杆菌的细胞器运输（Dot）/细胞内增殖（Icm）IV型分泌系统的缺陷将330多种效应物注射到感染的细胞中，以创造允许其细胞内增殖的最佳环境。迄今为止,已显示至少26个Dot/Icm底物通过多种机制操纵泛素信号传导。其中,14是与宿主E1和E2酶协作或采用E1/E2非依赖性催化机制的E3连接酶。在本研究中,我们证明嗜肺乳杆菌效应军团菌泛素连接酶基因15（Lug15）是一种新型的泛素E3连接酶。Lug15参与具有多泛素化物种的LCV的重塑。此外，Lug15催化宿主SNARE蛋白Sec22b的泛素化并介导其募集到LCV。Lug15对Sec22b的泛素化可促进其与质膜衍生的突触素的非规范配对（例如，Stx3).我们的研究进一步揭示了嗜肺乳杆菌通过劫持宿主泛素信号来干扰宿主功能的策略的复杂性。
