A Legionella pneumophila Effector Protein Encoded in a Region of Genomic Plasticity Binds to Dot/Icm-Modified Vacuoles

Yale University School of Medicine, Boyer Center for Molecular Medicine, New Haven, Connecticut, United States of America.
PLoS Pathogens (Impact Factor: 7.56). 02/2009; 5(1):e1000278. DOI: 10.1371/journal.ppat.1000278
Source: PubMed


Legionella pneumophila is an opportunistic pathogen that can cause a severe pneumonia called Legionnaires' disease. In the environment, L. pneumophila is found in fresh water reservoirs in a large spectrum of environmental conditions, where the bacteria are able to replicate within a variety of protozoan hosts. To survive within eukaryotic cells, L. pneumophila require a type IV secretion system, designated Dot/Icm, that delivers bacterial effector proteins into the host cell cytoplasm. In recent years, a number of Dot/Icm substrate proteins have been identified; however, the function of most of these proteins remains unknown, and it is unclear why the bacterium maintains such a large repertoire of effectors to promote its survival. Here we investigate a region of the L. pneumophila chromosome that displays a high degree of plasticity among four sequenced L. pneumophila strains. Analysis of GC content suggests that several genes encoded in this region were acquired through horizontal gene transfer. Protein translocation studies establish that this region of genomic plasticity encodes for multiple Dot/Icm effectors. Ectopic expression studies in mammalian cells indicate that one of these substrates, a protein called PieA, has unique effector activities. PieA is an effector that can alter lysosome morphology and associates specifically with vacuoles that support L. pneumophila replication. It was determined that the association of PieA with vacuoles containing L. pneumophila requires modifications to the vacuole mediated by other Dot/Icm effectors. Thus, the localization properties of PieA reveal that the Dot/Icm system has the ability to spatially and temporally control the association of an effector with vacuoles containing L. pneumophila through activities mediated by other effector proteins.

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    • "e Lsp T2SS or the Icm / Dot T4SS and as many as 60 Icm / Dot - translocated effectors . The intriguing discovery of the small GTPase Ran and its effector RanBP1 in the LCV proteome ( Urwyler et al . , 2009 ) , together with the finding that the Icm / Dot substrate LegG1 harbors a putative eukaryotic RCC1 Ran GEF domain ( de Felipe et al . , 2008 ; Ninio et al . , 2009 ) , led to the characterization of the Lpn effector protein as the first bacterial Ran activator ( Rothmeier et al . , 2013 ) . LegG1 localizes to the LCV membrane , promotes microtubule stabilization and intracellular LCV motility as well as replication of Lpn . Moreover , through the stabilization of microtubules , LegG1 antagonizes t"
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    ABSTRACT: Certain pathogenic bacteria adopt an intracellular lifestyle and proliferate in eukaryotic host cells. The intracellular niche protects the bacteria from cellular and humoral components of the mammalian immune system, and at the same time, allows the bacteria to gain access to otherwise restricted nutrient sources. Yet, intracellular protection and access to nutrients comes with a price, i.e. the bacteria need to overcome cell-autonomous defense mechanisms, such as the bactericidal endocytic pathway. While a few bacteria rupture the early phagosome and escape into the host cytoplasm, most intracellular pathogens form a distinct, degradation-resistant and replication-permissive membranous compartment. Intracellular bacteria that form unique pathogen vacuoles include Legionella, Mycobacterium, Chlamydia, Simkania and Salmonella species. In order to understand the formation of these pathogen niches on a global scale and in a comprehensive and quantitative manner, an inventory of compartment-associated host factors is required. To this end, the intact pathogen compartments need to be isolated, purified and biochemically characterized. Here, we review recent progress on the isolation and purification of pathogen-modified vacuoles and membranes, as well as their proteomic characterization by mass spectrometry and different validation approaches. These studies provide the basis for further investigations on the specific mechanisms of pathogen-driven compartment formation.
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    • "Interestingly, the L. pneumophila Icm/Dot substrate LegG1 (alias PieG) is homologous to the eukaryotic Ran GEF RCC1 (de Felipe et al., 2005; 2008; Ninio et al., 2009) and localizes to host membranes through lipidation by the host prenylation machinery at its C-terminal CAAX tetrapeptide motif (Ivanov et al., 2010). Validating the proteomics data, Ran and RanBP1 as well as LegG1 were found to localize to LCVs (Rothmeier et al., 2013). "
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    ABSTRACT: Legionella species are ubiquitous, water-borne bacteria that thrive in numerous ecological niches. Yet, in contrast to many other environmental bacteria, Legionella spp. are also able to grow intracellularly in predatory protozoa. This feature mainly accounts for the pathogenicity of Legionella pneumophila, which causes the majority of clinical cases of a severe pneumonia termed Legionnaires' disease. The pathomechanism underlying L. pneumophila infection is based on macrophage resistance, which in turn is largely defined by the opportunistic pathogen's resistance towards amoebae. L. pneumophila replicates in macrophages or amoebae in a unique membrane-bound compartment, the Legionella-containing vacuole (LCV). LCV formation requires the bacterial Icm/Dot type IV secretion system and involves a plethora of translocated effector proteins, which subvert pivotal processes in the host cell. Of the ∼300 different experimentally validated Icm/Dot substrates, about 50 have been studied and attributed a cellular function to date. The versatility and ingenuity of these effectors' mode of actions is striking. In this review, we summarize insight into the cellular functions and biochemical activities of well-characterized L. pneumophila effector proteins and the host pathways they target. Recent studies not only substantially increased our knowledge about pathogen-host interactions, but also shed light on novel biological mechanisms. This article is protected by copyright. All rights reserved.
    Preview · Article · Apr 2015 · Cellular Microbiology
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    • ") ATP transporter in mitochondrial membrane – PieA – lpg1963 A. castellanii (Ninio et al. 2009) ND – CHO-FccRII, BMMs and U937 (Ninio et al. 2009) "
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    ABSTRACT: Legionella pneumophila is a Gram-negative bacterium and the causative agent of Legionnaires' disease. It replicates within amoeba and infects accidentally human macrophages. Several similarities are seen in the L. pneumophila-infection cycle in both hosts, suggesting that the tools necessary for macrophage infection may have evolved during co-evolution of L. pneumophila and amoeba. The establishment of the Legionella-containing vacuole (LCV) within the host cytoplasm requires the remodeling of the LCV surface and the hijacking of vesicles and organelles. Then L. pneumophila replicates in a safe intracellular niche in amoeba and macrophages. In this review we will summarize the existing knowledge of the L. pneumophila infection cycle in both hosts at the molecular level and compare the factors involved within amoeba and macrophages. This knowledge will be discussed in the light of recent findings from the Acanthamoeba castellanii genome analyses suggesting the existence of a primitive immune-like system in amoeba.
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