Structure and Function of Interacting IcmR-IcmQ Domains from a Type IVb Secretion System in Legionella pneumophila

Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA 02118-2526, USA.
Structure (Impact Factor: 5.62). 05/2009; 17(4):590-601. DOI: 10.1016/j.str.2009.02.011
Source: PubMed


During infection, Legionella pneumophila creates a replication vacuole within eukaryotic cells and this requires a Type IVb secretion system (T4bSS). IcmQ plays a critical role in the translocase and associates with IcmR. In this paper, we show that the N-terminal domain of IcmQ (Qn) mediates self-dimerization, whereas the C-terminal domain with a basic linker promotes membrane association. In addition, the binding of IcmR to IcmQ prevents self-dimerization and also blocks membrane permeabilization. However, IcmR does not completely block membrane binding by IcmQ. We then determined crystal structures of Qn with the interacting region of IcmR. In this complex, each protein forms an alpha-helical hairpin within a parallel four-helix bundle. The amphipathic nature of helices in Qn suggests two possible models for membrane permeabilization by IcmQ. The Rm-Qn structure also suggests how IcmR-like proteins in other L. pneumophila species may interact with their IcmQ partners.

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    • "Purified IcmQ associates with synthetic lipid vesicles, leading to vesicle disruption, as evidenced by the release of preloaded calcein dye (Dumenil et al., 2004). The C-terminal domain plays a primary role in membrane targeting mediated by electrostatic interactions, while the N-terminal domain may be inserted into lipid bilayers and disrupts membranes (Dumenil et al., 2004; Raychaudhury et al., 2009). The N-terminal domain also binds to IcmR, which prevents IcmQ from the stable association with lipid vesicles. "
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    ABSTRACT: Type IV secretion systems (T4SSs) play a central role in the pathogenicity of many important pathogens, including Agrobacterium tumefaciens, Helicobacter pylori, and Legionella pneumophila. The T4SSs are related to bacterial conjugation systems, and are classified into two subgroups, type IVA (T4ASS) and type IVB (T4BSS). The T4BSS, which is closely related to conjugation systems of IncI plasmids, was originally found in human pathogen L. pneumophila; pathogenesis by L. pneumophila infection requires functional Dot/Icm T4BSS. A zoonotic pathogen, Coxiella burnetii, and an arthropod pathogen, Rickettsiella grylli - both of which carry T4BSSs highly similar to the Legionella Dot/Icm system - are evolutionarily closely related and comprise a monophyletic group. A growing body of bacterial genomic information now suggests that T4BSSs are not limited to Legionella and related bacteria and IncI plasmids. Here, we review the current knowledge on T4BSS apparatus and component proteins, gained mainly from studies on L. pneumophila Dot/Icm T4BSS. Recent structural studies, along with previous findings, suggest that the Dot/Icm T4BSS contains components with primary or higher-order structures similar to those in other types of secretion systems - types II, III, IVA, and VI, thus highlighting the mosaic nature of T4BSS architecture.
    Preview · Article · Jun 2011 · Frontiers in Microbiology
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    • "VpdA lpg2410[53][31]20 LegL7 pg2400[18,44]55 IcmP(DotM) lpg0445[54]21 LegLC4 lpg1948[18,25]56 IcmQ lpg0444[50]23 LegS2 lpg2176[18,42]57 IcmR lpg0443[50]24 LegU1 lpg0171[18,19]58 IcmT lpg0441[35][49]Table1. Genes of interest Table 2. Names and sequences of all designed probes immobilized on the microarray and primers used in linear multiplex PCR) was used as a reference strain. "
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    ABSTRACT: For the last five years, Legionella sp. infections and legionnaire's disease in Poland have been receiving a lot of attention, because of the new regulations concerning microbiological quality of drinking water. This was the inspiration to search for and develop a new assay to identify many virulence genes of Legionella pneumophila to better understand their distribution in environmental and clinical strains. The method might be an invaluable help in infection risk assessment and in epidemiological investigations. The microarray is based on Array Tube technology. It contains 3 positive and 1 negative control. Target genes encode structural elements of T4SS, effector proteins and factors not related to T4SS. Probes were designed using OligoWiz software and data analyzed using IconoClust software. To isolate environmental and clinical strains, BAL samples and samples of hot water from different and independent hot water distribution systems of public utility buildings were collected. We have developed a miniaturized DNA microarray for identification of 66 virulence genes of L. pneumophila. The assay is specific to L. pneumophila sg 1 with sensitivity sufficient to perform the assay using DNA isolated from a single L. pneumophila colony. Seven environmental strains were analyzed. Two exhibited a hybridization pattern distinct from the reference strain. The method is time- and cost-effective. Initial studies have shown that genes encoding effector proteins may vary among environmental strains. Further studies might help to identify set of genes increasing the risk of clinical disease and to determine the pathogenic potential of environmental strains.
    Full-text · Article · Jan 2011 · Postępy Higieny i Medycyny Doświadczalnej (Advances in Hygiene and Experimental Medicine)
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    • "Although a limited number of virulence proteins of L. pneumophila have been identified, structural information on these proteins is still scarce. From a total of 18 Legionella proteins with known three-dimensional structures, only three represent confirmed virulence factors [2] [3] [4]. Iron is essential for Legionella growth [5] and the pathogen has developed strategies for the efficient uptake of ferric (Fe 3+ ) iron using siderophores such as legiobactin [6]. "
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    ABSTRACT: Prokaryotic pathogens have developed specialized mechanisms for efficient uptake of ferrous iron (Fe(2+)) from the host. In Legionella pneumophila, the causative agent of Legionnaires' disease, the transmembrane GTPase FeoB plays a key role in Fe(2+) acquisition and virulence. FeoB consists of a membrane-embedded core and an N-terminal, cytosolic region (NFeoB). Here, we report the crystal structure of NFeoB from L. pneumophila, revealing a monomeric protein comprising two separate domains with GTPase and guanine-nucleotide dissociation inhibitor (GDI) functions. The GDI domain displays a novel fold, whereas the overall structure of the GTPase domain resembles that of known G domains but is in the rarely observed nucleotide-free state.
    Full-text · Article · Feb 2010 · FEBS letters
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