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.
    Frontiers in Microbiology 06/2011; 2:136. DOI:10.3389/fmicb.2011.00136 · 3.99 Impact Factor
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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.
    FEBS letters 02/2010; 584(4):733-8. DOI:10.1016/j.febslet.2009.12.045 · 3.17 Impact Factor
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    • "TFSS are promiscuous macromolecular transporters of Gram-negative and Gram-positive bacteria that mediate intercellular transfer of various substrates, e.g. proteins, DNA or protein-DNA complexes between bacteria or between bacteria and eukaryotic cells [1-5]. The bacterial conjugation machines form a subgroup of TFSS. "
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    ABSTRACT: Type four secretion systems (TFSS) are bacterial macromolecular transport systems responsible for transfer of various substrates such as proteins, DNA or protein-DNA complexes. TFSSs encode two or three ATPases generating energy for the secretion process. These enzymes exhibit highest sequence conservation among type four secretion components. Here, we report the biochemical characterization of three ATPases namely TraE, TraJ and TraK (VirB4, VirB11 and VirD4 homologs of the Agrobacterium tumefaciens transfer system, respectively) from the transfer system of Aeromonas veronii plasmid pAC3249A. ATPases were expressed as His-tag fusion proteins in E. coli and purified by affinity chromatography. ATP binding and ATP hydrolysis experiments were performed with the purified ATPases. TraE and TraK showed strong binding to TNP-ATP and TNP-CTP (fluorescent analogs of ATP and CTP respectively) whereas TraJ showed weak binding. The optimum temperature range for the three ATPases was between 42 degrees C and 50 degrees C. Highest ATP hydrolysis activity for all the ATPases was observed in the presence of Mg2+ and Mn2+. However, TraJ and TraK also showed activity in the presence of Co2+. TraJ exhibited the highest specific activity of all the three ATPases with vmax 118 +/- 5.68 nmol/min/mg protein and KM 0.58 +/- 0.10 mM. This is the first biochemical characterization of conjugative transport ATPases encoded by a conjugative plasmid from Aeromonas. Our study demonstrated that the three ATPases of a newly reported TFSS of A. veronii plasmid pAc3249A are functional in both ATP hydrolysis and ATP binding.
    BMC Biochemistry 02/2010; 11(1):10. DOI:10.1186/1471-2091-11-10 · 1.44 Impact Factor
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