Dataset Information

Francisella tularensis IglG Belongs to a Novel Family of PAAR-Like T6SS Proteins and Harbors a Unique N-terminal Extension Required for Virulence.

ABSTRACT: The virulence of Francisella tularensis, the etiological agent of tularemia, relies on an atypical type VI secretion system (T6SS) encoded by a genomic island termed the Francisella Pathogenicity Island (FPI). While the importance of the FPI in F. tularensis virulence is clearly established, the precise role of most of the FPI-encoded proteins remains to be deciphered. In this study, using highly virulent F. tularensis strains and the closely related species F. novicida, IglG was characterized as a protein featuring a unique ?-helical N-terminal extension and a domain of unknown function (DUF4280), present in more than 250 bacterial species. Three dimensional modeling of IglG and of the DUF4280 consensus protein sequence indicates that these proteins adopt a PAAR-like fold, suggesting they could cap the T6SS in a similar way as the recently described PAAR proteins. The newly identified PAAR-like motif is characterized by four conserved cysteine residues, also present in IglG, which may bind a metal atom. We demonstrate that IglG binds metal ions and that each individual cysteine is required for T6SS-dependent secretion of IglG and of the Hcp homologue, IglC and for the F. novicida intracellular life cycle. In contrast, the Francisella-specific N-terminal ?-helical extension is not required for IglG secretion, but is critical for F. novicida virulence and for the interaction of IglG with another FPI-encoded protein, IglF. Altogether, our data suggest that IglG is a PAAR-like protein acting as a bi-modal protein that may connect the tip of the Francisella T6SS with a putative T6SS effector, IglF.

SUBMITTER: Rigard M

PROVIDER: S-EPMC5014421 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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Francisella tularensis IglG Belongs to a Novel Family of PAAR-Like T6SS Proteins and Harbors a Unique N-terminal Extension Required for Virulence.

Rigard Mélanie M Bröms Jeanette E JE Mosnier Amandine A Hologne Maggy M Martin Amandine A Lindgren Lena L Punginelli Claire C Lays Claire C Walker Olivier O Charbit Alain A Telouk Philippe P Conlan Wayne W Terradot Laurent L Sjöstedt Anders A Henry Thomas T

PLoS pathogens 20160907 9

The virulence of Francisella tularensis, the etiological agent of tularemia, relies on an atypical type VI secretion system (T6SS) encoded by a genomic island termed the Francisella Pathogenicity Island (FPI). While the importance of the FPI in F. tularensis virulence is clearly established, the precise role of most of the FPI-encoded proteins remains to be deciphered. In this study, using highly virulent F. tularensis strains and the closely related species F. novicida, IglG was characterized a ...[more]

PMID: 27602570

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Project description:The alarmone ppGpp is a critical regulator of virulence gene expression in Francisella tularensis In this intracellular pathogen, ppGpp is thought to work in concert with the putative DNA-binding protein PigR and the SspA protein family members MglA and SspA to control a common set of genes. MglA and SspA form a complex that interacts with RNA polymerase (RNAP), and PigR functions by interacting with the RNAP-associated MglA-SspA complex. Prior work suggested that ppGpp indirectly exerts its regulatory effects in F. tularensis by promoting the accumulation of polyphosphate in the cell, which in turn was required for formation of the MglA-SspA complex. Here we show that in Escherichia coli, neither polyphosphate nor ppGpp is required for formation of the MglA-SspA complex but that ppGpp promotes the interaction between PigR and the MglA-SspA complex. Moreover, we show that polyphosphate kinase, the enzyme responsible for the synthesis of polyphosphate, antagonizes virulence gene expression in F. tularensis, a finding that is inconsistent with the notion that polyphosphate accumulation promotes virulence gene expression in this organism. Our findings identify polyphosphate kinase as a novel negative regulator of virulence gene expression in F. tularensis and support a model in which ppGpp exerts its positive regulatory effects by promoting the interaction between PigR and the MglA-SspA complex.IMPORTANCE In Francisella tularensis, MglA and SspA form a complex that associates with RNA polymerase to positively control the expression of key virulence genes. The MglA-SspA complex works together with the putative DNA-binding protein PigR and the alarmone ppGpp. PigR functions by interacting directly with the MglA-SspA complex, but how ppGpp exerts its effects was unclear. Prior work indicated that ppGpp acts by promoting the accumulation of polyphosphate, which is required for MglA and SspA to interact. Here we show that formation of the MglA-SspA complex does not require polyphosphate. Furthermore, we find that polyphosphate antagonizes the expression of virulence genes in F. tularensis Thus, ppGpp does not promote virulence gene expression in this organism through an effect on polyphosphate.

Project description:The highly infectious bacterium Francisella tularensis is a facultative intracellular pathogen, whose virulence requires proliferation inside host cells, including macrophages. Although some Francisella determinants of intracellular growth have been identified, much remains to be understood about the pathogenesis of this organism. In particular, how Francisella responds to its intracellular environment could provide clues about its intracellular biology and reveal pathogenic determinants based on their intracellular expression profiles. Here we have performed a global transcriptional profiling of the highly virulent F. tularensis subsp. tularensis Schu S4 strain during its intracellular cycle within primary murine macrophages. Phagocytosed bacteria rapidly responded to their intracellular environment and progressively altered their transcriptional profile over time. Differential gene expression profiles were revealed that correlated with specific intracellular locations of the bacteria. Upregulation of general and oxidative stress response genes was a hallmark of the early phagosomal and late endosomal stages, while induction of a subset of transport and metabolic genes characterized the cytosolic replication stages. Expression of the Francisella Pathogenicity Island (FPI) genes, the functions of which are associated with intracellular proliferation, increased during the intracellular cycle. Similarly, 27 chromosomal loci putatively encoding hypothetical, secreted, outer membrane proteins or transcriptional regulators were identified as upregulated during the intracellular cycle. In-frame deletion of FTT0383, the Schu S4 ortholog of fevR, of FTT0369c or FTT1676 abolished the ability of Schu S4 to either survive or proliferate intracellularly, demonstrating that bacterial factors of intracellular pathogenesis can be identified based on their intracellular expression profile. In conclusion, establishing the intracellular transcriptome of Francisella has revealed important aspects of its intracellular biology and identified novel virulence determinants of this pathogen. Keywords: Time series

Dataset Information

Francisella tularensis IglG Belongs to a Novel Family of PAAR-Like T6SS Proteins and Harbors a Unique N-terminal Extension Required for Virulence.

Publications

Francisella tularensis IglG Belongs to a Novel Family of PAAR-Like T6SS Proteins and Harbors a Unique N-terminal Extension Required for Virulence.

Similar Datasets

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