III Secretion (iii + secretion)

Distribution by Scientific Domains

Kinds of III Secretion

  • type iii secretion

  • Terms modified by III Secretion

  • iii secretion machinery
  • iii secretion system

  • Selected Abstracts

    Type III secretion: The bacteria-eukaryotic cell express

    Luís Jaime Mota
    Abstract Type III secretion (T3S) is an export pathway used by Gram-negative pathogenic bacteria to inject bacterial proteins into the cytosol of eukaryotic host cells. This pathway is characterized by (i) a secretion nanomachine related to the bacterial flagellum, but usually topped by a stiff needle-like structure; (ii) the assembly in the eukaryotic cell membrane of a translocation pore formed by T3S substrates; (iii) a non-cleavable N-terminal secretion signal; (iv) T3S chaperones, assisting the secretion of some substrates; (v) a control mechanism ensuring protein delivery at the right place and time. Here, we review these different aspects focusing in open questions that promise exciting findings in the near future. [source]

    C-ring requirement in flagellar type III secretion is bypassed by FlhDC upregulation

    Marc Erhardt
    Summary The cytoplasmic C-ring of the flagellum consists of FliG, FliM and FliN and acts as an affinity cup to localize secretion substrates for protein translocation via the flagellar-specific type III secretion system. Random T-POP transposon mutagenesis was employed to screen for insertion mutants that allowed flagellar type III secretion in the absence of the C-ring using the flagellar type III secretion system-specific hook,,-lactamase reporter (Lee and Hughes, 2006). Any condition resulting in at least a twofold increase in flhDC expression was sufficient to overcome the requirement for the C-ring and the ATPase complex FliHIJ in flagellar type III secretion. Insertions in known and unknown flagellar regulatory loci were isolated as well as chromosomal duplications of the flhDC region. The twofold increased flhDC mRNA level coincided in a twofold increase in the number of hook-basal bodies per cell as analysed by fluorescent microscopy. These results indicate that the C-ring functions as a nonessential affinity cup-like structure during flagellar type III secretion to enhance the specificity and efficiency of the secretion process. [source]

    A secreted anti-activator, OspD1, and its chaperone, Spa15, are involved in the control of transcription by the type III secretion apparatus activity in Shigella flexneri

    Claude Parsot
    Summary Bacteria of Shigella spp. are responsible for shigellosis in humans and use a type III secretion (TTS) system to enter epithelial cells and trigger apoptosis in macrophages. Transit of translocator and effector proteins through the TTS apparatus is activated upon contact of bacteria with host cells. Transcription of ,15 genes encoding effectors is regulated by the TTS apparatus activity and controlled by MxiE, an AraC family activator, and its coactivator IpgC, the chaperone of IpaB and IpaC translocators. Using a genetic screen, we identified ospD1 as a gene whose product negatively controls expression of genes regulated by secretion activity. OspD1 associates with the chaperone Spa15 and the activator MxiE and acts as an anti-activator until it is secreted. The mechanism regulating transcription in response to secretion activity involves an activator (MxiE), an anti-activator (OspD1), a co-anti-activator (Spa15), a coactivator (IpgC) and two anti-coactivators (IpaB and IpaC) whose alternative and mutually exclusive interactions are controlled by the duration of the TTS apparatus activity. [source]

    A novel sensor kinase,response regulator hybrid regulates type III secretion and is required for virulence in Pseudomonas aeruginosa

    Michelle A. Laskowski
    Summary The type III secretion system (TTSS) of Pseudomonas aeruginosa is induced by contact with eukaryotic cells and by growth in low-calcium media. We have identified a protein, RtsM, that is necessary for expression of the TTSS genes in P. aeruginosa. RtsM possesses both histidine kinase and response regulator domains common to two-component signalling proteins, as well as a large predicted periplasmic domain and seven transmembrane domains. Deletion of rtsM resulted in a defect in production and secretion of the type III effectors. Northern blot analysis revealed that mRNAs encoding the effectors ExoT and ExoU are absent in the ,rtsM strain under TTSS-inducing conditions. Using transcriptional fusions, we demonstrated that RtsM is required for transcription of the operons encoding the TTSS effectors and apparatus in response to calcium limitation or to host cell contact. The operon encoding the TTSS regulator ExsA does not respond to calcium limitation, but the basal transcription rate of this operon was lower in ,rtsM than in the wild-type parent, PA103. The defect in TTSS effector production and secretion of ,rtsM could be complemented by overexpressing ExsA or Vfr, two transcriptional activators involved in TTSS regulation. ,rtsM was markedly less virulent than PA103 in a murine model of acute pneumonia, demonstrating that RtsM is required in vivo. We propose that RtsM is a sensor protein at the start of a signalling cascade that induces expression of the TTSS in response to environmental signals. [source]

    Infection of human mucosal tissue by Pseudomonas aeruginosa requires sequential and mutually dependent virulence factors and a novel pilus-associated adhesin

    Ryan W. Heiniger
    Summary Tissue damage predisposes humans to life-threatening disseminating infection by the opportunistic pathogen Pseudomonas aeruginosa. Bacterial adherence to host tissue is a critical first step in this infection process. It is well established that P. aeruginosa attachment to host cells involves type IV pili (TFP), which are retractile surface fibres. The molecular details of attachment and the identity of the bacterial adhesin and host receptor remain controversial. Using a mucosal epithelium model system derived from primary human tissue, we show that the pilus-associated protein PilY1 is required for bacterial adherence. We establish that P. aeruginosa preferentially binds to exposed basolateral host cell surfaces, providing a mechanistic explanation for opportunistic infection of damaged tissue. Further, we demonstrate that invasion and fulminant infection of intact host tissue requires the coordinated and mutually dependent action of multiple bacterial factors, including pilus fibre retraction and the host cell intoxication system, termed type III secretion. Our findings offer new and important insights into the complex interactions between a pathogen and its human host and provide compelling evidence that PilY1 serves as the principal P. aeruginosa adhesin for human tissue and that it specifically recognizes a host receptor localized or enriched on basolateral epithelial cell surfaces. [source]

    Conserved features of type III secretion

    A. P. Tampakaki
    Summary Type III secretion systems (TTSSs) are essential mediators of the interaction of many Gram-negative bacteria with human, animal or plant hosts. Extensive sequence and functional similarities exist between components of TTSS from bacteria as diverse as animal and plant pathogens. Recent crystal structure determinations of TTSS proteins reveal extensive structural homologies and novel structural motifs and provide a basis on which protein interaction networks start to be drawn within the TTSSs, that are consistent with and help rationalize genetic and biochemical data. Such studies, along with electron microscopy, also established common architectural design and function among the TTSSs of plant and mammalian pathogens, as well as between the TTSS injectisome and the flagellum. Recent comparative genomic analysis, bioinformatic genome mining and genome-wide functional screening have revealed an unsuspected number of newly discovered effectors, especially in plant pathogens and uncovered a wider distribution of TTSS in pathogenic, symbiotic and commensal bacteria. Functional proteomics and analysis further reveals common themes in TTSS effector functions across phylogenetic host and pathogen boundaries. Based on advances in TTSS biology, new diagnostics, crop protection and drug development applications, as well as new cell biology research tools are beginning to emerge. [source]