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Type III Secretion Machinery (type + iii_secretion_machinery)

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Life Sciences100%

Selected Abstracts

IpgD, a protein secreted by the type III secretion machinery of Shigella flexneri, is chaperoned by IpgE and implicated in entry focus formation

MOLECULAR MICROBIOLOGY, Issue 1 2000
Kirsten Niebuhr
Invasion of epithelial cells by Shigella flexneri involves entry and intercellular dissemination. Entry of bacteria into non-phagocytic cells requires the IpaA,D proteins that are secreted by the Mxi,Spa type III secretion machinery. Type III secretion systems are found in several Gram-negative pathogens and serve to inject bacterial effector proteins directly into the cytoplasm of host cells. In this study, we have analysed the IpgD protein of S. flexneri, the gene of which is located on the virulence plasmid at the 5, end of the mxi,spa locus. We have shown that IpgD (i) is stored in the bacterial cytoplasm in association with a specific chaperone, IpgE; (ii) is secreted by the Mxi,Spa type III secretion system in amounts similar to those of the IpaA,D proteins; (iii) is associated with IpaA in the extracellular medium; and (iv) is involved in the modulation of the host cell response after contact of the bacterium with epithelial cells. This suggests that IpgD is an effector that might be injected into host cells to manipulate cellular processes during infection. [source]

From bacterial avirulence genes to effector functions via the hrp delivery system: an overview of 25 years of progress in our understanding of plant innate immunity

MOLECULAR PLANT PATHOLOGY, Issue 6 2009
JOHN W. MANSFIELD
SUMMARY Cloning the first avirulence (avr) gene has led not only to a deeper understanding of gene-for-gene interactions in plant disease, but also to fundamental insights into the suppression of basal defences against microbial attack. This article (focusing on Pseudomonas syringae) charts the development of ideas and research progress over the 25 years following the breakthrough achieved by Staskawicz and coworkers. Advances in gene cloning technology underpinned the identification of both avr and hrp genes, the latter being required for the activation of the defensive hypersensitive reaction (HR) and pathogenicity. The delivery of Avr proteins through the type III secretion machinery encoded by hrp gene clusters was demonstrated, and the activity of the proteins inside plant cells as elicitors of the HR was confirmed. Key roles for avr genes in pathogenic fitness have now been established. The rebranding of Avr proteins as effectors, proteins that suppress the HR and cell wall-based defences, has led to the ongoing search for their targets, and is generating new insights into the co-ordination of plant resistance against diverse microbes. Bioinformatics-led analysis of effector gene distribution in genomes has provided a remarkable view of the interchange of effectors and also their functional domains, as the arms race of attack and defence drives the evolution of microbial pathogenicity. The application of our accrued knowledge for the development of disease control strategies is considered. [source]

BopB is a type III secreted protein in Bordetella bronchiseptica and is required for cytotoxicity against cultured mammalian cells

CELLULAR MICROBIOLOGY, Issue 12 2003
Asaomi Kuwae
Summary The cytotoxicity of Bordetella bronchiseptica to infected cells is known to be dependent on a B. bronchiseptica type III secretion system. Although the precise mechanism of the type III secretion system is unknown, BopN, BopD and Bsp22 have been identified as type III secreted proteins. In order to identify other proteins secreted via the type III secretion machinery in Bordetella, a type III mutant was generated, and its secretion profile was compared with that of the wild-type strain. The results showed that the wild-type strain, but not the type III mutant, secreted a 40-kDa protein into the culture supernatant. This protein was identified as BopB by the analysis of its N-terminal amino acid sequence. Severe cytotoxicity such as necrosis was induced in L2 cells by infection with the wild-type B. bronchiseptica. In contrast, this effect was not observed by the BopB mutant infection. The haemolytic activity of the BopB mutant was greatly impaired compared with that of the wild-type strain. The results of a digitonin assay strongly suggested that BopB was translocated into HeLa cells infected with the wild-type strain. Taken together, our results demonstrate that Bordetella secretes BopB via a type III secretion system during infection. BopB may play a role in the formation of pores in the host plasma membrane which serve as a conduit for the translocation of effector proteins into host cells. [source]