Cognate gene clusters govern invasion of host epithelial cells by Salmonella typhimurium and Shigella flexneri.

120

SummaryMost of the structural components of the flagellum of Salmonella typhimurium are exported through a flagellum-specific pathway, which is a member of the family of type III secretory pathways. The export apparatus for this process is poorly understood. A previous study has shown that two proteins, about 23 and 26 kDa in size and of unknown genetic origin, are incorporated into the flagellar basal body at a very early stage of flagellar assembly. In the present study, we demonstrate that these basal body proteins are FliP (in its mature form after signal peptide cleavage) and FliR respectively. Both of these proteins have homologues in other type III secretion systems. By placing a FLAG epitope tag on FliR and the MS-ring protein FliF and immunoblotting isolated hook basal body complexes with anti-FLAG monoclonal antibody, we estimate (using the FLAG-tagged FliF as an internal reference) that the stoichiometry of FliR is fewer than three copies per basal body. An independent estimate of stoichiometry was made using data from an earlier quantitative radiolabelling analysis, yielding values of around four or five subunits per basal body for FliP and around one subunit per basal body for FliR. Immunoelectron microscopy using anti-FLAG antibody and gold-protein A suggests that FliR is located near the MS ring. We propose that the flagellar export apparatus contains FliP and FliR and that this apparatus is embedded in a patch of membrane in the central pore of the MS ring.

Section: How Do Flip and Flir Reach Their Location?mentioning

confidence: 99%

The FliP and FliR proteins of Salmonella typhimurium, putative components of the type III flagellar export apparatus, are located in the flagellar basal body

Fan

Ohnishi

Francis

et al. 1997

120

“…A growing number of animal and plant pathogens, including Salmonella, Shigella, Yersinia, Erwinia and Xanthomonas species, have been found to encode related type III secretion systems, which govern the secretion of virulence effectors (Groisman and Ochman, 1993;Van Gijsegem et al, 1993;1995;Bergman et al, 1994;Wood et al, 1996). Recently, the opportunistic pathogen P. aeruginosa was reported to possess a type III system by which it secretes several proteins including exoenzyme S (ExoS) (Yahr et al, 1996).…”

Section: Introductionmentioning

confidence: 99%

Intracellular targeting of exoenzyme S of Pseudomonas aeruginosa via type III‐dependent translocation induces phagocytosis resistance, cytotoxicity and disruption of actin microfilaments

Frithz‐Lindsten

Rosqvist

et al. 1997

198

262

SummaryExoenzyme S (ExoS) is an ADP-ribosyltransferase secreted by the opportunistic pathogen Pseudomonas aeruginosa. The amino-terminal half of ExoS exhibits homology to the YopE cytotoxin of pathogenic Yersinia. Recently, YopE was found to be translocated into the host cell by a bacteria-cell contact-dependent mechanism involving the ysc-encoded type III secretion system. By using an approach in which exoS was expressed in different strains of Yersinia, including secretion and translocation mutants, we could demonstrate that ExoS was secreted and translocated into HeLa cells by a similar mechanism to that described previously for YopE. Similarly to YopE, the presence of ExoS in the host cell elicited a cytotoxic response, correlating with disruption of the actin microfilament structure. A similar cytotoxic response was also induced by a mutated form of ExoS with a more than 2000-fold reduced ADP-ribosyltransferase activity. However, the enzymatically active ExoS elicited a more definite rounding up of the HeLa cells, which also correlated with decreased viability of the cells after prolonged infection compared with cells infected with strains expressing mutated ExoS or YopE. This suggests that ExoS can act through two different mechanisms on the host cell. The expression of ExoS by Yersinia also mediated an anti-phagocytic effect on macrophages. In addition, we present evidence that extracellularly located P. aeruginosa is able to target ExoS into eukaryotic cells. Taken together, our data suggest that P. aeruginosa, by analogy with Yersinia, targets virulence proteins into the eukaryotic cytosol via a type III secretion-dependent mechanism as part of an anti-phagocytic strategy.

“…Type III secretion systems have been found in a variety of bacterial pathogens of animals and plants including Yersinia spp., Shigella flexneri, Salmonella typhimurium, and Erwinia amylovora (van Gijsegem et al, 1993;Groisman and Ochman, 1993). Although many components of the secretion machinery have been conserved in the evolution of these bacteria, the effectors are species-specific and have different functions.…”

Section: Introductionmentioning

confidence: 99%

Functional analysis of ssaJ and the ssaK/U operon, 13 genes encoding components of the type III secretion apparatus of Salmonella Pathogenicity Island 2

Hensel

Shea

Raupach

et al. 1997

163

186

SummaryWe have investigated the structure and transcriptional organization of 13 genes of Salmonella Pathogenicity Island 2 (SPI2) that encode components of the second type III secretion apparatus of Salmonella typhimurium. ssaK, L, M, V, N, O, P, Q, R, S, T, U constitute one operon of 10 kb. ssaJ lies upstream of ssaK and is the terminal gene of another operon. The deduced products of ssaJ, ssaK, ssaV, ssaN, ssaO, ssaQ, ssaR, ssaS, ssaT, and ssaU show greatest similarity to the Yersinia spp. genes yscJ, yscL, lcrD, yscN, yscO, yscQ, yscR, yscS, yscT, and yscU, respectively. The products of the ssaL, ssaM and ssaP genes do not have significant similarity to products of other type III secretion systems, and might be important for the specific function of the SPI2 type III secretion system. Bacterial strains carrying different ssa mutations display minor alterations in terms of serum sensitivity when compared with the wild-type strain, but none are defective in replication within macrophage-like RAW 264.7 cells. However, some of the ssa mutant strains invade HEp2 cells less efficiently and are less cytotoxic to RAW 264.7 macrophages than the wild-type strain. We show that the invasion defect is correlated with a lack of SipC in culture supernatants of these mutant strains.SipC is a product of the SPI1 type III secretion system of S. typhimurium, and is important for epithelial cell invasion. Therefore, mutations in SPI2 can affect the SPI1 secretion system, which raises the possibility of an interaction between the two type III secretion systems.