Type III Secretion: Building and Operating a Remarkable Nanomachine

Portaliou, Athina G; Tsolis, Konstantinos C.; Loos, Maria S; Zorzini, Valentina; Economou, Anastassios

doi:10.1016/j.tibs.2015.09.005

Cited by 153 publications

(148 citation statements)

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“…Recent advances in assembly, structure, and mechanistic studies have considerably increased our current understanding of the function of this macromolecular complex (62)(63)(64)(65). Despite this, there are still several gaps in our knowledge on the molecular mechanisms underlying effector protein translocation into host cells.…”

Section: Discussionmentioning

confidence: 99%

Functional Characterization of EscK (Orf4), a Sorting Platform Component of the Enteropathogenic Escherichia coli Injectisome

et al. 2017

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The type III secretion system (T3SS) is a supramolecular machine used by many bacterial pathogens to translocate effector proteins directly into the eukaryotic host cell cytoplasm. Enteropathogenic Escherichia coli (EPEC) is an important cause of infantile diarrheal disease in underdeveloped countries. EPEC virulence relies on a T3SS encoded within a chromosomal pathogenicity island known as the locus of enterocyte effacement (LEE). In this work, we pursued the functional characterization of the LEE-encoded protein EscK (previously known as Orf4). We provide evidence indicating that EscK is crucial for efficient T3S and belongs to the SctK (OrgA/YscK/MxiK) protein family, whose members have been implicated in the formation of a sorting platform for secretion of T3S substrates. Bacterial fractionation studies showed that EscK localizes to the inner membrane independently of the presence of any other T3SS component. Combining yeast two-hybrid screening and pulldown assays, we identified an interaction between EscK and the C-ring/sorting platform component EscQ. Site-directed mutagenesis of conserved residues revealed amino acids that are critical for EscK function and for its interaction with EscQ. In addition, we found that T3S substrate overproduction is capable of compensating for the absence of EscK. Overall, our data suggest that EscK is a structural component of the EPEC T3SS sorting platform, playing a central role in the recruitment of T3S substrates for boosting the efficiency of the protein translocation process.IMPORTANCE The type III secretion system (T3SS) is an essential virulence determinant for enteropathogenic Escherichia coli (EPEC) colonization of intestinal epithelial cells. Multiple EPEC effector proteins are injected via the T3SS into enterocyte cells, leading to diarrheal disease. The T3SS is encoded within a genomic pathogenicity island termed the locus of enterocyte effacement (LEE). Here we unravel the function of EscK, a previously uncharacterized LEE-encoded protein. We show that EscK is central for T3SS biogenesis and function. EscK forms a protein complex with EscQ, the main component of the cytoplasmic sorting platform, serving as a docking site for T3S substrates. Our results provide a comprehensive functional analysis of an understudied component of T3SSs.

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Section: Discussionmentioning

confidence: 99%

Functional Characterization of EscK (Orf4), a Sorting Platform Component of the Enteropathogenic Escherichia coli Injectisome

et al. 2017

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“…Pathogenic isolates of V. parahaemolyticus encode two type III secretion systems (T3SSs), which are multiprotein structures that mediate the translocation of bacterial effector proteins directly into eukaryotic cells (4,6). All V. parahaemolyticus strains encode a T3SS on the large chromosome (T3SS1), and the vast majority of clinical isolates, but few environmental isolates possess a horizontally acquired pathogenicity island (VPaI-7) encoding a second T3SS (T3SS2) and one or more pore-forming toxins (TDH) (7).…”

mentioning

confidence: 99%

Genetic analysis of Vibrio parahaemolyticus intestinal colonization

Hubbard

Chao

Abel

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

104

122

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Vibrio parahaemolyticus is the most common cause of seafood-borne gastroenteritis worldwide and a blight on global aquaculture. This organism requires a horizontally acquired type III secretion system (T3SS2) to infect the small intestine, but knowledge of additional factors that underlie V. parahaemolyticus pathogenicity is limited. We used transposon-insertion sequencing to screen for genes that contribute to viability of V. parahaemolyticus in vitro and in the mammalian intestine. Our analysis enumerated and controlled for the host infection bottleneck, enabling robust assessment of genetic contributions to in vivo fitness. We identified genes that contribute to V. parahaemolyticus colonization of the intestine independent of known virulence mechanisms in addition to uncharacterized components of T3SS2. Our study revealed that toxR, an ancestral locus in Vibrio species, is required for V. parahaemolyticus fitness in vivo and for induction of T3SS2 gene expression. The regulatory mechanism by which V. parahaemolyticus ToxR activates expression of T3SS2 resembles Vibrio cholerae ToxR regulation of distinct virulence elements acquired via lateral gene transfer. Thus, disparate horizontally acquired virulence systems have been placed under the control of this ancestral transcription factor across independently evolved human pathogens.Vibrio parahaemolyticus | transposon-insertion sequencing | type III secretion | bacterial pathogenesis | pathogen evolution T he gram-negative γ-proteobacterium Vibrio parahaemolyticus thrives in either pathogenic or symbiotic association with marine organisms and as a planktonic bacterium (1). This facultative human pathogen, abundant in aquatic environments, was first isolated following a food poisoning outbreak in 1952 and has emerged as the leading cause of seafood-associated gastroenteritis worldwide and a blight on global aquaculture (2, 3). Sequencing of the V. parahaemolyticus genome and the development of animal models of infection have demonstrated a critical role for type III secretion in V. parahaemolyticus virulence (4, 5).Pathogenic isolates of V. parahaemolyticus encode two type III secretion systems (T3SSs), which are multiprotein structures that mediate the translocation of bacterial effector proteins directly into eukaryotic cells (4, 6). All V. parahaemolyticus strains encode a T3SS on the large chromosome (T3SS1), and the vast majority of clinical isolates, but few environmental isolates possess a horizontally acquired pathogenicity island (VPaI-7) encoding a second T3SS (T3SS2) and one or more pore-forming toxins (TDH) (7). Studies using the infant rabbit model of V. parahaemolyticus infection, which recapitulates manifestations of human gastrointestinal disease (e.g., profuse diarrhea, enteritis, epithelial disruption), revealed that although T3SS1 and TDH are dispensable for intestinal colonization and pathogenesis, colonization and pathology are dependent on T3SS2, consistent with the epidemiological association between T3SS2 and pathogenicity (5). Furthermor...

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“…The regulatory complexity of these systems appears to be even more enigmatic: a recent study proposes a "bistability" model for hrp/hrc-I systems involving the action of the doublenegative regulatory feedback loop involving HrpV and HrpG and a positive loop involving the main component of the pilus, HrpA (95). It appears that protein secretion through the T3SS is a highly regulated process, involving multiprotein interaction networks coupling expression regulation to secretion, making the T3SS one of the most complex bacterial protein secretion systems known (88). In contrast to the structural complexity of T3SSs, most hrp/hrc operons seem to be induced almost simultaneously without any pattern that would help integrate the ordered assembly of the export apparatus (74,110).…”

Section: Identification Of Hrpr/s/l Regulatory Trio: Only the Beginningmentioning

confidence: 99%

“…Gene Ontology, along with numerous biochemical studies, established the existence of at least six major protein secretion systems in gram-negative bacterial species. The pathways have been numbered Type I through VI (88).…”

Section: Sequence Similarities To Mammalian Type III Secretion Systemmentioning

confidence: 99%

A Career on Both Sides of the Atlantic: Memoirs of a Molecular Plant Pathologist

Panopoulos

2017

Annu. Rev. Phytopathol.

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This article recounts the experiences that shaped my career as a molecular plant pathologist. It focuses primarily on technical and conceptual developments in molecular phytobacteriology, shares some personal highlights and untold stories that impacted my professional development, and describes the early years of agricultural biotechnology. Writing this article required reflection on events occurring over several decades that were punctuated by a mid-career relocation across the Atlantic. I hope it will still be useful, informative, and enjoyable to read.

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Type III Secretion: Building and Operating a Remarkable Nanomachine

Cited by 153 publications

References 120 publications

Functional Characterization of EscK (Orf4), a Sorting Platform Component of the Enteropathogenic Escherichia coli Injectisome

Functional Characterization of EscK (Orf4), a Sorting Platform Component of the Enteropathogenic Escherichia coli Injectisome

Genetic analysis of Vibrio parahaemolyticus intestinal colonization

A Career on Both Sides of the Atlantic: Memoirs of a Molecular Plant Pathologist

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