scholarly journals Molecular Mechanisms of Bacterial Virulence: Type III Secretion and Pathogenicity Islands

1996 ◽  
Vol 2 (4) ◽  
pp. 271-288 ◽  
Author(s):  
Joan Mecsas
Keyword(s):  
Type Iii Secretion ◽  
Molecular Mechanisms ◽  
Bacterial Virulence ◽  
Pathogenicity Islands ◽  
Type Iii

scholarly journals A Phosphorylation Switch on Lon Protease Regulates Bacterial Type III Secretion System in Host

mBio ◽  
2018 ◽  
Vol 9 (1) ◽  
Author(s):  
Xiaofeng Zhou ◽  
Doron Teper ◽  
Maxuel O. Andrade ◽  
Tong Zhang ◽  
Sixue Chen ◽  
...  
Keyword(s):  
Proteolytic Activity ◽  
Virulence Factors ◽  
Type Iii Secretion ◽  
Molecular Mechanisms ◽  
Bacterial Virulence ◽  
Lon Protease ◽  
Rich Medium ◽  
Secretion Systems ◽  
Type Iii ◽  
Type Iii Secretion Systems

ABSTRACT Most pathogenic bacteria deliver virulence factors into host cytosol through type III secretion systems (T3SS) to perturb host immune responses. The expression of T3SS is often repressed in rich medium but is specifically induced in the host environment. The molecular mechanisms underlying host-specific induction of T3SS expression is not completely understood. Here we demonstrate in Xanthomonas citri that host-induced phosphorylation of the ATP-dependent protease Lon stabilizes HrpG, the master regulator of T3SS, conferring bacterial virulence. Ser/Thr/Tyr phosphoproteome analysis revealed that phosphorylation of Lon at serine 654 occurs in the citrus host. In rich medium, Lon represses T3SS by degradation of HrpG via recognition of its N terminus. Genetic and biochemical data indicate that phosphorylation at serine 654 deactivates Lon proteolytic activity and attenuates HrpG proteolysis. Substitution of alanine for Lon serine 654 resulted in repression of T3SS gene expression in the citrus host through robust degradation of HrpG and reduced bacterial virulence. Our work reveals a novel mechanism for distinct regulation of bacterial T3SS in different environments. Additionally, our data provide new insight into the role of protein posttranslational modification in the regulation of bacterial virulence. IMPORTANCE Type III secretion systems (T3SS) are an essential virulence trait of many bacterial pathogens because of their indispensable role in the delivery of virulence factors. However, expression of T3SS in the noninfection stage is energy consuming. Here, we established a model to explain the differential regulation of T3SS in host and nonhost environments. When Xanthomonas cells are grown in rich medium, the T3SS regulator HrpG is targeted by Lon protease for proteolysis. The degradation of HrpG leads to downregulated expression of HrpX and the hrp/hrc genes. When Xanthomonas cells infect the host, specific plant stimuli can be perceived and induce Lon phosphorylation at serine 654. Phosphorylation on Lon attenuates its proteolytic activity and protects HrpG from degradation. Consequently, enhanced stability of HrpG activates HrpX and turns on bacterial T3SS in the host. Our work provides a novel molecular mechanism underlying host-dependent activation of bacterial T3SS.

scholarly journals A NanoLuc luciferase-based assay enabling the real-time analysis of protein secretion and injection by bacterial type III secretion systems

2019 ◽  
Author(s):  
Sibel Westerhausen ◽  
Melanie Nowak ◽  
Claudia Torres-Vargas ◽  
Ursula Bilitewski ◽  
Erwin Bohn ◽  
...  
Keyword(s):  
Protein Secretion ◽  
High Throughput ◽  
Type Iii Secretion ◽  
Molecular Mechanisms ◽  
Host Cells ◽  
Target Cells ◽  
Secretion Systems ◽  
Type Iii ◽  
Nanoluc Luciferase ◽  
Type Iii Secretion Systems

AbstractThe elucidation of the molecular mechanisms of secretion through bacterial protein secretion systems is impeded by a lack of assays to quantitatively assess secretion kinetics. Also the analysis of the biological role of these secretion systems as well as the identification of inhibitors targeting these systems would greatly benefit from the availability of a simple, quick and quantitative assay to monitor principle secretion and injection into host cells. Here we present a versatile solution to this need, utilizing the small and very bright NanoLuc luciferase to assess secretion and injection through the type III secretion system encoded by Salmonella pathogenicity island 1. The NanoLuc-based secretion assay features a very high signal-to-noise ratio and sensitivity down to the nanoliter scale. The assay enables monitoring of secretion kinetics and is adaptable to a high throughput screening format in 384-well microplates. We further developed NanoLuc and split-NanoLuc-based assays that enable the monitoring of type III secretion-dependent injection of effector proteins into host cells.ImportanceThe ability to secrete proteins to the bacterial cell surface, to the extracellular environment, or even into target cells is one of the foundations of interbacterial as well as pathogen-host interaction. While great progress has been made in elucidating assembly and structure of secretion systems, our understanding of their secretion mechanism often lags behind, not last because of the challenge to quantitatively assess secretion function. Here, we developed a luciferase-based assay to enable the simple, quick, quantitative, and high throughput-compatible assessment of secretion and injection through virulence-associated type III secretion systems. The assay allows detection of minute amounts of secreted substrate proteins either in the supernatant of the bacterial culture or within eukaryotic host cells. It thus provides an enabling technology to elucidate the mechanisms of secretion and injection of type III secretion systems and is likely adaptable to assay secretion through other bacterial secretion systems.

scholarly journals Posttranscriptional Control of Microbe-Induced Rearrangement of Host Cell Actin

mBio ◽  
2014 ◽  
Vol 5 (1) ◽  
Author(s):  
Charley C. Gruber ◽  
Vanessa Sperandio
Keyword(s):  
Escherichia Coli ◽  
Host Cell ◽  
Type Iii Secretion ◽  
Cell Biology ◽  
Molecular Mechanisms ◽  
Bacterial Attachment ◽  
Posttranscriptional Control ◽  
Content Type ◽  
Type Iii ◽  
Pedestal Formation

ABSTRACTRemodeling of the host cytoskeleton is a common strategy employed by bacterial pathogens. Although there is vigorous investigation of the cell biology underlying these bacterially mediated cytoskeleton modifications, knowledge of the plasticity and dynamics of the bacterial signaling networks that regulate the expression of genes necessary for these phenotypes is lacking. EnterohemorrhagicEscherichia coliattaches to enterocytes, forming pedestal-like structures. Pedestal formation requires the expression of the locus-of-enterocyte-effacement (LEE) andespFugenes. The LEE encodes a molecular syringe, a type III secretion system (T3SS) used by pathogens to translocate effectors such as EspFu into the host cell. By using a combination of genetic, biochemical, and cell biology approaches, we show that pedestal formation relies on posttranscriptional regulation by two small RNAs (sRNAs), GlmY and GlmZ. The GlmY and GlmZ sRNAs are unique; they have extensive secondary structures and work in concert. Although these sRNAs may offer unique insights into RNA and posttranscriptional biology, thus far, only one target and one mechanism of action (exposure of the ribosome binding site from theglmSgene to promote its translation) has been described. Here we uncovered new targets and two different molecular mechanisms of action of these sRNAs. In the case of EspFu expression, they promote translation by cleavage of the transcript, while in regard to the LEE, they promote destabilization of the mRNA. Our findings reveal that two unique sRNAs act in concert through different molecular mechanisms to coordinate bacterial attachment to mammalian cells.IMPORTANCEPathogens evolve by horizontal acquisition of pathogenicity islands. We describe here how two sRNAs, GlmY and GlmZ, involved in cellular metabolism and cellular architecture, through the posttranscriptional control of GlmS (the previously only known target of GlmY and GlmZ), which controls amino sugar synthesis, have been coopted to modulate the expression of virulence. These sRNAs quickly allow for plasticity in gene expression in order for enterohemorrhagicEscherichia colito fine-tune the expression of its complex type III secretion machinery and its effectors to promote bacterial attachment and subsequent actin rearrangement on host cells. Pedestal formation is a very dynamic process. Many of the genes necessary for pedestal formation are located within the same operon to evolutionarily guarantee that they are inherited together. However, it is worth noting that within these operons, several genes need to yield more proteins than others and that these differences cannot be efficiently regulated at the transcriptional level.

scholarly journals The Ruler Protein EscP of the Enteropathogenic Escherichia coli Type III Secretion System Is Involved in Calcium Sensing and Secretion Hierarchy Regulation by Interacting with the Gatekeeper Protein SepL

mBio ◽  
2017 ◽  
Vol 8 (1) ◽  
Author(s):  
Lihi Shaulov ◽  
Jenia Gershberg ◽  
Wanyin Deng ◽  
B. Brett Finlay ◽  
Neta Sal-Man
Keyword(s):  
Host Cell ◽  
Type Iii Secretion ◽  
Bacterial Pathogens ◽  
Type Iii Secretion System ◽  
Secretion System ◽  
Bacterial Virulence ◽  
Effector Proteins ◽  
Host Cells ◽  
Gram Negative ◽  
Type Iii

ABSTRACT The type III secretion system (T3SS) is a multiprotein complex that plays a central role in the virulence of many Gram-negative bacterial pathogens. To ensure that effector proteins are efficiently translocated into the host cell, bacteria must be able to sense their contact with the host cell. In this study, we found that EscP, which was previously shown to function as the ruler protein of the enteropathogenic Escherichia coli T3SS, is also involved in the switch from the secretion of translocator proteins to the secretion of effector proteins. In addition, we demonstrated that EscP can interact with the gatekeeper protein SepL and that the EscP-SepL complex dissociates upon a calcium concentration drop. We suggest a model in which bacterial contact with the host cell is accompanied by a drop in the calcium concentration that causes SepL-EscP complex dissociation and triggers the secretion of effector proteins. IMPORTANCE The emergence of multidrug-resistant bacterial strains, especially those of pathogenic bacteria, has serious medical and clinical implications. At the same time, the development and approval of new antibiotics have been limited for years. Recently, antivirulence drugs have received considerable attention as a novel antibiotic strategy that specifically targets bacterial virulence rather than growth, an approach that applies milder evolutionary pressure on the bacteria to develop resistance. A highly attractive target for the development of antivirulence compounds is the type III secretion system, a specialized secretory system possessed by many Gram-negative bacterial pathogens for injecting virulence factors (effectors) into host cells. In this study, we shed light on the molecular mechanism that allows bacteria to sense their contact with the host cell and to respond with the timed secretion of effector proteins. Understanding this critical step for bacterial virulence may provide a new therapeutic strategy. IMPORTANCE The emergence of multidrug-resistant bacterial strains, especially those of pathogenic bacteria, has serious medical and clinical implications. At the same time, the development and approval of new antibiotics have been limited for years. Recently, antivirulence drugs have received considerable attention as a novel antibiotic strategy that specifically targets bacterial virulence rather than growth, an approach that applies milder evolutionary pressure on the bacteria to develop resistance. A highly attractive target for the development of antivirulence compounds is the type III secretion system, a specialized secretory system possessed by many Gram-negative bacterial pathogens for injecting virulence factors (effectors) into host cells. In this study, we shed light on the molecular mechanism that allows bacteria to sense their contact with the host cell and to respond with the timed secretion of effector proteins. Understanding this critical step for bacterial virulence may provide a new therapeutic strategy.

scholarly journals Small molecules aimed at type III secretion systems to inhibit bacterial virulence

MedChemComm ◽  
2013 ◽  
Vol 4 (1) ◽  
pp. 68-79 ◽  
Author(s):  
Lun K. Tsou ◽  
Paul D. Dossa ◽  
Howard C. Hang
Keyword(s):  
Small Molecules ◽  
Type Iii Secretion ◽  
Modern Medicine ◽  
Bacterial Virulence ◽  
Bacterial Strains ◽  
Secretion Systems ◽  
Type Iii ◽  
Type Iii Secretion Systems

The development of new anti-bacterial compounds presents a major challenge to modern medicine as bacterial strains resistant to traditional antibiotics are constantly emerging.

scholarly journals The Type III Secretion Chaperone HpaB Controls the Translocation of Effector and Noneffector Proteins From Xanthomonas campestris pv. vesicatoria

2018 ◽  
Vol 31 (1) ◽  
pp. 61-74 ◽  
Author(s):  
Felix Scheibner ◽  
Nadine Hartmann ◽  
Jens Hausner ◽  
Christian Lorenz ◽  
Anne-Katrin Hoffmeister ◽  
...  
Keyword(s):  
Type Iii Secretion ◽  
Type Strain ◽  
Xanthomonas Campestris ◽  
Molecular Mechanisms ◽  
Wild Type Strain ◽  
Effector Proteins ◽  
Wild Type ◽  
Type Iii ◽  
In The Wild ◽  
Secretion Chaperone

Pathogenicity of the gram-negative bacterium Xanthomonas campestris pv. vesicatoria depends on a type III secretion (T3S) system, which translocates effector proteins into plant cells. Effector proteins contain N-terminal T3S and translocation signals and interact with the T3S chaperone HpaB, which presumably escorts effectors to the secretion apparatus. The molecular mechanisms underlying the recognition of effectors by the T3S system are not yet understood. In the present study, we analyzed T3S and translocation signals in the type III effectors XopE2 and XopJ from X. campestris pv. vesicatoria. Both effectors contain minimal translocation signals, which are only recognized in the absence of HpaB. Additional N-terminal signals promote translocation of XopE2 and XopJ in the wild-type strain. The results of translocation and interaction studies revealed that the interaction of XopE2 and XopJ with HpaB and a predicted cytoplasmic substrate docking site of the T3S system is not sufficient for translocation. In agreement with this finding, we show that the presence of an artificial HpaB-binding site does not promote translocation of the noneffector XopA in the wild-type strain. Our data, therefore, suggest that the T3S chaperone HpaB not only acts as an escort protein but also controls the recognition of translocation signals.

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