Yersinia enterocolitica outer protein T (YopT)

Delivering the pain: an overview of the type III secretion system with special consideration for aquatic pathogens

Gram-negative bacteria are known to subvert eukaryotic cell physiological mechanisms using a wide array of virulence factors, among which the type three-secretion system (T3SS) is often one of the most important. The T3SS constitutes a needle-like apparatus that the bacterium uses to inject a diverse set of effector proteins directly into the cytoplasm of the host cells where they can hamper the host cellular machinery for a variety of purposes. While the structure of the T3SS is somewhat conserved and well described, effector proteins are much more diverse and specific for each pathogen. The T3SS can remodel the cytoskeleton integrity to promote intracellular invasion, as well as silence specific eukaryotic cell signals, notably to hinder or elude the immune response and cause apoptosis. This is also the case in aquatic bacterial pathogens where the T3SS can often play a central role in the establishment of disease, although it remains understudied in several species of important fish pathogens, notably in Yersinia ruckeri. In the present review, we summarise what is known of the T3SS, with a special focus on aquatic pathogens and suggest some possible avenues for research including the potential to target the T3SS for the development of new anti-virulence drugs.

Identification of Robinia pseudoacacia target proteins responsive to Mesorhizobium amphore CCNWGS0123 effector protein NopT

Nodulation outer proteins secreted via type 3 secretion systems are involved in the process of symbiosis between legume plants and rhizobia. To study the function of NopT in symbiosis, we mutated nopT in Mesorhizobium amphore CCNWGS0123 (GS0123), which can nodulate black locust (Robinia pseudoacacia). The nopT mutant induced higher levels of jasmonic acid, salicylic acid, and hydrogen peroxide accumulation in the roots of R. pseudoacacia compared with wild-type GS0123. The ΔnopT mutant induced higher disease-resistant gene expression 72 hours post-inoculation (hpi), whereas GS0123 induced higher disease-resistant gene expression earlier, at 36 hpi. Compared with the nopT mutant, GS0123 induced the up-regulation of most genes at 36 hpi and the down-regulation of most genes at 72 hpi. Proteolytically active NopT_GS0123 induced hypersensitive responses when expressed transiently in tobacco leaves (Nicotiana benthamiana). Two NopT_GS0123 targets in R. pseudoacacia were identified, ATP-citrate synthase alpha chain protein 2 and hypersensitive-induced response protein. Their interactions with NopT_GS0123 triggered resistance by the plant immune system. In conclusion, NopT_GS0123 inhibited the host plant immune system and had minimal effect on nodulation in R. pseudoacacia. Our results reveal the underlying molecular mechanism of NopT function in plant-symbiont interactions.

Yersinia YopT inhibits RLH-mediated NF-κB and IRF3 signal transduction

The Gram-negative bacterial pathogen Yersinia delivers six effector proteins into the host cells to block the host innate immune response. One of the effectors, YopT, is a potent cysteine protease that causes the disruption of the actin cytoskeleton to inhibit phagocytosis of the pathogen; however, its molecular mechanism and relevance to pathogenesis need further investigation. In this report, we show that RIG-I is a novel target of the YopT protein. Remarkably, YopT interacts with RIG-I and inhibits rat liver homogenate-mediated nuclear factor-κB and interferon regulatory factor-3 activation. Further studies revealed a YopT-dependent increase in the K48-polymerized ubiquitination of RIG-I. These findings suggest that YopT negatively regulates RIG-I-mediated cellular antibacterial response by targeting RIG-I.

The Most Important Virulence Markers of Yersinia enterocolitica and Their Role during Infection

Yersinia enterocolitica is the causative agent of yersiniosis, a zoonotic disease of growing epidemiological importance with significant consequences for public health. This pathogenic species has been intensively studied for many years. Six biotypes (1A, 1B, 2, 3, 4, 5) and more than 70 serotypes of Y. enterocolitica have been identified to date. The biotypes of Y. enterocolitica are divided according to their pathogenic properties: the non-pathogenic biotype 1A, weakly pathogenic biotypes 2⁻5, and the highly pathogenic biotype 1B. Due to the complex pathogenesis of yersiniosis, further research is needed to expand our knowledge of the molecular mechanisms involved in the infection process and the clinical course of the disease. Many factors, both plasmid and chromosomal, significantly influence these processes. The aim of this study was to present the most important virulence markers of Y. enterocolitica and their role during infection.

YopT domain of the PfhB2 toxin from Pasteurella multocida: protein expression, characterization, crystallization and crystallographic analysis

Pasteurella multocida causes respiratory-tract infections in a broad range of animals, as well as opportunistic infections in humans. P. multocida secretes a multidomain toxin called PfhB2, which contains a YopT-like cysteine protease domain at its C-terminus. The YopT domain of PfhB2 contains a well conserved Cys-His-Asp catalytic triad that defines YopT family members, and shares high sequence similarity with the prototype YopT from Yersinia sp. To date, only one crystal structure of a YopT family member has been reported; however, additional structural information is needed to help characterize the varied substrate specificity and enzymatic action of this large protease family. Here, a catalytically inactive C3733S mutant of PfhB2 YopT that provides enhanced protein stability was used with the aim of gaining structural insight into the diversity within the YopT protein family. To this end, the C3733S mutant of PfhB2 YopT has been successfully cloned, overexpressed, purified and crystallized. Diffraction data sets were collected from native crystals to 3.5 Å resolution and a single-wavelength anomalous data set was collected from an iodide-derivative crystal to 3.2 Å resolution. Data pertaining to crystals belonging to space group P31, with unit-cell parameters a = 136.9, b = 136.9, c = 74.7 Å for the native crystals and a = 139.2, b = 139.2, c = 74.7 Å for the iodide-derivative crystals, are discussed.

The Functions of Effector Proteins in Yersinia Virulence

Yersinia species are bacterial pathogens that can cause plague and intestinal diseases after invading into human cells through the Three Secretion System (TTSS). The effect of pathogenesis is mediated by Yersinia outer proteins (Yop) and manifested as down-regulation of the cytokine genes expression by inhibiting nuclear factor-κ-gene binding (NF-κB) and mitogen-activated protein kinase (MAPK) pathways. In addition, its pathogenesis can also manipulate the disorder of host innate immune system and cell death such as apoptosis, pyroptosis, and autophagy. Among the Yersinia effector proteins, YopB and YopD assist the injection of other virulence effectors into the host cytoplasm, while YopE, YopH, YopJ, YopO, and YopT target on disrupting host cell signaling pathways in the host cytosols. Many efforts have been applied to reveal that intracellular proteins such as Rho-GTPase, and transmembrane receptors such as Toll-like receptors (TLRs) both play critical roles in Yersinia pathogenesis, establishing a connection between the pathogenic process and the signaling response. This review will mainly focus on how the effector proteins of Yersinia modulate the intrinsic signals in host cells and disturb the innate immunity of hosts through TTSS.

Yersinia virulence factors - a sophisticated arsenal for combating host defences

The human pathogens Yersinia pseudotuberculosis and Yersinia enterocolitica cause enterocolitis, while Yersinia pestis is responsible for pneumonic, bubonic, and septicaemic plague. All three share an infection strategy that relies on a virulence factor arsenal to enable them to enter, adhere to, and colonise the host while evading host defences to avoid untimely clearance. Their arsenal includes a number of adhesins that allow the invading pathogens to establish a foothold in the host and to adhere to specific tissues later during infection. When the host innate immune system has been activated, all three pathogens produce a structure analogous to a hypodermic needle. In conjunction with the translocon, which forms a pore in the host membrane, the channel that is formed enables the transfer of six ‘effector’ proteins into the host cell cytoplasm. These proteins mimic host cell proteins but are more efficient than their native counterparts at modifying the host cell cytoskeleton, triggering the host cell suicide response. Such a sophisticated arsenal ensures that yersiniae maintain the upper hand despite the best efforts of the host to counteract the infecting pathogen.

Bacterial factors exploit eukaryotic Rho GTPase signaling cascades to promote invasion and proliferation within their host

Actin cytoskeleton is a main target of many bacterial pathogens. Among the multiple regulation steps of the actin cytoskeleton, bacterial factors interact preferentially with RhoGTPases. Pathogens secrete either toxins which diffuse in the surrounding environment, or directly inject virulence factors into target cells. Bacterial toxins, which interfere with RhoGTPases, and to some extent with RasGTPases, catalyze a covalent modification (ADPribosylation, glucosylation, deamidation, adenylation, proteolysis) blocking these molecules in their active or inactive state, resulting in alteration of epithelial and/or endothelial barriers, which contributes to dissemination of bacteria in the host. Injected bacterial virulence factors preferentially manipulate the RhoGTPase signaling cascade by mimicry of eukaryotic regulatory proteins leading to local actin cytoskeleton rearrangement, which mediates bacterial entry into host cells or in contrast escape to phagocytosis and immune defense. Invasive bacteria can also manipulate RhoGTPase signaling through recognition and stimulation of cell surface receptor(s). Changes in RhoGTPase activation state is sensed by the innate immunity pathways and allows the host cell to adapt an appropriate defense response.

Yersinia pestis: mechanisms of entry into and resistance to the host cell

During infection, Yersinia, a facultative intracellular bacterial species, exhibits the ability to first invade host cells and then counteract phagocytosis by the host cells. During these two distinct stages, invasion or antiphagocytic factors assist bacteria in manipulating host cells to accomplish each of these functions; however, the mechanism through which Yersinia regulates these functions during each step remains unclear. Here, we discuss those factors that seem to function reversely and give some hypothesis about how bacteria switch between the two distinct status.

Identification of secreted bacterial proteins by noncanonical amino acid tagging

Pathogenic microbes have evolved complex secretion systems to deliver virulence factors into host cells. Identification of these factors is critical for understanding the infection process. We report a powerful and versatile approach to the selective labeling and identification of secreted pathogen proteins. Selective labeling of microbial proteins is accomplished via translational incorporation of azidonorleucine (Anl), a methionine surrogate that requires a mutant form of the methionyl-tRNA synthetase for activation. Secreted pathogen proteins containing Anl can be tagged by azide-alkyne cycloaddition and enriched by affinity purification. Application of the method to analysis of the type III secretion system of the human pathogen Yersinia enterocolitica enabled efficient identification of secreted proteins, identification of distinct secretion profiles for intracellular and extracellular bacteria, and determination of the order of substrate injection into host cells. This approach should be widely useful for the identification of virulence factors in microbial pathogens and the development of potential new targets for antimicrobial therapy.

Cytotoxic necrotizing factor-Y boosts Yersinia effector translocation by activating Rac protein

Pathogenic Yersinia spp. translocate the effectors YopT, YopE, and YopO/YpkA into target cells to inactivate Rho family GTP-binding proteins and block immune responses. Some Yersinia spp. also secrete the Rho protein activator cytotoxic necrotizing factor-Y (CNF-Y), but it has been unclear how the bacteria may benefit from Rho protein activation. We show here that CNF-Y increases Yop translocation in Yersinia enterocolitica-infected cells up to 5-fold. CNF-Y strongly activated RhoA and also delayed in time Rac1 and Cdc42, but when individually expressed, constitutively active mutants of Rac1, but not of RhoA, increased Yop translocation. Consistently, knock-out or knockdown of Rac1 but not of RhoA, -B, or -C inhibited Yersinia effector translocation in CNF-Y-treated and control cells. Activation or knockdown of Cdc42 also affected Yop translocation but much less efficiently than Rac. The increase in Yop translocation induced by CNF-Y was essentially independent of the presence of YopE, YopT, or YopO in the infecting Yersinia strain, indicating that none of the Yops reported to inhibit translocation could reverse the CNF-Y effect. In summary, the CNF-Y activity of Yersinia strongly enhances Yop translocation through activation of Rac.

The papain inhibitor (SPI) of Streptomyces mobaraensis inhibits bacterial cysteine proteases and is an antagonist of bacterial growth

A novel papain inhibitory protein (SPI) from Streptomyces mobaraensis was studied to measure its inhibitory effect on bacterial cysteine protease activity (Staphylococcus aureus SspB) and culture supernatants (Porphyromonas gingivalis, Bacillus anthracis). Further, growth of Bacillus anthracis, Staphylococcus aureus, Pseudomonas aeruginosa, and Vibrio cholerae was completely inhibited by 10 μM SPI. At this concentration of SPI, no cytotoxicity was observed. We conclude that SPI inhibits bacterial virulence factors and has the potential to become a novel therapeutic treatment against a range of unrelated pathogenic bacteria.