Immunosuppressive Yersinia Effector YopM Binds DEAD Box Helicase DDX3 to Control Ribosomal S6 Kinase in the Nucleus of Host Cells

Pathogenicity and virulence of Yersinia

The genus Yersinia includes human, animal, insect, and plant pathogens as well as many symbionts and harmless bacteria. Within this genus are Yersinia enterocolitica and the Yersinia pseudotuberculosis complex, with four human pathogenic species that are highly related at the genomic level including the causative agent of plague, Yersinia pestis. Extensive laboratory, field work, and clinical research have been conducted to understand the underlying pathogenesis and zoonotic transmission of these pathogens. There are presently more than 500 whole genome sequences from which an evolutionary footprint can be developed that details shared and unique virulence properties. Whereas the virulence of Y. pestis now seems in apparent homoeostasis within its flea transmission cycle, substantial evolutionary changes that affect transmission and disease severity continue to ndergo apparent selective pressure within the other Yersiniae that cause intestinal diseases. In this review, we will summarize the present understanding of the virulence and pathogenesis of Yersinia, highlighting shared mechanisms of virulence and the differences that determine the infection niche and disease severity.

Protein-Protein Interaction: Tandem Affinity Purification in Bacteria

The discovery of protein-protein interaction networks can lead to the unveiling of protein complex(es) forming cellular machinerie(s) or reveal component proteins of a specific cellular pathway. Deciphering protein-protein interaction networks therefore contributes to a deeper understanding of how cells function. Here we describe the protocol to perform tandem affinity purification (TAP) in bacteria, which enables the identification of the partners of a bait protein under native conditions. This method consists in two sequential steps of affinity purification using two different tags. For that purpose, the bait protein is translationally fused to the TAP tag, which consists of a calmodulin-binding peptide (CBP) and two immunoglobulin G (IgG)-binding domains of Staphylococcus aureus protein A (ProtA) that are separated by the tobacco etch virus (TEV) protease cleavage site. After the first round of purification based on the binding of ProtA to IgG-coated beads, TEV protease cleavage releases CBP-tagged bait protein along with its partners for a second round of purification on calmodulin affinity resin and leaves behind protein contaminants bound to IgG. Creating the TAP-tag translational fusion at the chromosomal locus allows detection of protein interactions occurring in physiological conditions.

A bacterial effector protein promotes nuclear translocation of Stat3 to induce IL-10

The multifunctional Yersinia effector YopM inhibits effector triggered immunity and increases production of the anti-inflammatory cytokine Interleukin-10 (IL-10) to suppress the host immune response. Previously it was shown that YopM induces IL-10 gene expression by elevating phosphorylation of the serine-threonine kinase RSK1 in the nucleus of human macrophages. Using transcriptomics, we found that YopM strongly affects expression of genes belonging to the JAK-STAT signaling pathway. Further analysis revealed that YopM mediates nuclear translocation of the transcription factor Stat3 in Y. enterocolitica infected macrophages and that knockdown of Stat3 inhibited YopM-induced IL-10 gene expression. YopM-induced Stat3 translocation did not depend on autocrine IL-10, activation of RSK1 or tyrosine phosphorylation of Stat3. Thus, besides activation of RSK1, stimulation of nuclear translocation of Stat3 is another mechanism by which YopM increases IL-10 gene expression in macrophages.

C25-modified rifamycin derivatives with improved activity against Mycobacterium abscessus

Infections caused by Mycobacterium abscessus are difficult to treat due to its intrinsic resistance to most antibiotics. Formation of biofilms and the capacity of M. abscessus to survive inside host phagocytes further complicate eradication. Herein, we explored whether addition of a carbamate-linked group at the C25 position of rifamycin SV blocks enzymatic inactivation by Arr_Mab, an ADP-ribosyltransferase conferring resistance to rifampicin (RMP). Unlike RMP, 5j, a benzyl piperidine rifamycin derivative with a morpholino substituted C3 position and a naphthoquinone core, is not modified by purified Arr_Mab. Additionally, we show that the Arr_Mab D82 residue is essential for catalytic activity. Thermal profiling of Arr_Mab in the presence of 5j, RMP, or rifabutin shows that 5j does not bind to Arr_Mab. We found that the activity of 5j is comparable to amikacin against M. abscessus planktonic cultures and pellicles. Critically, 5j also exerts potent antimicrobial activity against M. abscessus in human macrophages and shows synergistic activity with amikacin and azithromycin.

A case of convergent evolution: Several viral and bacterial pathogens hijack RSK kinases through a common linear motif

Microbes have been coevolving with their host for millions of years, exploiting host resources to their own benefit. We show that viral and bacterial pathogens convergently evolved to hijack cellular mitogen-activated protein kinase (MAPK) p90-ribosomal S6-kinases (RSKs). Theiler's virus leader (L) protein binds RSKs and prevents their dephosphorylation, thus maintaining the kinases active. Recruitment of RSKs enables L-protein-mediated inhibition of eukaryotic translation initiation factor 2 alpha kinase 2 (EIF2AK2 or PKR) and stress granule formation. Strikingly, ORF45 protein of Kaposi's sarcoma-associated herpesvirus (KSHV) and YopM protein of Yersinia use the same peptide motif as L to recruit and activate RSKs. All three proteins interact with a conserved surface-located loop of RSKs, likely acting as an allosteric regulation site. Some unrelated viruses and bacteria thus evolved to harness RSKs in a common fashion, yet to target distinct aspects of innate immunity. As documented for Varicella zoster virus ORF11, additional pathogens likely evolved to hijack RSKs, using a similar short linear motif.

Role of the Yersinia pseudotuberculosis Virulence Plasmid in Pathogen-Phagocyte Interactions in Mesenteric Lymph Nodes

Yersinia pseudotuberculosis is an Enterobacteriaceae family member that is commonly transmitted by the fecal-oral route to cause infections. From the small intestine, Y. pseudotuberculosis can invade through Peyer's patches and lymph vessels to infect the mesenteric lymph nodes (MLNs). Infection of MLNs by Y. pseudotuberculosis results in the clinical presentation of mesenteric lymphadenitis. MLNs are important for immune responses to intestinal pathogens and microbiota in addition to their clinical relevance to Y. pseudotuberculosis infections. A characteristic of Y. pseudotuberculosis infection in MLNs is the formation of pyogranulomas. Pyogranulomas are composed of neutrophils, inflammatory monocytes, and lymphocytes surrounding extracellular microcolonies of Y. pseudotuberculosis. Key elements of the complex pathogen-host interaction in MLNs have been identified using mouse infection models. Y. pseudotuberculosis requires the virulence plasmid pYV to induce the formation of pyogranulomas in MLNs. The YadA adhesin and the Ysc-Yop type III secretion system (T3SS) are encoded on pYV. YadA mediates bacterial binding to host receptors, which engages the T3SS to preferentially translocate seven Yop effectors into phagocytes. The effectors promote pathogenesis by blocking innate immune defenses such as superoxide production, degranulation, and inflammasome activation, resulting in survival and growth of Y. pseudotuberculosis. On the other hand, certain effectors can trigger immune defenses in phagocytes. For example, YopJ triggers activation of caspase-8 and an apoptotic cell death response in monocytes within pyogranulomas that limits dissemination of Y. pseudotuberculosis from MLNs to the bloodstream. YopE can be processed as an antigen by phagocytes in MLNs, resulting in T and B cell responses to Y. pseudotuberculosis. Immune responses to Y. pseudotuberculosis in MLNs can also be detrimental to the host in the form of chronic lymphadenopathy. This review focuses on interactions between Y. pseudotuberculosis and phagocytes mediated by pYV that concurrently promote pathogenesis and host defense in MLNs. We propose that MLN pyogranulomas are immunological arenas in which opposing pYV-driven forces determine the outcome of infection in favor of the pathogen or host.

Bimolecular fluorescence complementation assay to explore protein-protein interactions of the Yersinia virulence factor YopM

Yersinia outer protein M (YopM) is one of the effector proteins and essential for virulence. YopM is delivered by the Yersinia type III secretion system (T3SS) into the host cell, where it shows immunosuppressive effect through interaction with host proteins. Therefore, protein-protein interactions of YopM is significant to understand its molecular mechanism. In this study, we aimed to explore protein-protein interactions of YopM with the two components of T3SS, namely LcrV and LcrG. We used bimolecular fluorescence complementation (BiFC) assay and monitored the reassembly of green fluorescence protein in Escherichia coli. As an indicator of the protein-protein interaction, we monitored the in vivo reconstitution of fluorescence by measuring fluorescence intensity and imaging the cells under fluorescence microscope. We showed, for the first time, that YopM interacts with LcrG, but not with LcrV. Here, we propose BiFC assay as a simple method to screen novel interaction partners of YopM.

Yersinia remodels epigenetic histone modifications in human macrophages

Various pathogens systematically reprogram gene expression in macrophages, but the underlying mechanisms are largely unknown. We investigated whether the enteropathogen Yersinia enterocolitica alters chromatin states to reprogram gene expression in primary human macrophages. Genome-wide chromatin immunoprecipitation (ChIP) seq analyses showed that pathogen-associated molecular patterns (PAMPs) induced up- or down-regulation of histone modifications (HMod) at approximately 14500 loci in promoters and enhancers. Effectors of Y. enterocolitica reorganized about half of these dynamic HMod, with the effector YopP being responsible for about half of these modulatory activities. The reorganized HMod were associated with genes involved in immune response and metabolism. Remarkably, the altered HMod also associated with 61% of all 534 known Rho GTPase pathway genes, revealing a new level in Rho GTPase regulation and a new aspect of bacterial pathogenicity. Changes in HMod were associated to varying degrees with corresponding gene expression, e. g. depending on chromatin localization and cooperation of the HMod. In summary, infection with Y. enterocolitica remodels HMod in human macrophages to modulate key gene expression programs of the innate immune response.

Human pathogenic bacteria can affect epigenetic histone modifications to modulate gene expression in host cells. However, a systems biology analysis of this bacterial virulence mechanism in immune cells has not been performed. Here we analyzed genome-wide epigenetic histone modifications and associated gene expression changes in primary human macrophages infected with enteropathogenic Yersinia enterocolitica. We demonstrate that Yersinia virulence factors extensively modulate histone modifications and associated gene expression triggered by the pathogen-associated molecular patterns (PAMPs) of the bacteria. The epigenetically modulated genes are involved in several key pathways of the macrophage immune response, including the Rho GTPase pathway, revealing a novel level of Rho GTPase regulation by a bacterial pathogen. Overall, our findings provide an in-depth view of epigenetic and gene expression changes during host-pathogen interaction and might have further implications for understanding of the innate immune memory in macrophages.

α-Helices in the Type III Secretion Effectors: A Prevalent Feature with Versatile Roles

Type III Secretion Systems (T3SSs) are multicomponent nanomachines located at the cell envelope of Gram-negative bacteria. Their main function is to transport bacterial proteins either extracellularly or directly into the eukaryotic host cell cytoplasm. Type III Secretion effectors (T3SEs), latest to be secreted T3S substrates, are destined to act at the eukaryotic host cell cytoplasm and occasionally at the nucleus, hijacking cellular processes through mimicking eukaryotic proteins. A broad range of functions is attributed to T3SEs, ranging from the manipulation of the host cell's metabolism for the benefit of the bacterium to bypassing the host's defense mechanisms. To perform this broad range of manipulations, T3SEs have evolved numerous novel folds that are compatible with some basic requirements: they should be able to easily unfold, pass through the narrow T3SS channel, and refold to an active form when on the other side. In this review, the various folds of T3SEs are presented with the emphasis placed on the functional and structural importance of α-helices and helical domains.

Bacterial nucleomodulins: A coevolutionary adaptation to the eukaryotic command center

Through long-term interactions with their hosts, bacterial pathogens have evolved unique arsenals of effector proteins that interact with specific host targets and reprogram the host cell into a permissive niche for pathogen proliferation. The targeting of effector proteins into the host cell nucleus for modulation of nuclear processes is an emerging theme among bacterial pathogens. These unique pathogen effector proteins have been termed in recent years as "nucleomodulins." The first nucleomodulins were discovered in the phytopathogens Agrobacterium and Xanthomonas, where their nucleomodulins functioned as eukaryotic transcription factors or integrated themselves into host cell DNA to promote tumor induction, respectively. Numerous nucleomodulins were recently identified in mammalian pathogens. Bacterial nucleomodulins are an emerging family of pathogen effector proteins that evolved to target specific components of the host cell command center through various mechanisms. These mechanisms include: chromatin dynamics, histone modification, DNA methylation, RNA splicing, DNA replication, cell cycle, and cell signaling pathways. Nucleomodulins may induce short- or long-term epigenetic modifications of the host cell. In this extensive review, we discuss the current knowledge of nucleomodulins from plant and mammalian pathogens. While many nucleomodulins are already identified, continued research is instrumental in understanding their mechanisms of action and the role they play during the progression of pathogenesis. The continued study of nucleomodulins will enhance our knowledge of their effects on nuclear chromatin dynamics, protein homeostasis, transcriptional landscapes, and the overall host cell epigenome.

The Role of Protein Disorder in Nuclear Transport and in Its Subversion by Viruses

The transport of host proteins into and out of the nucleus is key to host function. However, nuclear transport is restricted by nuclear pores that perforate the nuclear envelope. Protein intrinsic disorder is an inherent feature of this selective transport barrier and is also a feature of the nuclear transport receptors that facilitate the active nuclear transport of cargo, and the nuclear transport signals on the cargo itself. Furthermore, intrinsic disorder is an inherent feature of viral proteins and viral strategies to disrupt host nucleocytoplasmic transport to benefit their replication. In this review, we highlight the role that intrinsic disorder plays in the nuclear transport of host and viral proteins. We also describe viral subversion mechanisms of the host nuclear transport machinery in which intrinsic disorder is a feature. Finally, we discuss nuclear import and export as therapeutic targets for viral infectious disease.

The Yersinia Type III Secretion System as a Tool for Studying Cytosolic Innate Immune Surveillance

Microbial pathogens have evolved complex mechanisms to interface with host cells in order to evade host defenses and replicate. However, mammalian innate immune receptors detect the presence of molecules unique to the microbial world or sense the activity of virulence factors, activating antimicrobial and inflammatory pathways. We focus on how studies of the major virulence factor of one group of microbial pathogens, the type III secretion system (T3SS) of human pathogenic Yersinia, have shed light on these important innate immune responses. Yersinia are largely extracellular pathogens, yet they insert T3SS cargo into target host cells that modulate the activity of cytosolic innate immune receptors. This review covers both the host pathways that detect the Yersinia T3SS and the effector proteins used by Yersinia to manipulate innate immune signaling.

Host Epigenetics in Intracellular Pathogen Infections

Some intracellular pathogens are able to avoid the defense mechanisms contributing to host epigenetic modifications. These changes trigger alterations tothe chromatin structure and on the transcriptional level of genes involved in the pathogenesis of many bacterial diseases. In this way, pathogens manipulate the host cell for their own survival. The better understanding of epigenetic consequences in bacterial infection may open the door for designing new vaccine approaches and therapeutic implications. This article characterizes selected intracellular bacterial pathogens, including Mycobacterium spp., Listeria spp., Chlamydia spp., Mycoplasma spp., Rickettsia spp., Legionella spp. and Yersinia spp., which can modulate and reprogram of defense genes in host innate immune cells.

The cell-penetrating YopM protein-functionalized quantum dot-plasmid DNA conjugate as a novel gene delivery vector

Non-viral gene delivery systems have great potential for safe and efficient gene therapy, while inefficient cellular and nuclear uptake remain as the major hurdles. Novel approaches are needed to enhance the transfection efficiency of non-viral vectors. In accordance with this need, the objective of this study was to construct a non-viral vector that could achieve gene delivery without using additional lipid-based transfection agent. We aimed to impart self-delivery property to a non-viral vector by using the cell and nucleus penetrating properties of YopM proteins from the three Yersinia spp. (Y. pestis, Y. enterocolotica and Y. pseudotuberculosis). Plasmid DNA (pDNA) encoding green fluorescent protein (GFP) was labeled with quantum dots (QDs) via peptide-nucleic acid (PNA) recognition site. Recombinant YopM protein was then attached to the conjugate via a second PNA recognition site. The YopM ̶ QDs ̶ pDNA conjugate was transfected into HeLa cells without using additional transfection reagent. All three conjugates produced GFP fluorescence, indicating that the plasmid was successfully delivered to the nucleus. As control, naked pDNA was transfected into the cells by using a commercial transfection reagent. The Y. pseudotuberculosis YopM-functionalized conjugate achieved the highest GFP expression, compared to other two YopM proteins and the transfection reagent. To the best of our knowledge, YopM protein was used for the first time in a non-viral gene delivery vector.

Bacterial Factors Targeting the Nucleus: The Growing Family of Nucleomodulins

Pathogenic bacteria secrete a variety of proteins that manipulate host cell function by targeting components of the plasma membrane, cytosol, or organelles. In the last decade, several studies identified bacterial factors acting within the nucleus on gene expression or other nuclear processes, which has led to the emergence of a new family of effectors called “nucleomodulins”. In human and animal pathogens, Listeria monocytogenes for Gram-positive bacteria and Anaplasma phagocytophilum, Ehrlichia chaffeensis, Chlamydia trachomatis, Legionella pneumophila, Shigella flexneri, and Escherichia coli for Gram-negative bacteria, have led to pioneering discoveries. In this review, we present these paradigms and detail various mechanisms and core elements (e.g., DNA, histones, epigenetic regulators, transcription or splicing factors, signaling proteins) targeted by nucleomodulins. We particularly focus on nucleomodulins interacting with epifactors, such as LntA of Listeria and ankyrin repeat- or tandem repeat-containing effectors of Rickettsiales, and nucleomodulins from various bacterial species acting as post-translational modification enzymes. The study of bacterial nucleomodulins not only generates important knowledge about the control of host responses by microbes but also creates new tools to decipher the dynamic regulations that occur in the nucleus. This research also has potential applications in the field of biotechnology. Finally, this raises questions about the epigenetic effects of infectious diseases.

Protein-Protein and Protein-Peptide Docking with ClusPro Server

The process of creating a model of the structure formed by a pair of interacting molecules is commonly referred to as docking. Protein docking is one of the most studied topics in computational and structural biology with applications to drug design and beyond. In this chapter, we describe ClusPro, a web server for protein-protein and protein-peptide docking. As an input, the server requires two Protein Data Bank (PDB) files (protein-protein mode) or a PDB file for the protein and a sequence for the ligand (protein-peptide mode). Its output consists of ten models of the resulting structure formed by the two objects upon interaction. The server typically produces results in less than 4 h. The server also provides tools (via "Advanced Options" list) for a user to fine-tune the results using any additional knowledge about the interaction process, e.g., small-angle X-ray scattering (SAXS) profile or distance restraints.

Tandem Affinity Purification of SBP-CBP-tagged Type Three Secretion System Effectors

Identification of protein-protein interactions of bacterial effectors and cellular targets during infection is at the core to understand how bacteria manipulate the infected host to overcome the immune response. Potential interacting proteins might be identified by genetic methods, i.e., two hybrid screens and could be verified by co-immunoprecipitation. The tandem affinity purification (TAP) method allows an unbiased screen of potential interaction partners of bacterial effectors in a physiological approach: target cells can be infected with a bacterial strain harboring the TAP-tagged bacterial effector protein which is translocated in the host similar as under physiological infection conditions. No transfection and overexpression of the bacterial protein in the eukaryotic host are needed. Therefore, also host target cells not easy to transfect can be analyzed by this method. Moreover, the two consecutive affinity tags Calmodulin-Binding-Peptide (CBP) and Streptavidin-Binding-Peptide (SBP) fused to the translocated bacterial protein allow an outstanding clear purification of protein complexes formed between the bacterial protein of interest and host cell proteins with less occurrence of contaminants. Mass spectrometry allows an unbiased identification of interacting eukaryotic proteins.

Yersinia pestis and plague: an updated view on evolution, virulence determinants, immune subversion, vaccination, and diagnostics

Plague is a vector-borne disease caused by Yersinia pestis. Transmitted by fleas from rodent reservoirs, Y. pestis emerged <6000 years ago from an enteric bacterial ancestor through events of gene gain and genome reduction. It is a highly remarkable model for the understanding of pathogenic bacteria evolution, and a major concern for public health as highlighted by recent human outbreaks. A complex set of virulence determinants, including the Yersinia outer-membrane proteins (Yops), the broad-range protease Pla, pathogen-associated molecular patterns (PAMPs), and iron capture systems play critical roles in the molecular strategies that Y. pestis employs to subvert the human immune system, allowing unrestricted bacterial replication in lymph nodes (bubonic plague) and in lungs (pneumonic plague). Some of these immunogenic proteins as well as the capsular antigen F1 are exploited for diagnostic purposes, which are critical in the context of the rapid onset of death in the absence of antibiotic treatment (less than a week for bubonic plague and <48 h for pneumonic plague). Here, we review recent research advances on Y. pestis evolution, virulence factor function, bacterial strategies to subvert mammalian innate immune responses, vaccination, and problems associated with pneumonic plague diagnosis.

The species-spanning family of LPX-motif harbouring effector proteins

The delivery of effector proteins into infected eukaryotic cells represents a key virulence feature of many microbial pathogens in order to derail essential cellular processes and effectively counter the host defence system. Although bacterial effectors are truly numerous and exhibit a wide range of biochemical activities, commonalities in terms of protein structure and function shared by many bacterial pathogens exist. Recent progress has shed light on a species-spanning family of bacterial effectors containing an LPX repeat motif as a subtype of the leucine-rich repeat superfamily, partially combined with a novel E3 ubiquitin ligase domain. This review highlights the immunomodulatory effects of LPX effector proteins, with particular emphasis on the exploitation of the host ubiquitin system.

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.

Orientia tsutsugamushi uses two Ank effectors to modulate NF-κB p65 nuclear transport and inhibit NF-κB transcriptional activation

Orientia tsutsugamushi causes scrub typhus, a potentially fatal infection that threatens over one billion people. Nuclear translocation of the transcription factor, NF-κB, is the central initiating cellular event in the antimicrobial response. Here, we report that NF-κB p65 nuclear accumulation and NF-κB-dependent transcription are inhibited in O. tsutsugamushi infected HeLa cells and/or primary macrophages, even in the presence of TNFα. The bacterium modulates p65 subcellular localization by neither degrading it nor inhibiting IκBα degradation. Rather, it exploits host exportin 1 to mediate p65 nuclear export, as this phenomenon is leptomycin B-sensitive. O. tsutsugamushi antagonizes NF-κB-activated transcription even when exportin 1 is inhibited and NF-κB consequently remains in the nucleus. Two ankyrin repeat-containing effectors (Anks), Ank1 and Ank6, each of which possess a C-terminal F-box and exhibit 58.5% amino acid identity, are linked to the pathogen's ability to modulate NF-κB. When ectopically expressed, both translocate to the nucleus, abrogate NF-κB-activated transcription in an exportin 1-independent manner, and pronouncedly reduce TNFα-induced p65 nuclear levels by exportin 1-dependent means. Flag-tagged Ank 1 and Ank6 co-immunoprecipitate p65 and exportin 1. Both also bind importin β1, a host protein that is essential for the classical nuclear import pathway. Importazole, which blocks importin β1 activity, abrogates Ank1 and Ank6 nuclear translocation. The Ank1 and Ank6 regions that bind importin β1 also mediate their transport into the nucleus. Yet, these regions are distinct from those that bind p65/exportin 1. The Ank1 and Ank6 F-box and the region that lies between it and the ankyrin repeat domain are essential for blocking p65 nuclear accumulation. These data reveal a novel mechanism by which O. tsutsugamushi modulates the activity and nuclear transport of NF-κB p65 and identify the first microbial proteins that co-opt both importin β1 and exportin 1 to antagonize a critical arm of the antimicrobial response.

The Type III Secretion System Cleans up Its Act(in)

Inflammasome-associated innate immune receptors sense host-cell targeting by the type III secretion system (T3SS) of pathogenic Yersinia. In this issue of Cell Host & Microbe, Chung et al. (2016) show that the Yersinia T3SS effector protein YopM counteracts this recognition pathway by restricting the pyrin inflammasome, thus increasing bacterial fitness.

Immunomodulatory Yersinia outer proteins (Yops)-useful tools for bacteria and humans alike

Human-pathogenic Yersinia produce plasmid-encoded Yersinia outer proteins (Yops), which are necessary to down-regulate anti-bacterial responses that constrict bacterial survival in the host. These Yops are effectively translocated directly from the bacterial into the target cell cytosol by the type III secretion system (T3SS). Cell-penetrating peptides (CPPs) in contrast are characterized by their ability to autonomously cross cell membranes and to transport cargo - independent of additional translocation systems. The recent discovery of bacterial cell-penetrating effector proteins (CPEs) - with the prototype being the T3SS effector protein YopM - established a new class of autonomously translocating immunomodulatory proteins. CPEs represent a vast source of potential self-delivering, anti-inflammatory therapeutics. In this review, we give an update on the characteristic features of the plasmid-encoded Yops and, based on recent findings, propose the further development of these proteins for potential therapeutic applications as natural or artificial cell-penetrating forms of Yops might be of value as bacteria-derived biologics.

The Yersinia Virulence Factor YopM Hijacks Host Kinases to Inhibit Type III Effector-Triggered Activation of the Pyrin Inflammasome

Pathogenic Yersinia, including Y. pestis, the agent of plague in humans, and Y. pseudotuberculosis, the related enteric pathogen, deliver virulence effectors into host cells via a prototypical type III secretion system to promote pathogenesis. These effectors, termed Yersinia outer proteins (Yops), modulate multiple host signaling responses. Studies in Y. pestis and Y. pseudotuberculosis have shown that YopM suppresses infection-induced inflammasome activation; however, the underlying molecular mechanism is largely unknown. Here we show that YopM specifically restricts the pyrin inflammasome, which is triggered by the RhoA-inactivating enzymatic activities of YopE and YopT, in Y. pseudotuberculosis-infected macrophages. The attenuation of a yopM mutant is fully reversed in pyrin knockout mice, demonstrating that YopM inhibits pyrin to promote virulence. Mechanistically, YopM recruits and activates the host kinases PRK1 and PRK2 to negatively regulate pyrin by phosphorylation. These results show how a virulence factor can hijack host kinases to inhibit effector-triggered pyrin inflammasome activation.