RESUMO
Studying the dynamic interaction between host cells and pathogen is vital but remains technically challenging. We describe herein a time-resolved chemical proteomics strategy enabling host and pathogen temporal interaction profiling (HAPTIP) for tracking the entry of a pathogen into the host cell. A novel multifunctional chemical proteomics probe was introduced to label living bacteria followed by inâ vivo crosslinking of bacteria proteins to their interacting host-cell proteins at different time points initiated by UV for label-free quantitative proteomics analysis. We observed over 400 specific interacting proteins crosslinked with the probe during the formation of Salmonella-containing vacuole (SCV). This novel chemical proteomics approach provides a temporal interaction profile of host and pathogen in high throughput and would facilitate better understanding of the infection process at the molecular level.
Assuntos
Proteínas de Bactérias/química , Sondas Moleculares/química , Proteômica/métodos , Salmonella typhimurium/metabolismo , Proteínas de Bactérias/metabolismo , Antígeno CD11b/química , Antígeno CD11b/metabolismo , Interações Hospedeiro-Patógeno , Humanos , Lipopolissacarídeos/química , Lipopolissacarídeos/metabolismo , Macrófagos/imunologia , Macrófagos/metabolismo , Maleimidas/química , Análise de Componente Principal , Infecções por Salmonella/diagnóstico , Infecções por Salmonella/metabolismo , Infecções por Salmonella/microbiologia , Succinimidas/química , Fatores de Tempo , Raios UltravioletaRESUMO
Salmonella virulence requires the initial invasion of host cells, followed by modulation of the intracellular environment for survival and replication. In an effort to characterize the role of small RNAs in Salmonella pathogenesis, we inadvertently identified a 5-kDa protein named YshB that is involved in the intracellular survival of Salmonella We show here that yshB expression is upregulated upon entry into macrophages. When yshB expression is upregulated before bacterial entry, invasion efficiency is inhibited. Lack of YshB resulted in reduced bacterial survival within the macrophages and led to reduced virulence in a mouse model of infection.IMPORTANCESalmonella gastroenteritis is one of the most common causes of foodborne disease, possibly affecting millions of people globally each year. Here we characterize the role of a novel small protein, YshB, in mediating Salmonella intracellular survival. This elucidation adds to the body of knowledge regarding how this bacterium achieves intracellular survival.
Assuntos
Proteínas de Bactérias/imunologia , Salmonelose Animal/prevenção & controle , Vacinas contra Salmonella/imunologia , Salmonella typhimurium/metabolismo , Salmonella typhimurium/patogenicidade , Animais , Proteínas de Bactérias/metabolismo , Feminino , Regulação Bacteriana da Expressão Gênica , Células HeLa , Humanos , Macrófagos , Camundongos , Células RAW 264.7 , Salmonelose Animal/microbiologia , Virulência , Fatores de Virulência/metabolismoRESUMO
Salmonella enterica serovar Typhimurium is arguably one of the most studied bacterial pathogens and successful infection requires the delivery of its virulence factors (effectors) directly into host cells via the type III secretion systems (T3SSs). Central to Salmonella pathogenesis, these effector proteins have been subjected to extensive studies over the years. Nevertheless, whether additional effectors exist remains unclear. Here we report the identification of a novel Salmonella T3SS effector STM1239 (which we renamed SopF) via quantitative secretome profiling. Immunoblotting and ß-lactamase reporter assays confirmed the secretion and translocation of SopF in a T3SS-dependent manner. Moreover, ectopic expression of SopF caused significant toxicity in yeast cells. Importantly, genetic ablation of sopF led to Salmonella strains defective in intracellular replication within macrophages and the mutant were also markedly attenuated in a mouse model of infection. Our study underscores the use of quantitative secretome profiling in identifying novel virulence factors for bacterial pathogens.
Assuntos
Proteômica/métodos , Infecções por Salmonella/microbiologia , Salmonella typhimurium/patogenicidade , Fatores de Virulência/genética , Fatores de Virulência/metabolismo , Animais , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Modelos Animais de Doenças , Regulação Bacteriana da Expressão Gênica , Camundongos , Mutação , Transporte Proteico , Infecções por Salmonella/metabolismo , Salmonella typhimurium/genética , Salmonella typhimurium/metabolismo , Sistemas de Secreção Tipo III/metabolismoRESUMO
In order to deploy virulence factors at appropriate times and locations, microbes must rapidly sense and respond to various metabolite signals. Previously, we showed a transient elevation of the methionine-derived metabolite methylthioadenosine (MTA) concentration in serum during systemic Salmonella enterica serovar Typhimurium infection. Here we explored the functional consequences of increased MTA concentrations on S Typhimurium virulence. We found that MTA, but not other related metabolites involved in polyamine synthesis and methionine salvage, reduced motility, host cell pyroptosis, and cellular invasion. Further, we developed a genetic model of increased bacterial endogenous MTA production by knocking out the master repressor of the methionine regulon, metJ Like MTA-treated S Typhimurium, the ΔmetJ mutant displayed reduced motility, host cell pyroptosis, and invasion. These phenotypic effects of MTA correlated with suppression of flagellar and Salmonella pathogenicity island 1 (SPI-1) networks. S Typhimurium ΔmetJ had reduced virulence in oral and intraperitoneal infection of C57BL/6J mice independently of the effects of MTA on SPI-1. Finally, ΔmetJ bacteria induced a less severe inflammatory cytokine response in a mouse sepsis model. Together, these data indicate that exposure of S Typhimurium to MTA or disruption of the bacterial methionine metabolism pathway suppresses S Typhimurium virulence.
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Adenosina/metabolismo , Metionina/metabolismo , Salmonella typhimurium/patogenicidade , Adenosina/análogos & derivados , Animais , Proteínas de Bactérias/genética , Modelos Animais de Doenças , Flagelos , Regulação Bacteriana da Expressão Gênica , Ilhas Genômicas , Camundongos , Camundongos Endogâmicos C57BL , Poliaminas/metabolismo , Proteínas Repressoras/genética , Salmonelose Animal/microbiologia , Virulência/efeitos dos fármacos , Fatores de Virulência/genéticaRESUMO
Deep sequencing has revolutionized our understanding of the bacterial RNA world and has facilitated the identification of 280 small RNAs (sRNAs) in Salmonella Despite the suspicions that sRNAs may play important roles in Salmonella pathogenesis, the functions of most sRNAs remain unknown. To advance our understanding of RNA biology in Salmonella virulence, we searched for sRNAs required for bacterial invasion into nonphagocytic cells. After screening 75 sRNAs, we discovered that the ablation of InvS caused a significant decrease of Salmonella invasion into epithelial cells. A proteomic analysis showed that InvS modulated the levels of several type III secreted Salmonella proteins. The level of PrgH, a type III secretion apparatus protein, was significantly lower in the absence of InvS, consistent with the known roles of PrgH in effector secretion and bacterial invasion. We discovered that InvS modulates fimZ expression and hence flagellar gene expression and motility. We propose that InvS coordinates the increase of PrgH and decrease in FimZ that promote efficient Salmonella invasion into nonphagocytic cells.IMPORTANCE Salmonellosis continues to be the most common foodborne infection reported by the CDC in the United States. Central to Salmonella pathogenesis is the ability to invade nonphagocytic cells and to replicate inside host cells. Invasion genes are known to be regulated by protein transcriptional networks, but little is known about the role played by small RNAs (sRNAs) in this process. We have identified a novel sRNA, InvS, that is involved in Salmonella invasion. Our result will likely provide an opportunity to better understand the fundamental question of how Salmonella regulates invasion gene expression and may inform strategies for therapeutic intervention.
Assuntos
Proteínas de Bactérias/metabolismo , Células Epiteliais/microbiologia , Salmonella typhimurium/fisiologia , Antibacterianos/farmacologia , Proteínas de Bactérias/genética , Regulação Bacteriana da Expressão Gênica , Gentamicinas/farmacologia , Células HeLa , Humanos , RNA Bacteriano/genética , RNA Bacteriano/metabolismo , RNA não Traduzido/genética , Salmonella typhimurium/efeitos dos fármacos , Salmonella typhimurium/genéticaRESUMO
Salmonella are able to invade non-phagocytic cells such as intestinal epithelial cells by modulating the host actin cytoskeleton to produce membrane ruffles. Two type III effector proteins SopB and SopE play key roles to this modulation. SopE is a known guanine nucleotide exchange factor (GEF) capable of activating Rac1 and CDC42. SopB is a phosphatidylinositol 4-phosphatase and 5-phosphatase promoting membrane ruffles and invasion of Salmonella through undefined mechanisms. Previous studies have demonstrated that the 4-phosphatase activity of SopB is required for PtdIns-3-phosphate (PtdIns(3)P) accumulation and SopB-mediated invasion. We show here that both the 4-phosphatase as well as the 5-phosphatase activities of SopB are essential in ruffle formation and subsequent invasion. We found that the 5-phosphatase activity of SopB is likely responsible for generating PtdIns-3,4-bisphosphate (PtdIns(3,4)P(2)) and subsequent recruitment of sorting nexin 9 (SNX9), an actin modulating protein. Intriguingly, the 4-phosphatase activity is responsible for the dephosphorylation of PtdIns(3,4)P(2) into PtdIns(3)P. Alone, neither activity is sufficient for ruffling but when acting in conjunction with one another, the 4-phosphatase and 5-phosphatase activities led to SNX9-mediated ruffling and Salmonella invasion. This work reveals the unique ability of bacterial effector protein SopB to utilize both its 4- and 5-phosphatase activities to regulate phosphoinositide dynamics to promote bacterial entry.
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Citoesqueleto de Actina/metabolismo , Proteínas de Bactérias/metabolismo , Membrana Celular/metabolismo , Fosfatidilinositóis/metabolismo , Citoesqueleto de Actina/microbiologia , Actinas/metabolismo , Animais , Proteínas de Bactérias/genética , Células COS , Membrana Celular/microbiologia , Extensões da Superfície Celular , Chlorocebus aethiops , Células HeLa , Humanos , Salmonella typhimurium/metabolismo , Salmonella typhimurium/patogenicidadeRESUMO
Salmonella enterica serovar Typhimurium depends on type III secretion systems to inject effector proteins into host cells to promote bacterial invasion and to induce intestinal inflammation. SipA, a type III effector, is known to play important roles in both the invasion and the elicitation of intestinal inflammation. The actin-modulating activity of SipA has been shown to promote Salmonella entry into epithelial cells. To investigate whether the actin-modulating activity of SipA is required for its ability to induce an inflammatory response in vivo, we generated the SipA(K635A E637W) mutant, which is deficient in actin-modulating activity. Salmonella strains expressing the chromosomal SipA(K635A E637W) point mutation had reduced invasion abilities but still caused colitis similar to that caused by the wild-type strain in a mouse model of infection. Our data indicate that the SipA actin-polymerizing activity is not essential for the SipA-induced inflammatory response in the mouse model of infection.
Assuntos
Actinas/fisiologia , Proteínas de Bactérias/fisiologia , Inflamação/etiologia , Enteropatias/microbiologia , Proteínas dos Microfilamentos/fisiologia , Infecções por Salmonella/complicações , Salmonella typhimurium/patogenicidade , Actinas/metabolismo , Animais , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Modelos Animais de Doenças , Células HeLa/microbiologia , Humanos , Enteropatias/patologia , Mucosa Intestinal , Camundongos , Camundongos Endogâmicos BALB C , Proteínas dos Microfilamentos/genética , Proteínas dos Microfilamentos/metabolismo , Mutação Puntual , Polimerização , Infecções por Salmonella/metabolismoRESUMO
DT104 emerged as a new branch of Salmonella typhimurium with resistance to multiple antimicrobials. To reveal some general genomic features of DT104 for clues of evolutionary events possibly associated with the emergence of this relatively new type of this pathogen, we mapped 11 independent DT104 strains and compared them with non-DT104 S. typhimurium strains. We found that all 11 DT104 strains contained three insertions absent in non-DT104 strains, i.e., the previously reported ST104, ST104B and ST64B. However, SGI-1, a genomic island known to be responsible for DT104 multidrug resistance, was not present in all DT104 strains examined in this study: one DT104 strain did not contain SGI-1 but carried a 144 kb plasmid, suggesting possible evolutionary relationships between the two DNA elements in the development of antimicrobial resistance.
Assuntos
Genoma Bacteriano/genética , Genômica , Infecções por Salmonella/microbiologia , Salmonella typhimurium/genética , Evolução Biológica , Mapeamento Cromossômico , DNA Bacteriano/química , DNA Bacteriano/genética , Desoxirribonucleases de Sítio Específico do Tipo II , Farmacorresistência Bacteriana Múltipla/genética , Endodesoxirribonucleases , Rearranjo Gênico , Ilhas Genômicas/fisiologia , Plasmídeos/genética , Especificidade da EspécieRESUMO
The exocyst is a multiprotein complex essential for tethering secretory vesicles to specific domains of the plasma membrane for exocytosis. Here, we report that the exocyst component Exo70 interacts with the Arp2/3 complex, a key regulator of actin polymerization. We further show that the exocyst-Arp2/3 interaction is regulated by epidermal growth factor (EGF) signalling. Inhibition of Exo70 by RNA interference (RNAi) or antibody microinjection blocks the formation of actin-based membrane protrusions and affects various aspects of cell motility. We propose that Exo70, in addition to functioning in exocytosis, also regulates actin at the leading edges of migrating cells, therefore coordinating cytoskeleton and membrane traffic during cell migration.
Assuntos
Complexo 2-3 de Proteínas Relacionadas à Actina/metabolismo , Movimento Celular , Proteínas de Membrana/metabolismo , Animais , Movimento Celular/efeitos dos fármacos , Fator de Crescimento Epidérmico/farmacologia , Células HeLa , Humanos , Proteínas de Membrana/química , Camundongos , Células NIH 3T3 , Ligação Proteica/efeitos dos fármacos , Ratos , Proteínas de Transporte VesicularRESUMO
Many microbial pathogens deliver effector proteins via the type III secretion system into infected host cells. Elucidating the function of these effectors is essential for our understanding of pathogenesis. Here, we describe biochemical and structural characterization of an effector protein (NleL) from Escherichia coli O157:H7, a widespread pathogen causing severe foodborne diseases. We show that NleL functionally and structurally mimics eukaryotic HECT E3 ligases and catalyzes formation of unanchored polyubiquitin chains using Lys(6) and Lys(48) linkage. The catalytic cysteine residue forms a thioester intermediate with ubiquitin. The structure of NleL contains two domains, a ß-helix domain formed by pentapeptide repeats and a bilobed catalytic domain reminiscent of the N- and C-lobe architecture of HECT E3s. Six structures of NleL observed in two crystal forms revealed a large range of different positions of the C-lobe relative to the N-lobe, indicating that the helix linking the two lobes is extremely flexible. Comparing the structure of NleL with that of the Salmonella homolog SopA showed that the orientation of the C-lobes differ by as much as 108°, suggesting that large movements of the C-lobe may be required to facilitate the transfer of ubiquitin from E2 to the substrate. These results provide critical knowledge toward understanding the molecular mechanism by which pathogens utilize the host ubiquitination system during infection.
Assuntos
Escherichia coli O157/enzimologia , Proteínas de Escherichia coli/química , Proteínas de Escherichia coli/metabolismo , Ubiquitina-Proteína Ligases/química , Ubiquitina-Proteína Ligases/metabolismo , Sequência de Aminoácidos , Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Biocatálise , Domínio Catalítico , Cisteína/metabolismo , Ésteres , Modelos Moleculares , Dados de Sequência Molecular , Fenilalanina , Homologia de Sequência de Aminoácidos , Ubiquitina/metabolismo , Enzimas de Conjugação de Ubiquitina/metabolismoRESUMO
Salmonella enterica serovar Typhimurium invade non-phagocytic cells by injecting bacterial effector proteins to exploit the host actin cytoskeleton network. SipC is such a Salmonella effector known to nucleate actin, bundle F-actin, and translocate type III effectors. The molecular mechanism of how SipC bundles F-actin and SipC domains responsible for these activities are not well characterized. We successfully separated these activities through a series of genetic deletion/insertions in SipC. We found that the C terminus (amino acids 200-409) of SipC bundled actin filaments using in vitro biochemical assays. We further demonstrated that amino acid residues 221-260 and 381-409 of full-length SipC were indispensable for its actin binding and bundling activities. Furthermore, Salmonella mutant strains lacking the actin bundling activity were less invasive into HeLa cells. These studies indicate that the C terminus of SipC bundles F-actin to promote Salmonella invasion.
Assuntos
Actinas/metabolismo , Aderência Bacteriana/fisiologia , Proteínas de Bactérias/metabolismo , Infecções por Salmonella/metabolismo , Salmonella typhimurium/metabolismo , Salmonella typhimurium/patogenicidade , Actinas/genética , Proteínas de Bactérias/genética , Células HeLa , Humanos , Estrutura Terciária de Proteína , Infecções por Salmonella/genética , Salmonella typhimurium/genética , Deleção de SequênciaRESUMO
BACKGROUND: Salmonella enterica is a facultative intracellular pathogen that replicates within a membrane-bound compartment termed Salmonella containing vacuole (SCV). The biogenesis of SCV requires Salmonella type III protein secretion/translocation system and their effector proteins which are translocated into host cells to exploit the vesicle trafficking pathways. SseF is one of these effectors required for SCV formation and Intracellular Salmonella replication through unknown mechanisms. RESULTS: In an attempt to identify host proteins that interact with SseF, we conduct a yeast two-hybrid screening of human cell cDNA library using SseF as the bait. We identified that TIP60, an acetyltransferase, interacts with SseF. We showed that the TIP60 acetylation activity was increased in the presence of SseF, and TIP60 was upregulated upon Salmonella infection. In addition, TIP60 is required for efficient intracellular Salmonella replication in macrophages. CONCLUSION: Taken together, our data suggest that Salmonella may use SseF to exploit the host TIP60 acetyltransferase activity to promote efficient Salmonella replication inside host cells.
Assuntos
Replicação do DNA , Histona Acetiltransferases/metabolismo , Infecções por Salmonella/enzimologia , Infecções por Salmonella/microbiologia , Salmonella typhimurium/genética , Animais , Proteínas de Bactérias/genética , Proteínas de Bactérias/metabolismo , Linhagem Celular , Células HeLa , Histona Acetiltransferases/genética , Humanos , Lisina Acetiltransferase 5 , Macrófagos/enzimologia , Macrófagos/microbiologia , Camundongos , Ligação Proteica , Infecções por Salmonella/genética , Salmonella typhimurium/metabolismoRESUMO
Salmonella are Gram-negative rod-shaped facultative anaerobic bacteria that are comprised of over 2,000 serovars. They cause gastroenteritis (salmonellosis) with headache, abdominal pain and diarrhea clinical symptoms. Salmonellosis brings a heavy burden for the public health in both developing and developed countries. Antibiotics are usually effective in treating the infected patients with severe gastroenteritis, although antibiotic resistance is on the rise. Understanding the molecular mechanisms of Salmonella infection is vital to combat the disease. In vitro immortalized 2-D cell lines, ex vivo tissues/organs and several animal models have been successfully utilized to study Salmonella infections. Although these infection models have contributed to uncovering the molecular virulence mechanisms, some intrinsic shortcomings have limited their wider applications. Notably, cell lines only contain a single cell type, which cannot reproduce some of the hallmarks of natural infections. While ex vivo tissues/organs alleviate some of these concerns, they are more difficult to maintain, in particular for long term experiments. In addition, non-human animal models are known to reflect only part of the human disease process. Enteroids and induced intestinal organoids are emerging as effective infection models due to their closeness in mimicking the infected tissues/organs. Induced intestinal organoids are derived from iPSCs and contain mesenchymal cells whereas enteroids are derive from intestinal stem cells and are comprised of epithelial cells only. Both enteroids and induced intestinal organoids mimic the villus and crypt domains comparable to the architectures of the in vivo intestine. We review here that enteroids and induced intestinal organoids are emerging as desired infection models to study bacterial-host interactions of Salmonella.
Assuntos
Mucosa Intestinal/microbiologia , Mucosa Intestinal/patologia , Organoides/microbiologia , Infecções por Salmonella/patologia , Salmonella/patogenicidade , Animais , Humanos , Macrófagos/imunologia , Camundongos , Infecções por Salmonella/imunologia , Infecções por Salmonella/microbiologia , Fatores de VirulênciaRESUMO
[This corrects the article DOI: 10.3389/fcimb.2018.00102.].
RESUMO
Skeletal myogenesis involves sequential activation, proliferation, self-renewal/differentiation and fusion of myogenic stem cells (satellite cells). Notch signaling is known to be essential for the maintenance of satellite cells, but its function in late-stage myogenesis, i.e. post-differentiation myocytes and post-fusion myotubes, is unknown. Using stage-specific Cre alleles, we uncovered distinct roles of Notch1 in mononucleated myocytes and multinucleated myotubes. Specifically, constitutive Notch1 activation dedifferentiates myocytes into Pax7 quiescent satellite cells, leading to severe defects in muscle growth and regeneration, and postnatal lethality. By contrast, myotube-specific Notch1 activation improves the regeneration and exercise performance of aged and dystrophic muscles. Mechanistically, Notch1 activation in myotubes upregulates the expression of Notch ligands, which modulate Notch signaling in the adjacent satellite cells to enhance their regenerative capacity. These results highlight context-dependent effects of Notch activation during myogenesis, and demonstrate that Notch1 activity improves myotube's function as a stem cell niche.
Assuntos
Desenvolvimento Muscular , Fibras Musculares Esqueléticas/fisiologia , Músculo Esquelético/embriologia , Receptor Notch1/metabolismo , Células Satélites de Músculo Esquelético/fisiologia , Transdução de Sinais , Diferenciação Celular , Proliferação de Células , HumanosRESUMO
Salmonella enterica pathogenesis is dependent on its ability to enter and replicate inside host cells. Replication occurs inside the Salmonella-containing vacuole (SCV), a vacuolar compartment that is modified by bacterial effectors secreted through the two type III secretion systems (T3SS-1 and T3SS-2). Type III effectors interact with the host cell endocytic pathway to aid replication. We investigated whether Salmonella effector proteins may also interact with the host's exocytic pathway. A secreted alkaline phosphatase (SEAP) assay indicated three Salmonella effectors inhibited the secretory pathway, although only Salmonella outer protein B (SopB) was confirmed to block exocytosis using a vesicular stomatitis virus glycoprotein-green fluorescent protein (VSVG-GFP) transport assay. The 4-phosphatase activity of SopB was crucial to its effect on exocytosis. The interaction with the secretory pathway could potentially be important for providing replicating Salmonella with nutrients, contributing membrane material necessary for SCV biogenesis, altering antibacterial peptide/protein secretion or manipulating cell surface proteins important in the host response to infection.
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[This corrects the article DOI: 10.1038/emi.2013.31.].
RESUMO
The delivery of effector proteins by Salmonella across the host cell membrane requires a subset of effectors secreted by the type III secretion system (TTSS) known as translocators. SipC and SipB are translocator proteins that are inserted into host membranes and presumably form a channel that translocates type III effectors into the host cell. The molecular events of how these translocators insert into the host cell membrane remain unknown. We have previously shown that the SipC C-terminal amino acid region (321-409) is required for the translocation of effectors into host cells. In this study, we demonstrate that the ability to form SipC-SipB complex is essential for their insertion into the host membrane. The SipB-interacting domain of SipC is near its C-terminal amino acid region (340-409). In the absence of SipB, SipC was not detected in the membrane fraction. Furthermore, SipC mutants that no longer interact with SipB are defective in inserting into the host cell membrane. We propose a mechanism whereby SipC binds SipB through its C-terminal region to facilitate membrane-insertion and subsequent translocon formation in the host cell membrane.
Assuntos
Proteínas de Bactérias/metabolismo , Proteínas de Membrana/metabolismo , Animais , Membrana Celular/metabolismo , Células HEK293 , Células HeLa , Interações Hospedeiro-Patógeno , Humanos , Chaperonas Moleculares/metabolismo , Proteínas Mutantes/química , Proteínas Mutantes/metabolismo , Mutação/genética , Ligação Proteica , Transporte Proteico , Infecções por Salmonella/metabolismo , Salmonella typhimurium/metabolismo , Ovinos , Relação Estrutura-AtividadeRESUMO
Ubiquitination is a post-translational modification in which one or more 76 amino acid polypeptide ubiquitin molecules are covalently linked to the lysine residues of target proteins. Ubiquitination is the main pathway for protein degradation that governs a variety of eukaryotic cellular processes, including the cell-cycle, vesicle trafficking, antigen presentation, and signal transduction. Not surprisingly, aberrations in the system have been implicated in the pathogenesis of many diseases including inflammatory and neurodegenerative disorders. Recent studies have revealed that viruses and bacterial pathogens exploit the host ubiquitination pathways to gain entry and to aid their survival/replication inside host cells. This review will summarize recent developments in understanding the biochemical and structural mechanisms utilized by bacterial pathogens to interact with the host ubiquitination pathways.
RESUMO
Enterohemorrhagic Escherichia coli (EHEC) O157:H7 causes hemorrhagic colitis and may result in potentially fatal hemolytic uremia syndrome in humans. EHEC colonize the intestinal mucosa and promote the formation of actin-rich pedestals via translocated type III effectors. Two EHEC type III secreted effectors, Tir and EspFu/TccP, are key players for pedestal formation. We discovered that an EHEC effector protein called Non-LEE-encoded Ligase (NleL) is an E3 ubiquitin ligase. In vitro, we showed that the NleL C753 residue is critical for its E3 ligase activity. Functionally, we demonstrated that NleL E3 ubiquitin ligase activity is involved in modulating Tir-mediated pedestal formation. Surprisingly, EHEC mutant strain deficient in the E3 ligase activity induced more pedestals than the wild-type strain. The canonical EPEC strain E2348/69 normally lacks the nleL gene, and the ectopic expression of the wild-type EHEC nleL, but not the catalytically-deficient nleL(C753A) mutant, in this strain resulted in fewer actin-rich pedestals. Furthermore, we showed that the C. rodentium NleL homolog is a E3 ubiquitin ligase and is required for efficient infection of murine colonic epithelial cells in vivo. In summary, our study demonstrated that EHEC utilizes NleL E3 ubiquitin ligase activity to modulate Tir-mediated pedestal formation.