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Gupta S, Biswas P, Das B, Mondal S, Gupta P, Das D, Mallick AI. Selective depletion of Campylobacter jejuni via T6SS dependent functionality: an approach for improving chickens gut health. Gut Pathog 2024; 16:38. [PMID: 38997758 PMCID: PMC11245787 DOI: 10.1186/s13099-024-00628-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2024] [Accepted: 06/28/2024] [Indexed: 07/14/2024] Open
Abstract
The targeted depletion of potential gut pathogens is often challenging because of their intrinsic ability to thrive in harsh gut environments. Earlier, we showed that Campylobacter jejuni (C. jejuni) exclusively uses the Type-VI Secretion System (T6SS) to target its prey such as Escherichia coli (E. coli), and phenotypic differences between T6SS-negative and T6SS-positive C. jejuni isolates toward bile salt sensitivity. However, it remains unclear how the target-driven T6SS functionality prevails in a polymicrobial gut environment. Here, we investigated the fate of microbial competition in an altered gut environment via bacterial T6SS using a T6SS-negative and -positive C. jejuni or its isogenic mutant of the hemolysin-coregulated protein (hcp). We showed that in the presence of bile salt and prey bacteria (E. coli), T6SS-positive C. jejuni experiences enhanced intracellular stress leading to cell death. Intracellular tracking of fluorophore-conjugated bile salts confirmed that T6SS-mediated bile salt influx into C. jejuni can enhance intracellular oxidative stress, affecting C. jejuni viability. We further investigated whether the T6SS activity in the presence of prey (E. coli) perturbs the in vivo colonization of C. jejuni. Using chickens as primary hosts of C. jejuni and non-pathogenic E. coli as prey, we showed a marked reduction of C. jejuni load in chickens cecum when bile salt solution was administered orally. Analysis of local antibody responses and pro-inflammatory gene expression showed a reduced risk of tissue damage, indicating that T6SS activity in the complex gut environment can be exploited as a possible measure to clear the persistent colonization of C. jejuni in chickens.
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Affiliation(s)
- Subhadeep Gupta
- Department of Biological Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, Nadia, West Bengal, 741246, India
| | - Prakash Biswas
- Department of Biological Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, Nadia, West Bengal, 741246, India
| | - Bishnu Das
- Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, Nadia, West Bengal, 741246, India
| | - Samiran Mondal
- Department of Veterinary Pathology, West Bengal University of Animal and Fishery Sciences, Kolkata, West Bengal, 700037, India
| | - Parna Gupta
- Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, Nadia, West Bengal, 741246, India
| | - Dipjyoti Das
- Department of Biological Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, Nadia, West Bengal, 741246, India.
| | - Amirul Islam Mallick
- Department of Biological Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, Nadia, West Bengal, 741246, India.
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2
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Oka GU, Souza DP, Sgro GG, Guzzo CR, Dunger G, Farah CS. Xanthomonas immunity proteins protect against the cis-toxic effects of their cognate T4SS effectors. EMBO Rep 2024; 25:1436-1452. [PMID: 38332152 PMCID: PMC10933484 DOI: 10.1038/s44319-024-00060-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2023] [Revised: 12/22/2023] [Accepted: 01/08/2024] [Indexed: 02/10/2024] Open
Abstract
Many bacteria kill rival species by translocating toxic effectors into target cells. Effectors are often encoded along with cognate immunity proteins that could (i) protect against "friendly-fire" (trans-intoxication) from neighboring sister cells and/or (ii) protect against internal cis-intoxication (suicide). Here, we distinguish between these two mechanisms in the case of the bactericidal Xanthomonas citri Type IV Secretion System (X-T4SS). We use a set of X. citri mutants lacking multiple effector/immunity protein (X-Tfe/X-Tfi) pairs to show that X-Tfis are not absolutely required to protect against trans-intoxication by wild-type cells. Our investigation then focused on the in vivo function of the lysozyme-like effector X-TfeXAC2609 and its cognate immunity protein X-TfiXAC2610. In the absence of X-TfiXAC2610, we observe X-TfeXAC2609-dependent and X-T4SS-independent accumulation of damage in the X. citri cell envelope, cell death, and inhibition of biofilm formation. While immunity proteins in other systems have been shown to protect against attacks by sister cells (trans-intoxication), this is an example of an antibacterial secretion system in which the immunity proteins are dedicated to protecting cells against cis-intoxication.
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Affiliation(s)
- Gabriel U Oka
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brazil
- Structure and Function of Bacterial Nanomachines, Institut Européen de Chimie et Biologie-CNRS, UMR 5234 Microbiologie Fondamentale et Pathogénicité University of Bordeaux, Pessac, France
| | - Diorge P Souza
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brazil
- Division of Cell Biology, MRC Laboratory of Molecular Biology, Cambridge, UK
| | - Germán G Sgro
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brazil
- Departamento de Ciências BioMoleculares, Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil
| | - Cristiane R Guzzo
- Departamento de Microbiologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, SP, Brazil
| | - German Dunger
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brazil
- Instituto de Ciencias Agropecuarias del Litoral (ICiAgro Litoral), Universidad Nacional del Litoral, CONICET, Facultad de Ciencias Agrarias, Esperanza, Argentina
| | - Chuck S Farah
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, SP, Brazil.
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3
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Ahmad S, Whitney JC. Location, Location, Location: an Antidote That Both Activates and Neutralizes a Toxin Used in Bacterial Warfare. J Bacteriol 2023; 205:e0016123. [PMID: 37366633 DOI: 10.1128/jb.00161-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/28/2023] Open
Abstract
S.J. Jensen, Z.C. Ruhe, A.F. Williams, D.Q. Nhan, et al. (J Bacteriol 205:e00113-23, 2023, https://doi.org/10.1128/jb.00113-23) demonstrate that a type VI secretion system (T6SS) immunity protein, Tli, functions to both neutralize and activate its cognate toxin, Tle, in Enterobacter cloacae. Their results reveal the surprising finding that Tli function differs, depending on its subcellular localization. Overall, this study enhances our understanding of T6SS immunity proteins, which are commonly viewed as monofunctional toxin-neutralizing antidotes.
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Affiliation(s)
- Shehryar Ahmad
- Temerty Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
| | - John C Whitney
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario Canada
- Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada
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4
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Rudzite M, Subramoni S, Endres RG, Filloux A. Effectiveness of Pseudomonas aeruginosa type VI secretion system relies on toxin potency and type IV pili-dependent interaction. PLoS Pathog 2023; 19:e1011428. [PMID: 37253075 PMCID: PMC10281587 DOI: 10.1371/journal.ppat.1011428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Revised: 06/20/2023] [Accepted: 05/17/2023] [Indexed: 06/01/2023] Open
Abstract
The type VI secretion system (T6SS) is an antibacterial weapon that is used by numerous Gram-negative bacteria to gain competitive advantage by injecting toxins into adjacent prey cells. Predicting the outcome of a T6SS-dependent competition is not only reliant on presence-absence of the system but instead involves a multiplicity of factors. Pseudomonas aeruginosa possesses 3 distinct T6SSs and a set of more than 20 toxic effectors with diverse functions including disruption of cell wall integrity, degradation of nucleic acids or metabolic impairment. We generated a comprehensive collection of mutants with various degrees of T6SS activity and/or sensitivity to each individual T6SS toxin. By imaging whole mixed bacterial macrocolonies, we then investigated how these P. aeruginosa strains gain a competitive edge in multiple attacker/prey combinations. We observed that the potency of single T6SS toxin varies significantly from one another as measured by monitoring the community structure, with some toxins acting better in synergy or requiring a higher payload. Remarkably the degree of intermixing between preys and attackers is also key to the competition outcome and is driven by the frequency of contact as well as the ability of the prey to move away from the attacker using type IV pili-dependent twitching motility. Finally, we implemented a computational model to better understand how changes in T6SS firing behaviours or cell-cell contacts lead to population level competitive advantages, thus providing conceptual insight applicable to all types of contact-based competition.
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Affiliation(s)
- Marta Rudzite
- MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London, United Kingdom
| | - Sujatha Subramoni
- Singapore Centre for Environmental Life Sciences Engineering, Nanyang Technological University, Singapore
| | - Robert G. Endres
- Centre for Integrative Systems Biology and Bioinformatics, Department of Life Sciences, Imperial College London, London, United Kingdom
| | - Alain Filloux
- MRC Centre for Molecular Bacteriology and Infection, Department of Life Sciences, Imperial College London, London, United Kingdom
- Singapore Centre for Environmental Life Sciences Engineering, Nanyang Technological University, Singapore
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5
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Snead KJ, Moore LL, Bourne CR. ParD Antitoxin Hotspot Alters a Disorder-to-Order Transition upon Binding to Its Cognate ParE Toxin, Lessening Its Interaction Affinity and Increasing Its Protease Degradation Kinetics. Biochemistry 2022; 61:34-45. [PMID: 34914378 PMCID: PMC9805813 DOI: 10.1021/acs.biochem.1c00584] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Type-II toxin-antitoxin (TA) systems are comprised of two tightly interacting proteins, and operons encoding these systems have been identified throughout the genomes of bacteria. In contrast to secretion system effector-immunity pairs, TA systems must remain paired to protect the host cell from toxicity. Continual depletion of the antitoxin results in a shorter half-life than that of the toxin, though it is unclear if antitoxins can be effectively degraded when complexed with toxins. The current work probed the protein-protein interface of the PaParDE1 TA system, guided by an X-ray crystal structure, to determine contributions of antitoxin amino acids to interaction kinetics and affinity. These studies identified a "hotspot" position that alters the binding mode and resulting affinity (KD) from 152 pM for a 1:1 model for wild type to 25.5 and 626 nM for a 2:1 model with mutated antitoxin. This correlates with an altered induced secondary structure upon complexation with PaParE1 and increased kinetics of Lon protease digestion of the antitoxin despite the toxin presence. However, the decreased affinity at this hotspot was essentially reversed when the antitoxin dimerization region was deleted, yielding insights into complex interactions involved in the tight association. Removal of the antitoxin C-terminal seven amino acids, corresponding to the site of a disorder-to-order transition, completely prevents association. These studies combine to provide a model for the initiation of the TA interaction and highlight how manipulation of the sequence can impact the antitoxin disorder-to-order transition, weakening the affinity and resulting in increased antitoxin susceptibility to degradation.
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Affiliation(s)
- Kevin J. Snead
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, United States
| | - Landon L. Moore
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, United States; Present Address: Department of Internal Medicine, Digestive Diseases and Nutrition Section, The University of Oklahoma Health Science Center, 800 Stanton L Young Blvd, Oklahoma City, OK 73104, USA
| | - Christina R. Bourne
- Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, United States
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6
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Abstract
The type VI secretion system (T6SS) is a bacterial nanoscale weapon that delivers toxins into prey ranging from bacteria and fungi to animal hosts. The cytosolic contractile sheath of the system wraps around stacked hexameric rings of Hcp proteins, which form an inner tube. At the tip of this tube is a puncturing device comprising a trimeric VgrG topped by a monomeric PAAR protein. The number of toxins a single system delivers per firing event remains unknown, since effectors can be loaded on diverse sites of the T6SS apparatus, notably the inner tube and the puncturing device. Each VgrG or PAAR can bind one effector, and additional effector cargoes can be carried in the Hcp ring lumen. While many VgrG- and PAAR-bound toxins have been characterized, to date, very few Hcp-bound effectors are known. Here, we used 3 known Pseudomonas aeruginosa Hcp proteins (Hcp1 to -3), each of which associates with one of the three T6SSs in this organism (H1-T6SS, H2-T6SS, and H3-T6SS), to perform in vivo pulldown assays. We confirmed the known interactions of Hcp1 with Tse1 to -4, further copurified a Hcp1-Tse4 complex, and identified potential novel Hcp1-bound effectors. Moreover, we demonstrated that Hcp2 and Hcp3 can shuttle T6SS cargoes toxic to Escherichia coli. Finally, we used a Tse1-Bla chimera to probe the loading strategy for Hcp passengers and found that while large effectors can be loaded onto Hcp, the formed complex jams the system, abrogating T6SS function.
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7
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Zhu PC, Li YM, Yang X, Zou HF, Zhu XL, Niu XN, Xu LH, Jiang W, Huang S, Tang JL, He YQ. Type VI secretion system is not required for virulence on rice but for inter-bacterial competition in Xanthomonas oryzae pv. oryzicola. Res Microbiol 2019; 171:64-73. [PMID: 31676435 DOI: 10.1016/j.resmic.2019.10.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2019] [Revised: 10/17/2019] [Accepted: 10/17/2019] [Indexed: 11/28/2022]
Abstract
The type VI secretion system (T6SS), a multifunctional protein secretion device, plays very important roles in bacterial killing and/or virulence to eukaryotic cells. Although T6SS genes have been found in many Xanthomonas species, the biological function of T6SSs has not been elucidated in most xanthomonads. In this study, we identified two phylogenetically distinct T6SS clusters, T6SS1 and T6SS2, in a newly sequenced Chinese strain GX01 of Xanthomonas oryzea pv. oryzicola (Xoc) which causes bacterial leaf streak (BLS) of rice (Oryza sativa L.). Mutational assays demonstrated that T6SS1 and T6SS2 are not required for the virulence of Xoc GX01 on rice. Nevertheless, we found that T6SS2, but not T6SS1, played an important role in bacterial killing. Transcription and secretion analysis revealed that hcp2 gene is actively expressed and that Hcp2 protein is secreted via T6SS. Moreover, several candidate T6SS effectors were predicted by bioinformatics analysis that might play a role in the antibacterial activity of Xoc. This is the first report to investigate the type VI secretion system in Xanthomonas oryzae. We speculate that Xoc T6SS2 might play an important role in inter-bacterial competition, allowing this plant pathogen to gain niche advantage by killing other bacteria.
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Affiliation(s)
- Ping-Chuan Zhu
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China
| | - Yi-Ming Li
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China
| | - Xia Yang
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China
| | - Hai-Fan Zou
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China
| | - Xiao-Lin Zhu
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China
| | - Xiang-Na Niu
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China
| | - Ling-Hui Xu
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China
| | - Wei Jiang
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China
| | - Sheng Huang
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China
| | - Ji-Liang Tang
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China.
| | - Yong-Qiang He
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Life Science and Technology, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China; National Demonstration Center for Experimental Plant Science Education, College of Agriculture, Guangxi University, 100 Daxue Road, Nanning, Guangxi, 530004, China.
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8
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Zeng C, Zou L. An account of in silico identification tools of secreted effector proteins in bacteria and future challenges. Brief Bioinform 2019; 20:110-129. [PMID: 28981574 DOI: 10.1093/bib/bbx078] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Indexed: 01/08/2023] Open
Abstract
Bacterial pathogens secrete numerous effector proteins via six secretion systems, type I to type VI secretion systems, to adapt to new environments or to promote virulence by bacterium-host interactions. Many computational approaches have been used in the identification of effector proteins before the subsequent experimental verification because they tolerate laborious biological procedures and are genome scale, automated and highly efficient. Prevalent examples include machine learning methods and statistical techniques. In this article, we summarize the computational progress toward predicting secreted effector proteins in bacteria, with an opening of an introduction of features that are used to discriminate effectors from non-effectors. The mechanism, contribution and deficiency of previous developed detection tools are presented, which are further benchmarked based on a curated testing data set. According to the results of benchmarking, potential improvements of the prediction performance are discussed, which include (1) more informative features for discriminating the effectors from non-effectors; (2) the construction of comprehensive training data set of the machine learning algorithms; (3) the advancement of reliable prediction methods and (4) a better interpretation of the mechanisms behind the molecular processes. The future of in silico identification of bacterial secreted effectors includes both opportunities and challenges.
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Affiliation(s)
- Cong Zeng
- Bioinformatics Center, Third Military Medical University (TMMU), China
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9
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Bao Y, Zhang H, Huang X, Ma J, Logue CM, Nolan LK, Li G. O-specific polysaccharide confers lysozyme resistance to extraintestinal pathogenic Escherichia coli. Virulence 2018; 9:666-680. [PMID: 29405825 PMCID: PMC5955474 DOI: 10.1080/21505594.2018.1433979] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Extraintestinal pathogenic Escherichia coli (ExPEC) is the leading cause of bloodstream and other extraintestinal infections in human and animals. The greatest challenge encountered by ExPEC during an infection is posed by the host defense mechanisms, including lysozyme. ExPEC have developed diverse strategies to overcome this challenge. The aim of this study was to characterize the molecular mechanism of ExPEC resistance to lysozyme. For this, 15,000 transposon mutants of a lysozyme-resistant ExPEC strain NMEC38 were screened; 20 genes were identified as involved in ExPEC resistance to lysozyme—of which five were located in the gene cluster between galF and gnd, and were further confirmed to be involved in O-specific polysaccharide biosynthesis. The O-specific polysaccharide was able to inhibit the hydrolytic activity of lysozyme; it was also required by the complete lipopolysaccharide (LPS)-mediated protection of ExPEC against the bactericidal activity of lysozyme. The O-specific polysaccharide was further shown to be able to directly interact with lysozyme. Furthermore, LPS from ExPEC strains of different O serotypes was also able to inhibit the hydrolytic activity of lysozyme. Because of their cell surface localization and wide distribution in Gram-negative bacteria, O-specific polysaccharides appear to play a long-overlooked role in protecting bacteria against exogenous lysozyme.
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Affiliation(s)
- Yinli Bao
- a Department of Veterinary Diagnostic and Production Animal Medicine , College of Veterinary Medicine, Iowa State University , Ames , IA , USA.,b Department of Veterinary Preventive Medicine , College of Veterinary Medicine, Nanjing Agricultural University , Nanjing , China
| | - Haobo Zhang
- b Department of Veterinary Preventive Medicine , College of Veterinary Medicine, Nanjing Agricultural University , Nanjing , China
| | - Xinxin Huang
- c Shanghai Entry-Exit Inspection and Quarantine Bureau , Shanghai , China
| | - Jiale Ma
- a Department of Veterinary Diagnostic and Production Animal Medicine , College of Veterinary Medicine, Iowa State University , Ames , IA , USA.,b Department of Veterinary Preventive Medicine , College of Veterinary Medicine, Nanjing Agricultural University , Nanjing , China
| | - Catherine M Logue
- d Department of Veterinary Microbiology and Preventive Medicine , College of Veterinary Medicine, Iowa State University , Ames , IA , USA
| | - Lisa K Nolan
- d Department of Veterinary Microbiology and Preventive Medicine , College of Veterinary Medicine, Iowa State University , Ames , IA , USA
| | - Ganwu Li
- a Department of Veterinary Diagnostic and Production Animal Medicine , College of Veterinary Medicine, Iowa State University , Ames , IA , USA.,e State Key Laboratory of Veterinary Biotechnology , Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences , Harbin , China
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10
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Molecular Basis for Immunity Protein Recognition of a Type VII Secretion System Exported Antibacterial Toxin. J Mol Biol 2018; 430:4344-4358. [PMID: 30194969 PMCID: PMC6193138 DOI: 10.1016/j.jmb.2018.08.027] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2018] [Revised: 08/29/2018] [Accepted: 08/30/2018] [Indexed: 02/07/2023]
Abstract
Gram-positive bacteria deploy the type VII secretion system (T7SS) to facilitate interactions between eukaryotic and prokaryotic cells. In recent work, we identified the TelC protein from Streptococcus intermedius as a T7SS-exported lipid II phosphatase that mediates interbacterial competition. TelC exerts toxicity in the inner wall zone of Gram-positive bacteria; however, intercellular intoxication of sister cells does not occur because they express the TipC immunity protein. In the present study, we sought to characterize the molecular basis of self-protection by TipC. Using sub-cellular localization and protease protection assays, we show that TipC is a membrane protein with an N-terminal transmembrane segment and a C-terminal TelC-inhibitory domain that protrudes into the inner wall zone. The 1.9-Å X-ray crystal structure of a non-protective TipC paralogue reveals that the soluble domain of TipC proteins adopts a crescent-shaped fold that is composed of three α-helices and a seven-stranded β-sheet. Subsequent homology-guided mutagenesis demonstrates that a concave surface formed by the predicted β-sheet of TipC is required for both its interaction with TelC and its TelC-inhibitory activity. S. intermedius cells lacking the tipC gene are susceptible to growth inhibition by TelC delivered between cells; however, we find that the growth of this strain is unaffected by endogenous or overexpressed TelC, although the toxin accumulates in culture supernatants. Together, these data indicate that the TelC-inhibitory activity of TipC is only required for intercellularly transferred TelC and that the T7SS apparatus transports TelC across the cell envelope in a single step, bypassing the cellular compartment in which it exerts toxicity en route. Antibacterial TelC toxin is neutralized in the inner wall zone by membrane-anchored TipC immunity protein. TipC is a crescent-shaped protein that interacts with TelC via its concave surface. TelC and TipC are physically separated by the plasma membrane in TelC-producing cells. The type VII secretion system prevents TelC access to the inner wall zone in TelC-producing bacteria.
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11
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Quentin D, Ahmad S, Shanthamoorthy P, Mougous JD, Whitney JC, Raunser S. Mechanism of loading and translocation of type VI secretion system effector Tse6. Nat Microbiol 2018; 3:1142-1152. [PMID: 30177742 DOI: 10.1038/s41564-018-0238-z] [Citation(s) in RCA: 64] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2018] [Accepted: 08/02/2018] [Indexed: 12/26/2022]
Abstract
The type VI secretion system (T6SS) primarily functions to mediate antagonistic interactions between contacting bacterial cells, but also mediates interactions with eukaryotic hosts. This molecular machine secretes antibacterial effector proteins by undergoing cycles of extension and contraction; however, how effectors are loaded into the T6SS and subsequently delivered to target bacteria remains poorly understood. Here, using electron cryomicroscopy, we analysed the structures of the Pseudomonas aeruginosa effector Tse6 loaded onto the T6SS spike protein VgrG1 in solution and embedded in lipid nanodiscs. In the absence of membranes, Tse6 stability requires the chaperone EagT6, two dimers of which interact with the hydrophobic transmembrane domains of Tse6. EagT6 is not directly involved in Tse6 delivery but is crucial for its loading onto VgrG1. VgrG1-loaded Tse6 spontaneously enters membranes and its toxin domain translocates across a lipid bilayer, indicating that effector delivery by the T6SS does not require puncturing of the target cell inner membrane by VgrG1. Eag chaperone family members from diverse Proteobacteria are often encoded adjacent to putative toxins with predicted transmembrane domains and we therefore anticipate that our findings will be generalizable to numerous T6SS-exported membrane-associated effectors.
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Affiliation(s)
- Dennis Quentin
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Shehryar Ahmad
- Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada.,Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada
| | - Premy Shanthamoorthy
- Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada.,Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada
| | - Joseph D Mougous
- Department of Microbiology, University of Washington, Seattle, WA, USA.,Howard Hughes Medical Institute, Seattle, WA, USA
| | - John C Whitney
- Michael DeGroote Institute for Infectious Disease Research, McMaster University, Hamilton, Ontario, Canada. .,Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
| | - Stefan Raunser
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Dortmund, Germany.
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12
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Effector⁻Immunity Pairs Provide the T6SS Nanomachine its Offensive and Defensive Capabilities. Molecules 2018; 23:molecules23051009. [PMID: 29701633 PMCID: PMC6099711 DOI: 10.3390/molecules23051009] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 04/13/2018] [Accepted: 04/23/2018] [Indexed: 01/23/2023] Open
Abstract
Type VI protein secretion systems (T6SSs) are specialized transport apparatus which can target both eukaryotic and prokaryotic cells and play key roles in host⁻pathogen⁻microbiota interactions. Therefore, T6SSs have attracted much attention as a research topic during the past ten years. In this review, we particularly summarized the T6SS antibacterial function, which involves an interesting offensive and defensive mechanism of the effector⁻immunity (E⁻I) pairs. The three main categories of effectors that target the cell wall, membranes, and nucleic acids during bacterial interaction, along with their corresponding immunity proteins are presented. We also discuss structural analyses of several effectors and E⁻I pairs, which explain the offensive and defensive mechanisms underpinning T6SS function during bacterial competition for niche-space, as well as the bioinformatics, proteomics, and protein⁻protein interaction (PPI) methods used to identify and characterize T6SS mediated E⁻I pairs. Additionally, we described PPI methods for verifying E⁻I pairs.
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13
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Ge X, Wei W, Li G, Sun M, Li H, Wu J, Hu F. Isolated Pseudomonas aeruginosa strain VIH2 and antagonistic properties against Ralstonia solanacearum. Microb Pathog 2017; 111:519-526. [PMID: 28847494 DOI: 10.1016/j.micpath.2017.08.020] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Revised: 08/10/2017] [Accepted: 08/16/2017] [Indexed: 11/29/2022]
Abstract
The aim of this study was to isolates with antagonist activity against R. solanacearum. Thirty-two bacterial isolates were obtained from samples, and they were screened for potential antagonistic activity against R. Solanacearum. Using the agar spot method, ten out of the 21 tested bacteria showed antilisterial activity. VIH2 had the highest inhibitory effect on the growth of R. Solanacearum. Based on 16S rDNA and Biolog test analysis, the strain VIH2 was identified as Pseudomonas aeruginosa. Single-factor and Response Surface Methodology experiments were used to optimize the culture medium and conditions. This study was to explore whether the hemolysin-co-regulated protein secretion island I (HSI-I)-encoded type VI secretion system (T6SS) in Pseudomonas can be used as a biological control approach against Ralstonia solanacearum under field conditions. Bacterial competition assay showed that the HSI-I type T6SS of strain VIH2 exhibited dramatic antibacterial killing activity against R. solanacearum. The HSI-I T6SS of P. aeruginosa was regulated by the ppKA gene. We disrupted the gene ppKA in VIH2 by a single crossover to yield the VIH2 (ΔppKA) mutant. The antagonism of VIH2 was significantly decreased by ppKA gene disruption. In conclusion, our data supported the idea that HSI-I T6SS plays a crucial role in the antagonistic action of strain VIH2 against R. solanacearum. This alternative approach for antagonism against R. solanacearum might help develop attenuated strains of engineered bacteria for biological control.
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Affiliation(s)
- Xincheng Ge
- Soil Ecology Lab, College of Resources and Environmental Sciences, Nanjing Agricultural University, No. 6 TongWei Road, Nanjing 210095, Jiangsu Province, People's Republic of China
| | - Wei Wei
- Soil Ecology Lab, College of Resources and Environmental Sciences, Nanjing Agricultural University, No. 6 TongWei Road, Nanjing 210095, Jiangsu Province, People's Republic of China
| | - Gen Li
- Soil Ecology Lab, College of Resources and Environmental Sciences, Nanjing Agricultural University, No. 6 TongWei Road, Nanjing 210095, Jiangsu Province, People's Republic of China
| | - Mingming Sun
- Soil Ecology Lab, College of Resources and Environmental Sciences, Nanjing Agricultural University, No. 6 TongWei Road, Nanjing 210095, Jiangsu Province, People's Republic of China
| | - Huixin Li
- Soil Ecology Lab, College of Resources and Environmental Sciences, Nanjing Agricultural University, No. 6 TongWei Road, Nanjing 210095, Jiangsu Province, People's Republic of China
| | - Jun Wu
- Soil Ecology Lab, College of Resources and Environmental Sciences, Nanjing Agricultural University, No. 6 TongWei Road, Nanjing 210095, Jiangsu Province, People's Republic of China.
| | - Feng Hu
- Soil Ecology Lab, College of Resources and Environmental Sciences, Nanjing Agricultural University, No. 6 TongWei Road, Nanjing 210095, Jiangsu Province, People's Republic of China.
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14
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Saak CC, Gibbs KA. The Self-Identity Protein IdsD Is Communicated between Cells in Swarming Proteus mirabilis Colonies. J Bacteriol 2016; 198:3278-3286. [PMID: 27672195 PMCID: PMC5116931 DOI: 10.1128/jb.00402-16] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 09/20/2016] [Indexed: 11/20/2022] Open
Abstract
Proteus mirabilis is a social bacterium that is capable of self (kin) versus nonself recognition. Swarming colonies of this bacterium expand outward on surfaces to centimeter-scale distances due to the collective motility of individual cells. Colonies of genetically distinct populations remain separate, while those of identical populations merge. Ids proteins are essential for this recognition behavior. Two of these proteins, IdsD and IdsE, encode identity information for each strain. These two proteins bind in vitro in an allele-restrictive manner. IdsD-IdsE binding is correlated with the merging of populations, whereas a lack of binding is correlated with the separation of populations. Key questions remained about the in vivo interactions of IdsD and IdsE, specifically, whether IdsD and IdsE bind within single cells or whether IdsD-IdsE interactions occur across neighboring cells and, if so, which of the two proteins is exchanged. Here we demonstrate that IdsD must originate from another cell to communicate identity and that this nonresident IdsD interacts with IdsE resident in the recipient cell. Furthermore, we show that unbound IdsD in recipient cells does not cause cell death and instead appears to contribute to a restriction in the expansion radius of the swarming colony. We conclude that P. mirabilis communicates IdsD between neighboring cells for nonlethal kin recognition, which suggests that the Ids proteins constitute a type of cell-cell communication. IMPORTANCE We demonstrate that self (kin) versus nonself recognition in P. mirabilis entails the cell-cell communication of an identity-encoding protein that is exported from one cell and received by another. We further show that this intercellular exchange affects swarm colony expansion in a nonlethal manner, which adds social communication to the list of potential swarm-related regulatory factors.
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Affiliation(s)
- Christina C Saak
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA
| | - Karine A Gibbs
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA
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15
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Sana TG, Berni B, Bleves S. The T6SSs of Pseudomonas aeruginosa Strain PAO1 and Their Effectors: Beyond Bacterial-Cell Targeting. Front Cell Infect Microbiol 2016; 6:61. [PMID: 27376031 PMCID: PMC4899435 DOI: 10.3389/fcimb.2016.00061] [Citation(s) in RCA: 74] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2016] [Accepted: 05/23/2016] [Indexed: 02/05/2023] Open
Abstract
Pseudomonas aeruginosa is an opportunistic pathogen responsible for many diseases such as chronic lung colonization in cystic fibrosis patients and acute infections in hospitals. The capacity of P. aeruginosa to be pathogenic toward several hosts is notably due to different secretion systems. Amongst them, P. aeruginosa encodes three Type Six Secretion Systems (T6SS), named H1- to H3-T6SS, that act against either prokaryotes and/or eukaryotic cells. They are independent from each other and inject diverse toxins that interact with different components in the host cell. Here we summarize the roles of these T6SSs in the PAO1 strain, as well as the toxins injected and their targets. While H1-T6SS is only involved in antiprokaryotic activity through at least seven different toxins, H2-T6SS and H3-T6SS are also able to target prokaryotic as well as eukaryotic cells. Moreover, recent studies proposed that H2- and H3-T6SS have a role in epithelial cells invasion by injecting at least three different toxins. The diversity of T6SS effectors is astounding and other effectors still remain to be discovered. In this review, we present a table with other putative P. aeruginosa strain PAO1 T6SS-dependent effectors. Altogether, the T6SSs of P. aeruginosa are important systems that help fight other bacteria for their ecological niche, and are important in the pathogenicity process.
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Affiliation(s)
- Thibault G Sana
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (UMR7255), IMM, Centre National de la Recherche Scientifique and Aix-Marseille UniversityMarseille, France; Department of Microbiology and Immunology, Stanford School of Medicine, Stanford UniversityStanford, CA, USA
| | - Benjamin Berni
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (UMR7255), IMM, Centre National de la Recherche Scientifique and Aix-Marseille University Marseille, France
| | - Sophie Bleves
- Laboratoire d'Ingénierie des Systèmes Macromoléculaires (UMR7255), IMM, Centre National de la Recherche Scientifique and Aix-Marseille University Marseille, France
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16
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Wagner S, Sommer R, Hinsberger S, Lu C, Hartmann RW, Empting M, Titz A. Novel Strategies for the Treatment of Pseudomonas aeruginosa Infections. J Med Chem 2016; 59:5929-69. [DOI: 10.1021/acs.jmedchem.5b01698] [Citation(s) in RCA: 176] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Stefanie Wagner
- Chemical
Biology of Carbohydrates, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), D-66123 Saarbrücken, Germany
- Deutsches Zentrum für Infektionsforschung (DZIF), 30625 Standort Hannover-Braunschweig, Germany
| | - Roman Sommer
- Chemical
Biology of Carbohydrates, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), D-66123 Saarbrücken, Germany
- Deutsches Zentrum für Infektionsforschung (DZIF), 30625 Standort Hannover-Braunschweig, Germany
| | - Stefan Hinsberger
- Deutsches Zentrum für Infektionsforschung (DZIF), 30625 Standort Hannover-Braunschweig, Germany
- Drug
Design and Optimization, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), D-66123 Saarbrücken, Germany
| | - Cenbin Lu
- Deutsches Zentrum für Infektionsforschung (DZIF), 30625 Standort Hannover-Braunschweig, Germany
- Drug
Design and Optimization, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), D-66123 Saarbrücken, Germany
| | - Rolf W. Hartmann
- Deutsches Zentrum für Infektionsforschung (DZIF), 30625 Standort Hannover-Braunschweig, Germany
- Drug
Design and Optimization, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), D-66123 Saarbrücken, Germany
| | - Martin Empting
- Deutsches Zentrum für Infektionsforschung (DZIF), 30625 Standort Hannover-Braunschweig, Germany
- Drug
Design and Optimization, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), D-66123 Saarbrücken, Germany
| | - Alexander Titz
- Chemical
Biology of Carbohydrates, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), D-66123 Saarbrücken, Germany
- Deutsches Zentrum für Infektionsforschung (DZIF), 30625 Standort Hannover-Braunschweig, Germany
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17
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Robb C, Robb M, Nano F, Boraston A. The Structure of the Toxin and Type Six Secretion System Substrate Tse2 in Complex with Its Immunity Protein. Structure 2016; 24:277-84. [DOI: 10.1016/j.str.2015.11.012] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Revised: 11/04/2015] [Accepted: 11/23/2015] [Indexed: 01/11/2023]
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18
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Alcoforado Diniz J, Liu YC, Coulthurst SJ. Molecular weaponry: diverse effectors delivered by the Type VI secretion system. Cell Microbiol 2015; 17:1742-51. [PMID: 26432982 PMCID: PMC4832377 DOI: 10.1111/cmi.12532] [Citation(s) in RCA: 114] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Revised: 09/22/2015] [Accepted: 09/25/2015] [Indexed: 12/18/2022]
Abstract
The Type VI secretion system is a widespread bacterial nanomachine, used to deliver toxins directly into eukaryotic or prokaryotic target cells. These secreted toxins, or effectors, act on diverse cellular targets, and their action provides the attacking bacterial cell with a significant fitness advantage, either against rival bacteria or eukaryotic host organisms. In this review, we discuss the delivery of diverse effectors by the Type VI secretion system, the modes of action of the so-called 'anti-bacterial' and 'anti-eukaryotic' effectors, the mechanism of self-resistance against anti-bacterial effectors and the evolutionary implications of horizontal transfer of Type VI secretion system-associated toxins. Whilst it is likely that many more effectors remain to be identified, it is already clear that toxins delivered by this secretion system represent efficient weapons against both bacteria and eukaryotes.
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Affiliation(s)
- Juliana Alcoforado Diniz
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Yi-Chia Liu
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
| | - Sarah J Coulthurst
- Division of Molecular Microbiology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK
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19
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Whitney JC, Quentin D, Sawai S, LeRoux M, Harding BN, Ledvina HE, Tran BQ, Robinson H, Goo YA, Goodlett DR, Raunser S, Mougous JD. An interbacterial NAD(P)(+) glycohydrolase toxin requires elongation factor Tu for delivery to target cells. Cell 2015; 163:607-19. [PMID: 26456113 DOI: 10.1016/j.cell.2015.09.027] [Citation(s) in RCA: 163] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Revised: 07/15/2015] [Accepted: 08/19/2015] [Indexed: 11/17/2022]
Abstract
Type VI secretion (T6S) influences the composition of microbial communities by catalyzing the delivery of toxins between adjacent bacterial cells. Here, we demonstrate that a T6S integral membrane toxin from Pseudomonas aeruginosa, Tse6, acts on target cells by degrading the universally essential dinucleotides NAD(+) and NADP(+). Structural analyses of Tse6 show that it resembles mono-ADP-ribosyltransferase proteins, such as diphtheria toxin, with the exception of a unique loop that both excludes proteinaceous ADP-ribose acceptors and contributes to hydrolysis. We find that entry of Tse6 into target cells requires its binding to an essential housekeeping protein, translation elongation factor Tu (EF-Tu). These proteins participate in a larger assembly that additionally directs toxin export and provides chaperone activity. Visualization of this complex by electron microscopy defines the architecture of a toxin-loaded T6S apparatus and provides mechanistic insight into intercellular membrane protein delivery between bacteria.
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Affiliation(s)
- John C Whitney
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA
| | - Dennis Quentin
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany
| | - Shin Sawai
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA
| | - Michele LeRoux
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA
| | - Brittany N Harding
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA
| | - Hannah E Ledvina
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA
| | - Bao Q Tran
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD 21201, USA
| | - Howard Robinson
- Biology Department, Brookhaven National Laboratory, Upton, NY 11973, USA
| | - Young Ah Goo
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD 21201, USA
| | - David R Goodlett
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MD 21201, USA
| | - Stefan Raunser
- Department of Structural Biochemistry, Max Planck Institute of Molecular Physiology, Otto-Hahn-Strasse 11, 44227 Dortmund, Germany
| | - Joseph D Mougous
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA; Howard Hughes Medical Institute, Seattle, WA 98195, USA.
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20
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LeRoux M, Kirkpatrick RL, Montauti EI, Tran BQ, Peterson SB, Harding BN, Whitney JC, Russell AB, Traxler B, Goo YA, Goodlett DR, Wiggins PA, Mougous JD. Kin cell lysis is a danger signal that activates antibacterial pathways of Pseudomonas aeruginosa. eLife 2015; 4. [PMID: 25643398 PMCID: PMC4348357 DOI: 10.7554/elife.05701] [Citation(s) in RCA: 95] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2014] [Accepted: 01/30/2015] [Indexed: 12/21/2022] Open
Abstract
The perception and response to cellular death is an important aspect of multicellular eukaryotic life. For example, damage-associated molecular patterns activate an inflammatory cascade that leads to removal of cellular debris and promotion of healing. We demonstrate that lysis of Pseudomonas aeruginosa cells triggers a program in the remaining population that confers fitness in interspecies co-culture. We find that this program, termed P. aeruginosa response to antagonism (PARA), involves rapid deployment of antibacterial factors and is mediated by the Gac/Rsm global regulatory pathway. Type VI secretion, and, unexpectedly, conjugative type IV secretion within competing bacteria, induce P. aeruginosa lysis and activate PARA, thus providing a mechanism for the enhanced capacity of P. aeruginosa to target bacteria that elaborate these factors. Our finding that bacteria sense damaged kin and respond via a widely distributed pathway to mount a complex response raises the possibility that danger sensing is an evolutionarily conserved process. DOI:http://dx.doi.org/10.7554/eLife.05701.001 Bacteria live in diverse and changing environments where resources such as nutrients and space are often limited. They have thus evolved many survival strategies, including competitive and cooperative behaviors. In the first case, bacteria antagonize or prevent the growth of other microorganisms competing with them for resources, such as by generating antibiotics that specifically target rivals. During cooperation, bacteria may coordinate the production of compounds that have a shared benefit for members of their community. In multicellular organisms, some cell types sense harmful microorganisms by the injury they cause in neighboring cells. This triggers a process that can lead to the production of molecules that kill the invaders and factors that promote the repair of cellular damage. An equivalent process has so far not been described for single-celled organisms such as bacteria. However, bacteria often live in structured groups containing many different species. In this type of growth environment, the ability of bacteria to sense when others of their species are attacked and to respond by taking measures to defend themselves could improve their chances of survival. Now, LeRoux et al. reveal that the bacterium Pseudomonas aeruginosa is able to detect ‘danger signals’ released when neighboring P. aeruginosa cells are killed by other bacteria. These signals trigger a response in surviving cells by turning on a pathway that controls a number of antibacterial factors. These include the production of the so-called ‘type VI secretion system’, a molecular machine that delivers a potent cocktail of antibacterial toxins directly into nearby bacteria. This process, which LeRoux et al. have named ‘P. aeruginosa response to antagonism’, or PARA for short, enables P. aeruginosa to thrive when grown with competing bacterial species. P. aeruginosa is notorious for infecting the lungs of people with the genetic disease cystic fibrosis, as well as chronic wounds often found in people with diabetes. In both cases, when P. aeruginosa is present, the numbers of other, often less harmful organisms, tend to decrease. PARA may be one reason for the success of P. aeruginosa in these multi-species infections. DOI:http://dx.doi.org/10.7554/eLife.05701.002
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Affiliation(s)
- Michele LeRoux
- Department of Microbiology, University of Washington, Seattle, United States
| | - Robin L Kirkpatrick
- Department of Microbiology, University of Washington, Seattle, United States
| | - Elena I Montauti
- Department of Microbiology, University of Washington, Seattle, United States
| | - Bao Q Tran
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, United States
| | - S Brook Peterson
- Department of Microbiology, University of Washington, Seattle, United States
| | - Brittany N Harding
- Department of Microbiology, University of Washington, Seattle, United States
| | - John C Whitney
- Department of Microbiology, University of Washington, Seattle, United States
| | - Alistair B Russell
- Department of Microbiology, University of Washington, Seattle, United States
| | - Beth Traxler
- Department of Microbiology, University of Washington, Seattle, United States
| | - Young Ah Goo
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, United States
| | - David R Goodlett
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, United States
| | - Paul A Wiggins
- Department of Physics, University of Washington, Seattle, United States
| | - Joseph D Mougous
- Department of Microbiology, University of Washington, Seattle, United States
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21
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Chen L, Zou Y, She P, Wu Y. Composition, function, and regulation of T6SS in Pseudomonas aeruginosa. Microbiol Res 2015; 172:19-25. [PMID: 25721475 DOI: 10.1016/j.micres.2015.01.004] [Citation(s) in RCA: 100] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2014] [Revised: 01/03/2015] [Accepted: 01/03/2015] [Indexed: 11/17/2022]
Abstract
Bacterial cells can communicate with their surrounding environment through secretion systems. Type VI secretion system (T6SS) is one of the most recently discovered secretion systems, which is distributed widely in Gram-negative bacteria such as Pseudomonas aeruginosa (P. aeruginosa), an important opportunistic pathogen. This protein secretion system shares similarity with the puncturing device of bacteriophages in structure. P. aeruginosa is an important opportunistic pathogen and distributes widely in diverse environment. T6SS is beneficial to survival advantage of P. aeruginosa by delivering toxins to its neighboring pathogens and translocating protein effectors into the host cells. T6SS is also the virulence factor and takes part in biofilm formation of P. aeruginosa. The functions of T6SS in P. aeruginosa are regulated at transcriptional, posttranscriptional and posttranslational levels by diverse mechanisms. This article reviews the latest progress in the structure, effector proteins, biological function, and regulation mechanisms of P. aeruginosa T6SS.
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Affiliation(s)
- Lihua Chen
- Department of Medicine Clinical Laboratory, The Third Xiangya Hospital of Central South University, Changsha 410013, Hunan, PR China
| | - Yaru Zou
- Department of Medicine Clinical Laboratory, The Third Xiangya Hospital of Central South University, Changsha 410013, Hunan, PR China
| | - Pengfei She
- Department of Medicine Clinical Laboratory, The Third Xiangya Hospital of Central South University, Changsha 410013, Hunan, PR China
| | - Yong Wu
- Department of Medicine Clinical Laboratory, The Third Xiangya Hospital of Central South University, Changsha 410013, Hunan, PR China.
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22
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Durand E, Cambillau C, Cascales E, Journet L. VgrG, Tae, Tle, and beyond: the versatile arsenal of Type VI secretion effectors. Trends Microbiol 2014; 22:498-507. [DOI: 10.1016/j.tim.2014.06.004] [Citation(s) in RCA: 156] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Revised: 06/16/2014] [Accepted: 06/18/2014] [Indexed: 12/20/2022]
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23
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Ghequire MGK, De Mot R. Ribosomally encoded antibacterial proteins and peptides from Pseudomonas. FEMS Microbiol Rev 2014; 38:523-68. [PMID: 24923764 DOI: 10.1111/1574-6976.12079] [Citation(s) in RCA: 139] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Revised: 05/05/2014] [Accepted: 05/16/2014] [Indexed: 12/26/2022] Open
Abstract
Members of the Pseudomonas genus produce diverse secondary metabolites affecting other bacteria, fungi or predating nematodes and protozoa but are also equipped with the capacity to secrete different types of ribosomally encoded toxic peptides and proteins, ranging from small microcins to large tailocins. Studies with the human pathogen Pseudomonas aeruginosa have revealed that effector proteins of type VI secretion systems are part of the antibacterial armamentarium deployed by pseudomonads. A novel class of antibacterial proteins with structural similarity to plant lectins was discovered by studying antagonism among plant-associated Pseudomonas strains. A genomic perspective on pseudomonad bacteriocinogeny shows that the modular architecture of S pyocins of P. aeruginosa is retained in a large diversified group of bacteriocins, most of which target DNA or RNA. Similar modularity is present in as yet poorly characterized Rhs (recombination hot spot) proteins and CDI (contact-dependent inhibition) proteins. Well-delimited domains for receptor recognition or cytotoxicity enable the design of chimeric toxins with novel functionalities, which has been applied successfully for S and R pyocins. Little is known regarding how these antibacterials are released and ultimately reach their targets. Other remaining issues concern the identification of environmental triggers activating these systems and assessment of their ecological impact in niches populated by pseudomonads.
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24
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Lu D, Shang G, Zhang H, Yu Q, Cong X, Yuan J, He F, Zhu C, Zhao Y, Yin K, Chen Y, Hu J, Zhang X, Yuan Z, Xu S, Hu W, Cang H, Gu L. Structural insights into the T6SS effector protein Tse3 and the Tse3-Tsi3 complex fromPseudomonas aeruginosareveal a calcium-dependent membrane-binding mechanism. Mol Microbiol 2014; 92:1092-112. [DOI: 10.1111/mmi.12616] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/10/2014] [Indexed: 12/22/2022]
Affiliation(s)
- Defen Lu
- State Key Laboratory of Microbial Technology; Shandong University; Jinan 250100 Shandong China
- The Liver Centre of Fujian Province; MengChao Hepatobiliary Hospital of Fujian Medical University; Fuzhou 350025 Fujian China
| | - Guijun Shang
- State Key Laboratory of Microbial Technology; Shandong University; Jinan 250100 Shandong China
| | - Heqiao Zhang
- Institute of Biophysics; Chinese Academy of Sciences; Beijing 100101 China
- School of Life Sciences; Tsinghua University; Beijing 100084 China
| | - Qian Yu
- State Key Laboratory of Microbial Technology; Shandong University; Jinan 250100 Shandong China
| | - Xiaoyan Cong
- State Key Laboratory of Microbial Technology; Shandong University; Jinan 250100 Shandong China
| | - Jupeng Yuan
- Institute of Medical Genetics; Shandong University School of Medicine; Jinan 250012 Shandong China
| | - Fengjuan He
- Institute of Medical Genetics; Shandong University School of Medicine; Jinan 250012 Shandong China
| | - Chunyuan Zhu
- State Key Laboratory of Microbial Technology; Shandong University; Jinan 250100 Shandong China
| | - Yanyu Zhao
- State Key Laboratory of Microbial Technology; Shandong University; Jinan 250100 Shandong China
| | - Kun Yin
- State Key Laboratory of Microbial Technology; Shandong University; Jinan 250100 Shandong China
| | - Yuanyuan Chen
- Institute of Biophysics; Chinese Academy of Sciences; Beijing 100101 China
| | - Junqiang Hu
- State Key Laboratory of Microbial Technology; Shandong University; Jinan 250100 Shandong China
| | - Xiaodan Zhang
- State Key Laboratory of Microbial Technology; Shandong University; Jinan 250100 Shandong China
| | - Zenglin Yuan
- State Key Laboratory of Microbial Technology; Shandong University; Jinan 250100 Shandong China
| | - Sujuan Xu
- State Key Laboratory of Microbial Technology; Shandong University; Jinan 250100 Shandong China
| | - Wei Hu
- State Key Laboratory of Microbial Technology; Shandong University; Jinan 250100 Shandong China
| | - Huaixing Cang
- Institute of Biophysics; Chinese Academy of Sciences; Beijing 100101 China
| | - Lichuan Gu
- State Key Laboratory of Microbial Technology; Shandong University; Jinan 250100 Shandong China
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25
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Jiang F, Waterfield N, Yang J, Yang G, Jin Q. A Pseudomonas aeruginosa Type VI Secretion Phospholipase D Effector Targets Both Prokaryotic and Eukaryotic Cells. Cell Host Microbe 2014; 15:600-10. [DOI: 10.1016/j.chom.2014.04.010] [Citation(s) in RCA: 175] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2013] [Revised: 01/28/2014] [Accepted: 03/21/2014] [Indexed: 02/06/2023]
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26
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Whitney JC, Beck CM, Goo YA, Russell AB, Harding BN, De Leon JA, Cunningham DA, Tran BQ, Low DA, Goodlett DR, Hayes CS, Mougous JD. Genetically distinct pathways guide effector export through the type VI secretion system. Mol Microbiol 2014; 92:529-42. [PMID: 24589350 DOI: 10.1111/mmi.12571] [Citation(s) in RCA: 139] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/28/2014] [Indexed: 12/01/2022]
Abstract
Bacterial secretion systems often employ molecular chaperones to recognize and facilitate export of their substrates. Recent work demonstrated that a secreted component of the type VI secretion system (T6SS), haemolysin co-regulated protein (Hcp), binds directly to effectors, enhancing their stability in the bacterial cytoplasm. Herein, we describe a quantitative cellular proteomics screen for T6S substrates that exploits this chaperone-like quality of Hcp. Application of this approach to the Hcp secretion island I-encoded T6SS (H1-T6SS) of Pseudomonas aeruginosa led to the identification of a novel effector protein, termed Tse4 (type VI secretion exported 4), subsequently shown to act as a potent intra-specific H1-T6SS-delivered antibacterial toxin. Interestingly, our screen failed to identify two predicted H1-T6SS effectors, Tse5 and Tse6, which differ from Hcp-stabilized substrates by the presence of toxin-associated PAAR-repeat motifs and genetic linkage to members of the valine-glycine repeat protein G (vgrG) genes. Genetic studies further distinguished these two groups of effectors: Hcp-stabilized effectors were found to display redundancy in interbacterial competition with respect to the requirement for the two H1-T6SS-exported VgrG proteins, whereas Tse5 and Tse6 delivery strictly required a cognate VgrG. Together, we propose that interaction with either VgrG or Hcp defines distinct pathways for T6S effector export.
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Affiliation(s)
- John C Whitney
- Department of Microbiology, University of Washington, Seattle, WA, 98195, USA
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Zhang J, Zhang H, Liu Y, Zhan L, She Z, Dong C, Dong Y. Crystallization and preliminary X-ray study of TsiV3 from Vibrio cholerae. Acta Crystallogr F Struct Biol Commun 2014; 70:335-8. [PMID: 24598921 PMCID: PMC3944696 DOI: 10.1107/s2053230x14001599] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2013] [Accepted: 01/22/2014] [Indexed: 11/10/2022] Open
Abstract
The bacterial type VI secretion system (T6SS), a dynamic organelle, participates in microbial competition by transporting toxic effector molecules to neighbouring cells to kill competitors. TsiV3, a recently defined T6SS immunity protein in Vibrio cholerae, possesses self-protection against killing by T6SS predatory cells by directly binding to and inhibiting their effector protein VgrG-3. Structural information about TsiV3 could help to illuminate its specific mechanism. In this study, TsiV3 from V. cholerae was cloned, expressed and crystallized and single-crystal X-ray diffraction data sets were collected to a resolution of 2.55 Å. Specifically, the crystal belonged to space group P212121, with unit-cell parameters a = 73.3, b = 78.12, c = 106.18 Å. Matthews coefficient calculations indicated that the crystal may contain six TsiV3 molecules in one asymmetric unit, with a VM value of 2.25 Å(3) Da(-1) and a solvent content of 45.42%.
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Affiliation(s)
- Jiulong Zhang
- School of Life Sciences, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026, People’s Republic of China
| | - Heng Zhang
- State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, No. 5 Yiheyuan Road, Beijing 100871, People’s Republic of China
| | - Ying Liu
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
| | - Lihong Zhan
- School of Life Sciences, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026, People’s Republic of China
| | - Zhun She
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
| | - Cheng Dong
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
- State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin 300071, People’s Republic of China
| | - Yuhui Dong
- Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
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Douzi B, Spinelli S, Blangy S, Roussel A, Durand E, Brunet YR, Cascales E, Cambillau C. Crystal structure and self-interaction of the type VI secretion tail-tube protein from enteroaggregative Escherichia coli. PLoS One 2014; 9:e86918. [PMID: 24551044 PMCID: PMC3925092 DOI: 10.1371/journal.pone.0086918] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2013] [Accepted: 12/15/2013] [Indexed: 11/29/2022] Open
Abstract
The type VI secretion system (T6SS) is a widespread machine used by bacteria to control their environment and kill or disable bacterial species or eukaryotes through toxin injection. The T6SS comprises a central tube formed of stacked hexamers of hemolysin co-regulated proteins (Hcp) and terminated by a trimeric valine-glycine repeat protein G (VgrG) component, the cell puncturing device. A contractile tail sheath, formed by the TssB and TssC proteins, surrounds this tube. This syringe-like machine has been compared to an inverted phage, as both Hcp and VgrG share structural homology with tail components of Caudovirales. Here we solved the crystal structure of a tryptophan-substituted double mutant of Hcp1 from enteroaggregative Escherichia coli and compared it to the structures of other Hcps. Interestingly, we observed that the purified Hcp native protein is unable to form tubes in vitro. To better understand the rationale for observation, we measured the affinity of Hcp1 hexamers with themselves by surface plasmon resonance. The intra-hexamer interaction is weak, with a KD value of 7.2 µM. However, by engineering double cysteine mutants at defined positions, tubes of Hcp1 gathering up to 15 stacked hexamers formed in oxidative conditions. These results, together with those available in the literature regarding TssB and TssC, suggest that assembly of the T6SS tube differs significantly from that of Sipho- or Myoviridae.
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Affiliation(s)
- Badreddine Douzi
- Aix-Marseille Université, Architecture et Fonction des Macromolécules Biologiques, UMR 7257, Campus de Luminy, Case 932, Marseille, France
- Centre National de la Recherche Scientifique, Architecture et Fonction des Macromolécules Biologiques, UMR 7257, Campus de Luminy, Case 932, Marseille, France
| | - Silvia Spinelli
- Aix-Marseille Université, Architecture et Fonction des Macromolécules Biologiques, UMR 7257, Campus de Luminy, Case 932, Marseille, France
- Centre National de la Recherche Scientifique, Architecture et Fonction des Macromolécules Biologiques, UMR 7257, Campus de Luminy, Case 932, Marseille, France
| | - Stéphanie Blangy
- Aix-Marseille Université, Architecture et Fonction des Macromolécules Biologiques, UMR 7257, Campus de Luminy, Case 932, Marseille, France
- Centre National de la Recherche Scientifique, Architecture et Fonction des Macromolécules Biologiques, UMR 7257, Campus de Luminy, Case 932, Marseille, France
| | - Alain Roussel
- Aix-Marseille Université, Architecture et Fonction des Macromolécules Biologiques, UMR 7257, Campus de Luminy, Case 932, Marseille, France
- Centre National de la Recherche Scientifique, Architecture et Fonction des Macromolécules Biologiques, UMR 7257, Campus de Luminy, Case 932, Marseille, France
| | - Eric Durand
- Aix-Marseille Université, Architecture et Fonction des Macromolécules Biologiques, UMR 7257, Campus de Luminy, Case 932, Marseille, France
- Centre National de la Recherche Scientifique, Architecture et Fonction des Macromolécules Biologiques, UMR 7257, Campus de Luminy, Case 932, Marseille, France
| | - Yannick R. Brunet
- Laboratoire d’Ingénierie des Systèmes Macromoléculaires, Institut de Microbiologie de la Méditerranée, Centre National de la Recherche Scientifique UMR7255, Aix-Marseille Université, Marseille, France
| | - Eric Cascales
- Laboratoire d’Ingénierie des Systèmes Macromoléculaires, Institut de Microbiologie de la Méditerranée, Centre National de la Recherche Scientifique UMR7255, Aix-Marseille Université, Marseille, France
| | - Christian Cambillau
- Aix-Marseille Université, Architecture et Fonction des Macromolécules Biologiques, UMR 7257, Campus de Luminy, Case 932, Marseille, France
- Centre National de la Recherche Scientifique, Architecture et Fonction des Macromolécules Biologiques, UMR 7257, Campus de Luminy, Case 932, Marseille, France
- * E-mail:
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Tümmler B, Wiehlmann L, Klockgether J, Cramer N. Advances in understanding Pseudomonas. F1000PRIME REPORTS 2014; 6:9. [PMID: 24592321 PMCID: PMC3913036 DOI: 10.12703/p6-9] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Pseudomonas aeruginosa, the type species of pseudomonads, is an opportunistic pathogen that colonizes a wide range of niches. Current genome sequencing projects are producing previously inconceivable detail about the population biology and evolution of P. aeruginosa. Its pan-genome has a larger genetic repertoire than the human genome, which explains the broad metabolic capabilities of P. aeruginosa and its ubiquitous distribution in aquatic habitats. P. aeruginosa may persist in the airways of individuals with cystic fibrosis for decades. The ongoing whole-genome analyses of serial isolates from cystic fibrosis patients provide the so far singular opportunity to monitor the microevolution of a bacterial pathogen during chronic infection over thousands of generations. Although the evolution in cystic fibrosis lungs is neutral overall, some pathoadaptive mutations are selected during the within-host evolutionary process. Even a single mutation may be sufficient to generate novel complex traits provided that predisposing mutational events have previously occurred in the clonal lineage.
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Russell AB, Peterson SB, Mougous JD. Type VI secretion system effectors: poisons with a purpose. Nat Rev Microbiol 2014; 12:137-48. [PMID: 24384601 DOI: 10.1038/nrmicro3185] [Citation(s) in RCA: 501] [Impact Index Per Article: 50.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The type VI secretion system (T6SS) mediates interactions between a broad range of Gram-negative bacterial species. Recent studies have led to a substantial increase in the number of characterized T6SS effector proteins and a more complete and nuanced view of the adaptive importance of the system. Although the T6SS is most often implicated in antagonism, in this Review, we consider the case for its involvement in both antagonistic and non-antagonistic behaviours. Clarifying the roles that type VI secretion has in microbial communities will contribute to broader efforts to understand the importance of microbial interactions in maintaining human and environmental health, and will inform efforts to manipulate these interactions for therapeutic or environmental benefit.
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Affiliation(s)
- Alistair B Russell
- Department of Microbiology, University of Washington, Seattle, Washington 98195, USA
| | - S Brook Peterson
- Department of Microbiology, University of Washington, Seattle, Washington 98195, USA
| | - Joseph D Mougous
- Department of Microbiology, University of Washington, Seattle, Washington 98195, USA
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31
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Chang JH, Desveaux D, Creason AL. The ABCs and 123s of bacterial secretion systems in plant pathogenesis. ANNUAL REVIEW OF PHYTOPATHOLOGY 2014; 52:317-45. [PMID: 24906130 DOI: 10.1146/annurev-phyto-011014-015624] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Bacteria have many export and secretion systems that translocate cargo into and across biological membranes. Seven secretion systems contribute to pathogenicity by translocating proteinaceous cargos that can be released into the extracellular milieu or directly into recipient cells. In this review, we describe these secretion systems and how their complexities and functions reflect differences in the destinations, states, functions, and sizes of the translocated cargos as well as the architecture of the bacterial cell envelope. We examine the secretion systems from the perspective of pathogenic bacteria that proliferate within plant tissues and highlight examples of translocated proteins that contribute to the infection and disease of plant hosts.
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Affiliation(s)
- Jeff H Chang
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331; ,
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Benz J, Meinhart A. Antibacterial effector/immunity systems: it's just the tip of the iceberg. Curr Opin Microbiol 2013; 17:1-10. [PMID: 24581686 DOI: 10.1016/j.mib.2013.11.002] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2013] [Revised: 10/31/2013] [Accepted: 11/09/2013] [Indexed: 01/22/2023]
Abstract
Bacteria do not live anchoretic; rather they are constantly in touch with their eukaryotic hosts and with other bacteria sharing their habitat. Therefore, bacteria have evolved sophisticated proteinaceous weapons. To harm other bacteria, they produce antibacterial effector proteins, which they either release into the environment or export via direct intercellular contact. Contact-dependent killing is mediated by two specialized secretion systems, the type V and VI secretion system, whereas contact-independent processes hijack other transport mechanisms. Regardless of the transport system, cells co-express immunity proteins to protect themselves from suicide and fratricide. In general, effector protein activities and secretion mechanisms differ between Gram-positive and Gram-negative bacteria and evidence is emerging that different effector/immunity systems act synergistically and thus extend the bacterial armory.
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Affiliation(s)
- Juliane Benz
- Department of Biomolecular Mechanisms, Max-Planck Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany
| | - Anton Meinhart
- Department of Biomolecular Mechanisms, Max-Planck Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany.
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Srikannathasan V, English G, Bui NK, Trunk K, O’Rourke PEF, Rao VA, Vollmer W, Coulthurst SJ, Hunter WN. Structural basis for type VI secreted peptidoglycan DL-endopeptidase function, specificity and neutralization in Serratia marcescens. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2013; 69:2468-82. [PMID: 24311588 PMCID: PMC3852654 DOI: 10.1107/s0907444913022725] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/16/2013] [Accepted: 08/13/2013] [Indexed: 11/10/2022]
Abstract
Some Gram-negative bacteria target their competitors by exploiting the type VI secretion system to extrude toxic effector proteins. To prevent self-harm, these bacteria also produce highly specific immunity proteins that neutralize these antagonistic effectors. Here, the peptidoglycan endopeptidase specificity of two type VI secretion-system-associated effectors from Serratia marcescens is characterized. These small secreted proteins, Ssp1 and Ssp2, cleave between γ-D-glutamic acid and L-meso-diaminopimelic acid with different specificities. Ssp2 degrades the acceptor part of cross-linked tetratetrapeptides. Ssp1 displays greater promiscuity and cleaves monomeric tripeptides, tetrapeptides and pentapeptides and dimeric tetratetra and tetrapenta muropeptides on both the acceptor and donor strands. Functional assays confirm the identity of a catalytic cysteine in these endopeptidases and crystal structures provide information on the structure-activity relationships of Ssp1 and, by comparison, of related effectors. Functional assays also reveal that neutralization of these effectors by their cognate immunity proteins, which are called resistance-associated proteins (Raps), contributes an essential role to cell fitness. The structures of two immunity proteins, Rap1a and Rap2a, responsible for the neutralization of Ssp1 and Ssp2-like endopeptidases, respectively, revealed two distinct folds, with that of Rap1a not having previously been observed. The structure of the Ssp1-Rap1a complex revealed a tightly bound heteromeric assembly with two effector molecules flanking a Rap1a dimer. A highly effective steric block of the Ssp1 active site forms the basis of effector neutralization. Comparisons with Ssp2-Rap2a orthologues suggest that the specificity of these immunity proteins for neutralizing effectors is fold-dependent and that in cases where the fold is conserved sequence differences contribute to the specificity of effector-immunity protein interactions.
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Affiliation(s)
- Velupillai Srikannathasan
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
| | - Grant English
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
| | - Nhat Khai Bui
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, England
| | - Katharina Trunk
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
| | - Patrick E. F. O’Rourke
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
| | - Vincenzo A. Rao
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
| | - Waldemar Vollmer
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, England
| | - Sarah J. Coulthurst
- Division of Molecular Microbiology, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
| | - William N. Hunter
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH, Scotland
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Wang T, Ding J, Zhang Y, Wang DC, Liu W. Complex structure of type VI peptidoglycan muramidase effector and a cognate immunity protein. ACTA CRYSTALLOGRAPHICA. SECTION D, BIOLOGICAL CRYSTALLOGRAPHY 2013; 69:1889-900. [PMID: 24100309 PMCID: PMC3792639 DOI: 10.1107/s090744491301576x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/09/2013] [Accepted: 06/06/2013] [Indexed: 11/19/2022]
Abstract
The type VI secretion system (T6SS) is a bacterial protein-export machine that is capable of delivering virulence effectors between Gram-negative bacteria. The T6SS of Pseudomonas aeruginosa transports two lytic enzymes, Tse1 and Tse3, to degrade cell-wall peptidoglycan in the periplasm of rival bacteria that are competing for niches via amidase and muramidase activities, respectively. Two cognate immunity proteins, Tsi1 and Tsi3, are produced by the bacterium to inactivate the two antibacterial effectors, thereby protecting its siblings from self-intoxication. Recently, Tse1-Tsi1 has been structurally characterized. Here, the structure of the Tse3-Tsi3 complex is reported at 1.9 Å resolution. The results reveal that Tse3 contains a C-terminal catalytic domain that adopts a soluble lytic transglycosylase (SLT) fold in which three calcium-binding sites were surprisingly observed close to the catalytic Glu residue. The electrostatic properties of the substrate-binding groove are also distinctive from those of known structures with a similar fold. All of these features imply that a unique catalytic mechanism is utilized by Tse3 in cleaving glycosidic bonds. Tsi3 comprises a single domain showing a β-sandwich architecture that is reminiscent of the immunoglobulin fold. Three loops of Tsi3 insert deeply into the groove of Tse3 and completely occlude its active site, which forms the structural basis of Tse3 inactivation. This work is the first crystallographic report describing the three-dimensional structure of the Tse3-Tsi3 effector-immunity pair.
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Affiliation(s)
- Tianyu Wang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China
- University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
| | - Jinjing Ding
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China
| | - Ying Zhang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China
| | - Da-Cheng Wang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, People’s Republic of China
| | - Wei Liu
- Institute of Immunology, The Third Military Medical University, Chongqing 400038, People’s Republic of China
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Li L, Zhang W, Liu Q, Gao Y, Gao Y, Wang Y, Wang DZ, Li Z, Wang T. Structural Insights on the bacteriolytic and self-protection mechanism of muramidase effector Tse3 in Pseudomonas aeruginosa. J Biol Chem 2013; 288:30607-30613. [PMID: 24025333 DOI: 10.1074/jbc.c113.506097] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The warfare among microbial species as well as between pathogens and hosts is fierce, complicated, and continuous. In Pseudomonas aeruginosa, the muramidase effector Tse3 (Type VI secretion exported 3) can be injected into the periplasm of neighboring bacterial competitors by a Type VI secretion apparatus, eventually leading to cell lysis and death. However, P. aeruginosa protects itself from lysis by expressing immune protein Tsi3 (Type six secretion immunity 3). Here, we report the crystal structure of the Tse3-Tsi3 complex at 1.8 Å resolution, revealing that Tse3 possesses one open accessible, goose-type lysozyme-like domain with peptidoglycan hydrolysis activity. Calcium ions bind specifically in the Tse3 active site and are identified to be crucial for its bacteriolytic activity. In combination with biochemical studies, the structural basis of self-protection mechanism of Tsi3 is also elucidated, thus providing an understanding and new insights into the effectors of Type VI secretion system.
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Affiliation(s)
- Lianbo Li
- From the Laboratory for Computational Chemistry and Drug Design and
| | - Weili Zhang
- From the Laboratory for Computational Chemistry and Drug Design and
| | - Qisong Liu
- Key Laboratory of Chemical Genomics, School of Chemical Biology & Biotechnology, Peking University, Shenzhen Graduate School, Shenzhen 518055, China
| | - Yu Gao
- From the Laboratory for Computational Chemistry and Drug Design and
| | - Ying Gao
- From the Laboratory for Computational Chemistry and Drug Design and
| | - Yun Wang
- From the Laboratory for Computational Chemistry and Drug Design and
| | - David Zhigang Wang
- Key Laboratory of Chemical Genomics, School of Chemical Biology & Biotechnology, Peking University, Shenzhen Graduate School, Shenzhen 518055, China.
| | - Zigang Li
- Key Laboratory of Chemical Genomics, School of Chemical Biology & Biotechnology, Peking University, Shenzhen Graduate School, Shenzhen 518055, China.
| | - Tao Wang
- From the Laboratory for Computational Chemistry and Drug Design and.
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36
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Silverman JM, Agnello DM, Zheng H, Andrews BT, Li M, Catalano CE, Gonen T, Mougous JD. Haemolysin coregulated protein is an exported receptor and chaperone of type VI secretion substrates. Mol Cell 2013; 51:584-93. [PMID: 23954347 DOI: 10.1016/j.molcel.2013.07.025] [Citation(s) in RCA: 205] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2013] [Revised: 06/27/2013] [Accepted: 07/25/2013] [Indexed: 10/26/2022]
Abstract
Secretion systems require high-fidelity mechanisms to discriminate substrates among the vast cytoplasmic pool of proteins. Factors mediating substrate recognition by the type VI secretion system (T6SS) of Gram-negative bacteria, a widespread pathway that translocates effector proteins into target bacterial cells, have not been defined. We report that haemolysin coregulated protein (Hcp), a ring-shaped hexamer secreted by all characterized T6SSs, binds specifically to cognate effector molecules. Electron microscopy analysis of an Hcp-effector complex from Pseudomonas aeruginosa revealed the effector bound to the inner surface of Hcp. Further studies demonstrated that interaction with the Hcp pore is a general requirement for secretion of diverse effectors encompassing several enzymatic classes. Though previous models depict Hcp as a static conduit, our data indicate it is a chaperone and receptor of substrates. These unique functions of a secreted protein highlight fundamental differences between the export mechanism of T6 and other characterized secretory pathways.
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Affiliation(s)
- Julie M Silverman
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA
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37
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Structural insights into the inhibition of type VI effector Tae3 by its immunity protein Tai3. Biochem J 2013; 454:59-68. [DOI: 10.1042/bj20130193] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The recently described T6SS (type VI secretion system) acts as a needle that punctures the membrane of the target cells to deliver effector proteins. Type VI amidase effectors can be classified into four divergent families (Tae1–Tae4). These effectors are secreted into the periplasmic space of neighbouring cells via the T6SS and subsequently rupture peptidoglycan. However, the donor cells are protected from damage because of the presence of their cognate immunity proteins [Tai1 (type VI amidase immunity 1)–Tai4]. In the present paper, we describe the structure of Tae3 in complex with Tai3. The Tae3–Tai3 complex exists as a stable heterohexamer, which is composed of two Tae3 molecules and two Tai3 homodimers (Tae3–Tai34–Tae3). Tae3 shares a common NlpC/P60 fold, which consists of N-terminal and C-terminal subdomains. Structural analysis indicates that two unique loops around the catalytic cleft adopt a closed conformation, resulting in a narrow and extended groove involved in the binding of the substrate. The inhibition of Tae3 is attributed to the insertion of the Ω-loop (loop of α3–α4) of Tai3 into the catalytic groove. Furthermore, a cell viability assay confirmed that a conserved motif (Gln-Asp-Xaa) in Tai3 members may play a key role in the inhibition process. Taken together, the present study has revealed a novel inhibition mechanism and provides insights into the role played by T6SS in interspecific competition.
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38
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Bleumink-Pluym NMC, van Alphen LB, Bouwman LI, Wösten MMSM, van Putten JPM. Identification of a functional type VI secretion system in Campylobacter jejuni conferring capsule polysaccharide sensitive cytotoxicity. PLoS Pathog 2013; 9:e1003393. [PMID: 23737749 PMCID: PMC3667781 DOI: 10.1371/journal.ppat.1003393] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Accepted: 04/10/2013] [Indexed: 11/27/2022] Open
Abstract
The pathogen Campylobacter jejuni is the principal cause of bacterial food-borne infections. The mechanism(s) that contribute to bacterial survival and disease are still poorly understood. In other bacterial species, type VI secretion systems (T6SS) are increasingly recognized to contribute to bacterial pathogenesis by toxic effects on host cells or competing bacterial species. Here we report the presence of a functional Type VI secretion system in C. jejuni. Proteome and genetic analyses revealed that C. jejuni strain 108 contains a 17-kb T6SS gene cluster consisting of 13 T6SS-conserved genes, including the T6SS hallmark genes hcp and vgrG. The cluster lacks an ortholog of the ClpV ATPase considered important for T6SS function. The sequence and organization of the C. jejuni T6SS genes resemble those of the T6SS located on the HHGI1 pathogenicity island of Helicobacter hepaticus. The C. jejuni T6SS is integrated into the earlier acquired Campylobacter integrated element CJIE3 and is present in about 10% of C. jejuni isolates including several isolates derived from patients with the rare clinical feature of C. jejuni bacteremia. Targeted mutagenesis of C. jejuni T6SS genes revealed T6SS-dependent secretion of the Hcp needle protein into the culture supernatant. Infection assays provided evidence that the C. jejuni T6SS confers contact-dependent cytotoxicity towards red blood cells but not macrophages. This trait was observed only in a capsule-deficient bacterial phenotype. The unique C. jejuni T6SS phenotype of capsule-sensitive contact-mediated hemolysis represents a novel evolutionary pathway of T6SS in bacteria and expands the repertoire of virulence properties associated with T6SS. Bacteria contain a number of secretion systems to export macromolecules to the environment. The bacterial type VI secretion system (T6SS) forms a needle-like structure that delivers toxic effector molecules to neighboring eukaryotic and/or prokaryotic cells. Here we report that the important human pathogen Campylobacter jejuni contains a functional T6SS gene cluster. The cluster comprises 13 conserved T6SS genes including genes encoding the typical T6SS Hcp and VgrG proteins. The gene cluster is part of a larger DNA element and is present in about 10% of C. jejuni strains including several blood isolates. The identified C. jejuni T6SS has unique properties compared to similar systems in other bacterial species. C. jejuni T6SS lacks the ClpV ATPase that supposedly energizes part of T6SS function in other species, causes contact-dependent lysis of red blood cells, and requires downregulation of the C. jejuni capsule polysaccharide to be effective. The unique cytotoxic properties of C. jejuni T6SS, the effect of the capsule on T6SS function, and the possible association with systemic C. jejuni infection broaden the scope of the existing bacterial T6SS phenotypes and point to a different evolution of C. jejuni T6SS compared to other bacterial species.
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Affiliation(s)
| | - Lieke B. van Alphen
- Department of Infectious Diseases & Immunology, Utrecht University, Utrecht, the Netherlands
| | - Lieneke I. Bouwman
- Department of Infectious Diseases & Immunology, Utrecht University, Utrecht, the Netherlands
| | - Marc M. S. M. Wösten
- Department of Infectious Diseases & Immunology, Utrecht University, Utrecht, the Netherlands
| | - Jos P. M. van Putten
- Department of Infectious Diseases & Immunology, Utrecht University, Utrecht, the Netherlands
- * E-mail:
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39
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Lu D, Shang G, Yu Q, Zhang H, Zhao Y, Cang H, Gu L, Xu S, Huang Y. Expression, purification and preliminary crystallographic analysis of the T6SS effector protein Tse3 from Pseudomonas aeruginosa. Acta Crystallogr Sect F Struct Biol Cryst Commun 2013; 69:524-7. [PMID: 23695568 DOI: 10.1107/s1744309113007148] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2013] [Accepted: 03/14/2013] [Indexed: 01/13/2023]
Abstract
Pseudomonas aeruginosa uses the type VI secretion system (T6SS) to inject effector proteins into rival cells in niche competition. Tse3, one of the effectors of T6SS, is delivered into the periplasm of recipient cells. Tse3 functions as a muramidase that degrades the β-1,4-linkage between N-acetylmuramic acid (MurNAc) and N-acetylglucosamine (GlcNAc) in peptidoglycan, thus leading to lysis of the recipient cells and providing a competitive advantage to the donor cells. Here, the preliminary crystallographic study of Tse3 is reported. A crystal of Tse3 diffracted to 1.5 Å resolution. It belonged to space group C121, with unit-cell parameters a = 166.99, b = 70.13, c = 41.94 Å, α = 90.00, β = 90.52, γ = 90.00° and one molecule per asymmetric unit.
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Affiliation(s)
- Defen Lu
- State Key Laboratory of Microbial Technology, Shandong University, Jinan 250100, PR China
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40
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Tit-for-tat: type VI secretion system counterattack during bacterial cell-cell interactions. Cell 2013; 152:884-94. [PMID: 23415234 DOI: 10.1016/j.cell.2013.01.042] [Citation(s) in RCA: 375] [Impact Index Per Article: 34.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2012] [Revised: 11/08/2012] [Accepted: 01/24/2013] [Indexed: 12/24/2022]
Abstract
The bacterial type VI secretion system (T6SS) is a dynamic organelle that bacteria use to target prey cells for inhibition via translocation of effector proteins. Time-lapse fluorescence microscopy has documented striking dynamics of opposed T6SS organelles in adjacent sister cells of Pseudomonas aeruginosa. Such cell-cell interactions have been termed "T6SS dueling" and likely reflect a biological process that is driven by T6SS antibacterial attack. Here, we show that T6SS dueling behavior strongly influences the ability of P. aeruginosa to prey upon heterologous bacterial species. We show that, in the case of P. aeruginosa, T6SS-dependent killing of either Vibrio cholerae or Acinetobacter baylyi is greatly stimulated by T6SS activity occurring in those prey species. Our data suggest that, in P. aeruginosa, T6SS organelle assembly and lethal counterattack are regulated by a signal that corresponds to the point of attack of the T6SS apparatus elaborated by a second aggressive T6SS(+) bacterial cell. PAPERFLICK:
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41
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Coulthurst SJ. The Type VI secretion system - a widespread and versatile cell targeting system. Res Microbiol 2013; 164:640-54. [PMID: 23542428 DOI: 10.1016/j.resmic.2013.03.017] [Citation(s) in RCA: 135] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Accepted: 02/05/2013] [Indexed: 12/31/2022]
Abstract
The Type VI secretion system (T6SS) is the most recently described of the Gram-negative bacterial secretion systems and is widely distributed amongst diverse species. T6SSs are currently believed to be complex molecular machines which inject effector proteins into target cells and which incorporate a bacteriophage-like cell-puncturing device. T6SSs have been implicated in eukaryotic cell targeting and virulence in a range of important pathogens. More recently, 'antibacterial' T6SSs have been reported, which are used to efficiently target competitor bacterial cells by the injection of antibacterial toxins. Although it is clear that T6SSs can be deployed as versatile weapons to compete with other bacteria or attack simple or higher eukaryotes, much remains to be determined about this intriguing system.
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Affiliation(s)
- Sarah J Coulthurst
- Department of Molecular Microbiology, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK.
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42
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Hachani A, Lossi NS, Filloux A. A visual assay to monitor T6SS-mediated bacterial competition. J Vis Exp 2013:e50103. [PMID: 23542679 PMCID: PMC3639552 DOI: 10.3791/50103] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Type VI secretion systems (T6SSs) are molecular nanomachines allowing Gram-negative bacteria to transport and inject proteins into a wide variety of target cells1,2. The T6SS is composed of 13 core components and displays structural similarities with the tail-tube of bacteriophages3. The phage uses a tube and a puncturing device to penetrate the cell envelope of target bacteria and inject DNA. It is proposed that the T6SS is an inverted bacteriophage device creating a specific path in the bacterial cell envelope to drive effectors and toxins to the surface. The process could be taken further and the T6SS device could perforate other cells with which the bacterium is in contact, thus injecting the effectors into these targets. The tail tube and puncturing device parts of the T6SS are made with Hcp and VgrG proteins, respectively4,5. The versatility of the T6SS has been demonstrated through studies using various bacterial pathogens. The Vibrio cholerae T6SS can remodel the cytoskeleton of eukaryotic host cells by injecting an "evolved" VgrG carrying a C-terminal actin cross-linking domain6,7. Another striking example was recently documented using Pseudomonas aeruginosa which is able to target and kill bacteria in a T6SS-dependent manner, therefore promoting the establishment of bacteria in specific microbial niches and competitive environment8,9,10. In the latter case, three T6SS-secreted proteins, namely Tse1, Tse2 and Tse3 have been identified as the toxins injected in the target bacteria (Figure 1). The donor cell is protected from the deleterious effect of these effectors via an anti-toxin mechanism, mediated by the Tsi1, Tsi2 and Tsi3 immunity proteins8,9,10. This antimicrobial activity can be monitored when T6SS-proficient bacteria are co-cultivated on solid surfaces in competition with other bacterial species or with T6SS-inactive bacteria of the same species8,11,12,13. The data available emphasized a numerical approach to the bacterial competition assay, including time-consuming CFU counting that depends greatly on antibiotic makers. In the case of antibiotic resistant strains like P. aeruginosa, these methods can be inappropriate. Moreover, with the identification of about 200 different T6SS loci in more than 100 bacterial genomes14, a convenient screening tool is highly desirable. We developed an assay that is easy to use and requires standard laboratory material and reagents. The method offers a rapid and qualitative technique to monitor the T6SS-dependent bactericidal/bacteriostasis activity by using a reporter strain as a prey (in this case Escherichia coli DH5α) allowing a-complementation of the lacZ gene. Overall, this method is graphic and allows rapid identification of T6SS-related phenotypes on agar plates. This experimental protocol may be adapted to other strains or bacterial species taking into account specific conditions such as growth media, temperature or time of contact.
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Affiliation(s)
- Abderrahman Hachani
- MRC Centre for Molecular Bacteriology and Infection, Division of Cell and Molecular Biology, Imperial College London
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43
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Brooks TM, Unterweger D, Bachmann V, Kostiuk B, Pukatzki S. Lytic activity of the Vibrio cholerae type VI secretion toxin VgrG-3 is inhibited by the antitoxin TsaB. J Biol Chem 2013; 288:7618-7625. [PMID: 23341465 DOI: 10.1074/jbc.m112.436725] [Citation(s) in RCA: 137] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The type VI secretion system (T6SS) of Gram-negative bacteria has been implicated in microbial competition; however, which components serve purely structural roles, and which serve as toxic effectors remains unresolved. Here, we present evidence that VgrG-3 of the Vibrio cholerae T6SS has both structural and toxin activity. Specifically, we demonstrate that the C-terminal extension of VgrG-3 acts to degrade peptidoglycan and hypothesize that this assists in the delivery of accessory T6SS toxins of V. cholerae. To avoid self-intoxication, V. cholerae expresses an anti-toxin encoded immediately downstream of vgrG-3 that inhibits VgrG-3-mediated lysis through direct interaction.
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Affiliation(s)
- Teresa M Brooks
- Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
| | - Daniel Unterweger
- Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
| | - Verena Bachmann
- Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
| | - Benjamin Kostiuk
- Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
| | - Stefan Pukatzki
- Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada T6G 2S2.
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Zhang H, Zhang H, Gao ZQ, Wang WJ, Liu GF, Xu JH, Su XD, Dong YH. Structure of the type VI effector-immunity complex (Tae4-Tai4) provides novel insights into the inhibition mechanism of the effector by its immunity protein. J Biol Chem 2013; 288:5928-39. [PMID: 23288853 DOI: 10.1074/jbc.m112.434357] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
The type VI secretion system (T6SS), a multisubunit needle-like apparatus, has recently been found to play a role in interspecies interactions. The gram-negative bacteria harboring T6SS (donor) deliver the effectors into their neighboring cells (recipient) to kill them. Meanwhile, the cognate immunity proteins were employed to protect the donor cells against the toxic effectors. Tae4 (type VI amidase effector 4) and Tai4 (type VI amidase immunity 4) are newly identified T6SS effector-immunity pairs. Here, we report the crystal structures of Tae4 from Enterobacter cloacae and Tae4-Tai4 complexes from both E. cloacae and Salmonella typhimurium. Tae4 acts as a DL-endopeptidase and displays a typical N1pC/P60 domain. Unlike Tsi1 (type VI secretion immunity 1), Tai4 is an all-helical protein and forms a dimer in solution. The small angle x-ray scattering study combined with the analytical ultracentrifugation reveal that the Tae4-Tai4 complex is a compact heterotetramer that consists of a Tai4 dimer and two Tae4 molecules in solution. Structure-based mutational analysis of the Tae4-Tai4 interface shows that a helix (α3) of one subunit in dimeric Tai4 plays a major role in binding of Tae4, whereas a protruding loop (L4) in the other subunit is mainly responsible for inhibiting Tae4 activity. The inhibition process requires collaboration between the Tai4 dimer. These results reveal a novel and unique inhibition mechanism in effector-immunity pairs and suggest a new strategy to develop antipathogen drugs.
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Affiliation(s)
- Heng Zhang
- State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking University, No. 5 Yiheyuan Road, Beijing 100871, China
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45
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Quantitative single-cell characterization of bacterial interactions reveals type VI secretion is a double-edged sword. Proc Natl Acad Sci U S A 2012; 109:19804-9. [PMID: 23150540 DOI: 10.1073/pnas.1213963109] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Interbacterial interaction pathways play an important role in defining the structure and complexity of bacterial associations. A quantitative description of such pathways offers promise for understanding the forces that contribute to community composition. We developed time-lapse fluorescence microscopy methods for quantitation of interbacterial interactions and applied these to the characterization of type VI secretion (T6S) in Pseudomonas aeruginosa. Our analyses allowed a direct determination of the efficiency of recipient cell lysis catalyzed by this intercellular toxin delivery pathway and provided evidence that its arsenal extends beyond known effector proteins. Measurement of T6S apparatus localization revealed correlated activation among neighboring cells, which, taken together with genetic data, implicate the elaboration of a functional T6S apparatus with a marked increase in susceptibility to intoxication. This possibility was supported by the identification of T6S-inactivating mutations in a genome-wide screen for resistance to T6S-mediated intoxication and by time-lapse fluorescence microscopy analyses showing a decreased lysis rate of recipient cells lacking T6S function. Our discoveries highlight the utility of single-cell approaches for measuring interbacterial phenomena and provide a foundation for studying the contribution of a widespread bacterial interaction pathway to community structure.
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46
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English G, Trunk K, Rao VA, Srikannathasan V, Hunter WN, Coulthurst SJ. New secreted toxins and immunity proteins encoded within the Type VI secretion system gene cluster of Serratia marcescens. Mol Microbiol 2012; 86:921-36. [PMID: 22957938 PMCID: PMC3533786 DOI: 10.1111/mmi.12028] [Citation(s) in RCA: 99] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/03/2012] [Indexed: 12/29/2022]
Abstract
Protein secretion systems are critical to bacterial virulence and interactions with other organisms. The Type VI secretion system (T6SS) is found in many bacterial species and is used to target either eukaryotic cells or competitor bacteria. However, T6SS-secreted proteins have proven surprisingly elusive. Here, we identified two secreted substrates of the antibacterial T6SS from the opportunistic human pathogen, Serratia marcescens. Ssp1 and Ssp2, both encoded within the T6SS gene cluster, were confirmed as antibacterial toxins delivered by the T6SS. Four related proteins encoded around the Ssp proteins ('Rap' proteins) included two specifically conferring self-resistance ('immunity') against T6SS-dependent Ssp1 or Ssp2 toxicity. Biochemical characterization revealed specific, tight binding between cognate Ssp-Rap pairs, forming complexes of 2:2 stoichiometry. The atomic structures of two Rap proteins were solved, revealing a novel helical fold, dependent on a structural disulphide bond, a structural feature consistent with their functional localization. Homologues of the Serratia Ssp and Rap proteins are found encoded together within other T6SS gene clusters, thus they represent founder members of new families of T6SS-secreted and cognate immunity proteins. We suggest that Ssp proteins are the original substrates of the S. marcescens T6SS, before horizontal acquisition of other T6SS-secreted toxins. Molecular insight has been provided into how pathogens utilize antibacterial T6SSs to overcome competitors and succeed in polymicrobial niches.
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Affiliation(s)
- Grant English
- Division of Molecular Microbiology, College of Life Sciences, University of DundeeDundee, UK
| | - Katharina Trunk
- Division of Molecular Microbiology, College of Life Sciences, University of DundeeDundee, UK
| | - Vincenzo A Rao
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of DundeeDundee, UK
| | - Velupillai Srikannathasan
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of DundeeDundee, UK
| | - William N Hunter
- Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of DundeeDundee, UK
| | - Sarah J Coulthurst
- Division of Molecular Microbiology, College of Life Sciences, University of DundeeDundee, UK
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Russell AB, Singh P, Brittnacher M, Bui NK, Hood RD, Carl MA, Agnello DM, Schwarz S, Goodlett DR, Vollmer W, Mougous JD. A widespread bacterial type VI secretion effector superfamily identified using a heuristic approach. Cell Host Microbe 2012; 11:538-49. [PMID: 22607806 DOI: 10.1016/j.chom.2012.04.007] [Citation(s) in RCA: 215] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2012] [Revised: 03/20/2012] [Accepted: 04/10/2012] [Indexed: 01/15/2023]
Abstract
Sophisticated mechanisms are employed to facilitate information exchange between interfacing bacteria. A type VI secretion system (T6SS) of Pseudomonas aeruginosa was shown to deliver cell wall-targeting effectors to neighboring cells. However, the generality of bacteriolytic effectors and, moreover, of antibacterial T6S remained unknown. Using parameters derived from experimentally validated bacterial T6SS effectors we identified a phylogenetically disperse superfamily of T6SS-associated peptidoglycan-degrading effectors. The effectors separate into four families composed of peptidoglycan amidase enzymes of differing specificities. Effectors strictly co-occur with cognate immunity proteins, indicating that self-intoxication is a general property of antibacterial T6SSs and effector delivery by the system exerts a strong selective pressure in nature. The presence of antibacterial effectors in a plethora of organisms, including many that inhabit or infect polymicrobial niches in the human body, suggests that the system could mediate interbacterial interactions of both environmental and clinical significance.
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Affiliation(s)
- Alistair B Russell
- Department of Microbiology, University of Washington, Seattle, WA 98195, USA
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48
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Lossi NS, Manoli E, Simpson P, Jones C, Hui K, Dajani R, Coulthurst SJ, Freemont P, Filloux A. The archetypePseudomonas aeruginosaproteins TssB and TagJ form a novel subcomplex in the bacterial type VI secretion system. Mol Microbiol 2012; 86:437-56. [DOI: 10.1111/j.1365-2958.2012.08204.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/04/2012] [Indexed: 12/25/2022]
Affiliation(s)
- Nadine S. Lossi
- MRC Centre for Molecular Bacteriology and Infection (CMBI); Division of Cell and Molecular Biology; Imperial College London; London; SW7 2AZ; UK
| | - Eleni Manoli
- MRC Centre for Molecular Bacteriology and Infection (CMBI); Division of Cell and Molecular Biology; Imperial College London; London; SW7 2AZ; UK
| | - Pete Simpson
- Division of Molecular Biosciences; Imperial College London; London; SW7 2AZ; UK
| | - Cerith Jones
- MRC Centre for Molecular Bacteriology and Infection (CMBI); Division of Cell and Molecular Biology; Imperial College London; London; SW7 2AZ; UK
| | - Kailyn Hui
- MRC Centre for Molecular Bacteriology and Infection (CMBI); Division of Cell and Molecular Biology; Imperial College London; London; SW7 2AZ; UK
| | - Rana Dajani
- MRC Centre for Molecular Bacteriology and Infection (CMBI); Division of Cell and Molecular Biology; Imperial College London; London; SW7 2AZ; UK
| | - Sarah J. Coulthurst
- Division of Molecular Microbiology; College of Life Sciences; University of Dundee; Dow Street; Dundee; DD1 5EH; UK
| | - Paul Freemont
- Division of Molecular Biosciences; Imperial College London; London; SW7 2AZ; UK
| | - Alain Filloux
- MRC Centre for Molecular Bacteriology and Infection (CMBI); Division of Cell and Molecular Biology; Imperial College London; London; SW7 2AZ; UK
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49
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Benz J, Sendlmeier C, Barends TRM, Meinhart A. Structural insights into the effector-immunity system Tse1/Tsi1 from Pseudomonas aeruginosa. PLoS One 2012; 7:e40453. [PMID: 22792331 PMCID: PMC3391265 DOI: 10.1371/journal.pone.0040453] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Accepted: 06/07/2012] [Indexed: 11/19/2022] Open
Abstract
During an interbacterial battle, the type-6-secretion-system (T6SS) of the human pathogen Pseudomonas aeruginosa injects the peptidoglycan(PG)-hydrolase Tse1 into the periplasm of gram-negative enemy cells and induces their lysis. However, for its own benefit, P. aeruginosa produces and transports the immunity-protein Tsi1 into its own periplasm where in prevents accidental exo- and endogenous intoxication. Here we present the high-resolution X-ray crystal structure of the lytic enzyme Tse1 and describe the mechanism by which Tse1 cleaves the γ-D-glutamyl-l-meso-diaminopimelic acid amide bond of crosslinked PG. Tse1 belongs to the superfamily of N1pC/P60 peptidases but is unique among described members of this family of which the structure was described, since it is a single domain protein without any putative localization domain. Most importantly, we present the crystal structure of Tse1 bound to its immunity-protein Tsi1 as well and describe the mechanism of enzyme inhibition. Tsi1 occludes the active site of Tse1 and abolishes its enzyme activity by forming a hydrogen bond to a catalytically important histidine residue in Tse1. Based on our structural findings in combination with a bioinfomatic approach we also identified a related system in Burkholderia phytofirmans. Not only do our findings point to a common catalytic mechanism of the Tse1 PG-hydrolases, but we can also show that it is distinct from other members of this superfamily. Furthermore, we provide strong evidence that the mechanism of enzyme inhibition between Tsi1 orthologues is conserved. This work is the first structural description of an entire effector/immunity pair injected by the T6SS system. Moreover, it is also the first example of a member of the N1pC/P60 superfamily which becomes inhibited upon binding to its cognate immunity protein.
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Affiliation(s)
- Juliane Benz
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
| | - Christina Sendlmeier
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
| | - Thomas R. M. Barends
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
| | - Anton Meinhart
- Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Heidelberg, Germany
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50
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Zhang H, Gao ZQ, Su XD, Dong YH. Crystal structure of type VI effector Tse1 from Pseudomonas aeruginosa. FEBS Lett 2012; 586:3193-9. [DOI: 10.1016/j.febslet.2012.06.036] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2012] [Revised: 05/30/2012] [Accepted: 06/20/2012] [Indexed: 11/27/2022]
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