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Achi SC, Karimilangi S, Lie D, Sayed IM, Das S. The WxxxE proteins in microbial pathogenesis. Crit Rev Microbiol 2023; 49:197-213. [PMID: 35287539 PMCID: PMC9737147 DOI: 10.1080/1040841x.2022.2046546] [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: 10/23/2021] [Revised: 02/10/2022] [Accepted: 02/19/2022] [Indexed: 12/14/2022]
Abstract
Effector proteins secreted by pathogens modulate various host cellular processes and help in bacterial pathogenesis. Some of these proteins, injected by enteric pathogens via Type Three Secretion System (T3SS) were grouped together based on a conserved signature motif (WxxxE) present in them. The presence of WxxxE motif is not limited to effectors released by enteric pathogens or the T3SS but has been detected in non-enteric pathogens, plant pathogens and in association with Type II and Type IV secretion systems. WxxxE effectors are involved in actin organization, inflammation regulation, vacuole or tubule formation, endolysosomal signalling regulation, tight junction disruption, and apoptosis. The WxxxE sequence has also been identified in TIR [Toll/interleukin-1 (IL-1) receptor] domains of bacteria and host. In the present review, we have focussed on the established and predicted functions of WxxxE effectors secreted by several pathogens, including enteric, non-enteric, and plant pathogens.
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Affiliation(s)
| | - Sareh Karimilangi
- Department of Pathology, University of California San Diego, La Jolla, CA, USA
| | - Dominique Lie
- Department of Pathology, University of California San Diego, La Jolla, CA, USA
| | - Ibrahim M. Sayed
- Department of Pathology, University of California San Diego, La Jolla, CA, USA
| | - Soumita Das
- Department of Pathology, University of California San Diego, La Jolla, CA, USA
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2
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Burns DL. Secretion of Pertussis Toxin from Bordetella pertussis. Toxins (Basel) 2021; 13:toxins13080574. [PMID: 34437445 PMCID: PMC8402538 DOI: 10.3390/toxins13080574] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Revised: 08/12/2021] [Accepted: 08/16/2021] [Indexed: 11/24/2022] Open
Abstract
Production and secretion of pertussis toxin (PT) is essential for the virulence of Bordetella pertussis. Due to the large oligomeric structure of PT, transport of the toxin across bacterial membrane barriers represents a significant hurdle that the bacteria must overcome in order to maintain pathogenicity. During the secretion process, PT undergoes a two-step transport process. The first step involves transport of the individual polypeptide chains of PT across the inner membrane utilizing a generalized secretion pathway, most likely the bacterial Sec system. The second step involves the use of a specialized apparatus to transport the toxin across the outer membrane of the bacterial cell. This apparatus, which has been termed the Ptl transporter and which is unique to the PT secretion pathway, is a member of the type IV family of bacterial transporters. Here, the current understanding of the PT secretion process is reviewed including a description of the Ptl proteins that assemble to form the transporter, the general structure of type IV transporters, the known similarities and differences between canonical type IV substrate transport and Ptl-mediated transport of PT, as well as the known sequence of events in the assembly and secretion of PT.
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Affiliation(s)
- Drusilla L Burns
- Center for Biologics Evaluation and Research, U.S. Food and Drug Administration, Silver Spring, MD 20993, USA
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3
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González-Rivera C, Khara P, Awad D, Patel R, Li YG, Bogisch M, Christie PJ. Two pKM101-encoded proteins, the pilus-tip protein TraC and Pep, assemble on the Escherichia coli cell surface as adhesins required for efficient conjugative DNA transfer. Mol Microbiol 2018; 111:96-117. [PMID: 30264928 DOI: 10.1111/mmi.14141] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Revised: 09/20/2018] [Accepted: 09/22/2018] [Indexed: 01/10/2023]
Abstract
Mobile genetic elements (MGEs) encode type IV secretion systems (T4SSs) known as conjugation machines for their transmission between bacterial cells. Conjugation machines are composed of an envelope-spanning translocation channel, and those functioning in Gram-negative species additionally elaborate an extracellular pilus to initiate donor-recipient cell contacts. We report that pKM101, a self-transmissible MGE functioning in the Enterobacteriaceae, has evolved a second target cell attachment mechanism. Two pKM101-encoded proteins, the pilus-tip adhesin TraC and a protein termed Pep, are exported to the cell surface where they interact and also form higher order complexes appearing as distinct foci or patches around the cell envelope. Surface-displayed TraC and Pep are required for an efficient conjugative transfer, 'extracellular complementation' potentially involving intercellular protein transfer, and activation of a Pseudomonas aeruginosa type VI secretion system. Both proteins are also required for bacteriophage PRD1 infection. TraC and Pep are exported across the outer membrane by a mechanism potentially involving the β-barrel assembly machinery. The pKM101 T4SS, thus, deploys alternative routing pathways for the delivery of TraC to the pilus tip or both TraC and Pep to the cell surface. We propose that T4SS-encoded, pilus-independent attachment mechanisms maximize the probability of MGE propagation and might be widespread among this translocation superfamily.
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Affiliation(s)
- Christian González-Rivera
- Department of Microbiology and Molecular Genetics, McGovern Medical School, 6431 Fannin St, Houston, TX, 77030, USA
| | - Pratick Khara
- Department of Microbiology and Molecular Genetics, McGovern Medical School, 6431 Fannin St, Houston, TX, 77030, USA
| | - Dominik Awad
- Department of Microbiology and Molecular Genetics, McGovern Medical School, 6431 Fannin St, Houston, TX, 77030, USA
| | - Roosheel Patel
- Department of Microbiology and Molecular Genetics, McGovern Medical School, 6431 Fannin St, Houston, TX, 77030, USA
| | - Yang Grace Li
- Department of Microbiology and Molecular Genetics, McGovern Medical School, 6431 Fannin St, Houston, TX, 77030, USA
| | | | - Peter J Christie
- Department of Microbiology and Molecular Genetics, McGovern Medical School, 6431 Fannin St, Houston, TX, 77030, USA
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Coutte L, Locht C. Investigating pertussis toxin and its impact on vaccination. Future Microbiol 2015; 10:241-54. [PMID: 25689536 DOI: 10.2217/fmb.14.123] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Whooping cough, caused by Bordetella pertussis, remains a major global health problem. Each year around 40 million of pertussis cases resulting in 200,000-400,000 annual deaths occur worldwide. Pertussis toxin is a major virulence factor of B. pertussis. Murine studies have shown its importance in bacterial colonization and in immunomodulation to evade innate or adaptive immunity. The toxin is composed of an A protomer expressing ADP-ribosyltransferase activity and a B oligomer, responsible for toxin binding to target cells. The toxin is also a major protective antigen in all currently available vaccines. However, vaccine escape mutants with altered toxin expression have recently been isolated in countries with high vaccination coverage illustrating the need for improved pertussis vaccines.
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Affiliation(s)
- Loic Coutte
- Center for Infection & Immunity of Lille, Institut Pasteur de Lille, 1, rue du Prof. Calmette, F-59019 Lille Cedex, France
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5
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Abstract
Bordetella pertussis is a Gram-negative pathogen causing the human respiratory disease called pertussis or whooping cough. Here we examined the role of the RNA chaperone Hfq in B. pertussis virulence. Hfq mediates interactions between small regulatory RNAs and their mRNA targets and thus plays an important role in posttranscriptional regulation of many cellular processes in bacteria, including production of virulence factors. We characterized an hfq deletion mutant (Δhfq) of B. pertussis 18323 and show that the Δhfq strain produces decreased amounts of the adenylate cyclase toxin that plays a central role in B. pertussis virulence. Production of pertussis toxin and filamentous hemagglutinin was affected to a lesser extent. In vitro, the ability of the Δhfq strain to survive within macrophages was significantly reduced compared to that of the wild-type (wt) strain. The virulence of the Δhfq strain in the mouse respiratory model of infection was attenuated, with its capacity to colonize mouse lungs being strongly reduced and its 50% lethal dose value being increased by one order of magnitude over that of the wt strain. In mixed-infection experiments, the Δhfq strain was then clearly outcompeted by the wt strain. This requirement for Hfq suggests involvement of small noncoding RNA regulation in B. pertussis virulence.
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6
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Structural independence of conjugative coupling protein TrwB from its Type IV secretion machinery. Plasmid 2013; 70:146-53. [PMID: 23583564 DOI: 10.1016/j.plasmid.2013.03.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2013] [Revised: 03/27/2013] [Accepted: 03/30/2013] [Indexed: 11/21/2022]
Abstract
The stability of components of multiprotein complexes often relies on the presence of the functional complex. To assess structural dependence among the components of the R388 Type IV secretion system (T4SS), the steady-state level of several Trw proteins was determined in the absence of other Trw components. While several Trw proteins were affected by the lack of others, we found that the coupling protein TrwB is not affected by the absence of other T4SS components, nor did its absence alter significantly the levels of integral components of the complex, underscoring the independent role of the coupling protein on the T4SS architecture. The cytoplasmic ATPases TrwK (VirB4) and TrwD (VirB11) were affected by the absence of several core complex components, while the pilus component TrwJ (VirB5) required the presence of all other Trw proteins (except for TrwB) to be detectable. Overall, the results delineate a possible assembly pathway for the T4SS of R388. We have also tested structural complementation of TrwD (VirB11) and TrwJ (VirB5) by their homologues in the highly related Trw system of Bartonella tribocorum (Bt). The results reveal a correlation with the functional complementation data previously reported.
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Abstract
Pertussis toxin, produced and secreted by the whooping cough agent Bordetella pertussis, is one of the most complex soluble bacterial proteins. It is actively secreted through the B. pertussis cell envelope by the Ptl secretion system, a member of the widespread type IV secretion systems. The toxin is composed of five subunits (named S1 to S5 according to their decreasing molecular weights) arranged in an A-B structure. The A protomer is composed of the enzymatically active S1 subunit, which catalyzes ADP-ribosylation of the α subunit of trimeric G proteins, thereby disturbing the metabolic functions of the target cells, leading to a variety of biological activities. The B oligomer is composed of 1S2:1S3:2S4:1S5 and is responsible for binding of the toxin to the target cell receptors and for intracellular trafficking via receptor-mediated endocytosis and retrograde transport. The toxin is one of the most important virulence factors of B. pertussis and is a component of all current vaccines against whooping cough.
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Affiliation(s)
- Camille Locht
- Inserm U1019, CNRS UMR8204, Center for Infection and Immunity of Lille, Institut Pasteur de Lille, Univ Lille Nord de France, France.
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Alvarez-Martinez CE, Christie PJ. Biological diversity of prokaryotic type IV secretion systems. Microbiol Mol Biol Rev 2009; 73:775-808. [PMID: 19946141 PMCID: PMC2786583 DOI: 10.1128/mmbr.00023-09] [Citation(s) in RCA: 524] [Impact Index Per Article: 34.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Type IV secretion systems (T4SS) translocate DNA and protein substrates across prokaryotic cell envelopes generally by a mechanism requiring direct contact with a target cell. Three types of T4SS have been described: (i) conjugation systems, operationally defined as machines that translocate DNA substrates intercellularly by a contact-dependent process; (ii) effector translocator systems, functioning to deliver proteins or other macromolecules to eukaryotic target cells; and (iii) DNA release/uptake systems, which translocate DNA to or from the extracellular milieu. Studies of a few paradigmatic systems, notably the conjugation systems of plasmids F, R388, RP4, and pKM101 and the Agrobacterium tumefaciens VirB/VirD4 system, have supplied important insights into the structure, function, and mechanism of action of type IV secretion machines. Information on these systems is updated, with emphasis on recent exciting structural advances. An underappreciated feature of T4SS, most notably of the conjugation subfamily, is that they are widely distributed among many species of gram-negative and -positive bacteria, wall-less bacteria, and the Archaea. Conjugation-mediated lateral gene transfer has shaped the genomes of most if not all prokaryotes over evolutionary time and also contributed in the short term to the dissemination of antibiotic resistance and other virulence traits among medically important pathogens. How have these machines adapted to function across envelopes of distantly related microorganisms? A survey of T4SS functioning in phylogenetically diverse species highlights the biological complexity of these translocation systems and identifies common mechanistic themes as well as novel adaptations for specialized purposes relating to the modulation of the donor-target cell interaction.
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Affiliation(s)
- Cristina E. Alvarez-Martinez
- Department of Microbiology and Molecular Genetics, University of Texas Medical School at Houston, 6431 Fannin, Houston, Texas 77030
| | - Peter J. Christie
- Department of Microbiology and Molecular Genetics, University of Texas Medical School at Houston, 6431 Fannin, Houston, Texas 77030
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Fronzes R, Christie PJ, Waksman G. The structural biology of type IV secretion systems. Nat Rev Microbiol 2009; 7:703-14. [PMID: 19756009 DOI: 10.1038/nrmicro2218] [Citation(s) in RCA: 281] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Type IV secretion systems (T4SSs) are versatile secretion systems that are found in both Gram-negative and Gram-positive bacteria and secrete a wide range of substrates, from single proteins to protein-protein and protein-DNA complexes. They usually consist of 12 components that are organized into ATP-powered, double-membrane-spanning complexes. The structures of single soluble components or domains have been solved, but an understanding of how these structures come together has only recently begun to emerge. This Review focuses on the structural advances that have been made over the past 10 years and how the corresponding structural insights have helped to elucidate many of the details of the mechanism of type IV secretion.
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Affiliation(s)
- Rémi Fronzes
- Institute of Structural and Molecular Biology, Malet Street, London WC1E 7HX, UK
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10
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Stabilization of the pertussis toxin secretion apparatus by the C terminus of PtlD. J Bacteriol 2008; 190:7285-90. [PMID: 18723610 DOI: 10.1128/jb.01106-08] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pertussis toxin (PT) is secreted from Bordetella pertussis by a type IV secretion system, known as the Ptl transporter, that comprises nine different proteins, PtlA to PtlI. In this study, we found that PtlD is required for the stability of three Ptl proteins, PtlE, PtlF, and PtlH. A region limited to the C-terminal 72 amino acids of PtlD (amino acids 392 to 463) was sufficient for maintaining the stability of PtlE, PtlF, and PtlH, although this region was not sufficient to support secretion of the toxin. Further analysis demonstrated that a stretch of 10 amino acids at the C-terminal end of PtlD (amino acids 425 to 434) contributes to transporter stability.
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11
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Verma A, Burns DL. Requirements for assembly of PtlH with the pertussis toxin transporter apparatus of Bordetella pertussis. Infect Immun 2007; 75:2297-306. [PMID: 17339350 PMCID: PMC1865746 DOI: 10.1128/iai.00008-07] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
PtlH is an essential component of the Ptl system, the type IV transporter responsible for secretion of pertussis toxin (PT) across the outer membrane of Bordetella pertussis. The nine Ptl proteins are believed to interact to form a membrane-spanning apparatus through which the toxin is secreted. In this study, we monitored the subcellular localization of PtlH in strains of B. pertussis lacking PT, lacking other Ptl proteins, or from which ATP has been depleted in order to gain insight into the requirements for assembly of PtlH with the remainder of the Ptl transporter complex that is thought to be tightly embedded in the membrane. We found that PtlH is exclusively localized to the inner membrane fraction of the cell in a wild-type strain of B. pertussis. In contrast, PtlH localized to both the cytoplasmic and inner membrane fractions of a mutant strain of B. pertussis that does not produce PT. In comparison to how it localized in wild-type strains of B. pertussis, PtlH exhibited aberrant localization in strains lacking PtlD, PtlE, PtlF, and PtlG. We also found that localization of PtlH was perturbed in B. pertussis strains that were treated with carbonyl cyanide m-chlorophenylhydrazone and sodium arsenate, which are capable of depleting cellular ATP levels, and in strains of B. pertussis that produce an altered form of PtlH that lacks ATPase activity. When taken together, these results indicate that tight association of PtlH with the membrane, likely through interactions with components of the transporter-PT complex, requires the toxin substrate, a specific subset of the Ptl proteins, and ATP. Based on these data, a model for the assembly of the Ptl transporter-PT complex is presented.
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Affiliation(s)
- Anita Verma
- Laboratory of Respiratory and Special Pathogens, Food and Drug Administration, Bethesda, Maryland 20892, USA
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12
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de Paz HD, Sangari FJ, Bolland S, García-Lobo JM, Dehio C, de la Cruz F, Llosa M. Functional interactions between type IV secretion systems involved in DNA transfer and virulence. MICROBIOLOGY-SGM 2005; 151:3505-3516. [PMID: 16272374 DOI: 10.1099/mic.0.28410-0] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
This paper reports an analysis of the functional interactions between type IV secretion systems (T4SS) that are part of the conjugative machinery for horizontal DNA transfer (cT4SS), and T4SS involved in bacterial pathogenicity (pT4SS). The authors' previous work showed that a conjugative coupling protein (T4CP) interacts with the VirB10-type component of the T4SS in order to recruit the protein-DNA complex to the transporter for conjugative DNA transfer. This study now shows by two-hybrid analysis that conjugative T4CPs also interact with the VirB10 element of the pT4SS of Agrobacterium tumefaciens (At), Bartonella tribocorum (Bt) and Brucella suis (Bs). Moreover, the VirB10 component of a cT4SS (protein TrwE of plasmid R388) could be partially substituted by that of a pT4SS (protein TrwE of Bt) for conjugation. This result opens the way for the construction of hybrid T4SS that deliver DNA into animal cells. Interestingly, in the presence of part of the Bs T4SS the R388 T4SS protein levels were decreased and R388 conjugation was strongly inhibited. Complementation assays between the Trw systems of R388 and Bt showed that only individual components from the so-called 'core complex' could be exchanged, supporting the concept that this core is the common scaffold for the transport apparatus while the other 'peripheral components' are largely system-specific.
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Affiliation(s)
- Héctor D de Paz
- Departamento de Biología Molecular (Unidad Asociada al CIB-CSIC), Universidad de Cantabria, C. Herrera Oria s/n, 39011 Santander, Spain
| | - Félix J Sangari
- Departamento de Biología Molecular (Unidad Asociada al CIB-CSIC), Universidad de Cantabria, C. Herrera Oria s/n, 39011 Santander, Spain
| | - Silvia Bolland
- Departamento de Biología Molecular (Unidad Asociada al CIB-CSIC), Universidad de Cantabria, C. Herrera Oria s/n, 39011 Santander, Spain
| | - Juan M García-Lobo
- Departamento de Biología Molecular (Unidad Asociada al CIB-CSIC), Universidad de Cantabria, C. Herrera Oria s/n, 39011 Santander, Spain
| | - Christoph Dehio
- Division of Molecular Microbiology, Biozentrum of the University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland
| | - Fernando de la Cruz
- Departamento de Biología Molecular (Unidad Asociada al CIB-CSIC), Universidad de Cantabria, C. Herrera Oria s/n, 39011 Santander, Spain
| | - Matxalen Llosa
- Departamento de Biología Molecular (Unidad Asociada al CIB-CSIC), Universidad de Cantabria, C. Herrera Oria s/n, 39011 Santander, Spain
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13
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Schröder G, Lanka E. The mating pair formation system of conjugative plasmids-A versatile secretion machinery for transfer of proteins and DNA. Plasmid 2005; 54:1-25. [PMID: 15907535 DOI: 10.1016/j.plasmid.2005.02.001] [Citation(s) in RCA: 132] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2005] [Revised: 02/21/2005] [Accepted: 02/23/2005] [Indexed: 10/25/2022]
Abstract
The mating pair formation (Mpf) system functions as a secretion machinery for intercellular DNA transfer during bacterial conjugation. The components of the Mpf system, comprising a minimal set of 10 conserved proteins, form a membrane-spanning protein complex and a surface-exposed sex pilus, which both serve to establish intimate physical contacts with a recipient bacterium. To function as a DNA secretion apparatus the Mpf complex additionally requires the coupling protein (CP). The CP interacts with the DNA substrate and couples it to the secretion pore formed by the Mpf system. Mpf/CP conjugation systems belong to the family of type IV secretion systems (T4SS), which also includes DNA-uptake and -release systems, as well as effector protein translocation systems of bacterial pathogens such as Agrobacterium tumefaciens (VirB/VirD4) and Helicobacter pylori (Cag). The increased efforts to unravel the molecular mechanisms of type IV secretion have largely advanced our current understanding of the Mpf/CP system of bacterial conjugation systems. It has become apparent that proteins coupled to DNA rather than DNA itself are the actively transported substrates during bacterial conjugation. We here present a unified and updated view of the functioning and the molecular architecture of the Mpf/CP machinery.
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Affiliation(s)
- Gunnar Schröder
- Division of Molecular Microbiology, Biozentrum, University of Basel, Klingelbergstrasse 50/70, CH-4056 Basel, Switzerland.
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14
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Judd PK, Kumar RB, Das A. Spatial location and requirements for the assembly of the Agrobacterium tumefaciens type IV secretion apparatus. Proc Natl Acad Sci U S A 2005; 102:11498-503. [PMID: 16076948 PMCID: PMC1183602 DOI: 10.1073/pnas.0505290102] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2005] [Indexed: 12/27/2022] Open
Abstract
Type IV secretion is used by pathogenic microorganisms to transfer effector macromolecules to eukaryotic target cells. The VirB/D4 apparatus of Agrobacterium tumefaciens transfers DNA and proteins to plant cells. We postulated that the cell pole is the site of assembly of the A. tumefaciens type IV apparatus. Using immunofluorescence microscopy, we now demonstrate that 10 of the VirB proteins localized primarily to one cell pole and a macromolecular VirB complex is assembled at the pole. Neither the assembly of the complex nor polar localization of a VirB protein requires ATP utilization by the VirB ATPases. The requirement of other VirB proteins for the polar localization of at least six VirB proteins indicates an essential role of protein-protein interaction in polar targeting. Four proteins (VirB3, VirB4, VirB8, and VirB11) could target themselves to a cell pole independent of a VirB protein. We provide evidence that VirB6-VirB10 are the structural components of the type IV apparatus. Using strains that express defined subsets of the virB genes, we demonstrate that VirB7-VirB10 are the minimum components sufficient for the assembly of a polar VirB complex. VirB6 associates with this complex to form the type IV secretion apparatus. VirB8 functions as the assembly factor and targets the apparatus to the cell pole.
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Affiliation(s)
- Paul K Judd
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
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15
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Mattoo S, Cherry JD. Molecular pathogenesis, epidemiology, and clinical manifestations of respiratory infections due to Bordetella pertussis and other Bordetella subspecies. Clin Microbiol Rev 2005; 18:326-82. [PMID: 15831828 PMCID: PMC1082800 DOI: 10.1128/cmr.18.2.326-382.2005] [Citation(s) in RCA: 778] [Impact Index Per Article: 40.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Bordetella respiratory infections are common in people (B. pertussis) and in animals (B. bronchiseptica). During the last two decades, much has been learned about the virulence determinants, pathogenesis, and immunity of Bordetella. Clinically, the full spectrum of disease due to B. pertussis infection is now understood, and infections in adolescents and adults are recognized as the reservoir for cyclic outbreaks of disease. DTaP vaccines, which are less reactogenic than DTP vaccines, are now in general use in many developed countries, and it is expected that the expansion of their use to adolescents and adults will have a significant impact on reducing pertussis and perhaps decrease the circulation of B. pertussis. Future studies should seek to determine the cause of the unique cough which is associated with Bordetella respiratory infections. It is also hoped that data gathered from molecular Bordetella research will lead to a new generation of DTaP vaccines which provide greater efficacy than is provided by today's vaccines.
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Affiliation(s)
- Seema Mattoo
- Department of Microbiology, Immunology, and Molecular Genetics, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1752, USA
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16
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Burns DL, Fiddner S, Cheung AM, Verma A. Analysis of subassemblies of pertussis toxin subunits in vivo and their interaction with the ptl transport apparatus. Infect Immun 2004; 72:5365-72. [PMID: 15322034 PMCID: PMC517454 DOI: 10.1128/iai.72.9.5365-5372.2004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pertussis toxin (PT) has an AB(5) structure that is typical of many bacterial protein toxins; however, this toxin is more complex than many toxins since it is composed of five different subunit types, subunits S1 to S5. Little is known about how PT assembles in vivo and how and when it interacts with its secretion apparatus, known as the Ptl transporter. In order to better understand these events, we expressed subsets of the genes encoding the S1, S2, and/or S4 subunits of PT in strains of Bordetella pertussis that either did or did not produce the Ptl proteins. We found evidence to suggest that certain subassemblies of the toxin, including subassemblies consisting of the S1 subunit and incomplete forms of the B oligomer, can form in vivo, at least transiently. These results suggest that the B oligomer of the toxin does not need to completely form before interactions between the S1 subunit and B-oligomer subunits can occur in vivo. All subassemblies localized primarily to the membrane fraction of the cell. Moreover, we found that Ptl-mediated secretion occurs in a strain that produces S1 and an incomplete complement of B-oligomer subunits. These results indicate that subassemblies of the toxin consisting of the S1 subunit and a partial B oligomer can interact with the Ptl system.
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Affiliation(s)
- Drusilla L Burns
- Laboratory of Respiratory and Special Pathogens, Food and Drug Administration, Bethesda, Maryland, USA.
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17
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Shamaei-Tousi A, Cahill R, Frankel G. Interaction between protein subunits of the type IV secretion system of Bartonella henselae. J Bacteriol 2004; 186:4796-801. [PMID: 15231811 PMCID: PMC438546 DOI: 10.1128/jb.186.14.4796-4801.2004] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In this study we used the yeast two-hybrid system to identify interactions between protein subunits of the virB type IV secretion system of Bartonella henselae. We report interactions between inner membrane and periplasmic proteins, the pilus polypeptide, and the core complex and a novel interaction between VirB3 and VirB5.
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Affiliation(s)
- Alireza Shamaei-Tousi
- Centre for Molecular Microbiology and Infection, Department of Biological Sciences, Imperial College London, London SW7 2AZ, United Kingdom
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Cheung AM, Farizo KM, Burns DL. Analysis of relative levels of production of pertussis toxin subunits and Ptl proteins in Bordetella pertussis. Infect Immun 2004; 72:2057-66. [PMID: 15039327 PMCID: PMC375219 DOI: 10.1128/iai.72.4.2057-2066.2004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pertussis toxin is transported across the outer membrane of Bordetella pertussis by the type IV secretion system known as the Ptl transporter, which is composed of nine different proteins. In order to determine the relative levels of production of pertussis toxin subunits and Ptl proteins in B. pertussis, we constructed translational fusions of the gene for alkaline phosphatase, phoA, with various ptx and ptl genes. Comparison of the alkaline phosphatase activity of strains containing ptx'- or ptl'-phoA fusions indicated that pertussis toxin subunits are produced at higher levels than Ptl proteins, which are encoded by genes located toward the 3' end of the ptx-ptl operon. We also engineered strains of B. pertussis by introducing multiple copies of the ptl genes or subsets of these genes and then examined the ability of each of these strains to secrete pertussis toxin. From these studies, we determined that certain Ptl proteins appear to be limiting in the secretion of pertussis toxin from the bacteria. These results represent an important first step in assessing the stoichiometric relationship of pertussis toxin and its transporter within the bacterial cell.
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Affiliation(s)
- Anissa M Cheung
- Laboratory of Respiratory and Special Pathogens, Food and Drug Administration, Bethesda, Maryland 20892, USA
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19
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Abstract
Bacteria use type IV secretion systems for two fundamental objectives related to pathogenesis--genetic exchange and the delivery of effector molecules to eukaryotic target cells. Whereas gene acquisition is an important adaptive mechanism that enables pathogens to cope with a changing environment during invasion of the host, interactions between effector and host molecules can suppress defence mechanisms, facilitate intracellular growth and even induce the synthesis of nutrients that are beneficial to bacterial colonization. Rapid progress has been made towards defining the structures and functions of type IV secretion machines, identifying the effector molecules, and elucidating the mechanisms by which the translocated effectors subvert eukaryotic cellular processes during infection.
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Affiliation(s)
- Eric Cascales
- Department of Microbiology and Molecular Genetics, University of Texas-Houston Medical School, Houston, Texas 77030, USA
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20
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Stenson TH, Patton AK, Weiss AA. Reduced glutathione is required for pertussis toxin secretion by Bordetella pertussis. Infect Immun 2003; 71:1316-20. [PMID: 12595447 PMCID: PMC148887 DOI: 10.1128/iai.71.3.1316-1320.2003] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The abilities of cysteine-containing compounds to support growth of Bordetella pertussis and influence pertussis toxin transcription, assembly, and secretion were examined. Cysteine is an essential amino acid for B. pertussis and must be present for protein synthesis and bacterial growth. However, cysteine can be metabolized to sulfate, and high concentrations of sulfate can selectively inhibit transcription of the virulence factors, including pertussis toxin, via the BvgAS two-component regulatory system in a process called modulation. In addition, pertussis toxin possesses several disulfide bonds, and the cysteine-containing compound glutathione can influence oxidation-reduction reactions and perhaps disulfide bond formation. Bacterial growth was not observed in the absence of a source of cysteine. Oxidized glutathione, as a sole source of cysteine, also did not support bacterial growth. Cysteine, cystine, and reduced glutathione did support bacterial growth, and none of these compounds caused modulation at the concentrations tested. Similar amounts of periplasmic pertussis toxin were detected regardless of the source of cysteine; however, in the absence of reduced glutathione, pertussis toxin was not efficiently secreted. Addition of the reducing agent dithiothreitol was unable to compensate for the lack of reduced glutathione and did not promote secretion of pertussis toxin. These results suggest that reduced glutathione does not affect the accumulation of assembled active pertussis toxin in the periplasm but plays a role in efficient pertussis toxin secretion by the bacterium.
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Affiliation(s)
- Trevor H Stenson
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, Cincinnati, Ohio 45267-0524, USA
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21
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Stenson TH, Weiss AA. DsbA and DsbC are required for secretion of pertussis toxin by Bordetella pertussis. Infect Immun 2002; 70:2297-303. [PMID: 11953363 PMCID: PMC127938 DOI: 10.1128/iai.70.5.2297-2303.2002] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Dsb family of enzymes catalyzes disulfide bond formation in the gram-negative periplasm, which is required for folding and assembly of many secreted proteins. Pertussis toxin is arguably the most complex toxin known: it is assembled from six subunits encoded by five genes (for subunits S1 to S5), with 11 intramolecular disulfide bonds. To examine the role of the Dsb enzymes in assembly and secretion of pertussis toxin, we identified and mutated the Bordetella pertussis dsbA, dsbB, and dsbC homologues. Mutations in dsbA or dsbB resulted in decreased levels of S1 (the A subunit) and S2 (a B-subunit protein), demonstrating that DsbA and DsbB are required for toxin assembly. Mutations in dsbC did not impair assembly of periplasmic toxin but resulted in decreased toxin secretion, suggesting a defect in the formation of the Ptl secretion complex.
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Affiliation(s)
- Trevor H Stenson
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, Cincinnati, Ohio 45267-0524, USA
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22
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Farizo KM, Fiddner S, Cheung AM, Burns DL. Membrane localization of the S1 subunit of pertussis toxin in Bordetella pertussis and implications for pertussis toxin secretion. Infect Immun 2002; 70:1193-201. [PMID: 11854200 PMCID: PMC127780 DOI: 10.1128/iai.70.3.1193-1201.2002] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Pertussis toxin is secreted from Bordetella pertussis with the assistance of the Ptl transport system, a member of the type IV family of macromolecular transporters. The S1 subunit and the B oligomer combine to form the holotoxin prior to export from the bacterial cell, although the site of assembly is not known. To better understand the pathway of pertussis toxin assembly and secretion, we examined the subcellular location of the S1 subunit, expressed with or without the B oligomer and the Ptl proteins. In wild-type B. pertussis, the majority of the S1 subunit that remained cell associated localized to the bacterial membranes. In mutants of B. pertussis that do not express pertussis toxin and/or the Ptl proteins, full-length S1, expressed from a plasmid, partitioned almost entirely to the bacterial membranes. Several lines of evidence strongly suggest that the S1 subunit localizes to the outer membrane of B. pertussis. First, we found that membrane-bound full-length S1 was almost completely insoluble in Triton X-100. Second, recombinant S1 previously has been shown to localize to the outer membrane of Escherichia coli (J. T. Barbieri, M. Pizza, G. Cortina, and R. Rappuoli, Infect. Immun. 58:999-1003, 1990). Third, the S1 subunit possesses a distinctive amino acid motif at its carboxy terminus, including a terminal phenylalanine, which is highly conserved among bacterial outer membrane proteins. By using site-directed mutagenesis, we determined that the terminal phenylalanine is critical for stable expression of the S1 subunit. Our findings provide evidence that prior to assembly with the B oligomer and independent of the Ptl proteins, the S1 subunit localizes to the outer membrane of B. pertussis. Thus, outer membrane-bound S1 may serve as a nucleation site for assembly with the B oligomer and for interactions with the Ptl transport system.
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Affiliation(s)
- Karen M Farizo
- Laboratory of Respiratory and Special Pathogens, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892, USA
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23
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Novak KF, Dougherty B, Peláez M. Actinobacillus actinomycetemcomitans harbours type IV secretion system genes on a plasmid and in the chromosome. MICROBIOLOGY (READING, ENGLAND) 2001; 147:3027-35. [PMID: 11700353 DOI: 10.1099/00221287-147-11-3027] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Nine contiguous genes encoding a potential type IV secretion system have been identified in the chromosome of Actinobacillus actinomycetemcomitans strain VT747 and on a plasmid (pVT745) in strain VT745. Seven of these genes encode predicted proteins that share significant homology with type IV secretion proteins in Bordetella pertussis (ptl operon), Brucella melitensis biovar suis and Agrobacterium tumefaciens (virB operons), where they are involved in protein secretion, pathogen intracellular survival and multiplication, and DNA transport, respectively. Results of previous studies have demonstrated that pVT745 is a conjugative plasmid and that a secondary plasmid, pMMB67, can be mobilized from strain VT745. Given these results, it was hypothesized that (1) the type IV secretion genes on pVT745 are responsible for these two functions and (2) the type IV VT747 chromosomal genes also play a role in the transport of DNA. Wild-type and mutant strains of VT745 were evaluated for their conjugative abilities. Wild-type mating efficiency was 10(-6) transconjugants per donor, while the mutant strain yielded no transconjugants. Wild-type VT745 harbouring a co-resident plasmid, pMMB67, mobilized pMMB67 at a frequency of 10(-6), while VT747 was unable to mobilize this plasmid. These results support the hypothesis that the plasmid-encoded type IV secretion system on pVT745 is involved in DNA transport. However, the chromosomally encoded secretion system may not play a role in DNA transport in strain VT747. While the precise function of these chromosomal genes in strain VT747 has not been determined, Northern blot analyses demonstrated that these genes are expressed in both ACT: actinomycetemcomitans strains VT745 and VT747.
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Affiliation(s)
- K F Novak
- University of Kentucky, College of Dentistry, Center for Oral Health Research, Lexington, KY 40536-0297, USA.
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24
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Smith AM, Guzmán CA, Walker MJ. The virulence factors ofBordetella pertussis: a matter of control. FEMS Microbiol Rev 2001; 25:309-33. [PMID: 11348687 DOI: 10.1111/j.1574-6976.2001.tb00580.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Bordetella pertussis is the causative agent of whooping cough, a contagious childhood respiratory disease. Increasing public concern over the safety of whole-cell vaccines led to decreased immunisation rates and a subsequent increase in the incidence of the disease. Research into the development of safer, more efficacious, less reactogenic vaccine preparations was concentrated on the production and purification of detoxified B. pertussis virulence factors. These virulence factors include adhesins such as filamentous haemagglutinin, fimbriae and pertactin, which allow B. pertussis to bind to ciliated epithelial cells in the upper respiratory tract. Once attachment is initiated, toxins produced by the bacterium enable colonisation to proceed by interfering with host clearance mechanisms. B. pertussis co-ordinately regulates the expression of virulence factors via the Bordetella virulence gene (bvg) locus, which encodes a response regulator responsible for signal-mediated activation and repression. This strict regulation mechanism allows the bacterium to express different gene subsets in different environmental niches within the host, according to the stage of disease progression.
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Affiliation(s)
- A M Smith
- Department of Biological Sciences, University of Wollongong, Wollongong. N.S.W. 2522, Australia
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25
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Stathopoulos C, Hendrixson DR, Thanassi DG, Hultgren SJ, St Geme JW, Curtiss R. Secretion of virulence determinants by the general secretory pathway in gram-negative pathogens: an evolving story. Microbes Infect 2000; 2:1061-72. [PMID: 10967286 DOI: 10.1016/s1286-4579(00)01260-0] [Citation(s) in RCA: 114] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Secretion of proteins by the general secretory pathway (GSP) is a two-step process requiring the Sec translocase in the inner membrane and a separate substrate-specific secretion apparatus for translocation across the outer membrane. Gram-negative bacteria with pathogenic potential use the GSP to deliver virulence factors into the extracellular environment for interaction with the host. Well-studied examples of virulence determinants using the GSP for secretion include extracellular toxins, pili, curli, autotransporters, and crystaline S-layers. This article reviews our current understanding of the GSP and discusses examples of terminal branches of the GSP which are utilized by factors implicated in bacterial virulence.
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Affiliation(s)
- C Stathopoulos
- Department of Biology, Washington University, One Brookings Drive, St. Louis, MO 63110, USA
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26
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Craig-Mylius KA, Weiss AA. Antibacterial agents and release of periplasmic pertussis toxin from Bordetella pertussis. Antimicrob Agents Chemother 2000; 44:1383-6. [PMID: 10770786 PMCID: PMC89879 DOI: 10.1128/aac.44.5.1383-1386.2000] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pertussis toxin accumulates in the periplasm of Bordetella pertussis prior to secretion, and we examined its fate following treatment with antimicrobial agents. Both antibiotics that inhibit protein synthesis (erythromycin and chloramphenicol), transcription (rifampin), or cell wall biosynthesis (cefoperazone and piperacillin) and magnesium sulfate (which inhibits transcription of pertussis toxin, but not bacterial growth) did not prevent release of preformed toxin. In contrast, agents that affect bacterial membranes, such as polymyxin B, lidocaine, procaine, and ethanol, inhibited release of preformed pertussis toxin. These results suggest new protein synthesis is not required for pertussis toxin secretion, but a functional membrane complex is required.
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Affiliation(s)
- K A Craig-Mylius
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, Cincinnati, Ohio 45267-0524, USA
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27
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Craig-Mylius KA, Stenson TH, Weiss AA. Mutations in the S1 subunit of pertussis toxin that affect secretion. Infect Immun 2000; 68:1276-81. [PMID: 10678938 PMCID: PMC97279 DOI: 10.1128/iai.68.3.1276-1281.2000] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pertussis toxin is a member of the AB(5) family of toxins and is composed of five subunits (S1 to S5) present in a 1:1:1:2:1 ratio. Secretion is a complex process. Each subunit has a secretion signal that mediates transport to the periplasm, where processing and assembly occur. Secretion of the assembled 105-kDa toxin past the outer membrane is mediated by the nine proteins encoded in the ptl operon. Previous studies have shown that S1, the catalytically active A subunit of pertussis toxin, is necessary for efficient secretion, suggesting that a domain on S1 may be required for interaction with the secretion apparatus. Previously, recombinant S1 from four different mutants (serine 54 to glycine, serine 55 to glycine, serine 56 to glycine, and arginine 57 to lysine) was shown to retain catalytic activity. We introduced these mutations into Bordetella pertussis and monitored pertussis toxin production and secretion. No pertussis toxin was detected in the serine 54-to-glycine mutant. The other S1 mutants produced periplasmic pertussis toxin, but little pertussis toxin secretion was observed. The arginine 57-to-lysine mutant had the most dramatic secretion defect. It produced wild-type levels of periplasmic pertussis toxin but secreted only 8% as much toxin as the wild-type strain. This phenotype was similar to that observed for strains with mutations in the ptl genes, suggesting that this region may have a role in pertussis toxin secretion.
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Affiliation(s)
- K A Craig-Mylius
- Department of Molecular Genetics, University of Cincinnati, Cincinnati, Ohio 45267-0524, USA
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28
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O'Callaghan D, Cazevieille C, Allardet-Servent A, Boschiroli ML, Bourg G, Foulongne V, Frutos P, Kulakov Y, Ramuz M. A homologue of the Agrobacterium tumefaciens VirB and Bordetella pertussis Ptl type IV secretion systems is essential for intracellular survival of Brucella suis. Mol Microbiol 1999; 33:1210-20. [PMID: 10510235 DOI: 10.1046/j.1365-2958.1999.01569.x] [Citation(s) in RCA: 336] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Analysis of a TnblaM mutant of Brucella suis 1330, identified as being unable to multiply in Hela cells, allowed us to identify a 11 860 bp region of the B. suis genome encoding a type IV secretion system, homologous to the VirB system of Agrobacterium tumefaciens and the Ptl system of Bordetella pertussis. DNA sequence revealed 12 open reading frames (ORFs) encoding homologues of the 11 VirB proteins present in the pTi plasmid of Agrobacterium with a similar genetic organization, and a twelfth ORF encoding a putative lipoprotein, homologous to a protein involved in mating pair formation during bacterial conjugation and to adhesins used by Pseudomonas species to bind to plant roots. Phylogenetic trees based on the sequences of VirB4 and VirB9 protein homologues suggest that evolution of the systems from DNA transfer towards protein secretion did not stem from a single event but that the protein secretion systems have evolved independently. Four independent mutants in virB5, virB9 or virB10 were highly attenuated in an in vitro infection model with human macrophages. The virulence was restored by complementation with a plasmid containing the full virB region. The virB region appears to be essential for the intracellular survival and multiplication of B. suis.
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Affiliation(s)
- D O'Callaghan
- INSERM U431, Faculté de Médecine, Avenue Kennedy, 30900 Nîmes, France.
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29
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Li PL, Hwang I, Miyagi H, True H, Farrand SK. Essential components of the Ti plasmid trb system, a type IV macromolecular transporter. J Bacteriol 1999; 181:5033-41. [PMID: 10438776 PMCID: PMC93993 DOI: 10.1128/jb.181.16.5033-5041.1999] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The trb operon from pTiC58 is one of three loci that are required for conjugal transfer of this Ti plasmid. The operon, which probably codes for the mating bridge responsible for pair formation and DNA transfer, contains 12 genes, 11 of which are related to genes from other members of the type IV secretion system family. The 12th gene, traI, codes for production of Agrobacterium autoinducer (AAI). Insertion mutations were constructed in each of the 12 genes, contained on a full-length clone of the trb region, using antibiotic resistance cassettes or a newly constructed transposon. This transposon, called mini-Tn5Ptrb, was designed to express genes downstream of the insertion site from a promoter regulated by TraR and AAI. Each mutation could trans complement downstream Tn3HoHo1 insertions in the trb operon of full-sized Ti plasmids. When marker-exchanged into the transfer-constitutive Ti plasmid pTiC58DeltaaccR mutations in trbB, -C, -D, -E, -L, -F, -G, and -H abolished conjugal transfer from strain UIA5, which lacks the 450-kb catabolic plasmid pAtC58. However, these mutants retained residual conjugal transfer activity when tested in strain NT1, which contains this large plasmid. The trbJ mutant failed to transfer at a detectable frequency from either strain, while the trbI mutant transferred at very low but detectable levels from both donors. Only the trbK mutant was unaffected in conjugal transfer from either donor. Transfer of each of the marker-exchange mutants was restored by a clone expressing only the wild-type allele of the corresponding mutant trb gene. An insertion mutation in traI abolished the production of AAI and also conjugal transfer. This defect was restored by culturing the mutant donor in the presence of AAI. We conclude that all of the trb genes except trbI and trbK are essential for conjugal transfer of pTiC58. We also conclude that mutations in any one of the trb genes except traI and trbJ can be complemented by functions coded for by pAtC58.
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Affiliation(s)
- P L Li
- Departments of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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30
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Abstract
In the past year, our knowledge of type IV transporters of Gram-negative bacteria has further expanded. Advances include the discovery of additional members of this family of proteins, increased knowledge of the morphologies of type IV transporters, and a better understanding of the mechanisms by which macromolecules are exported by these systems.
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Affiliation(s)
- D L Burns
- CBER, US Food and Drug Administration HFM-434, Building 29 Room 418 8800 Rockville Pike Bethesda MD 20892 USA.
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31
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Cook DM, Farizo KM, Burns DL. Identification and characterization of PtlC, an essential component of the pertussis toxin secretion system. Infect Immun 1999; 67:754-9. [PMID: 9916087 PMCID: PMC96383 DOI: 10.1128/iai.67.2.754-759.1999] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
PtlC is a member of a set of proteins necessary for the secretion of pertussis toxin (PT) from Bordetella pertussis. Using polyclonal antibodies specific for PtlC, we identified PtlC as a protein with an apparent molecular weight of 85,000 that localizes to the membrane fraction of bacterial cell extracts. We found that a mutant strain of B. pertussis that contains an in-frame deletion in ptlC is unable to secrete PT and that PT secretion is fully restored by expressing ptlC in trans, indicating that PtlC is essential for transport of PT across the bacterial membrane(s). PT secretion was inhibited in wild-type B. pertussis after introduction of a plasmid expressing a mutant ptlC altered in the putative nucleotide-binding region, suggesting that this region of PtlC is essential for proper function. Moreover, the observed dominant negative phenotype suggests that PtlC either functions as a multimer or interacts with some other component(s) necessary for secretion of PT.
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Affiliation(s)
- D M Cook
- Laboratory of Pertussis, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892, USA
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32
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Banta LM, Bohne J, Lovejoy SD, Dostal K. Stability of the Agrobacterium tumefaciens VirB10 protein is modulated by growth temperature and periplasmic osmoadaption. J Bacteriol 1998; 180:6597-606. [PMID: 9852004 PMCID: PMC107763 DOI: 10.1128/jb.180.24.6597-6606.1998] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Export of oncogenic T-DNA from the phytopathogen Agrobacterium tumefaciens is mediated by the products of the virB operon. It has recently been reported (K. J. Fullner and E. W. Nester, J. Bacteriol. 178:1498-1504, 1996) that DNA transfer does not occur at elevated temperatures; these observations correlate well with much earlier studies on the temperature sensitivity of crown gall tumor development on plants. In testing the hypothesis that this loss of DNA movement reflects a defect in assembly or maintenance of a stable DNA transfer machinery at high temperature, we have found that steady-state levels of VirB10 are sensitive to growth temperature while levels of several other VirB proteins are considerably less affected. This temperature-dependent failure to accumulate VirB10 is exacerbated in an attachment-deficient mutant strain (chvB) which exhibits pleiotropic defects in periplasmic osmoadaption, and virulence of a chvB mutant can be partially restored by lowering the temperature at which the bacteria and the plant tissue are cocultivated. Furthermore, the stability of VirB10 is diminished in cells lacking functional VirB9, but only under conditions of low osmolarity. We propose that newly synthesized VirB10 is inherently labile in the presence of a large osmotic gradient across the inner membrane and is rapidly degraded unless it is stabilized by VirB9-dependent assembly into oligomeric complexes. The possibility that VirB10-containing complexes are not assembled properly at elevated temperatures suggests an explanation for the decades-old observation that tumor formation is exquisitely sensitive to ambient temperature.
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Affiliation(s)
- L M Banta
- Department of Biology, Haverford College, Haverford, Pennsylvania 19041, USA.
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33
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Stahl LE, Jacobs A, Binns AN. The conjugal intermediate of plasmid RSF1010 inhibits Agrobacterium tumefaciens virulence and VirB-dependent export of VirE2. J Bacteriol 1998; 180:3933-9. [PMID: 9683491 PMCID: PMC107378 DOI: 10.1128/jb.180.15.3933-3939.1998] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Agrobacterium tumefaciens causes crown gall disease by transferring oncogenic, single-stranded DNA (T strand), covalently attached to the VirD2 protein, across the bacterial envelope into plant cells where its expression results in tumor formation. The single-stranded DNA binding protein VirE2 is also transferred into the plant cell, though the location at which VirE2 interacts with the T strand is still under investigation. The movement of the transferred DNA and VirE2 from A. tumefaciens to the plant cell depends on the membrane-localized VirB and VirD4 proteins. Further, the movement of the IncQ broad-host-range plasmid RSF1010 between Agrobacterium strains or from Agrobacterium to plants also requires the virB-encoded transfer system. Our earlier studies showed that the presence of the RSF1010 plasmid in wild-type strains of Agrobacterium inhibits both their virulence and their capacity to transport VirE2, as assayed by coinfection with virE mutants. Here we demonstrate that the capacity to form a conjugal intermediate of RSF1010 is necessary for this inhibition, suggesting that the transferred form of the plasmid competes with the VirD2-T strand and/or VirE2 for a common export site.
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Affiliation(s)
- L E Stahl
- Plant Science Institute, Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania
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34
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Lory S. Secretion of proteins and assembly of bacterial surface organelles: shared pathways of extracellular protein targeting. Curr Opin Microbiol 1998; 1:27-35. [PMID: 10066461 DOI: 10.1016/s1369-5274(98)80139-2] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Extracellular or surface localization of virulence determinants is an important attribute of pathogenic microorganisms. The past decade has seen significant research advances in defining the steps and identifying the necessary machinery for protein secretion from bacterial cells. In Gram-negative pathogens, four distinct classes of secretion pathways have been identified that deliver virulence factors to their sites of action. These pathways are responsible for the delivery of soluble extracellular enzymes into the surrounding medium, or for specifically targeting proteins to the host cell. In several instances protein secretion pathways are similar to those involved in assembly of bacterial appendages. Combination of biochemical and genetic analyses has recently revealed that the pathways of protein secretion and surface localization of various organelles are mechanistically similar which was not apparent simply by comparing amino acid sequences of related proteins. The choice of the pathway that a protein will utilize may not be dictated only by the specific requirement of the secreted protein to traverse the cell envelope in the functional form, but also by the need to assure its delivery to the correct site of action outside the bacterial cell.
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Affiliation(s)
- S Lory
- Department of Microbiology, School of Medicine, University of Washington, Seattle, WA 98195, USA.
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35
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Kotob SI, Burns DL. Essential role of the consensus nucleotide-binding site of PtlH in secretion of pertussis toxin from Bordetella pertussis. J Bacteriol 1997; 179:7577-80. [PMID: 9393726 PMCID: PMC179712 DOI: 10.1128/jb.179.23.7577-7580.1997] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
PtlH is a member of a specialized set of transport proteins that is essential for secretion of pertussis toxin (PT) from Bordetella pertussis. Previously, PtlH was shown to contain a consensus nucleotide-binding motif. Here, we demonstrate that introduction of plasmids containing mutant forms of ptlH, altered in the putative nucleotide-binding region, into a wild-type strain of B. pertussis resulted in inhibition of PT secretion. Thus, this region of PtlH appears to be essential for protein function. Moreover, the observed dominant negative phenotype suggests that PtlH either functions as a multimer or interacts with another component necessary for secretion of PT.
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Affiliation(s)
- S I Kotob
- Laboratory of Pertussis, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892, USA
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Zhou XR, Christie PJ. Suppression of mutant phenotypes of the Agrobacterium tumefaciens VirB11 ATPase by overproduction of VirB proteins. J Bacteriol 1997; 179:5835-42. [PMID: 9294442 PMCID: PMC179474 DOI: 10.1128/jb.179.18.5835-5842.1997] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The Agrobacterium tumefaciens VirB11 ATPase is postulated to assemble with VirB proteins and the VirD4 protein into a transport system which is dedicated to the export of oncogenic nucleoprotein particles to plant cells. To gain genetic evidence for interactions between VirB11 and other subunits of this transport system, we screened a PCR-mutagenized virB11 library for alleles that diminish the virulence of the wild-type strain A348. Two classes of alleles displaying negative dominance were identified. One class failed to complement a delta virB11 mutation, indicating that the corresponding mutant proteins are nonfunctional. The second class complemented the delta virB11 mutation, indicating that the mutant proteins are fully functional in strains devoid of native VirB11. Mutations of both classes of alleles were in codons for residues clustered in two regions of VirB11, both located outside the Walker A nucleotide binding motif. All dominant alleles were suppressed at least to some extent by multicopy expression of the virB9, virB10, and/or virB11 genes. Taken together, results of these investigations indicate that (i) a functional T-complex transporter is composed of more than one VirB11 subunit and (ii) VirB11 undergoes complex formation with VirB9 and VirB10 during transporter biogenesis.
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Affiliation(s)
- X R Zhou
- Department of Microbiology and Molecular Genetics, University of Texas Health Science Center, Houston 77030, USA
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Das A, Anderson LB, Xie YH. Delineation of the interaction domains of Agrobacterium tumefaciens VirB7 and VirB9 by use of the yeast two-hybrid assay. J Bacteriol 1997; 179:3404-9. [PMID: 9171381 PMCID: PMC179129 DOI: 10.1128/jb.179.11.3404-3409.1997] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The Agrobacterium tumefaciens VirB proteins are postulated to form a transport pore for the transfer of T-DNA. Formation of the transport pore will involve interactions among the VirB proteins. A powerful genetic method to study protein-protein interaction is the yeast two-hybrid assay. To test whether this method can be used to study interactions among the VirB membrane proteins, we studied the interaction of VirB7 and VirB9 in yeast. We recently demonstrated that VirB7 and VirB9 form a protein complex linked by a disulfide bond between cysteine 24 of VirB7 and cysteine 262 of VirB9 (L. Anderson, A. Hertzel, and A. Das, Proc. Natl. Acad. Sci. USA 93:8889-8894, 1996). We now demonstrate that VirB7 and VirB9 interact in yeast, and this interaction does not require the cysteine residues essential for the disulfide linkage. By using defined segments in fusion constructions, we mapped the VirB7 interaction domain of VirB9 to residues 173 to 275. In tumor formation assays, both virB7C24S and virB9C262S expressed from a multicopy plasmid complemented the respective deletion mutation, indicating that the cysteine residues may not be essential for DNA transfer.
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Affiliation(s)
- A Das
- Department of Biochemistry, University of Minnesota, St. Paul 55108, USA.
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Christie PJ. Agrobacterium tumefaciens T-complex transport apparatus: a paradigm for a new family of multifunctional transporters in eubacteria. J Bacteriol 1997; 179:3085-94. [PMID: 9150199 PMCID: PMC179082 DOI: 10.1128/jb.179.10.3085-3094.1997] [Citation(s) in RCA: 257] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Affiliation(s)
- P J Christie
- Department of Microbiology and Molecular Genetics, The University of Texas Health Science Center at Houston 77030, USA.
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