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Al Mamun AAM, Kissoon K, Li YG, Hancock E, Christie PJ. The F plasmid conjutome: the repertoire of E. coli proteins translocated through an F-encoded type IV secretion system. mSphere 2024; 9:e0035424. [PMID: 38940509 PMCID: PMC11288057 DOI: 10.1128/msphere.00354-24] [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: 04/25/2024] [Accepted: 06/10/2024] [Indexed: 06/29/2024] Open
Abstract
Bacterial conjugation systems pose a major threat to human health through their widespread dissemination of mobile genetic elements (MGEs) carrying cargoes of antibiotic resistance genes. Using the Cre Recombinase Assay for Translocation (CRAfT), we recently reported that the IncFV pED208 conjugation system also translocates at least 16 plasmid-encoded proteins to recipient bacteria. Here, we deployed a high-throughput CRAfT screen to identify the repertoire of chromosomally encoded protein substrates of the pED208 system. We identified 32 substrates encoded by the Escherichia coli W3110 genome with functions associated with (i) DNA/nucleotide metabolism, (ii) stress tolerance/physiology, (iii) transcriptional regulation, or (iv) toxin inhibition. The respective gene deletions did not impact pED208 transfer proficiencies, nor did Group 1 (DNA/nucleotide metabolism) mutations detectably alter the SOS response elicited in new transconjugants upon acquisition of pED208. However, MC4100(pED208) donor cells intrinsically exhibit significantly higher SOS activation than plasmid-free MC4100 cells, and this plasmid carriage-induced stress response is further elevated in donor cells deleted of several Group 1 genes. Among 10 characterized substrates, we gained evidence of C-terminal or internal translocation signals that could function independently or synergistically for optimal protein transfer. Remarkably, nearly all tested proteins were also translocated through the IncN pKM101 and IncP RP4 conjugation systems. This repertoire of E. coli protein substrates, here termed the F plasmid "conjutome," is thus characterized by functions of potential benefit to new transconjugants, diverse TSs, and the capacity for promiscuous transfer through heterologous conjugation systems. IMPORTANCE Conjugation systems comprise a major subfamily of the type IV secretion systems (T4SSs) and are the progenitors of a second large T4SS subfamily dedicated to translocation of protein effectors. This study examined the capacity of conjugation machines to function as protein translocators. Using a high-throughput reporter screen, we determined that 32 chromosomally encoded proteins are delivered through an F plasmid conjugation system. The translocated proteins potentially enhance the establishment of the co-transferred F plasmid or mitigate mating-induced stresses. Translocation signals located C-terminally or internally conferred substrate recognition by the F system and, remarkably, many substrates also were translocated through heterologous conjugation systems. Our findings highlight the plasticity of conjugation systems in their capacities to co-translocate DNA and many protein substrates.
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Affiliation(s)
- Abu Amar M. Al Mamun
- Department of Microbiology and Molecular Genetics, McGovern Medical School at UTHealth, Houston, Texas, USA
| | - Kimberley Kissoon
- Department of Microbiology and Molecular Genetics, McGovern Medical School at UTHealth, Houston, Texas, USA
| | - Yang Grace Li
- Department of Microbiology and Molecular Genetics, McGovern Medical School at UTHealth, Houston, Texas, USA
| | - Erin Hancock
- Department of Microbiology and Molecular Genetics, McGovern Medical School at UTHealth, Houston, Texas, USA
| | - Peter J. Christie
- Department of Microbiology and Molecular Genetics, McGovern Medical School at UTHealth, Houston, Texas, USA
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Ota Y, Prah I, Mahazu S, Gu Y, Nukui Y, Koike R, Saito R. Novel insights into genetic characteristics of blaGES-encoding plasmids from hospital sewage. Front Microbiol 2023; 14:1209195. [PMID: 37664110 PMCID: PMC10469963 DOI: 10.3389/fmicb.2023.1209195] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2023] [Accepted: 08/01/2023] [Indexed: 09/05/2023] Open
Abstract
Introduction The prevalence of Guiana extended-spectrum (GES)-type carbapenemase producers is increasing worldwide, and hospital water environments are considered as potential reservoirs. However, the genetic features underlying this resistance are not yet fully understood. This study aimed to characterize blaGES-encoding plasmids from a single-hospital sewage sample in Japan. Methods Carbapenemase producers were screened using carbapenemase-selective agar and polymerase chain reaction. Whole-genome sequencing analyzes were performed on the carbapenemase-producing isolates. Results Eleven gram-negative bacteria (four Enterobacter spp., three Klebsiella spp., three Aeromonas spp., and one Serratia spp.) with blaGES-24 (n = 6), blaGES-6 (n = 4), and blaGES-5 (n = 1) were isolated from the sewage sample. Five blaGES-24 and a blaGES-5 were localized in IncP-6 plasmids, whereas three blaGES-6 plasmids were localized in IncC plasmids with IncF-like regions. The remaining blaGES-6 and blaGES-24 were, respectively, localized on IncFIB-containing plasmids with IncF-like regions and a plasmid with an IncW-like replication protein. The IncP-6 and IncW-like plasmids had a close genetic relationship with plasmids from Japan, whereas the IncC/IncF-like and IncFIB/IncF-like plasmids were closely related to those from the United States and Europe. All blaGES genes were located on the class 1 integron cassette of the Tn3 transposon-related region, and the IncC/IncF-like plasmid carried two copies of the integron cassette. Eight of the eleven blaGES-encoding plasmids contained toxin-antitoxin system genes. Discussion The findings on the plasmids and the novel genetic content from a single wastewater sample extend our understanding regarding the diversity of resistance and the associated spread of blaGES, suggesting their high adaptability to hospital effluents. These findings highlight the need for the continuous monitoring of environmental GES-type carbapenemase producers to control their dissemination.
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Affiliation(s)
- Yusuke Ota
- Department of Molecular Microbiology and Immunology, Tokyo Medical and Dental University, Tokyo, Japan
| | - Isaac Prah
- Department of Molecular Microbiology and Immunology, Tokyo Medical and Dental University, Tokyo, Japan
| | - Samiratu Mahazu
- Department of Molecular Microbiology and Immunology, Tokyo Medical and Dental University, Tokyo, Japan
- Department of Parasitology and Tropical Medicine, Tokyo Medical and Dental University, Tokyo, Japan
| | - Yoshiaki Gu
- Department of Infectious Diseases, Tokyo Medical and Dental University, Tokyo, Japan
| | - Yoko Nukui
- Department of Infection Control and Laboratory Medicine, Kyoto Prefectural University of Medicine, Kyoto, Japan
| | - Ryuji Koike
- Clinical Research Center, Tokyo Medical and Dental University Hospital, Tokyo, Japan
| | - Ryoichi Saito
- Department of Molecular Microbiology and Immunology, Tokyo Medical and Dental University, Tokyo, Japan
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Cooke MB, Herman C. Conjugation's Toolkit: the Roles of Nonstructural Proteins in Bacterial Sex. J Bacteriol 2023; 205:e0043822. [PMID: 36847532 PMCID: PMC10029717 DOI: 10.1128/jb.00438-22] [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] [Indexed: 03/01/2023] Open
Abstract
Bacterial conjugation, a form of horizontal gene transfer, relies on a type 4 secretion system (T4SS) and a set of nonstructural genes that are closely linked. These nonstructural genes aid in the mobile lifestyle of conjugative elements but are not part of the T4SS apparatus for conjugative transfer, such as the membrane pore and relaxosome, or the plasmid maintenance and replication machineries. While these nonstructural genes are not essential for conjugation, they assist in core conjugative functions and mitigate the cellular burden on the host. This review compiles and categorizes known functions of nonstructural genes by the stage of conjugation they modulate: dormancy, transfer, and new host establishment. Themes include establishing a commensalistic relationship with the host, manipulating the host for efficient T4SS assembly and function and assisting in conjugative evasion of recipient cell immune functions. These genes, taken in a broad ecological context, play important roles in ensuring proper propagation of the conjugation system in a natural environment.
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Affiliation(s)
- Matthew B. Cooke
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA
| | - Christophe Herman
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, USA
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, USA
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Couturier A, Virolle C, Goldlust K, Berne-Dedieu A, Reuter A, Nolivos S, Yamaichi Y, Bigot S, Lesterlin C. Real-time visualisation of the intracellular dynamics of conjugative plasmid transfer. Nat Commun 2023; 14:294. [PMID: 36653393 PMCID: PMC9849209 DOI: 10.1038/s41467-023-35978-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2022] [Accepted: 01/11/2023] [Indexed: 01/19/2023] Open
Abstract
Conjugation is a contact-dependent mechanism for the transfer of plasmid DNA between bacterial cells, which contributes to the dissemination of antibiotic resistance. Here, we use live-cell microscopy to visualise the intracellular dynamics of conjugative transfer of F-plasmid in E. coli, in real time. We show that the transfer of plasmid in single-stranded form (ssDNA) and its subsequent conversion into double-stranded DNA (dsDNA) are fast and efficient processes that occur with specific timing and subcellular localisation. Notably, the ssDNA-to-dsDNA conversion determines the timing of plasmid-encoded protein production. The leading region that first enters the recipient cell carries single-stranded promoters that allow the early and transient synthesis of leading proteins immediately upon entry of the ssDNA plasmid. The subsequent conversion into dsDNA turns off leading gene expression, and activates the expression of other plasmid genes under the control of conventional double-stranded promoters. This molecular strategy allows for the timely production of factors sequentially involved in establishing, maintaining and disseminating the plasmid.
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Affiliation(s)
- Agathe Couturier
- Molecular Microbiology and Structural Biochemistry (MMSB), Université Lyon 1, CNRS, Inserm, UMR5086, 69007, Lyon, France
| | - Chloé Virolle
- Molecular Microbiology and Structural Biochemistry (MMSB), Université Lyon 1, CNRS, Inserm, UMR5086, 69007, Lyon, France
| | - Kelly Goldlust
- Molecular Microbiology and Structural Biochemistry (MMSB), Université Lyon 1, CNRS, Inserm, UMR5086, 69007, Lyon, France
| | - Annick Berne-Dedieu
- Molecular Microbiology and Structural Biochemistry (MMSB), Université Lyon 1, CNRS, Inserm, UMR5086, 69007, Lyon, France
| | - Audrey Reuter
- Molecular Microbiology and Structural Biochemistry (MMSB), Université Lyon 1, CNRS, Inserm, UMR5086, 69007, Lyon, France
| | - Sophie Nolivos
- Molecular Microbiology and Structural Biochemistry (MMSB), Université Lyon 1, CNRS, Inserm, UMR5086, 69007, Lyon, France
| | - Yoshiharu Yamaichi
- Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198, Gif-sur-Yvette, France
| | - Sarah Bigot
- Molecular Microbiology and Structural Biochemistry (MMSB), Université Lyon 1, CNRS, Inserm, UMR5086, 69007, Lyon, France.
| | - Christian Lesterlin
- Molecular Microbiology and Structural Biochemistry (MMSB), Université Lyon 1, CNRS, Inserm, UMR5086, 69007, Lyon, France.
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Bragagnolo N, Audette GF. Solution characterization of the dynamic conjugative entry exclusion protein TraG. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2022; 9:064702. [PMID: 36590369 PMCID: PMC9797247 DOI: 10.1063/4.0000171] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/27/2022] [Accepted: 12/07/2022] [Indexed: 06/17/2023]
Abstract
The R100 plasmid and the secretion system it encodes are representative of F-like conjugative type IV secretion systems for the transmission of mobile DNA elements in gram-negative bacteria, serving as a major contributor to the spread of antibiotic resistance in bacterial pathogens. The TraG protein of F-like systems consists of a membrane-bound N-terminal domain and a periplasmic C-terminal domain, denoted TraG*. TraG* is essential in preventing redundant DNA transfer through a process termed entry exclusion. In the donor cell, it interacts with TraN to facilitate mating pair stabilization; however, if a mating pore forms between bacteria with identical plasmids, TraG* interacts with its cognate TraS in the inner membrane of the recipient bacterium to prevent redundant donor-donor conjugation. Structural studies of TraG* from the R100 plasmid have revealed the presence of a dynamic region between the N- and C-terminal domains of TraG. Thermofluor, circular dichroism, collision-induced unfolding-mass spectrometry, and size exclusion chromatography linked to multiangle light scattering and small angle x-ray scattering experiments indicated an N-terminal truncation mutant displayed higher stability and less disordered content relative to full-length TraG*. The 45 N-terminal residues of TraG* are hypothesized to serve as part of a flexible linker between the two independently functioning domains.
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Al Mamun AAM, Kissoon K, Kishida K, Shropshire WC, Hanson B, Christie PJ. IncFV plasmid pED208: Sequence analysis and evidence for translocation of maintenance/leading region proteins through diverse type IV secretion systems. Plasmid 2022; 123-124:102652. [PMID: 36228885 PMCID: PMC10018792 DOI: 10.1016/j.plasmid.2022.102652] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2022] [Revised: 10/02/2022] [Accepted: 10/04/2022] [Indexed: 12/04/2022]
Abstract
Two phylogenetically distantly-related IncF plasmids, F and pED208, serve as important models for mechanistic and structural studies of F-like type IV secretion systems (T4SSFs) and F pili. Here, we present the pED208 sequence and compare it to F and pUMNF18, the closest match to pED208 in the NCBI database. As expected, gene content of the three cargo regions varies extensively, although the maintenance/leading regions (MLRs) and transfer (Tra) regions also carry novel genes or motifs with predicted modulatory effects on plasmid stability, dissemination and host range. By use of a Cre recombinase assay for translocation (CRAfT), we recently reported that pED208-carrying donors translocate several products of the MLR (ParA, ParB1, ParB2, SSB, PsiB, PsiA) intercellularly through the T4SSF. Here, we extend these findings by reporting that pED208-carrying donors translocate 10 additional MLR proteins during conjugation. In contrast, two F plasmid-encoded toxin components of toxin-antitoxin (TA) modules, CcdB and SrnB, were not translocated at detectable levels through the T4SSF. Remarkably, most or all of the pED208-encoded MLR proteins and CcdB and SrnB were translocated through heterologous T4SSs encoded by IncN and IncP plasmids pKM101 and RP4, respectively. Together, our sequence analyses underscore the genomic diversity of the F plasmid superfamily, and our experimental data demonstrate the promiscuous nature of conjugation machines for protein translocation. Our findings raise intriguing questions about the nature of T4SS translocation signals and of the biological and evolutionary consequences of conjugative protein transfer.
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Affiliation(s)
- Abu Amar M Al Mamun
- Department of Microbiology and Molecular Genetics, University of Texas Health Science Center, McGovern School of Medicine, Fannin St, Houston, TX 77030, United States of America.
| | - Kimberly Kissoon
- Department of Microbiology and Molecular Genetics, University of Texas Health Science Center, McGovern School of Medicine, Fannin St, Houston, TX 77030, United States of America
| | - Kouhei Kishida
- Department of Microbiology and Molecular Genetics, University of Texas Health Science Center, McGovern School of Medicine, Fannin St, Houston, TX 77030, United States of America
| | - William C Shropshire
- Center for Antimicrobial Resistance and Microbial Genomics, University of Texas Health Science Center, McGovern School of Medicine, Houston, TX, USA; Center for Infectious Diseases, University of Texas Health Science Center, School of Public Health, Houston, TX, USA
| | - Blake Hanson
- Center for Antimicrobial Resistance and Microbial Genomics, University of Texas Health Science Center, McGovern School of Medicine, Houston, TX, USA; Center for Infectious Diseases, University of Texas Health Science Center, School of Public Health, Houston, TX, USA
| | - Peter J Christie
- Department of Microbiology and Molecular Genetics, University of Texas Health Science Center, McGovern School of Medicine, Fannin St, Houston, TX 77030, United States of America.
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Protein Transfer through an F Plasmid-Encoded Type IV Secretion System Suppresses the Mating-Induced SOS Response. mBio 2021; 12:e0162921. [PMID: 34253063 PMCID: PMC8406263 DOI: 10.1128/mbio.01629-21] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Bacterial type IV secretion systems (T4SSs) mediate the conjugative transfer of mobile genetic elements (MGEs) and their cargoes of antibiotic resistance and virulence genes. Here, we report that the pED208-encoded T4SS (TrapED208) translocates not only this F plasmid but several plasmid-encoded proteins, including ParA, ParB1, single-stranded DNA-binding protein SSB, ParB2, PsiB, and PsiA, to recipient cells. Conjugative protein translocation through the TrapED208 T4SS required engagement of the pED208 relaxosome with the TraD substrate receptor or coupling protein. T4SSs translocate MGEs as single-stranded DNA intermediates (T-strands), which triggers the SOS response in recipient cells. Transfer of pED208 deleted of psiB or ssb, which, respectively, encode the SOS inhibitor protein PsiB and single-stranded DNA-binding protein SSB, elicited a significantly stronger SOS response than pED208 or mutant plasmids deleted of psiA, parA, parB1, or parB2. Conversely, translocation of PsiB or SSB, but not PsiA, through the TrapED208 T4SS suppressed the mating-induced SOS response. Our findings expand the repertoire of known substrates of conjugation systems to include proteins with functions associated with plasmid maintenance. Furthermore, for this and other F-encoded Tra systems, docking of the DNA substrate with the TraD receptor appears to serve as a critical activating signal for protein translocation. Finally, the observed effects of PsiB and SSB on suppression of the mating-induced SOS response establishes a novel biological function for conjugative protein translocation and suggests the potential for interbacterial protein translocation to manifest in diverse outcomes influencing bacterial communication, physiology, and evolution.
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Álvarez-Rodríguez I, Arana L, Ugarte-Uribe B, Gómez-Rubio E, Martín-Santamaría S, Garbisu C, Alkorta I. Type IV Coupling Proteins as Potential Targets to Control the Dissemination of Antibiotic Resistance. Front Mol Biosci 2020; 7:201. [PMID: 32903459 PMCID: PMC7434980 DOI: 10.3389/fmolb.2020.00201] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Accepted: 07/27/2020] [Indexed: 12/18/2022] Open
Abstract
The increase of infections caused by multidrug-resistant bacteria, together with the loss of effectiveness of currently available antibiotics, represents one of the most serious threats to public health worldwide. The loss of human lives and the economic costs associated to the problem of the dissemination of antibiotic resistance require immediate action. Bacteria, known by their great genetic plasticity, are capable not only of mutating their genes to adapt to disturbances and environmental changes but also of acquiring new genes that allow them to survive in hostile environments, such as in the presence of antibiotics. One of the major mechanisms responsible for the horizontal acquisition of new genes (e.g., antibiotic resistance genes) is bacterial conjugation, a process mediated by mobile genetic elements such as conjugative plasmids and integrative conjugative elements. Conjugative plasmids harboring antibiotic resistance genes can be transferred from a donor to a recipient bacterium in a process that requires physical contact. After conjugation, the recipient bacterium not only harbors the antibiotic resistance genes but it can also transfer the acquired plasmid to other bacteria, thus contributing to the spread of antibiotic resistance. Conjugative plasmids have genes that encode all the proteins necessary for the conjugation to take place, such as the type IV coupling proteins (T4CPs) present in all conjugative plasmids. Type VI coupling proteins constitute a heterogeneous family of hexameric ATPases that use energy from the ATP hydrolysis for plasmid transfer. Taking into account their essential role in bacterial conjugation, T4CPs are attractive targets for the inhibition of bacterial conjugation and, concomitantly, the limitation of antibiotic resistance dissemination. This review aims to compile present knowledge on T4CPs as a starting point for delving into their molecular structure and functioning in future studies. Likewise, the scientific literature on bacterial conjugation inhibitors has been reviewed here, in an attempt to elucidate the possibility of designing T4CP-inhibitors as a potential solution to the dissemination of multidrug-resistant bacteria.
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Affiliation(s)
- Itxaso Álvarez-Rodríguez
- Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain
| | - Lide Arana
- Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain
| | - Begoña Ugarte-Uribe
- Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain
| | - Elena Gómez-Rubio
- Department of Structural and Chemical Biology, Centro de Investigaciones Biológicas Margarita Salas, CIB-CSIC, Madrid, Spain
| | - Sonsoles Martín-Santamaría
- Department of Structural and Chemical Biology, Centro de Investigaciones Biológicas Margarita Salas, CIB-CSIC, Madrid, Spain
| | - Carlos Garbisu
- Department of Conservation of Natural Resources, Soil Microbial Ecology Group, NEIKER - Basque Institute for Agricultural Research and Development, Basque Research and Technology Alliance (BRTA), Parque Cient fico y Tecnológico de Bizkaia, Derio, Spain
| | - Itziar Alkorta
- Department of Biochemistry and Molecular Biology, University of the Basque Country, Leioa, Spain
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9
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Li YG, Christie PJ. The TraK accessory factor activates substrate transfer through the pKM101 type IV secretion system independently of its role in relaxosome assembly. Mol Microbiol 2020; 114:214-229. [PMID: 32239779 DOI: 10.1111/mmi.14507] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2020] [Revised: 03/24/2020] [Indexed: 12/12/2022]
Abstract
A large subfamily of the type IV secretion systems (T4SSs), termed the conjugation systems, transmit mobile genetic elements (MGEs) among many bacterial species. In the initiating steps of conjugative transfer, DNA transfer and replication (Dtr) proteins assemble at the origin-of-transfer (oriT) sequence as the relaxosome, which nicks the DNA strand destined for transfer and couples the nicked substrate with the VirD4-like substrate receptor. Here, we defined contributions of the Dtr protein TraK, a predicted member of the Ribbon-Helix-Helix (RHH) family of DNA-binding proteins, to transfer of DNA and protein substrates through the pKM101-encoded T4SS. Using a combination of cross-linking/affinity pull-downs and two-hybrid assays, we determined that TraK self-associates as a probable tetramer and also forms heteromeric contacts with pKM101-encoded TraI relaxase, VirD4-like TraJ receptor, and VirB11-like and VirB4-like ATPases, TraG and TraB, respectively. TraK also promotes stable TraJ-TraB complex formation and stimulates binding of TraI with TraB. Finally, TraK is required for or strongly stimulates the transfer of cognate (pKM101, TraI relaxase) and noncognate (RSF1010, MobA relaxase) substrates. We propose that TraK functions not only to nucleate pKM101 relaxosome assembly, but also to activate the TrapKM101 T4SS via interactions with the ATPase energy center positioned at the channel entrance.
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Affiliation(s)
- Yang Grace Li
- Department of Microbiology and Molecular Genetics, McGovern Medical School, Houston, TX, USA
| | - Peter J Christie
- Department of Microbiology and Molecular Genetics, McGovern Medical School, Houston, TX, USA
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10
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Abstract
The translocation of proteins across membranes is a fundamental cellular function. Bacteria have evolved a striking array of pathways for delivering proteins into or across cytoplasmic membranes and, when present, outer membranes. Translocated proteins can form part of the membrane landscape, reside in the periplasmic space situated between the inner and outer membranes of Gram-negative bacteria, deposit on the cell surface, or be released to the extracellular milieu or injected directly into target cells. One protein translocation system, the general secretory pathway, is conserved in all domains of life. A second, the twin-arginine translocation pathway, is also phylogenetically distributed among most bacteria and plant chloroplasts. While all cell types have evolved additional systems dedicated to the translocation of protein cargoes, the number of such systems in bacteria is now known to exceed nine. These dedicated protein translocation systems, which include the types 1 through 9 secretion systems (T1SSs-T9SSs), the chaperone-usher pathway, and type IV pilus system, are the subject of this review. Most of these systems were originally identified and have been extensively characterized in Gram-negative or diderm (two-membrane) species. It is now known that several of these systems also have been adapted to function in Gram-positive or monoderm (single-membrane) species, and at least one pathway is found only in monoderms. This review briefly summarizes the distinctive mechanistic and structural features of each dedicated pathway, as well as the shared properties, that together account for the broad biological diversity of protein translocation in bacteria.
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Affiliation(s)
- Peter J Christie
- Department of Microbiology and Molecular Genetics, McGovern Medical School, 6431 Fannin St., Houston, TX, USA.
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11
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Abstract
The bacterial type IV secretion systems (T4SSs) are a functionally diverse superfamily of secretion systems found in many species of bacteria. Collectively, the T4SSs translocate DNA and monomeric and multimeric protein substrates to bacterial and eukaryotic cell types. T4SSs are composed of two large subfamilies, the conjugation machines and the effector translocators that transmit their cargoes through establishment of direct donor-target cell contacts, and a third small subfamily capable of importing or exporting substrates from or to the milieu. This review summarizes recent mechanistic and structural findings that are shedding new light on how T4SSs have evolved such functional diversity. Translocation signals are now known to be located C terminally or embedded internally in structural folds; these signals in combination with substrate-associated adaptor proteins mediate the docking of specific substrate repertoires to cognate VirD4-like receptors. For the Legionella pneumophila Dot/Icm system, recent work has elucidated the structural basis for adaptor-dependent substrate loading onto the VirD4-like DotL receptor. Advances in definition of T4SS machine structures now allow for detailed comparisons of nanomachines closely related to the Agrobacterium tumefaciens VirB/VirD4 T4SS with those more distantly related, e.g., the Dot/Icm and Helicobacter pylori Cag T4SSs. Finally, it is increasingly evident that T4SSs have evolved a variety of mechanisms dependent on elaboration of conjugative pili, membrane tubes, or surface adhesins to establish productive contacts with target cells. T4SSs thus have evolved extreme functional diversity through a plethora of adaptations impacting substrate selection, machine architecture, and target cell binding.
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12
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Gordon JE, Costa TRD, Patel RS, Gonzalez-Rivera C, Sarkar MK, Orlova EV, Waksman G, Christie PJ. Use of chimeric type IV secretion systems to define contributions of outer membrane subassemblies for contact-dependent translocation. Mol Microbiol 2017; 105:273-293. [PMID: 28452085 DOI: 10.1111/mmi.13700] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/25/2017] [Indexed: 01/26/2023]
Abstract
Recent studies have shown that conjugation systems of Gram-negative bacteria are composed of distinct inner and outer membrane core complexes (IMCs and OMCCs, respectively). Here, we characterized the OMCC by focusing first on a cap domain that forms a channel across the outer membrane. Strikingly, the OMCC caps of the Escherichia coli pKM101 Tra and Agrobacterium tumefaciens VirB/VirD4 systems are completely dispensable for substrate transfer, but required for formation of conjugative pili. The pKM101 OMCC cap and extended pilus also are dispensable for activation of a Pseudomonas aeruginosa type VI secretion system (T6SS). Chimeric conjugation systems composed of the IMCpKM101 joined to OMCCs from the A. tumefaciens VirB/VirD4, E. coli R388 Trw, and Bordetella pertussis Ptl systems support conjugative DNA transfer in E. coli and trigger P. aeruginosa T6SS killing, but not pilus production. The A. tumefaciens VirB/VirD4 OMCC, solved by transmission electron microscopy, adopts a cage structure similar to the pKM101 OMCC. The findings establish that OMCCs are highly structurally and functionally conserved - but also intrinsically conformationally flexible - scaffolds for translocation channels. Furthermore, the OMCC cap and a pilus tip protein coregulate pilus extension but are not required for channel assembly or function.
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Affiliation(s)
- Jay E Gordon
- Department of Microbiology and Molecular Genetics, McGovern Medical School, 6431 Fannin St, Houston, TX, 77030, USA
| | - Tiago R D Costa
- Institute of Structural and Molecular Biology, University College London and Birkbeck, Malet Street, London, WC1E 7HX, UK
| | - Roosheel S Patel
- Department of Microbiology and Molecular Genetics, McGovern Medical School, 6431 Fannin St, Houston, TX, 77030, USA
| | - Christian Gonzalez-Rivera
- Department of Microbiology and Molecular Genetics, McGovern Medical School, 6431 Fannin St, Houston, TX, 77030, USA
| | - Mayukh K Sarkar
- Department of Microbiology and Molecular Genetics, McGovern Medical School, 6431 Fannin St, Houston, TX, 77030, USA
| | - Elena V Orlova
- Institute of Structural and Molecular Biology, University College London and Birkbeck, Malet Street, London, WC1E 7HX, UK
| | - Gabriel Waksman
- Institute of Structural and Molecular Biology, University College London and Birkbeck, Malet Street, London, WC1E 7HX, UK
| | - Peter J Christie
- Department of Microbiology and Molecular Genetics, McGovern Medical School, 6431 Fannin St, Houston, TX, 77030, USA
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13
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Ilangovan A, Kay CWM, Roier S, El Mkami H, Salvadori E, Zechner EL, Zanetti G, Waksman G. Cryo-EM Structure of a Relaxase Reveals the Molecular Basis of DNA Unwinding during Bacterial Conjugation. Cell 2017; 169:708-721.e12. [PMID: 28457609 PMCID: PMC5422253 DOI: 10.1016/j.cell.2017.04.010] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Revised: 02/28/2017] [Accepted: 04/06/2017] [Indexed: 11/20/2022]
Abstract
Relaxases play essential roles in conjugation, the main process by which bacteria exchange genetic material, notably antibiotic resistance genes. They are bifunctional enzymes containing a trans-esterase activity, which is responsible for nicking the DNA strand to be transferred and for covalent attachment to the resulting 5'-phosphate end, and a helicase activity, which is responsible for unwinding the DNA while it is being transported to a recipient cell. Here we show that these two activities are carried out by two conformers that can both load simultaneously on the origin of transfer DNA. We solve the structure of one of these conformers by cryo electron microscopy to near-atomic resolution, elucidating the molecular basis of helicase function by relaxases and revealing insights into the mechanistic events taking place in the cell prior to substrate transport during conjugation.
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Affiliation(s)
- Aravindan Ilangovan
- Institute of Structural and Molecular Biology, Birkbeck, Malet Street, London WC1E 7HX, UK
| | - Christopher W M Kay
- Institute of Structural and Molecular Biology, University College London, Gower Street, London WC1E 6BT, UK; London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, UK
| | - Sandro Roier
- Institute of Molecular Biosciences, University of Graz, BioTechMed-Graz, Humboldtstrasse 50, 8010 Graz, Austria
| | - Hassane El Mkami
- School of Physics and Astronomy, University of St Andrews, St Andrews KY16 9SS, UK
| | - Enrico Salvadori
- Institute of Structural and Molecular Biology, University College London, Gower Street, London WC1E 6BT, UK; London Centre for Nanotechnology, University College London, 17-19 Gordon Street, London WC1H 0AH, UK
| | - Ellen L Zechner
- Institute of Molecular Biosciences, University of Graz, BioTechMed-Graz, Humboldtstrasse 50, 8010 Graz, Austria
| | - Giulia Zanetti
- Institute of Structural and Molecular Biology, Birkbeck, Malet Street, London WC1E 7HX, UK.
| | - Gabriel Waksman
- Institute of Structural and Molecular Biology, Birkbeck, Malet Street, London WC1E 7HX, UK; Institute of Structural and Molecular Biology, University College London, Gower Street, London WC1E 6BT, UK.
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14
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Abstract
Type IV coupling proteins (T4CPs) are essential constituents of most type IV secretion systems (T4SSs), and probably the most intriguing component in terms of their evolutionary origin and functional role. Coupling proteins have coevolved with their cognate secretion system and translocated substrates. They are present in all conjugative systems, leading to the suggestion that they play a specific role in DNA transfer. However, they are also part of many T4SSs involved in bacterial virulence, where they are required for protein translocation, with no apparent involvement in DNA secretion. Their name reflects genetic and biochemical evidence of a connecting role between the substrate and the T4SS, thus probably playing a major role in substrate recruitment. Increasing evidence supports also a role in signal transmission leading to activation of secretion. Most studies have addressed conjugative coupling proteins of the VirD4-like protein family. Their conserved features include a nucleotide-binding domain, essential for substrate translocation, a C-terminal domain involved in substrate interactions, and a transmembrane domain anchoring them to the inner membrane, which is an important regulator of protein function. Purified soluble deletion mutants display ATP hydrolysis activity and unspecific DNA binding. Elucidation of the 3D structure of the soluble deletion mutant of the conjugative coupling protein TrwB, TrwBΔN70, provided the basis for further mutagenesis studies rendering interesting insights into the structure-function of these proteins. Their key role as couplers between substrate and transporter provides biotechnological potential as targets for anti-virulence strategies, as well as for customization of substrate delivery through heterologous secretion systems.
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Affiliation(s)
- Matxalen Llosa
- Departamento de Biología Molecular, Universidad de Cantabria (UC), and Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC), UC-CSIC-SODERCAN, C/Albert Einstein 22, 39011, Santander, Spain.
| | - Itziar Alkorta
- Departamento de Bioquímica y Biología Molecular (UPV/EHU), Instituto Biofisika (UPV/EHU, CSIC), Barrio Sarriena S/N, 48940, Leioa, Spain
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15
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Chimeric Coupling Proteins Mediate Transfer of Heterologous Type IV Effectors through the Escherichia coli pKM101-Encoded Conjugation Machine. J Bacteriol 2016; 198:2701-18. [PMID: 27432829 PMCID: PMC5019051 DOI: 10.1128/jb.00378-16] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Accepted: 07/13/2016] [Indexed: 12/12/2022] Open
Abstract
UNLABELLED Bacterial type IV secretion systems (T4SSs) are composed of two major subfamilies, conjugation machines dedicated to DNA transfer and effector translocators for protein transfer. We show here that the Escherichia coli pKM101-encoded conjugation system, coupled with chimeric substrate receptors, can be repurposed for transfer of heterologous effector proteins. The chimeric receptors were composed of the N-terminal transmembrane domain of pKM101-encoded TraJ fused to soluble domains of VirD4 homologs functioning in Agrobacterium tumefaciens, Anaplasma phagocytophilum, or Wolbachia pipientis A chimeric receptor assembled from A. tumefaciens VirD4 (VirD4At) mediated transfer of a MOBQ plasmid (pML122) and A. tumefaciens effector proteins (VirE2, VirE3, and VirF) through the pKM101 transfer channel. Equivalent chimeric receptors assembled from the rickettsial VirD4 homologs similarly supported the transfer of known or candidate effectors from rickettsial species. These findings establish a proof of principle for use of the dedicated pKM101 conjugation channel, coupled with chimeric substrate receptors, to screen for translocation competency of protein effectors from recalcitrant species. Many T4SS receptors carry sequence-variable C-terminal domains (CTDs) with unknown function. While VirD4At and the TraJ/VirD4At chimera with their CTDs deleted supported pML122 transfer at wild-type levels, ΔCTD variants supported transfer of protein substrates at strongly diminished or elevated levels. We were unable to detect binding of VirD4At's CTD to the VirE2 effector, although other VirD4At domains bound this substrate in vitro We propose that CTDs evolved to govern the dynamics of substrate presentation to the T4SS either through transient substrate contacts or by controlling substrate access to other receptor domains. IMPORTANCE Bacterial type IV secretion systems (T4SSs) display striking versatility in their capacity to translocate DNA and protein substrates to prokaryotic and eukaryotic target cells. A hexameric ATPase, the type IV coupling protein (T4CP), functions as a substrate receptor for nearly all T4SSs. Here, we report that chimeric T4CPs mediate transfer of effector proteins through the Escherichia coli pKM101-encoded conjugation system. Studies with these repurposed conjugation systems established a role for acidic C-terminal domains of T4CPs in regulating substrate translocation. Our findings advance a mechanistic understanding of T4CP receptor activity and, further, support a model in which T4SS channels function as passive conduits for any DNA or protein substrates that successfully engage with and pass through the T4CP specificity checkpoint.
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16
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Gruber CJ, Lang S, Rajendra VKH, Nuk M, Raffl S, Schildbach JF, Zechner EL. Conjugative DNA Transfer Is Enhanced by Plasmid R1 Partitioning Proteins. Front Mol Biosci 2016; 3:32. [PMID: 27486582 PMCID: PMC4949242 DOI: 10.3389/fmolb.2016.00032] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Accepted: 07/01/2016] [Indexed: 11/22/2022] Open
Abstract
Bacterial conjugation is a form of type IV secretion used to transport protein and DNA directly to recipient bacteria. The process is cell contact-dependent, yet the mechanisms enabling extracellular events to trigger plasmid transfer to begin inside the cell remain obscure. In this study of plasmid R1 we investigated the role of plasmid proteins in the initiation of gene transfer. We find that TraI, the central regulator of conjugative DNA processing, interacts physically, and functionally with the plasmid partitioning proteins ParM and ParR. These interactions stimulate TraI catalyzed relaxation of plasmid DNA in vivo and in vitro and increase ParM ATPase activity. ParM also binds the coupling protein TraD and VirB4-like channel ATPase TraC. Together, these protein-protein interactions probably act to co-localize the transfer components intracellularly and promote assembly of the conjugation machinery. Importantly these data also indicate that the continued association of ParM and ParR at the conjugative pore is necessary for plasmid transfer to start efficiently. Moreover, the conjugative pilus and underlying secretion machinery assembled in the absence of Par proteins mediate poor biofilm formation and are completely dysfunctional for pilus specific R17 bacteriophage uptake. Thus, functional integration of Par components at the interface of relaxosome, coupling protein, and channel ATPases appears important for an optimal conformation and effective activation of the transfer machinery. We conclude that low copy plasmid R1 has evolved an active segregation system that optimizes both its vertical and lateral modes of dissemination.
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Affiliation(s)
- Christian J Gruber
- Institute of Molecular Biosciences, University of Graz, BioTechMed-Graz Graz, Austria
| | - Silvia Lang
- Institute of Molecular Biosciences, University of Graz, BioTechMed-Graz Graz, Austria
| | - Vinod K H Rajendra
- Institute of Molecular Biosciences, University of Graz, BioTechMed-Graz Graz, Austria
| | - Monika Nuk
- Institute of Molecular Biosciences, University of Graz, BioTechMed-Graz Graz, Austria
| | - Sandra Raffl
- Institute of Molecular Biosciences, University of Graz, BioTechMed-Graz Graz, Austria
| | | | - Ellen L Zechner
- Institute of Molecular Biosciences, University of Graz, BioTechMed-Graz Graz, Austria
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17
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Garcillán-Barcia MP, de la Cruz F. Ordering the bestiary of genetic elements transmissible by conjugation. Mob Genet Elements 2014; 3:e24263. [PMID: 23734300 PMCID: PMC3661145 DOI: 10.4161/mge.24263] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2012] [Revised: 03/08/2013] [Accepted: 03/11/2013] [Indexed: 11/19/2022] Open
Abstract
Phylogenetic reconstruction of three highly conserved proteins involved in bacterial conjugation (relaxase, coupling protein and a type IV secretion system ATPase) allowed the classification of transmissible elements in relaxase MOB families and mating pair formation MPF groups. These evolutionary studies point to the existence of a limited number of module combinations in transmissible elements, preferentially associated with specific genetic or environmental backgrounds. A practical protocol based on the MOB classification was implemented to detect and assort transmissible plasmids and integrative elements from γ-Proteobacteria. It was called “Degenerate Primer MOB Typing” or DPMT. It resulted in a powerful technique that discovers not only backbones related to previously classified elements (typically by PCR-based replicon typing or PBRT), but also distant new members sharing a common evolutionary ancestor. The DPMT method, conjointly with PBRT, promises to be useful to gain information on plasmid backbones and helpful to investigate the dissemination routes of transmissible elements in microbial ecosystems.
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Affiliation(s)
- Maria Pilar Garcillán-Barcia
- Departamento de Biología Molecular e Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC); Universidad de Cantabria-CSIC-SODERCAN; Santander, Cantabria Spain
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18
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Common requirement for the relaxosome of plasmid R1 in multiple activities of the conjugative type IV secretion system. J Bacteriol 2014; 196:2108-21. [PMID: 24682328 DOI: 10.1128/jb.00045-13] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Macromolecular transport by bacterial type IV secretion systems involves regulated uptake of (nucleo)protein complexes by the cell envelope-spanning transport channel. A coupling protein receptor is believed to recognize the specific proteins destined for transfer, but the steps initiating their translocation remain unknown. Here, we investigate the contribution of a complex of transfer initiation proteins, the relaxosome, of plasmid R1 to translocation of competing transferable substrates from mobilizable plasmids ColE1 and CloDF13 or the bacteriophage R17. We found that not only does the R1 translocation machinery engage the R1 relaxosome during conjugative self-transfer and during infection by R17 phage but it is also activated by its cognate relaxosome to mediate the export of an alternative plasmid. Transporter activity was optimized by the R1 relaxosome even when this complex itself could not be transferred, i.e., when the N-terminal activation domain (amino acids 1 to 992 [N1-992]) of TraI was present without the C-terminal conjugative helicase domain. We propose that the functional dependence of the transfer machinery on the R1 relaxosome for initiating translocation ensures that dissemination of heterologous plasmids does not occur at the expense of self-transfer.
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19
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A translocation motif in relaxase TrwC specifically affects recruitment by its conjugative type IV secretion system. J Bacteriol 2013; 195:4999-5006. [PMID: 23995644 DOI: 10.1128/jb.00367-13] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Type IV secretion system (T4SS) substrates are recruited through a translocation signal that is poorly defined for conjugative relaxases. The relaxase TrwC of plasmid R388 is translocated by its cognate conjugative T4SS, and it can also be translocated by the VirB/D4 T4SS of Bartonella henselae, causing DNA transfer to human cells. In this work, we constructed a series of TrwC variants and assayed them for DNA transfer to bacteria and human cells to compare recruitment requirements by both T4SSs. Comparison with other reported relaxase translocation signals allowed us to determine two putative translocation sequence (TS) motifs, TS1 and TS2. Mutations affecting TS1 drastically affected conjugation frequencies, while mutations affecting either motif had only a mild effect on DNA transfer rates through the VirB/D4 T4SS of B. henselae. These results indicate that a single substrate can be recruited by two different T4SSs through different signals. The C terminus affected DNA transfer rates through both T4SSs tested, but no specific sequence requirement was detected. The addition of a Bartonella intracellular delivery (BID) domain, the translocation signal for the Bartonella VirB/D4 T4SS, increased DNA transfer up to 4% of infected human cells, providing an excellent tool for DNA delivery to specific cell types. We show that the R388 coupling protein TrwB is also required for this high-efficiency TrwC-BID translocation. Other elements apart from the coupling protein may also be involved in substrate recognition by T4SSs.
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20
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F conjugation: Back to the beginning. Plasmid 2013; 70:18-32. [DOI: 10.1016/j.plasmid.2013.03.010] [Citation(s) in RCA: 107] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2012] [Revised: 03/26/2013] [Accepted: 03/28/2013] [Indexed: 11/19/2022]
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