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The Facts and Family Secrets of Plasmids That Replicate via the Rolling-Circle Mechanism. Microbiol Mol Biol Rev 2021; 86:e0022220. [PMID: 34878299 DOI: 10.1128/mmbr.00222-20] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Plasmids are self-replicative DNA elements that are transferred between bacteria. Plasmids encode not only antibiotic resistance genes but also adaptive genes that allow their hosts to colonize new niches. Plasmid transfer is achieved by conjugation (or mobilization), phage-mediated transduction, and natural transformation. Thousands of plasmids use the rolling-circle mechanism for their propagation (RCR plasmids). They are ubiquitous, have a high copy number, exhibit a broad host range, and often can be mobilized among bacterial species. Based upon the replicon, RCR plasmids have been grouped into several families, the best known of them being pC194 and pUB110 (Rep_1 family), pMV158 and pE194 (Rep_2 family), and pT181 and pC221 (Rep_trans family). Genetic traits of RCR plasmids are analyzed concerning (i) replication mediated by a DNA-relaxing initiator protein and its interactions with the cognate DNA origin, (ii) lagging-strand origins of replication, (iii) antibiotic resistance genes, (iv) mobilization functions, (v) replication control, performed by proteins and/or antisense RNAs, and (vi) the participating host-encoded functions. The mobilization functions include a relaxase initiator of transfer (Mob), an origin of transfer, and one or two small auxiliary proteins. There is a family of relaxases, the MOBV family represented by plasmid pMV158, which has been revisited and updated. Family secrets, like a putative open reading frame of unknown function, are reported. We conclude that basic research on RCR plasmids is of importance, and our perspectives contemplate the concept of One Earth because we should incorporate bacteria into our daily life by diminishing their virulence and, at the same time, respecting their genetic diversity.
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Lorenzo-Diaz F, Moreno-Córdoba I, Espinosa M. Complete labelling of pneumococcal DNA-binding proteins with seleno-L-methionine. J Microbiol Methods 2019; 166:105720. [PMID: 31518592 DOI: 10.1016/j.mimet.2019.105720] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Revised: 09/06/2019] [Accepted: 09/09/2019] [Indexed: 10/26/2022]
Abstract
Streptococcus pneumoniae is a pathogenic and opportunistic Gram-positive bacterium that is the leading cause of community-acquired respiratory diseases, varying from mild- to deathly- infections. The appearance of antibiotic-resistant isolates has prompted the search for novel strategies and targets to tackle the bacterial resistances. One of the most promising approaches is the structure-based knowledge of possible targets in conjunction with rational design and docking of inhibitors of the chosen targets. A useful technique that helps to solve protein structures is to label them with an amino acid derivative like seleno-methionine that facilitates tracing of some of the amino acid residues. We have chosen two pneumococcal DNA-binding proteins, namely the relaxase domain of MobM protein from plasmid pMV158, and the RelB-RelE antitoxin-toxin protein complex. Through several changes that improve substantially a previous protocol (Budisa et al., 1995), we have used seleno-L-methionine to incorporate selenium into the amino acid sequence of the selected proteins. We have achieved 100% labelling of the proteins and could demonstrate that the labelled proteins retained full activity as judged from the relaxation of supercoiled plasmid DNA and from gel-retardation assays.
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Affiliation(s)
- Fabián Lorenzo-Diaz
- Departamento de Bioquímica, Microbiología, Biología Celular y Genética, Universidad de La Laguna, Santa Cruz de Tenerife, Spain
| | - Inmaculada Moreno-Córdoba
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu, 9, 28040 Madrid, Spain
| | - Manuel Espinosa
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maeztu, 9, 28040 Madrid, Spain.
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Lorenzo-Diaz F, Fernández-Lopez C, Douarre PE, Baez-Ortega A, Flores C, Glaser P, Espinosa M. Streptococcal group B integrative and mobilizable element IMESag-rpsI encodes a functional relaxase involved in its transfer. Open Biol 2017; 6:rsob.160084. [PMID: 27707895 PMCID: PMC5090054 DOI: 10.1098/rsob.160084] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2016] [Accepted: 09/12/2016] [Indexed: 12/13/2022] Open
Abstract
Streptococcus agalactiae or Group B Streptococcus (GBS) are opportunistic bacteria that can cause lethal sepsis in children and immuno-compromised patients. Their genome is a reservoir of mobile genetic elements that can be horizontally transferred. Among them, integrative and conjugative elements (ICEs) and the smaller integrative and mobilizable elements (IMEs) primarily reside in the bacterial chromosome, yet have the ability to be transferred between cells by conjugation. ICEs and IMEs are therefore a source of genetic variability that participates in the spread of antibiotic resistance. Although IMEs seem to be the most prevalent class of elements transferable by conjugation, they are poorly known. Here, we have studied a GBS-IME, termed IMESag-rpsI, which is widely distributed in GBS despite not carrying any apparent virulence trait. Analyses of 240 whole genomes showed that IMESag-rpsI is present in approximately 47% of the genomes, has a roughly constant size (approx. 9 kb) and is always integrated at a single location, the 3′-end of the gene encoding the ribosomal protein S9 (rpsI). Based on their genetic variation, several IMESag-rpsI types were defined (A–J) and classified in clonal complexes (CCs). CC1 was the most populated by IMESag-rpsI (more than 95%), mostly of type-A (71%). One CC1 strain (S. agalactiae HRC) was deep-sequenced to understand the rationale underlying type-A IMESag-rpsI enrichment in GBS. Thirteen open reading frames were identified, one of them encoding a protein (MobSag) belonging to the broadly distributed family of relaxases MOBV1. Protein MobSag was purified and, by a newly developed method, shown to cleave DNA at a specific dinucleotide. The S. agalactiae HRC-IMESag-rpsI is able to excise from the chromosome, as shown by the presence of circular intermediates, and it harbours a fully functional mobilization module. Further, the mobSag gene encoded by this mobile element is able to promote plasmid transfer among pneumococcal strains, suggesting that MobSag facilitates the spread of IMESag-rpsI and that this spread would explain the presence of the same IMESag-rpsI type in GBS strains belonging to different CCs.
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Affiliation(s)
- Fabian Lorenzo-Diaz
- Departamento de Bioquímica, Microbiología, Biología Celular y Genética, Instituto Universitario de Enfermedades Tropicales y Salud Pública de Canarias, Universidad de La Laguna, Av. Astrofísico Francisco Sánchez s/n, 38071 Santa Cruz de Tenerife, Spain Unidad de Investigación, Hospital Universitario Nuestra Señora de Candelaria, Santa Cruz de Tenerife, Spain
| | | | - Pierre-Emmanuel Douarre
- Institut Pasteur, Unité Ecologie et Evolution de la Résistance aux Antibiotiques, Paris CNRS UMR3525, France
| | - Adrian Baez-Ortega
- Department of Veterinary Medicine, University of Cambridge, Madingley Road, Cambridge, UK
| | - Carlos Flores
- Unidad de Investigación, Hospital Universitario Nuestra Señora de Candelaria, Santa Cruz de Tenerife, Spain CIBER de Enfermedades Respiratorias, Instituto de Salud Carlos III, Madrid, Spain
| | - Philippe Glaser
- Institut Pasteur, Unité Ecologie et Evolution de la Résistance aux Antibiotiques, Paris CNRS UMR3525, France
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Structural basis of a histidine-DNA nicking/joining mechanism for gene transfer and promiscuous spread of antibiotic resistance. Proc Natl Acad Sci U S A 2017; 114:E6526-E6535. [PMID: 28739894 DOI: 10.1073/pnas.1702971114] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Relaxases are metal-dependent nucleases that break and join DNA for the initiation and completion of conjugative bacterial gene transfer. Conjugation is the main process through which antibiotic resistance spreads among bacteria, with multidrug-resistant staphylococci and streptococci infections posing major threats to human health. The MOBV family of relaxases accounts for approximately 85% of all relaxases found in Staphylococcus aureus isolates. Here, we present six structures of the MOBV relaxase MobM from the promiscuous plasmid pMV158 in complex with several origin of transfer DNA fragments. A combined structural, biochemical, and computational approach reveals that MobM follows a previously uncharacterized histidine/metal-dependent DNA processing mechanism, which involves the formation of a covalent phosphoramidate histidine-DNA adduct for cell-to-cell transfer. We discuss how the chemical features of the high-energy phosphorus-nitrogen bond shape the dominant position of MOBV histidine relaxases among small promiscuous plasmids and their preference toward Gram-positive bacteria.
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Ramsay JP, Firth N. Diverse mobilization strategies facilitate transfer of non-conjugative mobile genetic elements. Curr Opin Microbiol 2017; 38:1-9. [PMID: 28391142 DOI: 10.1016/j.mib.2017.03.003] [Citation(s) in RCA: 76] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2017] [Accepted: 03/14/2017] [Indexed: 10/19/2022]
Abstract
Conjugation is a dominant mechanism of horizontal gene transfer and substantially contributes to the plasticity and evolvability of prokaryotic genomes. The impact of conjugation on genetic flux extends well beyond self-transmissible conjugative elements, because non-conjugative 'mobilizable elements' utilize other elements' conjugative apparatus for transfer. Bacterial genome comparisons highlight plasmids as vehicles for dissemination of pathogenesis and antimicrobial-resistance determinants, but for most non-conjugative plasmids, a mobilization mechanism is not apparent. Recently we discovered many Staphylococcus aureus plasmids lacking mobilization genes carry oriT sequences that mimic those on conjugative plasmids, suggesting that significantly more elements may be mobilizable than previously recognized. Here we summarize our findings, review the diverse mobilization strategies employed by mobile genetic elements and discuss implications for future gene-transfer research.
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Affiliation(s)
- Joshua P Ramsay
- School of Biomedical Sciences and Curtin Health Innovation Research Institute, Curtin University, Perth, Western Australia, Australia.
| | - Neville Firth
- School of Life and Environmental Sciences, University of Sydney, Sydney, NSW 2006, Australia
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Wisniewski JA, Rood JI. The Tcp conjugation system of Clostridium perfringens. Plasmid 2017; 91:28-36. [PMID: 28286218 DOI: 10.1016/j.plasmid.2017.03.001] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2017] [Revised: 02/24/2017] [Accepted: 03/06/2017] [Indexed: 11/18/2022]
Abstract
The Gram-positive pathogen Clostridium perfringens possesses a family of large conjugative plasmids that is typified by the tetracycline resistance plasmid pCW3. Since these plasmids may carry antibiotic resistance genes or genes encoding extracellular or sporulation-associated toxins, the conjugative transfer of these plasmids appears to be important for the epidemiology of C. perfringens-mediated diseases. Sequence analysis of members of this plasmid family identified a highly conserved 35kb region that encodes proteins with various functions, including plasmid replication and partitioning. The tcp conjugation locus also was identified in this region, initially based on low-level amino acid sequence identity to conjugation proteins from the integrative conjugative element Tn916. Genetic studies confirmed that the tcp locus is required for conjugative transfer and combined with biochemical and structural analyses have led to the development of a functional model of the Tcp conjugation apparatus. This review summarises our current understanding of the Tcp conjugation system, which is now one of the best-characterized conjugation systems in Gram-positive bacteria.
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Affiliation(s)
- Jessica A Wisniewski
- Infection and Immunity Program, Monash Biomedicine Discovery Institute, Department of Microbiology, Monash University, Victoria 3800, Australia
| | - Julian I Rood
- Infection and Immunity Program, Monash Biomedicine Discovery Institute, Department of Microbiology, Monash University, Victoria 3800, Australia.
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Fernández-González E, Bakioui S, Gomes MC, O'Callaghan D, Vergunst AC, Sangari FJ, Llosa M. A Functional oriT in the Ptw Plasmid of Burkholderia cenocepacia Can Be Recognized by the R388 Relaxase TrwC. Front Mol Biosci 2016; 3:16. [PMID: 27200362 PMCID: PMC4853378 DOI: 10.3389/fmolb.2016.00016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2016] [Accepted: 04/14/2016] [Indexed: 12/14/2022] Open
Abstract
Burkholderia cenocepacia is both a plant pathogen and the cause of serious opportunistic infections, particularly in cystic fibrosis patients. B. cenocepacia K56-2 harbors a native plasmid named Ptw for its involvement in the Plant Tissue Watersoaking phenotype. Ptw has also been reported to be important for survival in human cells. Interestingly, the presence of PtwC, a homolog of the conjugative relaxase TrwC of plasmid R388, suggests a possible function for Ptw in conjugative DNA transfer. The ptw region includes Type IV Secretion System genes related to those of the F plasmid. However, genes in the adjacent region shared stronger homology with the R388 genes involved in conjugative DNA metabolism. This region included the putative relaxase ptwC, a putative coupling protein and accessory nicking protein, and a DNA segment with high number of inverted repeats and elevated AT content, suggesting a possible oriT. Although we were unable to detect conjugative transfer of the Ptw resident plasmid, we detected conjugal mobilization of a co-resident plasmid containing the ptw region homologous to R388, demonstrating the cloned ptw region contains an oriT. A similar plasmid lacking ptwC could not be mobilized, suggesting that the putative relaxase PtwC must act in cis on its oriT. Remarkably, we also detected mobilization of a plasmid containing the Ptw oriT by the R388 relaxase TrwC, yet we could not detect PtwC-mediated mobilization of an R388 oriT-containing plasmid. Our data unambiguously show that the Ptw plasmid harbors DNA transfer functions, and suggests the Ptw plasmid may play a dual role in horizontal DNA transfer and eukaryotic infection.
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Affiliation(s)
- Esther Fernández-González
- Departamento de Biología Molecular, Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria, UC-SODERCAN-Consejo Superior de Investigaciones Científicas Santander, Spain
| | - Sawsane Bakioui
- Institut National de la Santé et de la Recherche Médicale, U1047Nimes, France; UFR de Médecine Site de Nimes, U1047, Université de MontpellierFrance
| | - Margarida C Gomes
- Institut National de la Santé et de la Recherche Médicale, U1047Nimes, France; UFR de Médecine Site de Nimes, U1047, Université de MontpellierFrance
| | - David O'Callaghan
- Institut National de la Santé et de la Recherche Médicale, U1047Nimes, France; UFR de Médecine Site de Nimes, U1047, Université de MontpellierFrance
| | - Annette C Vergunst
- Institut National de la Santé et de la Recherche Médicale, U1047Nimes, France; UFR de Médecine Site de Nimes, U1047, Université de MontpellierFrance
| | - Félix J Sangari
- Departamento de Biología Molecular, Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria, UC-SODERCAN-Consejo Superior de Investigaciones Científicas Santander, Spain
| | - Matxalen Llosa
- Departamento de Biología Molecular, Instituto de Biomedicina y Biotecnología de Cantabria, Universidad de Cantabria, UC-SODERCAN-Consejo Superior de Investigaciones Científicas Santander, Spain
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Wisniewski JA, Traore DA, Bannam TL, Lyras D, Whisstock JC, Rood JI. TcpM: a novel relaxase that mediates transfer of large conjugative plasmids from Clostridium perfringens. Mol Microbiol 2015; 99:884-96. [PMID: 26560080 DOI: 10.1111/mmi.13270] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/09/2015] [Indexed: 11/30/2022]
Abstract
Conjugative transfer of toxin and antibiotic resistance plasmids in Clostridium perfringens is mediated by the tcp conjugation locus. Surprisingly, neither a relaxase gene nor an origin of transfer (oriT) has been identified on these plasmids, which are typified by the 47 kb tetracycline resistance plasmid pCW3. The tcpM gene (previously called intP) encodes a potential tyrosine recombinase that was postulated to be an atypical relaxase. Mutagenesis and complementation studies showed that TcpM was required for wild-type transfer of pCW3 and that a tyrosine residue, Y259, was essential for TcpM activity, which was consistent with the need for a relaxase-mediated hydrophilic attack at the oriT site. Other catalytic residues conserved in tyrosine recombinases were not required for TcpM activity, suggesting that TcpM was not a site-specific recombinase. Mobilization studies led to the identification of the oriT site, which was located in the 391 bp intergenic region upstream of tcpM. The oriT site was localized to a 150 bp region, and gel mobility shift studies showed that TcpM could bind to this region. Based on these studies we postulate that conjugative transfer of pCW3 involves the atypical relaxase TcpM binding to and processing the oriT site to initiate plasmid transfer.
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Affiliation(s)
- Jessica A Wisniewski
- Australian Research Council Centre of Excellence in Structural and Functional Microbial Genomics, and Infection and Immunity Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria, 3800, Australia.,Department of Microbiology, Monash University, Clayton, Victoria, 3800, Australia
| | - Daouda A Traore
- Australian Research Council Centre of Excellence in Structural and Functional Microbial Genomics, and Infection and Immunity Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria, 3800, Australia.,Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, 3800, Australia
| | - Trudi L Bannam
- Australian Research Council Centre of Excellence in Structural and Functional Microbial Genomics, and Infection and Immunity Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria, 3800, Australia.,Department of Microbiology, Monash University, Clayton, Victoria, 3800, Australia
| | - Dena Lyras
- Australian Research Council Centre of Excellence in Structural and Functional Microbial Genomics, and Infection and Immunity Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria, 3800, Australia.,Department of Microbiology, Monash University, Clayton, Victoria, 3800, Australia
| | - James C Whisstock
- Australian Research Council Centre of Excellence in Structural and Functional Microbial Genomics, and Infection and Immunity Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria, 3800, Australia.,Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, 3800, Australia
| | - Julian I Rood
- Australian Research Council Centre of Excellence in Structural and Functional Microbial Genomics, and Infection and Immunity Program, Biomedicine Discovery Institute, Monash University, Clayton, Victoria, 3800, Australia.,Department of Microbiology, Monash University, Clayton, Victoria, 3800, Australia
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Mobilizable Rolling-Circle Replicating Plasmids from Gram-Positive Bacteria: A Low-Cost Conjugative Transfer. Microbiol Spectr 2014; 2:8. [PMID: 25606350 DOI: 10.1128/microbiolspec.plas-0008-2013] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Conjugation is a key mechanism for horizontal gene transfer in bacteria. Some plasmids are not self-transmissible but can be mobilized by functions encoded in trans provided by other auxiliary conjugative elements. Although the transfer efficiency of mobilizable plasmids is usually lower than that of conjugative elements, mobilizable plasmidsare more frequently found in nature. In this sense, replication and mobilization can be considered as important mechanisms influencing plasmid promiscuity. Here we review the present available information on two families of small mobilizable plasmids from Gram-positive bacteria that replicate via the rolling-circle mechanism. One of these families, represented by the streptococcal plasmid pMV158, is an interesting model since it contains a specific mobilization module (MOBV) that is widely distributed among mobilizable plasmids. We discuss a mechanism in which the promiscuity of the pMV158 replicon is based on the presence of two origins of lagging strand synthesis. The current strategies to assess plasmid transfer efficiency as well as to inhibit conjugative plasmid transfer are presented. Some applications of these plasmids as biotechnological tools are also reviewed.
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Lorenzo-Díaz F, Fernández-López C, Garcillán-Barcia MP, Espinosa M. Bringing them together: plasmid pMV158 rolling circle replication and conjugation under an evolutionary perspective. Plasmid 2014; 74:15-31. [PMID: 24942190 PMCID: PMC7103276 DOI: 10.1016/j.plasmid.2014.05.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2014] [Revised: 05/21/2014] [Accepted: 05/22/2014] [Indexed: 11/29/2022]
Abstract
Rolling circle-replicating plasmids constitute a vast family that is particularly abundant in, but not exclusive of, Gram-positive bacteria. These plasmids are constructed as cassettes that harbor genes involved in replication and its control, mobilization, resistance determinants and one or two origins of lagging strand synthesis. Any given plasmid may contain all, some, or just only the replication cassette. We discuss here the family of the promiscuous streptococcal plasmid pMV158, with emphasis on its mobilization functions: the product of the mobM gene, prototype of the MOBV relaxase family, and its cognate origin of transfer, oriT. Amongst the subfamily of MOBV1 plasmids, three groups of oriT sequences, represented by plasmids pMV158, pT181, and p1414 were identified. In the same subfamily, we found four types of single-strand origins, namely ssoA, ssoU, ssoW, and ssoT. We found that plasmids of the rolling-circle Rep_2 family (to which pMV158 belongs) are more frequently found in Lactobacillales than in any other bacterial order, whereas Rep_1 initiators seemed to prefer hosts included in the Bacillales order. In parallel, MOBV1 relaxases associated with Rep_2 initiators tended to cluster separately from those linked to Rep_1 plasmids. The updated inventory of MOBV1 plasmids still contains exclusively mobilizable elements, since no genes associated with conjugative transfer (other than the relaxase) were detected. These plasmids proved to have a great plasticity at using a wide variety of conjugative apparatuses. The promiscuous recognition of non-cognate oriT sequences and the role of replication origins for lagging-strand origin in the host range of these plasmids are also discussed.
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Affiliation(s)
- Fabián Lorenzo-Díaz
- Unidad de Investigación, Hospital Universitario Nuestra Señora de Candelaria and Instituto Universitario de Enfermedades Tropicales y Salud Pública de Canarias, Centro de Investigaciones Biomédicas de Canarias, Universidad de La Laguna, Santa Cruz de Tenerife, Spain.
| | - Cris Fernández-López
- Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu, 9, E-28040 Madrid, Spain.
| | - M Pilar Garcillán-Barcia
- Instituto de Biomedicina y Biotecnología de Cantabria (IBBTEC), Universidad de Cantabria - CSIC-SODERCAN, Santander, Cantabria, Spain.
| | - Manuel Espinosa
- Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu, 9, E-28040 Madrid, Spain.
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Functional properties and structural requirements of the plasmid pMV158-encoded MobM relaxase domain. J Bacteriol 2013; 195:3000-8. [PMID: 23625844 DOI: 10.1128/jb.02264-12] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A crucial element in the horizontal transfer of mobilizable and conjugative plasmids is the relaxase, a single-stranded endonuclease that nicks the origin of transfer (oriT) of the plasmid DNA. The relaxase of the pMV158 mobilizable plasmid is MobM (494 residues). In solution, MobM forms a dimer through its C-terminal domain, which is proposed to anchor the protein to the cell membrane and to participate in type 4 secretion system (T4SS) protein-protein interactions. In order to gain a deeper insight into the structural MobM requirements for efficient DNA catalysis, we studied two endonuclease domain variants that include the first 199 or 243 amino acid residues (MobMN199 and MobMN243, respectively). Our results confirmed that the two proteins behaved as monomers in solution. Interestingly, MobMN243 relaxed supercoiled DNA and cleaved single-stranded oligonucleotides harboring oriTpMV158, whereas MobMN199 was active only on supercoiled DNA. Protein stability studies using gel electrophoresis and mass spectrometry showed increased susceptibility to degradation at the domain boundary between the N- and C-terminal domains, suggesting that the domains change their relative orientation upon DNA binding. Overall, these results demonstrate that MobMN243 is capable of nicking the DNA substrate independently of its topology and that the amino acids 200 to 243 modulate substrate specificity but not the nicking activity per se. These findings suggest that these amino acids are involved in positioning the DNA for the nuclease reaction rather than in the nicking mechanism itself.
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