1
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Ardissone S, Greub G. The Chlamydia-related Waddlia chondrophila encodes functional type II toxin-antitoxin systems. Appl Environ Microbiol 2024; 90:e0068123. [PMID: 38214519 PMCID: PMC10880633 DOI: 10.1128/aem.00681-23] [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: 04/25/2023] [Accepted: 11/13/2023] [Indexed: 01/13/2024] Open
Abstract
Bacterial toxin-antitoxin (TA) systems are widespread in chromosomes and plasmids of free-living microorganisms, but only a few have been identified in obligate intracellular species. We found seven putative type II TA modules in Waddlia chondrophila, a Chlamydia-related species that is able to infect a very broad series of eukaryotic hosts, ranging from protists to mammalian cells. The RNA levels of Waddlia TA systems are significantly upregulated by iron starvation and novobiocin, but they are not affected by antibiotics such as β-lactams and glycopeptides, which suggests different mechanisms underlying stress responses. Five of the identified TA modules, including HigBA1 and MazEF1, encoded on the Waddlia cryptic plasmid, proved to be functional when expressed in a heterologous host. TA systems have been associated with the maintenance of mobile genetic elements, bacterial defense against bacteriophages, and persistence upon exposure to adverse conditions. As their RNA levels are upregulated upon exposure to adverse conditions, Waddlia TA modules may be involved in survival to stress. Moreover, as Waddlia can infect a wide range of hosts including free-living amoebae, TA modules could also represent an innate immunity system to fight against bacteriophages and other microorganisms with which Waddlia has to share its replicative niche.IMPORTANCEThe response to adverse conditions, such as exposure to antibiotics, nutrient starvation and competition with other microorganisms, is essential for the survival of a bacterial population. TA systems are modules composed of two elements, a toxic protein and an antitoxin (protein or RNA) that counteracts the toxin. Although many aspects of TA biological functions still await to be elucidated, TAs have often been implicated in bacterial response to stress, including the response to nutrient starvation, antibiotic treatment and bacteriophage infection. TAs are ubiquitous in free-living bacteria but rare in obligate intracellular species such as chlamydiae. We identified functional TA systems in Waddlia chondrophila, a chlamydial species with a strikingly broad host range compared to other chlamydiae. Our work contributes to understand how obligate intracellular bacteria react to adverse conditions that might arise from competition with other viruses/bacteria for the same replicative niche and would threaten their ability to replicate.
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Affiliation(s)
- Silvia Ardissone
- Institute of Microbiology, Lausanne University Hospital and Lausanne University, Lausanne, Switzerland
| | - Gilbert Greub
- Institute of Microbiology, Lausanne University Hospital and Lausanne University, Lausanne, Switzerland
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2
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Wang X, Kan Y, Bai K, Xu X, Chen X, Yu C, Shi J, Jiang N, Li J, Luo L. A novel double-ribonuclease toxin-antitoxin system linked to the stress response and survival of Acidovorax citrulli. Microbiol Spectr 2023; 11:e0216923. [PMID: 37819152 PMCID: PMC10714953 DOI: 10.1128/spectrum.02169-23] [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: 05/25/2023] [Accepted: 08/30/2023] [Indexed: 10/13/2023] Open
Abstract
IMPORTANCE Bacterial fruit blotch (BFB), which is caused by the seed-borne bacterium Acidovorax citrulli, is a devastating disease affecting cucurbit crops throughout the world. Although seed fermentation and treatment with disinfectants can provide effective management of BFB, they cannot completely guarantee pathogen-free seedstock, which suggests that A. citrulli is a highly stress-resistant pathogen. Toxin-antitoxin (TA) systems are common among a diverse range of bacteria and have been reported to play a role in bacterial stress response. However, there is currently much debate about the relationship between TA systems and stress response in bacteria. The current study characterized a novel TA system (Aave_1720-Aave_1719) from A. citrulli that affects both biofilm formation and survival in response to sodium hypochlorite stress. The mechanism of neutralization differed from typical TA systems as two separate mechanisms were associated with the antitoxin, which exhibited characteristics of both type II and type V TA systems. The Aave_1720-Aave_1719 system described here also constitutes the first known report of a double-ribonuclease TA system in bacteria, which expands our understanding of the range of regulatory mechanisms utilized by bacterial TA systems, providing new insight into the survival of A. citrulli in response to stress.
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Affiliation(s)
- Xudong Wang
- Department of Plant Pathology, College of Plant Protection, China Agricultural University, Beijing, China
- Key Laboratory of Surveillance and Management for Plant Quarantine Pests, Ministry of Agriculture and Rural Affairs, Beijing, China
- Beijing Key Laboratory of Seed Disease Testing and Control, Beijing, China
| | - Yumin Kan
- Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, New York, USA
| | - Kaihong Bai
- School of Life Sciences, Zhengzhou University, Zhengzhou, Henan, China
| | - Xiaoli Xu
- Department of Plant Pathology, College of Plant Protection, China Agricultural University, Beijing, China
- Key Laboratory of Surveillance and Management for Plant Quarantine Pests, Ministry of Agriculture and Rural Affairs, Beijing, China
- Beijing Key Laboratory of Seed Disease Testing and Control, Beijing, China
| | - Xing Chen
- Department of Plant Pathology, College of Plant Protection, China Agricultural University, Beijing, China
- Key Laboratory of Surveillance and Management for Plant Quarantine Pests, Ministry of Agriculture and Rural Affairs, Beijing, China
- Beijing Key Laboratory of Seed Disease Testing and Control, Beijing, China
| | - Chengxuan Yu
- Department of Plant Pathology, College of Plant Protection, China Agricultural University, Beijing, China
- Key Laboratory of Surveillance and Management for Plant Quarantine Pests, Ministry of Agriculture and Rural Affairs, Beijing, China
- Beijing Key Laboratory of Seed Disease Testing and Control, Beijing, China
| | - Jia Shi
- Department of Plant Pathology, College of Plant Protection, China Agricultural University, Beijing, China
- Key Laboratory of Surveillance and Management for Plant Quarantine Pests, Ministry of Agriculture and Rural Affairs, Beijing, China
- Beijing Key Laboratory of Seed Disease Testing and Control, Beijing, China
| | - Na Jiang
- Department of Plant Pathology, College of Plant Protection, China Agricultural University, Beijing, China
- Beijing Key Laboratory of Seed Disease Testing and Control, Beijing, China
| | - Jianqiang Li
- Department of Plant Pathology, College of Plant Protection, China Agricultural University, Beijing, China
- Key Laboratory of Surveillance and Management for Plant Quarantine Pests, Ministry of Agriculture and Rural Affairs, Beijing, China
- Beijing Key Laboratory of Seed Disease Testing and Control, Beijing, China
| | - Laixin Luo
- Department of Plant Pathology, College of Plant Protection, China Agricultural University, Beijing, China
- Key Laboratory of Surveillance and Management for Plant Quarantine Pests, Ministry of Agriculture and Rural Affairs, Beijing, China
- Beijing Key Laboratory of Seed Disease Testing and Control, Beijing, China
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3
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Boss L, Kędzierska B. Bacterial Toxin-Antitoxin Systems' Cross-Interactions-Implications for Practical Use in Medicine and Biotechnology. Toxins (Basel) 2023; 15:380. [PMID: 37368681 DOI: 10.3390/toxins15060380] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2023] [Revised: 05/30/2023] [Accepted: 06/02/2023] [Indexed: 06/29/2023] Open
Abstract
Toxin-antitoxin (TA) systems are widely present in bacterial genomes. They consist of stable toxins and unstable antitoxins that are classified into distinct groups based on their structure and biological activity. TA systems are mostly related to mobile genetic elements and can be easily acquired through horizontal gene transfer. The ubiquity of different homologous and non-homologous TA systems within a single bacterial genome raises questions about their potential cross-interactions. Unspecific cross-talk between toxins and antitoxins of non-cognate modules may unbalance the ratio of the interacting partners and cause an increase in the free toxin level, which can be deleterious to the cell. Moreover, TA systems can be involved in broadly understood molecular networks as transcriptional regulators of other genes' expression or modulators of cellular mRNA stability. In nature, multiple copies of highly similar or identical TA systems are rather infrequent and probably represent a transition stage during evolution to complete insulation or decay of one of them. Nevertheless, several types of cross-interactions have been described in the literature to date. This implies a question of the possibility and consequences of the TA system cross-interactions, especially in the context of the practical application of the TA-based biotechnological and medical strategies, in which such TAs will be used outside their natural context, will be artificially introduced and induced in the new hosts. Thus, in this review, we discuss the prospective challenges of system cross-talks in the safety and effectiveness of TA system usage.
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Affiliation(s)
- Lidia Boss
- Department of Bacterial Molecular Genetics, Faculty of Biology, University of Gdańsk, 80-309 Gdańsk, Poland
| | - Barbara Kędzierska
- Department of Bacterial Molecular Genetics, Faculty of Biology, University of Gdańsk, 80-309 Gdańsk, Poland
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4
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Gupta RK, Singh AK, Bajaj A, Khardenavis AA, Purohit HJ. Phylogenomic analysis of Citrobacter sp. strain AAK_AS5 and its metabolic capabilities to support nitrogen removal behavior. J Basic Microbiol 2023; 63:359-376. [PMID: 36453555 DOI: 10.1002/jobm.202200323] [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: 06/03/2022] [Revised: 09/02/2022] [Accepted: 10/22/2022] [Indexed: 12/03/2022]
Abstract
Despite the ubiquity of the genus Citrobacter in clinical, industrial, and environmental scenarios, a large number of Citrobacter strains have not been explored at the genome-scale level. In this study, accurate taxonomic assignment of strain AAK_AS5 isolated from activated sludge was achieved by in-silico genomic comparison using Overall Genome-based Relatedness Indices (ANI(OAT): 97.55%, ANIb:97.28%, and ANIm: 97.83%) that indicated its closest identity to the related strain Citrobacter portucalensis A60T . Results were consistent with a digital DNA-DNA hybridization value of 80% with C. portucalensis A60T which was greater than the species boundary value >70% for delineating closely related bacterial species. Gene mining through Kyoto Encyclopedia of Genes and Genomes (KEGG), and annotation using rapid annotation subsystem technology (RAST) revealed the notable gene contents for nitrogen metabolism and other pathways associated with nitrate/nitrite ammonification (28 genes), ammonia assimilation (22 genes), and denitrification pathways (14 genes). Furthermore, the strain AAK_AS5 also exhibited a high soluble chemical oxygen demand (sCOD), NH4 + -N, and NO3 - -N removal efficiency of 91.4%, 90%, and 93.6%, respectively thus validating its genetic capability for utilizing both (NH4 )2 SO4 and KNO3 as the nitrogen source. The study provided deeper insights into the phylogenomics and the genetic potential of Citrobacter, sp. strain AAK AS5 associated with nitrogen metabolism thus signifying the potential application of the isolate for treating nitrogen-rich wastewaters.
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Affiliation(s)
- Rakesh K Gupta
- Environmental Biotechnology and Genomics Division (EBGD), CSIR-National Environmental Engineering Research Institute (NEERI), Nagpur, India.,Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India
| | - Ashish K Singh
- Environmental Biotechnology and Genomics Division (EBGD), CSIR-National Environmental Engineering Research Institute (NEERI), Nagpur, India.,Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India
| | - Abhay Bajaj
- Environmental Biotechnology and Genomics Division (EBGD), CSIR-National Environmental Engineering Research Institute (NEERI), Nagpur, India.,Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India
| | - Anshuman A Khardenavis
- Environmental Biotechnology and Genomics Division (EBGD), CSIR-National Environmental Engineering Research Institute (NEERI), Nagpur, India.,Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India
| | - Hemant J Purohit
- Environmental Biotechnology and Genomics Division (EBGD), CSIR-National Environmental Engineering Research Institute (NEERI), Nagpur, India
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5
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Li M, Guo N, Song G, Huang Y, Wang L, Zhang Y, Wang T. Type II Toxin-Antitoxin Systems in Pseudomonas aeruginosa. Toxins (Basel) 2023; 15:164. [PMID: 36828478 PMCID: PMC9966142 DOI: 10.3390/toxins15020164] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Revised: 02/03/2023] [Accepted: 02/14/2023] [Indexed: 02/22/2023] Open
Abstract
Toxin-antitoxin (TA) systems are typically composed of a stable toxin and a labile antitoxin; the latter counteracts the toxicity of the former under suitable conditions. TA systems are classified into eight types based on the nature and molecular modes of action of the antitoxin component so far. The 10 pairs of TA systems discovered and experimentally characterised in Pseudomonas aeruginosa are type II TA systems. Type II TA systems have various physiological functions, such as virulence and biofilm formation, protection host against antibiotics, persistence, plasmid maintenance, and prophage production. Here, we review the type II TA systems of P. aeruginosa, focusing on their biological functions and regulatory mechanisms, providing potential applications for the novel drug design.
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Affiliation(s)
| | | | | | | | | | - Yani Zhang
- Provincial Key Laboratory of Biotechnology, Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, College of Life Sciences, Northwest University, Xi’an 710069, China
| | - Tietao Wang
- Provincial Key Laboratory of Biotechnology, Key Laboratory of Resource Biology and Biotechnology in Western China, Ministry of Education, College of Life Sciences, Northwest University, Xi’an 710069, China
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6
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Bajaj P, Manjunath K, Varadarajan R. Structural and functional determinants inferred from deep mutational scans. Protein Sci 2022; 31:e4357. [PMID: 35762712 PMCID: PMC9202547 DOI: 10.1002/pro.4357] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 04/04/2022] [Accepted: 05/11/2022] [Indexed: 11/08/2022]
Abstract
Mutations that affect protein binding to a cognate partner primarily occur either at buried residues or at exposed residues directly involved in partner binding. Distinguishing between these two categories based solely on mutational phenotypes is challenging. The bacterial toxin CcdB kills cells by binding to DNA Gyrase. Cell death is prevented by binding to its cognate antitoxin CcdA, at an extended interface that partially overlaps with the GyrA binding site. Using the CcdAB toxin-antitoxin (TA) system as a model, a comprehensive site-saturation mutagenesis library of CcdB was generated in its native operonic context. The mutational sensitivity of each mutant was estimated by evaluating the relative abundance of each mutant in two strains, one resistant and the other sensitive to the toxic activity of the CcdB toxin, through deep sequencing. The ability to bind CcdA was inferred through a RelE reporter gene assay, since the CcdAB complex binds to its own promoter, repressing transcription. By analyzing mutant phenotypes in the CcdB-sensitive, CcdB-resistant, and RelE reporter strains, it was possible to assign residues to buried, CcdA interacting or GyrA interacting sites. A few mutants were individually constructed, expressed, and biophysically characterized to validate molecular mechanisms responsible for the observed phenotypes. Residues inferred to be important for antitoxin binding, are also likely to be important for rejuvenating CcdB from the CcdB-Gyrase complex. Therefore, even in the absence of structural information, when coupled to appropriate genetic screens, such high-throughput strategies can be deployed for predicting structural and functional determinants of proteins.
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Affiliation(s)
- Priyanka Bajaj
- Molecular Biophysics UnitIndian Institute of ScienceBangaloreIndia
| | - Kavyashree Manjunath
- Centre for Chemical Biology and TherapeuticsInstitute for Stem Cell Science and Regenerative MedicineBangaloreIndia
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7
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Abstract
Toxin-antitoxin systems are widespread in bacterial genomes. They are usually composed of two elements: a toxin that inhibits an essential cellular process and an antitoxin that counteracts its cognate toxin. In the past decade, a number of new toxin-antitoxin systems have been described, bringing new growth inhibition mechanisms to light as well as novel modes of antitoxicity. However, recent advances in the field profoundly questioned the role of these systems in bacterial physiology, stress response and antimicrobial persistence. This shifted the paradigm of the functions of toxin-antitoxin systems to roles related to interactions between hosts and their mobile genetic elements, such as viral defence or plasmid stability. In this Review, we summarize the recent progress in understanding the biology and evolution of these small genetic elements, and discuss how genomic conflicts could shape the diversification of toxin-antitoxin systems.
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8
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Jeon H, Choi E, Hwang J. Identification and characterization of VapBC toxin-antitoxin system in Bosea sp. PAMC 26642 isolated from Arctic lichens. RNA (NEW YORK, N.Y.) 2021; 27:1374-1389. [PMID: 34429367 PMCID: PMC8522696 DOI: 10.1261/rna.078786.121] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/12/2021] [Accepted: 08/19/2021] [Indexed: 06/13/2023]
Abstract
Toxin-antitoxin (TA) systems are genetic modules composed of a toxin interfering with cellular processes and its cognate antitoxin, which counteracts the activity of the toxin. TA modules are widespread in bacterial and archaeal genomes. It has been suggested that TA modules participate in the adaptation of prokaryotes to unfavorable conditions. The Bosea sp. PAMC 26642 used in this study was isolated from the Arctic lichen Stereocaulon sp. There are 12 putative type II TA loci in the genome of Bosea sp. PAMC 26642. Of these, nine functional TA systems have been shown to be toxic in Escherichia coli The toxin inhibits growth, but this inhibition is reversed when the cognate antitoxin genes are coexpressed, indicating that these putative TA loci were bona fide TA modules. Only the BoVapC1 (AXW83_01405) toxin, a homolog of VapC, showed growth inhibition specific to low temperatures, which was recovered by the coexpression of BoVapB1 (AXW83_01400). Microscopic observation and growth monitoring revealed that the BoVapC1 toxin had bacteriostatic effects on the growth of E. coli and induced morphological changes. Quantitative real time polymerase chain reaction and northern blotting analyses showed that the BoVapC1 toxin had a ribonuclease activity on the initiator tRNAfMet, implying that degradation of tRNAfMet might trigger growth arrest in E. coli Furthermore, the BoVapBC1 system was found to contribute to survival against prolonged exposure at 4°C. This is the first study to identify the function of TA systems in cold adaptation.
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Affiliation(s)
- Hyerin Jeon
- Department of Microbiology, Pusan National University, Busan 46241, Republic of Korea
| | - Eunsil Choi
- Department of Microbiology, Pusan National University, Busan 46241, Republic of Korea
- Microbiological Resource Research Institute, Pusan National University, Busan 46241, Republic of Korea
| | - Jihwan Hwang
- Department of Microbiology, Pusan National University, Busan 46241, Republic of Korea
- Microbiological Resource Research Institute, Pusan National University, Busan 46241, Republic of Korea
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9
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Abstract
In life's constant battle for survival, it takes one to kill but two to conquer. Toxin-antitoxin or toxin-antidote (TA) elements are genetic dyads that cheat the laws of inheritance to guarantee their transmission to the next generation. This seemingly simple genetic arrangement—a toxin linked to its antidote—is capable of quickly spreading and persisting in natural populations. TA elements were first discovered in bacterial plasmids in the 1980s and have recently been characterized in fungi, plants, and animals, where they underlie genetic incompatibilities and sterility in crosses between wild isolates. In this review, we provide a unified view of TA elements in both prokaryotic and eukaryotic organisms and highlight their similarities and differences at the evolutionary, genetic, and molecular levels. Finally, we propose several scenarios that could explain the paradox of the evolutionary origin of TA elements and argue that these elements may be key evolutionary players and that the full scope of their roles is only beginning to be uncovered.
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Affiliation(s)
- Alejandro Burga
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), 1030 Vienna, Austria
| | - Eyal Ben-David
- Department of Human Genetics, Department of Biological Chemistry, and Howard Hughes Medical Institute, University of California, Los Angeles, California 90095, USA
- Department of Biochemistry and Molecular Biology, Institute for Medical Research Israel-Canada, The Hebrew University School of Medicine, Jerusalem 91120, Israel
| | - Leonid Kruglyak
- Department of Human Genetics, Department of Biological Chemistry, and Howard Hughes Medical Institute, University of California, Los Angeles, California 90095, USA
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10
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Jurėnas D, Van Melderen L. The Variety in the Common Theme of Translation Inhibition by Type II Toxin-Antitoxin Systems. Front Genet 2020; 11:262. [PMID: 32362907 PMCID: PMC7180214 DOI: 10.3389/fgene.2020.00262] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Accepted: 03/05/2020] [Indexed: 12/12/2022] Open
Abstract
Type II Toxin-antitoxin (TA) modules are bacterial operons that encode a toxic protein and its antidote, which form a self-regulating genetic system. Antitoxins put a halter on toxins in many ways that distinguish different types of TA modules. In type II TA modules, toxin and antitoxin are proteins that form a complex which physically sequesters the toxin, thereby preventing its toxic activity. Type II toxins inhibit various cellular processes, however, the translation process appears to be their favorite target and nearly every step of this complex process is inhibited by type II toxins. The structural features, enzymatic activities and target specificities of the different toxin families are discussed. Finally, this review emphasizes that the structural folds presented by these toxins are not restricted to type II TA toxins or to one particular cellular target, and discusses why so many of them evolved to target translation as well as the recent developments regarding the role(s) of these systems in bacterial physiology and evolution.
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Affiliation(s)
- Dukas Jurėnas
- Laboratoire d’Ingénierie des Systèmes Macromoléculaires, Institut de Microbiologie de la Méditerranée, CNRS, Aix-Marseille Université, Marseille, France
| | - Laurence Van Melderen
- Cellular and Molecular Microbiology, Faculté des Sciences, Université libre de Bruxelles, Gosselies, Belgium
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11
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Abstract
Type II toxin-antitoxin (TA) systems are small genetic elements composed of a toxic protein and its cognate antitoxin protein, the latter counteracting the toxicity of the former. While TA systems were initially discovered on plasmids, functioning as addiction modules through a phenomenon called postsegregational killing, they were later shown to be massively present in bacterial chromosomes, often in association with mobile genetic elements. Extensive research has been conducted in recent decades to better understand the physiological roles of these chromosomally encoded modules and to characterize the conditions leading to their activation. Type II toxin-antitoxin (TA) systems are small genetic elements composed of a toxic protein and its cognate antitoxin protein, the latter counteracting the toxicity of the former. While TA systems were initially discovered on plasmids, functioning as addiction modules through a phenomenon called postsegregational killing, they were later shown to be massively present in bacterial chromosomes, often in association with mobile genetic elements. Extensive research has been conducted in recent decades to better understand the physiological roles of these chromosomally encoded modules and to characterize the conditions leading to their activation. The diversity of their proposed roles, ranging from genomic stabilization and abortive phage infection to stress modulation and antibiotic persistence, in conjunction with the poor understanding of TA system regulation, resulted in the generation of simplistic models, often refuted by contradictory results. This review provides an epistemological and critical retrospective on TA modules and highlights fundamental questions concerning their roles and regulations that still remain unanswered.
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12
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Burger VM, Vandervelde A, Hendrix J, Konijnenberg A, Sobott F, Loris R, Stultz CM. Hidden States within Disordered Regions of the CcdA Antitoxin Protein. J Am Chem Soc 2017; 139:2693-2701. [PMID: 28124913 DOI: 10.1021/jacs.6b11450] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The bacterial toxin-antitoxin system CcdB-CcdA provides a mechanism for the control of cell death and quiescence. The antitoxin protein CcdA is a homodimer composed of two monomers that each contain a folded N-terminal region and an intrinsically disordered C-terminal arm. Binding of the intrinsically disordered C-terminal arm of CcdA to the toxin CcdB prevents CcdB from inhibiting DNA gyrase and thereby averts cell death. Accurate models of the unfolded state of the partially disordered CcdA antitoxin can therefore provide insight into general mechanisms whereby protein disorder regulates events that are crucial to cell survival. Previous structural studies were able to model only two of three distinct structural states, a closed state and an open state, that are adopted by the C-terminal arm of CcdA. Using a combination of free energy simulations, single-pair Förster resonance energy transfer experiments, and existing NMR data, we developed structural models for all three states of the protein. Contrary to prior studies, we find that CcdA samples a previously unknown state where only one of the disordered C-terminal arms makes extensive contacts with the folded N-terminal domain. Moreover, our data suggest that previously unobserved conformational states play a role in regulating antitoxin concentrations and the activity of CcdA's cognate toxin. These data demonstrate that intrinsic disorder in CcdA provides a mechanism for regulating cell fate.
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Affiliation(s)
| | - Alexandra Vandervelde
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel , B-1050 Brussels, Belgium.,Molecular Recognition Unit, Structural Biology Research Center, Vlaams Instituut voor Biotechnologie , B-1050 Brussels, Belgium
| | - Jelle Hendrix
- Laboratory for Photochemistry and Spectroscopy, Department of Chemistry, University of Leuven , B-3000 Leuven, Belgium.,Faculty of Medicine and Life Sciences and Biomedical Research Institute, Hasselt University , B-3500 Hasselt, Belgium
| | - Albert Konijnenberg
- Biomolecular & Analytical Mass Spectrometry, Department of Chemistry, University of Antwerp , B-2020 Antwerp, Belgium
| | - Frank Sobott
- Biomolecular & Analytical Mass Spectrometry, Department of Chemistry, University of Antwerp , B-2020 Antwerp, Belgium
| | - Remy Loris
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel , B-1050 Brussels, Belgium.,Molecular Recognition Unit, Structural Biology Research Center, Vlaams Instituut voor Biotechnologie , B-1050 Brussels, Belgium
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13
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Berger P, Knödler M, Förstner KU, Berger M, Bertling C, Sharma CM, Vogel J, Karch H, Dobrindt U, Mellmann A. The primary transcriptome of the Escherichia coli O104:H4 pAA plasmid and novel insights into its virulence gene expression and regulation. Sci Rep 2016; 6:35307. [PMID: 27748404 PMCID: PMC5066232 DOI: 10.1038/srep35307] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Accepted: 09/27/2016] [Indexed: 11/30/2022] Open
Abstract
Escherichia coli O104:H4 (E. coli O104:H4), which caused a massive outbreak of acute gastroenteritis and hemolytic uremic syndrome in 2011, carries an aggregative adherence fimbriae I (AAF/I) encoding virulence plasmid, pAA. The importance of pAA in host-pathogen interaction and disease severity has been demonstrated, however, not much is known about its transcriptional organization and gene regulation. Here, we analyzed the pAA primary transcriptome using differential RNA sequencing, which allows for the high-throughput mapping of transcription start site (TSS) and non-coding RNA candidates. We identified 248 TSS candidates in the 74-kb pAA and only 21% of them could be assigned as TSS of annotated genes. We detected TSS for the majority of pAA-encoded virulence factors. Interestingly, we mapped TSS, which could allow for the transcriptional uncoupling of the AAF/I operon, and potentially regulatory antisense RNA candidates against the genes encoding dispersin and the serine protease SepA. Moreover, a computational search for transcription factor binding sites suggested for AggR-mediated activation of SepA expression, which was additionally experimentally validated. This work advances our understanding of the molecular basis of E. coli O104:H4 pathogenicity and provides a valuable resource for further characterization of pAA virulence gene regulation.
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Affiliation(s)
- Petya Berger
- Institute of Hygiene, University of Münster, Münster, Germany
| | - Michael Knödler
- Institute of Hygiene, University of Münster, Münster, Germany
| | - Konrad U Förstner
- Core Unit Systems Medicine, University of Würzburg, Würzburg, Germany.,Institute for Molecular Infection Biology, University of Würzburg, Würzburg, Germany.,Research Center for Infectious Diseases, University of Würzburg, Würzburg, Germany
| | - Michael Berger
- Institute of Hygiene, University of Münster, Münster, Germany
| | | | - Cynthia M Sharma
- Research Center for Infectious Diseases, University of Würzburg, Würzburg, Germany
| | - Jörg Vogel
- Institute for Molecular Infection Biology, University of Würzburg, Würzburg, Germany
| | - Helge Karch
- Institute of Hygiene, University of Münster, Münster, Germany
| | - Ulrich Dobrindt
- Institute of Hygiene, University of Münster, Münster, Germany
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14
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Loris R, Garcia-Pino A. Disorder- and Dynamics-Based Regulatory Mechanisms in Toxin–Antitoxin Modules. Chem Rev 2014; 114:6933-47. [DOI: 10.1021/cr400656f] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- Remy Loris
- Molecular
Recognition Unit, Structural Biology Research Center, VIB, Pleinlaan 2, B-1050 Brussel, Belgium
- Structural
Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussel, Belgium
| | - Abel Garcia-Pino
- Molecular
Recognition Unit, Structural Biology Research Center, VIB, Pleinlaan 2, B-1050 Brussel, Belgium
- Structural
Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussel, Belgium
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15
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Hayes F, Kędzierska B. Regulating toxin-antitoxin expression: controlled detonation of intracellular molecular timebombs. Toxins (Basel) 2014; 6:337-58. [PMID: 24434949 PMCID: PMC3920265 DOI: 10.3390/toxins6010337] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Revised: 12/20/2013] [Accepted: 01/08/2014] [Indexed: 11/24/2022] Open
Abstract
Genes for toxin-antitoxin (TA) complexes are widely disseminated in bacteria, including in pathogenic and antibiotic resistant species. The toxins are liberated from association with the cognate antitoxins by certain physiological triggers to impair vital cellular functions. TAs also are implicated in antibiotic persistence, biofilm formation, and bacteriophage resistance. Among the ever increasing number of TA modules that have been identified, the most numerous are complexes in which both toxin and antitoxin are proteins. Transcriptional autoregulation of the operons encoding these complexes is key to ensuring balanced TA production and to prevent inadvertent toxin release. Control typically is exerted by binding of the antitoxin to regulatory sequences upstream of the operons. The toxin protein commonly works as a transcriptional corepressor that remodels and stabilizes the antitoxin. However, there are notable exceptions to this paradigm. Moreover, it is becoming clear that TA complexes often form one strand in an interconnected web of stress responses suggesting that their transcriptional regulation may prove to be more intricate than currently understood. Furthermore, interference with TA gene transcriptional autoregulation holds considerable promise as a novel antibacterial strategy: artificial release of the toxin factor using designer drugs is a potential approach to induce bacterial suicide from within.
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Affiliation(s)
- Finbarr Hayes
- Faculty of Life Sciences and Manchester Institute of Biotechnology, The University of Manchester, 131 Princess Street, Manchester M1 7DN, UK.
| | - Barbara Kędzierska
- Faculty of Life Sciences and Manchester Institute of Biotechnology, The University of Manchester, 131 Princess Street, Manchester M1 7DN, UK.
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16
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Brown BL, Lord DM, Grigoriu S, Peti W, Page R. The Escherichia coli toxin MqsR destabilizes the transcriptional repression complex formed between the antitoxin MqsA and the mqsRA operon promoter. J Biol Chem 2012; 288:1286-94. [PMID: 23172222 DOI: 10.1074/jbc.m112.421008] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Bacterial biofilms are complex communities of cells containing an increased prevalence of dormant cells known as persisters, which are characterized by an up-regulation of genes known as toxin-antitoxin (TA) modules. The association of toxins with their cognate antitoxins neutralizes toxin activity, allowing for normal cell growth. Additionally, protein antitoxins bind their own promoters and repress transcription, whereas the toxins serve as co-repressors. Recently, TA pairs have been shown to regulate their own transcription through a phenomenon known as conditional cooperativity, where the TA complexes bind operator DNA and repress transcription only when present in the proper stoichiometric amounts. The most differentially up-regulated gene in persister cells is mqsR, a gene that, with the antitoxin mqsA, constitutes a TA module. Here, we reveal that, unlike other TA systems, MqsR is not a transcription co-repressor but instead functions to destabilize the MqsA-DNA complex. We further show that DNA binding is not regulated by conditional cooperativity. Finally, using biophysical studies, we show that complex formation between MqsR and MqsA results in an exceptionally stable interaction, resulting in a subnanomolar dissociation constant that is similar to that observed between MqsA and DNA. In combination with crystallographic studies, this work reveals that MqsA binding to DNA and MqsR is mutually exclusive. To our knowledge, this is the first TA system in which the toxin does not function as a transcriptional co-repressor, but instead functions to destabilize the antitoxin-operator complex under all conditions, and thus defines another unique feature of the mqsRA TA module.
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Affiliation(s)
- Breann L Brown
- Department of Molecular Pharmacology, Physiology, and Biotechnology, Brown University, Providence, Rhode Island 02912, USA
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17
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The three vibrio cholerae chromosome II-encoded ParE toxins degrade chromosome I following loss of chromosome II. J Bacteriol 2010; 193:611-9. [PMID: 21115657 DOI: 10.1128/jb.01185-10] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Three homologues of the plasmid RK2 ParDE toxin-antitoxin system are present in the Vibrio cholerae genome within the superintegron on chromosome II. Here we found that these three loci-two of which have identical open reading frames and regulatory sequences-encode functional toxin-antitoxin systems. The ParE toxins inhibit bacterial division and reduce viability, presumably due to their capacity to damage DNA. The in vivo effects of ParE1/3 mimic those of ParE2, which we have previously demonstrated to be a DNA gyrase inhibitor in vitro, suggesting that ParE1/3 is likewise a gyrase inhibitor, despite its relatively low degree of sequence identity. ParE-mediated DNA damage activates the V. cholerae SOS response, which in turn likely accounts for ParE's inhibition of cell division. Each toxin's effects can be prevented by the expression of its cognate ParD antitoxin, which acts in a toxin-specific fashion both to block toxicity and to repress the expression of its parDE operon. Derepression of ParE activity in ΔparAB2 mutant V. cholerae cells that have lost chromosome II contributes to the prominent DNA degradation that accompanies the death of these cells. Overall, our findings suggest that the ParE toxins lead to the postsegregational killing of cells missing chromosome II in a manner that closely mimics postsegregational killing mediated by plasmid-encoded homologs. Thus, the parDE loci aid in the maintenance of the integrity of the V. cholerae superintegron and in ensuring the inheritance of chromosome II.
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18
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Brown BL, Wood TK, Peti W, Page R. Structure of the Escherichia coli antitoxin MqsA (YgiT/b3021) bound to its gene promoter reveals extensive domain rearrangements and the specificity of transcriptional regulation. J Biol Chem 2010; 286:2285-96. [PMID: 21068382 DOI: 10.1074/jbc.m110.172643] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Bacterial cultures, especially biofilms, produce a small number of persister cells, a genetically identical subpopulation of wild type cells that are metabolically dormant, exhibit multidrug tolerance, and are highly enriched in bacterial toxins. The gene most highly up-regulated in Escherichia coli persisters is mqsR, a ribonuclease toxin that, along with mqsA, forms a novel toxin·antitoxin (TA) system. Like all known TA systems, both the MqsR·MqsA complex and MqsA alone regulate their own transcription. Despite the importance of TA systems in persistence and biofilms, very little is known about how TA modules, and antitoxins in particular, bind and recognize DNA at a molecular level. Here, we report the crystal structure of MqsA bound to a 26-bp fragment from the mqsRA promoter. We show that MqsA binds DNA predominantly via its C-terminal helix-turn-helix domain, with direct binding of recognition helix residues Asn(97) and Arg(101) to the DNA major groove. Unexpectedly, the structure also revealed that the MqsA N-terminal domain interacts with the DNA phosphate backbone. This results in a more than 105° rotation of the N-terminal domains between the free and complexed states, an unprecedented rearrangement for an antitoxin. The structure also shows that MqsA bends the DNA by more than 55° in order to achieve symmetrical binding. Finally, using a combination of biochemical and NMR studies, we show that the DNA sequence specificity of MqsA is mediated by direct readout.
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Affiliation(s)
- Breann L Brown
- Department of Molecular Pharmacology, Physiology, and Biotechnology, Brown University, Providence, Rhode Island 02912, USA
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19
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Kroll J, Klinter S, Schneider C, Voss I, Steinbüchel A. Plasmid addiction systems: perspectives and applications in biotechnology. Microb Biotechnol 2010; 3:634-57. [PMID: 21255361 PMCID: PMC3815339 DOI: 10.1111/j.1751-7915.2010.00170.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2009] [Accepted: 02/17/2010] [Indexed: 11/26/2022] Open
Abstract
Biotechnical production processes often operate with plasmid-based expression systems in well-established prokaryotic and eukaryotic hosts such as Escherichia coli or Saccharomyces cerevisiae, respectively. Genetically engineered organisms produce important chemicals, biopolymers, biofuels and high-value proteins like insulin. In those bioprocesses plasmids in recombinant hosts have an essential impact on productivity. Plasmid-free cells lead to losses in the entire product recovery and decrease the profitability of the whole process. Use of antibiotics in industrial fermentations is not an applicable option to maintain plasmid stability. Especially in pharmaceutical or GMP-based fermentation processes, deployed antibiotics must be inactivated and removed. Several plasmid addiction systems (PAS) were described in the literature. However, not every system has reached a full applicable state. This review compares most known addiction systems and is focusing on biotechnical applications.
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Affiliation(s)
- Jens Kroll
- Institut für Molekulare Mikrobiologie und Biotechnologie, Westfälische Wilhelms-Universität, D-48149 Münster, Germany
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20
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Brown BL, Grigoriu S, Kim Y, Arruda JM, Davenport A, Wood TK, Peti W, Page R. Three dimensional structure of the MqsR:MqsA complex: a novel TA pair comprised of a toxin homologous to RelE and an antitoxin with unique properties. PLoS Pathog 2009; 5:e1000706. [PMID: 20041169 PMCID: PMC2791442 DOI: 10.1371/journal.ppat.1000706] [Citation(s) in RCA: 144] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2009] [Accepted: 11/24/2009] [Indexed: 11/19/2022] Open
Abstract
One mechanism by which bacteria survive environmental stress is through the formation of bacterial persisters, a sub-population of genetically identical quiescent cells that exhibit multidrug tolerance and are highly enriched in bacterial toxins. Recently, the Escherichia coli gene mqsR (b3022) was identified as the gene most highly upregulated in persisters. Here, we report multiple individual and complex three-dimensional structures of MqsR and its antitoxin MqsA (B3021), which reveal that MqsR:MqsA form a novel toxin:antitoxin (TA) pair. MqsR adopts an α/β fold that is homologous with the RelE/YoeB family of bacterial ribonuclease toxins. MqsA is an elongated dimer that neutralizes MqsR toxicity. As expected for a TA pair, MqsA binds its own promoter. Unexpectedly, it also binds the promoters of genes important for E. coli physiology (e.g., mcbR, spy). Unlike canonical antitoxins, MqsA is also structured throughout its entire sequence, binds zinc and coordinates DNA via its C- and not N-terminal domain. These studies reveal that TA systems, especially the antitoxins, are significantly more diverse than previously recognized and provide new insights into the role of toxins in maintaining the persister state. Most bacteria live in biofilms, microbial communities that cause more than 80% of human infections. Biofilms have a genetically identical sub-population of dormant cells, named persister cells, which are the well-recognized source of antibiotic resistance. Recently, it was demonstrated that toxins are highly upregulated in persisters and have therefore been postulated to play a role in the persister state. Using an inter-disciplinary approach, we reveal how mqsR, the gene most highly upregulated in persisters, together with mqsA, function: they are the founding members of a new family of toxin:antitoxin (TA) systems. Unexpectedly, the structure of MqsR reveals that it is a ribonuclease, a protein that controls the production of other essential proteins. Moreover, we identified multiple features of this TA system that are so unique that each is a starting point for drug development. Unlike other antitoxins, MqsA is structured throughout its entire sequence, its structure is unchanged between the free and toxin-bound states and it binds zinc. It also binds DNA via its C- and not N-terminal domain. Finally, MqsA binds both its own promoter and additional genes important for E. coli physiology. Taken together, our data provide fundamental new insights into the role of MqsR and MqsA in bacterial persistence and biofilms.
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Affiliation(s)
- Breann L. Brown
- Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, Rhode Island, United States of America
| | - Simina Grigoriu
- Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, Rhode Island, United States of America
| | - Younghoon Kim
- Artie McFerrin Department of Chemical Engineering, Texas A & M University, College Station, Texas, United States of America
| | - Jennifer M. Arruda
- Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, Rhode Island, United States of America
| | - Andrew Davenport
- Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, Rhode Island, United States of America
| | - Thomas K. Wood
- Artie McFerrin Department of Chemical Engineering, Texas A & M University, College Station, Texas, United States of America
- Department of Biology, Texas A & M University, College Station, Texas, United States of America
- Zachry Department of Civil Engineering, Texas A & M University, College Station, Texas, United States of America
| | - Wolfgang Peti
- Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, Rhode Island, United States of America
| | - Rebecca Page
- Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, Rhode Island, United States of America
- * E-mail:
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21
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De Jonge N, Garcia-Pino A, Buts L, Haesaerts S, Charlier D, Zangger K, Wyns L, De Greve H, Loris R. Rejuvenation of CcdB-poisoned gyrase by an intrinsically disordered protein domain. Mol Cell 2009; 35:154-63. [PMID: 19647513 DOI: 10.1016/j.molcel.2009.05.025] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2008] [Revised: 04/14/2009] [Accepted: 05/21/2009] [Indexed: 10/20/2022]
Abstract
Toxin-antitoxin modules are small regulatory circuits that ensure survival of bacterial populations under challenging environmental conditions. The ccd toxin-antitoxin module on the F plasmid codes for the toxin CcdB and its antitoxin CcdA. CcdB poisons gyrase while CcdA actively dissociates CcdB:gyrase complexes in a process called rejuvenation. The CcdA:CcdB ratio modulates autorepression of the ccd operon. The mechanisms behind both rejuvenation and regulation of expression are poorly understood. We show that CcdA binds consecutively to two partially overlapping sites on CcdB, which differ in affinity by six orders of magnitude. The first, picomolar affinity interaction triggers a conformational change in CcdB that initiates the dissociation of CcdB:gyrase complexes by an allosteric segmental binding mechanism. The second, micromolar affinity binding event regulates expression of the ccd operon. Both functions of CcdA, rejuvenation and autoregulation, are mechanistically intertwined and depend crucially on the intrinsically disordered nature of the CcdA C-terminal domain.
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Affiliation(s)
- Natalie De Jonge
- Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
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22
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Abstract
Are plasmids selfish parasitic DNA molecules or an integrated part of the bacterial genome? This chapter reviews the current understanding of the persistence mechanisms of conjugative plasmids harbored by bacterial cells and populations. The diversity and intricacy of mechanisms affecting the successful propagation and long-term continued existence of these extra-chromosomal elements is extensive. Apart from the accessory genetic elements that may provide plasmid-harboring cells a selective advantage, special focus is placed on the mechanisms conjugative plasmids employ to ensure their stable maintenance in the host cell. These importantly include the ability to self-mobilize in a process termed conjugative transfer, which may occur across species barriers. Other plasmid stabilizing mechanisms include the multimer resolution system, active partitioning, and post-segregational-killing of plasmid-free cells. Finally, various molecular adaptations of plasmids to better match the genetic background of their bacterial host cell will be described.
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23
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Overgaard M, Borch J, Jørgensen MG, Gerdes K. Messenger RNA interferase RelE controls relBE transcription by conditional cooperativity. Mol Microbiol 2008; 69:841-57. [PMID: 18532983 DOI: 10.1111/j.1365-2958.2008.06313.x] [Citation(s) in RCA: 149] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Prokaryotic toxin-antitoxin (TA) loci consist of two genes in an operon that encodes a metabolically stable toxin and an unstable antitoxin. The antitoxin neutralizes its cognate toxin by forming a tight complex with it. In all cases known, the antitoxin autoregulates TA operon transcription by binding to one or more operators in the promoter region while the toxin functions as a co-repressor of transcription. Interestingly, the toxin can also stimulate TA operon transcription. Here we analyse mechanistic aspects of how RelE of Escherichia coli can function both as a co-repressor and as a derepressor of relBE transcription. When RelB was in excess to RelE, two trimeric RelB(2)*RelE complexes bound cooperatively to two adjacent operator sites in the relBE promoter region and repressed transcription. In contrast, RelE in excess stimulated relBE transcription and released the RelB(2)*RelE complex from operator DNA. A mutational analysis of the operator sites showed that RelE in excess counteracted cooperative binding of the RelB(2)*RelE complexes to the operator sites. Thus, RelE controls relBE transcription by conditional cooperativity.
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Affiliation(s)
- Martin Overgaard
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
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24
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Sevin EW, Barloy-Hubler F. RASTA-Bacteria: a web-based tool for identifying toxin-antitoxin loci in prokaryotes. Genome Biol 2008; 8:R155. [PMID: 17678530 PMCID: PMC2374986 DOI: 10.1186/gb-2007-8-8-r155] [Citation(s) in RCA: 174] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2007] [Revised: 06/14/2007] [Accepted: 08/01/2007] [Indexed: 11/22/2022] Open
Abstract
RASTA-Bacteria is an automated method that allows quick and reliable identification of toxin/antitoxin loci in sequenced prokaryotic genomes, whether they are annotated Open Reading Frames or not. Toxin/antitoxin (TA) systems, viewed as essential regulators of growth arrest and programmed cell death, are widespread among prokaryotes, but remain sparsely annotated. We present RASTA-Bacteria, an automated method allowing quick and reliable identification of TA loci in sequenced prokaryotic genomes, whether they are annotated open reading frames or not. The tool successfully confirmed all reported TA systems, and spotted new putative loci upon screening of sequenced genomes. RASTA-Bacteria is publicly available at .
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Affiliation(s)
- Emeric W Sevin
- CNRS UMR6061 Génétique et Développement, Université de Rennes 1, IFR 140, Av. du Prof. Léon Bernard, CS 34317, 35043 Rennes, France
| | - Frédérique Barloy-Hubler
- CNRS UMR6061 Génétique et Développement, Université de Rennes 1, IFR 140, Av. du Prof. Léon Bernard, CS 34317, 35043 Rennes, France
- CNRS UMR6026 Interactions Cellulaires et Moléculaires, Groupe DUALS, Université de Rennes 1, IFR140, Campus de Beaulieu, Av. du Général Leclerc, 35042 Rennes, France
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25
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Prevalence and characterization of multidrug-resistant (type ACSSuT) Salmonella enterica serovar Typhimurium strains in isolates from four gosling farms and a hatchery farm. J Clin Microbiol 2007; 46:522-6. [PMID: 18077649 DOI: 10.1128/jcm.00709-07] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Salmonella enterica serovar Typhimurium strains of phage types DT104 and U302 are often resistant to ampicillin, chloramphenicol, streptomycin, sulfonamides, and tetracycline (the ACSSuT resistance type) and are major zoonotic pathogens. Increased consumption of goose meat may enhance the risk of transferring S. enterica serovar Typhimurium and other enteric pathogens from geese to human due to the consumption of meats from infected geese or improper preparation of meats. Therefore, we characterized S. enterica serovar Typhimurium strains isolated from four goose farms (farms A, B, C, and D) and one hatchery farm (farm E) to determine the epidemic and genetic differences among them. Antibiotic susceptibility tests and multiplex PCR confirmed that 77.6% (52/67) of strains were ACSSuT strains isolated from farms A, C, and E. Antibiotic-susceptible strains were isolated mostly from farm B, and no strain was observed in farm D. All ACSSuT strains harbored a 94.7-kb virulence plasmid and contained one 1.1-kb conserved segment identical to that of Salmonella genomic island 1. Four genotypes were determined among these S. enterica serovar Typhimurium isolates by pulsed-field gel electrophoresis analysis of XbaI-digested DNA fragments. Most isolates (85.29%; 29/34) of major genotype Ib were ACSSuT strains isolated mainly from goslings of farm C and egg membranes of farm E, a hatchery farm, suggesting that S. enterica serovar Typhimurium strains in isolates from goslings might originate from its hatchery, from the egg membranes to the gosling fluff after hatching. Multiple phage types, types 8, 12, U283, DT104, and U302, were identified. In conclusion, geese were a reservoir of diverse multidrug-resistant (type ACSSuT) S. enterica serovar Typhimurium strains, and each farm was colonized with genetically closely related S. enterica serovar Typhimurium strains.
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26
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Liu Y, Kobayashi I. Negative regulation of the EcoRI restriction enzyme gene is associated with intragenic reverse promoters. J Bacteriol 2007; 189:6928-35. [PMID: 17616602 PMCID: PMC2045195 DOI: 10.1128/jb.00127-07] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Type II restriction-modification systems are expected to possess mechanisms for tight regulation of their expression to suppress the potential of lethal attack on their host bacteria when they establish and maintain themselves within them. Although the EcoRI restriction enzyme has been well characterized, regulation of its expression is still poorly understood. In this study, mutational analysis with lacZ gene fusion and primer extension assay identified a promoter for the transcription of the ecoRIR gene. Further analyses revealed that an intragenic region containing two overlapping reverse promoter-like elements acted as a negative regulator for ecoRIR gene expression. The activity of these putative reverse promoters was verified by transcriptional gene fusion, primer extension and in vitro transcription. Mutations in these reverse promoters resulted in increased gene expression in both translational and transcriptional gene fusions. An RNase protection assay revealed that the transcript level of the wild type relative to that of the reverse promoter mutant at the downstream regions was much lower than the level at the upstream regions. This suggests that these reverse promoter-like elements affect their downstream transcript level. The possible mechanisms of this kind of negative regulation, in addition to their possible biological roles, are discussed.
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Affiliation(s)
- Yaoping Liu
- Department of Medical Genome Sciences, Graduate Schol of Frontier Science, University of Tokyo, Tokyo 108-8639, Japan
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27
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Wilbaux M, Mine N, Guérout AM, Mazel D, Van Melderen L. Functional interactions between coexisting toxin-antitoxin systems of the ccd family in Escherichia coli O157:H7. J Bacteriol 2007; 189:2712-9. [PMID: 17259320 PMCID: PMC1855815 DOI: 10.1128/jb.01679-06] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Toxin-antitoxin (TA) systems are widely represented on mobile genetic elements as well as in bacterial chromosomes. TA systems encode a toxin and an antitoxin neutralizing it. We have characterized a homolog of the ccd TA system of the F plasmid (ccd(F)) located in the chromosomal backbone of the pathogenic O157:H7 Escherichia coli strain (ccd(O157)). The ccd(F) and the ccd(O157) systems coexist in O157:H7 isolates, as these pathogenic strains contain an F-related virulence plasmid carrying the ccd(F) system. We have shown that the chromosomal ccd(O157) system encodes functional toxin and antitoxin proteins that share properties with their plasmidic homologs: the CcdB(O157) toxin targets the DNA gyrase, and the CcdA(O157) antitoxin is degraded by the Lon protease. The ccd(O157) chromosomal system is expressed in its natural context, although promoter activity analyses revealed that its expression is weaker than that of ccd(F). ccd(O157) is unable to mediate postsegregational killing when cloned in an unstable plasmid, supporting the idea that chromosomal TA systems play a role(s) other than stabilization in bacterial physiology. Our cross-interaction experiments revealed that the chromosomal toxin is neutralized by the plasmidic antitoxin while the plasmidic toxin is not neutralized by the chromosomal antitoxin, whether expressed ectopically or from its natural context. Moreover, the ccd(F) system is able to mediate postsegregational killing in an E. coli strain harboring the ccd(O157) system in its chromosome. This shows that the plasmidic ccd(F) system is functional in the presence of its chromosomal counterpart.
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Affiliation(s)
- Myriam Wilbaux
- Laboratoire de Génétique des Procaryotes, Institut de Biologie et Médecine Moléculaires, Université Libre de Bruxelles, 12 Rue des Professeurs Jeener et Brachet, 6041 Gosselies, Belgium
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28
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Madl T, Van Melderen L, Mine N, Respondek M, Oberer M, Keller W, Khatai L, Zangger K. Structural basis for nucleic acid and toxin recognition of the bacterial antitoxin CcdA. J Mol Biol 2006; 364:170-85. [PMID: 17007877 DOI: 10.1016/j.jmb.2006.08.082] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2006] [Revised: 08/25/2006] [Accepted: 08/29/2006] [Indexed: 11/28/2022]
Abstract
Toxin-antitoxin systems are highly abundant in plasmids and bacterial chromosomes. They ensure plasmid maintenance by killing bacteria that have lost the plasmid. Their expression is autoregulated at the level of transcription. Here, we present the solution structure of CcdA, the antitoxin of the ccd system, as a free protein (16.7 kDa) and in complex with its cognate DNA (25.3 kDa). CcdA is composed of two distinct and independent domains: the N-terminal domain, responsible for DNA binding, which establishes a new family of the ribbon-helix-helix fold and the C-terminal region, which is responsible for the interaction with the toxin CcdB. The C-terminal domain is intrinsically unstructured and forms a tight complex with the toxin. We show that CcdA specifically recognizes a 6 bp palindromic DNA sequence within the operator-promoter (OP) region of the ccd operon and binds to DNA by insertion of the positively charged N-terminal beta-sheet into the major groove. The binding of up to three CcdA dimers to a 33mer DNA of its operator-promoter region was studied by NMR spectroscopy, isothermal titration calorimetry and single point mutation. The highly flexible C-terminal region of free CcdA explains its susceptibility to proteolysis by the Lon ATP-dependent protease.
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Affiliation(s)
- Tobias Madl
- Institute of Chemistry, University of Graz, Graz 8010, Austria
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29
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Buts L, Lah J, Dao-Thi MH, Wyns L, Loris R. Toxin-antitoxin modules as bacterial metabolic stress managers. Trends Biochem Sci 2005; 30:672-9. [PMID: 16257530 DOI: 10.1016/j.tibs.2005.10.004] [Citation(s) in RCA: 219] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2005] [Revised: 09/27/2005] [Accepted: 10/13/2005] [Indexed: 11/25/2022]
Abstract
Bacterial genomes frequently contain operons that encode a toxin and its antidote. These 'toxin-antitoxin (TA) modules' have an important role in bacterial stress physiology and might form the basis of multidrug resistance. The toxins in TA modules act as gyrase poisons or stall the ribosome by mediating the cleavage of mRNA. The antidotes contain an N-terminal DNA-binding region of variable fold and a C-terminal toxin-inhibiting domain. When bound to toxin, the C-terminal domain adopts an extended conformation. In the absence of toxin, by contrast, this domain (and sometimes the whole antidote protein) remains unstructured, allowing its fast degradation by proteolysis. Under silent conditions the antidote inhibits the toxin and the toxin-antidote complex acts as a repressor for the TA operon, whereas under conditions of activation proteolytic degradation of the antidote outpaces its synthesis.
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Affiliation(s)
- Lieven Buts
- Laboratorium voor Ultrastructuur, Vrije Universiteit Brussel, and Department of Molecular and Cellular Interactions, Vlaams Interuniversitair Instituut voor Biotechnologie, Pleinlaan 2, B-1050 Brussel, Belgium
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Gerdes K, Christensen SK, Løbner-Olesen A. Prokaryotic toxin–antitoxin stress response loci. Nat Rev Microbiol 2005; 3:371-82. [PMID: 15864262 DOI: 10.1038/nrmicro1147] [Citation(s) in RCA: 822] [Impact Index Per Article: 43.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Although toxin-antitoxin gene cassettes were first found in plasmids, recent database mining has shown that these loci are abundant in free-living prokaryotes, including many pathogenic bacteria. For example, Mycobacterium tuberculosis has 38 chromosomal toxin-antitoxin loci, including 3 relBE and 9 mazEF loci. RelE and MazF are toxins that cleave mRNA in response to nutritional stress. RelE cleaves mRNAs that are positioned at the ribosomal A-site, between the second and third nucleotides of the A-site codon. It has been proposed that toxin-antitoxin loci function in bacterial programmed cell death, but evidence now indicates that these loci provide a control mechanism that helps free-living prokaryotes cope with nutritional stress.
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Affiliation(s)
- Kenn Gerdes
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, DK-5230 Odense M, Denmark.
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31
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Abstract
Transcription of the P1 plasmid addiction operon, a prototypical toxin-antitoxin system, is negatively autoregulated by the products of the operon. The Phd repressor-antitoxin protein binds to 8-bp palindromic Phd-binding sites in the promoter region and thereby represses transcription. The toxin, Doc, mediates cooperative interactions between adjacent Phd-binding sites and thereby enhances repression. Here, we describe a homologous operon from Salmonella enterica serovar Typhimurium which has the same pattern of regulation but an altered repressor-operator specificity. This difference in specificity maps to the seventh amino acid of the repressor and to the symmetric first and eighth positions of the corresponding palindromic repressor-binding sites. Thus, the repressor-operator interface has coevolved so as to retain the interaction while altering the specificity. Within an alignment of homologous repressors, the seventh amino acid of the repressor is highly variable, indicating that evolutionary changes in repressor specificity may be common in this protein family. We suggest that the robust properties of the negative feedback loop, the fuzzy recognition in the operator-repressor interface, and the duplication and divergence of the repressor-binding sites have facilitated the speciation of this repressor-operator interface. These three features may allow the repressor-operator system to percolate within a nearly neutral network of single-step mutations without the necessity of invoking simultaneous mutations, low-fitness intermediates, or other improbable or rate-limiting mechanisms.
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Affiliation(s)
- Xueyan Zhao
- Department of Biological Sciences, University of Alabama, Huntsville, AL 35758, USA
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Dao-Thi MH, Van Melderen L, De Genst E, Afif H, Buts L, Wyns L, Loris R. Molecular basis of gyrase poisoning by the addiction toxin CcdB. J Mol Biol 2005; 348:1091-102. [PMID: 15854646 DOI: 10.1016/j.jmb.2005.03.049] [Citation(s) in RCA: 112] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2005] [Revised: 03/17/2005] [Accepted: 03/18/2005] [Indexed: 11/20/2022]
Abstract
Gyrase is an ubiquitous bacterial enzyme that is responsible for disentangling DNA during DNA replication and transcription. It is the target of the toxin CcdB, a paradigm for plasmid addiction systems and related bacterial toxin-antitoxin systems. The crystal structure of CcdB and the dimerization domain of the A subunit of gyrase (GyrA14) dictates an open conformation for the catalytic domain of gyrase when CcdB is bound. The action of CcdB is one of a wedge that stabilizes a dead-end covalent gyrase:DNA adduct. Although CcdB and GyrA14 form a globally symmetric complex where the two 2-fold axes of both dimers align, the complex is asymmetric in its details. At the centre of the interaction site, the Trp99 pair of CcdB stacks with the Arg462 pair of GyrA14, explaining why the Arg462Cys mutation in the A subunit of gyrase confers resistance to CcdB. Overexpression of GyrA14 protects Escherichia coli cells against CcdB, mimicking the action of the antidote CcdA.
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Affiliation(s)
- Minh-Hoa Dao-Thi
- Laboratorium voor Ultrastructuur, Vrije Universiteit Brussel and Department of Molecular and Cellular Interactions, Vlaams Instituut voor Biotechnologie, Building E, Pleinlaan 2, B-1050 Brussels, Belgium
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Lah J, Simic M, Vesnaver G, Marianovsky I, Glaser G, Engelberg-Kulka H, Loris R. Energetics of Structural Transitions of the Addiction Antitoxin MazE. J Biol Chem 2005; 280:17397-407. [PMID: 15735309 DOI: 10.1074/jbc.m501128200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Escherichia coli mazEF addiction module plays a crucial role in the cell death program that is triggered under various stress conditions. It codes for the toxin MazF and the antitoxin MazE, which interferes with the lethal action of the toxin. To better understand the role of various conformations of MazE in bacterial life, its order-disorder transitions were monitored by differential scanning calorimetry, spectropolarimetry, and fluorimetry. The changes in spectral and thermodynamic properties accompanying MazE dimer denaturation can be described in terms of a compensating reversible process of the partial folding of the unstructured C-terminal half (high mean net charge, low mean hydrophobicity) and monomerization coupled with the partial unfolding of the structured N-terminal half (low mean net charge, high mean hydrophobicity). At pH<or=4.5 and T<50 degrees C, the unstructured polypeptide chains of the MazE dimer fold into (pre)molten globule-like conformations that thermally stabilize the dimeric form of the protein. The simulation based on the thermodynamic and structural information on various addiction modules suggests that both the conformational adaptability of the dimeric antitoxin form (binding to the toxins and DNA) and the reversible transformation to the more flexible monomeric form are essential for the regulation of bacterial cell life and death.
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Affiliation(s)
- Jurij Lah
- University of Ljubljana, Faculty of Chemistry and Chemical Technology, Askerceva 5, 1000 Ljubljana, Slovenia.
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Pellegrini O, Mathy N, Gogos A, Shapiro L, Condon C. The Bacillus subtilis ydcDE operon encodes an endoribonuclease of the MazF/PemK family and its inhibitor. Mol Microbiol 2005; 56:1139-48. [PMID: 15882409 DOI: 10.1111/j.1365-2958.2005.04606.x] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Operons encoding stable toxins and their labile antidote are widespread in prokaryotes and play important roles in plasmid partitioning and cellular responses to stress. One such family of toxins MazF/ChpAK/PemK encodes an endoribonuclease that inactivates cellular mRNAs by cleaving them at specific, but frequently occurring sites. Here we show that the Bacillus subtilis ydcE gene encodes a member of this family of RNases, which we have called EndoA. Overexpression of EndoA is toxic for bacterial cell growth and this toxicity is reversed by coexpression of the gene immediately upstream, ydcD. Furthermore, YdcD inhibits EndoA activity directly in vitro. EndoA has similar cleavage specificity to MazF and PemK and yields cleavage products with 3'-phosphate and 5'-hydroxyl groups, typical of EDTA-resistant degradative RNases. This is the first example of an antitoxin-toxin system in B. subtilis.
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Affiliation(s)
- Olivier Pellegrini
- CNRS UPR 9073 (affiliated with Université de Paris 7 - Denis Diderot), Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, 75005 Paris, France
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Zhang YX, Li J, Guo XK, Wu C, Bi B, Ren SX, Wu CF, Zhao GP. Characterization of a novel toxin-antitoxin module, VapBC, encoded by Leptospira interrogans chromosome. Cell Res 2004; 14:208-16. [PMID: 15225414 DOI: 10.1038/sj.cr.7290221] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Comparative genomic analysis of the coding sequences (CDSs) of Leptospira interrogans revealed a pair of closely linked genes homologous to the vapBC loci of many other bacteria with respect to both deduced amino acid sequences and operon organizations. Expression of single vapC gene in Escherichia coli resulted in inhibition of bacterial growth, whereas co-expression of vapBC restored the growth effectively. This phenotype is typical for three other characterized toxin-antitoxin systems of bacteria, i.e., mazEF, relBE and chpIK. The VapC proteins of bacteria and a thermophilic archeae, Solfolobus tokodaii, form a structurally distinguished group of toxin different from the other known toxins of bacteria. Phylogenetic analysis of both toxins and antitoxins of all categories indicated that although toxins were evolved from divergent sources and may or may not follow their speciation paths (as indicated by their 16s RNA sequences), co-evolution with their antitoxins was obvious.
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Affiliation(s)
- Yi Xuan Zhang
- Research Center of Biotechnology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 500 Caobao Road, Shanghai 200233, China
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36
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Santos-Sierra S, Lemonnier M, Nuñez B, Hargreaves D, Rafferty J, Giraldo R, Andreu JM, Díaz-Orejas R. Non-cytotoxic variants of the Kid protein that retain their auto-regulatory activity. Plasmid 2003; 50:120-30. [PMID: 12932738 DOI: 10.1016/s0147-619x(03)00048-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Kid and Kis are, respectively, the toxin and antitoxin encoded by the parD operon of plasmid R1. The recently solved crystal structure of Kid has revealed that this protein closely resembles the CcdB toxin of plasmid F. In CcdB, the residues involved in toxicity are located at the carboxy-terminal end of the protein. However, an analogous information on the Kid toxin was not available. Here, we have characterized a collection of non-toxic mutants of the Kid protein and identified the residues that affected the toxicity but not the co-regulatory activity of Kid. These are located in two discrete regions of the protein, at the amino and carboxy-terminal ends. Particularly, residues E18 and R85, that are conserved in the Escherichia coli ChpAK and RelE toxins, are affected by amino-acid changes that alter neither the overall structure of the protein nor its state of association, as shown by CD and sedimentation equilibrium analyses. However, thermal denaturation and intrinsic tryptophan fluorescence emission data point to subtle local changes at the N-terminal end of the protein. The implications of these results in the current model on the structure and function of Kid-related bacterial toxins are discussed.
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Affiliation(s)
- Sandra Santos-Sierra
- Departemento de Microbiologia Molecular, Centro de Investigaciones Biológicas, CSIC, Velázquez 144, Madrid E-28006, Spain
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37
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Loris R, Marianovsky I, Lah J, Laeremans T, Engelberg-Kulka H, Glaser G, Muyldermans S, Wyns L. Crystal structure of the intrinsically flexible addiction antidote MazE. J Biol Chem 2003; 278:28252-7. [PMID: 12743116 DOI: 10.1074/jbc.m302336200] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A specific camel VHH (variable domain of dromedary heavy chain antibody) fragment was used to crystallize the intrinsically flexible addiction antidote MazE. Only 45% of the polypeptide chain is found ordered in the crystal. The MazE monomer consisting of two beta-hairpins connected by a short alpha-helix has no hydrophobic core on its own and represents only one half of a typical protein domain. A complete domain structure is formed by the association of two chains, creating a hydrophobic core between two four-stranded beta-sheets. This hydrophobic core consists exclusively of short aliphatic residues. The folded part of MazE contains a novel DNA binding motif. A model for DNA binding that is consistent with the available biochemical data is presented.
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Affiliation(s)
- Remy Loris
- Laboratorium voor Ultrastructuur en Vlaams instituut voor Biotechnologie, Vrije Universiteit Brussel, Gebouw E, Pleinlaan 2, 1050 Brussel, Belgium.
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38
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Lah J, Marianovsky I, Glaser G, Engelberg-Kulka H, Kinne J, Wyns L, Loris R. Recognition of the intrinsically flexible addiction antidote MazE by a dromedary single domain antibody fragment. Structure, thermodynamics of binding, stability, and influence on interactions with DNA. J Biol Chem 2003; 278:14101-11. [PMID: 12533537 DOI: 10.1074/jbc.m209855200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Escherichia coli mazEF operon defines a chromosomal addiction module that programs cell death under various stress conditions. It encodes the toxic and long-lived MazF and the labile antidote MazE. The denaturation of MazE is a two-state reversible dimer-monomer transition. At lower concentrations the denatured state is significantly populated. This leads to a new aspect of the regulation of MazE concentration, which may decide about the life and death of the cell. Interactions of MazE with a dromedary antibody domain, cAbMaz1 (previously used as a crystallization aid), as well as with promoter DNA were studied using microcalorimetric and spectroscopic techniques. Unique features of cAbMaz1 enable a specific enthalpy-driven recognition of MazE and, thus, a significant stabilization of its dimeric native conformation. The MazE dimer and the MazE dimer-cAbMaz1 complex show very similar binding characteristics with promoter DNA, i.e. three binding sites with apparent affinities in micromolar range and highly exothermic binding accompanied by large negative entropy contributions. A working model for the MazE-DNA assembly is proposed on the basis of the structural and binding data. Both binding and stability studies lead to a picture of MazE solution structure that is significantly more unfolded than the structure observed in a crystal of the MazE-cAbMaz1 complex.
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Affiliation(s)
- Jurij Lah
- Department of Ultrastructure, Vrije Universiteit Brussel, Paardenstraat 65, B-1640 St. Genesius Rode, Belgium.
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Allali N, Afif H, Couturier M, Van Melderen L. The highly conserved TldD and TldE proteins of Escherichia coli are involved in microcin B17 processing and in CcdA degradation. J Bacteriol 2002; 184:3224-31. [PMID: 12029038 PMCID: PMC135094 DOI: 10.1128/jb.184.12.3224-3231.2002] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Microcin B17 (MccB17) is a peptide antibiotic produced by Escherichia coli strains carrying the pMccB17 plasmid. MccB17 is synthesized as a precursor containing an amino-terminal leader peptide that is cleaved during maturation. Maturation requires the product of the chromosomal tldE (pmbA) gene. Mature microcin is exported across the cytoplasmic membrane by a dedicated ABC transporter. In sensitive cells, MccB17 targets the essential topoisomerase II DNA gyrase. Independently, tldE as well as tldD mutants were isolated as being resistant to CcdB, another natural poison of gyrase encoded by the ccd poison-antidote system of plasmid F. This led to the idea that TldD and TldE could regulate gyrase function. We present in vivo evidence supporting the hypothesis that TldD and TldE have proteolytic activity. We show that in bacterial mutants devoid of either TldD or TldE activity, the MccB17 precursor accumulates and is not exported. Similarly, in the ccd system, we found that TldD and TldE are involved in CcdA and CcdA41 antidote degradation rather than being involved in the CcdB resistance mechanism. Interestingly, sequence database comparisons revealed that these two proteins have homologues in eubacteria and archaebacteria, suggesting a broader physiological role.
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Affiliation(s)
- Noureddine Allali
- Laboratoire de Génétique des Procaryotes, Institut de Biologie et de Médecine Moléculaires, Université Libre de Bruxelles, 6041 Gosselies, Belgium
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40
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Van Melderen L. Molecular interactions of the CcdB poison with its bacterial target, the DNA gyrase. Int J Med Microbiol 2002; 291:537-44. [PMID: 11890555 DOI: 10.1078/1438-4221-00164] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The ccd poison/antidote system of the F plasmid encodes CcdB, a toxin targeting the essential DNA gyrase of E. coli, and CcdA, the unstable antidote that interacts with CcdB to neutralise its toxicity. Gyrase belongs to the topoisomerase II class of enzymes and is a well-validated target for efficient therapeutic drugs, i. e. the quinolones. CcdB acts on gyrase in a similar way as quinolones do, both compounds induce double-strand breaks in DNA. Interestingly, the CcdB-binding domain of gyrase is different than that of quinolones. Therefore, novel classes of therapeutic drugs could be derived from the analysis of the interaction between CcdB and gyrase.
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Affiliation(s)
- Laurence Van Melderen
- Laboratoire de Génétique des Procaryotes, Institut de Biologie et Médecine Moléculaires, Université Libre de Bruxelles, Gosselies, Belgium.
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41
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Dao-Thi MH, Charlier D, Loris R, Maes D, Messens J, Wyns L, Backmann J. Intricate interactions within the ccd plasmid addiction system. J Biol Chem 2002; 277:3733-42. [PMID: 11741897 DOI: 10.1074/jbc.m105505200] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The ccd addiction system plays a crucial role in the stable maintenance of the Escherichia coli F plasmid. It codes for a stable toxin (CcdB) and a less stable antidote (CcdA). Both are expressed at low levels during normal cell growth. Upon plasmid loss, CcdB outlives CcdA and kills the cell by poisoning gyrase. The interactions between CcdB, CcdA, and its promoter DNA were analyzed. In solution, the CcdA-CcdB interaction is complex, leading to various complexes with different stoichiometry. CcdA has two binding sites for CcdB and vice versa, permitting soluble hexamer formation but also causing precipitation, especially at CcdA:CcdB ratios close to one. CcdA alone, but not CcdB, binds to promoter DNA with high on and off rates. The presence of CcdB enhances the affinity and the specificity of CcdA-DNA binding and results in a stable CcdA*CcdB*DNA complex with a CcdA:CcdB ratio of one. This (CcdA(2)CcdB(2))(n) complex has multiple DNA-binding sites and spirals around the 120-bp promoter region.
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Affiliation(s)
- Minh-Hoa Dao-Thi
- Vlaams interuniversitair Instituut voor Biotechnologie, Vrije Universiteit Brussel, Laboratorium voor Ultrastructuur, Paardenstraat 65, B-1640 Sint-Genesius-Rode, Belgium
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42
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Santos-Sierra S, Pardo-Abarrio C, Giraldo R, Díaz-Orejas R. Genetic identification of two functional regions in the antitoxin of the parD killer system of plasmid R1. FEMS Microbiol Lett 2002; 206:115-9. [PMID: 11786266 DOI: 10.1111/j.1574-6968.2002.tb10995.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
We report the identification and genetic analysis of mutants in the antitoxin of the parD (kis, kid) killer system of plasmid R1. Missense mutants placed at codons 10, 11, 12 and 18 maintained the antitoxin activity of Kis, but not the ability of this protein to co-regulate the parD system together with the Kid toxin. Deletion of the last 33 amino acids of Kis inactivated the antitoxin activity of the protein and reduced substantially, but not completely, its regulatory activity. These results define two functional regions in Kis: an amino-terminal region which is specifically involved in regulation, and a carboxy-terminal region of the protein, which is important both for its regulatory and antitoxin activities.
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Affiliation(s)
- Sandra Santos-Sierra
- Centro de Investigaciones Biológicas (CSIC), Department of Molecular Microbiology, Velázquez 144, 28006, Madrid, Spain
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43
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Afif H, Allali N, Couturier M, Van Melderen L. The ratio between CcdA and CcdB modulates the transcriptional repression of the ccd poison-antidote system. Mol Microbiol 2001; 41:73-82. [PMID: 11454201 DOI: 10.1046/j.1365-2958.2001.02492.x] [Citation(s) in RCA: 112] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The ccd operon of the F plasmid encodes CcdB, a toxin targeting the essential gyrase of Escherichia coli, and CcdA, the unstable antidote that interacts with CcdB to neutralize its toxicity. Although work from our group and others has established that CcdA and CcdB are required for transcriptional repression of the operon, the underlying mechanism remains unclear. The results presented here indicate that, although CcdA is the DNA-binding element of the CcdA-CcdB complex, the stoichiometry of the two proteins determines whether or not the complex binds to the ccd operator-promoter region. Using electrophoretic mobility shift assays, we show that a (CcdA)2-(CcdB)2 complex binds DNA. The addition of extra CcdB to that protein-DNA complex completely abolishes DNA retardation. Based on these results, we propose a model in which the ratio between CcdA and CcdB regulates the repression state of the ccd operon. When the level of CcdA is superior or equal to that of CcdB, repression results. In contrast, derepression occurs when CcdB is in excess of CcdA. By ensuring an antidote-toxin ratio greater than one, this mechanism could prevent the harmful effect of CcdB in plasmid-containing bacteria.
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Affiliation(s)
- H Afif
- Laboratoire de Génétique des Procaryotes, Institut de Biologie et de Médecine Moléculaires, Université Libre de Bruxelles, 12 Rue des Professeurs Jeener et Brachet, 6041 Gosselies, Belgium
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44
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Marianovsky I, Aizenman E, Engelberg-Kulka H, Glaser G. The regulation of the Escherichia coli mazEF promoter involves an unusual alternating palindrome. J Biol Chem 2001; 276:5975-84. [PMID: 11071896 DOI: 10.1074/jbc.m008832200] [Citation(s) in RCA: 110] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Escherichia coli mazEF system is a chromosomal "addiction module" that, under starvation conditions in which guanosine-3',5'-bispyrophosphate (ppGpp) is produced, is responsible for programmed cell death. This module specifies for the toxic stable protein MazF and the labile antitoxic protein MazE. Upstream from the mazEF module are two promoters, P(2) and P(3) that are strongly negatively autoregulated by MazE and MazF. We show that the expression of this module is positively regulated by the factor for inversion stimulation. What seems to be responsible for the negative autoregulation of mazEF is an unusual DNA structure, which we have called an "alternating palindrome." The middle part, "a," of this structure may complement either the downstream fragment, "b," or the upstream fragment, "c". When the MazE.MazF complex binds either of these arms of the alternating palindrome, strong negative autoregulation results. We suggest that the combined presence of the two promoters, the alternating palindrome structure and the factor for inversion stimulation-binding site, all permit the expression of the mazEF module to be sensitively regulated under various growth conditions.
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Affiliation(s)
- I Marianovsky
- Department of Cellular Biochemistry, Hebrew University-Hadassah Medical School, Ein Kerem, Jerusalem, 91120 Israel
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45
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Dao-Thi MH, Messens J, Wyns L, Backmann J. The thermodynamic stability of the proteins of the ccd plasmid addiction system. J Mol Biol 2000; 299:1373-86. [PMID: 10873460 DOI: 10.1006/jmbi.2000.3815] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The two opponents, toxin (CcdB, LetB or LetD, protein G, LynB) and antidote (CcdA, LetA, protein H, LynA), in the plasmid addiction system ccd of the F plasmid were studied by different biophysical methods. The thermodynamic stability was measured at different temperatures combining denaturant and thermally induced unfolding. It was found that both proteins denature in a two-state equilibrium (native dimer versus unfolded monomer) and that CcdA has a significantly lower thermodynamic stability. Using a numerical model, which was developed earlier by us, and on the basis of the determined thermodynamic parameters the concentration dependence of the denaturation transition temperature was obtained for both proteins. This concentration dependence may be of physiological significance, as the concentration of both ccd addiction proteins cannot exceed a certain limit because their expression is controlled by autoregulation. The influence of DNA on the thermal stability of the two proteins was probed. It was found that cognate DNA increases the melting temperature of CcdA. In the presence of non-specific DNA the thermal stability was not changed. The melting temperature of CcdB was not influenced by the applied double-stranded oligonucleotides, neither cognate nor unspecific.
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Affiliation(s)
- M H Dao-Thi
- Dienst Ultrastruktuur, Vrije Universiteit Brussel, Paardenstraat 65, Sint-Genesius-Rode, B-1640, Belgium
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46
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Gerdes K. Toxin-antitoxin modules may regulate synthesis of macromolecules during nutritional stress. J Bacteriol 2000; 182:561-72. [PMID: 10633087 PMCID: PMC94316 DOI: 10.1128/jb.182.3.561-572.2000] [Citation(s) in RCA: 241] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Affiliation(s)
- K Gerdes
- Department of Molecular Biology, Odense University, SDU, DK-5230 Odense M, Denmark.
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47
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Engelberg-Kulka H, Glaser G. Addiction modules and programmed cell death and antideath in bacterial cultures. Annu Rev Microbiol 1999; 53:43-70. [PMID: 10547685 DOI: 10.1146/annurev.micro.53.1.43] [Citation(s) in RCA: 281] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In bacteria, programmed cell death is mediated through "addiction modules" consisting of two genes. The product of the second gene is a stable toxin, whereas the product of the first is a labile antitoxin. Here we extensively review what is known about those modules that are borne by one of a number of Escherichia coli extrachromosomal elements and are responsible for the postsegregational killing effect. We focus on a recently discovered chromosomally borne regulatable addiction module in E. coli that responds to nutritional stress and also on an antideath gene of the E. coli bacteriophage lambda. We consider the relation of these two to programmed cell death and antideath in bacterial cultures. Finally, we discuss the similarities between basic features of programmed cell death and antideath in both prokaryotes and eukaryotes and the possibility that they share a common evolutionary origin.
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Affiliation(s)
- H Engelberg-Kulka
- Department of Molecular Biology, Hebrew University Hadassah-Medical School, Jerusalem, Israel.
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48
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Kampranis SC, Howells AJ, Maxwell A. The interaction of DNA gyrase with the bacterial toxin CcdB: evidence for the existence of two gyrase-CcdB complexes. J Mol Biol 1999; 293:733-44. [PMID: 10543963 DOI: 10.1006/jmbi.1999.3182] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
CcdB is a bacterial toxin that targets DNA gyrase. Analysis of the interaction of CcdB with gyrase reveals two distinct complexes. An initial complex (alpha) is formed by direct interaction between GyrA and CcdB; this complex can be detected by affinity column and gel-shift analysis, and has a proteolytic signature which is characterised by a 49 kDa fragment of GyrA. Surface plasmon resonance shows that CcdB binds to the N-terminal domain of GyrA with high affinity. In this mode of binding, CcdB does not affect the ability of gyrase to hydrolyse ATP or promote supercoiling. Incubation of this initial complex with ATP in the presence of GyrB and DNA slowly converts it to a second complex (beta), which has a lower rate of ATP hydrolysis and is unable to catalyse supercoiling. The efficiency of formation of this inactive complex is dependent on the concentrations of ATP and CcdB. We suggest that the conversion between the two complexes proceeds via an intermediate, whose formation is dependent on the rate of ATP hydrolysis.
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Affiliation(s)
- S C Kampranis
- Department of Biochemistry, University of Leicester, Leicester, LE1 7RH, UK
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49
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Rawlings DE. Proteic toxin-antitoxin, bacterial plasmid addiction systems and their evolution with special reference to the pas system of pTF-FC2. FEMS Microbiol Lett 1999; 176:269-77. [PMID: 10427709 DOI: 10.1111/j.1574-6968.1999.tb13672.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Genes encoding toxin-antitoxin proteins are frequently found on plasmids where they serve to stabilize the plasmid within a bacterial population. The toxin-antitoxin proteins do not increase the likelihood of a progeny cell receiving a plasmid but rather function as post-segregational killing mechanisms which decrease the proportion of cells that survive after losing the plasmid. These toxin-antitoxin couples therefore act as plasmid addiction systems. Several new proteic toxin-antitoxin systems have been identified and these systems appear to be ubiquitous on the chromosomes of bacteria and archaea. When placed on plasmids, these chromosomal systems also have the ability to stabilize plasmids and in at least one case, chromosomal- and plasmid-based toxin-antitoxin systems have been shown to interact. Recent findings regarding toxin-antitoxin systems and questions that have arisen as a result of these findings are reviewed.
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Affiliation(s)
- D E Rawlings
- Department of Microbiology, University of Stellenbosch, Matieland, South Africa.
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50
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Bahassi EM, O'Dea MH, Allali N, Messens J, Gellert M, Couturier M. Interactions of CcdB with DNA gyrase. Inactivation of Gyra, poisoning of the gyrase-DNA complex, and the antidote action of CcdA. J Biol Chem 1999; 274:10936-44. [PMID: 10196173 DOI: 10.1074/jbc.274.16.10936] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The F plasmid-carried bacterial toxin, the CcdB protein, is known to act on DNA gyrase in two different ways. CcdB poisons the gyrase-DNA complex, blocking the passage of polymerases and leading to double-strand breakage of the DNA. Alternatively, in cells that overexpress CcdB, the A subunit of DNA gyrase (GyrA) has been found as an inactive complex with CcdB. We have reconstituted the inactive GyrA-CcdB complex by denaturation and renaturation of the purified GyrA dimer in the presence of CcdB. This inactivating interaction involves the N-terminal domain of GyrA, because similar inactive complexes were formed by denaturing and renaturing N-terminal fragments of the GyrA protein in the presence of CcdB. Single amino acid mutations, both in GyrA and in CcdB, that prevent CcdB-induced DNA cleavage also prevent formation of the inactive complexes, indicating that some essential interaction sites of GyrA and of CcdB are common to both the poisoning and the inactivation processes. Whereas the lethal effect of CcdB is most probably due to poisoning of the gyrase-DNA complex, the inactivation pathway may prevent cell death through formation of a toxin-antitoxin-like complex between CcdB and newly translated GyrA subunits. Both poisoning and inactivation can be prevented and reversed in the presence of the F plasmid-encoded antidote, the CcdA protein. The products of treating the inactive GyrA-CcdB complex with CcdA are free GyrA and a CcdB-CcdA complex of approximately 44 kDa, which may correspond to a (CcdB)2(CcdA)2 heterotetramer.
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Affiliation(s)
- E M Bahassi
- Laboratoire de Génétique des Procaryotes, Département de Biologie Moléculaire, Université Libre de Bruxelles, rue des Chevaux 67, B-1640 Rhode-Saint-Genèse, Belgium
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