1
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Girardin Y, Galle M, Vanden Abeele Y, De Greve H, Loris R. Evaluation of different strategies to produce Vibrio cholerae ParE2 toxin. Protein Expr Purif 2024; 215:106403. [PMID: 37977515 DOI: 10.1016/j.pep.2023.106403] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2023] [Revised: 11/08/2023] [Accepted: 11/12/2023] [Indexed: 11/19/2023]
Abstract
Toxin-antitoxin (TA) systems are small operons that are omnipresent in bacteria and archaea with suggested roles in stabilization of mobile genetic elements, bacteriophage protection, stress response and possibly persister formation. A major bottleneck in the study of TA toxins is the production of sufficient amounts of well-folded, functional protein. Here we examine alternative approaches for obtaining the VcParE2 toxin from Vibrio cholerae. VcParE2 can be successfully produced via bacterial expression in presence of its cognate antitoxin VcParD2, followed by on-column unfolding and refolding. Alternatively, the toxin can be expressed in Spodoptera frugiperda (Sf9) insect cells. The latter requires disruption of the VcparE2 gene via introduction of an insect cell intron. Both methods provide protein with similar structural and functional characteristics.
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Affiliation(s)
- Yana Girardin
- Molecular Recognition Unit, Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050, Brussels, Belgium; Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Pleinlaan 2, 1050, Brussels, Belgium
| | - Margot Galle
- Molecular Recognition Unit, Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050, Brussels, Belgium; Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Pleinlaan 2, 1050, Brussels, Belgium
| | - Yaël Vanden Abeele
- Molecular Recognition Unit, Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050, Brussels, Belgium
| | - Henri De Greve
- Molecular Recognition Unit, Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050, Brussels, Belgium
| | - Remy Loris
- Molecular Recognition Unit, Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050, Brussels, Belgium; Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Pleinlaan 2, 1050, Brussels, Belgium.
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2
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Yamamoto K, Nagatoishi S, Matsunaga R, Nakakido M, Kuroda D, Tsumoto K. Conformational features and interaction mechanisms of V H H antibodies with β-hairpin CDR3: A case of Nb8-HigB2 interaction. Protein Sci 2023; 32:e4827. [PMID: 37916305 PMCID: PMC10661080 DOI: 10.1002/pro.4827] [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: 06/15/2023] [Revised: 10/07/2023] [Accepted: 10/30/2023] [Indexed: 11/03/2023]
Abstract
The β-hairpin conformation is regarded as an important basic motif to form and regulate protein-protein interactions. Single-domain VH H antibodies are potential therapeutic and diagnostic tools, and the third complementarity-determining regions of the heavy chains (CDR3s) of these antibodies are critical for antigen recognition. Although the sequences and conformations of the CDR3s are diverse, CDR3s sometimes adopt β-hairpin conformations. However, characteristic features and interaction mechanisms of β-hairpin CDR3s remain to be fully elucidated. In this study, we investigated the molecular recognition of the anti-HigB2 VH H antibody Nb8, which has a CDR3 that forms a β-hairpin conformation. The interaction was analyzed by evaluation of alanine-scanning mutants, molecular dynamics simulations, and hydrogen/deuterium exchange mass spectrometry. These experiments demonstrated that positions 93 and 94 (Chothia numbering) in framework region 3, which is right outside CDR3 by definition, play pivotal roles in maintaining structural stability and binding properties of Nb8. These findings will facilitate the design and optimization of single-domain antibodies.
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Affiliation(s)
- Koichi Yamamoto
- Department of Bioengineering, Graduate School of EngineeringThe University of TokyoTokyoJapan
| | - Satoru Nagatoishi
- Department of Bioengineering, Graduate School of EngineeringThe University of TokyoTokyoJapan
- The Institute of Medical ScienceThe University of TokyoTokyoJapan
- Medical Device Development and Regulation Research Center, School of EngineeringThe University of TokyoTokyoJapan
| | - Ryo Matsunaga
- Department of Bioengineering, Graduate School of EngineeringThe University of TokyoTokyoJapan
| | - Makoto Nakakido
- Department of Bioengineering, Graduate School of EngineeringThe University of TokyoTokyoJapan
| | - Daisuke Kuroda
- Department of Bioengineering, Graduate School of EngineeringThe University of TokyoTokyoJapan
- Research Center for Drug and Vaccine DevelopmentNational Institute of Infectious DiseasesTokyoJapan
| | - Kouhei Tsumoto
- Department of Bioengineering, Graduate School of EngineeringThe University of TokyoTokyoJapan
- The Institute of Medical ScienceThe University of TokyoTokyoJapan
- Medical Device Development and Regulation Research Center, School of EngineeringThe University of TokyoTokyoJapan
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3
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Dominguez-Molina L, Talavera A, Cepauskas A, Kurata T, Echemendia-Blanco D, Hauryliuk V, Garcia-Pino A. Biochemical and X-ray analyses of the players involved in the faRel2/aTfaRel2 toxin-antitoxin operon. Acta Crystallogr F Struct Biol Commun 2023; 79:247-256. [PMID: 37728608 PMCID: PMC10565793 DOI: 10.1107/s2053230x23007288] [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: 07/11/2023] [Accepted: 08/19/2023] [Indexed: 09/21/2023] Open
Abstract
The aTfaRel2/faRel2 operon from Coprobacillus sp. D7 encodes a bicistronic type II toxin-antitoxin (TA) module. The FaRel2 toxin is a toxic small alarmone synthetase (toxSAS) that inhibits translation through the pyrophosphorylation of uncharged tRNAs at the 3'-CCA end. The toxin is neutralized by the antitoxin ATfaRel2 through the formation of an inactive TA complex. Here, the production, biophysical analysis and crystallization of ATfaRel2 and FaRel2 as well as of the ATfaRel2-FaRel2 complex are reported. ATfaRel2 is monomeric in solution. The antitoxin crystallized in space group P21212 with unit-cell parameters a = 53.3, b = 34.2, c = 37.6 Å, and the best crystal diffracted to a resolution of 1.24 Å. Crystals of FaRel2 in complex with APCPP, a nonhydrolysable ATP analogue, belonged to space group P21, with unit-cell parameters a = 31.5, b = 60.6, c = 177.2 Å, β = 90.6°, and diffracted to 2.6 Å resolution. The ATfaRel2-FaRel2Y128F complex forms a heterotetramer in solution composed of two toxins and two antitoxins. This complex crystallized in two space groups: F4132, with unit-cell parameters a = b = c = 227.1 Å, and P212121, with unit-cell parameters a = 51.7, b = 106.2, c = 135.1 Å. The crystals diffracted to 1.98 and 2.1 Å resolution, respectively.
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Affiliation(s)
- Lucia Dominguez-Molina
- Cellular and Molecular Microbiology, Faculté des Sciences, Université Libre de Bruxelles (ULB), Boulevard du Triomphe, Building BC (1C4 203), 1050 Brussels, Belgium
| | - Ariel Talavera
- Cellular and Molecular Microbiology, Faculté des Sciences, Université Libre de Bruxelles (ULB), Boulevard du Triomphe, Building BC (1C4 203), 1050 Brussels, Belgium
| | - Albinas Cepauskas
- Cellular and Molecular Microbiology, Faculté des Sciences, Université Libre de Bruxelles (ULB), Boulevard du Triomphe, Building BC (1C4 203), 1050 Brussels, Belgium
| | - Tatsuaki Kurata
- Department of Experimental Medical Science, Lund University, Lund, Sweden
| | - Dannele Echemendia-Blanco
- Cellular and Molecular Microbiology, Faculté des Sciences, Université Libre de Bruxelles (ULB), Boulevard du Triomphe, Building BC (1C4 203), 1050 Brussels, Belgium
| | - Vasili Hauryliuk
- Department of Experimental Medical Science, Lund University, Lund, Sweden
- University of Tartu Institute of Technology, Tartu, Estonia
- Science for Life Laboratory, Lund, Sweden
| | - Abel Garcia-Pino
- Cellular and Molecular Microbiology, Faculté des Sciences, Université Libre de Bruxelles (ULB), Boulevard du Triomphe, Building BC (1C4 203), 1050 Brussels, Belgium
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4
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de Castro GV, Worm DJ, Grabe GJ, Rowan FC, Haggerty L, de la Lastra AL, Popescu O, Helaine S, Barnard A. Characterization of the Key Determinants of Phd Antitoxin Mediated Doc Toxin Inactivation in Salmonella. ACS Chem Biol 2022; 17:1598-1606. [PMID: 35647667 PMCID: PMC9207808 DOI: 10.1021/acschembio.2c00276] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In the search for novel antimicrobial therapeutics, toxin-antitoxin (TA) modules are promising yet underexplored targets for overcoming antibiotic failure. The bacterial toxin Doc has been associated with the persistence of Salmonella in macrophages, enabling its survival upon antibiotic exposure. After developing a novel method to produce the recombinant toxin, we have used antitoxin-mimicking peptides to thoroughly investigate the mechanism by which its cognate antitoxin Phd neutralizes the activity of Doc. We reveal insights into the molecular detail of the Phd-Doc relationship and discriminate antitoxin residues that stabilize the TA complex from those essential for inhibiting the activity of the toxin. Coexpression of Doc and antitoxin peptides in Salmonella was able to counteract the activity of the toxin, confirming our in vitro results with equivalent sequences. Our findings provide key principles for the development of chemical tools to study and therapeutically interrogate this important class of protein-protein interactions.
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Affiliation(s)
- Guilherme V. de Castro
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, 82 Wood Lane, London W12 0BZ, United Kingdom
| | - Dennis J. Worm
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, 82 Wood Lane, London W12 0BZ, United Kingdom
| | - Grzegorz J. Grabe
- Department of Microbiology, Harvard Medical School, 4 Blackfan Circle, Boston, Massachusetts 02115, United States
| | - Fiona C. Rowan
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, 82 Wood Lane, London W12 0BZ, United Kingdom
| | - Lucy Haggerty
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, 82 Wood Lane, London W12 0BZ, United Kingdom
| | - Ana L. de la Lastra
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, 82 Wood Lane, London W12 0BZ, United Kingdom
| | - Oana Popescu
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, 82 Wood Lane, London W12 0BZ, United Kingdom
| | - Sophie Helaine
- Department of Microbiology, Harvard Medical School, 4 Blackfan Circle, Boston, Massachusetts 02115, United States
| | - Anna Barnard
- Department of Chemistry, Molecular Sciences Research Hub, Imperial College London, 82 Wood Lane, London W12 0BZ, United Kingdom
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5
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Tamiya-Ishitsuka H, Tsuruga M, Noda N, Yokota A. Conserved Amino Acid Moieties of Candidatus Desulforudis audaxviator MazF Determine Ribonuclease Activity and Specificity. Front Microbiol 2021; 12:748619. [PMID: 34867867 PMCID: PMC8634880 DOI: 10.3389/fmicb.2021.748619] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Accepted: 10/21/2021] [Indexed: 11/17/2022] Open
Abstract
The toxin-antitoxin (TA) system, inherent to various prokaryotes, plays a critical role in survival and adaptation to diverse environmental stresses. The toxin MazF, belonging to the type II TA system, functions as a sequence-specific ribonuclease that recognizes 3 to 7 bases. In recent studies, crystallographic analysis of MazFs from several species have suggested the presence of amino acid sites important for MazF substrate RNA binding and for its catalytic activity. Herein, we characterized MazF obtained from Candidatus Desulforudis audaxviator (MazF-Da) and identified the amino acid residues necessary for its catalytic function. MazF-Da, expressed using a cell-free protein synthesis system, is a six-base-recognition-specific ribonuclease that preferentially cleaves UACAAA sequences and weakly cleaves UACGAA and UACUAA sequences. We found that MazF-Da exhibited the highest activity at around 60°C. Analysis using mutants with a single mutation at an amino acid residue site that is well conserved across various MazF toxins showed that G18, E20, R25, and P26 were important for the ribonuclease activity of MazF-Da. The recognition sequence of the N36A mutant differed from that of the wild type. This mutant cleaved UACAAG sequences in addition to UACAAA sequences, but did not cleave UACGAA or UACUAA sequences, suggesting that Asn36 affects the loosening and narrowing of MazF-Da cleavage sequence recognition. Our study posits UACAAA as the recognition sequence of MazF-Da and provides insight into the amino acid sites that are key to its unique enzymatic properties.
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Affiliation(s)
- Hiroko Tamiya-Ishitsuka
- Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
| | - Masako Tsuruga
- Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
| | - Naohiro Noda
- Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
| | - Akiko Yokota
- Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
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6
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Garcia-Rodriguez G, Girardin Y, Volkov AN, Singh RK, Muruganandam G, Van Dyck J, Sobott F, Versées W, Charlier D, Loris R. Entropic pressure controls the oligomerization of the Vibrio cholerae ParD2 antitoxin. Acta Crystallogr D Struct Biol 2021; 77:904-920. [PMID: 34196617 PMCID: PMC8251345 DOI: 10.1107/s2059798321004873] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2021] [Accepted: 05/07/2021] [Indexed: 11/22/2022] Open
Abstract
ParD2 is the antitoxin component of the parDE2 toxin-antitoxin module from Vibrio cholerae and consists of an ordered DNA-binding domain followed by an intrinsically disordered ParE-neutralizing domain. In the absence of the C-terminal intrinsically disordered protein (IDP) domain, V. cholerae ParD2 (VcParD2) crystallizes as a doughnut-shaped hexadecamer formed by the association of eight dimers. This assembly is stabilized via hydrogen bonds and salt bridges rather than by hydrophobic contacts. In solution, oligomerization of the full-length protein is restricted to a stable, open decamer or dodecamer, which is likely to be a consequence of entropic pressure from the IDP tails. The relative positioning of successive VcParD2 dimers mimics the arrangement of Streptococcus agalactiae CopG dimers on their operator and allows an extended operator to wrap around the VcParD2 oligomer.
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Affiliation(s)
- Gabriela Garcia-Rodriguez
- Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
- VIB–VUB Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Pleinlaan 2, 1050 Brussels, Belgium
| | - Yana Girardin
- Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
- VIB–VUB Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Pleinlaan 2, 1050 Brussels, Belgium
| | - Alexander N. Volkov
- Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
- VIB–VUB Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Pleinlaan 2, 1050 Brussels, Belgium
- Jean Jeener NMR Center, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
| | - Ranjan Kumar Singh
- Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
- VIB–VUB Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Pleinlaan 2, 1050 Brussels, Belgium
| | - Gopinath Muruganandam
- Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
- VIB–VUB Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Pleinlaan 2, 1050 Brussels, Belgium
| | - Jeroen Van Dyck
- Department of Chemistry, Universiteit Antwerpen, Groenenborgerlaan 171, 2020 Antwerp, Belgium
| | - Frank Sobott
- Department of Chemistry, Universiteit Antwerpen, Groenenborgerlaan 171, 2020 Antwerp, Belgium
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Wim Versées
- Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
- VIB–VUB Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Pleinlaan 2, 1050 Brussels, Belgium
| | - Daniel Charlier
- Research Group of Microbiology, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
| | - Remy Loris
- Structural Biology Brussels, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
- VIB–VUB Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Pleinlaan 2, 1050 Brussels, Belgium
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7
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Functional Characterization of the mazEF Toxin-Antitoxin System in the Pathogenic Bacterium Agrobacterium tumefaciens. Microorganisms 2021; 9:microorganisms9051107. [PMID: 34065548 PMCID: PMC8160871 DOI: 10.3390/microorganisms9051107] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Revised: 05/14/2021] [Accepted: 05/16/2021] [Indexed: 11/16/2022] Open
Abstract
Agrobacterium tumefaciens is a pathogen of various plants which transfers its own DNA (T-DNA) to the host plants. It is used for producing genetically modified plants with this ability. To control T-DNA transfer to the right place, toxin-antitoxin (TA) systems of A. tumefaciens were used to control the target site of transfer without any unintentional targeting. Here, we describe a toxin-antitoxin system, Atu0939 (mazE-at) and Atu0940 (mazF-at), in the chromosome of Agrobacterium tumefaciens. The toxin in the TA system has 33.3% identity and 45.5% similarity with MazF in Escherichia coli. The expression of MazF-at caused cell growth inhibition, while cells with MazF-at co-expressed with MazE-at grew normally. In vivo and in vitro assays revealed that MazF-at inhibited protein synthesis by decreasing the cellular mRNA stability. Moreover, the catalytic residue of MazF-at was determined to be the 24th glutamic acid using site-directed mutagenesis. From the results, we concluded that MazF-at is a type II toxin-antitoxin system and a ribosome-independent endoribonuclease. Here, we characterized a TA system in A. tumefaciens whose understanding might help to find its physiological function and to develop further applications.
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8
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Jiang T, Yu N, Kim J, Murgo JR, Kissai M, Ravichandran K, Miracco EJ, Presnyak V, Hua S. Oligonucleotide Sequence Mapping of Large Therapeutic mRNAs via Parallel Ribonuclease Digestions and LC-MS/MS. Anal Chem 2019; 91:8500-8506. [PMID: 31129964 DOI: 10.1021/acs.analchem.9b01664] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Characterization of mRNA sequences is a critical aspect of mRNA drug development and regulatory filing. Herein, we developed a novel bottom-up oligonucleotide sequence mapping workflow combining multiple endonucleases that cleave mRNA at different frequencies. RNase T1, colicin E5, and mazF were applied in parallel to provide complementary sequence coverage for large mRNAs. Combined use of multiple endonucleases resulted in significantly improved sequence coverage: greater than 70% sequence coverage was achieved on mRNAs near 3000 nucleotides long. Oligonucleotide mapping simulations with large human RNA databases demonstrate that the proposed workflow can positively identify a single correct sequence from hundreds of similarly sized sequences. In addition, the workflow is sensitive and specific enough to detect minor sequence impurities such as single nucleotide polymorphisms (SNPs) with a sensitivity of less than 1%. LC-MS/MS-based oligonucleotide sequence mapping can serve as an orthogonal sequence characterization method to techniques such as Sanger sequencing or next-generation sequencing (NGS), providing high-throughput sequence identification and sensitive impurity detection.
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Affiliation(s)
- Tao Jiang
- Moderna Inc. , 500 Technology Square , Cambridge , Massachusetts 02139 , United States
| | - Ningxi Yu
- Department of Chemistry , University of Cincinnati , Cincinnati , Ohio 45221 , United States
| | - Jaeah Kim
- Department of Pharmaceutical and Biomedical Sciences, College of Pharmacy , University of Georgia , Athens , Georgia 30602 , United States
| | - John-Ross Murgo
- Moderna Inc. , 500 Technology Square , Cambridge , Massachusetts 02139 , United States
| | - Mildred Kissai
- Moderna Inc. , 500 Technology Square , Cambridge , Massachusetts 02139 , United States
| | - Kanchana Ravichandran
- Moderna Inc. , 500 Technology Square , Cambridge , Massachusetts 02139 , United States
| | - Edward J Miracco
- Moderna Inc. , 500 Technology Square , Cambridge , Massachusetts 02139 , United States
| | - Vladimir Presnyak
- Moderna Inc. , 500 Technology Square , Cambridge , Massachusetts 02139 , United States
| | - Serenus Hua
- Moderna Inc. , 500 Technology Square , Cambridge , Massachusetts 02139 , United States
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9
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Armalytė J, Jurėnas D, Krasauskas R, Čepauskas A, Sužiedėlienė E. The higBA Toxin-Antitoxin Module From the Opportunistic Pathogen Acinetobacter baumannii - Regulation, Activity, and Evolution. Front Microbiol 2018; 9:732. [PMID: 29706946 PMCID: PMC5906591 DOI: 10.3389/fmicb.2018.00732] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2018] [Accepted: 03/28/2018] [Indexed: 01/08/2023] Open
Abstract
Acinetobacter baumannii is one of the major causes of hard to treat multidrug-resistant hospital infections. A. baumannii features contributing to its spread and persistence in clinical environment are only beginning to be explored. Bacterial toxin-antitoxin (TA) systems are genetic loci shown to be involved in plasmid maintenance and proposed to function as components of stress response networks. Here we present a thorough characterization of type II system of A. baumannii, which is the most ubiquitous TA module present in A. baumannii plasmids. higBA of A. baumannii is a reverse TA (the toxin gene is the first in the operon) and shows little homology to other TA systems of RelE superfamily. It is represented by two variants, which both are functional albeit exhibit strong difference in sequence conservation. The higBA2 operon is found on ubiquitous 11 Kb pAB120 plasmid, conferring carbapenem resistance to clinical A. baumannii isolates and represents a higBA variant that can be found with multiple sequence variations. We show here that higBA2 is capable to confer maintenance of unstable plasmid in Acinetobacter species. HigB2 toxin functions as a ribonuclease and its activity is neutralized by HigA2 antitoxin through formation of an unusually large heterooligomeric complex. Based on the in vivo expression analysis of gfp reporter gene we propose that HigA2 antitoxin and HigBA2 protein complex bind the higBA2 promoter region to downregulate its transcription. We also demonstrate that higBA2 is a stress responsive locus, whose transcription changes in conditions encountered by A. baumannii in clinical environment and within the host. We show elevated expression of higBA2 during stationary phase, under iron deficiency and downregulated expression after antibiotic (rifampicin) treatment.
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Affiliation(s)
- Julija Armalytė
- Institute of Biosciences, Life Sciences Center, Vilnius University, Vilnius, Lithuania
| | - Dukas Jurėnas
- Institute of Biosciences, Life Sciences Center, Vilnius University, Vilnius, Lithuania
- Cellular and Molecular Microbiology, Department of Molecular Biology, Université Libre de Bruxelles, Brussels, Belgium
| | - Renatas Krasauskas
- Institute of Biosciences, Life Sciences Center, Vilnius University, Vilnius, Lithuania
| | - Albinas Čepauskas
- Institute of Biosciences, Life Sciences Center, Vilnius University, Vilnius, Lithuania
| | - Edita Sužiedėlienė
- Institute of Biosciences, Life Sciences Center, Vilnius University, Vilnius, Lithuania
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10
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Talavera A, Hendrix J, Versées W, Jurėnas D, Van Nerom K, Vandenberk N, Singh RK, Konijnenberg A, De Gieter S, Castro-Roa D, Barth A, De Greve H, Sobott F, Hofkens J, Zenkin N, Loris R, Garcia-Pino A. Phosphorylation decelerates conformational dynamics in bacterial translation elongation factors. SCIENCE ADVANCES 2018; 4:eaap9714. [PMID: 29546243 PMCID: PMC5851678 DOI: 10.1126/sciadv.aap9714] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/18/2017] [Accepted: 02/07/2018] [Indexed: 06/08/2023]
Abstract
Bacterial protein synthesis is intricately connected to metabolic rate. One of the ways in which bacteria respond to environmental stress is through posttranslational modifications of translation factors. Translation elongation factor Tu (EF-Tu) is methylated and phosphorylated in response to nutrient starvation upon entering stationary phase, and its phosphorylation is a crucial step in the pathway toward sporulation. We analyze how phosphorylation leads to inactivation of Escherichia coli EF-Tu. We provide structural and biophysical evidence that phosphorylation of EF-Tu at T382 acts as an efficient switch that turns off protein synthesis by decoupling nucleotide binding from the EF-Tu conformational cycle. Direct modifications of the EF-Tu switch I region or modifications in other regions stabilizing the β-hairpin state of switch I result in an effective allosteric trap that restricts the normal dynamics of EF-Tu and enables the evasion of the control exerted by nucleotides on G proteins. These results highlight stabilization of a phosphorylation-induced conformational trap as an essential mechanism for phosphoregulation of bacterial translation and metabolism. We propose that this mechanism may lead to the multisite phosphorylation state observed during dormancy and stationary phase.
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Affiliation(s)
- Ariel Talavera
- Structural Biology Brussels, Department of Bio-engineering Sciences, Vrije Universiteit Brussel, Brussels, Belgium
- Center for Structural Biology, VIB, Flanders, Belgium
| | - Jelle Hendrix
- Molecular Imaging and Photonics, University of Leuven, B-3001 Leuven, Belgium
- Biomedical Research Institute, Hasselt University, B-3590 Hasselt, Belgium
| | - Wim Versées
- Structural Biology Brussels, Department of Bio-engineering Sciences, Vrije Universiteit Brussel, Brussels, Belgium
- Center for Structural Biology, VIB, Flanders, Belgium
| | - Dukas Jurėnas
- Cellular and Molecular Microbiology, Department of Molecular Biology, Université Libre de Bruxelles, Brussels, Belgium
| | - Katleen Van Nerom
- Cellular and Molecular Microbiology, Department of Molecular Biology, Université Libre de Bruxelles, Brussels, Belgium
| | - Niels Vandenberk
- Molecular Imaging and Photonics, University of Leuven, B-3001 Leuven, Belgium
| | - Ranjan Kumar Singh
- Structural Biology Brussels, Department of Bio-engineering Sciences, Vrije Universiteit Brussel, Brussels, Belgium
- Center for Structural Biology, VIB, Flanders, Belgium
| | - Albert Konijnenberg
- Structural Biology Brussels, Department of Bio-engineering Sciences, Vrije Universiteit Brussel, Brussels, Belgium
- Center for Structural Biology, VIB, Flanders, Belgium
- Biomolecular and Analytical Mass Spectrometry Group, Department of Chemistry, University of Antwerp, Antwerp, Belgium
| | - Steven De Gieter
- Structural Biology Brussels, Department of Bio-engineering Sciences, Vrije Universiteit Brussel, Brussels, Belgium
- Center for Structural Biology, VIB, Flanders, Belgium
| | - Daniel Castro-Roa
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Baddiley-Clark Building, Richardson Road, Newcastle upon Tyne NE2 4AX, UK
| | - Anders Barth
- Fluorescence Applications in Biology Laboratory, Department of Chemistry and Pharmacy, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Henri De Greve
- Structural Biology Brussels, Department of Bio-engineering Sciences, Vrije Universiteit Brussel, Brussels, Belgium
- Center for Structural Biology, VIB, Flanders, Belgium
| | - Frank Sobott
- Biomolecular and Analytical Mass Spectrometry Group, Department of Chemistry, University of Antwerp, Antwerp, Belgium
- School of Molecular and Cellular Biology, University of Leeds, Leeds LS2 9JT, UK
- Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
| | - Johan Hofkens
- Molecular Imaging and Photonics, University of Leuven, B-3001 Leuven, Belgium
- Nano-Science Center, Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen, Denmark
| | - Nikolay Zenkin
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Baddiley-Clark Building, Richardson Road, Newcastle upon Tyne NE2 4AX, UK
| | - Remy Loris
- Structural Biology Brussels, Department of Bio-engineering Sciences, Vrije Universiteit Brussel, Brussels, Belgium
- Center for Structural Biology, VIB, Flanders, Belgium
| | - Abel Garcia-Pino
- Cellular and Molecular Microbiology, Department of Molecular Biology, Université Libre de Bruxelles, Brussels, Belgium
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11
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Hadži S, Garcia-Pino A, Haesaerts S, Jurenas D, Gerdes K, Lah J, Loris R. Ribosome-dependent Vibrio cholerae mRNAse HigB2 is regulated by a β-strand sliding mechanism. Nucleic Acids Res 2017; 45:4972-4983. [PMID: 28334932 PMCID: PMC5416850 DOI: 10.1093/nar/gkx138] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2016] [Accepted: 02/25/2017] [Indexed: 11/12/2022] Open
Abstract
Toxin–antitoxin (TA) modules are small operons involved in bacterial stress response and persistence. higBA operons form a family of TA modules with an inverted gene organization and a toxin belonging to the RelE/ParE superfamily. Here, we present the crystal structures of chromosomally encoded Vibrio cholerae antitoxin (VcHigA2), toxin (VcHigB2) and their complex, which show significant differences in structure and mechanisms of function compared to the higBA module from plasmid Rts1, the defining member of the family. The VcHigB2 is more closely related to Escherichia coli RelE both in terms of overall structure and the organization of its active site. VcHigB2 is neutralized by VcHigA2, a modular protein with an N-terminal intrinsically disordered toxin-neutralizing segment followed by a C-terminal helix-turn-helix dimerization and DNA binding domain. VcHigA2 binds VcHigB2 with picomolar affinity, which is mainly a consequence of entropically favorable de-solvation of a large hydrophobic binding interface and enthalpically favorable folding of the N-terminal domain into an α-helix followed by a β-strand. This interaction displaces helix α3 of VcHigB2 and at the same time induces a one-residue shift in the register of β-strand β3, thereby flipping the catalytically important Arg64 out of the active site.
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Affiliation(s)
- San Hadži
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel, B-1050 Brussel, Belgium.,Molecular Recognition Unit, Center for Structural Biology, Vlaams Instituut voor Biotechnologie, B-1050 Brussel, Belgium.,Department of Physical Chemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, 1000 Ljubljana, Slovenia
| | - Abel Garcia-Pino
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel, B-1050 Brussel, Belgium.,Biologie Structurale et Biophysique, IBMM-DBM, Université Libre de Bruxelles (ULB), B-6041 Gosselies, Belgium
| | - Sarah Haesaerts
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel, B-1050 Brussel, Belgium.,Molecular Recognition Unit, Center for Structural Biology, Vlaams Instituut voor Biotechnologie, B-1050 Brussel, Belgium
| | - Dukas Jurenas
- Biologie Structurale et Biophysique, IBMM-DBM, Université Libre de Bruxelles (ULB), B-6041 Gosselies, Belgium
| | - Kenn Gerdes
- Department of Biology, University of Copenhagen, DK-2200 Copenhagen, Denmark
| | - Jurij Lah
- Department of Physical Chemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, 1000 Ljubljana, Slovenia
| | - Remy Loris
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel, B-1050 Brussel, Belgium.,Molecular Recognition Unit, Center for Structural Biology, Vlaams Instituut voor Biotechnologie, B-1050 Brussel, Belgium
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12
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Identification and characterization of chromosomal relBE toxin-antitoxin locus in Streptomyces cattleya DSM46488. Sci Rep 2016; 6:32047. [PMID: 27534445 PMCID: PMC4989188 DOI: 10.1038/srep32047] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2016] [Accepted: 08/01/2016] [Indexed: 01/25/2023] Open
Abstract
The relBE family of Type II toxin-antitoxin (TA) systems have been widely reported in bacteria but none in Streptomyces. With the conserved domain searches for TA pairs in the sequenced Streptomyces genomes, we identified two putative relBE loci, relBE1sca and relBE2sca, on the chromosome of Streptomyces cattleya DSM 46488. Overexpression of the S. cattleya toxin RelE2sca caused severe growth inhibition of E. coli and S. lividans, but RelE1sca had no toxic effect. The toxicity of RelE2sca could be abolished by the co-expression of its cognate RelB2sca antitoxin. Moreover, the RelBE2sca complex, or the antitoxin RelB2sca alone, specifically interacted with the relBE2sca operon and repressed its transcription. The relBE2sca operon transcription was induced under osmotic stress, along with the ClpP proteinase genes. The subsequent in vivo analysis showed that the antitoxin was degraded by ClpP. Interestingly, the E. coli antitoxin RelBeco was able to alleviate the toxicity of S. cattleya RelE2sca while the mutant RelB2sca(N61V&M68L) but not the wild type could alleviate the toxicity of E. coli RelEeco as well. The experimental demonstration of the relBEsca locus might be helpful to investigate the key roles of type II TA systems in Streptomyces physiology and environmental stress responses.
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13
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Garcia-Pino A, De Gieter S, Talavera A, De Greve H, Efremov RG, Loris R. An intrinsically disordered entropic switch determines allostery in Phd-Doc regulation. Nat Chem Biol 2016; 12:490-6. [PMID: 27159580 DOI: 10.1038/nchembio.2078] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Accepted: 03/11/2016] [Indexed: 12/31/2022]
Abstract
Conditional cooperativity is a common mechanism involved in transcriptional regulation of prokaryotic type II toxin-antitoxin operons and is intricately related to bacterial persistence. It allows the toxin component of a toxin-antitoxin module to act as a co-repressor at low doses of toxin as compared to antitoxin. When toxin level exceeds a certain threshold, however, the toxin becomes a de-repressor. Most antitoxins contain an intrinsically disordered region (IDR) that typically is involved in toxin neutralization and repressor complex formation. To address how the antitoxin IDR is involved in transcription regulation, we studied the phd-doc operon from bacteriophage P1. We provide evidence that the IDR of Phd provides an entropic barrier precluding full operon repression in the absence of Doc. Binding of Doc results in a cooperativity switch and consequent strong operon repression, enabling context-specific modulation of the regulatory process. Variations of this theme are likely to be a common mechanism in the autoregulation of bacterial operons that involve intrinsically disordered regions.
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Affiliation(s)
- Abel Garcia-Pino
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel (VUB), Brussels, Belgium.,Biologie Structurale et Biophysique, Université Libre de Bruxelles (ULB), Gosselies, Belgium
| | - Steven De Gieter
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel (VUB), Brussels, Belgium.,Structural Biology Research Center, VIB, Brussels, Belgium
| | - Ariel Talavera
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel (VUB), Brussels, Belgium.,Structural Biology Research Center, VIB, Brussels, Belgium
| | - Henri De Greve
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel (VUB), Brussels, Belgium.,Structural Biology Research Center, VIB, Brussels, Belgium
| | - Rouslan G Efremov
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel (VUB), Brussels, Belgium.,Structural Biology Research Center, VIB, Brussels, Belgium
| | - Remy Loris
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel (VUB), Brussels, Belgium.,Structural Biology Research Center, VIB, Brussels, Belgium
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14
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Zorzini V, Mernik A, Lah J, Sterckx YGJ, De Jonge N, Garcia-Pino A, De Greve H, Versées W, Loris R. Substrate Recognition and Activity Regulation of the Escherichia coli mRNA Endonuclease MazF. J Biol Chem 2016; 291:10950-60. [PMID: 27026704 DOI: 10.1074/jbc.m116.715912] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Indexed: 11/06/2022] Open
Abstract
Escherichia coli MazF (EcMazF) is the archetype of a large family of ribonucleases involved in bacterial stress response. The crystal structure of EcMazF in complex with a 7-nucleotide substrate mimic explains the relaxed substrate specificity of the E. coli enzyme relative to its Bacillus subtilis counterpart and provides a framework for rationalizing specificity in this enzyme family. In contrast to a conserved mode of substrate recognition and a conserved active site, regulation of enzymatic activity by the antitoxin EcMazE diverges from its B. subtilis homolog. Central in this regulation is an EcMazE-induced double conformational change as follows: a rearrangement of a crucial active site loop and a relative rotation of the two monomers in the EcMazF dimer. Both are induced by the C-terminal residues Asp-78-Trp-82 of EcMazE, which are also responsible for strong negative cooperativity in EcMazE-EcMazF binding. This situation shows unexpected parallels to the regulation of the F-plasmid CcdB activity by CcdA and further supports a common ancestor despite the different activities of the MazF and CcdB toxins. In addition, we pinpoint the origin of the lack of activity of the E24A point mutant of EcMazF in its inability to support the substrate binding-competent conformation of EcMazF.
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Affiliation(s)
- Valentina Zorzini
- From the Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium, the Structural Biology Research Center, VIB, Pleinlaan 2, B-1050 Brussels, Belgium
| | - Andrej Mernik
- the Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, 1000 Ljubljana, Slovenia, and
| | - Jurij Lah
- the Faculty of Chemistry and Chemical Technology, University of Ljubljana, Večna pot 113, 1000 Ljubljana, Slovenia, and
| | - Yann G J Sterckx
- From the Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium, the Structural Biology Research Center, VIB, Pleinlaan 2, B-1050 Brussels, Belgium
| | - Natalie De Jonge
- From the Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium, the Structural Biology Research Center, VIB, Pleinlaan 2, B-1050 Brussels, Belgium
| | - Abel Garcia-Pino
- From the Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium, the Biologie Structurale et Biophysique, Université Libre de Bruxelles, Rue des Professeurs Jeener et Brachet 12, 6041 B-Gosselies, Belgium
| | - Henri De Greve
- From the Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium, the Structural Biology Research Center, VIB, Pleinlaan 2, B-1050 Brussels, Belgium
| | - Wim Versées
- From the Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium, the Structural Biology Research Center, VIB, Pleinlaan 2, B-1050 Brussels, Belgium
| | - Remy Loris
- From the Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium, the Structural Biology Research Center, VIB, Pleinlaan 2, B-1050 Brussels, Belgium,
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15
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Sterckx YGJ, Jové T, Shkumatov AV, Garcia-Pino A, Geerts L, De Kerpel M, Lah J, De Greve H, Van Melderen L, Loris R. A unique hetero-hexadecameric architecture displayed by the Escherichia coli O157 PaaA2-ParE2 antitoxin-toxin complex. J Mol Biol 2016; 428:1589-603. [PMID: 26996937 DOI: 10.1016/j.jmb.2016.03.007] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2015] [Revised: 03/08/2016] [Accepted: 03/09/2016] [Indexed: 10/24/2022]
Abstract
Many bacterial pathogens modulate their metabolic activity, virulence and pathogenicity through so-called "toxin-antitoxin" (TA) modules. The genome of the human pathogen Escherichia coli O157 contains two three-component TA modules related to the known parDE module. Here, we show that the toxin EcParE2 maps in a branch of the RelE/ParE toxin superfamily that is distinct from the branches that contain verified gyrase and ribosome inhibitors. The structure of EcParE2 closely resembles that of Caulobacter crescentus ParE but shows a distinct pattern of conserved surface residues, in agreement with its apparent inability to interact with GyrA. The antitoxin EcPaaA2 is characterized by two α-helices (H1 and H2) that serve as molecular recognition elements to wrap itself around EcParE2. Both EcPaaA2 H1 and H2 are required to sustain a high-affinity interaction with EcParE2 and for the inhibition of EcParE2-mediated killing in vivo. Furthermore, evidence demonstrates that EcPaaA2 H2, but not H1, determines specificity for EcParE2. The initially formed EcPaaA2-EcParE2 heterodimer then assembles into a hetero-hexadecamer, which is stable in solution and is formed in a highly cooperative manner. Together these findings provide novel data on quaternary structure, TA interactions and activity of a hitherto poorly characterized family of TA modules.
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Affiliation(s)
- Yann G-J Sterckx
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussel, Belgium; Structural Biology Research Centre, VIB, Pleinlaan 2, B-1050 Brussel, Belgium
| | - Thomas Jové
- Génétique et Physiologie Bactérienne, Faculté des Sciences, Université Libre de Bruxelles (ULB), 12 rue des Professeurs Jeener et Brachet, B-6041 Gosselies, Belgium
| | - Alexander V Shkumatov
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussel, Belgium; Structural Biology Research Centre, VIB, Pleinlaan 2, B-1050 Brussel, Belgium
| | - Abel Garcia-Pino
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussel, Belgium; Structural Biology Research Centre, VIB, Pleinlaan 2, B-1050 Brussel, Belgium; Génétique et Physiologie Bactérienne, Faculté des Sciences, Université Libre de Bruxelles (ULB), 12 rue des Professeurs Jeener et Brachet, B-6041 Gosselies, Belgium
| | - Lieselotte Geerts
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussel, Belgium
| | - Maia De Kerpel
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussel, Belgium; Structural Biology Research Centre, VIB, Pleinlaan 2, B-1050 Brussel, Belgium
| | - Jurij Lah
- Department of Physical Chemistry, Faculty of Chemistry and Chemical Technology, University of Ljubljana, 1000 Ljubljana, Slovenia
| | - Henri De Greve
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussel, Belgium; Structural Biology Research Centre, VIB, Pleinlaan 2, B-1050 Brussel, Belgium
| | - Laurence Van Melderen
- Génétique et Physiologie Bactérienne, Faculté des Sciences, Université Libre de Bruxelles (ULB), 12 rue des Professeurs Jeener et Brachet, B-6041 Gosselies, Belgium
| | - Remy Loris
- Structural Biology Brussels, Department of Biotechnology, Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussel, Belgium; Structural Biology Research Centre, VIB, Pleinlaan 2, B-1050 Brussel, Belgium.
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