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Huang W, Markantonis JE, Yin C, Pozdol JR, Briley KP, Fallon JT. Local Genomic Surveillance of Invasive Streptococcus pyogenes in Eastern North Carolina (ENC) in 2022-2023. Int J Mol Sci 2024; 25:8179. [PMID: 39125755 PMCID: PMC11311789 DOI: 10.3390/ijms25158179] [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: 04/24/2024] [Revised: 07/13/2024] [Accepted: 07/15/2024] [Indexed: 08/12/2024] Open
Abstract
The recent increase in Group A Streptococcus (GAS) incidences in several countries across Europe and some areas of the Unites States (U.S.) has raised concerns. To understand GAS diversity and prevalence, we conducted a local genomic surveillance in Eastern North Carolina (ENC) in 2022-2023 with 95 isolates and compared its results to those of the existing national genomic surveillance in the U.S. in 2015-2021 with 13,064 isolates. We observed their epidemiological changes before and during the COVID-19 pandemic and detected a unique sub-lineage in ENC among the most common invasive GAS strain, ST28/emm1. We further discovered a multiple-copy insertion sequence, ISLgar5, in ST399/emm77 and its single-copy variants in some other GAS strains. We discovered ISLgar5 was linked to a Tn5801-like tetM-carrying integrative and conjugative element, and its copy number was associated with an ermT-carrying pRW35-like plasmid. The dynamic insertions of ISLgar5 may play a vital role in genome fitness and adaptation, driving GAS evolution relevant to antimicrobial resistance and potentially GAS virulence.
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Affiliation(s)
- Weihua Huang
- Department of Pathology and Laboratory Medicine, Brody School of Medicine, Eastern Carolina University, Greenville, NC 27834, USA; (J.E.M.); (C.Y.); (J.R.P.); (K.P.B.); (J.T.F.)
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2
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Kirsch JM, Hryckowian AJ, Duerkop BA. A metagenomics pipeline reveals insertion sequence-driven evolution of the microbiota. Cell Host Microbe 2024; 32:739-754.e4. [PMID: 38565143 PMCID: PMC11081829 DOI: 10.1016/j.chom.2024.03.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Revised: 02/06/2024] [Accepted: 03/08/2024] [Indexed: 04/04/2024]
Abstract
Insertion sequence (IS) elements are mobile genetic elements in bacterial genomes that support adaptation. We developed a database of IS elements coupled to a computational pipeline that identifies IS element insertions in the microbiota. We discovered that diverse IS elements insert into the genomes of intestinal bacteria regardless of human host lifestyle. These insertions target bacterial accessory genes that aid in their adaptation to unique environmental conditions. Using IS expansion in Bacteroides, we show that IS activity leads to the insertion of "hot spots" in accessory genes. We show that IS insertions are stable and can be transferred between humans. Extreme environmental perturbations force IS elements to fall out of the microbiota, and many fail to rebound following homeostasis. Our work shows that IS elements drive bacterial genome diversification within the microbiota and establishes a framework for understanding how strain-level variation within the microbiota impacts human health.
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Affiliation(s)
- Joshua M Kirsch
- Department of Immunology and Microbiology, University of Colorado Anschutz Medical Campus, School of Medicine, Aurora, CO 80045, USA
| | - Andrew J Hryckowian
- Department of Medicine, Division of Gastroenterology and Hepatology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, USA; Department of Medical Microbiology & Immunology, University of Wisconsin School of Medicine and Public Health, Madison, WI 53706, USA
| | - Breck A Duerkop
- Department of Immunology and Microbiology, University of Colorado Anschutz Medical Campus, School of Medicine, Aurora, CO 80045, USA.
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3
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Kirsch JM, Hryckowian AJ, Duerkop BA. A metagenomics pipeline reveals insertion sequence-driven evolution of the microbiota. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.10.06.561241. [PMID: 37873088 PMCID: PMC10592638 DOI: 10.1101/2023.10.06.561241] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2023]
Abstract
Insertion sequence (IS) elements are mobile genetic elements in bacterial genomes that support adaptation. We developed a database of IS elements coupled to a computational pipeline that identifies IS element insertions in the microbiota. We discovered that diverse IS elements insert into the genomes of intestinal bacteria regardless of human host lifestyle. These insertions target bacterial accessory genes that aid in their adaptation to unique environmental conditions. Using IS expansion in Bacteroides, we show that IS activity leads to insertion "hot spots" in accessory genes. We show that IS insertions are stable and can be transferred between humans. Extreme environmental perturbations force IS elements to fall out of the microbiota and many fail to rebound following homeostasis. Our work shows that IS elements drive bacterial genome diversification within the microbiota and establishes a framework for understanding how strain level variation within the microbiota impacts human health.
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Affiliation(s)
- Joshua M. Kirsch
- Department of Immunology and Microbiology, University of Colorado - Anschutz Medical Campus, School of Medicine, Aurora, Colorado, 80045, USA
| | - Andrew J. Hryckowian
- Department of Medicine, Division of Gastroenterology and Hepatology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, 53706, USA
- Department of Medical Microbiology & Immunology, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, 53706, USA
| | - Breck A. Duerkop
- Department of Immunology and Microbiology, University of Colorado - Anschutz Medical Campus, School of Medicine, Aurora, Colorado, 80045, USA
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4
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Li W, He Z, Di W, Xu W, Li Y, Sun B. Transposition mechanism of IS Apl1-the determinant of colistin resistance dissemination. Antimicrob Agents Chemother 2024; 68:e0123123. [PMID: 38289082 PMCID: PMC10916398 DOI: 10.1128/aac.01231-23] [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: 09/25/2023] [Accepted: 12/18/2023] [Indexed: 03/07/2024] Open
Abstract
Multidrug-resistant Enterobacteriaceae, a prominent family of gram-negative pathogenic bacteria, causes a wide range of severe diseases. Strains carrying the mobile colistin resistance (mcr-1) gene show resistance to polymyxin, the last line of defense against multidrug-resistant gram-negative bacteria. However, the transmission of mcr-1 is not well understood. In this study, genomes of mcr-1-positive strains were obtained from the NCBI database, revealing their widespread distribution in China. We also showed that ISApl1, a crucial factor in mcr-1 transmission, is capable of self-transposition. Moreover, the self-cyclization of ISApl1 is mediated by its own encoded transposase. The electrophoretic mobility shift assay experiment validated that the transposase can bind to the inverted repeats (IRs) on both ends, facilitating the cyclization of ISApl1. Through knockout or shortening of IRs at both ends of ISApl1, we demonstrated that the cyclization of ISApl1 is dependent on the sequences of the IRs at both ends. Simultaneously, altering the ATCG content of the bases at both ends of ISApl1 can impact the excision rate by modifying the binding ability between IRs and ISAPL1. Finally, we showed that heat-unstable nucleoid protein (HU) can inhibit ISApl1 transposition by binding to the IRs and preventing ISAPL1 binding and expression. In conclusion, the regulation of ISApl1-self-circling is predominantly controlled by the inverted repeat (IR) sequence and the HU protein. This molecular mechanism deepens our comprehension of mcr-1 dissemination.
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Affiliation(s)
- Wei Li
- Department of Oncology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui, China
| | - Zhien He
- Department of Oncology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui, China
| | - Wei Di
- Department of Oncology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui, China
| | - Weifeng Xu
- Department of Oncology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui, China
| | - Yujie Li
- Department of Oncology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui, China
| | - Baolin Sun
- Department of Oncology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui, China
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5
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Lannes L, Furman CM, Hickman AB, Dyda F. Zinc-finger BED domains drive the formation of the active Hermes transpososome by asymmetric DNA binding. Nat Commun 2023; 14:4470. [PMID: 37491363 PMCID: PMC10368747 DOI: 10.1038/s41467-023-40210-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2022] [Accepted: 07/18/2023] [Indexed: 07/27/2023] Open
Abstract
The Hermes DNA transposon is a member of the eukaryotic hAT superfamily, and its transposase forms a ring-shaped tetramer of dimers. Our investigation, combining biochemical, crystallography and cryo-electron microscopy, and in-cell assays, shows that the full-length Hermes octamer extensively interacts with its transposon left-end through multiple BED domains of three Hermes protomers contributed by three dimers explaining the role of the unusual higher-order assembly. By contrast, the right-end is bound to no BED domains at all. Thus, this work supports a model in which Hermes multimerizes to gather enough BED domains to find its left-end among the abundant genomic DNA, facilitating the subsequent interaction with the right-end.
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Affiliation(s)
- Laurie Lannes
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Christopher M Furman
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Alison B Hickman
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Fred Dyda
- Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, 20892, USA.
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6
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Widen SA, Bes IC, Koreshova A, Pliota P, Krogull D, Burga A. Virus-like transposons cross the species barrier and drive the evolution of genetic incompatibilities. Science 2023; 380:eade0705. [PMID: 37384706 DOI: 10.1126/science.ade0705] [Citation(s) in RCA: 15] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Accepted: 05/17/2023] [Indexed: 07/01/2023]
Abstract
Horizontal gene transfer, the movement of genetic material between species, has been reported across all major eukaryotic lineages. However, the underlying mechanisms of transfer and their impact on genome evolution are still poorly understood. While studying the evolutionary origin of a selfish element in the nematode Caenorhabditis briggsae, we discovered that Mavericks, ancient virus-like transposons related to giant viruses and virophages, are one of the long-sought vectors of horizontal gene transfer. We found that Mavericks gained a novel herpesvirus-like fusogen in nematodes, leading to the widespread exchange of cargo genes between extremely divergent species, bypassing sexual and genetic barriers spanning hundreds of millions of years. Our results show how the union between viruses and transposons causes horizontal gene transfer and ultimately genetic incompatibilities in natural populations.
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Affiliation(s)
- Sonya A Widen
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), 1030 Vienna, Austria
| | - Israel Campo Bes
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), 1030 Vienna, Austria
| | - Alevtina Koreshova
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), 1030 Vienna, Austria
- Vienna BioCenter PhD Program, Doctoral School of the University of Vienna and Medical University of Vienna, A-1030 Vienna, Austria
| | - Pinelopi Pliota
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), 1030 Vienna, Austria
| | - Daniel Krogull
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), 1030 Vienna, Austria
- Vienna BioCenter PhD Program, Doctoral School of the University of Vienna and Medical University of Vienna, A-1030 Vienna, Austria
| | - Alejandro Burga
- Institute of Molecular Biotechnology of the Austrian Academy of Sciences (IMBA), Vienna BioCenter (VBC), 1030 Vienna, Austria
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7
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Kirsch JM, Ely S, Stellfox ME, Hullahalli K, Luong P, Palmer KL, Van Tyne D, Duerkop BA. Targeted IS-element sequencing uncovers transposition dynamics during selective pressure in enterococci. PLoS Pathog 2023; 19:e1011424. [PMID: 37267422 PMCID: PMC10266640 DOI: 10.1371/journal.ppat.1011424] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Revised: 06/14/2023] [Accepted: 05/15/2023] [Indexed: 06/04/2023] Open
Abstract
Insertion sequences (IS) are simple transposons implicated in the genome evolution of diverse pathogenic bacterial species. Enterococci have emerged as important human intestinal pathogens with newly adapted virulence potential and antibiotic resistance. These genetic features arose in tandem with large-scale genome evolution mediated by mobile elements. Pathoadaptation in enterococci is thought to be mediated in part by the IS element IS256 through gene inactivation and recombination events. However, the regulation of IS256 and the mechanisms controlling its activation are not well understood. Here, we adapt an IS256-specfic deep sequencing method to describe how chronic lytic phage infection drives widespread diversification of IS256 in E. faecalis and how antibiotic exposure is associated with IS256 diversification in E. faecium during a clinical human infection. We show through comparative genomics that IS256 is primarily found in hospital-adapted enterococcal isolates. Analyses of IS256 transposase gene levels reveal that IS256 mobility is regulated at the transcriptional level by multiple mechanisms in E. faecalis, indicating tight control of IS256 activation in the absence of selective pressure. Our findings reveal that stressors such as phages and antibiotic exposure drives rapid genome-scale transposition in the enterococci. IS256 diversification can therefore explain how selective pressures mediate evolution of the enterococcal genome, ultimately leading to the emergence of dominant nosocomial lineages that threaten human health.
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Affiliation(s)
- Joshua M. Kirsch
- Department of Immunology and Microbiology, University of Colorado–Anschutz Medical Campus, School of Medicine, Aurora, Colorado, United States of America
| | - Shannon Ely
- Department of Immunology and Microbiology, University of Colorado–Anschutz Medical Campus, School of Medicine, Aurora, Colorado, United States of America
| | - Madison E. Stellfox
- Department of Medicine, Division of Infectious Diseases, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Karthik Hullahalli
- Department of Biological Sciences, University of Texas at Dallas, Richardson, Texas, United States of America
| | - Phat Luong
- Department of Immunology and Microbiology, University of Colorado–Anschutz Medical Campus, School of Medicine, Aurora, Colorado, United States of America
| | - Kelli L. Palmer
- Department of Biological Sciences, University of Texas at Dallas, Richardson, Texas, United States of America
| | - Daria Van Tyne
- Department of Medicine, Division of Infectious Diseases, University of Pittsburgh, Pittsburgh, Pennsylvania, United States of America
| | - Breck A. Duerkop
- Department of Immunology and Microbiology, University of Colorado–Anschutz Medical Campus, School of Medicine, Aurora, Colorado, United States of America
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8
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Spínola-Amilibia M, Araújo-Bazán L, de la Gándara Á, Berger JM, Arias-Palomo E. IS21 family transposase cleaved donor complex traps two right-handed superhelical crossings. Nat Commun 2023; 14:2335. [PMID: 37087515 PMCID: PMC10122671 DOI: 10.1038/s41467-023-38071-x] [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: 09/23/2022] [Accepted: 04/14/2023] [Indexed: 04/24/2023] Open
Abstract
Transposases are ubiquitous enzymes that catalyze DNA rearrangement events with broad impacts on gene expression, genome evolution, and the spread of drug-resistance in bacteria. Here, we use biochemical and structural approaches to define the molecular determinants by which IstA, a transposase present in the widespread IS21 family of mobile elements, catalyzes efficient DNA transposition. Solution studies show that IstA engages the transposon terminal sequences to form a high-molecular weight complex and promote DNA integration. A 3.4 Å resolution structure of the transposase bound to transposon ends corroborates our biochemical findings and reveals that IstA self-assembles into a highly intertwined tetramer that synapses two supercoiled terminal inverted repeats. The three-dimensional organization of the IstA•DNA cleaved donor complex reveals remarkable similarities with retroviral integrases and classic transposase systems, such as Tn7 and bacteriophage Mu, and provides insights into IS21 transposition.
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Affiliation(s)
- Mercedes Spínola-Amilibia
- Department of Structural & Chemical Biology, Centro de Investigaciones Biológicas Margarita Salas, CSIC, Madrid, 28040, Spain
| | - Lidia Araújo-Bazán
- Department of Structural & Chemical Biology, Centro de Investigaciones Biológicas Margarita Salas, CSIC, Madrid, 28040, Spain
| | - Álvaro de la Gándara
- Department of Structural & Chemical Biology, Centro de Investigaciones Biológicas Margarita Salas, CSIC, Madrid, 28040, Spain
| | - James M Berger
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA
| | - Ernesto Arias-Palomo
- Department of Structural & Chemical Biology, Centro de Investigaciones Biológicas Margarita Salas, CSIC, Madrid, 28040, Spain.
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Shkumatov AV, Aryanpour N, Oger CA, Goossens G, Hallet BF, Efremov RG. Structural insight into Tn3 family transposition mechanism. Nat Commun 2022; 13:6155. [PMID: 36257990 PMCID: PMC9579193 DOI: 10.1038/s41467-022-33871-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Accepted: 10/05/2022] [Indexed: 12/24/2022] Open
Abstract
Transposons are diverse mobile genetic elements that play the critical role as genome architects in all domains of life. Tn3 is a widespread family and among the first identified bacterial transposons famed for their contribution to the dissemination of antibiotic resistance. Transposition within this family is mediated by a large TnpA transposase, which facilitates both transposition and target immunity. Howtever, a structural framework required for understanding the mechanism of TnpA transposition is lacking. Here, we describe the cryo-EM structures of TnpA from Tn4430 in the apo form and paired with transposon ends before and after DNA cleavage and strand transfer. We show that TnpA has an unusual architecture and exhibits a family specific regulatory mechanism involving metamorphic refolding of the RNase H-like catalytic domain. The TnpA structure, constrained by a double dimerization interface, creates a peculiar topology that suggests a specific role for the target DNA in transpososome assembly and activation.
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Affiliation(s)
- Alexander V. Shkumatov
- grid.11486.3a0000000104788040Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Brussels, Belgium ,grid.8767.e0000 0001 2290 8069Structural Biology Brussels, Department of Bioengineering Sciences, Vrije Universiteit Brussel, Brussels, Belgium ,Present Address: Confo Therapeutics, Brussels, Belgium
| | - Nicolas Aryanpour
- grid.7942.80000 0001 2294 713XLouvain Institue of Biomolecular Science and Technology, Université Catholique de Louvain (UCLouvain), Croix du Sud 4/5, 1348 Louvain-la-Neuve, Belgium
| | - Cédric A. Oger
- grid.7942.80000 0001 2294 713XLouvain Institue of Biomolecular Science and Technology, Université Catholique de Louvain (UCLouvain), Croix du Sud 4/5, 1348 Louvain-la-Neuve, Belgium
| | - Gérôme Goossens
- grid.7942.80000 0001 2294 713XLouvain Institue of Biomolecular Science and Technology, Université Catholique de Louvain (UCLouvain), Croix du Sud 4/5, 1348 Louvain-la-Neuve, Belgium ,Present Address: Thermo Fisher Scientific, Seneffe, Belgium
| | - Bernard F. Hallet
- grid.7942.80000 0001 2294 713XLouvain Institue of Biomolecular Science and Technology, Université Catholique de Louvain (UCLouvain), Croix du Sud 4/5, 1348 Louvain-la-Neuve, Belgium
| | - Rouslan G. Efremov
- grid.11486.3a0000000104788040Center for Structural Biology, Vlaams Instituut voor Biotechnologie, Brussels, Belgium ,grid.8767.e0000 0001 2290 8069Structural Biology Brussels, Department of Bioengineering Sciences, Vrije Universiteit Brussel, Brussels, Belgium
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10
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The large bat Helitron DNA transposase forms a compact monomeric assembly that buries and protects its covalently bound 5'-transposon end. Mol Cell 2021; 81:4271-4286.e4. [PMID: 34403695 DOI: 10.1016/j.molcel.2021.07.028] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Revised: 07/23/2021] [Accepted: 07/23/2021] [Indexed: 12/22/2022]
Abstract
Helitrons are widespread eukaryotic DNA transposons that have significantly contributed to genome variability and evolution, in part because of their distinctive, replicative rolling-circle mechanism, which often mobilizes adjacent genes. Although most eukaryotic transposases form oligomers and use RNase H-like domains to break and rejoin double-stranded DNA (dsDNA), Helitron transposases contain a single-stranded DNA (ssDNA)-specific HUH endonuclease domain. Here, we report the cryo-electron microscopy structure of a Helitron transposase bound to the 5'-transposon end, providing insight into its multidomain architecture and function. The monomeric transposase forms a tightly packed assembly that buries the covalently attached cleaved end, protecting it until the second end becomes available. The structure reveals unexpected architectural similarity to TraI, a bacterial relaxase that also catalyzes ssDNA movement. The HUH active site suggests how two juxtaposed tyrosines, a feature of many replication initiators that use HUH nucleases, couple the conformational shift of an α-helix to control strand cleavage and ligation reactions.
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11
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Characterization of the specific DNA-binding properties of Tnp26, the transposase of insertion sequence IS26. J Biol Chem 2021; 297:101165. [PMID: 34487761 PMCID: PMC8477213 DOI: 10.1016/j.jbc.2021.101165] [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: 07/19/2021] [Revised: 08/31/2021] [Accepted: 09/01/2021] [Indexed: 11/21/2022] Open
Abstract
The bacterial insertion sequence (IS) IS26 mobilizes and disseminates antibiotic resistance genes. It differs from bacterial IS that have been studied to date as it exclusively forms cointegrates via either a copy-in (replicative) or a recently discovered targeted conservative mode. To investigate how the Tnp26 transposase recognizes the 14-bp terminal inverted repeats (TIRs) that bound the IS, amino acids in two domains in the N-terminal (amino acids M1-P56) region were replaced. These changes substantially reduced cointegration in both modes. Tnp26 was purified as a maltose-binding fusion protein and shown to bind specifically to dsDNA fragments that included an IS26 TIR. However, Tnp26 with an R49A or a W50A substitution in helix 3 of a predicted trihelical helix-turn-helix domain (amino acids I13-R53) or an F4A or F9A substitution replacing the conserved amino acids in a unique disordered N-terminal domain (amino acids M1-D12) did not bind. The N-terminal M1-P56 fragment also bound to the TIR but only at substantially higher concentrations, indicating that other parts of Tnp26 enhance the binding affinity. The binding site was confined to the internal part of the TIR, and a G to T nucleotide substitution in the TGT at positions 6 to 8 of the TIR that is conserved in most IS26 family members abolished binding of both Tnp26 (M1-M234) and Tnp26 M1-P56 fragment. These findings indicate that the helix-turn-helix and disordered domains of Tnp26 play a role in Tnp26-TIR complex formation. Both domains are conserved in all members of the IS26 family.
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