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Chand MK, Carle V, Anuvind KG, Saikrishnan K. DNA-mediated coupling of ATPase, translocase and nuclease activities of a Type ISP restriction-modification enzyme. Nucleic Acids Res 2020; 48:2594-2603. [PMID: 31974580 PMCID: PMC7049714 DOI: 10.1093/nar/gkaa023] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2019] [Revised: 01/06/2020] [Accepted: 01/13/2020] [Indexed: 12/20/2022] Open
Abstract
Enzymes involved in nucleic acid transactions often have a helicase-like ATPase coordinating and driving their functional activities, but our understanding of the mechanistic details of their coordination is limited. For example, DNA cleavage by the antiphage defense system Type ISP restriction-modification enzyme requires convergence of two such enzymes that are actively translocating on DNA powered by Superfamily 2 ATPases. The ATPase is activated when the enzyme recognizes a DNA target sequence. Here, we show that the activation is a two-stage process of partial ATPase stimulation upon recognition of the target sequence by the methyltransferase and the target recognition domains, and complete stimulation that additionally requires the DNA to interact with the ATPase domain. Mutagenesis revealed that a β-hairpin loop and motif V of the ATPase couples DNA translocation to ATP hydrolysis. Deletion of the loop inhibited translocation, while mutation of motif V slowed the rate of translocation. Both the mutations inhibited the double-strand (ds) DNA cleavage activity of the enzyme. However, a translocating motif V mutant cleaved dsDNA on encountering a translocating wild-type enzyme. Based on these results, we conclude that the ATPase-driven translocation not only brings two nucleases spatially close to catalyze dsDNA break, but that the rate of translocation influences dsDNA cleavage.
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Affiliation(s)
- Mahesh Kumar Chand
- Division of Biology, Indian Institute of Science Education and Research, Pune 411008, India
| | - Vanessa Carle
- Division of Biology, Indian Institute of Science Education and Research, Pune 411008, India
| | - K G Anuvind
- Division of Biology, Indian Institute of Science Education and Research, Pune 411008, India
| | - Kayarat Saikrishnan
- Division of Biology, Indian Institute of Science Education and Research, Pune 411008, India
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2
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Bahhir D, Yalgin C, Ots L, Järvinen S, George J, Naudí A, Krama T, Krams I, Tamm M, Andjelković A, Dufour E, González de Cózar JM, Gerards M, Parhiala M, Pamplona R, Jacobs HT, Jõers P. Manipulating mtDNA in vivo reprograms metabolism via novel response mechanisms. PLoS Genet 2019; 15:e1008410. [PMID: 31584940 PMCID: PMC6795474 DOI: 10.1371/journal.pgen.1008410] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Revised: 10/16/2019] [Accepted: 09/10/2019] [Indexed: 11/18/2022] Open
Abstract
Mitochondria have been increasingly recognized as a central regulatory nexus for multiple metabolic pathways, in addition to ATP production via oxidative phosphorylation (OXPHOS). Here we show that inducing mitochondrial DNA (mtDNA) stress in Drosophila using a mitochondrially-targeted Type I restriction endonuclease (mtEcoBI) results in unexpected metabolic reprogramming in adult flies, distinct from effects on OXPHOS. Carbohydrate utilization was repressed, with catabolism shifted towards lipid oxidation, accompanied by elevated serine synthesis. Cleavage and translocation, the two modes of mtEcoBI action, repressed carbohydrate rmetabolism via two different mechanisms. DNA cleavage activity induced a type II diabetes-like phenotype involving deactivation of Akt kinase and inhibition of pyruvate dehydrogenase, whilst translocation decreased post-translational protein acetylation by cytonuclear depletion of acetyl-CoA (AcCoA). The associated decrease in the concentrations of ketogenic amino acids also produced downstream effects on physiology and behavior, attributable to decreased neurotransmitter levels. We thus provide evidence for novel signaling pathways connecting mtDNA to metabolism, distinct from its role in supporting OXPHOS. Mitochondria, subcellular compartments (organelles) found in virtually all eukaryotes, contain DNA which is believed to be a remnant of an ancestral bacterial genome. They are best known for the synthesis of the universal energy carrier ATP, but also serve as the hub of various metabolic and signalling pathways. We report here that mtDNA integrity is linked to a signaling system that influences metabolic fuel selection between fats and sugars. By disrupting mtDNA in the fruit fly we induced a strong shift towards lipid catabolism. This was caused both by a widespread decrease in post-translational acetylation of proteins, as well as specific inhibition of the machinery that transports glucose into cells across the plasma membrane. This phenomenon is very similar to the pathophysiology of diabetes, where the inability to transport glucose to cells is considered the main hallmark of the disease. Moreover, decreased protein acetylation was associated with lower levels of certain neurotransmitters, causing various effects on feeding and fertility. Our discovery reveals an unexpected role for mtDNA stability in regulating global metabolic balance and suggests that it could be instrumental in pandemic metabolic disorders such as diabetes and obesity.
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Affiliation(s)
- Diana Bahhir
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
| | - Cagri Yalgin
- Institute of Biotechnology, University of Helsinki, Helsinki, Finland
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
| | - Liina Ots
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
| | - Sampsa Järvinen
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
| | - Jack George
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
| | - Alba Naudí
- Experimental Medicine Department, University of Lleida-Institute for Research in Biomedicine of Lleida (UdL-IRBLLEIDA), Lleida, Spain
| | - Tatjana Krama
- Institute of Ecology and Earth Sciences, University of Tartu, Tartu, Estonia
- Department of Plant Health, Institute of Agricultural and Environmental Sciences, Estonian University of Life Science, Tartu, Estonia
| | - Indrikis Krams
- Institute of Ecology and Earth Sciences, University of Tartu, Tartu, Estonia
- Department of Zoology and Animal Ecology, Faculty of Biology, University of Latvia, Rīga, Latvia
- Department of Biotechnology, Daugavpils University, Daugavpils, Latvia
| | - Mairi Tamm
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
| | - Ana Andjelković
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
| | - Eric Dufour
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
| | | | - Mike Gerards
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
- Maastricht Centre for Systems Biology (MaCSBio), Maastricht University, Maastricht, The Netherlands
| | - Mikael Parhiala
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
| | - Reinald Pamplona
- Experimental Medicine Department, University of Lleida-Institute for Research in Biomedicine of Lleida (UdL-IRBLLEIDA), Lleida, Spain
| | - Howard T. Jacobs
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
| | - Priit Jõers
- Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
- Faculty of Medicine and Health Technology, Tampere University, Tampere, Finland
- * E-mail:
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3
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Kanwar N, Roberts GA, Cooper LP, Stephanou AS, Dryden DTF. The evolutionary pathway from a biologically inactive polypeptide sequence to a folded, active structural mimic of DNA. Nucleic Acids Res 2016; 44:4289-303. [PMID: 27095198 PMCID: PMC4872106 DOI: 10.1093/nar/gkw234] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Accepted: 03/24/2016] [Indexed: 11/13/2022] Open
Abstract
The protein Ocr (overcome classical restriction) from bacteriophage T7 acts as a mimic of DNA and inhibits all Type I restriction/modification (RM) enzymes. Ocr is a homodimer of 116 amino acids and adopts an elongated structure that resembles the shape of a bent 24 bp DNA molecule. Each monomer includes 34 acidic residues and only six basic residues. We have delineated the mimicry of Ocr by focusing on the electrostatic contribution of its negatively charged amino acids using directed evolution of a synthetic form of Ocr, termed pocr, in which all of the 34 acidic residues were substituted for a neutral amino acid. In vivo analyses confirmed that pocr did not display any antirestriction activity. Here, we have subjected the gene encoding pocr to several rounds of directed evolution in which codons for the corresponding acidic residues found in Ocr were specifically re-introduced. An in vivo selection assay was used to detect antirestriction activity after each round of mutation. Our results demonstrate the variation in importance of the acidic residues in regions of Ocr corresponding to different parts of the DNA target which it is mimicking and for the avoidance of deleterious effects on the growth of the host.
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Affiliation(s)
- Nisha Kanwar
- EaStCHEM School of Chemistry, University of Edinburgh, The King's Buildings, Edinburgh EH9 3FJ, UK
| | - Gareth A Roberts
- EaStCHEM School of Chemistry, University of Edinburgh, The King's Buildings, Edinburgh EH9 3FJ, UK
| | - Laurie P Cooper
- EaStCHEM School of Chemistry, University of Edinburgh, The King's Buildings, Edinburgh EH9 3FJ, UK
| | - Augoustinos S Stephanou
- EaStCHEM School of Chemistry, University of Edinburgh, The King's Buildings, Edinburgh EH9 3FJ, UK
| | - David T F Dryden
- EaStCHEM School of Chemistry, University of Edinburgh, The King's Buildings, Edinburgh EH9 3FJ, UK
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4
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Simons M, Diffin FM, Szczelkun MD. ClpXP protease targets long-lived DNA translocation states of a helicase-like motor to cause restriction alleviation. Nucleic Acids Res 2014; 42:12082-91. [PMID: 25260590 PMCID: PMC4231737 DOI: 10.1093/nar/gku851] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
We investigated how Escherichia coli ClpXP targets the helicase-nuclease (HsdR) subunit of the bacterial Type I restriction–modification enzyme EcoKI during restriction alleviation (RA). RA is a temporary reduction in endonuclease activity that occurs when Type I enzymes bind unmodified recognition sites on the host genome. These conditions arise upon acquisition of a new system by a naïve host, upon generation of new sites by genome rearrangement/mutation or during homologous recombination between hemimethylated DNA. Using recombinant DNA and proteins in vitro, we demonstrate that ClpXP targets EcoKI HsdR during dsDNA translocation on circular DNA but not on linear DNA. Protein roadblocks did not activate HsdR proteolysis. We suggest that DNA translocation lifetime, which is elevated on circular DNA relative to linear DNA, is important to RA. To identify the ClpX degradation tag (degron) in HsdR, we used bioinformatics and biochemical assays to design N- and C-terminal mutations that were analysed in vitro and in vivo. None of the mutants produced a phenotype consistent with loss of the degron, suggesting an as-yet-unidentified recognition pathway. We note that an EcoKI nuclease mutant still produces cell death in a clpx− strain, consistent with DNA damage induced by unregulated motor activity.
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Affiliation(s)
- Michelle Simons
- DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
| | - Fiona M Diffin
- DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
| | - Mark D Szczelkun
- DNA-Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
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5
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Loenen WAM, Dryden DTF, Raleigh EA, Wilson GG. Type I restriction enzymes and their relatives. Nucleic Acids Res 2014; 42:20-44. [PMID: 24068554 PMCID: PMC3874165 DOI: 10.1093/nar/gkt847] [Citation(s) in RCA: 171] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Revised: 08/26/2013] [Accepted: 08/29/2013] [Indexed: 12/24/2022] Open
Abstract
Type I restriction enzymes (REases) are large pentameric proteins with separate restriction (R), methylation (M) and DNA sequence-recognition (S) subunits. They were the first REases to be discovered and purified, but unlike the enormously useful Type II REases, they have yet to find a place in the enzymatic toolbox of molecular biologists. Type I enzymes have been difficult to characterize, but this is changing as genome analysis reveals their genes, and methylome analysis reveals their recognition sequences. Several Type I REases have been studied in detail and what has been learned about them invites greater attention. In this article, we discuss aspects of the biochemistry, biology and regulation of Type I REases, and of the mechanisms that bacteriophages and plasmids have evolved to evade them. Type I REases have a remarkable ability to change sequence specificity by domain shuffling and rearrangements. We summarize the classic experiments and observations that led to this discovery, and we discuss how this ability depends on the modular organizations of the enzymes and of their S subunits. Finally, we describe examples of Type II restriction-modification systems that have features in common with Type I enzymes, with emphasis on the varied Type IIG enzymes.
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Affiliation(s)
- Wil A. M. Loenen
- Leiden University Medical Center, P.O. Box 9600, 2300 RC, Leiden, The Netherlands, EastChem School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9, 3JJ, Scotland, UK and New England Biolabs Inc., 240 County Road Ipswich, MA 01938-2723, USA
| | - David T. F. Dryden
- Leiden University Medical Center, P.O. Box 9600, 2300 RC, Leiden, The Netherlands, EastChem School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9, 3JJ, Scotland, UK and New England Biolabs Inc., 240 County Road Ipswich, MA 01938-2723, USA
| | - Elisabeth A. Raleigh
- Leiden University Medical Center, P.O. Box 9600, 2300 RC, Leiden, The Netherlands, EastChem School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9, 3JJ, Scotland, UK and New England Biolabs Inc., 240 County Road Ipswich, MA 01938-2723, USA
| | - Geoffrey G. Wilson
- Leiden University Medical Center, P.O. Box 9600, 2300 RC, Leiden, The Netherlands, EastChem School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9, 3JJ, Scotland, UK and New England Biolabs Inc., 240 County Road Ipswich, MA 01938-2723, USA
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6
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Roles for Helicases as ATP-Dependent Molecular Switches. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 767:225-44. [PMID: 23161014 DOI: 10.1007/978-1-4614-5037-5_11] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
On the basis of the familial name, a "helicase" might be expected to have an enzymatic activity that unwinds duplex polynucleotides to form single strands. A more encompassing taxonomy that captures alternative enzymatic roles has defined helicases as a sub-class of molecular motors that move directionally and processively along nucleic acids, the so-called "translocases". However, even this definition may be limiting in capturing the full scope of helicase mechanism and activity. Discussed here is another, alternative view of helicases-as machines which couple NTP-binding and hydrolysis to changes in protein conformation to resolve stable nucleoprotein assembly states. This "molecular switch" role differs from the classical view of helicases as molecular motors in that only a single catalytic NTPase cycle may be involved. This is illustrated using results obtained with the DEAD-box family of RNA helicases and with a model bacterial system, the ATP-dependent Type III restriction-modification enzymes. Further examples are discussed and illustrate the wide-ranging examples of molecular switches in genome metabolism.
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7
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Roberts GA, Chen K, Cooper LP, White JH, Blakely GW, Dryden DTF. Removal of a frameshift between the hsdM and hsdS genes of the EcoKI Type IA DNA restriction and modification system produces a new type of system and links the different families of Type I systems. Nucleic Acids Res 2012; 40:10916-24. [PMID: 23002145 PMCID: PMC3510504 DOI: 10.1093/nar/gks876] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The EcoKI DNA methyltransferase is a trimeric protein comprised of two modification subunits (M) and one sequence specificity subunit (S). This enzyme forms the core of the EcoKI restriction/modification (RM) enzyme. The 3' end of the gene encoding the M subunit overlaps by 1 nt the start of the gene for the S subunit. Translation from the two different open reading frames is translationally coupled. Mutagenesis to remove the frameshift and fuse the two subunits together produces a functional RM enzyme in vivo with the same properties as the natural EcoKI system. The fusion protein can be purified and forms an active restriction enzyme upon addition of restriction subunits and of additional M subunit. The Type I RM systems are grouped into families, IA to IE, defined by complementation, hybridization and sequence similarity. The fusion protein forms an evolutionary intermediate form lying between the Type IA family of RM enzymes and the Type IB family of RM enzymes which have the frameshift located at a different part of the gene sequence.
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Affiliation(s)
- Gareth A Roberts
- EastChem School of Chemistry, The University of Edinburgh, The King's Buildings, Edinburgh, EH9 3JJ, UK
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8
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Roberts GA, Stephanou AS, Kanwar N, Dawson A, Cooper LP, Chen K, Nutley M, Cooper A, Blakely GW, Dryden DTF. Exploring the DNA mimicry of the Ocr protein of phage T7. Nucleic Acids Res 2012; 40:8129-43. [PMID: 22684506 PMCID: PMC3439906 DOI: 10.1093/nar/gks516] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2012] [Revised: 05/07/2012] [Accepted: 05/09/2012] [Indexed: 11/30/2022] Open
Abstract
DNA mimic proteins have evolved to control DNA-binding proteins by competing with the target DNA for binding to the protein. The Ocr protein of bacteriophage T7 is the most studied DNA mimic and functions to block the DNA-binding groove of Type I DNA restriction/modification enzymes. This binding prevents the enzyme from cleaving invading phage DNA. Each 116 amino acid monomer of the Ocr dimer has an unusual amino acid composition with 34 negatively charged side chains but only 6 positively charged side chains. Extensive mutagenesis of the charges of Ocr revealed a regression of Ocr activity from wild-type activity to partial activity then to variants inactive in antirestriction but deleterious for cell viability and lastly to totally inactive variants with no deleterious effect on cell viability. Throughout the mutagenesis the Ocr mutant proteins retained their folding. Our results show that the extreme bias in charged amino acids is not necessary for antirestriction activity but that less charged variants can affect cell viability by leading to restriction proficient but modification deficient cell phenotypes.
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Affiliation(s)
- Gareth A. Roberts
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Augoustinos S. Stephanou
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Nisha Kanwar
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Angela Dawson
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Laurie P. Cooper
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Kai Chen
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Margaret Nutley
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Alan Cooper
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - Garry W. Blakely
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
| | - David T. F. Dryden
- EastChem School of Chemistry, School of Physics and Astronomy, The University of Edinburgh, The King’s Buildings, Edinburgh, EH9 3JZ, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ and Institute of Cell Biology, School of Biological Sciences, The University of Edinburgh, The King’s Buildings, Edinburgh EH9 3JR, UK
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9
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Simons M, Szczelkun MD. Recycling of protein subunits during DNA translocation and cleavage by Type I restriction-modification enzymes. Nucleic Acids Res 2011; 39:7656-66. [PMID: 21712244 PMCID: PMC3177213 DOI: 10.1093/nar/gkr479] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The Type I restriction-modification enzymes comprise three protein subunits; HsdS and HsdM that form a methyltransferase (MTase) and HsdR that associates with the MTase and catalyses Adenosine-5′-triphosphate (ATP)-dependent DNA translocation and cleavage. Here, we examine whether the MTase and HsdR components can ‘turnover’ in vitro, i.e. whether they can catalyse translocation and cleavage events on one DNA molecule, dissociate and then re-bind a second DNA molecule. Translocation termination by both EcoKI and EcoR124I leads to HsdR dissociation from linear DNA but not from circular DNA. Following DNA cleavage, the HsdR subunits appear unable to dissociate even though the DNA is linear, suggesting a tight interaction with the cleaved product. The MTases of EcoKI and EcoAI can dissociate from DNA following either translocation or cleavage and can initiate reactions on new DNA molecules as long as free HsdR molecules are available. In contrast, the MTase of EcoR124I does not turnover and additional cleavage of circular DNA is not observed by inclusion of RecBCD, a helicase–nuclease that degrades the linear DNA product resulting from Type I cleavage. Roles for Type I restriction endonuclease subunit dynamics in restriction alleviation in the cell are discussed.
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Affiliation(s)
- Michelle Simons
- School of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
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10
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Roberts GA, Cooper LP, White JH, Su TJ, Zipprich JT, Geary P, Kennedy C, Dryden DTF. An investigation of the structural requirements for ATP hydrolysis and DNA cleavage by the EcoKI Type I DNA restriction and modification enzyme. Nucleic Acids Res 2011; 39:7667-76. [PMID: 21685455 PMCID: PMC3177214 DOI: 10.1093/nar/gkr480] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
Type I DNA restriction/modification systems are oligomeric enzymes capable of switching between a methyltransferase function on hemimethylated host DNA and an endonuclease function on unmethylated foreign DNA. They have long been believed to not turnover as endonucleases with the enzyme becoming inactive after cleavage. Cleavage is preceded and followed by extensive ATP hydrolysis and DNA translocation. A role for dissociation of subunits to allow their reuse has been proposed for the EcoR124I enzyme. The EcoKI enzyme is a stable assembly in the absence of DNA, so recycling was thought impossible. Here, we demonstrate that EcoKI becomes unstable on long unmethylated DNA; reuse of the methyltransferase subunits is possible so that restriction proceeds until the restriction subunits have been depleted. We observed that RecBCD exonuclease halts restriction and does not assist recycling. We examined the DNA structure required to initiate ATP hydrolysis by EcoKI and find that a 21-bp duplex with single-stranded extensions of 12 bases on either side of the target sequence is sufficient to support hydrolysis. Lastly, we discuss whether turnover is an evolutionary requirement for restriction, show that the ATP hydrolysis is not deleterious to the host cell and discuss how foreign DNA occasionally becomes fully methylated by these systems.
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11
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The phasevarion: phase variation of type III DNA methyltransferases controls coordinated switching in multiple genes. Nat Rev Microbiol 2010; 8:196-206. [PMID: 20140025 DOI: 10.1038/nrmicro2283] [Citation(s) in RCA: 133] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
In several host-adapted pathogens, phase variation has been found to occur in genes that encode methyltransferases associated with type III restriction-modification systems. It was recently shown that in the human pathogens Haemophilus influenzae, Neisseria gonorrhoeae and Neisseria meningitidis phase variation of a type III DNA methyltransferase, encoded by members of the mod gene family, regulates the expression of multiple genes. This novel genetic system has been termed the 'phasevarion' (phase-variable regulon). The wide distribution of phase-variable mod family genes indicates that this may be a common strategy used by host-adapted bacterial pathogens to randomly switch between distinct cell types.
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12
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Stephanou AS, Roberts GA, Cooper LP, Clarke DJ, Thomson AR, MacKay CL, Nutley M, Cooper A, Dryden DT. Dissection of the DNA mimicry of the bacteriophage T7 Ocr protein using chemical modification. J Mol Biol 2009; 391:565-76. [PMID: 19523474 PMCID: PMC2806950 DOI: 10.1016/j.jmb.2009.06.020] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2009] [Revised: 06/04/2009] [Accepted: 06/05/2009] [Indexed: 12/02/2022]
Abstract
The homodimeric Ocr (overcome classical restriction) protein of bacteriophage T7 is a molecular mimic of double-stranded DNA and a highly effective competitive inhibitor of the bacterial type I restriction/modification system. The surface of Ocr is replete with acidic residues that mimic the phosphate backbone of DNA. In addition, Ocr also mimics the overall dimensions of a bent 24-bp DNA molecule. In this study, we attempted to delineate these two mechanisms of DNA mimicry by chemically modifying the negative charges on the Ocr surface. Our analysis reveals that removal of about 46% of the carboxylate groups per Ocr monomer results in an approximately 50-fold reduction in binding affinity for a methyltransferase from a model type I restriction/modification system. The reduced affinity between Ocr with this degree of modification and the methyltransferase is comparable with the affinity of DNA for the methyltransferase. Additional modification to remove approximately 86% of the carboxylate groups further reduces its binding affinity, although the modified Ocr still binds to the methyltransferase via a mechanism attributable to the shape mimicry of a bent DNA molecule. Our results show that the electrostatic mimicry of Ocr increases the binding affinity for its target enzyme by up to approximately 800-fold.
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Key Words
- ocr, overcome classical restriction
- r/m, restriction/modification
- edc, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride
- hobt, hydroxybenzotriazole
- ms, mass spectrometry
- maldi-tof, matrix-assisted laser desorption/ionization time of flight
- ft-icr, fourier transform ion cyclotron resonance
- gdmcl, guanidinium hydrochloride
- sam, s-adenosyl-l-methionine
- itc, isothermal titration calorimetry
- wt, wild type
- dna mimic
- chemical modification
- restriction/modification system
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Affiliation(s)
| | - Gareth A. Roberts
- EastChem School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, UK
| | - Laurie P. Cooper
- EastChem School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, UK
| | - David J. Clarke
- EastChem School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, UK
| | - Andrew R. Thomson
- EastChem School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, UK
| | - C. Logan MacKay
- EastChem School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, UK
| | - Margaret Nutley
- West Chem Department of Chemistry, University of Glasgow, Glasgow G12 8QQ, UK
| | - Alan Cooper
- West Chem Department of Chemistry, University of Glasgow, Glasgow G12 8QQ, UK
| | - David T.F. Dryden
- EastChem School of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, UK
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13
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Neaves KJ, Cooper LP, White JH, Carnally SM, Dryden DTF, Edwardson JM, Henderson RM. Atomic force microscopy of the EcoKI Type I DNA restriction enzyme bound to DNA shows enzyme dimerization and DNA looping. Nucleic Acids Res 2009; 37:2053-63. [PMID: 19223329 PMCID: PMC2665228 DOI: 10.1093/nar/gkp042] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Atomic force microscopy (AFM) allows the study of single protein–DNA interactions such as those observed with the Type I Restriction–Modification systems. The mechanisms employed by these systems are complicated and understanding them has proved problematic. It has been known for years that these enzymes translocate DNA during the restriction reaction, but more recent AFM work suggested that the archetypal EcoKI protein went through an additional dimerization stage before the onset of translocation. The results presented here extend earlier findings confirming the dimerization. Dimerization is particularly common if the DNA molecule contains two EcoKI recognition sites. DNA loops with dimers at their apex form if the DNA is sufficiently long, and also form in the presence of ATPγS, a non-hydrolysable analogue of the ATP required for translocation, indicating that the looping is on the reaction pathway of the enzyme. Visualization of specific DNA loops in the protein–DNA constructs was achieved by improved sample preparation and analysis techniques. The reported dimerization and looping mechanism is unlikely to be exclusive to EcoKI, and offers greater insight into the detailed functioning of this and other higher order assemblies of proteins operating by bringing distant sites on DNA into close proximity via DNA looping.
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Affiliation(s)
- Kelly J Neaves
- Department of Pharmacology, University of Cambridge, Cambridge, UK
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14
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Kennaway CK, Obarska-Kosinska A, White JH, Tuszynska I, Cooper LP, Bujnicki JM, Trinick J, Dryden DTF. The structure of M.EcoKI Type I DNA methyltransferase with a DNA mimic antirestriction protein. Nucleic Acids Res 2009; 37:762-70. [PMID: 19074193 PMCID: PMC2647291 DOI: 10.1093/nar/gkn988] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2008] [Revised: 11/20/2008] [Accepted: 11/21/2008] [Indexed: 12/25/2022] Open
Abstract
Type-I DNA restriction-modification (R/M) systems are important agents in limiting the transmission of mobile genetic elements responsible for spreading bacterial resistance to antibiotics. EcoKI, a Type I R/M enzyme from Escherichia coli, acts by methylation- and sequence-specific recognition, leading to either methylation of DNA or translocation and cutting at a random site, often hundreds of base pairs away. Consisting of one specificity subunit, two modification subunits, and two DNA translocase/endonuclease subunits, EcoKI is inhibited by the T7 phage antirestriction protein ocr, a DNA mimic. We present a 3D density map generated by negative-stain electron microscopy and single particle analysis of the central core of the restriction complex, the M.EcoKI M(2)S(1) methyltransferase, bound to ocr. We also present complete atomic models of M.EcoKI in complex with ocr and its cognate DNA giving a clear picture of the overall clamp-like operation of the enzyme. The model is consistent with a large body of experimental data on EcoKI published over 40 years.
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Affiliation(s)
- Christopher K. Kennaway
- Astbury Centre, Institute of Molecular and Cellular Biology, University of Leeds, UK, Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology in Warsaw, Trojdena 4, PL-02-109 Warsaw, Institute of Biochemistry and Biophysics PAS, Pawinskiego 5A, 02-106 Warsaw, Poland, School of Chemistry, University of Edinburgh, The Kings’ Buildings, Edinburgh, EH9 3JJ, UK and Bioinformatics Laboratory, Institute of Molecular Biology and Biotechnology, Adam Mickiewicz University, Umultowska 89, PL-61-614 Poznan, Poland
| | - Agnieszka Obarska-Kosinska
- Astbury Centre, Institute of Molecular and Cellular Biology, University of Leeds, UK, Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology in Warsaw, Trojdena 4, PL-02-109 Warsaw, Institute of Biochemistry and Biophysics PAS, Pawinskiego 5A, 02-106 Warsaw, Poland, School of Chemistry, University of Edinburgh, The Kings’ Buildings, Edinburgh, EH9 3JJ, UK and Bioinformatics Laboratory, Institute of Molecular Biology and Biotechnology, Adam Mickiewicz University, Umultowska 89, PL-61-614 Poznan, Poland
| | - John H. White
- Astbury Centre, Institute of Molecular and Cellular Biology, University of Leeds, UK, Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology in Warsaw, Trojdena 4, PL-02-109 Warsaw, Institute of Biochemistry and Biophysics PAS, Pawinskiego 5A, 02-106 Warsaw, Poland, School of Chemistry, University of Edinburgh, The Kings’ Buildings, Edinburgh, EH9 3JJ, UK and Bioinformatics Laboratory, Institute of Molecular Biology and Biotechnology, Adam Mickiewicz University, Umultowska 89, PL-61-614 Poznan, Poland
| | - Irina Tuszynska
- Astbury Centre, Institute of Molecular and Cellular Biology, University of Leeds, UK, Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology in Warsaw, Trojdena 4, PL-02-109 Warsaw, Institute of Biochemistry and Biophysics PAS, Pawinskiego 5A, 02-106 Warsaw, Poland, School of Chemistry, University of Edinburgh, The Kings’ Buildings, Edinburgh, EH9 3JJ, UK and Bioinformatics Laboratory, Institute of Molecular Biology and Biotechnology, Adam Mickiewicz University, Umultowska 89, PL-61-614 Poznan, Poland
| | - Laurie P. Cooper
- Astbury Centre, Institute of Molecular and Cellular Biology, University of Leeds, UK, Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology in Warsaw, Trojdena 4, PL-02-109 Warsaw, Institute of Biochemistry and Biophysics PAS, Pawinskiego 5A, 02-106 Warsaw, Poland, School of Chemistry, University of Edinburgh, The Kings’ Buildings, Edinburgh, EH9 3JJ, UK and Bioinformatics Laboratory, Institute of Molecular Biology and Biotechnology, Adam Mickiewicz University, Umultowska 89, PL-61-614 Poznan, Poland
| | - Janusz M. Bujnicki
- Astbury Centre, Institute of Molecular and Cellular Biology, University of Leeds, UK, Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology in Warsaw, Trojdena 4, PL-02-109 Warsaw, Institute of Biochemistry and Biophysics PAS, Pawinskiego 5A, 02-106 Warsaw, Poland, School of Chemistry, University of Edinburgh, The Kings’ Buildings, Edinburgh, EH9 3JJ, UK and Bioinformatics Laboratory, Institute of Molecular Biology and Biotechnology, Adam Mickiewicz University, Umultowska 89, PL-61-614 Poznan, Poland
| | - John Trinick
- Astbury Centre, Institute of Molecular and Cellular Biology, University of Leeds, UK, Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology in Warsaw, Trojdena 4, PL-02-109 Warsaw, Institute of Biochemistry and Biophysics PAS, Pawinskiego 5A, 02-106 Warsaw, Poland, School of Chemistry, University of Edinburgh, The Kings’ Buildings, Edinburgh, EH9 3JJ, UK and Bioinformatics Laboratory, Institute of Molecular Biology and Biotechnology, Adam Mickiewicz University, Umultowska 89, PL-61-614 Poznan, Poland
| | - David T. F. Dryden
- Astbury Centre, Institute of Molecular and Cellular Biology, University of Leeds, UK, Laboratory of Bioinformatics and Protein Engineering, International Institute of Molecular and Cell Biology in Warsaw, Trojdena 4, PL-02-109 Warsaw, Institute of Biochemistry and Biophysics PAS, Pawinskiego 5A, 02-106 Warsaw, Poland, School of Chemistry, University of Edinburgh, The Kings’ Buildings, Edinburgh, EH9 3JJ, UK and Bioinformatics Laboratory, Institute of Molecular Biology and Biotechnology, Adam Mickiewicz University, Umultowska 89, PL-61-614 Poznan, Poland
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15
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Sisáková E, Weiserová M, Dekker C, Seidel R, Szczelkun MD. The interrelationship of helicase and nuclease domains during DNA translocation by the molecular motor EcoR124I. J Mol Biol 2008; 384:1273-86. [PMID: 18952104 PMCID: PMC2602864 DOI: 10.1016/j.jmb.2008.10.017] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Revised: 10/02/2008] [Accepted: 10/02/2008] [Indexed: 11/25/2022]
Abstract
The type I restriction–modification enzyme EcoR124I comprises three subunits with the stoichiometry HsdR2/HsdM2/HsdS1. The HsdR subunits are archetypical examples of the fusion between nuclease and helicase domains into a single polypeptide, a linkage that is found in a great many other DNA processing enzymes. To explore the interrelationship between these physically linked domains, we examined the DNA translocation properties of EcoR124I complexes in which the HsdR subunits had been mutated in the RecB-like nuclease motif II or III. We found that nuclease mutations can have multiple effects on DNA translocation despite being distinct from the helicase domain. In addition to reductions in DNA cleavage activity, we also observed decreased translocation and ATPase rates, different enzyme populations with different characteristic translocation rates, a tendency to stall during initiation and altered HsdR turnover dynamics. The significance of these observations to our understanding of domain interactions in molecular machines is discussed.
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Affiliation(s)
- Eva Sisáková
- Institute of Microbiology, v.v.i., Academy of Sciences of the Czech Republic, Prague, Czech Republic
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16
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Šišáková E, Stanley LK, Weiserová M, Szczelkun MD. A RecB-family nuclease motif in the Type I restriction endonuclease EcoR124I. Nucleic Acids Res 2008; 36:3939-49. [PMID: 18511464 PMCID: PMC2475608 DOI: 10.1093/nar/gkn333] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2008] [Revised: 04/30/2008] [Accepted: 05/08/2008] [Indexed: 12/03/2022] Open
Abstract
The Type I restriction-modification enzyme EcoR124I is an ATP-dependent endonuclease that uses dsDNA translocation to locate and cleave distant non-specific DNA sites. Bioinformatic analysis of the HsdR subunits of EcoR124I and related Type I enzymes showed that in addition to the principal PD-(E/D)xK Motifs, I, II and III, a QxxxY motif is also present that is characteristic of RecB-family nucleases. The QxxxY motif resides immediately C-terminal to Motif III within a region of predicted alpha-helix. Using mutagenesis, we examined the role of the Q and Y residues in DNA binding, translocation and cleavage. Roles for the QxxxY motif in coordinating the catalytic residues or in stabilizing the nuclease domain on the DNA are discussed.
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Affiliation(s)
- Eva Šišáková
- Institute of Microbiology v.v.i., Academy of Sciences of the Czech Republic, Prague, Czech Republic and DNA-Protein Interactions Unit, Department of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
| | - Louise K. Stanley
- Institute of Microbiology v.v.i., Academy of Sciences of the Czech Republic, Prague, Czech Republic and DNA-Protein Interactions Unit, Department of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
| | - Marie Weiserová
- Institute of Microbiology v.v.i., Academy of Sciences of the Czech Republic, Prague, Czech Republic and DNA-Protein Interactions Unit, Department of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
| | - Mark D. Szczelkun
- Institute of Microbiology v.v.i., Academy of Sciences of the Czech Republic, Prague, Czech Republic and DNA-Protein Interactions Unit, Department of Biochemistry, University of Bristol, Bristol, BS8 1TD, UK
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17
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The Orf18 gene product from conjugative transposon Tn916 is an ArdA antirestriction protein that inhibits type I DNA restriction-modification systems. J Mol Biol 2008; 383:970-81. [PMID: 18838147 DOI: 10.1016/j.jmb.2008.06.005] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2008] [Revised: 05/30/2008] [Accepted: 06/02/2008] [Indexed: 11/20/2022]
Abstract
Gene orf18, which is situated within the intercellular transposition region of the conjugative transposon Tn916 from the bacterial pathogen Enterococcus faecalis, encodes a putative ArdA (alleviation of restriction of DNA A) protein. Conjugative transposons are generally resistant to DNA restriction upon transfer to a new host. ArdA from Tn916 may be responsible for the apparent immunity of the transposon to DNA restriction and modification (R/M) systems and for ensuring that the transposon has a broad host range. The orf18 gene was engineered for overexpression in Escherichia coli, and the recombinant ArdA protein was purified to homogeneity. The protein appears to exist as a dimer at nanomolar concentrations but can form larger assemblies at micromolar concentrations. R/M assays revealed that ArdA can efficiently inhibit R/M by all four major classes of Type I R/M enzymes both in vivo and in vitro. These R/M systems are present in over 50% of sequenced prokaryotic genomes. Our results suggest that ArdA can overcome the restriction barrier following conjugation and so helps increase the spread of antibiotic resistance genes by horizontal gene transfer.
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18
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Seidel R, Bloom JGP, Dekker C, Szczelkun MD. Motor step size and ATP coupling efficiency of the dsDNA translocase EcoR124I. EMBO J 2008; 27:1388-98. [PMID: 18388857 PMCID: PMC2291450 DOI: 10.1038/emboj.2008.69] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2007] [Accepted: 03/03/2008] [Indexed: 11/30/2022] Open
Abstract
The Type I restriction-modification enzyme EcoR124I is an archetypical helicase-based dsDNA translocase that moves unidirectionally along the 3′–5′ strand of intact duplex DNA. Using a combination of ensemble and single-molecule measurements, we provide estimates of two physicochemical constants that are fundamental to a full description of motor protein activity—the ATP coupling efficiency (the number of ATP consumed per base pair) and the step size (the number of base pairs transported per motor step). Our data indicate that EcoR124I makes small steps along the DNA of 1 bp in length with 1 ATP consumed per step, but with some uncoupling of the ATPase and translocase cycles occurring so that the average number of ATP consumed per base pair slightly exceeds unity. Our observations form a framework for understanding energy coupling in a great many other motors that translocate along dsDNA rather than ssDNA.
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Affiliation(s)
- Ralf Seidel
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, The Netherlands
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19
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Crampton N, Roes S, Dryden DTF, Rao DN, Edwardson JM, Henderson RM. DNA looping and translocation provide an optimal cleavage mechanism for the type III restriction enzymes. EMBO J 2007; 26:3815-25. [PMID: 17660745 PMCID: PMC1952222 DOI: 10.1038/sj.emboj.7601807] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2007] [Accepted: 07/02/2007] [Indexed: 11/09/2022] Open
Abstract
EcoP15I is a type III restriction enzyme that requires two recognition sites in a defined orientation separated by up to 3.5 kbp to efficiently cleave DNA. The mechanism through which site-bound EcoP15I enzymes communicate between the two sites is unclear. Here, we use atomic force microscopy to study EcoP15I-DNA pre-cleavage complexes. From the number and size distribution of loops formed, we conclude that the loops observed do not result from translocation, but are instead formed by a contact between site-bound EcoP15I and a nonspecific region of DNA. This conclusion is confirmed by a theoretical polymer model. It is further shown that translocation must play some role, because when translocation is blocked by a Lac repressor protein, DNA cleavage is similarly blocked. On the basis of these results, we present a model for restriction by type III restriction enzymes and highlight the similarities between this and other classes of restriction enzymes.
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Affiliation(s)
- Neal Crampton
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, UK
| | - Stefanie Roes
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, UK
| | | | - Desirazu N Rao
- Department of Biochemistry, Indian Institute of Science, Bangalore, India
| | - J Michael Edwardson
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, UK
| | - Robert M Henderson
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, UK
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK. Tel.: +44 1223 334 053; Fax: +44 1223 334 100; E-mail:
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20
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Flyvbjerg H, Keatch SA, Dryden DT. Strong physical constraints on sequence-specific target location by proteins on DNA molecules. Nucleic Acids Res 2006; 34:2550-7. [PMID: 16698961 PMCID: PMC3303175 DOI: 10.1093/nar/gkl271] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Sequence-specific binding to DNA in the presence of competing non-sequence-specific ligands is a problem faced by proteins in all organisms. It is akin to the problem of parking a truck at a loading bay by the side of a road in the presence of cars parked at random along the road. Cars even partially covering the loading bay prevent correct parking of the truck. Similarly on DNA, non-specific ligands interfere with the binding and function of sequence-specific proteins. We derive a formula for the probability that the loading bay is free from parked cars. The probability depends on the size of the loading bay and allows an estimation of the size of the footprint on the DNA of the sequence-specific protein by assaying protein binding or function in the presence of increasing concentrations of non-specific ligand. Assaying for function gives an 'activity footprint'; the minimum length of DNA required for function rather than the more commonly measured physical footprint. Assaying the complex type I restriction enzyme, EcoKI, gives an activity footprint of approximately 66 bp for ATP hydrolysis and 300 bp for the DNA cleavage function which is intimately linked with translocation of DNA by EcoKI. Furthermore, considering the coverage of chromosomal DNA by proteins in vivo, our theory shows that the search for a specific DNA sequence is very difficult; most sites are obscured by parked cars. This effectively rules out any significant role in target location for mechanisms invoking one-dimensional, linear diffusion along DNA.
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Affiliation(s)
- Henrik Flyvbjerg
- Risø National Laboratory, Biosystems Department and Danish Polymer Centre Building BIO-776, PO Box 49, Frederiksborgvej 399, DK-4000 Roskilde, Denmark
- Isaac Newton Institute for Mathematical Sciences 20 Clarkson Road, Cambridge, CB3 0EH, UK
| | - Steven A. Keatch
- School of Chemistry, The King's Buildings, The University of Edinburgh Edinburgh, EH9 3JJ, UK
| | - David T.F. Dryden
- School of Chemistry, The King's Buildings, The University of Edinburgh Edinburgh, EH9 3JJ, UK
- Isaac Newton Institute for Mathematical Sciences 20 Clarkson Road, Cambridge, CB3 0EH, UK
- To whom correspondence should be adressed. Tel: +0131 650 4735; Fax: +0131 650 6453;
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21
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Keatch SA, Leonard PG, Ladbury JE, Dryden DTF. StpA protein from Escherichia coli condenses supercoiled DNA in preference to linear DNA and protects it from digestion by DNase I and EcoKI. Nucleic Acids Res 2005; 33:6540-6. [PMID: 16299353 PMCID: PMC1289078 DOI: 10.1093/nar/gki951] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
The nucleoid-associated protein, StpA, of Escherichia coli binds non-specifically to double-stranded DNA (dsDNA) and apparently forms bridges between adjacent segments of the DNA. Such a coating of protein on the DNA would be expected to hinder the action of nucleases. We demonstrate that StpA binding hinders dsDNA cleavage by both the non-specific endonuclease, DNase I, and by the site-specific type I restriction endonuclease, EcoKI. It requires approximately one StpA molecule per 250–300 bp of supercoiled DNA and approximately one StpA molecule per 60–100 bp on linear DNA for strong inhibition of the nucleases. These results support the role of StpA as a nucleoid-structuring protein which binds DNA segments together. The inhibition of EcoKI, which cleaves DNA at a site remote from its initial target sequence after extensive DNA translocation driven by ATP hydrolysis, suggests that these enzymes would be unable to function on chromosomal DNA even during times of DNA damage when potentially lethal, unmodified target sites occur on the chromosome. This supports a role for nucleoid-associated proteins in restriction alleviation during times of cell stress.
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Affiliation(s)
| | - P. G. Leonard
- Department of Biochemistry and Molecular Biology, University College LondonGower Street, London WC1E 6BT, UK
| | - J. E. Ladbury
- Department of Biochemistry and Molecular Biology, University College LondonGower Street, London WC1E 6BT, UK
| | - D. T. F. Dryden
- To whom correspondence should be addressed. Tel: +44 131 650 4735; Fax: +44 131 650 6453;
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22
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McClelland SE, Dryden DTF, Szczelkun MD. Continuous assays for DNA translocation using fluorescent triplex dissociation: application to type I restriction endonucleases. J Mol Biol 2005; 348:895-915. [PMID: 15843021 DOI: 10.1016/j.jmb.2005.03.018] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2004] [Revised: 02/14/2005] [Accepted: 03/04/2005] [Indexed: 11/25/2022]
Abstract
Fluorescent assays and accompanying kinetic models are described for the analysis of DNA translocation independent of duplex unwinding. A triplex binding site (TBS) was introduced into DNA substrates at precise loci downstream of recognition sequences for type IA, IB and IC restriction endonucleases (EcoKI, EcoAI and EcoR124I, respectively). Each endonuclease was incubated (without ATP) with substrates on which a hexachlorofluoroscein-labelled triplex-forming oligonucleotide (HEX-TFO) was pre-bound. Following addition of ATP, 1-D enzyme motion resulted in collision with, and displacement of, the HEX-TFO, producing a >twofold increase in fluorescent intensity. Alternatively, a decrease in anisotropy following displacement of a rhodamine-labelled TFO was monitored. Using rapid mixing in a stopped-flow fluorimeter, continuous kinetic profiles were produced in which displacement is preceded by a lag-phase, directly proportional to the distance moved. For each enzyme, we obtained not only the translocation rate but also information on slow isomerisation step(s) at initiation. Furthermore, we demonstrated that enzymes deficient in DNA cleavage but with maximal ATPase activity showed initiation and translocation rates identical to wild-type, confirming that DNA strand breaks are not a pre-requisite of motion.
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Affiliation(s)
- Sarah E McClelland
- DNA-Protein Interactions Group, Department of Biochemistry, University of Bristol, Bristol BS8 1TD, UK
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23
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Keatch SA, Su TJ, Dryden DTF. Alleviation of restriction by DNA condensation and non-specific DNA binding ligands. Nucleic Acids Res 2004; 32:5841-50. [PMID: 15520467 PMCID: PMC528803 DOI: 10.1093/nar/gkh918] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
During conditions of cell stress, the type I restriction and modification enzymes of bacteria show reduced, but not zero, levels of restriction of unmethylated foreign DNA. In such conditions, chemically identical unmethylated recognition sequences also occur on the chromosome of the host but restriction alleviation prevents the enzymes from destroying the host DNA. How is this distinction between chemically identical DNA molecules achieved? For some, but not all, type I restriction enzymes, alleviation is partially due to proteolytic degradation of a subunit of the enzyme. We identify that the additional alleviation factor is attributable to the structural difference between foreign DNA entering the cell as a random coil and host DNA, which exists in a condensed nucleoid structure coated with many non-specific ligands. The type I restriction enzyme is able to destroy the 'naked' DNA using a complex reaction linked to DNA translocation, but this essential translocation process is inhibited by DNA condensation and the presence of non-specific ligands bound along the DNA.
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Affiliation(s)
- Steven A Keatch
- School of Chemistry, The University of Edinburgh, The King's Buildings, Edinburgh, EH9 3JJ, UK
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24
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Pennadam SS, Firman K, Alexander C, Górecki DC. Protein-polymer nano-machines. Towards synthetic control of biological processes. J Nanobiotechnology 2004; 2:8. [PMID: 15350203 PMCID: PMC519025 DOI: 10.1186/1477-3155-2-8] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2004] [Accepted: 09/06/2004] [Indexed: 11/10/2022] Open
Abstract
The exploitation of nature's machinery at length scales below the dimensions of a cell is an exciting challenge for biologists, chemists and physicists, while advances in our understanding of these biological motifs are now providing an opportunity to develop real single molecule devices for technological applications. Single molecule studies are already well advanced and biological molecular motors are being used to guide the design of nano-scale machines. However, controlling the specific functions of these devices in biological systems under changing conditions is difficult. In this review we describe the principles underlying the development of a molecular motor with numerous potential applications in nanotechnology and the use of specific synthetic polymers as prototypic molecular switches for control of the motor function. The molecular motor is a derivative of a TypeI Restriction-Modification (R-M) enzyme and the synthetic polymer is drawn from the class of materials that exhibit a temperature-dependent phase transition. The potential exploitation of single molecules as functional devices has been heralded as the dawn of new era in biotechnology and medicine. It is not surprising, therefore, that the efforts of numerous multidisciplinary teams [1,2]. have been focused in attempts to develop these systems. as machines capable of functioning at the low sub-micron and nanometre length-scales [3]. However, one of the obstacles for the practical application of single molecule devices is the lack of functional control methods in biological media, under changing conditions. In this review we describe the conceptual basis for a molecular motor (a derivative of a TypeI Restriction-Modification enzyme) with numerous potential applications in nanotechnology and the use of specific synthetic polymers as prototypic molecular switches for controlling the motor function [4].
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Affiliation(s)
- Sivanand S Pennadam
- School of Pharmacy and Biomedical Sciences, Institute of Biomedical and Biomolecular Sciences, University of Portsmouth, Portsmouth, PO1 2DT UK
| | - Keith Firman
- School of Biological Sciences, Institute of Biomedical and Biomolecular Sciences, University of Portsmouth, Portsmouth PO1 2DT, UK
| | - Cameron Alexander
- School of Pharmacy and Biomedical Sciences, Institute of Biomedical and Biomolecular Sciences, University of Portsmouth, Portsmouth, PO1 2DT UK
| | - Dariusz C Górecki
- School of Pharmacy and Biomedical Sciences, Institute of Biomedical and Biomolecular Sciences, University of Portsmouth, Portsmouth, PO1 2DT UK
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25
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Peakman LJ, Szczelkun MD. DNA communications by Type III restriction endonucleases--confirmation of 1D translocation over 3D looping. Nucleic Acids Res 2004; 32:4166-74. [PMID: 15302916 PMCID: PMC514383 DOI: 10.1093/nar/gkh762] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
DNA cleavage by Type III restriction enzymes is governed strictly by the relative arrangement of recognition sites on a DNA substrate--endonuclease activity is usually only triggered by sequences in head-to-head orientation. Tens to thousands of base pairs can separate these sites. Long distance communication over such distances could occur by either one-dimensional (1D) DNA translocation or 3D DNA looping. To distinguish between these alternatives, we analysed the activity of EcoPI and EcoP15I on DNA catenanes in which the recognition sites were either on the same or separate rings. While substrates with a pair of sites located on the same ring were cleaved efficiently, catenanes with sites on separate rings were not cleaved. These results exclude a simple 3D DNA-looping activity. To characterize the interactions further, EcoPI was incubated with plasmids carrying two recognition sites interspersed with two 21res sites for site-specific recombination by Tn21 resolvase; inhibition of recombination would indicate the formation of stable DNA loops. No inhibition was observed, even under conditions where EcoPI translocation could also occur.
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Affiliation(s)
- Luke J Peakman
- DNA-Protein Interactions Group, Department of Biochemistry, School of Medical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK
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Kainov DE, Lísal J, Bamford DH, Tuma R. Packaging motor from double-stranded RNA bacteriophage phi12 acts as an obligatory passive conduit during transcription. Nucleic Acids Res 2004; 32:3515-21. [PMID: 15247341 PMCID: PMC484169 DOI: 10.1093/nar/gkh680] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Double-stranded RNA viruses sequester their genomes within a protein shell, called the polymerase complex. Translocation of ssRNA into (packaging) and out (transcription) of the polymerase complex are essential steps in the life cycle of the dsRNA bacteriophages of the Cystoviridae family (phi6-phi14). Both processes require a viral molecular motor P4, an NTPase, which bears structural and functional similarities to hexameric helicases. In effect, switching between the packaging and the transcription mode requires the translocation direction of the P4 motor to reverse. However, the mechanism of the reversal remains elusive. Here we characterize the P4 protein from bacteriophage phi12 and exploit its purine nucleotide specificity to delineate P4 role in transcription. The results indicate that while P4 actively translocates RNA during packaging it acts as a passive conduit for RNA export. The directionality switching is accomplished via the regulation of P4 NTPase activity within the polymerase core.
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Affiliation(s)
- Denis E Kainov
- Institute of Biotechnology and Faculty of Biological Science, Viikki Biocenter, University of Helsinki, PO Box 65, Viikinkaari 1, Helsinki FIN-00014, Finland
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27
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Längst G, Becker PB. Nucleosome remodeling: one mechanism, many phenomena? ACTA ACUST UNITED AC 2004; 1677:58-63. [PMID: 15020046 DOI: 10.1016/j.bbaexp.2003.10.011] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2003] [Accepted: 10/14/2003] [Indexed: 11/18/2022]
Abstract
The term 'nucleosome remodeling' subsumes a large number of energy-dependent alterations of canonical nucleosome structure, catalyzed by dedicated ATPases in large multiprotein complexes. The importance of these factors for gene regulation and other processes with chromatin substrate have emerged from genetic studies. Mechanistic analyses of nucleosome remodeling by different enzymes provided a diverse, almost confusing phenomenology of ATP-dependent derangement of nucleosomes in vitro, suggesting that different remodeling machines follow different strategies to disrupt histone-DNA interactions. This review explores the alternative possibility that the rich phenomenology of nucleosome remodeling may be brought about by variations of one basic remodeling reaction.
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Affiliation(s)
- Gernot Längst
- Adolf-Butenandt-Institut, Molekularbiologie, Ludwig-Maximilians-University Munchen, Schillerstrasse 44, D-80336 Munich, Germany
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28
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Loenen WAM. Tracking EcoKI and DNA fifty years on: a golden story full of surprises. Nucleic Acids Res 2004; 31:7059-69. [PMID: 14654681 PMCID: PMC291878 DOI: 10.1093/nar/gkg944] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
1953 was a historical year for biology, as it marked the birth of the DNA helix, but also a report by Bertani and Weigle on 'a barrier to infection' of bacteriophage lambda in its natural host, Escherichia coli K-12, that could be lifted by 'host-controlled variation' of the virus. This paper lay dormant till Nobel laureate Arber and PhD student Dussoix showed that the lambda DNA was rejected and degraded upon infection of different bacterial hosts, unless it carried host-specific modification of that DNA, thus laying the foundations for the phenomenon of restriction and modification (R-M). The restriction enzyme of E.coli K-12, EcoKI, was purified in 1968 and required S-adenosylmethionine (AdoMet) and ATP as cofactors. By the end of the decade there was substantial evidence for a chromosomal locus hsdK with three genes encoding restriction (R), modification (M) and specificity (S) subunits that assembled into a large complex of >400 kDa. The 1970s brought the message that EcoKI cut away from its DNA recognition target, to which site the enzyme remained bound while translocating the DNA past itself, with concomitant ATP hydrolysis and subsequent double-strand nicks. This translocation event created clearly visible DNA loops in the electron microscope. EcoKI became the archetypal Type I R-M enzyme with curious DNA translocating properties reminiscent of helicases, recognizing the bipartite asymmetric site AAC(N6)GTGC. Cloning of the hsdK locus in 1976 facilitated molecular understanding of this sophisticated R-M complex and in an elegant 'pas de deux' Murray and Dryden constructed the present model based on a large body of experimental data plus bioinformatics. This review celebrates the golden anniversary of EcoKI and ends with the exciting progress on the vital issue of restriction alleviation after DNA damage, also first reported in 1953, which involves intricate control of R subunit activity by the bacterial proteasome ClpXP, important results that will keep scientists on the EcoKI track for another 50 years to come.
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Affiliation(s)
- Wil A M Loenen
- Department of Medical Microbiology, University Maastricht, Maastricht, The Netherlands.
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Whitehouse I, Stockdale C, Flaus A, Szczelkun MD, Owen-Hughes T. Evidence for DNA translocation by the ISWI chromatin-remodeling enzyme. Mol Cell Biol 2003; 23:1935-45. [PMID: 12612068 PMCID: PMC149479 DOI: 10.1128/mcb.23.6.1935-1945.2003] [Citation(s) in RCA: 126] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2002] [Revised: 10/31/2002] [Accepted: 12/19/2002] [Indexed: 11/20/2022] Open
Abstract
The ISWI proteins form the catalytic core of a subset of ATP-dependent chromatin-remodeling activities. Here, we studied the interaction of the ISWI protein with nucleosomal substrates. We found that the ability of nucleic acids to bind and stimulate the ATPase activity of ISWI depends on length. We also found that ISWI is able to displace triplex-forming oligonucleotides efficiently when they are introduced at sites close to a nucleosome but successively less efficiently 30 to 60 bp from its edge. The ability of ISWI to direct triplex displacement was specifically impeded by the introduction of 5- or 10-bp gaps in the 3'-5' strand between the triplex and the nucleosome. In combination, these observations suggest that ISWI is a 3'-5'-strand-specific, ATP-dependent DNA translocase that may be capable of forcing DNA over the surface of nucleosomes.
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Affiliation(s)
- Iestyn Whitehouse
- Division of Gene Regulation and Expression, The Wellcome Trust Biocentre, Department of Biochemistry, University of Dundee, Dundee DD1 5EH, Scotland, UK
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32
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Mahdi AA, Briggs GS, Sharples GJ, Wen Q, Lloyd RG. A model for dsDNA translocation revealed by a structural motif common to RecG and Mfd proteins. EMBO J 2003; 22:724-34. [PMID: 12554672 PMCID: PMC140728 DOI: 10.1093/emboj/cdg043] [Citation(s) in RCA: 82] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
RecG protein differs from other helicases analysed to atomic resolution in that it mediates strand separation via translocation on double-stranded (ds) rather than single-stranded (ss) DNA. We describe a highly conserved helical hairpin motif in RecG and show it to be important for helicase activity. It places two arginines (R609 and R630) in opposing positions within the component helices where they are stabilized by a network of hydrogen bonds involving a glutamate from helicase motif VI. We suggest that disruption of this feature, triggered by ATP hydrolysis, moves an adjacent loop structure in the dsDNA-binding channel and that a swinging arm motion of this loop drives translocation. Substitutions that reverse the charge at R609 or R630 reduce DNA unwinding and ATPase activities, and increase dsDNA binding, but do not affect branched DNA binding. Sequences forming the helical hairpin and loop structures are highly conserved in Mfd protein, a transcription-coupled DNA repair factor that also translocates on dsDNA. The possibility of type I restriction enzymes and chromatin-remodelling factors using similar structures to drive translocation on dsDNA is discussed.
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Affiliation(s)
| | | | - Gary J. Sharples
- Institute of Genetics, University of Nottingham, Queen’s Medical Centre, Nottingham NG7 2UH, UK
Present address: Centre for Infectious Diseases, Wolfson Research Institute, University of Durham, Queen’s Campus, Stockton-on-Tees TS17 6BH, UK Corresponding author e-mail:
| | | | - Robert G. Lloyd
- Institute of Genetics, University of Nottingham, Queen’s Medical Centre, Nottingham NG7 2UH, UK
Present address: Centre for Infectious Diseases, Wolfson Research Institute, University of Durham, Queen’s Campus, Stockton-on-Tees TS17 6BH, UK Corresponding author e-mail:
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33
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Abstract
Survival is assuredly the prime directive for all living organisms either as individuals or as a species. One of the main challenges encountered by bacterial populations is the danger of bacteriophage attacks, since infection of a single bacterium may rapidly propagate, decimating the entire population. In order to protect themselves against this acute threat, bacteria have developed an array of defence mechanisms, which range from preventing the infection itself via interference with bacteriophage adsorption to the cell surface and prevention of phage DNA injection, to degradation of the injected phage DNA. This last defence mechanism is catalysed by the bacterial restriction-modification (R-M) systems, and in particular, by nucleoside 5'-triphosphate (NTP)-dependent restriction enzymes, e.g. type I and type III R-M systems or the modification-dependent endonucleases. Type I and type III restriction systems have dual properties. They may either act as methylases and protect the host's own DNA against restriction by methylating specific residues, or they catalyse ATP-dependent endonuclease activity so that invading foreign DNA lacking the host-specific methylation is degraded. These defence mechanism systems are further complemented by the presence of methylation-dependent, GTP-dependent endonucleases, that restricts specifically methylated DNA. Although all three types of endonucleases are structurally very different, they share a common functional mechanism. They recognise and bind to specific DNA sequences but do not cleave DNA within those target sites. They belong to the general class of DNA motor proteins, which use the free energy associated with nucleoside 5'-triphosphate hydrolysis to translocate DNA so that the subsequent DNA cleavage event occurs at a distance from the endonuclease recognition site. Moreover, DNA cleavage appears to be a random process triggered upon stalling of the DNA translocation process and requiring dimerisation of the bound endonucleases for a concerted break of both DNA strands. In this review, we present a detailed description and analysis of the functional mechanism of the three known NTP-dependent restriction systems: type I and type III restriction-modification enzymes, as well as the methylation-dependent McrBC endonuclease.
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Affiliation(s)
- Aude A Bourniquel
- Department of Molecular Microbiology, Biozentrum, University of Basel, Klingelbergstrasse 50-70, Switzerland.
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Szczelkun MD. Kinetic models of translocation, head-on collision, and DNA cleavage by type I restriction endonucleases. Biochemistry 2002; 41:2067-74. [PMID: 11827554 DOI: 10.1021/bi011824b] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Digestion of linear DNA by type I restriction endonucleases is generally activated following the head-on collision of two translocating enzymes. However, the resulting distributions of cleavage loci along the DNA vary with different enzymes; in some cases, cleavage is located in a discrete region midway between a pair of recognition sites while in other cases cleavage is broadly distributed and occurs at nearly every intervening locus. Statistical models for DNA translocation, collision, and cleavage are described that can account for these observations and that are generally applicable to other DNA-based motor proteins. If translocation is processive (stepping forward is significantly more likely than DNA dissociation), then the linear distribution of an ensemble of proteins can be described simply using a Poisson relationship. The pattern of cleavage sites resulting from collision between two processive type I enzymes over a distance d can then be described by a binomial distribution with a standard deviation 0.5 x d1/2. Alternatively, if translocation is nonprocessive (stepping forward or dissociating become equally likely events), the linear distribution is described by a continuum of populated states and is thus extended. Comparisons of model data to the kinetics of DNA translocation and cleavage discount the nonprocessive model. Instead, the observed differences between enzymes are due to asynchronous events that occur upon collision. Therefore, type I restriction enzymes can be described as having processive DNA translocation but, in some cases, nonprocessive DNA cleavage.
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Affiliation(s)
- Mark D Szczelkun
- Department of Biochemistry, University of Bristol, Bristol BS8 1TD, UK.
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35
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Dillingham MS, Wigley DB, Webb MR. Direct measurement of single-stranded DNA translocation by PcrA helicase using the fluorescent base analogue 2-aminopurine. Biochemistry 2002; 41:643-51. [PMID: 11781105 DOI: 10.1021/bi011137k] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Use of the fluorescent base analogue 2-aminopurine has provided a direct demonstration of the translocation of PcrA helicase toward the 5'-end of single-stranded DNA. Single 2-aminopurine bases are introduced into otherwise standard oligonucleotides and produce a fluorescence signal when PcrA reaches their position. We demonstrate that random binding of PcrA to ssDNA is followed by translocation in an ATP-dependent manner toward the 5'-terminus at 80 bases per second at 20 degrees C. The data also provide information on the kinetics of ssDNA binding to the helicase and of the protein dissociation from the 5'-end of ssDNA. A full kinetic model is presented for ATP-dependent DNA translocation by PcrA helicase.
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Affiliation(s)
- Mark S Dillingham
- Imperial Cancer Research Fund, Clare Hall Laboratories, Blanche Lane, South Mimms, Potters Bar, Hertfordshire EN6 3LD, UK
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36
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Murray NE. 2001 Fred Griffith review lecture. Immigration control of DNA in bacteria: self versus non-self. MICROBIOLOGY (READING, ENGLAND) 2002; 148:3-20. [PMID: 11782494 DOI: 10.1099/00221287-148-1-3] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Affiliation(s)
- Noreen E Murray
- Institute of Cell and Molecular Biology, Darwin Building, Mayfield Road, Edinburgh EH9 3JR, Scotland, UK1
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37
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Abstract
The known nucleoside triphosphate-dependent restriction enzymes are hetero-oligomeric proteins that behave as molecular machines in response to their target sequences. They translocate DNA in a process dependent on the hydrolysis of a nucleoside triphosphate. For the ATP-dependent type I and type III restriction and modification systems, the collision of translocating complexes triggers hydrolysis of phosphodiester bonds in unmodified DNA to generate double-strand breaks. Type I endonucleases break the DNA at unspecified sequences remote from the target sequence, type III endonucleases at a fixed position close to the target sequence. Type I and type III restriction and modification (R-M) systems are notable for effective post-translational control of their endonuclease activity. For some type I enzymes, this control is mediated by proteolytic degradation of that subunit of the complex which is essential for DNA translocation and breakage. This control, lacking in the well-studied type II R-M systems, provides extraordinarily effective protection of resident DNA should it acquire unmodified target sequences. The only well-documented GTP-dependent restriction enzyme, McrBC, requires methylated target sequences for the initiation of phosphodiester bond cleavage.
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Affiliation(s)
- D T Dryden
- Department of Chemistry, University of Edinburgh, Joseph Black Building, The King's Buildings, Mayfield Road, Edinburgh EH9 3JJ, UK.
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38
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Madsen A, Josephsen J. The LlaGI restriction and modification system of Lactococcus lactis W10 consists of only one single polypeptide. FEMS Microbiol Lett 2001; 200:91-6. [PMID: 11410355 DOI: 10.1111/j.1574-6968.2001.tb10698.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
The naturally occurring 12.1-kb plasmid, pEW104, in Lactococcus lactis ssp. cremoris W10 was found to confer decreased bacteriophage sensitivity to its host. Plasmid pEW104 encodes a non-classic restriction and modification (R/M) system, named LlaGI, consisting of only one single polypeptide. Analysis of the amino acid sequence revealed the presence of a catalytic motif and seven helicase-like motifs (DEAD-box motifs) characteristic of type I and III endonucleases, followed by four conserved methylase motifs characteristic of adenine-methylases. A comparison between LlaGI and the very similar R/M system, LlaBIII, suggests that the C-terminal region of LlaGI, apparently containing no known motifs, could possibly specify target DNA recognition. Conceivably, the LlaGI gene is included in the operon of the plasmid replication machinery. Finally, it is proposed that LlaGI represents a variant of the type I R/M systems.
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Affiliation(s)
- A Madsen
- Department of Dairy and Food Science, The Royal Veterinary and Agricultural University, Rolighedsvej 30, 4, DK-1958 Frederiksberg C, Denmark
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39
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Abstract
Development of a sensitive assay that measures the rate of cellular internalization of an infecting bacteriophage T7 genome has led to surprising observations on the initiation of infection. Proteins ejected from the phage virion probably function as an extensible tail to form a channel across the cell envelope. This channel is subsequently used for translocating the phage genome into the cell. One of these ejected proteins also controls the amount of DNA that enters the cell, rendering subsequent internalization of the remainder of the genome dependent on transcription. Mutations affecting this protein allow the entire phage genome to enter a cell by the transcription-independent process. This process exhibits pseudo-zero-order reaction kinetics and a temperature dependence of translocation rate that are not expected if DNA ejection from a phage capsid were caused by a physical process. The temperature dependence of transcription-independent T7 DNA translocation rate is similar to those of enzyme-catalysed reactions. Current data suggest a highly speculative model, in which two of the proteins ejected from the phage head establish a molecular motor that ratchets the phage genome into the cell.
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Affiliation(s)
- I J Molineux
- Molecular Genetics and Microbiology, University of Texas, Austin, TX 78712-1095, USA.
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40
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Abstract
During the past year, major advances have been made towards understanding the function of ATP-dependent chromatin-remodelling activities both in vitro and in vivo. These suggest that ATP-dependent chromatin-remodelling activities are capable of both altering the structure of individual nucleosomes and acting in concert with other forms of chromatin-modifying enzymes, to regulate the formation and decondensation of chromatin fibres.
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Affiliation(s)
- A Flaus
- The Wellcome Trust Biocentre, School of Life Sciences, University of Dundee, DD1 5EH, Dundee, UK.
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41
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O'Neill M, Powell LM, Murray NE. Target recognition by EcoKI: the recognition domain is robust and restriction-deficiency commonly results from the proteolytic control of enzyme activity. J Mol Biol 2001; 307:951-63. [PMID: 11273713 DOI: 10.1006/jmbi.2001.4543] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We report a genetic and biochemical analysis of a target recognition domain (TRD) of EcoKI, a type I restriction and modification enzyme. The TRDs of type I R-M systems are within the specificity subunit (HsdS) and HsdS confers sequence specificity to a complex endowed with both restriction and modification activities. Random mutagenesis has revealed that most substitutions within the amino TRD of EcoKI, a region comprising 157 amino acid residues, have no detectable effect on the phenotype of the bacterium, even when the substitutions are non- conservative. The structure of the TRD appears to be robust. All but one of the six substitutions that confer a restriction-deficient, modification-deficient (r(-)m(-)) phenotype were found to be in the interval between residues 80 and 110, a region predicted by sequence comparisons to form part of the protein-DNA interface. Additional site-directed mutations affecting this interval commonly impair both restriction and modification. However, we show that an r(-) phenotype cannot be taken as evidence that the EcoKI complex lacks endonuclease activity; in response to even a slightly impaired modification efficiency, the endonuclease activity of EcoKI is destroyed by a process dependent upon the ClpXP protease. Enzymes from mutants with an r(-)m(-) phenotype commonly retain some sequence-specific activity; methylase activity can be detected on hemimethylated DNA substrates and residual endonuclease activity is implied whenever the viability of the r(-)m(-) bacterium is dependent on ClpXP. Conversely, the viability of ClpX(-) r(-)m(-) bacteria can be used as evidence for little, or no, endonuclease activity. Of 14 mutants with an r(-)m(-) phenotype, only six are viable in the absence of ClpXP. The significance of four of the six residues (G91, G105, F107 and G141) is enhanced by the finding that even conservative substitutions for these residues impair modification, thereby conferring an r(-)m(-) phenotype.
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Affiliation(s)
- M O'Neill
- Institute of Cell and Molecular Biology, University of Edinburgh, Darwin Building, Mayfield Road, King's Buildings, Edinburgh, EH9 3JR, UK
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42
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Janscak P, Sandmeier U, Szczelkun MD, Bickle TA. Subunit assembly and mode of DNA cleavage of the type III restriction endonucleases EcoP1I and EcoP15I. J Mol Biol 2001; 306:417-31. [PMID: 11178902 DOI: 10.1006/jmbi.2000.4411] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
DNA cleavage by type III restriction endonucleases requires two inversely oriented asymmetric recognition sequences and results from ATP-dependent DNA translocation and collision of two enzyme molecules. Here, we characterized the structure and mode of action of the related EcoP1I and EcoP15I enzymes. Analytical ultracentrifugation and gel quantification revealed a common Res(2)Mod(2) subunit stoichiometry. Single alanine substitutions in the putative nuclease active site of ResP1 and ResP15 abolished DNA but not ATP hydrolysis, whilst a substitution in helicase motif VI abolished both activities. Positively supercoiled DNA substrates containing a pair of inversely oriented recognition sites were cleaved inefficiently, whereas the corresponding relaxed and negatively supercoiled substrates were cleaved efficiently, suggesting that DNA overtwisting impedes the convergence of the translocating enzymes. EcoP1I and EcoP15I could co-operate in DNA cleavage on circular substrate containing several EcoP1I sites inversely oriented to a single EcoP15I site; cleavage occurred predominantly at the EcoP15I site. EcoP15I alone showed nicking activity on these molecules, cutting exclusively the top DNA strand at its recognition site. This activity was dependent on enzyme concentration and local DNA sequence. The EcoP1I nuclease mutant greatly stimulated the EcoP15I nicking activity, while the EcoP1I motif VI mutant did not. Moreover, combining an EcoP15I nuclease mutant with wild-type EcoP1I resulted in cutting the bottom DNA strand at the EcoP15I site. These data suggest that double-strand breaks result from top strand cleavage by a Res subunit proximal to the site of cleavage, whilst bottom strand cleavage is catalysed by a Res subunit supplied in trans by the distal endonuclease in the collision complex.
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Affiliation(s)
- P Janscak
- Division of Molecular Microbiology, Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056, Switzerland
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43
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Abstract
Helicases are enzymes involved in every aspect of nucleic acid metabolism. Recent structural and biochemical evidence is beginning to provide details of their molecular mechanism of action. Crystal structures of helicases have revealed an underlying common structural fold. However, although there are many similarities between the mechanisms of different classes of helicase, not all aspects of the helicase activity are the same in all members of this enzyme family.
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Affiliation(s)
- P Soultanas
- School of Chemistry, University of Nottingham, University Park, NG7 2RD, Nottingham, UK
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44
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Abstract
The endonuclease activity of EcoKI is regulated by the ClpXP-dependent degradation of the subunit that is essential for restriction, but not modification. We monitored proteolysis in mutants blocked at different steps in the restriction pathway. Mutations that prevent DNA translocation render EcoKI refractory to proteolysis, whereas those that permit DNA translocation, but block endonuclease activity, do not. Although proteolysis alleviates restriction in a mutant that lacks modification activity, some restriction activity remains; our evidence indicates residual EcoKI associated with the membrane fraction. ClpXP protects the bacterial chromosome, but little effect was detected on unmodified foreign DNA within the cytoplasm of a restriction-proficient cell. The molecular basis for the distinction between unmodified resident and foreign DNA remains to be determined.
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Affiliation(s)
- V A Doronina
- Institute of Cell and Molecular Biology, Kings Buildings, Mayfield Road, Edinburgh EH9 3JR, UK
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45
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Havas K, Flaus A, Phelan M, Kingston R, Wade PA, Lilley DM, Owen-Hughes T. Generation of superhelical torsion by ATP-dependent chromatin remodeling activities. Cell 2000; 103:1133-42. [PMID: 11163188 DOI: 10.1016/s0092-8674(00)00215-4] [Citation(s) in RCA: 222] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
ATP-dependent chromatin remodeling activities participate in the alteration of chromatin structure during gene regulation. All have DNA- or chromatin-stimulated ATPase activity and many can alter the structure of chromatin; however, the means by which they do this have remained unclear. Here we describe a novel activity for ATP-dependent chromatin remodeling activities, the ability to generate unconstrained negative superhelical torsion in DNA and chromatin. We find that the ability to distort DNA is shared by the yeast SWI/SNF complex, Xenopus Mi-2 complex, recombinant ISWI, and recombinant BRG1, suggesting that the generation of superhelical torsion represents a primary biomechanical activity shared by all Snf2p-related ATPase motors. The generation of superhelical torque provides a potent means by which ATP-dependent chromatin remodeling activities can manipulate chromatin structure.
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Affiliation(s)
- K Havas
- Division of Gene Regulation, The Wellcome Trust Biocentre, Dundee DD1 5EH, Scotland, United Kingdom
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46
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Abstract
The single-stranded adeno-associated virus type 2 (AAV) genome is flanked by terminal repeats (TRs) that fold back on themselves to form hairpinned structures. During AAV DNA replication, the TRs are nicked by the virus-encoded Rep proteins at the terminal resolution site (trs). This origin function apparently requires three sequence elements, the Rep binding element (RBE), a small palindrome that comprises a single tip of an internal hairpin within the TR (RBE'), and the trs. Previously, we determined the sequences at the trs required for Rep-mediated cleavage and demonstrated that the trs endonuclease reaction occurs in two discrete steps. In the first step, the Rep DNA helicase activity unwinds the TR, thereby extruding a stem-loop structure at the trs. In the second step, Rep transesterification activity cleaves the trs. Here we investigate the contribution of the RBE and RBE' during this process. Our data indicate that Rep is tethered to the RBE in a specific orientation during trs nicking. This orientation appears to align Rep on the AAV TR, allowing specific nucleotide contacts with the RBE' and directing nicking to the trs. Accordingly, alterations in the polarity or position of the RBE relative to the trs greatly inhibit Rep nicking. Substitutions within the RBE' also reduce Rep specific activity, but to a lesser extent. Interestingly, Rep interactions with the RBE and RBE' during nicking seem to be functionally distinct. Rep contacts with the RBE appear necessary for both the DNA helicase and trs cleavage steps of the endonuclease reaction. On the other hand, RBE' contacts seem to be required primarily for TR unwinding and formation of the trs stem-loop structure, not cleavage. Together, these results suggest a model of Rep interaction with the AAV TR during origin nicking through a tripartite cleavage signal comprised of the RBE, the RBE', and the trs.
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Affiliation(s)
- J R Brister
- Department of Molecular Genetics and Microbiology and Powell Gene Therapy Center, College of Medicine, University of Florida, Gainesville, Florida 32610, USA
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47
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Murray NE. Type I restriction systems: sophisticated molecular machines (a legacy of Bertani and Weigle). Microbiol Mol Biol Rev 2000; 64:412-34. [PMID: 10839821 PMCID: PMC98998 DOI: 10.1128/mmbr.64.2.412-434.2000] [Citation(s) in RCA: 318] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Restriction enzymes are well known as reagents widely used by molecular biologists for genetic manipulation and analysis, but these reagents represent only one class (type II) of a wider range of enzymes that recognize specific nucleotide sequences in DNA molecules and detect the provenance of the DNA on the basis of specific modifications to their target sequence. Type I restriction and modification (R-M) systems are complex; a single multifunctional enzyme can respond to the modification state of its target sequence with the alternative activities of modification or restriction. In the absence of DNA modification, a type I R-M enzyme behaves like a molecular motor, translocating vast stretches of DNA towards itself before eventually breaking the DNA molecule. These sophisticated enzymes are the focus of this review, which will emphasize those aspects that give insights into more general problems of molecular and microbial biology. Current molecular experiments explore target recognition, intramolecular communication, and enzyme activities, including DNA translocation. Type I R-M systems are notable for their ability to evolve new specificities, even in laboratory cultures. This observation raises the important question of how bacteria protect their chromosomes from destruction by newly acquired restriction specifities. Recent experiments demonstrate proteolytic mechanisms by which cells avoid DNA breakage by a type I R-M system whenever their chromosomal DNA acquires unmodified target sequences. Finally, the review will reflect the present impact of genomic sequences on a field that has previously derived information almost exclusively from the analysis of bacteria commonly studied in the laboratory.
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Affiliation(s)
- N E Murray
- Institute of Cell and Molecular Biology, University of Edinburgh, Edinburgh EH9 3JR, United Kingdom.
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48
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Firman K, Szczelkun MD. Measuring motion on DNA by the type I restriction endonuclease EcoR124I using triplex displacement. EMBO J 2000; 19:2094-102. [PMID: 10790375 PMCID: PMC305691 DOI: 10.1093/emboj/19.9.2094] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The type I restriction enzyme EcoR124I cleaves DNA following extensive linear translocation dependent upon ATP hydrolysis. Using protein-directed displacement of a DNA triplex, we have determined the kinetics of one-dimensional motion without the necessity of measuring DNA or ATP hydrolysis. The triplex was pre-formed specifically on linear DNA, 4370 bp from an EcoR124I site, and then incubated with endonuclease. Upon ATP addition, a distinct lag phase was observed before the triplex-forming oligonucleotide was displaced with exponential kinetics. As the distance between type I and triplex sites was shortened, the lag time decreased whilst the displacement reaction remained exponential. This is indicative of processive DNA translocation followed by collision with the triplex and oligonucleotide displacement. A linear relationship between lag duration and inter-site distance gives a translocation velocity of 400+/-32 bp/s at 20 degrees C. Furthermore, the data can only be explained by bi-directional translocation. An endonuclease with only one of the two HsdR subunits responsible for motion could still catalyse translocation. The reaction is less processive, but can 'reset' in either direction whenever the DNA is released.
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Affiliation(s)
- K Firman
- Biophysics Laboratories, University of Portsmouth, White Swan Road, Portsmouth PO1 2DT, UK
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49
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Janscak P, Bickle TA. DNA supercoiling during ATP-dependent DNA translocation by the type I restriction enzyme EcoAI. J Mol Biol 2000; 295:1089-99. [PMID: 10656812 DOI: 10.1006/jmbi.1999.3414] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Type I restriction enzymes cleave DNA at non-specific sites far from their recognition sequence as a consequence of ATP-dependent DNA translocation past the enzyme. During this reaction, the enzyme remains bound to the recognition sequence and translocates DNA towards itself simultaneously from both directions, generating DNA loops, which appear to be supercoiled when visualised by electron microscopy. To further investigate the mechanism of DNA translocation by type I restriction enzymes, we have probed the reaction intermediates with DNA topoisomerases. A DNA cleavage-deficient mutant of EcoAI, which has normal DNA translocation and ATPase activities, was used in these DNA supercoiling assays. In the presence of eubacterial DNA topoisomerase I, which specifically removes negative supercoils, the EcoAI mutant introduced positive supercoils into relaxed plasmid DNA substrate in a reaction dependent on ATP hydrolysis. The same DNA supercoiling activity followed by DNA cleavage was observed with the wild-type EcoAI endonuclease. Positive supercoils were not seen when eubacterial DNA topoisomerase I was replaced by eukaryotic DNA topoisomerase I, which removes both positive and negative supercoils. Furthermore, addition of eukaryotic DNA topoisomerase I to the product of the supercoiling reaction resulted in its rapid relaxation. These results are consistent with a model in which EcoAI translocation along the helical path of closed circular DNA duplex simultaneously generates positive supercoils ahead and negative supercoils behind the moving complex in the contracting and expanding DNA loops, respectively. In addition, we show that the highly positively supercoiled DNA generated by the EcoAI mutant is cleaved by EcoAI wild-type endonuclease much more slowly than relaxed DNA. This suggests that the topological changes in the DNA substrate associated with DNA translocation by type I restriction enzymes do not appear to be the trigger for DNA cleavage.
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Affiliation(s)
- P Janscak
- Department of Microbiology, University of Basel, Klingelbergstrasse 70, Basel, CH-4056, Switzerland
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