51
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Lohman TM, Fazio NT. How Does a Helicase Unwind DNA? Insights from RecBCD Helicase. Bioessays 2018; 40:e1800009. [PMID: 29603305 DOI: 10.1002/bies.201800009] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2018] [Revised: 02/26/2018] [Indexed: 01/06/2023]
Abstract
DNA helicases are a class of molecular motors that catalyze processive unwinding of double stranded DNA. In spite of much study, we know relatively little about the mechanisms by which these enzymes carry out the function for which they are named. Most current views are based on inferences from crystal structures. A prominent view is that the canonical ATPase motor exerts a force on the ssDNA resulting in "pulling" the duplex across a "pin" or "wedge" in the enzyme leading to a mechanical separation of the two DNA strands. In such models, DNA base pair separation is tightly coupled to ssDNA translocation of the motors. However, recent studies of the Escherichia coli RecBCD helicase suggest an alternative model in which DNA base pair melting and ssDNA translocation occur separately. In this view, the enzyme-DNA binding free energy is used to melt multiple DNA base pairs in an ATP-independent manner, followed by ATP-dependent translocation of the canonical motors along the newly formed ssDNA tracks. Repetition of these two steps results in processive DNA unwinding. We summarize recent evidence suggesting this mechanism for RecBCD helicase action.
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Affiliation(s)
- Timothy M Lohman
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis, School of Medicine, St. Louis, MO, 63110, USA
| | - Nicole T Fazio
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis, School of Medicine, St. Louis, MO, 63110, USA
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52
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Buchachenko AL, Breslavskaya NN. An Insight into the Helicase Functioning Through the Hydrogen Isotope Effects. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY B 2018. [DOI: 10.1134/s1990793117060185] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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53
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Li H, O'Donnell ME. The Eukaryotic CMG Helicase at the Replication Fork: Emerging Architecture Reveals an Unexpected Mechanism. Bioessays 2018; 40. [PMID: 29405332 DOI: 10.1002/bies.201700208] [Citation(s) in RCA: 57] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2017] [Revised: 12/27/2017] [Indexed: 01/12/2023]
Abstract
The eukaryotic helicase is an 11-subunit machine containing an Mcm2-7 motor ring that encircles DNA, Cdc45 and the GINS tetramer, referred to as CMG (Cdc45, Mcm2-7, GINS). CMG is "built" on DNA at origins in two steps. First, two Mcm2-7 rings are assembled around duplex DNA at origins in G1 phase, forming the Mcm2-7 "double hexamer." In a second step, in S phase Cdc45 and GINS are assembled onto each Mcm2-7 ring, hence producing two CMGs that ultimately form two replication forks that travel in opposite directions. Here, we review recent findings about CMG structure and function. The CMG unwinds the parental duplex and is also the organizing center of the replisome: it binds DNA polymerases and other factors. EM studies reveal a 20-subunit core replisome with the leading Pol ϵ and lagging Pol α-primase on opposite faces of CMG, forming a fundamentally asymmetric architecture. Structural studies of CMG at a replication fork reveal unexpected details of how CMG engages the DNA fork. The structures of CMG and the Mcm2-7 double hexamer on DNA suggest a completely unanticipated process for formation of bidirectional replication forks at origins.
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Affiliation(s)
- Huilin Li
- Cryo-EM Structural Biology Laboratory, Van Andel Research Institute, Grand Rapids, MI 49503, USA
| | - Michael E O'Donnell
- Department of DNA Replication, Rockefeller University and HHMI, New York, NY 10065, USA
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54
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Malik O, Khamis H, Rudnizky S, Kaplan A. The mechano-chemistry of a monomeric reverse transcriptase. Nucleic Acids Res 2018; 45:12954-12962. [PMID: 29165701 PMCID: PMC5728418 DOI: 10.1093/nar/gkx1168] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Accepted: 11/08/2017] [Indexed: 01/28/2023] Open
Abstract
Retroviral reverse transcriptase catalyses the synthesis of an integration-competent dsDNA molecule, using as a substrate the viral RNA. Using optical tweezers, we follow the Murine Leukemia Virus reverse transcriptase as it performs strand-displacement polymerization on a template under mechanical force. Our results indicate that reverse transcriptase functions as a Brownian ratchet, with dNTP binding as the rectifying reaction of the ratchet. We also found that reverse transcriptase is a relatively passive enzyme, able to polymerize on structured templates by exploiting their thermal breathing. Finally, our results indicate that the enzyme enters the recently characterized backtracking state from the pre-translocation complex.
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Affiliation(s)
- Omri Malik
- Faculty of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel.,Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Hadeel Khamis
- Faculty of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel.,Faculty of Physics, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Sergei Rudnizky
- Faculty of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel
| | - Ariel Kaplan
- Faculty of Biology, Technion-Israel Institute of Technology, Haifa 32000, Israel.,Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa 32000, Israel
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55
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Seol Y, Neuman KC. Combined Magnetic Tweezers and Micro-mirror Total Internal Reflection Fluorescence Microscope for Single-Molecule Manipulation and Visualization. Methods Mol Biol 2018; 1665:297-316. [PMID: 28940076 PMCID: PMC5672814 DOI: 10.1007/978-1-4939-7271-5_16] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/18/2023]
Abstract
Magnetic tweezers is a versatile yet simple single-molecule manipulation technique that has been used to study a broad range of nucleic acids and nucleic acid-based molecular motors. In this chapter, we combine micro-mirror-based total internal reflection microscopy with a magnetic tweezers instrument, permitting simultaneous single-molecule visualization and mechanical manipulation. We provide a simple method to calibrate the evanescent wave penetration depth via supercoiling of DNA with a fluorescent nanodiamond-labeled magnetic bead and a complementary method employing a surface-immobilized fluorescent nanodiamond.
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Affiliation(s)
- Yeonee Seol
- Laboratory of Single Molecule Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, Building 50, Room 3517, 50 South Drive, Bethesda, 20892, MD, USA
| | - Keir C Neuman
- Laboratory of Single Molecule Biophysics, National Heart, Lung, and Blood Institute, National Institutes of Health, Building 50, Room 3517, 50 South Drive, Bethesda, 20892, MD, USA.
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56
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Dynamics of DNA unwinding by helicases with frequent backward steps. Math Biosci 2017; 294:33-45. [DOI: 10.1016/j.mbs.2017.10.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 10/02/2017] [Accepted: 10/08/2017] [Indexed: 01/07/2023]
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57
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Tomko EJ, Lohman TM. Modulation of Escherichia coli UvrD Single-Stranded DNA Translocation by DNA Base Composition. Biophys J 2017; 113:1405-1415. [PMID: 28978435 DOI: 10.1016/j.bpj.2017.08.023] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 08/15/2017] [Accepted: 08/16/2017] [Indexed: 10/18/2022] Open
Abstract
Escherichia coli UvrD is an SF1A DNA helicase/translocase that functions in chromosomal DNA repair and replication of some plasmids. UvrD can also displace proteins such as RecA from DNA in its capacity as an anti-recombinase. Central to all of these activities is its ATP-driven 3'-5' single-stranded (ss) DNA translocation activity. Previous ensemble transient kinetic studies have estimated the average translocation rate of a UvrD monomer on ssDNA composed solely of deoxythymidylates. Here we show that the rate of UvrD monomer translocation along ssDNA is influenced by DNA base composition, with UvrD having the fastest rate along polypyrimidines although decreasing nearly twofold on ssDNA containing equal amounts of the four bases. Experiments with DNA containing abasic sites and polyethylene glycol spacers show that the ssDNA base also influences translocation processivity. These results indicate that changes in base composition and backbone insertions influence the translocation rates, with increased ssDNA base stacking correlated with decreased translocation rates, supporting the proposal that base-stacking interactions are involved in the translocation mechanism.
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Affiliation(s)
- Eric J Tomko
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri
| | - Timothy M Lohman
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri.
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58
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Hodeib S, Raj S, Manosas M, Zhang W, Bagchi D, Ducos B, Fiorini F, Kanaan J, Le Hir H, Allemand J, Bensimon D, Croquette V. A mechanistic study of helicases with magnetic traps. Protein Sci 2017; 26:1314-1336. [PMID: 28474797 PMCID: PMC5477542 DOI: 10.1002/pro.3187] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Revised: 04/29/2017] [Accepted: 05/02/2017] [Indexed: 01/08/2023]
Abstract
Helicases are a broad family of enzymes that separate nucleic acid double strand structures (DNA/DNA, DNA/RNA, or RNA/RNA) and thus are essential to DNA replication and the maintenance of nucleic acid integrity. We review the picture that has emerged from single molecule studies of the mechanisms of DNA and RNA helicases and their interactions with other proteins. Many features have been uncovered by these studies that were obscured by bulk studies, such as DNA strands switching, mechanical (rather than biochemical) coupling between helicases and polymerases, helicase-induced re-hybridization and stalled fork rescue.
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Affiliation(s)
- Samar Hodeib
- Laboratoire de physique statistiqueDépartement de physique de l'ENS, École normale supérieure, PSL Research University, Université Paris Diderot, Sorbonne Paris Cité, Sorbonne Universités, UPMC Univ. Paris 06, CNRS75005ParisFrance
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS)Département de biologie, École normale supérieure, CNRS, INSERM, PSL Research University75005ParisFrance
| | - Saurabh Raj
- Laboratoire de physique statistiqueDépartement de physique de l'ENS, École normale supérieure, PSL Research University, Université Paris Diderot, Sorbonne Paris Cité, Sorbonne Universités, UPMC Univ. Paris 06, CNRS75005ParisFrance
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS)Département de biologie, École normale supérieure, CNRS, INSERM, PSL Research University75005ParisFrance
| | - Maria Manosas
- Departament de Física FonamentalFacultat de Física, Universitat de BarcelonaBarcelona08028Spain
- CIBER‐BBN de BioingenieriaBiomateriales y Nanomedicina, Instituto de Sanidad Carlos IIIMadridSpain
| | - Weiting Zhang
- Laboratoire de physique statistiqueDépartement de physique de l'ENS, École normale supérieure, PSL Research University, Université Paris Diderot, Sorbonne Paris Cité, Sorbonne Universités, UPMC Univ. Paris 06, CNRS75005ParisFrance
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS)Département de biologie, École normale supérieure, CNRS, INSERM, PSL Research University75005ParisFrance
| | - Debjani Bagchi
- Laboratoire de physique statistiqueDépartement de physique de l'ENS, École normale supérieure, PSL Research University, Université Paris Diderot, Sorbonne Paris Cité, Sorbonne Universités, UPMC Univ. Paris 06, CNRS75005ParisFrance
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS)Département de biologie, École normale supérieure, CNRS, INSERM, PSL Research University75005ParisFrance
- Present address: Physics DepartmentFaculty of Science, The M.S. University of BarodaVadodaraGujarat390002India
| | - Bertrand Ducos
- Laboratoire de physique statistiqueDépartement de physique de l'ENS, École normale supérieure, PSL Research University, Université Paris Diderot, Sorbonne Paris Cité, Sorbonne Universités, UPMC Univ. Paris 06, CNRS75005ParisFrance
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS)Département de biologie, École normale supérieure, CNRS, INSERM, PSL Research University75005ParisFrance
| | - Francesca Fiorini
- Univ Lyon, Molecular Microbiology and Structural Biochemistry, MMSB‐IBCP UMR5086 CNRS/Lyon1Lyon Cedex 769367France
| | - Joanne Kanaan
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS)Département de biologie, École normale supérieure, CNRS, INSERM, PSL Research University75005ParisFrance
| | - Hervé Le Hir
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS)Département de biologie, École normale supérieure, CNRS, INSERM, PSL Research University75005ParisFrance
| | - Jean‐François Allemand
- Laboratoire de physique statistiqueDépartement de physique de l'ENS, École normale supérieure, PSL Research University, Université Paris Diderot, Sorbonne Paris Cité, Sorbonne Universités, UPMC Univ. Paris 06, CNRS75005ParisFrance
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS)Département de biologie, École normale supérieure, CNRS, INSERM, PSL Research University75005ParisFrance
| | - David Bensimon
- Laboratoire de physique statistiqueDépartement de physique de l'ENS, École normale supérieure, PSL Research University, Université Paris Diderot, Sorbonne Paris Cité, Sorbonne Universités, UPMC Univ. Paris 06, CNRS75005ParisFrance
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS)Département de biologie, École normale supérieure, CNRS, INSERM, PSL Research University75005ParisFrance
- Department of Chemistry and BiochemistryUniversity of California Los AngelesLos AngelesCalifornia90095
| | - Vincent Croquette
- Laboratoire de physique statistiqueDépartement de physique de l'ENS, École normale supérieure, PSL Research University, Université Paris Diderot, Sorbonne Paris Cité, Sorbonne Universités, UPMC Univ. Paris 06, CNRS75005ParisFrance
- Institut de Biologie de l'Ecole Normale Supérieure (IBENS)Département de biologie, École normale supérieure, CNRS, INSERM, PSL Research University75005ParisFrance
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59
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Galburt EA, Tomko EJ. Conformational selection and induced fit as a useful framework for molecular motor mechanisms. Biophys Chem 2017; 223:11-16. [PMID: 28187350 PMCID: PMC5357456 DOI: 10.1016/j.bpc.2017.01.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 01/27/2017] [Accepted: 01/27/2017] [Indexed: 11/15/2022]
Abstract
The linkage between macromolecular binding and conformational change that is ubiquitous in biological molecules can be understood in the context of the mechanisms of conformational selection and induced fit. Here, we explore mappings between these mechanisms of ligand binding and those underlying the translocation of molecular motors and the nucleic acid unwinding of helicases. The mechanism of biased motion exhibited by molecular motors is typically described as either a thermal ratchet or a power-stroke and nucleic acid helicases are characterized by either active or passive unwinding mechanisms. We posit that both Brownian ratchet translocation and passive unwinding are examples of conformational selection and that both power-stroke translocation and active unwinding are examples of induced fit. Furthermore, in ligand-binding reactions, both conformational selection and induced fit may exist in parallel leading to a ligand-dependent flux through the different mechanistic pathways. Given the mappings we describe, we propose that motors may be able to function via parallel ratchet and stroke mechanisms and that helicases may be able to function via parallel active and passive mechanisms.
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Affiliation(s)
- Eric A Galburt
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA.
| | - Eric J Tomko
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA
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60
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Single-molecule studies reveal reciprocating of WRN helicase core along ssDNA during DNA unwinding. Sci Rep 2017; 7:43954. [PMID: 28266653 PMCID: PMC5339710 DOI: 10.1038/srep43954] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2016] [Accepted: 02/01/2017] [Indexed: 01/08/2023] Open
Abstract
Werner syndrome is caused by mutations in the WRN gene encoding WRN helicase. A knowledge of WRN helicase's DNA unwinding mechanism in vitro is helpful for predicting its behaviors in vivo, and then understanding their biological functions. In the present study, for deeply understanding the DNA unwinding mechanism of WRN, we comprehensively characterized the DNA unwinding properties of chicken WRN helicase core in details, by taking advantages of single-molecule fluorescence resonance energy transfer (smFRET) method. We showed that WRN exhibits repetitive DNA unwinding and translocation behaviors on different DNA structures, including forked, overhanging and G-quadruplex-containing DNAs with an apparently limited unwinding processivity. It was further revealed that the repetitive behaviors were caused by reciprocating of WRN along the same ssDNA, rather than by complete dissociation from and rebinding to substrates or by strand switching. The present study sheds new light on the mechanism for WRN functioning.
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61
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Shuttling along DNA and directed processing of D-loops by RecQ helicase support quality control of homologous recombination. Proc Natl Acad Sci U S A 2017; 114:E466-E475. [PMID: 28069956 DOI: 10.1073/pnas.1615439114] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cells must continuously repair inevitable DNA damage while avoiding the deleterious consequences of imprecise repair. Distinction between legitimate and illegitimate repair processes is thought to be achieved in part through differential recognition and processing of specific noncanonical DNA structures, although the mechanistic basis of discrimination remains poorly defined. Here, we show that Escherichia coli RecQ, a central DNA recombination and repair enzyme, exhibits differential processing of DNA substrates based on their geometry and structure. Through single-molecule and ensemble biophysical experiments, we elucidate how the conserved domain architecture of RecQ supports geometry-dependent shuttling and directed processing of recombination-intermediate [displacement loop (D-loop)] substrates. Our study shows that these activities together suppress illegitimate recombination in vivo, whereas unregulated duplex unwinding is detrimental for recombination precision. Based on these results, we propose a mechanism through which RecQ helicases achieve recombination precision and efficiency.
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62
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Pavankumar TL, Exell JC, Kowalczykowski SC. Direct Fluorescent Imaging of Translocation and Unwinding by Individual DNA Helicases. Methods Enzymol 2016; 581:1-32. [PMID: 27793277 DOI: 10.1016/bs.mie.2016.09.010] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
The unique translocation and DNA unwinding properties of DNA helicases can be concealed by the stochastic behavior of enzyme molecules within the necessarily large populations used in ensemble experiments. With recent technological advances, the direct visualization of helicases acting on individual DNA molecules has contributed significantly to the current understanding of their mechanisms of action and biological functions. The combination of single-molecule techniques that enable both manipulation of individual protein or DNA molecules and visualization of their actions has made it possible to literally see novel and unique biochemical characteristics that were previously masked. Here, we describe the execution and use of single-molecule fluorescence imaging techniques, focusing on methods that include optical trapping in conjunction with epifluorescent imaging, and also surface immobilization in conjunction with total internal reflection fluorescence visualization. Combined with microchannel flow cells and microfluidic control, these methods allow individual fluorescently labeled protein and DNA molecules to be imaged and tracked, affording measurement of DNA unwinding and translocation at single-molecule resolution.
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Affiliation(s)
| | - J C Exell
- University of California, Davis, CA, United States
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63
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Hodeib S, Raj S, Manosas M, Zhang W, Bagchi D, Ducos B, Allemand JF, Bensimon D, Croquette V. Single molecule studies of helicases with magnetic tweezers. Methods 2016; 105:3-15. [DOI: 10.1016/j.ymeth.2016.06.019] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Revised: 05/31/2016] [Accepted: 06/20/2016] [Indexed: 10/21/2022] Open
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64
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Seol Y, Strub MP, Neuman KC. Single molecule measurements of DNA helicase activity with magnetic tweezers and t-test based step-finding analysis. Methods 2016; 105:119-27. [PMID: 27131595 PMCID: PMC4967025 DOI: 10.1016/j.ymeth.2016.04.030] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 04/25/2016] [Accepted: 04/27/2016] [Indexed: 01/26/2023] Open
Abstract
Magnetic tweezers is a versatile and easy to implement single-molecule technique that has become increasingly prevalent in the study of nucleic acid based molecular motors. Here, we provide a description of the magnetic tweezers instrument and guidelines for measuring and analyzing DNA helicase activity. Along with experimental methods, we describe a robust method of single-molecule trajectory analysis based on the Student's t-test that accommodates continuous transitions in addition to the discrete transitions assumed in most widely employed analysis routines. To illustrate the single-molecule unwinding assay and the analysis routine, we provide DNA unwinding measurements of Escherichia coli RecQ helicase under a variety of conditions (Na+, ATP, temperature, and DNA substrate geometry). These examples reveal that DNA unwinding measurements under various conditions can aid in elucidating the unwinding mechanism of DNA helicase but also emphasize that environmental effects on DNA helicase activity must be considered in relation to in vivo activity and mechanism.
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Affiliation(s)
- Yeonee Seol
- Laboratory of Single Molecule Biophysics, NHLBI, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Marie-Paule Strub
- Laboratory of Single Molecule Biophysics, NHLBI, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Keir C Neuman
- Laboratory of Single Molecule Biophysics, NHLBI, National Institutes of Health, Bethesda, MD 20892, USA.
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65
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Xie P. Processivity of nucleic acid unwinding and translocation by helicases. Proteins 2016; 84:1590-1605. [PMID: 27410462 DOI: 10.1002/prot.25102] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2016] [Revised: 06/24/2016] [Accepted: 06/24/2016] [Indexed: 11/05/2022]
Abstract
Helicases are a class of enzymes that use the chemical energy of NTP hydrolysis to drive mechanical processes such as translocation and nucleic acid (NA) strand separation. Besides the NA unwinding speed, another important factor for the helicase activity is the NA unwinding processivity. Here, we study the NA unwinding processivity with an analytical model that captures the phenomenology of the NA unwinding process. First, we study the processivity of the non-hexameric helicase that can unwind NA efficiently in the form of a monomer and the processivity of the hexameric helicase that can unwind DNA effectively, providing quantitative explanations of the available single-molecule experimental data. Then, we study the processivity of the non-hexameric helicases, in particular UvrD, in the form of a dimer and compare with that in the form of a monomer. The available single-molecule and some biochemical data showing that while UvrD monomer is a highly processive single-stranded DNA translocase it is inactive in DNA unwinding, whereas other biochemical data showing that UvrD is active in both single-stranded DNA translocation and DNA unwinding in the form of a monomer can be explained quantitatively and consistently. In addition, the recent single-molecule data are also explained quantitatively showing that constraining the 2B subdomain in closed conformation by intramolecular cross-linking can convert Rep monomer with a very poor DNA unwinding activity into a superhelicase that can unwind more than thousands of DNA base pairs processively, even against a large opposing force. Proteins 2016; 84:1590-1605. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Ping Xie
- Key Laboratory of Soft Matter Physics and Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China.
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66
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Simon MJ, Sokoloski JE, Hao L, Weiland E, Lohman TM. Processive DNA Unwinding by RecBCD Helicase in the Absence of Canonical Motor Translocation. J Mol Biol 2016; 428:2997-3012. [PMID: 27422010 DOI: 10.1016/j.jmb.2016.07.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Revised: 06/13/2016] [Accepted: 07/06/2016] [Indexed: 11/25/2022]
Abstract
Escherichia coli RecBCD is a DNA helicase/nuclease that functions in double-stranded DNA break repair. RecBCD possesses two motors (RecB, a 3' to 5' translocase, and RecD, a 5' to 3' translocase). Current DNA unwinding models propose that motor translocation is tightly coupled to base pair melting. However, some biochemical evidence suggests that DNA melting of multiple base pairs may occur separately from single-stranded DNA translocation. To test this hypothesis, we designed DNA substrates containing reverse backbone polarity linkages that prevent ssDNA translocation of the canonical RecB and RecD motors. Surprisingly, we find that RecBCD can processively unwind DNA for at least 80bp beyond the reverse polarity linkages. This ability requires an ATPase active RecB motor, the RecB "arm" domain, and also the RecB nuclease domain, but not its nuclease activity. These results indicate that RecBCD can unwind duplex DNA processively in the absence of ssDNA translocation by the canonical motors and that the nuclease domain regulates the helicase activity of RecBCD.
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Affiliation(s)
- Michael J Simon
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 S. Euclid Avenue, Box 8231, Saint Louis, MO 63110, USA
| | - Joshua E Sokoloski
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 S. Euclid Avenue, Box 8231, Saint Louis, MO 63110, USA
| | - Linxuan Hao
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 S. Euclid Avenue, Box 8231, Saint Louis, MO 63110, USA
| | - Elizabeth Weiland
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 S. Euclid Avenue, Box 8231, Saint Louis, MO 63110, USA
| | - Timothy M Lohman
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 S. Euclid Avenue, Box 8231, Saint Louis, MO 63110, USA.
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67
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Kemmerich FE, Kasaciunaite K, Seidel R. Modular magnetic tweezers for single-molecule characterizations of helicases. Methods 2016; 108:4-13. [PMID: 27402355 DOI: 10.1016/j.ymeth.2016.07.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Revised: 07/05/2016] [Accepted: 07/06/2016] [Indexed: 01/09/2023] Open
Abstract
Magnetic tweezers provide a versatile toolkit supporting the mechanistic investigation of helicases. In the present article, we show that custom magnetic tweezers setups are straightforward to construct and can easily be extended to provide adaptable platforms, capable of addressing a multitude of enquiries regarding the functions of these fascinating molecular machines. We first address the fundamental components of a basic magnetic tweezers scheme and review some previous results to demonstrate the versatility of this instrument. We then elaborate on several extensions to the basic magnetic tweezers scheme, and demonstrate their applications with data from ongoing research. As our methodological overview illustrates, magnetic tweezers are an extremely useful tool for the characterization of helicases and a custom built instrument can be specifically tailored to suit the experimenter's needs.
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Affiliation(s)
- Felix E Kemmerich
- Molecular Biophysics Group, Institute of Experimental Physics I, Universität Leipzig, 04103 Leipzig, Germany
| | - Kristina Kasaciunaite
- Molecular Biophysics Group, Institute of Experimental Physics I, Universität Leipzig, 04103 Leipzig, Germany
| | - Ralf Seidel
- Molecular Biophysics Group, Institute of Experimental Physics I, Universität Leipzig, 04103 Leipzig, Germany.
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68
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Carter AR, Seaberg MH, Fan HF, Sun G, Wilds CJ, Li HW, Perkins TT. Sequence-dependent nanometer-scale conformational dynamics of individual RecBCD-DNA complexes. Nucleic Acids Res 2016; 44:5849-60. [PMID: 27220465 PMCID: PMC4937329 DOI: 10.1093/nar/gkw445] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 05/09/2016] [Indexed: 01/02/2023] Open
Abstract
RecBCD is a multifunctional enzyme that possesses both helicase and nuclease activities. To gain insight into the mechanism of its helicase function, RecBCD unwinding at low adenosine triphosphate (ATP) (2-4 μM) was measured using an optical-trapping assay featuring 1 base-pair (bp) precision. Instead of uniformly sized steps, we observed forward motion convolved with rapid, large-scale (∼4 bp) variations in DNA length. We interpret this motion as conformational dynamics of the RecBCD-DNA complex in an unwinding-competent state, arising, in part, by an enzyme-induced, back-and-forth motion relative to the dsDNA that opens and closes the duplex. Five observations support this interpretation. First, these dynamics were present in the absence of ATP. Second, the onset of the dynamics was coupled to RecBCD entering into an unwinding-competent state that required a sufficiently long 5' strand to engage the RecD helicase. Third, the dynamics were modulated by the GC-content of the dsDNA. Fourth, the dynamics were suppressed by an engineered interstrand cross-link in the dsDNA that prevented unwinding. Finally, these dynamics were suppressed by binding of a specific non-hydrolyzable ATP analog. Collectively, these observations show that during unwinding, RecBCD binds to DNA in a dynamic mode that is modulated by the nucleotide state of the ATP-binding pocket.
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Affiliation(s)
- Ashley R Carter
- Department of Physics, Amherst College, Amherst, MA 01002, USA
| | - Maasa H Seaberg
- Department of Physics, University of Colorado, Boulder, CO 80309, USA JILA, National Institute of Standards and Technology and University of Colorado, Boulder, CO 80309, USA
| | - Hsiu-Fang Fan
- Department of Life Sciences and Institute of Genome Sciences, National Yang-Ming University, Taipei 11221, Taiwan Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec H4B1R6, Canada
| | - Gang Sun
- Department of Chemistry, National Taiwan University, Taipei 10617, Taiwan
| | | | - Hung-Wen Li
- Department of Chemistry and Biochemistry, Concordia University, Montreal, Quebec H4B1R6, Canada
| | - Thomas T Perkins
- JILA, National Institute of Standards and Technology and University of Colorado, Boulder, CO 80309, USA Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO 80309, USA
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69
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Camunas-Soler J, Ribezzi-Crivellari M, Ritort F. Elastic Properties of Nucleic Acids by Single-Molecule Force Spectroscopy. Annu Rev Biophys 2016; 45:65-84. [PMID: 27145878 DOI: 10.1146/annurev-biophys-062215-011158] [Citation(s) in RCA: 53] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
We review the current knowledge on the use of single-molecule force spectroscopy techniques to extrapolate the elastic properties of nucleic acids. We emphasize the lesser-known elastic properties of single-stranded DNA. We discuss the importance of accurately determining the elastic response in pulling experiments, and we review the simplest models used to rationalize the experimental data as well as the experimental approaches used to pull single-stranded DNA. Applications used to investigate DNA conformational transitions and secondary structure formation are also highlighted. Finally, we provide an overview of the effects of salt and temperature and briefly discuss the effects of contour length and sequence dependence.
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Affiliation(s)
- Joan Camunas-Soler
- Departament de Física Fonamental, Universitat de Barcelona, 08028 Barcelona, Spain; .,CIBER-BBN de Bioingeniería, Biomateriales y Nanomedicina, Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Marco Ribezzi-Crivellari
- Departament de Física Fonamental, Universitat de Barcelona, 08028 Barcelona, Spain; .,CIBER-BBN de Bioingeniería, Biomateriales y Nanomedicina, Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Felix Ritort
- Departament de Física Fonamental, Universitat de Barcelona, 08028 Barcelona, Spain; .,CIBER-BBN de Bioingeniería, Biomateriales y Nanomedicina, Instituto de Salud Carlos III, 28029 Madrid, Spain
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70
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Pincus DL, Chakrabarti S, Thirumalai D. Helicase processivity and not the unwinding velocity exhibits universal increase with force. Biophys J 2016. [PMID: 26200858 DOI: 10.1016/j.bpj.2015.05.020] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Helicases, involved in a number of cellular functions, are motors that translocate along single-stranded nucleic acid and couple the motion to unwinding double-strands of a duplex nucleic acid. The junction between double- and single-strands creates a barrier to the movement of the helicase, which can be manipulated in vitro by applying mechanical forces directly on the nucleic acid strands. Single-molecule experiments have demonstrated that the unwinding velocities of some helicases increase dramatically with increase in the external force, while others show little response. In contrast, the unwinding processivity always increases when the force increases. The differing responses of the unwinding velocity and processivity to force have lacked explanation. By generalizing a previous model of processive unwinding by helicases, we provide a unified framework for understanding the dependence of velocity and processivity on force and the nucleic acid sequence. We predict that the sensitivity of unwinding processivity to external force is a universal feature that should be observed in all helicases. Our prediction is illustrated using T7 and NS3 helicases as case studies. Interestingly, the increase in unwinding processivity with force depends on whether the helicase forces basepair opening by direct interaction or if such a disruption occurs spontaneously due to thermal fluctuations. Based on the theoretical results, we propose that proteins like single-strand binding proteins associated with helicases in the replisome may have coevolved with helicases to increase the unwinding processivity even if the velocity remains unaffected.
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Affiliation(s)
- David L Pincus
- Biophysics Program, Institute for Physical Science and Technology, University of Maryland, College Park, Maryland.
| | - Shaon Chakrabarti
- Biophysics Program, Institute for Physical Science and Technology, University of Maryland, College Park, Maryland.
| | - D Thirumalai
- Biophysics Program, Institute for Physical Science and Technology, University of Maryland, College Park, Maryland.
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71
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Xie P. Dynamics of monomeric and hexameric helicases. Biophys Chem 2016; 211:49-58. [DOI: 10.1016/j.bpc.2016.02.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2015] [Revised: 02/11/2016] [Accepted: 02/12/2016] [Indexed: 01/19/2023]
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72
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Functional Importance of Mobile Ribosomal Proteins. BIOMED RESEARCH INTERNATIONAL 2015; 2015:539238. [PMID: 26457300 PMCID: PMC4592705 DOI: 10.1155/2015/539238] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/26/2015] [Accepted: 08/12/2015] [Indexed: 01/07/2023]
Abstract
Although the dynamic motions and peptidyl transferase activity seem to be embedded in the rRNAs, the ribosome contains more than 50 ribosomal proteins (r-proteins), whose functions remain largely elusive. Also, the precise forms of some of these r-proteins, as being part of the ribosome, are not structurally solved due to their high flexibility, which hinders the efforts in their functional elucidation. Owing to recent advances in cryo-electron microscopy, single-molecule techniques, and theoretical modeling, much has been learned about the dynamics of these r-proteins. Surprisingly, allosteric regulations have been found in between spatially separated components as distant as those in the opposite sides of the ribosome. Here, we focus on the functional roles and intricate regulations of the mobile L1 and L12 stalks and L9 and S1 proteins. Conformational flexibility also enables versatile functions for r-proteins beyond translation. The arrangement of r-proteins may be under evolutionary pressure that fine-tunes mass distributions for optimal structural dynamics and catalytic activity of the ribosome.
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73
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Fiorini F, Bagchi D, Le Hir H, Croquette V. Human Upf1 is a highly processive RNA helicase and translocase with RNP remodelling activities. Nat Commun 2015; 6:7581. [PMID: 26138914 PMCID: PMC4506499 DOI: 10.1038/ncomms8581] [Citation(s) in RCA: 100] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Accepted: 05/21/2015] [Indexed: 12/26/2022] Open
Abstract
RNA helicases are implicated in most cellular RNA-dependent events. In eukaryotes however, only few have been functionally characterized. Upf1 is a RNA helicase essential for nonsense-mediated mRNA decay (NMD). Here, using magnetic tweezers and bulk assays, we observe that human Upf1 is able to translocate slowly over long single-stranded nucleic acids with a processivity >10 kb. Upf1 efficiently translocates through double-stranded structures and protein-bound sequences, demonstrating that Upf1 is an efficient ribonucleoprotein complex remodeler. Our observation of processive unwinding by an eukaryotic RNA helicase reveals that Upf1, once recruited onto NMD mRNA targets, can scan the entire transcript to irreversibly remodel the mRNP, facilitating its degradation by the NMD machinery. Upf1 is a multifunctional helicase involved in various DNA- and RNA-related processes, including nonsense-mediated mRNA decay (NMD). Here the authors demonstrate that Upf1 is a highly processive ribonucleoprotein complex remodeler—a capability likely important for Upf1's NMD function.
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Affiliation(s)
- Francesca Fiorini
- 1] Institut de Biologie de l'Ecole Normale Supérieure, CNRS UMR8197, Paris 75230, France [2] Institut de Biologie de l'Ecole Normale Supérieure, INSERM U1024, Paris 75230, France
| | - Debjani Bagchi
- 1] Institut de Biologie de l'Ecole Normale Supérieure, CNRS UMR8197, Paris 75230, France [2] Institut de Biologie de l'Ecole Normale Supérieure, INSERM U1024, Paris 75230, France [3] Laboratoire de Physique Statistique, Ecole Normale Supérieure, Université Pierre et Marie Curie Paris, Université Paris Diderot, CNRS, 24 rue Lhomond, Paris 75005, France
| | - Hervé Le Hir
- 1] Institut de Biologie de l'Ecole Normale Supérieure, CNRS UMR8197, Paris 75230, France [2] Institut de Biologie de l'Ecole Normale Supérieure, INSERM U1024, Paris 75230, France
| | - Vincent Croquette
- 1] Institut de Biologie de l'Ecole Normale Supérieure, CNRS UMR8197, Paris 75230, France [2] Institut de Biologie de l'Ecole Normale Supérieure, INSERM U1024, Paris 75230, France [3] Laboratoire de Physique Statistique, Ecole Normale Supérieure, Université Pierre et Marie Curie Paris, Université Paris Diderot, CNRS, 24 rue Lhomond, Paris 75005, France
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74
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Gollnick B, Carrasco C, Zuttion F, Gilhooly NS, Dillingham MS, Moreno-Herrero F. Probing DNA helicase kinetics with temperature-controlled magnetic tweezers. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2015; 11:1273-84. [PMID: 25400244 PMCID: PMC4473356 DOI: 10.1002/smll.201402686] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2014] [Indexed: 05/04/2023]
Abstract
Motor protein functions like adenosine triphosphate (ATP) hydrolysis or translocation along molecular substrates take place at nanometric scales and consequently depend on the amount of available thermal energy. The associated rates can hence be investigated by actively varying the temperature conditions. In this article, a thermally controlled magnetic tweezers (MT) system for single-molecule experiments at up to 40 °C is presented. Its compact thermostat module yields a precision of 0.1 °C and can in principle be tailored to any other surface-coupled microscopy technique, such as tethered particle motion (TPM), nanopore-based sensing of biomolecules, or super-resolution fluorescence imaging. The instrument is used to examine the temperature dependence of translocation along double-stranded (ds)DNA by individual copies of the protein complex AddAB, a helicase-nuclease motor involved in dsDNA break repair. Despite moderately lower mean velocities measured at sub-saturating ATP concentrations, almost identical estimates of the enzymatic reaction barrier (around 21-24 k(B)T) are obtained by comparing results from MT and stopped-flow bulk assays. Single-molecule rates approach ensemble values at optimized chemical energy conditions near the motor, which can withstand opposing loads of up to 14 piconewtons (pN). Having proven its reliability, the temperature-controlled MT described herein will eventually represent a routinely applied method within the toolbox for nano-biotechnology.
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Affiliation(s)
- Benjamin Gollnick
- Centro Nacional de Biotecnología, CSIC, Darwin 3, Campus de Cantoblanco, 28049, Madrid, Spain
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75
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Chen MC, Murat P, Abecassis K, Ferré-D'Amaré AR, Balasubramanian S. Insights into the mechanism of a G-quadruplex-unwinding DEAH-box helicase. Nucleic Acids Res 2015; 43:2223-31. [PMID: 25653156 PMCID: PMC4344499 DOI: 10.1093/nar/gkv051] [Citation(s) in RCA: 73] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
The unwinding of nucleic acid secondary structures within cells is crucial to maintain genomic integrity and prevent abortive transcription and translation initiation. DHX36, also known as RHAU or G4R1, is a DEAH-box ATP-dependent helicase highly specific for DNA and RNA G-quadruplexes (G4s). A fundamental mechanistic understanding of the interaction between helicases and their G4 substrates is important to elucidate G4 biology and pave the way toward G4-targeted therapies. Here we analyze how the thermodynamic stability of G4 substrates affects binding and unwinding by DHX36. We modulated the stability of the G4 substrates by varying the sequence and the number of G-tetrads and by using small, G4-stabilizing molecules. We found an inverse correlation between the thermodynamic stability of the G4 substrates and rates of unwinding by DHX36. In stark contrast, the ATPase activity of the helicase was largely independent of substrate stability pointing toward a decoupling mechanism akin to what has been observed for many double-stranded DEAD-box RNA helicases. Our study provides the first evidence that DHX36 uses a local, non-processive mechanism to unwind G4 substrates, reminiscent of that of eukaryotic initiation factor 4A (eIF4A) on double-stranded substrates.
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Affiliation(s)
- Michael C Chen
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK National Heart, Lung and Blood Institute, 50 South Drive, MSC-8012, Bethesda, MD 20892-8012, USA
| | - Pierre Murat
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
| | - Keren Abecassis
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
| | - Adrian R Ferré-D'Amaré
- National Heart, Lung and Blood Institute, 50 South Drive, MSC-8012, Bethesda, MD 20892-8012, USA
| | - Shankar Balasubramanian
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK Cancer Research UK Cambridge Institute, Li Ka Shing Centre, Cambridge, UK
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76
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Liu S, Chistol G, Bustamante C. Mechanical operation and intersubunit coordination of ring-shaped molecular motors: insights from single-molecule studies. Biophys J 2014; 106:1844-58. [PMID: 24806916 DOI: 10.1016/j.bpj.2014.03.029] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Accepted: 03/19/2014] [Indexed: 01/27/2023] Open
Abstract
Ring NTPases represent a large and diverse group of proteins that couple their nucleotide hydrolysis activity to a mechanical task involving force generation and some type of transport process in the cell. Because of their shape, these enzymes often operate as gates that separate distinct cellular compartments to control and regulate the passage of chemical species across them. In this manner, ions and small molecules are moved across membranes, biopolymer substrates are segregated between cells or moved into confined spaces, double-stranded nucleic acids are separated into single strands to provide access to the genetic information, and polypeptides are unfolded and processed for recycling. Here we review the recent advances in the characterization of these motors using single-molecule manipulation and detection approaches. We describe the various mechanisms by which ring motors convert chemical energy to mechanical force or torque and coordinate the activities of individual subunits that constitute the ring. We also examine how single-molecule studies have contributed to a better understanding of the structural elements involved in motor-substrate interaction, mechanochemical coupling, and intersubunit coordination. Finally, we discuss how these molecular motors tailor their operation-often through regulation by other cofactors-to suit their unique biological functions.
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Affiliation(s)
- Shixin Liu
- Jason L. Choy Laboratory of Single-Molecule Biophysics, University of California, Berkeley, and Lawrence Berkeley National Laboratory, Berkeley, California; California Institute for Quantitative Biosciences, University of California, Berkeley, and Lawrence Berkeley National Laboratory, Berkeley, California
| | - Gheorghe Chistol
- Jason L. Choy Laboratory of Single-Molecule Biophysics, University of California, Berkeley, and Lawrence Berkeley National Laboratory, Berkeley, California; Department of Physics, University of California, Berkeley, and Lawrence Berkeley National Laboratory, Berkeley, California
| | - Carlos Bustamante
- Jason L. Choy Laboratory of Single-Molecule Biophysics, University of California, Berkeley, and Lawrence Berkeley National Laboratory, Berkeley, California; California Institute for Quantitative Biosciences, University of California, Berkeley, and Lawrence Berkeley National Laboratory, Berkeley, California; Department of Physics, University of California, Berkeley, and Lawrence Berkeley National Laboratory, Berkeley, California; Department of Molecular and Cell Biology, Department of Chemistry, Howard Hughes Medical Institute, and Kavli Energy NanoSciences Institute, University of California, Berkeley, and Lawrence Berkeley National Laboratory, Berkeley, California.
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77
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Lehmann KC, Snijder EJ, Posthuma CC, Gorbalenya AE. What we know but do not understand about nidovirus helicases. Virus Res 2014; 202:12-32. [PMID: 25497126 PMCID: PMC7114383 DOI: 10.1016/j.virusres.2014.12.001] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2014] [Revised: 11/28/2014] [Accepted: 12/01/2014] [Indexed: 01/24/2023]
Abstract
The ubiquitous nidovirus helicase is a multi-functional enzyme of superfamily 1. Its unique N-terminal domain is most similar to the Upf1 multinuclear zinc-binding domain. It has been implicated in replication, transcription, virion biogenesis, translation and post-transcriptional viral RNA processing. Four different classes of antiviral compounds targeting the helicase have been identified.
Helicases are versatile NTP-dependent motor proteins of monophyletic origin that are found in all kingdoms of life. Their functions range from nucleic acid duplex unwinding to protein displacement and double-strand translocation. This explains their participation in virtually every metabolic process that involves nucleic acids, including DNA replication, recombination and repair, transcription, translation, as well as RNA processing. Helicases are encoded by all plant and animal viruses with a positive-sense RNA genome that is larger than 7 kb, indicating a link to genome size evolution in this virus class. Viral helicases belong to three out of the six currently recognized superfamilies, SF1, SF2, and SF3. Despite being omnipresent, highly conserved and essential, only a few viral helicases, mostly from SF2, have been studied extensively. In general, their specific roles in the viral replication cycle remain poorly understood at present. The SF1 helicase protein of viruses classified in the order Nidovirales is encoded in replicase open reading frame 1b (ORF1b), which is translated to give rise to a large polyprotein following a ribosomal frameshift from the upstream ORF1a. Proteolytic processing of the replicase polyprotein yields a dozen or so mature proteins, one of which includes a helicase. Its hallmark is the presence of an N-terminal multi-nuclear zinc-binding domain, the nidoviral genetic marker and one of the most conserved domains across members of the order. This review summarizes biochemical, structural, and genetic data, including drug development studies, obtained using helicases originating from several mammalian nidoviruses, along with the results of the genomics characterization of a much larger number of (putative) helicases of vertebrate and invertebrate nidoviruses. In the context of our knowledge of related helicases of cellular and viral origin, it discusses the implications of these results for the protein's emerging critical function(s) in nidovirus evolution, genome replication and expression, virion biogenesis, and possibly also post-transcriptional processing of viral RNAs. Using our accumulated knowledge and highlighting gaps in our data, concepts and approaches, it concludes with a perspective on future research aimed at elucidating the role of helicases in the nidovirus replication cycle.
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Affiliation(s)
- Kathleen C Lehmann
- Department of Medical Microbiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Eric J Snijder
- Department of Medical Microbiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Clara C Posthuma
- Department of Medical Microbiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Alexander E Gorbalenya
- Department of Medical Microbiology, Leiden University Medical Center, Leiden, The Netherlands; Faculty of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Russia.
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78
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Accessory Replicative Helicases and the Replication of Protein-Bound DNA. J Mol Biol 2014; 426:3917-3928. [DOI: 10.1016/j.jmb.2014.10.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2014] [Revised: 09/29/2014] [Accepted: 10/06/2014] [Indexed: 12/29/2022]
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79
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Venø ST, Witt MB, Kulikowicz T, Bohr VA, Stevnsner T. Regulation of the human Suv3 helicase on DNA by inorganic cofactors. Biochimie 2014; 108:160-8. [PMID: 25446650 DOI: 10.1016/j.biochi.2014.11.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2014] [Accepted: 11/05/2014] [Indexed: 11/19/2022]
Abstract
Mitochondria are essential organelles and consequently proper expression and maintenance of the mitochondrial genome are indispensable for proper cell function. The mitochondrial Suv3 (SUPV3L1) helicase is known to have a central role in mitochondrial RNA metabolism and to be essential for maintenance of mitochondrial DNA stability. Here we have performed biochemical investigations to determine the potential regulation of the human Suv3 (hSuv3) helicase function by inorganic cofactors. We find that hSuv3 helicase and ATPase activity in vitro is strictly dependent on the presence of specific divalent cations. Interestingly, we show that divalent cations and nucleotide concentration have a direct effect on helicase substrate stability. Also, hSuv3 helicase is able to utilize several different nucleotide cofactors including both NTPs and dNTPs. Intriguingly, the potency of the individual nucleotide as energy source for hSuv3 unwinding differed depending on the included divalent cation and nucleotide concentration. At low concentrations, all four NTPs could support helicase activity with varying effectiveness depending on the included divalent cation. However, at higher nucleotide concentrations, only ATP was able to elicit the helicase activity of hSuv3. Consequently, we speculate that the capacity of hSuv3 DNA unwinding activity might be sensitive to the local availability of specific inorganic cofactors.
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Affiliation(s)
- Susanne T Venø
- Danish Center of Molecular Gerontology and Danish Aging Research Center, University of Aarhus, Department of Molecular Biology and Genetics, Aarhus C DK-8000, Denmark
| | - Marie B Witt
- Danish Center of Molecular Gerontology and Danish Aging Research Center, University of Aarhus, Department of Molecular Biology and Genetics, Aarhus C DK-8000, Denmark
| | - Tomasz Kulikowicz
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Vilhelm A Bohr
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224, USA
| | - Tinna Stevnsner
- Danish Center of Molecular Gerontology and Danish Aging Research Center, University of Aarhus, Department of Molecular Biology and Genetics, Aarhus C DK-8000, Denmark.
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80
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DEAD-box helicase proteins disrupt RNA tertiary structure through helix capture. PLoS Biol 2014; 12:e1001981. [PMID: 25350280 PMCID: PMC4211656 DOI: 10.1371/journal.pbio.1001981] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Accepted: 09/18/2014] [Indexed: 01/11/2023] Open
Abstract
Single-molecule fluorescence experiments reveal how DEAD-box proteins unfold structured RNAs to promote conformational transitions and refolding to the native functional state. DEAD-box helicase proteins accelerate folding and rearrangements of highly structured RNAs and RNA–protein complexes (RNPs) in many essential cellular processes. Although DEAD-box proteins have been shown to use ATP to unwind short RNA helices, it is not known how they disrupt RNA tertiary structure. Here, we use single molecule fluorescence to show that the DEAD-box protein CYT-19 disrupts tertiary structure in a group I intron using a helix capture mechanism. CYT-19 binds to a helix within the structured RNA only after the helix spontaneously loses its tertiary contacts, and then CYT-19 uses ATP to unwind the helix, liberating the product strands. Ded1, a multifunctional yeast DEAD-box protein, gives analogous results with small but reproducible differences that may reflect its in vivo roles. The requirement for spontaneous dynamics likely targets DEAD-box proteins toward less stable RNA structures, which are likely to experience greater dynamic fluctuations, and provides a satisfying explanation for previous correlations between RNA stability and CYT-19 unfolding efficiency. Biologically, the ability to sense RNA stability probably biases DEAD-box proteins to act preferentially on less stable misfolded structures and thereby to promote native folding while minimizing spurious interactions with stable, natively folded RNAs. In addition, this straightforward mechanism for RNA remodeling does not require any specific structural environment of the helicase core and is likely to be relevant for DEAD-box proteins that promote RNA rearrangements of RNP complexes including the spliceosome and ribosome. In addition to carrying genetic information from DNA to protein, RNAs function in many essential cellular processes. This often requires the RNA to form a specific three-dimensional structure, and some functions require cycling between multiple structures. However, RNAs have a strong propensity to become trapped in nonfunctional, misfolded structures. Due to the intrinsic stability of local structure for RNA, these misfolded species can be long-lived and therefore accumulate. ATP-dependent RNA chaperone proteins called DEAD-box proteins are known to promote native RNA folding by disrupting misfolded structures. Although these proteins can unwind short RNA helices, the mechanism by which they act upon higher order tertiary contacts is unknown. Our current work shows that DEAD-box proteins capture transiently exposed RNA helices, preventing any tertiary contacts from reforming and potentially destabilizing the global RNA architecture. Helix unwinding by the DEAD-box protein then allows the product RNA strands to form new contacts. This helix capture mechanism for manipulation of RNA tertiary structure does not require a specific binding motif or structural environment and may be general for DEAD-box helicase proteins that act on structured RNAs.
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81
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Aarattuthodiyil S, Byrd AK, Raney KD. Simultaneous binding to the tracking strand, displaced strand and the duplex of a DNA fork enhances unwinding by Dda helicase. Nucleic Acids Res 2014; 42:11707-20. [PMID: 25249618 PMCID: PMC4191417 DOI: 10.1093/nar/gku845] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Interactions between helicases and the tracking strand of a DNA substrate are well-characterized; however, the role of the displaced strand is a less understood characteristic of DNA unwinding. Dda helicase exhibited greater processivity when unwinding a DNA fork compared to a ss/ds DNA junction substrate. The lag phase in the unwinding progress curve was reduced for the forked DNA compared to the ss/ds junction. Fewer kinetic steps were required to unwind the fork compared to the ss/ds junction, suggesting that binding to the fork leads to disruption of the duplex. DNA footprinting confirmed that interaction of Dda with a fork leads to two base pairs being disrupted whereas no disruption of base pairing was observed with the ss/ds junction. Neutralization of the phosphodiester backbone resulted in a DNA-footprinting pattern similar to that observed with the ss/ds junction, consistent with disruption of the interaction between Dda and the displaced strand. Several basic residues in the 1A domain which were previously proposed to bind to the incoming duplex DNA were replaced with alanines, resulting in apparent loss of interaction with the duplex. Taken together, these results suggest that Dda interaction with the tracking strand, displaced strand and duplex coordinates DNA unwinding.
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Affiliation(s)
- Suja Aarattuthodiyil
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
| | - Alicia K Byrd
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
| | - Kevin D Raney
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
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82
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RecG and UvsW catalyse robust DNA rewinding critical for stalled DNA replication fork rescue. Nat Commun 2014; 4:2368. [PMID: 24013402 PMCID: PMC3778716 DOI: 10.1038/ncomms3368] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2013] [Accepted: 07/30/2013] [Indexed: 11/09/2022] Open
Abstract
Helicases that both unwind and rewind DNA have central roles in DNA repair and genetic recombination. In contrast to unwinding, DNA rewinding by helicases has proved difficult to characterize biochemically because of its thermodynamically downhill nature. Here we use single-molecule assays to mechanically destabilize a DNA molecule and follow, in real time, unwinding and rewinding by two DNA repair helicases, bacteriophage T4 UvsW and Escherichia coli RecG. We find that both enzymes are robust rewinding enzymes, which can work against opposing forces as large as 35 pN, revealing their active character. The generation of work during the rewinding reaction allows them to couple rewinding to DNA unwinding and/or protein displacement reactions central to the rescue of stalled DNA replication forks. The overall results support a general mechanism for monomeric rewinding enzymes.
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83
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Spies M. Two steps forward, one step back: determining XPD helicase mechanism by single-molecule fluorescence and high-resolution optical tweezers. DNA Repair (Amst) 2014; 20:58-70. [PMID: 24560558 DOI: 10.1016/j.dnarep.2014.01.013] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2013] [Revised: 12/31/2013] [Accepted: 01/13/2014] [Indexed: 11/17/2022]
Abstract
XPD-like helicases constitute a prominent DNA helicase family critical for many aspects of genome maintenance. These enzymes share a unique structural feature, an auxiliary domain stabilized by an iron-sulphur (FeS) cluster, and a 5'-3' polarity of DNA translocation and duplex unwinding. Biochemical analyses alongside two single-molecule approaches, total internal reflection fluorescence microscopy and high-resolution optical tweezers, have shown how the unique structural features of XPD helicase and its specific patterns of substrate interactions tune the helicase for its specific cellular function and shape its molecular mechanism. The FeS domain forms a duplex separation wedge and contributes to an extended DNA binding site. Interactions within this site position the helicase in an orientation to unwind the duplex, control the helicase rate, and verify the integrity of the translocating strand. Consistent with its cellular role, processivity of XPD is limited and is defined by an idiosyncratic stepping kinetics. DNA duplex separation occurs in single base pair steps punctuated by frequent backward steps and conformational rearrangements of the protein-DNA complex. As such, the helicase in isolation mainly stabilizes spontaneous base pair opening and exhibits a limited ability to unwind stable DNA duplexes. The presence of a cognate ssDNA binding protein converts XPD into a vigorous helicase by destabilizing the upstream dsDNA as well as by trapping the unwound strands. Remarkably, the two proteins can co-exist on the same DNA strand without competing for binding. The current model of the XPD unwinding mechanism will be discussed along with possible modifications to this mechanism by the helicase interacting partners and unique features of such bio-medically important XPD-like helicases as FANCJ (BACH1), RTEL1 and CHLR1 (DDX11).
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Affiliation(s)
- Maria Spies
- Department of Biochemistry, University of Iowa Carver College of Medicine, IA 52242, United States.
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84
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Bosco A, Camunas-Soler J, Ritort F. Elastic properties and secondary structure formation of single-stranded DNA at monovalent and divalent salt conditions. Nucleic Acids Res 2014; 42:2064-74. [PMID: 24225314 PMCID: PMC3919573 DOI: 10.1093/nar/gkt1089] [Citation(s) in RCA: 96] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Revised: 10/16/2013] [Accepted: 10/17/2013] [Indexed: 11/16/2022] Open
Abstract
Single-stranded DNA (ssDNA) plays a major role in several biological processes. It is therefore of fundamental interest to understand how the elastic response and the formation of secondary structures are modulated by the interplay between base pairing and electrostatic interactions. Here we measure force-extension curves (FECs) of ssDNA molecules in optical tweezers set up over two orders of magnitude of monovalent and divalent salt conditions, and obtain its elastic parameters by fitting the FECs to semiflexible models of polymers. For both monovalent and divalent salts, we find that the electrostatic contribution to the persistence length is proportional to the Debye screening length, varying as the inverse of the square root of cation concentration. The intrinsic persistence length is equal to 0.7 nm for both types of salts, and the effectivity of divalent cations in screening electrostatic interactions appears to be 100-fold as compared with monovalent salt, in line with what has been recently reported for single-stranded RNA. Finally, we propose an analysis of the FECs using a model that accounts for the effective thickness of the filament at low salt condition and a simple phenomenological description that quantifies the formation of non-specific secondary structure at low forces.
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Affiliation(s)
- Alessandro Bosco
- SISSA - Scuola Internazionale Superiore di Studi Avanzati, via Bonomea 265, 34136 Trieste, Italy, Elettra-Sincrotrone Trieste S.C.p.A., Strada Statale 14 - km 163,5 in AREA Science Park, 34149 Basovizza Trieste, Italy, Departament de Física Fonamental, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain and CIBER de Bioingeniería, Biomateriales y Nanomedicina, Instituto de Salud Carlos III, Madrid, Spain
| | - Joan Camunas-Soler
- SISSA - Scuola Internazionale Superiore di Studi Avanzati, via Bonomea 265, 34136 Trieste, Italy, Elettra-Sincrotrone Trieste S.C.p.A., Strada Statale 14 - km 163,5 in AREA Science Park, 34149 Basovizza Trieste, Italy, Departament de Física Fonamental, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain and CIBER de Bioingeniería, Biomateriales y Nanomedicina, Instituto de Salud Carlos III, Madrid, Spain
| | - Felix Ritort
- SISSA - Scuola Internazionale Superiore di Studi Avanzati, via Bonomea 265, 34136 Trieste, Italy, Elettra-Sincrotrone Trieste S.C.p.A., Strada Statale 14 - km 163,5 in AREA Science Park, 34149 Basovizza Trieste, Italy, Departament de Física Fonamental, Universitat de Barcelona, Diagonal 647, 08028 Barcelona, Spain and CIBER de Bioingeniería, Biomateriales y Nanomedicina, Instituto de Salud Carlos III, Madrid, Spain
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85
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Klaue D, Kobbe D, Kemmerich F, Kozikowska A, Puchta H, Seidel R. Fork sensing and strand switching control antagonistic activities of RecQ helicases. Nat Commun 2013; 4:2024. [PMID: 23771268 PMCID: PMC3709500 DOI: 10.1038/ncomms3024] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2012] [Accepted: 05/17/2013] [Indexed: 12/16/2022] Open
Abstract
RecQ helicases have essential roles in maintaining genome stability during replication and in controlling double-strand break repair by homologous recombination. Little is known about how the different RecQ helicases found in higher eukaryotes achieve their specialized and partially opposing functions. Here, we investigate the DNA unwinding of RecQ helicases from Arabidopsis thaliana, AtRECQ2 and AtRECQ3 at the single-molecule level using magnetic tweezers. Although AtRECQ2 predominantly unwinds forked DNA substrates in a highly repetitive fashion, AtRECQ3 prefers to rewind, that is, to close preopened DNA forks. For both enzymes, this process is controlled by frequent strand switches and active sensing of the unwinding fork. The relative extent of the strand switches towards unwinding or towards rewinding determines the predominant direction of the enzyme. Our results provide a simple explanation for how different biological activities can be achieved by rather similar members of the RecQ family. RecQ helicases are enzymes that play a central role in maintaining genome stability in the DNA repair cascade. Klaue et al. show that RecQ2 and RecQ3 from Arabidopsis thaliana process DNA by, respectively, unwinding and rewinding forked DNA substrates, using a frequent strand switching mechanism.
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Affiliation(s)
- Daniel Klaue
- Biotechnology Center, Technische Universität Dresden, Dresden 01062, Germany
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86
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Yokota H, Chujo YA, Harada Y. Single-molecule imaging of the oligomer formation of the nonhexameric Escherichia coli UvrD helicase. Biophys J 2013; 104:924-33. [PMID: 23442971 DOI: 10.1016/j.bpj.2013.01.014] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2012] [Revised: 12/06/2012] [Accepted: 01/08/2013] [Indexed: 11/18/2022] Open
Abstract
Superfamily I helicases are nonhexameric helicases responsible for the unwinding of nucleic acids. However, whether they unwind DNA in the form of monomers or oligomers remains a controversy. In this study, we addressed this question using direct single-molecule fluorescence visualization of Escherichia coli UvrD, a superfamily I DNA helicase. We performed a photobleaching-step analysis of dye-labeled helicases and determined that the helicase is bound to 18-basepair (bp) double-stranded DNA (dsDNA) with a 3' single-stranded DNA (ssDNA) tail (12, 20, or 40 nt) in a dimeric or trimeric form in the absence of ATP. We also discovered through simultaneous visualization of association/dissociation of the helicase with/from DNA and the DNA unwinding dynamics of the helicase in the presence of ATP that these dimeric and trimeric forms are responsible for the unwinding of DNA. We can therefore propose a new kinetic scheme for the helicase-DNA interaction in which not only a dimeric helicase but also a trimeric helicase can unwind DNA. This is, to our knowledge, the first direct single-molecule nonhexameric helicase quantification study, and it strongly supports a model in which an oligomer is the active form of the helicase, which carries important implications for the DNA unwinding mechanism of all superfamily I helicases.
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Affiliation(s)
- Hiroaki Yokota
- Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Yoshida-Honmachi, Kyoto, Japan.
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87
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Toseland CP, Webb MR. ATPase mechanism of the 5'-3' DNA helicase, RecD2: evidence for a pre-hydrolysis conformation change. J Biol Chem 2013; 288:25183-25193. [PMID: 23839989 PMCID: PMC3757182 DOI: 10.1074/jbc.m113.484667] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
The superfamily 1 helicase, RecD2, is a monomeric, bacterial enzyme with a role in DNA repair, but with 5′-3′ activity unlike most enzymes from this superfamily. Rate constants were determined for steps within the ATPase cycle of RecD2 in the presence of ssDNA. The fluorescent ATP analog, mantATP (2′(3′)-O-(N-methylanthraniloyl)ATP), was used throughout to provide a complete set of rate constants and determine the mechanism of the cycle for a single nucleotide species. Fluorescence stopped-flow measurements were used to determine rate constants for adenosine nucleotide binding and release, quenched-flow measurements were used for the hydrolytic cleavage step, and the fluorescent phosphate biosensor was used for phosphate release kinetics. Some rate constants could also be measured using the natural substrate, ATP, and these suggested a similar mechanism to that obtained with mantATP. The data show that a rearrangement linked to Mg2+ coordination, which occurs before the hydrolysis step, is rate-limiting in the cycle and that this step is greatly accelerated by bound DNA. This is also shown here for the PcrA 3′-5′ helicase and so may be a general mechanism governing superfamily 1 helicases. The mechanism accounts for the tight coupling between translocation and ATPase activity.
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Affiliation(s)
- Christopher P Toseland
- From the MRC National Institute for Medical Research, Mill Hill, London, NW7 1AA, United Kingdom and; Institut für Zelluläre Physiologie and Center for NanoScience, Physiologisches Institut, Ludwig Maximilians Universität, Munich 80336, Germany
| | - Martin R Webb
- From the MRC National Institute for Medical Research, Mill Hill, London, NW7 1AA, United Kingdom and.
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88
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On the mechanism of recombination hotspot scanning during double-stranded DNA break resection. Proc Natl Acad Sci U S A 2013; 110:E2562-71. [PMID: 23798400 DOI: 10.1073/pnas.1303035110] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Double-stranded DNA break repair by homologous recombination is initiated by resection of free DNA ends to produce a 3'-ssDNA overhang. In bacteria, this reaction is catalyzed by helicase-nuclease complexes such as AddAB in a manner regulated by specific recombination hotspot sequences called Crossover hotspot instigator (Chi). We have used magnetic tweezers to investigate the dynamics of AddAB translocation and hotspot scanning during double-stranded DNA break resection. AddAB was prone to stochastic pausing due to transient recognition of Chi-like sequences, unveiling an antagonistic relationship between DNA translocation and sequence-specific DNA recognition. Pauses at bona fide Chi sequences were longer, were nonexponentially distributed, and resulted in an altered velocity upon restart of translocation downstream of Chi. We propose a model for the recognition of Chi sequences to explain the origin of pausing during failed and successful hotspot recognition.
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89
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Qi Z, Pugh RA, Spies M, Chemla YR. Sequence-dependent base pair stepping dynamics in XPD helicase unwinding. eLife 2013; 2:e00334. [PMID: 23741615 PMCID: PMC3668415 DOI: 10.7554/elife.00334] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2012] [Accepted: 04/26/2013] [Indexed: 11/13/2022] Open
Abstract
Helicases couple the chemical energy of ATP hydrolysis to directional translocation along nucleic acids and transient duplex separation. Understanding helicase mechanism requires that the basic physicochemical process of base pair separation be understood. This necessitates monitoring helicase activity directly, at high spatio-temporal resolution. Using optical tweezers with single base pair (bp) resolution, we analyzed DNA unwinding by XPD helicase, a Superfamily 2 (SF2) DNA helicase involved in DNA repair and transcription initiation. We show that monomeric XPD unwinds duplex DNA in 1-bp steps, yet exhibits frequent backsteps and undergoes conformational transitions manifested in 5-bp backward and forward steps. Quantifying the sequence dependence of XPD stepping dynamics with near base pair resolution, we provide the strongest and most direct evidence thus far that forward, single-base pair stepping of a helicase utilizes the spontaneous opening of the duplex. The proposed unwinding mechanism may be a universal feature of DNA helicases that move along DNA phosphodiester backbones. DOI:http://dx.doi.org/10.7554/eLife.00334.001.
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Affiliation(s)
- Zhi Qi
- Center for Biophysics and Computational Biology , University of Illinois at Urbana-Champaign , Urbana , United States
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90
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Ramanagoudr-Bhojappa R, Chib S, Byrd AK, Aarattuthodiyil S, Pandey M, Patel SS, Raney KD. Yeast Pif1 helicase exhibits a one-base-pair stepping mechanism for unwinding duplex DNA. J Biol Chem 2013; 288:16185-95. [PMID: 23596008 DOI: 10.1074/jbc.m113.470013] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Kinetic analysis of the DNA unwinding and translocation activities of helicases is necessary for characterization of the biochemical mechanism(s) for this class of enzymes. Saccharomyces cerevisiae Pif1 helicase was characterized using presteady state kinetics to determine rates of DNA unwinding, displacement of streptavidin from biotinylated DNA, translocation on single-stranded DNA (ssDNA), and ATP hydrolysis activities. Unwinding of substrates containing varying duplex lengths was fit globally to a model for stepwise unwinding and resulted in an unwinding rate of ∼75 bp/s and a kinetic step size of 1 base pair. Pif1 is capable of displacing streptavidin from biotinylated oligonucleotides with a linear increase in the rates as the length of the oligonucleotides increased. The rate of translocation on ssDNA was determined by measuring dissociation from varying lengths of ssDNA and is essentially the same as the rate of unwinding of dsDNA, making Pif1 an active helicase. The ATPase activity of Pif1 on ssDNA was determined using fluorescently labeled phosphate-binding protein to measure the rate of phosphate release. The quantity of phosphate released corresponds to a chemical efficiency of 0.84 ATP/nucleotides translocated. Hence, when all of the kinetic data are considered, Pif1 appears to move along DNA in single nucleotide or base pair steps, powered by hydrolysis of 1 molecule of ATP.
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91
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Chisty LT, Toseland CP, Fili N, Mashanov GI, Dillingham MS, Molloy JE, Webb MR. Monomeric PcrA helicase processively unwinds plasmid lengths of DNA in the presence of the initiator protein RepD. Nucleic Acids Res 2013; 41:5010-23. [PMID: 23535146 PMCID: PMC3643603 DOI: 10.1093/nar/gkt194] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The helicase PcrA unwinds DNA during asymmetric replication of plasmids, acting with an initiator protein, in our case RepD. Detailed kinetics of PcrA activity were measured using bulk solution and a single-molecule imaging technique to investigate the oligomeric state of the active helicase complex, its processivity and the mechanism of unwinding. By tethering either DNA or PcrA to a microscope coverslip surface, unwinding of both linear and natural circular plasmid DNA by PcrA/RepD was followed in real-time using total internal reflection fluorescence microscopy. Visualization was achieved using a fluorescent single-stranded DNA-binding protein. The single-molecule data show that PcrA, in combination with RepD, can unwind plasmid lengths of DNA in a single run, and that PcrA is active as a monomer. Although the average rate of unwinding was similar in single-molecule and bulk solution assays, the single-molecule experiments revealed a wide distribution of unwinding speeds by different molecules. The average rate of unwinding was several-fold slower than the PcrA translocation rate on single-stranded DNA, suggesting that DNA unwinding may proceed via a partially passive mechanism. However, the fastest dsDNA unwinding rates measured in the single-molecule unwinding assays approached the PcrA translocation speed measured on ssDNA.
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Affiliation(s)
- Liisa T Chisty
- MRC National Institute for Medical Research, Mill Hill, London NW7 1AA, UK
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92
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Abstract
First discovered in the 1970s, DNA helicases were initially described as enzymes that use chemical energy to separate (i.e., to unwind) the complementary strands of DNA. Because helicases are ubiquitous, display a range of fascinating biochemical activities, and are involved in all aspects of DNA metabolism, defects in human helicases are linked to a variety of genetic disorders, and helicase research continues to be important in understanding the molecular basis of DNA replication, recombination, and repair. The purpose of this book is to organize this information and to update the traditional view of these enzymes, because it is now evident that not all helicases possess bona fide strand separation activity and may function instead as energy-dependent switches or translocases. In this chapter, we will first discuss the biochemical and structural features of DNA-the lattice on which helicases operate-and its cellular organization. We will then provide a historical overview of helicases, starting from their discovery and classification, leading to their structures, mechanisms, and biomedical significance. Finally, we will highlight several key advances and developments in helicase research, and summarize some remaining questions and active areas of investigation. The subsequent chapters will discuss these topics and others in greater detail and are written by experts of these respective fields.
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Affiliation(s)
- Colin G Wu
- Department of Biochemistry, University of Iowa Carver College of Medicine, Iowa City, IA, USA
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93
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Structure and Mechanisms of SF1 DNA Helicases. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 767:17-46. [PMID: 23161005 DOI: 10.1007/978-1-4614-5037-5_2] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Superfamily I is a large and diverse group of monomeric and dimeric helicases defined by a set of conserved sequence motifs. Members of this class are involved in essential processes in both DNA and RNA metabolism in all organisms. In addition to conserved amino acid sequences, they also share a common structure containing two RecA-like motifs involved in ATP binding and hydrolysis and nucleic acid binding and unwinding. Unwinding is facilitated by a "pin" structure which serves to split the incoming duplex. This activity has been measured using both ensemble and single-molecule conditions. SF1 helicase activity is modulated through interactions with other proteins.
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94
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Beyer DC, Ghoneim MK, Spies M. Structure and Mechanisms of SF2 DNA Helicases. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 767:47-73. [PMID: 23161006 DOI: 10.1007/978-1-4614-5037-5_3] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Effective transcription, replication, and maintenance of the genome require a diverse set of molecular machines to perform the many chemical transactions that constitute these processes. Many of these machines use single-stranded nucleic acids as templates, and their actions are often regulated by the participation of nucleic acids in multimeric structures and macromolecular assemblies that restrict access to chemical information. Superfamily II (SF2) DNA helicases and translocases are a group of molecular machines that remodel nucleic acid lattices and enable essential cellular processes to use the information stored in the duplex DNA of the packaged genome. Characteristic accessory domains associated with the subgroups of the superfamily direct the activity of the common motor core and expand the repertoire of activities and substrates available to SF2 DNA helicases, translocases, and large multiprotein complexes containing SF2 motors. In recent years, single-molecule studies have contributed extensively to the characterization of this ubiquitous and essential class of enzymes.
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Affiliation(s)
- David C Beyer
- Department of Biochemistry, University of Iowa Carver College of Medicine, Iowa City, IA, USA
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95
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Parisse P, Vindigni A, Scoles G, Casalis L. In Vitro Enzyme Comparative Kinetics: Unwinding of Surface-Bound DNA Nanostructures by RecQ and RecQ1. JOURNAL OF PHYSICAL CHEMISTRY LETTERS 2012; 3:3532-7. [PMID: 26290984 DOI: 10.1021/jz3018682] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- Pietro Parisse
- Sincrotrone Trieste S.C.p.A., s.s.14 km163,5 in Area Science Park, Trieste
34149, Italy
| | - Alessandro Vindigni
- Sincrotrone Trieste S.C.p.A., s.s.14 km163,5 in Area Science Park, Trieste
34149, Italy
- International Centre for Genetic Engineering and Biotechnology, Padriciano
99, Trieste 34149, Italy
- Department of Biochemistry and
Molecular Biology, St. Louis University School of Medicine, St. Louis, Missouri 63104, United States
| | - Giacinto Scoles
- Sincrotrone Trieste S.C.p.A., s.s.14 km163,5 in Area Science Park, Trieste
34149, Italy
- Department of Biological and
Medical Science, University of Udine, Ospedale
della Misericordia, Udine 33100, Italy
| | - Loredana Casalis
- Sincrotrone Trieste S.C.p.A., s.s.14 km163,5 in Area Science Park, Trieste
34149, Italy
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96
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Wang Q, Han Y, Qiu Y, Zhang S, Tang F, Wang Y, Zhang J, Hu Y, Zhou X. Identification and characterization of RNA duplex unwinding and ATPase activities of an alphatetravirus superfamily 1 helicase. Virology 2012; 433:440-8. [PMID: 22995190 PMCID: PMC7111927 DOI: 10.1016/j.virol.2012.08.045] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2012] [Revised: 08/24/2012] [Accepted: 08/28/2012] [Indexed: 12/20/2022]
Abstract
Dendrolimus punctatus tetravirus (DpTV) belongs to the genus omegatetravirus of the Alphatetraviridae family. Sequence analysis predicts that DpTV replicase contains a putative helicase domain (Hel). However, the helicase activity in alphatetraviruses has never been formally determined. In this study, we determined that DpTV Hel is a functional RNA helicase belonging to superfamily-1 helicase with 5′–3′ dsRNA unwinding directionality. Further characterization determined the length requirement of the 5′ single-stranded tail on the RNA template and the optimal reaction conditions for the unwinding activity of DpTV Hel. Moreover, DpTV Hel also contains NTPase activity. The ATPase activity of DpTV Hel could be significantly stimulated by dsRNA, and dsRNA could partially rescue the ATPase activity abolishment caused by mutations. Our study is the first to identify an alphatetravirus RNA helicase and further characterize its dsRNA unwinding and NTPase activities in detail and should foster our understanding of DpTV and other alphatetraviruses.
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Affiliation(s)
- Qinrong Wang
- State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China
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97
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Wu CG, Xie F, Lohman TM. The primary and secondary translocase activities within E. coli RecBC helicase are tightly coupled to ATP hydrolysis by the RecB motor. J Mol Biol 2012; 423:303-14. [PMID: 22820092 DOI: 10.1016/j.jmb.2012.07.009] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Revised: 06/29/2012] [Accepted: 07/10/2012] [Indexed: 11/19/2022]
Abstract
Escherichia coli RecBC, a rapid and processive DNA helicase with only a single ATPase motor (RecB), possesses two distinct single-stranded DNA (ssDNA) translocase activities that can operate on each strand of an unwound duplex DNA. Using a transient kinetic assay to detect phosphate release, we show that RecBC hydrolyzes the same amount of ATP when translocating along ssDNA using only its primary translocase (0.81±0.05ATP/nt), only its secondary translocase (1.12±0.06ATP/nt), or both translocases simultaneously (1.07±0.09ATP/nt). A mutation within RecB (Y803H) that slows the primary translocation rate of RecBC also slows the secondary translocation rate to the same extent. These results indicate that the ATPase activity of the single RecB motor drives both the primary and secondary RecBC translocases in a tightly coupled reaction. We further show that RecBC also hydrolyzes the same amount of ATP (0.95±0.08ATP/bp) while processively unwinding duplex DNA, suggesting that the large majority, possibly all, of the ATP hydrolyzed by RecBC during DNA unwinding is used to fuel ssDNA translocation rather than to facilitate base pair melting. A model for DNA unwinding is proposed based on these observations.
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Affiliation(s)
- Colin G Wu
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA
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Bianco PR, Webb MR. Helicase unwinding: active or merely perfect? J Mol Biol 2012; 420:139-40. [PMID: 22560995 PMCID: PMC5862422 DOI: 10.1016/j.jmb.2012.04.030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- Piero R Bianco
- Department of Microbiology and Immunology, Center for Single Molecule Biophysics, University at Buffalo, Buffalo, NY 14214, USA.
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Affiliation(s)
| | - Cees Dekker
- Kavli Institute of Nanoscience, Delft University of Technology, Delft, 2628 CJ, The Netherlands;
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RecQ helicase translocates along single-stranded DNA with a moderate processivity and tight mechanochemical coupling. Proc Natl Acad Sci U S A 2012; 109:9804-9. [PMID: 22665805 DOI: 10.1073/pnas.1114468109] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Maintenance of genome integrity is the major biological role of RecQ-family helicases via their participation in homologous recombination (HR)-mediated DNA repair processes. RecQ helicases exert their functions by using the free energy of ATP hydrolysis for mechanical movement along DNA tracks (translocation). In addition to the importance of translocation per se in recombination processes, knowledge of its mechanism is necessary for the understanding of more complex translocation-based activities, including nucleoprotein displacement, strand separation (unwinding), and branch migration. Here, we report the key properties of the ssDNA translocation mechanism of Escherichia coli RecQ helicase, the prototype of the RecQ family. We monitored the pre-steady-state kinetics of ATP hydrolysis by RecQ and the dissociation of the enzyme from ssDNA during single-round translocation. We also gained information on the translocation mechanism from the ssDNA length dependence of the steady-state ssDNA-activated ATPase activity. We show that RecQ occludes 18 ± 2 nt on ssDNA during translocation. The hydrolysis of ATP is noncooperative in the presence of ssDNA, indicating that RecQ active sites work independently during translocation. In the applied conditions, the enzyme hydrolyzes 35 ± 4 ATP molecules per second during ssDNA translocation. RecQ translocates at a moderate processivity, with a mean run length of 100-320 nt on ssDNA. The determined tight mechanochemical coupling of 1.1 ± 0.2 ATP consumed per nucleotide traveled indicates an inchworm-type mechanism.
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