101
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Mack AH, Schlingman DJ, Kamenetska M, Collins R, Regan L, Mochrie SGJ. The molecular yo-yo method: live jump detection improves throughput of single-molecule force spectroscopy for out-of-equilibrium transitions. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2013; 84:085119. [PMID: 24007119 DOI: 10.1063/1.4819026] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
By monitoring multiple molecular transitions, force-clamp, and trap-position-clamp methods have led to precise determinations of the free energies and free energy landscapes for molecular states populated in equilibrium at the same or similar forces. Here, we present a powerful new elaboration of the force-clamp and force-jump methods, applicable to transitions far from equilibrium. Specifically, we have implemented a live jump detection and force-clamp algorithm that intelligently adjusts and maintains the force on a single molecule in response to the measured state of that molecule. We are able to collect hundreds of individual molecular transitions at different forces, many times faster than previously, permitting us to accurately determine force-dependent lifetime distributions and reaction rates. Application of our method to unwinding and rewinding the nucleosome inner turn, using optical tweezers reveals experimental lifetime distributions that comprise a statistically meaningful number of transitions, and that are accurately single exponential. These measurements significantly reduce the error in the previously measured rates, and demonstrate the existence of a single, dominant free energy barrier at each force studied. A key benefit of the molecular yo-yo method for nucleosomes is that it reduces as far as possible the time spent in the tangentially bound state, which minimizes the loss of nucleosomes by dissociation.
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Affiliation(s)
- A H Mack
- Integrated Graduate Program in Physical and Engineering Biology, Yale University, New Haven, Connecticut 06511, USA
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102
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Geertsema HJ, van Oijen AM. A single-molecule view of DNA replication: the dynamic nature of multi-protein complexes revealed. Curr Opin Struct Biol 2013; 23:788-93. [PMID: 23890728 DOI: 10.1016/j.sbi.2013.06.018] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2013] [Accepted: 06/21/2013] [Indexed: 01/31/2023]
Abstract
Recent advances in the development of single-molecule approaches have made it possible to study the dynamics of biomolecular systems in great detail. More recently, such tools have been applied to study the dynamic nature of large multi-protein complexes that support multiple enzymatic activities. In this review, we will discuss single-molecule studies of the replisome, the protein complex responsible for the coordinated replication of double-stranded DNA. In particular, we will focus on new insights obtained into the dynamic nature of the composition of the DNA-replication machinery and how the dynamic replacement of components plays a role in the regulation of the DNA-replication process.
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Affiliation(s)
- Hylkje J Geertsema
- Zernike Institute for Advanced Materials, Centre for Synthetic Biology, University of Groningen, 9747 AG Groningen, The Netherlands
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103
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Abstract
Methods for exerting and measuring forces on single molecules have revolutionized the study of the physics of biology. However, it is often the case that biological processes involve rotation or torque generation, and these parameters have been more difficult to access experimentally. Recent advances in the single-molecule field have led to the development of techniques that add the capability of torque measurement. By combining force, displacement, torque, and rotational data, a more comprehensive description of the mechanics of a biomolecule can be achieved. In this review, we highlight a number of biological processes for which torque plays a key mechanical role. We describe the various techniques that have been developed to directly probe the torque experienced by a single molecule, and detail a variety of measurements made to date using these new technologies. We conclude by discussing a number of open questions and propose systems of study that would be well suited for analysis with torsional measurement techniques.
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Affiliation(s)
- Scott Forth
- Laboratory of Chemistry and Cell Biology, The Rockefeller University, New York, New York 10065, USA.
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104
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Kumar S, Mishra G. Statistical mechanics of DNA unzipping under periodic force: scaling behavior of hysteresis loops. PHYSICAL REVIEW LETTERS 2013; 110:258102. [PMID: 23829761 DOI: 10.1103/physrevlett.110.258102] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2012] [Indexed: 06/02/2023]
Abstract
A simple model of DNA based on two interacting polymers has been used to study the unzipping of a double stranded DNA subjected to a periodic force. We propose a dynamical transition where, without changing the physiological condition, it is possible to bring DNA from the zipped or unzipped state to a new dynamic (hysteretic) state by varying the frequency of the applied force. Our studies reveal that the area of the hysteresis loop grows with the same exponents as of the isotropic spin systems. These exponents are amenable to verification in the force spectroscopic experiments.
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Affiliation(s)
- Sanjay Kumar
- Department of Physics, Banaras Hindu University, Varanasi 221 005, India
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105
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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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106
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Jeong YJ, Rajagopal V, Patel SS. Switching from single-stranded to double-stranded DNA limits the unwinding processivity of ring-shaped T7 DNA helicase. Nucleic Acids Res 2013; 41:4219-29. [PMID: 23446275 PMCID: PMC3627605 DOI: 10.1093/nar/gkt133] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Phage T7 helicase unwinds double-stranded DNA (dsDNA) by encircling one strand while excluding the complementary strand from its central channel. When T7 helicase translocates on single-stranded DNA (ssDNA), it has kilobase processivity; yet, it is unable to processively unwind linear dsDNA, even 60 base-pairs long. Particularly, the GC-rich dsDNAs are unwound with lower amplitudes under single-turnover conditions. Here, we provide evidence that T7 helicase switches from ssDNA to dsDNA during DNA unwinding. The switching propensity is higher when dsDNA is GC-rich or when the 3′-overhang of forked DNA is <15 bases. Once helicase encircles dsDNA, it travels along dsDNA and dissociates from the end of linear DNA without strand separation, which explains the low unwinding amplitude of these substrates. Trapping the displaced strand with ssDNA binding protein or changing its composition to morpholino oligomer that does not interact with helicase increases the unwinding amplitude. We conclude that the displaced strand must be continuously excluded and kept away from the central channel for processive DNA unwinding. The finding that T7 helicase can switch from ssDNA to dsDNA binding mode during unwinding provides new insights into ways of limiting DNA unwinding and triggering fork regression when stalled forks need to be restarted.
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Affiliation(s)
- Yong-Joo Jeong
- Department of Biochemistry, UMDNJ-Robert Wood Johnson Medical School 675 Hoes Lane, Piscataway, NJ 08854, USA
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107
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Optical Methods to Study Protein-DNA Interactions in Vitro and in Living Cells at the Single-Molecule Level. Int J Mol Sci 2013; 14:3961-92. [PMID: 23429188 PMCID: PMC3588080 DOI: 10.3390/ijms14023961] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2012] [Revised: 01/13/2013] [Accepted: 02/04/2013] [Indexed: 12/13/2022] Open
Abstract
The maintenance of intact genetic information, as well as the deployment of transcription for specific sets of genes, critically rely on a family of proteins interacting with DNA and recognizing specific sequences or features. The mechanisms by which these proteins search for target DNA are the subject of intense investigations employing a variety of methods in biology. A large interest in these processes stems from the faster-than-diffusion association rates, explained in current models by a combination of 3D and 1D diffusion. Here, we present a review of the single-molecule approaches at the forefront of the study of protein-DNA interaction dynamics and target search in vitro and in vivo. Flow stretch, optical and magnetic manipulation, single fluorophore detection and localization as well as combinations of different methods are described and the results obtained with these techniques are discussed in the framework of the current facilitated diffusion model.
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108
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Severin PMD, Zou X, Schulten K, Gaub HE. Effects of cytosine hydroxymethylation on DNA strand separation. Biophys J 2013; 104:208-15. [PMID: 23332073 DOI: 10.1016/j.bpj.2012.11.013] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2012] [Revised: 10/10/2012] [Accepted: 11/13/2012] [Indexed: 12/22/2022] Open
Abstract
Cytosine hydroxymethylation is an epigenetic control factor in higher organisms. New discoveries of the biological roles of hydroxymethylation serve to raise questions about how this epigenetic modification exerts its functions and how organisms discriminate cytosine hydroxymethylation from methylation. Here, we report investigations that reveal an effect of cytosine hydroxymethylation on mechanical properties of DNA under load. The findings are based on molecular force assay measurements and steered molecular dynamics simulations. Molecular force assay experiments identified significant effects of hydroxymethylation on stretching-induced strand separation; the underlying physical mechanism has been revealed by steered molecular dynamics simulations. We find that hydroxymethylation can either upregulate or downregulate DNA's strand separation propensity, suggesting that hydroxymethylation can control gene expression by facilitating or obstructing the action of transcription machinery or the access to chromosomal DNA.
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Affiliation(s)
- Philip M D Severin
- Lehrstuhl für Angewandte Physik and Center for Nanoscience, Ludwig-Maximilians-Universität, Munich, Germany
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109
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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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110
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Studying genomic processes at the single-molecule level: introducing the tools and applications. Nat Rev Genet 2012; 14:9-22. [DOI: 10.1038/nrg3316] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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111
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Frey EW, Gooding AA, Wijeratne S, Kiang CH. Understanding the physics of DNA using nanoscale single-molecule manipulation. FRONTIERS OF PHYSICS 2012; 7:576-581. [PMID: 23467419 PMCID: PMC3586743 DOI: 10.1007/s11467-012-0261-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Processes for decoding the genetic information in cells, including transcription, replication, recombination and repair, involve the deformation of DNA from its equilibrium structures such as bending, stretching, twisting, and unzipping of the double helix. Single-molecule manipulation techniques have made it possible to control DNA conformation and simultaneously detect the induced changes, revealing a rich variety of mechanically-induced conformational changes and thermodynamic states. These single-molecule techniques helped us to reveal the physics of DNA and the processes involved in the passing on of the genetic code.
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112
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Ribosomal protein S1 unwinds double-stranded RNA in multiple steps. Proc Natl Acad Sci U S A 2012; 109:14458-63. [PMID: 22908248 DOI: 10.1073/pnas.1208950109] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The sequence and secondary structure of the 5'-end of mRNAs regulate translation by controlling ribosome initiation on the mRNA. Ribosomal protein S1 is crucial for ribosome initiation on many natural mRNAs, particularly for those with structured 5'-ends, or with no or weak Shine-Dalgarno sequences. Besides a critical role in translation, S1 has been implicated in several other cellular processes, such as transcription recycling, and the rescuing of stalled ribosomes by tmRNA. The mechanisms of S1 functions are still elusive but have been widely considered to be linked to the affinity of S1 for single-stranded RNA and its corresponding destabilization of mRNA secondary structures. Here, using optical tweezers techniques, we demonstrate that S1 promotes RNA unwinding by binding to the single-stranded RNA formed transiently during the thermal breathing of the RNA base pairs and that S1 dissociation results in RNA rezipping. We measured the dependence of the RNA unwinding and rezipping rates on S1 concentration, and the force applied to the ends of the RNA. We found that each S1 binds 10 nucleotides of RNA in a multistep fashion implying that S1 can facilitate ribosome initiation on structured mRNA by first binding to the single strand next to an RNA duplex structure ("stand-by site") before subsequent binding leads to RNA unwinding. Unwinding by multiple small substeps is much less rate limited by thermal breathing than unwinding in a single step. Thus, a multistep scheme greatly expedites S1 unwinding of an RNA structure compared to a single-step mode.
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113
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Morin JA, Cao FJ, Valpuesta JM, Carrascosa JL, Salas M, Ibarra B. Manipulation of single polymerase-DNA complexes: a mechanical view of DNA unwinding during replication. Cell Cycle 2012; 11:2967-8. [PMID: 22871727 PMCID: PMC3442898 DOI: 10.4161/cc.21389] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Comment on: Morin JA, et al. Proc Natl Acad Sci USA 2012; 109:8115-20.
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114
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Abstract
The predominant protein-centric perspective in protein-DNA-binding studies assumes that the protein drives the interaction. Research focuses on protein structural motifs, electrostatic surfaces and contact potentials, while DNA is often ignored as a passive polymer to be manipulated. Recent studies of DNA topology, the supercoiling, knotting, and linking of the helices, have shown that DNA has the capability to be an active participant in its transactions. DNA topology-induced structural and geometric changes can drive, or at least strongly influence, the interactions between protein and DNA. Deformations of the B-form structure arise from both the considerable elastic energy arising from supercoiling and from the electrostatic energy. Here, we discuss how these energies are harnessed for topology-driven, sequence-specific deformations that can allow DNA to direct its own metabolism.
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115
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Abstract
Duplication of double-stranded DNA (dsDNA) requires a fine-tuned coordination between the DNA replication and unwinding reactions. Using optical tweezers, we probed the coupling dynamics between these two activities when they are simultaneously carried out by individual Phi29 DNA polymerase molecules replicating a dsDNA hairpin. We used the wild-type and an unwinding deficient polymerase variant and found that mechanical tension applied on the DNA and the DNA sequence modulate in different ways the replication, unwinding rates, and pause kinetics of each polymerase. However, incorporation of pause kinetics in a model to quantify the unwinding reaction reveals that both polymerases destabilize the fork with the same active mechanism and offers insights into the topological strategies that could be used by the Phi29 DNA polymerase and other DNA replication systems to couple unwinding and replication reactions.
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116
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Byrd AK, Matlock DL, Bagchi D, Aarattuthodiyil S, Harrison D, Croquette V, Raney KD. Dda helicase tightly couples translocation on single-stranded DNA to unwinding of duplex DNA: Dda is an optimally active helicase. J Mol Biol 2012; 420:141-54. [PMID: 22504228 DOI: 10.1016/j.jmb.2012.04.007] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2012] [Revised: 03/04/2012] [Accepted: 04/01/2012] [Indexed: 01/06/2023]
Abstract
Helicases utilize the energy of ATP hydrolysis to unwind double-stranded DNA while translocating on the DNA. Mechanisms for melting the duplex have been characterized as active or passive, depending on whether the enzyme actively separates the base pairs or simply sequesters single-stranded DNA (ssDNA) that forms due to thermal fraying. Here, we show that Dda translocates unidirectionally on ssDNA at the same rate at which it unwinds double-stranded DNA in both ensemble and single-molecule experiments. Further, the unwinding rate is largely insensitive to the duplex stability and to the applied force. Thus, Dda transduces all of its translocase activity into DNA unwinding activity so that the rate of unwinding is limited by the rate of translocation and that the enzyme actively separates the duplex. Active and passive helicases have been characterized by dividing the velocity of DNA unwinding in base pairs per second (V(un)) by the velocity of translocation on ssDNA in nucleotides per second (V(trans)). If the resulting fraction is 0.25, then a helicase is considered to be at the lower end of the "active" range. In the case of Dda, the average DNA unwinding velocity was 257±42 bp/s, and the average translocation velocity was 267±15 nt/s. The V(un)/V(trans) value of 0.96 places Dda in a unique category of being an essentially "perfectly" active helicase.
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Affiliation(s)
- Alicia K Byrd
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, 4301 West Markham Street, Slot 516, Little Rock, AR 72205, USA
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117
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Manosas M, Spiering MM, Ding F, Bensimon D, Allemand JF, Benkovic SJ, Croquette V. Mechanism of strand displacement synthesis by DNA replicative polymerases. Nucleic Acids Res 2012; 40:6174-86. [PMID: 22434889 PMCID: PMC3401438 DOI: 10.1093/nar/gks253] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Replicative holoenzymes exhibit rapid and processive primer extension DNA synthesis, but inefficient strand displacement DNA synthesis. We investigated the bacteriophage T4 and T7 holoenzymes primer extension activity and strand displacement activity on a DNA hairpin substrate manipulated by a magnetic trap. Holoenzyme primer extension activity is moderately hindered by the applied force. In contrast, the strand displacement activity is strongly stimulated by the applied force; DNA polymerization is favoured at high force, while a processive exonuclease activity is triggered at low force. We propose that the DNA fork upstream of the holoenzyme generates a regression pressure which inhibits the polymerization-driven forward motion of the holoenzyme. The inhibition is generated by the distortion of the template strand within the polymerization active site thereby shifting the equilibrium to a DNA-protein exonuclease conformation. We conclude that stalling of the holoenzyme induced by the fork regression pressure is the basis for the inefficient strand displacement synthesis characteristic of replicative polymerases. The resulting processive exonuclease activity may be relevant in replisome disassembly to reset a stalled replication fork to a symmetrical situation. Our findings offer interesting applications for single-molecule DNA sequencing.
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Affiliation(s)
- Maria Manosas
- Département de Physique, Laboratoire de Physique Statistique, Ecole Normale Supérieure, Université Pierre et Marie Curie Université Paris 06, Université Paris Diderot, Centre National de la Recherche Scientifique, Paris, 75005, France
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118
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Manosas M, Spiering MM, Ding F, Croquette V, Benkovic SJ. Collaborative coupling between polymerase and helicase for leading-strand synthesis. Nucleic Acids Res 2012; 40:6187-98. [PMID: 22434886 PMCID: PMC3401439 DOI: 10.1093/nar/gks254] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022] Open
Abstract
Rapid and processive leading-strand DNA synthesis in the bacteriophage T4 system requires functional coupling between the helicase and the holoenzyme, consisting of the polymerase and trimeric clamp loaded by the clamp loader. We investigated the mechanism of this coupling on a DNA hairpin substrate manipulated by a magnetic trap. In stark contrast to the isolated enzymes, the coupled system synthesized DNA at the maximum rate without exhibiting fork regression or pauses. DNA synthesis and unwinding activities were coupled at low forces, but became uncoupled displaying separate activities at high forces or low dNTP concentration. We propose a collaborative model in which the helicase releases the fork regression pressure on the holoenzyme allowing it to adopt a processive polymerization conformation and the holoenzyme destabilizes the first few base pairs of the fork thereby increasing the efficiency of helicase unwinding. The model implies that both enzymes are localized at the fork, but does not require a specific interaction between them. The model quantitatively reproduces homologous and heterologous coupling results under various experimental conditions.
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Affiliation(s)
- Maria Manosas
- Département de Physique, Laboratoire de Physique Statistique, Ecole Normale Supérieure, Université Pierre et Marie Curie Université Paris 06, Université Paris Diderot, Centre National de la Recherche Scientifique, Paris 75005, France
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119
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Abstract
The advent of new technologies allowing the study of single biological molecules continues to have a major impact on studies of interacting systems as well as enzyme reactions. These approaches (fluorescence, optical, and magnetic tweezers), in combination with ensemble methods, have been particularly useful for mechanistic studies of protein-nucleic acid interactions and enzymes that function on nucleic acids. We review progress in the use of single-molecule methods to observe and perturb the activities of proteins and enzymes that function on flexible single-stranded DNA. These include single-stranded DNA binding proteins, recombinases (RecA/Rad51), and helicases/translocases that operate as motor proteins and play central roles in genome maintenance. We emphasize methods that have been used to detect and study the movement of these proteins (both ATP-dependent directional and random movement) along the single-stranded DNA and the mechanistic and functional information that can result from detailed analysis of such movement.
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Affiliation(s)
- Taekjip Ha
- Department of Physics and the Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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120
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Carter AS, Tahmaseb K, Compton SA, Matson SW. Resolving Holliday junctions with Escherichia coli UvrD helicase. J Biol Chem 2012; 287:8126-34. [PMID: 22267744 DOI: 10.1074/jbc.m111.314047] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The Escherichia coli UvrD helicase is known to function in the mismatch repair and nucleotide excision repair pathways and has also been suggested to have roles in recombination and replication restart. The primary intermediate DNA structure in these two processes is the Holliday junction. UvrD has been shown to unwind a variety of substrates including partial duplex DNA, nicked DNA, forked DNA structures, blunt duplex DNA and RNA-DNA hybrids. Here, we demonstrate that UvrD also catalyzes the robust unwinding of Holliday junction substrates. To characterize this unwinding reaction we have employed steady-state helicase assays, pre-steady-state rapid quench helicase assays, DNaseI footprinting, and electron microscopy. We conclude that UvrD binds initially to the junction compared with binding one of the blunt ends of the four-way junction to initiate unwinding and resolves the synthetic substrate into two double-stranded fork structures. We suggest that UvrD, along with its mismatch repair partners, MutS and MutL, may utilize its ability to unwind Holliday junctions directly in the prevention of homeologous recombination. UvrD may also be involved in the resolution of stalled replication forks by unwinding the Holliday junction intermediate to allow bypass of the blockage.
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Affiliation(s)
- Annamarie S Carter
- Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599, USA
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121
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Abstract
DNA unzipping is a powerful tool to study protein-DNA interactions at the single-molecule level. In this chapter, we provide a detailed and practical guide to performing this technique with an optical trap, using nucleosome studies as an example. We detail protocols for preparing an unzipping template, constructing and calibrating the instrument, and acquiring, processing, and analyzing unzipping data. We also summarize major results from utilization of this technique for the studies of nucleosome structure, dynamics, positioning, and remodeling.
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Affiliation(s)
- Ming Li
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, USA
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122
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Lo YH, Liu SW, Sun YJ, Li HW, Hsiao CD. Mutations altering the interplay between GkDnaC helicase and DNA reveal an insight into helicase unwinding. PLoS One 2011; 6:e29016. [PMID: 22174946 PMCID: PMC3236778 DOI: 10.1371/journal.pone.0029016] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2011] [Accepted: 11/17/2011] [Indexed: 11/18/2022] Open
Abstract
Replicative helicases are essential molecular machines that utilize energy derived from NTP hydrolysis to move along nucleic acids and to unwind double-stranded DNA (dsDNA). Our earlier crystal structure of the hexameric helicase from Geobacillus kaustophilus HTA426 (GkDnaC) in complex with single-stranded DNA (ssDNA) suggested several key residues responsible for DNA binding that likely play a role in DNA translocation during the unwinding process. Here, we demonstrated that the unwinding activities of mutants with substitutions at these key residues in GkDnaC are 2-4-fold higher than that of wild-type protein. We also observed the faster unwinding velocities in these mutants using single-molecule experiments. A partial loss in the interaction of helicase with ssDNA leads to an enhancement in helicase efficiency, while their ATPase activities remain unchanged. In strong contrast, adding accessory proteins (DnaG or DnaI) to GkDnaC helicase alters the ATPase, unwinding efficiency and the unwinding velocity of the helicase. It suggests that the unwinding velocity of helicase could be modulated by two different pathways, the efficiency of ATP hydrolysis or protein-DNA interaction.
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Affiliation(s)
- Yu-Hua Lo
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
- Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu, Taiwan
| | - Shih-Wei Liu
- Department of Chemistry, National Taiwan University, Taipei, Taiwan
| | - Yuh-Ju Sun
- Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu, Taiwan
| | - Hung-Wen Li
- Department of Chemistry, National Taiwan University, Taipei, Taiwan
- * ;
| | - Chwan-Deng Hsiao
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
- * ;
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123
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Burnside K, Lembo A, Harrell MI, Gurney M, Xue L, BinhTran NT, Connelly JE, Jewell KA, Schmidt BZ, de Los Reyes M, Tao WA, Doran KS, Rajagopal L. Serine/threonine phosphatase Stp1 mediates post-transcriptional regulation of hemolysin, autolysis, and virulence of group B Streptococcus. J Biol Chem 2011; 286:44197-44210. [PMID: 22081606 DOI: 10.1074/jbc.m111.313486] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Elucidating how serine/threonine phosphatases regulate kinase function and bacterial virulence is critical for our ability to combat these infections. Group B streptococci (GBS) are β-hemolytic Gram-positive bacteria that cause invasive infections in humans. To adapt to environmental changes, GBS encodes signaling mechanisms comprising two component systems and eukaryotic-like enzymes. We have previously described the importance of the serine/threonine kinase Stk1 to GBS pathogenesis. However, how the presence or absence of the cognate serine/threonine phosphatase Stp1 affects Stk1 function and GBS virulence is not known. Here, we show that GBS deficient only in Stp1 expression are markedly reduced for their ability to cause systemic infections, exhibit decreased β-hemolysin/cytolysin activity, and show increased sensitivity to autolysis. Although transcription of genes important for β-hemolysin/cytolysin expression and export is similar to the wild type (WT), 294 genes (excluding stp1) showed altered expression in the stp1 mutant and included autolysin genes. Furthermore, phosphopeptide enrichment analysis identified that 35 serine/threonine phosphopeptides, corresponding to 27 proteins, were unique to the stp1 mutant. This included phosphorylation of ATP synthase, DNA and RNA helicases, and proteins important for cell division and protein synthesis. Collectively, our results indicate that Stp1 is important for appropriate regulation of Stk1 function, hemolysin activity, autolysis, and GBS virulence.
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Affiliation(s)
- Kellie Burnside
- Department of Pediatric Infectious Diseases, University of Washington School of Medicine and Seattle Children's Hospital Research Institute, Seattle, Washington 98101
| | - Annalisa Lembo
- Department of Pediatric Infectious Diseases, University of Washington School of Medicine and Seattle Children's Hospital Research Institute, Seattle, Washington 98101
| | - Maria Isabel Harrell
- Department of Pediatric Infectious Diseases, University of Washington School of Medicine and Seattle Children's Hospital Research Institute, Seattle, Washington 98101
| | - Michael Gurney
- Department of Biology and Center for Microbial Sciences, San Diego State University, San Diego, California 92182
| | - Liang Xue
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
| | - Nguyen-Thao BinhTran
- Department of Pediatric Infectious Diseases, University of Washington School of Medicine and Seattle Children's Hospital Research Institute, Seattle, Washington 98101
| | - James E Connelly
- Department of Pediatric Infectious Diseases, University of Washington School of Medicine and Seattle Children's Hospital Research Institute, Seattle, Washington 98101
| | - Kelsea A Jewell
- Department of Pediatric Infectious Diseases, University of Washington School of Medicine and Seattle Children's Hospital Research Institute, Seattle, Washington 98101
| | - Byron Z Schmidt
- Department of Pediatric Infectious Diseases, University of Washington School of Medicine and Seattle Children's Hospital Research Institute, Seattle, Washington 98101
| | - Melissa de Los Reyes
- Department of Pediatric Infectious Diseases, University of Washington School of Medicine and Seattle Children's Hospital Research Institute, Seattle, Washington 98101
| | - Weiguo Andy Tao
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907
| | - Kelly S Doran
- Department of Biology and Center for Microbial Sciences, San Diego State University, San Diego, California 92182
| | - Lakshmi Rajagopal
- Department of Pediatric Infectious Diseases, University of Washington School of Medicine and Seattle Children's Hospital Research Institute, Seattle, Washington 98101.
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124
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Severin PMD, Zou X, Gaub HE, Schulten K. Cytosine methylation alters DNA mechanical properties. Nucleic Acids Res 2011; 39:8740-51. [PMID: 21775342 PMCID: PMC3203585 DOI: 10.1093/nar/gkr578] [Citation(s) in RCA: 105] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2011] [Revised: 06/14/2011] [Accepted: 06/28/2011] [Indexed: 12/22/2022] Open
Abstract
DNA methylation plays an essential role in transcriptional control of organismal development in epigenetics, from turning off a specific gene to inactivation of entire chromosomes. While the biological function of DNA methylation is becoming increasingly clear, the mechanism of methylation-induced gene regulation is still poorly understood. Through single-molecule force experiments and simulation we investigated the effects of methylation on strand separation of DNA, a crucial step in gene expression. Molecular force assay and single-molecule force spectroscopy revealed a strong methylation dependence of strand separation. Methylation is observed to either inhibit or facilitate strand separation, depending on methylation level and sequence context. Molecular dynamics simulations provided a detailed view of methylation effects on strand separation, suggesting the underlying physical mechanism. According to our study, methylation in epigenetics may regulate gene expression not only through mechanisms already known but also through changing mechanical properties of DNA.
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Affiliation(s)
- Philip M. D. Severin
- Lehrstuhl für Angewandte Physik and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität, Amalienstrasse 54, 80799 Munich, Munich Center For Integrated Protein Science (CIPSM), Ludwig-Maximilians-Universität, Butenandtstrasse 5-13, 81377 Munich, Germany, Beckman Institute, University of Illinois, Urbana, Illinois, USA, School of Physics, Peking University, Beijing, China and Department of Physics, University of Illinois, Urbana, Illinois, USA
| | - Xueqing Zou
- Lehrstuhl für Angewandte Physik and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität, Amalienstrasse 54, 80799 Munich, Munich Center For Integrated Protein Science (CIPSM), Ludwig-Maximilians-Universität, Butenandtstrasse 5-13, 81377 Munich, Germany, Beckman Institute, University of Illinois, Urbana, Illinois, USA, School of Physics, Peking University, Beijing, China and Department of Physics, University of Illinois, Urbana, Illinois, USA
| | - Hermann E. Gaub
- Lehrstuhl für Angewandte Physik and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität, Amalienstrasse 54, 80799 Munich, Munich Center For Integrated Protein Science (CIPSM), Ludwig-Maximilians-Universität, Butenandtstrasse 5-13, 81377 Munich, Germany, Beckman Institute, University of Illinois, Urbana, Illinois, USA, School of Physics, Peking University, Beijing, China and Department of Physics, University of Illinois, Urbana, Illinois, USA
| | - Klaus Schulten
- Lehrstuhl für Angewandte Physik and Center for Nanoscience (CeNS), Ludwig-Maximilians-Universität, Amalienstrasse 54, 80799 Munich, Munich Center For Integrated Protein Science (CIPSM), Ludwig-Maximilians-Universität, Butenandtstrasse 5-13, 81377 Munich, Germany, Beckman Institute, University of Illinois, Urbana, Illinois, USA, School of Physics, Peking University, Beijing, China and Department of Physics, University of Illinois, Urbana, Illinois, USA
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125
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Cheng W, Arunajadai SG, Moffitt JR, Tinoco I, Bustamante C. Single-base pair unwinding and asynchronous RNA release by the hepatitis C virus NS3 helicase. Science 2011; 333:1746-9. [PMID: 21940894 DOI: 10.1126/science.1206023] [Citation(s) in RCA: 116] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Nonhexameric helicases use adenosine triphosphate (ATP) to unzip base pairs in double-stranded nucleic acids (dsNAs). Studies have suggested that these helicases unzip dsNAs in single-base pair increments, consuming one ATP molecule per base pair, but direct evidence for this mechanism is lacking. We used optical tweezers to follow the unwinding of double-stranded RNA by the hepatitis C virus NS3 helicase. Single-base pair steps by NS3 were observed, along with nascent nucleotide release that was asynchronous with base pair opening. Asynchronous release of nascent nucleotides rationalizes various observations of its dsNA unwinding and may be used to coordinate the translocation speed of NS3 along the RNA during viral replication.
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Affiliation(s)
- Wei Cheng
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Michigan, Ann Arbor, MI 48109, USA.
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126
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Sun B, Johnson DS, Patel G, Smith BY, Pandey M, Patel SS, Wang MD. ATP-induced helicase slippage reveals highly coordinated subunits. Nature 2011; 478:132-5. [PMID: 21927003 PMCID: PMC3190587 DOI: 10.1038/nature10409] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2010] [Accepted: 08/01/2011] [Indexed: 11/10/2022]
Abstract
Helicases are vital enzymes that carry out strand separation of duplex nucleic acids during replication, repair, and recombination1,2. Bacteriophage T7 gene product 4 is a model hexameric helicase which has been observed to utilize dTTP, but not ATP, to unwind dsDNA as it translocates from 5′ to 3′ along ssDNA2–6. Whether and how different subunits of the helicase coordinate their chemo-mechanical activities and DNA binding during translocation is still under debate1,7. Here we address this question using a single molecule approach to monitor helicase unwinding. We discovered that T7 helicase does in fact unwind dsDNA in the presence of ATP and the unwinding rate is even faster than that with dTTP. However unwinding traces showed a remarkable sawtooth pattern where processive unwinding was repeatedly interrupted by sudden slippage events, ultimately preventing unwinding over a substantial distance. This behavior was not observed with dTTP alone and was greatly reduced when ATP solution was supplemented with a small amount of dTTP. These findings presented an opportunity to use nucleotide mixtures to investigate helicase subunit coordination. We found T7 helicase binds and hydrolyzes ATP and dTTP by competitive kinetics such that the unwinding rate is dictated simply by their respective Vmax, KM, and concentrations. In contrast, processivity does not follow a simple competitive behavior and shows a cooperative dependence on nucleotide concentrations. This does not agree with an uncoordinated mechanism where each subunit functions independently, but supports a model where nearly all subunits coordinate their chemo-mechanical activities and DNA binding. Our data indicate that only one subunit at a time can accept a nucleotide while other subunits are nucleotide-ligated and thus interact with the DNA to ensure processivity. Such subunit coordination may be general to many ring-shaped helicases and reveals a potential mechanism for regulation of DNA unwinding during replication.
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Affiliation(s)
- Bo Sun
- Department of Physics - Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
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127
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Choreography of bacteriophage T7 DNA replication. Curr Opin Chem Biol 2011; 15:580-6. [PMID: 21907611 DOI: 10.1016/j.cbpa.2011.07.024] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2011] [Revised: 07/25/2011] [Accepted: 07/27/2011] [Indexed: 11/21/2022]
Abstract
The replication system of phage T7 provides a model for DNA replication. Biochemical, structural, and single-molecule analyses together provide insight into replisome mechanics. A complex of polymerase, a processivity factor, and helicase mediates leading strand synthesis. Establishment of the complex requires an interaction of the C-terminal tail of the helicase with the polymerase. During synthesis the complex is stabilized by other interactions to provide for a processivity of 5 kilobase (kb). The C-terminal tail also interacts with a distinct region of the polymerase to captures dissociating polymerase to increase the processivity to >17kb. The lagging strand is synthesized discontinuously within a loop that forms and resolves during each cycle of Okazaki fragment synthesis. The synthesis of a primer as well as the termination of a fragment signal loop resolution.
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128
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Patel SS, Pandey M, Nandakumar D. Dynamic coupling between the motors of DNA replication: hexameric helicase, DNA polymerase, and primase. Curr Opin Chem Biol 2011; 15:595-605. [PMID: 21865075 DOI: 10.1016/j.cbpa.2011.08.003] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2011] [Revised: 07/29/2011] [Accepted: 08/02/2011] [Indexed: 01/05/2023]
Abstract
Helicases are molecular motor proteins that couple NTP hydrolysis to directional movement along nucleic acids. A class of helicases characterized by their ring-shaped hexameric structures translocate processively and unidirectionally along single-stranded (ss) DNA to separate the strands of double-stranded (ds) DNA, aiding both in the initiation and fork progression during DNA replication. These replicative ring-shaped helicases are found from virus to human. We review recent biochemical and structural studies that have expanded our understanding on how hexameric helicases use the NTPase reaction to translocate on ssDNA, unwind dsDNA, and how their physical and functional interactions with the DNA polymerase and primase enzymes coordinate replication of the two strands of dsDNA.
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Affiliation(s)
- Smita S Patel
- UMDNJ-Robert Wood Johnson Medical School, Piscataway, NJ, USA.
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129
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Satapathy AK, Kulczyk AW, Ghosh S, van Oijen AM, Richardson CC. Coupling dTTP hydrolysis with DNA unwinding by the DNA helicase of bacteriophage T7. J Biol Chem 2011; 286:34468-78. [PMID: 21840995 DOI: 10.1074/jbc.m111.283796] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The DNA helicase encoded by gene 4 of bacteriophage T7 assembles on single-stranded DNA as a hexamer of six identical subunits with the DNA passing through the center of the toroid. The helicase couples the hydrolysis of dTTP to unidirectional translocation on single-stranded DNA and the unwinding of duplex DNA. Phe(523), positioned in a β-hairpin loop at the subunit interface, plays a key role in coupling the hydrolysis of dTTP to DNA unwinding. Replacement of Phe(523) with alanine or valine abolishes the ability of the helicase to unwind DNA or allow T7 polymerase to mediate strand-displacement synthesis on duplex DNA. In vivo complementation studies reveal a requirement for a hydrophobic residue with long side chains at this position. In a crystal structure of T7 helicase, when a nucleotide is bound at a subunit interface, Phe(523) is buried within the interface. However, in the unbound state, it is more exposed on the outer surface of the helicase. This structural difference suggests that the β-hairpin bearing the Phe(523) may undergo a conformational change during nucleotide hydrolysis. We postulate that upon hydrolysis of dTTP, Phe(523) moves from within the subunit interface to a more exposed position where it contacts the displaced complementary strand and facilitates unwinding.
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Affiliation(s)
- Ajit K Satapathy
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA
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130
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Qu X, Wen JD, Lancaster L, Noller HF, Bustamante C, Tinoco I. The ribosome uses two active mechanisms to unwind messenger RNA during translation. Nature 2011; 475:118-21. [PMID: 21734708 PMCID: PMC4170678 DOI: 10.1038/nature10126] [Citation(s) in RCA: 249] [Impact Index Per Article: 19.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2010] [Accepted: 04/15/2011] [Indexed: 12/18/2022]
Abstract
The ribosome translates the genetic information encoded in messenger RNA into protein. Folded structures in the coding region of an mRNA represent a kinetic barrier that slows the peptide elongation rate, as the ribosome must disrupt structures it encounters in the mRNA at its entry site to enable translocation to the next codon. Such structures are exploited by the cell to create diverse strategies for translation regulation, such as programmed frameshifting1,2, protein expression levels3,4, ribosome localization5, and cotranslational protein folding6. Although strand separation activity is inherent to the ribosome, requiring no exogenous helicases7, its mechanism is still unknown. Here, using a single-molecule optical tweezers assay on mRNA hairpins, we find that the translation rate of identical codons at the decoding center is greatly influenced by the G•C content of folded structures at the mRNA entry site. Furthermore, force applied to the ends of the hairpin to favor its unfolding significantly speeds translation. Quantitative analysis of the force dependence of its helicase activity reveals that the ribosome, unlike previously studied helicases, uses two distinct active mechanisms to unwind mRNA structure: (i) it destabilizes the helical junction at the mRNA entry site by biasing its thermal fluctuations toward the open state, increasing the probability for the ribosome to translocate unhindered; and (ii) it also mechanically pulls apart the mRNA single-strands of the closed junction during the conformational changes that accompany ribosome translocation. Our results establish a quantitative mechanical basis for understanding the mechanism of regulation of the elongation rate of translation by structured mRNAs.
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Affiliation(s)
- Xiaohui Qu
- Jason L. Choy Laboratory of Single Molecule Biophysics and QB3 Institute, University of California, Berkeley, California 94720, USA
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131
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Zhu B, Lee SJ, Richardson CC. Bypass of a nick by the replisome of bacteriophage T7. J Biol Chem 2011; 286:28488-97. [PMID: 21701044 DOI: 10.1074/jbc.m111.252023] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
DNA polymerase and DNA helicase are essential components of DNA replication. The helicase unwinds duplex DNA to provide single-stranded templates for DNA synthesis by the DNA polymerase. In bacteriophage T7, movement of either the DNA helicase or the DNA polymerase alone terminates upon encountering a nick in duplex DNA. Using a minicircular DNA, we show that the helicase · polymerase complex can bypass a nick, albeit at reduced efficiency of 7%, on the non-template strand to continue rolling circle DNA synthesis. A gap in the non-template strand cannot be bypassed. The efficiency of bypass synthesis depends on the DNA sequence downstream of the nick. A nick on the template strand cannot be bypassed. Addition of T7 single-stranded DNA-binding protein to the complex stimulates nick bypass 2-fold. We propose that the association of helicase with the polymerase prevents dissociation of the helicase upon encountering a nick, allowing the helicase to continue unwinding of the duplex downstream of the nick.
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Affiliation(s)
- Bin Zhu
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA
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132
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Patel G, Johnson DS, Sun B, Pandey M, Yu X, Egelman EH, Wang MD, Patel SS. A257T linker region mutant of T7 helicase-primase protein is defective in DNA loading and rescued by T7 DNA polymerase. J Biol Chem 2011; 286:20490-9. [PMID: 21515672 DOI: 10.1074/jbc.m110.201657] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The helicase and primase activities of the hexameric ring-shaped T7 gp4 protein reside in two separate domains connected by a linker region. This linker region is part of the subunit interface between monomers, and point mutations in this region have deleterious effects on the helicase functions. One such linker region mutant, A257T, is analogous to the A359T mutant of the homologous human mitochondrial DNA helicase Twinkle, which is linked to diseases such as progressive external opthalmoplegia. Electron microscopy studies show that A257T gp4 is normal in forming rings with dTTP, but the rings do not assemble efficiently on the DNA. Therefore, A257T, unlike the WT gp4, does not preassemble on the unwinding DNA substrate with dTTP without Mg(II), and its DNA unwinding activity in ensemble assays is slow and limited by the DNA loading rate. Single molecule assays measured a 45 times slower rate of A257T loading on DNA compared with WT gp4. Interestingly, once loaded, A257T has almost WT-like translocation and DNA unwinding activities. Strikingly, A257T preassembles stably on the DNA in the presence of T7 DNA polymerase, which restores the ensemble unwinding activity of A257T to ∼75% of WT, and the rescue does not require DNA synthesis. The DNA loading rate of A257T, however, remains slow even in the presence of the polymerase, which explains why A257T does not support T7 phage growth. Similar types of defects in the related human mitochondrial DNA helicase may be responsible for inefficient DNA replication leading to the disease states.
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Affiliation(s)
- Gayatri Patel
- Department of Biochemistry, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey 08854, USA
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133
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Bustamante C, Cheng W, Mejia YX, Meija YX. Revisiting the central dogma one molecule at a time. Cell 2011; 144:480-97. [PMID: 21335233 PMCID: PMC3063003 DOI: 10.1016/j.cell.2011.01.033] [Citation(s) in RCA: 135] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2010] [Revised: 01/21/2011] [Accepted: 01/26/2011] [Indexed: 12/24/2022]
Abstract
The faithful relay and timely expression of genetic information depend on specialized molecular machines, many of which function as nucleic acid translocases. The emergence over the last decade of single-molecule fluorescence detection and manipulation techniques with nm and Å resolution and their application to the study of nucleic acid translocases are painting an increasingly sharp picture of the inner workings of these machines, the dynamics and coordination of their moving parts, their thermodynamic efficiency, and the nature of their transient intermediates. Here we present an overview of the main results arrived at by the application of single-molecule methods to the study of the main machines of the central dogma.
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Affiliation(s)
- Carlos Bustamante
- Jason L. Choy Laboratory of Single-Molecule Biophysics, University of California, Berkeley, 94720, USA.
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134
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Ribeck N, Kaplan DL, Bruck I, Saleh OA. DnaB helicase activity is modulated by DNA geometry and force. Biophys J 2011; 99:2170-9. [PMID: 20923651 DOI: 10.1016/j.bpj.2010.07.039] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2010] [Revised: 07/19/2010] [Accepted: 07/21/2010] [Indexed: 11/24/2022] Open
Abstract
The replicative helicase for Escherichia coli is DnaB, a hexameric, ring-shaped motor protein that encircles and translocates along ssDNA, unwinding dsDNA in advance of its motion. The microscopic mechanisms of DnaB are unknown; further, prior work has found that DnaB's activity is modified by other replication proteins, indicating some mechanistic flexibility. To investigate these issues, we quantified translocation and unwinding by single DnaB molecules in three tethered DNA geometries held under tension. Our data support the following conclusions: 1), Unwinding by DnaB is enhanced by force-induced destabilization of dsDNA. 2), The magnitude of this stimulation varies with the geometry of the tension applied to the DNA substrate, possibly due to interactions between the helicase and the occluded ssDNA strand. 3), DnaB unwinding and (to a lesser extent) translocation are interrupted by pauses, which are also dependent on force and DNA geometry. 4), DnaB moves slower when a large tension is applied to the helicase-bound strand, indicating that it must perform mechanical work to compact the strand against the applied force. Our results have implications for the molecular mechanisms of translocation and unwinding by DnaB and for the means of modulating DnaB activity.
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Affiliation(s)
- Noah Ribeck
- Department of Physics, University of California, Santa Barbara, CA, USA
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135
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Efremov A, Wang Z. Maximum directionality and systematic classification of molecular motors. Phys Chem Chem Phys 2011; 13:5159-70. [DOI: 10.1039/c0cp02519d] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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136
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Luzzietti N, Brutzer H, Klaue D, Schwarz FW, Staroske W, Clausing S, Seidel R. Efficient preparation of internally modified single-molecule constructs using nicking enzymes. Nucleic Acids Res 2010; 39:e15. [PMID: 21071409 PMCID: PMC3035433 DOI: 10.1093/nar/gkq1004] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Investigations of enzymes involved in DNA metabolism have strongly benefited from the establishment of single molecule techniques. These experiments frequently require elaborate DNA substrates, which carry chemical labels or nucleic acid tertiary structures. Preparing such constructs often represents a technical challenge: long modified DNA molecules are usually produced via multi-step processes, involving low efficiency intermolecular ligations of several fragments. Here, we show how long stretches of DNA (>50 bp) can be modified using nicking enzymes to produce complex DNA constructs. Multiple different chemical and structural modifications can be placed internally along DNA, in a specific and precise manner. Furthermore, the nicks created can be resealed efficiently yielding intact molecules, whose mechanical properties are preserved. Additionally, the same strategy is applied to obtain long single-strand overhangs subsequently used for efficient ligation of ss- to dsDNA molecules. This technique offers promise for a wide range of applications, in particular single-molecule experiments, where frequently multiple internal DNA modifications are required.
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Affiliation(s)
- Nicholas Luzzietti
- Biotechnology Center, Technische Universität Dresden, D-01062 Dresden, Germany
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137
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Coupling translocation with nucleic acid unwinding by NS3 helicase. J Mol Biol 2010; 404:439-55. [PMID: 20887735 DOI: 10.1016/j.jmb.2010.09.047] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2010] [Revised: 08/27/2010] [Accepted: 09/20/2010] [Indexed: 11/20/2022]
Abstract
We present a semiquantitative model for translocation and unwinding activities of monomeric nonstructural protein 3 (NS3) helicase. The model is based on structural, biochemical, and single-molecule measurements. The model predicts that the NS3 helicase actively unwinds duplex by reducing more than 50% the free energy that stabilizes base pairing/stacking. The unwinding activity slows the movement of the helicase in a sequence-dependent manner, lowering the average unwinding efficiency to less than 1 bp per ATP cycle. When bound with ATP, the NS3 helicase can display significant translocational diffusion. This increases displacement fluctuations of the helicase, decreases the average unwinding efficiency, and enhances the sequence dependence. Also, interactions between the helicase and the duplex stabilize the helicase at the junction, facilitating the helicase's unwinding activity while preventing it from dissociating. In the presence of translocational diffusion during active unwinding, the dissociation rate of the helicase also exhibits sequence dependence. Based on unwinding velocity fluctuations measured from single-molecule experiments, we estimate the diffusion rate to be on the order of 10 s(-1). The generic features of coupling single-stranded nucleic acid translocation with duplex unwinding presented in this work may apply generally to a class of helicases.
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138
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Single-molecule derivation of salt dependent base-pair free energies in DNA. Proc Natl Acad Sci U S A 2010; 107:15431-6. [PMID: 20716688 DOI: 10.1073/pnas.1001454107] [Citation(s) in RCA: 163] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Accurate knowledge of the thermodynamic properties of nucleic acids is crucial to predicting their structure and stability. To date most measurements of base-pair free energies in DNA are obtained in thermal denaturation experiments, which depend on several assumptions. Here we report measurements of the DNA base-pair free energies based on a simplified system, the mechanical unzipping of single DNA molecules. By combining experimental data with a physical model and an optimization algorithm for analysis, we measure the 10 unique nearest-neighbor base-pair free energies with 0.1 kcal mol(-1) precision over two orders of magnitude of monovalent salt concentration. We find an improved set of standard energy values compared with Unified Oligonucleotide energies and a unique set of 10 base-pair-specific salt-correction values. The latter are found to be strongest for AA/TT and weakest for CC/GG. Our unique energy values and salt corrections improve predictions of DNA unzipping forces and are fully compatible with melting temperatures for oligos. The method should make it possible to obtain free energies, enthalpies, and entropies in conditions not accessible by bulk methodologies.
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139
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Insight into helicase mechanism and function revealed through single-molecule approaches. Q Rev Biophys 2010; 43:185-217. [PMID: 20682090 DOI: 10.1017/s0033583510000107] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Helicases are a class of nucleic acid (NA) motors that catalyze NTP-dependent unwinding of NA duplexes into single strands, a reaction essential to all areas of NA metabolism. In the last decade, single-molecule (sm) technology has proven to be highly useful in revealing mechanistic insight into helicase activity that is not always detectable via ensemble assays. A combination of methods based on fluorescence, optical and magnetic tweezers, and flow-induced DNA stretching has enabled the study of helicase conformational dynamics, force generation, step size, pausing, reversal and repetitive behaviors during translocation and unwinding by helicases working alone and as part of multiprotein complexes. The contributions of these sm investigations to our understanding of helicase mechanism and function will be discussed.
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140
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Abstract
Replication of DNA is carried out by the replisome, a multiprotein complex responsible for the unwinding of parental DNA and the synthesis of DNA on each of the two DNA strands. The impressive speed and processivity with which the replisome duplicates DNA are a result of a set of tightly regulated interactions between the replication proteins. The transient nature of these protein interactions makes it challenging to study the dynamics of the replisome by ensemble-averaging techniques. This review describes single-molecule methods that allow the study of individual replication proteins and their functioning within the replisome. The ability to mechanically manipulate individual DNA molecules and record the dynamic behavior of the replisome while it duplicates DNA has led to an improved understanding of the molecular mechanisms underlying DNA replication.
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Affiliation(s)
- Antoine M van Oijen
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA.
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141
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Yoshimoto K, Arora K, Brooks CL. Hexameric helicase deconstructed: interplay of conformational changes and substrate coupling. Biophys J 2010; 98:1449-57. [PMID: 20409463 DOI: 10.1016/j.bpj.2009.12.4315] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2009] [Revised: 12/22/2009] [Accepted: 12/23/2009] [Indexed: 12/15/2022] Open
Abstract
Hexameric helicases are molecular motor proteins that utilize energy obtained from ATP hydrolysis to translocate along and/or unwind nucleic acids. In this study, we investigate the dynamic behavior of the Simian Virus 40 hexameric helicase bound to DNA by performing molecular dynamics simulations employing a coarse-grained model. Our results elucidate the two most important molecular features of the helicase motion. First, the attractive interactions between the DNA-binding domain of the helicase and the DNA backbone are essential for the helicase to exhibit a unidirectional motion along the DNA strand. Second, the sequence of ATP binding at multiple binding pockets affects the helicase motion. Specifically, concerted ATP binding does not generate a unidirectional motion of the helicase. It is only when the binding of ATP occurs sequentially from one pocket to the next that the helicase moves unidirectionally along the DNA. Interestingly, in the reverse order of sequential ATP binding, the helicase also moves unidirectionally but in the opposite direction. These observations suggest that in nature ATP molecules must distinguish between different available ATP binding pockets of the hexameric helicase in order to function efficiently. To this end, simulations reveal that the binding of ATP in one pocket induces an opening of the next ATP-binding pocket and such an asymmetric deformation may coordinate the sequential ATP binding in a unidirectional manner. Overall, these findings may provide clues toward understanding the mechanism of substrate translocation in other motor proteins.
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Affiliation(s)
- Kenji Yoshimoto
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, California, USA
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142
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Stevenson DJ, Gunn-Moore F, Dholakia K. Light forces the pace: optical manipulation for biophotonics. JOURNAL OF BIOMEDICAL OPTICS 2010; 15:041503. [PMID: 20799781 DOI: 10.1117/1.3475958] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The biomedical sciences have benefited immensely from photonics technologies in the last 50 years. This includes the application of minute forces that enable the trapping and manipulation of cells and single molecules. In terms of the area of biophotonics, optical manipulation has made a seminal contribution to our understanding of the dynamics of single molecules and the microrheology of cells. Here we present a review of optical manipulation, emphasizing its impact on the areas of single-molecule studies and single-cell biology, and indicating some of the key experiments in the fields.
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Affiliation(s)
- David James Stevenson
- University of St Andrews, Scottish Universities Physics Alliance, School of Physics and Astronomy, North Haugh, Fife, United Kingdom.
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143
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Manosas M, Xi XG, Bensimon D, Croquette V. Active and passive mechanisms of helicases. Nucleic Acids Res 2010; 38:5518-26. [PMID: 20423906 PMCID: PMC2938219 DOI: 10.1093/nar/gkq273] [Citation(s) in RCA: 107] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
In this work, we discuss the active or passive character of helicases. In the past years, several studies have used the theoretical framework proposed by Betterton and Julicher [Betterton, M.D. and Julicher, F. (2005) Opening of nucleic-acid double strands by helicases: active versus passive opening. Phys. Rev. E, 71, 11904-11911.] to analyse the unwinding data and assess the mechanism of the helicase under study (active versus passive). However, this procedure has given rise to apparently contradictory interpretations: helicases exhibiting similar behaviour have been classified as both active and passive enzymes [Johnson, D.S., Bai, L. Smith, B.Y., Patel, S.S. and Wang, M.D. (2007) Single-molecule studies reveal dynamics of DNA unwinding by the ring-shaped T7 helicase. Cell, 129, 1299-1309; Lionnet, T., Spiering, M.M., Benkovic, S.J., Bensimon, D. and Croquette, V. (2007) Real-time observation of bacteriophage T4 gp41 helicase reveals an unwinding mechanism Proc. Natl Acid. Sci., 104, 19790-19795]. In this work, we show that when the helicase under study has not been previously well characterized (namely, if its step size and rate of slippage are unknown) a multi-parameter fit to the afore-mentioned model can indeed lead to contradictory interpretations. We thus propose to differentiate between active and passive helicases on the basis of the comparison between their observed translocation velocity on single-stranded nucleic acid and their unwinding rate of double-stranded nucleic acid (with various GC content and under different tensions). A threshold separating active from passive behaviour is proposed following an analysis of the reported activities of different helicases. We study and contrast the mechanism of two helicases that exemplify these two behaviours: active for the RecQ helicase and passive for the gp41 helicase.
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Affiliation(s)
- Maria Manosas
- Laboratoire de Physique Statistique, Ecole Normale Superieure, UPMC Univ Paris 06, Universit Paris Diderot, CNRS, 24 rue Lhomond, 75005 Paris, France
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144
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Zhang H, Shu D, Browne M, Guo P. Construction of a laser combiner for dual fluorescent single molecule imaging of pRNA of phi29 DNA packaging motor. Biomed Microdevices 2010; 12:97-106. [PMID: 19809878 PMCID: PMC2812712 DOI: 10.1007/s10544-009-9364-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
A customized laser combiner was designed and constructed for dual channel single molecule imaging. The feasibility of a combiner-incorporated imaging system was demonstrated in studies of single molecule FRET. Distance rulers made of dual-labeled dsDNA were used to evaluate the system by determining the distance between one FRET pair. The results showed that the system is sensitive enough to distinguish between distances differing by two base pair and the distances calculated from FRET efficiencies are close to those documented in the literature. The single molecule FRET with the dual-color imaging system was also applied to reconstructed phi29 motor pRNA monomers. Finally, techniques for dual laser alignment and tuning of laser power for dual-color excitation are discussed.
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Affiliation(s)
- Hui Zhang
- Department of Biomedical Engineering, College of Engineering and College of Medicine, University of Cincinnati, Cincinnati, OH 45221, USA
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145
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Alkorta I, Blanco F, Elguero J, Schröder D. Distinction between homochiral and heterochiral dimers of 1-aza[n]helicenes (n=1–7) with alkaline cations. ACTA ACUST UNITED AC 2010. [DOI: 10.1016/j.tetasy.2010.05.032] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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146
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Residues in the central beta-hairpin of the DNA helicase of bacteriophage T7 are important in DNA unwinding. Proc Natl Acad Sci U S A 2010; 107:6782-7. [PMID: 20351255 DOI: 10.1073/pnas.1002734107] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The ring-shaped helicase of bacteriophage T7 (gp4), the product of gene 4, has basic beta-hairpin loops lining its central core where they are postulated to be the major sites of DNA interaction. We have altered multiple residues within the beta-hairpin loop to determine their role during dTTPase-driven DNA unwinding. Residues His-465, Leu-466, and Asn-468 are essential for both DNA unwinding and DNA synthesis mediated by T7 DNA polymerase during leading-strand DNA synthesis. Gp4-K467A, gp4-K471A, and gp4-K473A form fewer hexamers than heptamers compared to wild-type helicase and alone are deficient in DNA unwinding. However, they complement for the growth of T7 bacteriophage lacking gene 4. Single-molecule studies show that these three altered helicases support rates of leading-strand DNA synthesis comparable to that observed with wild-type gp4. Gp4-K467A, devoid of unwinding activity alone, supports leading-strand synthesis in the presence of T7 DNA polymerase. We propose that DNA polymerase limits the backward movement of the helicase during unwinding as well as assisting the forward movement necessary for strand separation.
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147
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Wickersham CE, Cash KJ, Pfeil SH, Bruck I, Kaplan DL, Plaxco KW, Lipman EA. Tracking a molecular motor with a nanoscale optical encoder. NANO LETTERS 2010; 10:1022-1027. [PMID: 20121107 PMCID: PMC2842186 DOI: 10.1021/nl904192m] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Optical encoders are commonly used in macroscopic machines to make precise measurements of distance and velocity by translating motion into a periodic signal. Here we show how Forster resonance energy transfer can be used to implement this technique at the single-molecule scale. We incorporate a series of acceptor dye molecules into self-assembling DNA, and the periodic signal resulting from unhindered motion of a donor-labeled molecular motor provides nanometer-scale resolution in milliseconds.
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Affiliation(s)
- Charles E. Wickersham
- Department of Physics, University of California, Santa Barbara, California 93106, USA
| | - Kevin J. Cash
- Department of Chemical Engineering, University of California, Santa Barbara, California 93106, USA
| | - Shawn H. Pfeil
- Department of Physics, University of California, Santa Barbara, California 93106, USA
| | - Irina Bruck
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37232, USA
| | - Daniel L. Kaplan
- Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37232, USA
| | - Kevin W. Plaxco
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, USA
- Biomolecular Science and Engineering Program, University of California, Santa Barbara, California 93106, USA
| | - Everett A. Lipman
- Department of Physics, University of California, Santa Barbara, California 93106, USA
- Biomolecular Science and Engineering Program, University of California, Santa Barbara, California 93106, USA
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148
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Gyimesi M, Sarlós K, Kovács M. Processive translocation mechanism of the human Bloom's syndrome helicase along single-stranded DNA. Nucleic Acids Res 2010; 38:4404-14. [PMID: 20211839 PMCID: PMC2910040 DOI: 10.1093/nar/gkq145] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
BLM, one of the human RecQ helicases, plays a fundamental role in homologous recombination-based error-free DNA repair pathways, which require its translocation and DNA unwinding activities. Although translocation is essential in vivo during DNA repair processes and it provides a framework for more complex activities of helicases, including strand separation and nucleoprotein displacement, its mechanism has not been resolved for any human DNA helicase. Here, we present a quantitative model for the translocation of a monomeric form of BLM along ssDNA. We show that BLM performs translocation at a low adenosine triphosphate (ATP) coupling ratio (1 ATP consumed/1 nucleotide traveled) and moderate processivity (with a mean number of 50 nucleotides traveled in a single run). We also show that the rate-limiting step of the translocation cycle is a transition between two ADP-bound enzyme states. Via opening of the helicase core, this structural change may drive the stepping of BLM along the DNA track by a directed inchworm mechanism. The data also support the conclusion that BLM performs double-stranded DNA unwinding by fully active duplex destabilization.
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Affiliation(s)
- Máté Gyimesi
- Department of Biochemistry, Eötvös University, Pázmány P. s. 1/c, H-1117 Budapest, Hungary
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149
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Efcavitch JW, Thompson JF. Single-molecule DNA analysis. ANNUAL REVIEW OF ANALYTICAL CHEMISTRY (PALO ALTO, CALIF.) 2010; 3:109-128. [PMID: 20636036 DOI: 10.1146/annurev.anchem.111808.073558] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
The ability to detect single molecules of DNA or RNA has led to an extremely rich area of exploration of the single most important biomolecule in nature. In cases in which the nucleic acid molecules are tethered to a solid support, confined to a channel, or simply allowed to diffuse into a detection volume, novel techniques have been developed to manipulate the DNA and to examine properties such as structural dynamics and protein-DNA interactions. Beyond the analysis of the properties of nucleic acids themselves, single-molecule detection has enabled dramatic improvements in the throughput of DNA sequencing and holds promise for continuing progress. Both optical and nonoptical detection methods that use surfaces, nanopores, and zero-mode waveguides have been attempted, and one optically based instrument is already commercially available. The breadth of literature related to single-molecule DNA analysis is vast; this review focuses on a survey of efforts in molecular dynamics and nucleic acid sequencing.
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150
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Manosas M, Meglio A, Spiering MM, Ding F, Benkovic SJ, Barre FX, Saleh OA, Allemand JF, Bensimon D, Croquette V. Magnetic tweezers for the study of DNA tracking motors. Methods Enzymol 2010; 475:297-320. [PMID: 20627163 DOI: 10.1016/s0076-6879(10)75013-8] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
Single-molecule manipulation methods have opened a new vista on the study of molecular motors. Here we describe the use of magnetic traps for the investigation of the mechanism of DNA based motors, in particular helicases and translocases.
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Affiliation(s)
- Maria Manosas
- Laboratoire de Physique Statistique, Ecole Normale Superieure, Université Paris Diderot, Paris, France
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