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Fazio NT, Mersch KN, Hao L, Lohman TM. E. coli RecB Nuclease Domain Regulates RecBCD Helicase Activity but not Single Stranded DNA Translocase Activity. J Mol Biol 2024; 436:168381. [PMID: 38081382 PMCID: PMC11131135 DOI: 10.1016/j.jmb.2023.168381] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2023] [Revised: 11/30/2023] [Accepted: 12/01/2023] [Indexed: 12/23/2023]
Abstract
Much is still unknown about the mechanisms by which helicases unwind duplex DNA. Whereas structure-based models describe DNA unwinding as occurring by the ATPase motors mechanically pulling the DNA duplex across a wedge domain in the helicase, biochemical data show that processive DNA unwinding by E. coli RecBCD helicase can occur in the absence of ssDNA translocation by the canonical RecB and RecD motors. Here we show that DNA unwinding is not a simple consequence of ssDNA translocation by the motors. Using stopped-flow fluorescence approaches, we show that a RecB nuclease domain deletion variant (RecBΔNucCD) unwinds dsDNA at significantly slower rates than RecBCD, while the ssDNA translocation rate is unaffected. This effect is primarily due to the absence of the nuclease domain since a nuclease-dead mutant (RecBD1080ACD), which retains the nuclease domain, showed no change in ssDNA translocation or dsDNA unwinding rates relative to RecBCD on short DNA substrates (≤60 base pairs). Hence, ssDNA translocation is not rate-limiting for DNA unwinding. RecBΔNucCD also initiates unwinding much slower than RecBCD from a blunt-ended DNA. RecBΔNucCD also unwinds DNA ∼two-fold slower than RecBCD on long DNA (∼20 kilo base pair) in single molecule optical tweezer experiments, although the rates for RecBD1080ACD unwinding are intermediate between RecBCD and RecBΔNucCD. Surprisingly, significant pauses in DNA unwinding occur even in the absence of chi (crossover hotspot instigator) sites. We hypothesize that the nuclease domain influences the rate of DNA base pair melting, possibly allosterically and that RecBΔNucCD may mimic a post-chi state of RecBCD.
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Affiliation(s)
- Nicole T Fazio
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, United States
| | - Kacey N Mersch
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, United States
| | - Linxuan Hao
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, United States
| | - Timothy M Lohman
- Department of Biochemistry and Molecular Biophysics, Washington University in St. Louis School of Medicine, St. Louis, MO 63110, United States.
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2
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Fazio N, Mersch KN, Hao L, Lohman TM. E. coli RecBCD Nuclease Domain Regulates Helicase Activity but not Single Stranded DNA Translocase Activity. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.13.561901. [PMID: 37905078 PMCID: PMC10614803 DOI: 10.1101/2023.10.13.561901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/02/2023]
Abstract
Much is still unknown about the mechanisms by which helicases unwind duplex DNA. Whereas structure-based models describe DNA unwinding as a consequence of mechanically pulling the DNA duplex across a wedge domain in the helicase by the single stranded (ss)DNA translocase activity of the ATPase motors, biochemical data indicate that processive DNA unwinding by the E. coli RecBCD helicase can occur in the absence of ssDNA translocation of the canonical RecB and RecD motors. Here, we present evidence that dsDNA unwinding is not a simple consequence of ssDNA translocation by the RecBCD motors. Using stopped-flow fluorescence approaches, we show that a RecB nuclease domain deletion variant (RecB ΔNuc CD) unwinds dsDNA at significantly slower rates than RecBCD, while the rate of ssDNA translocation is unaffected. This effect is primarily due to the absence of the nuclease domain and not the absence of the nuclease activity, since a nuclease-dead mutant (RecB D1080A CD), which retains the nuclease domain, showed no significant change in rates of ssDNA translocation or dsDNA unwinding relative to RecBCD on short DNA substrates (≤ 60 base pairs). This indicates that ssDNA translocation is not rate-limiting for DNA unwinding. RecB ΔNuc CD also initiates unwinding much slower than RecBCD from a blunt-ended DNA, although it binds with higher affinity than RecBCD. RecB ΔNuc CD also unwinds DNA ∼two-fold slower than RecBCD on long DNA (∼20 kilo base pair) in single molecule optical tweezer experiments, although the rates for RecB D1080A CD unwinding are intermediate between RecBCD and RecB ΔNuc CD. Surprisingly, significant pauses occur even in the absence of chi (crossover hotspot instigator) sites. We hypothesize that the nuclease domain influences the rate of DNA base pair melting, rather than DNA translocation, possibly allosterically. Since the rate of DNA unwinding by RecBCD also slows after it recognizes a chi sequence, RecB ΔNuc CD may mimic a post- chi state of RecBCD.
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3
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Determining translocation orientations of nucleic acid helicases. Methods 2021; 204:160-171. [PMID: 34758393 PMCID: PMC9076756 DOI: 10.1016/j.ymeth.2021.11.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Revised: 10/29/2021] [Accepted: 11/02/2021] [Indexed: 11/20/2022] Open
Abstract
Helicase enzymes translocate along an RNA or DNA template with a defined polarity to unwind, separate, or remodel duplex strands for a variety of genome maintenance processes. Helicase mutations are commonly associated with a variety of diseases including aging, cancer, and neurodegeneration. Biochemical characterization of these enzymes has provided a wealth of information on the kinetics of unwinding and substrate preferences, and several high-resolution structures of helicases alone and bound to oligonucleotides have been solved. Together, they provide mechanistic insights into the structural translocation and unwinding orientations of helicases. However, these insights rely on structural inferences derived from static snapshots. Instead, continued efforts should be made to combine structure and kinetics to better define active translocation orientations of helicases. This review explores many of the biochemical and biophysical methods utilized to map helicase binding orientation to DNA or RNA substrates and includes several time-dependent methods to unequivocally map the active translocation orientation of these enzymes to better define the active leading and trailing faces.
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4
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Protein Environment and DNA Orientation Affect Protein-Induced Cy3 Fluorescence Enhancement. Biophys J 2019; 117:66-73. [PMID: 31235181 DOI: 10.1016/j.bpj.2019.05.026] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Revised: 05/23/2019] [Accepted: 05/29/2019] [Indexed: 11/20/2022] Open
Abstract
The cyanine dye Cy3 is a popular fluorophore used to probe the binding of proteins to nucleic acids as well as their conformational transitions. Nucleic acids labeled only with Cy3 can often be used to monitor interactions with unlabeled proteins because of an enhancement of Cy3 fluorescence intensity that results when the protein contacts Cy3, a property sometimes referred to as protein-induced fluorescence enhancement (PIFE). Although Cy3 fluorescence is enhanced upon contacting most proteins, we show here in studies of human replication protein A and Escherichia coli single-stranded DNA binding protein that the magnitude of the Cy3 enhancement is dependent on both the protein as well as the orientation of the protein with respect to the Cy3 label on the DNA. This difference in PIFE is due entirely to differences in the final protein-DNA complex. We also show that the origin of PIFE is the longer fluorescence lifetime induced by the local protein environment. These results indicate that PIFE is not a through space distance-dependent phenomenon but requires a direct interaction of Cy3 with the protein, and the magnitude of the effect is influenced by the region of the protein contacting Cy3. Hence, use of the Cy3 PIFE effect for quantitative studies may require careful calibration.
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Devarkar SC, Schweibenz B, Wang C, Marcotrigiano J, Patel SS. RIG-I Uses an ATPase-Powered Translocation-Throttling Mechanism for Kinetic Proofreading of RNAs and Oligomerization. Mol Cell 2018; 72:355-368.e4. [PMID: 30270105 PMCID: PMC6434538 DOI: 10.1016/j.molcel.2018.08.021] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2018] [Revised: 06/15/2018] [Accepted: 08/14/2018] [Indexed: 12/25/2022]
Abstract
RIG-I has a remarkable ability to specifically select viral 5'ppp dsRNAs for activation from a pool of cytosolic self-RNAs. The ATPase activity of RIG-I plays a role in RNA discrimination and activation, but the underlying mechanism was unclear. Using transient-state kinetics, we elucidated the ATPase-driven "kinetic proofreading" mechanism of RIG-I activation and RNA discrimination, akin to DNA polymerases, ribosomes, and T cell receptors. Even in the autoinhibited state of RIG-I, the C-terminal domain kinetically discriminates against self-RNAs by fast off rates. ATP binding facilitates dsRNA engagement but, interestingly, makes RIG-I promiscuous, explaining the constitutive signaling by Singleton-Merten syndrome-linked mutants that bind ATP without hydrolysis. ATP hydrolysis dissociates self-RNAs faster than 5'ppp dsRNA but, more importantly, drives RIG-I oligomerization through translocation, which we show to be regulated by helicase motif IVa. RIG-I translocates directionally from the dsRNA end into the stem region, and the 5'ppp end "throttles" translocation to provide a mechanism for threading and building a signaling-active oligomeric complex.
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Affiliation(s)
- Swapnil C Devarkar
- Department of Biochemistry and Molecular Biology, Robert Wood Johnson Medical School, Rutgers University, Piscataway, NJ 08854, USA
| | - Brandon Schweibenz
- Department of Biochemistry and Molecular Biology, Robert Wood Johnson Medical School, Rutgers University, Piscataway, NJ 08854, USA
| | - Chen Wang
- Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, NIH, Bethesda, MD 20892, USA
| | - Joseph Marcotrigiano
- Laboratory of Infectious Diseases, National Institute of Allergy and Infectious Diseases, NIH, Bethesda, MD 20892, USA.
| | - Smita S Patel
- Department of Biochemistry and Molecular Biology, Robert Wood Johnson Medical School, Rutgers University, Piscataway, NJ 08854, USA.
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Chen WF, Rety S, Guo HL, Dai YX, Wu WQ, Liu NN, Auguin D, Liu QW, Hou XM, Dou SX, Xi XG. Molecular Mechanistic Insights into Drosophila DHX36-Mediated G-Quadruplex Unfolding: A Structure-Based Model. Structure 2018; 26:403-415.e4. [PMID: 29429875 DOI: 10.1016/j.str.2018.01.008] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2017] [Revised: 12/13/2017] [Accepted: 01/12/2018] [Indexed: 11/29/2022]
Abstract
Helicase DHX36 plays essential roles in cell development and differentiation at least partially by resolving G-quadruplex (G4) structures. Here we report crystal structures of the Drosophila homolog of DHX36 (DmDHX36) in complex with RNA and a series of DNAs. By combining structural, small-angle X-ray scattering, molecular dynamics simulation, and single-molecule fluorescence studies, we revealed that positively charged amino acids in RecA2 and OB-like domains constitute an elaborate structural pocket at the nucleic acid entrance, in which negatively charged G4 DNA is tightly bound and partially destabilized. The G4 DNA is then completely unfolded through the 3'-5' translocation activity of the helicase. Furthermore, crystal structures and DNA binding assays show that G-rich DNA is preferentially recognized and in the presence of ATP, specifically bound by DmDHX36, which may cooperatively enhance the G-rich DNA translocation and G4 unfolding. On the basis of these results, a conceptual G4 DNA-resolving mechanism is proposed.
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Affiliation(s)
- Wei-Fei Chen
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Stephane Rety
- Université Lyon, ENS de Lyon, Université Claude Bernard, CNRS UMR 5239, INSERM U1210, LBMC, 46 allée d'Italie Site Jacques Monod, 69007, Lyon, France
| | - Hai-Lei Guo
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Yang-Xue Dai
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Wen-Qiang Wu
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Na-Nv Liu
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Daniel Auguin
- Laboratoire de Biologie des Ligneux et des Grandes Cultures, Université d'Orléans, UPRES EA 1207, INRA-USC1328, 45067 Orléans, France
| | - Qian-Wen Liu
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Xi-Miao Hou
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China
| | - Shuo-Xing Dou
- Beijing National Laboratory for Condensed Matter Physics and CAS Key Laboratory of Soft Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China; School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xu-Guang Xi
- College of Life Sciences, Northwest A&F University, Yangling, Shaanxi 712100, China; LBPA, ENS de Cachan, Université Paris-Saclay, Centre National de la Recherche Scientifique, 61 Avenue du Président Wilson, 94235 Cachan, France.
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7
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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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8
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Pokhrel N, Origanti S, Davenport EP, Gandhi D, Kaniecki K, Mehl RA, Greene EC, Dockendorff C, Antony E. Monitoring Replication Protein A (RPA) dynamics in homologous recombination through site-specific incorporation of non-canonical amino acids. Nucleic Acids Res 2017; 45:9413-9426. [PMID: 28934470 PMCID: PMC5766198 DOI: 10.1093/nar/gkx598] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2017] [Accepted: 07/09/2017] [Indexed: 12/23/2022] Open
Abstract
An essential coordinator of all DNA metabolic processes is Replication Protein A (RPA). RPA orchestrates these processes by binding to single-stranded DNA (ssDNA) and interacting with several other DNA binding proteins. Determining the real-time kinetics of single players such as RPA in the presence of multiple DNA processors to better understand the associated mechanistic events is technically challenging. To overcome this hurdle, we utilized non-canonical amino acids and bio-orthogonal chemistry to site-specifically incorporate a chemical fluorophore onto a single subunit of heterotrimeric RPA. Upon binding to ssDNA, this fluorescent RPA (RPAf) generates a quantifiable change in fluorescence, thus serving as a reporter of its dynamics on DNA in the presence of multiple other DNA binding proteins. Using RPAf, we describe the kinetics of facilitated self-exchange and exchange by Rad51 and mediator proteins during various stages in homologous recombination. RPAf is widely applicable to investigate its mechanism of action in processes such as DNA replication, repair and telomere maintenance.
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Affiliation(s)
- Nilisha Pokhrel
- Department of Biological Sciences, Marquette University, Milwaukee, WI 53201, USA
| | - Sofia Origanti
- Department of Biological Sciences, Marquette University, Milwaukee, WI 53201, USA
| | | | - Disha Gandhi
- Department of Chemistry, Marquette University, Milwaukee, WI 53201, USA
| | - Kyle Kaniecki
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA.,Department of Genetics and Development, Columbia University, New York, NY 10032, USA
| | - Ryan A Mehl
- Department of Biochemistry and Biophysics, Oregon State University, Corvallis, OR 97331, USA
| | - Eric C Greene
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Chris Dockendorff
- Department of Chemistry, Marquette University, Milwaukee, WI 53201, USA
| | - Edwin Antony
- Department of Biological Sciences, Marquette University, Milwaukee, WI 53201, USA
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9
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A rapid method for detecting protein-nucleic acid interactions by protein induced fluorescence enhancement. Sci Rep 2016; 6:39653. [PMID: 28008962 PMCID: PMC5180085 DOI: 10.1038/srep39653] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2016] [Accepted: 11/24/2016] [Indexed: 12/15/2022] Open
Abstract
Many fundamental biological processes depend on intricate networks of interactions between proteins and nucleic acids and a quantitative description of these interactions is important for understanding cellular mechanisms governing DNA replication, transcription, or translation. Here we present a versatile method for rapid and quantitative assessment of protein/nucleic acid (NA) interactions. This method is based on protein induced fluorescence enhancement (PIFE), a phenomenon whereby protein binding increases the fluorescence of Cy3-like dyes. PIFE has mainly been used in single molecule studies to detect protein association with DNA or RNA. Here we applied PIFE for steady state quantification of protein/NA interactions by using microwell plate fluorescence readers (mwPIFE). We demonstrate the general applicability of mwPIFE for examining various aspects of protein/DNA interactions with examples from the restriction enzyme BamHI, and the DNA repair complexes Ku and XPF/ERCC1. These include determination of sequence and structure binding specificities, dissociation constants, detection of weak interactions, and the ability of a protein to translocate along DNA. mwPIFE represents an easy and high throughput method that does not require protein labeling and can be applied to a wide range of applications involving protein/NA interactions.
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10
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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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11
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Gyimesi M, Harami GM, Kocsis ZS, Kovács M. Recent adaptations of fluorescence techniques for the determination of mechanistic parameters of helicases and translocases. Methods 2016; 108:24-39. [PMID: 27133766 DOI: 10.1016/j.ymeth.2016.04.028] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Revised: 04/22/2016] [Accepted: 04/25/2016] [Indexed: 01/11/2023] Open
Abstract
Helicases and translocases are nucleic acid (NA)-based molecular motors that use the free energy liberated during the nucleoside triphosphate (NTP, usually ATP) hydrolysis cycle for unidirectional translocation along their NA (DNA, RNA or heteroduplex) substrates. Determination of the kinetic and thermodynamic parameters of their mechanoenzymatic cycle serves as a basis for the exploration of their physiological behavior and various cellular functions. Here we describe how recent adaptations of fluorescence-based solution kinetic methods can be used to determine practically all important mechanistic parameters of NA-based motor proteins. We outline practically useful analysis procedures for equilibrium, steady-state and transient kinetic data. This analysis can be used to quantitatively characterize the enzymatic steps of the NTP hydrolytic cycle, the binding site size, stoichiometry and energetics of protein-NA interactions, the rate and processivity of translocation along and unwinding of NA strands, and the mechanochemical coupling between these processes. The described methods yield insights into the functional role of the enzymes, and also greatly aid the design and interpretation of single-molecule experiments as well as the engineering of enzymatic properties for biotechnological applications.
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Affiliation(s)
- Máté Gyimesi
- ELTE-MTA "Momentum" Motor Enzymology Research Group, Department of Biochemistry, Eötvös Loránd University, Pázmány Péter sétány 1/c, H-1117 Budapest, Hungary.
| | - Gábor M Harami
- ELTE-MTA "Momentum" Motor Enzymology Research Group, Department of Biochemistry, Eötvös Loránd University, Pázmány Péter sétány 1/c, H-1117 Budapest, Hungary.
| | - Zsuzsa S Kocsis
- ELTE-MTA "Momentum" Motor Enzymology Research Group, Department of Biochemistry, Eötvös Loránd University, Pázmány Péter sétány 1/c, H-1117 Budapest, Hungary.
| | - Mihály Kovács
- ELTE-MTA "Momentum" Motor Enzymology Research Group, Department of Biochemistry, Eötvös Loránd University, Pázmány Péter sétány 1/c, H-1117 Budapest, Hungary.
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12
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13
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Briggs K, Fischer CJ. All motors have to decide is what to do with the DNA that is given them. Biomol Concepts 2015; 5:383-95. [PMID: 25367619 DOI: 10.1515/bmc-2014-0017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2014] [Accepted: 09/09/2014] [Indexed: 11/15/2022] Open
Abstract
DNA translocases are a diverse group of molecular motors responsible for a wide variety of cellular functions. The goal of this review is to identify common aspects in the mechanisms for how these enzymes couple the binding and hydrolysis of ATP to their movement along DNA. Not surprisingly, the shared structural components contained within the catalytic domains of several of these motors appear to give rise to common aspects of DNA translocation. Perhaps more interesting, however, are the differences between the families of translocases and the potential associated implications both for the functions of the members of these families and for the evolution of these families. However, as there are few translocases for which complete characterizations of the mechanisms of DNA binding, DNA translocation, and DNA-stimulated ATPase have been completed, it is difficult to form many inferences. We therefore hope that this review motivates the necessary further experimentation required for broader comparisons and conclusions.
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14
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Reynolds KA, Cameron CE, Raney KD. Melting of Duplex DNA in the Absence of ATP by the NS3 Helicase Domain through Specific Interaction with a Single-Strand/Double-Strand Junction. Biochemistry 2015; 54:4248-58. [PMID: 26091150 DOI: 10.1021/acs.biochem.5b00214] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Helicases unwind double-stranded nucleic acids, remove secondary structures from single-stranded nucleic acids, and remove proteins bound to nucleic acids. For many helicases, the mechanisms for these different functions share the ability to translocate with a directional bias as a result of ATP binding and hydrolysis. Nonstructural protein 3 (NS3) is an essential enzyme expressed by the hepatitis C virus (HCV) and is known to catalyze the unwinding of both DNA and RNA substrates in a 3'-to-5' direction. We investigated the role of nucleic acid binding in the unwinding mechanism by examining ATP-independent unwinding. We observed that even in the absence of ATP, the NS3 helicase domain (NS3h) unwound duplexes only when they contained a 3'-tail (i.e., 3'-to-5' directionality). Blunt-ended duplexes and 5'-tailed duplexes were not melted even in the presence of a large excess concentration of the protein. NS3h was found to diffuse rapidly along single-stranded DNA at a rate of 30 nucleotides(2) s(-1). Upon encountering an appropriate single-strand/double-strand (ss/ds) junction, NS3h slowly melted the duplex under conditions with an excess protein concentration relative to DNA concentration. When a biotin-streptavidin block was placed into the ssDNA region, no melting of DNA was observed, suggesting that NS3h must diffuse along the ssDNA, and that the streptavidin blocked the diffusion. We conclude that the specific interaction between NS3h and the ss/dsDNA junction, coupled with diffusion, allows binding energy to melt duplex DNA with a directional bias. Alternatively, we found that the full-length NS3 protein did not exhibit strict directionality and was dependent on duplex DNA length. NS3 was able to unwind the duplex even in the presence of the biotin-streptavidin block. We propose a noncanonical model of unwinding for NS3 in which the enzyme binds directly to the duplex via protein-protein interactions to melt the substrate.
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Affiliation(s)
- Kimberly A Reynolds
- †Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205, United States
| | - Craig E Cameron
- ‡Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
| | - Kevin D Raney
- †Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205, United States
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15
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Low processivity for DNA translocation by the ISWI molecular motor. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2015; 1854:1487-93. [PMID: 26116984 DOI: 10.1016/j.bbapap.2015.06.011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 02/27/2015] [Revised: 04/23/2015] [Accepted: 06/24/2015] [Indexed: 11/21/2022]
Abstract
The motor protein ISWI (Imitation SWItch) is the conserved catalytic ATPase domain of the ISWI family of chromatin remodelers. Members of the ISWI family are involved in regulating the structure of cellular chromatin during times of transcription, translation, and repair. Current models for the nucleosome repositioning activity of ISWI and other chromatin remodelers require the translocation of the remodeling protein along double-stranded DNA through an ATP-dependent mechanism. Here we report results from spectrofluorometric stopped-flow experiments which demonstrate that ISWI displays very low processivity for free DNA translocation. By combining these results with those from experiments monitoring the DNA stimulated ATPase activity of ISWI we further demonstrate that the DNA translocation by ISWI is tightly coupled to ATP hydrolysis. The calculated coupling efficiency of 0.067±0.018 ATP/ISWI/bp is seemingly quite low in comparison to similar DNA translocases and we present potential models to account for this. Nevertheless, the tight coupling of ATP hydrolysis to DNA translocation suggests that DNA translocation is not energetically rate limiting for nucleosome repositioning by ISWI.
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16
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Hwang H, Myong S. Protein induced fluorescence enhancement (PIFE) for probing protein-nucleic acid interactions. Chem Soc Rev 2014; 43:1221-9. [PMID: 24056732 DOI: 10.1039/c3cs60201j] [Citation(s) in RCA: 161] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Single molecule studies of protein-nucleic acid interactions shed light on molecular mechanisms and kinetics involved in protein binding, translocation, and unwinding of DNA and RNA substrates. In this review, we provide an overview of a single molecule fluorescence method, termed "protein induced fluorescence enhancement" (PIFE). Unlike FRET where two dyes are required, PIFE employs a single dye attached to DNA or RNA to which an unlabeled protein is applied. We discuss both ensemble and single molecule studies in which PIFE was utilized.
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Affiliation(s)
- Helen Hwang
- Bioengineering Department, University of Illinois at Urbana-Champaign, USA.
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17
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Nguyen B, Sokoloski J, Galletto R, Elson EL, Wold MS, Lohman TM. Diffusion of human replication protein A along single-stranded DNA. J Mol Biol 2014; 426:3246-3261. [PMID: 25058683 DOI: 10.1016/j.jmb.2014.07.014] [Citation(s) in RCA: 108] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Revised: 06/30/2014] [Accepted: 07/08/2014] [Indexed: 10/25/2022]
Abstract
Replication protein A (RPA) is a eukaryotic single-stranded DNA (ssDNA) binding protein that plays critical roles in most aspects of genome maintenance, including replication, recombination and repair. RPA binds ssDNA with high affinity, destabilizes DNA secondary structure and facilitates binding of other proteins to ssDNA. However, RPA must be removed from or redistributed along ssDNA during these processes. To probe the dynamics of RPA-DNA interactions, we combined ensemble and single-molecule fluorescence approaches to examine human RPA (hRPA) diffusion along ssDNA and find that an hRPA heterotrimer can diffuse rapidly along ssDNA. Diffusion of hRPA is functional in that it provides the mechanism by which hRPA can transiently disrupt DNA hairpins by diffusing in from ssDNA regions adjacent to the DNA hairpin. hRPA diffusion was also monitored by the fluctuations in fluorescence intensity of a Cy3 fluorophore attached to the end of ssDNA. Using a novel method to calibrate the Cy3 fluorescence intensity as a function of hRPA position on the ssDNA, we estimate a one-dimensional diffusion coefficient of hRPA on ssDNA of D1~5000nt(2) s(-1) at 37°C. Diffusion of hRPA while bound to ssDNA enables it to be readily repositioned to allow other proteins access to ssDNA.
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Affiliation(s)
- Binh Nguyen
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Joshua Sokoloski
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Roberto Galletto
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Elliot L Elson
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Marc S Wold
- Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
| | - Timothy M Lohman
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, Saint Louis, MO 63110, USA.
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18
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Raney KD. Chemical modifications of DNA for study of helicase mechanisms. Bioorg Med Chem 2014; 22:4399-406. [PMID: 24931273 DOI: 10.1016/j.bmc.2014.05.049] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2014] [Revised: 05/16/2014] [Accepted: 05/22/2014] [Indexed: 12/28/2022]
Abstract
Helicases are ubiquitous enzymes that are required for virtually all processes in DNA and RNA metabolism including replication, repair, recombination, transcription, and translation. The mechanisms for helicase-catalyzed unwinding of double-stranded DNA or remodeling of RNA have been the subject of intense investigation for more than two decades. The central function of these enzymes is to transduce the energy available from ATP binding and hydrolysis to alter the conformation of nucleic acids. Specific interactions between helicases and nucleic acids have been investigated by chemical approaches in which the nucleic acid substrate has been modified in order to provide specific insight into the enzymatic mechanism.
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Affiliation(s)
- Kevin D Raney
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, 4301 W. Markham St., Slot 516, Little Rock, AR 72205, USA.
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19
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Galletto R, Tomko EJ. Translocation of Saccharomyces cerevisiae Pif1 helicase monomers on single-stranded DNA. Nucleic Acids Res 2013; 41:4613-27. [PMID: 23446274 PMCID: PMC3632115 DOI: 10.1093/nar/gkt117] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
In Saccharomyces cerevisiae Pif1 participates in a wide variety of DNA metabolic pathways both in the nucleus and in mitochondria. The ability of Pif1 to hydrolyse ATP and catalyse unwinding of duplex nucleic acid is proposed to be at the core of its functions. We recently showed that upon binding to DNA Pif1 dimerizes and we proposed that a dimer of Pif1 might be the species poised to catalysed DNA unwinding. In this work we show that monomers of Pif1 are able to translocate on single-stranded DNA with 5′ to 3′ directionality. We provide evidence that the translocation activity of Pif1 could be used in activities other than unwinding, possibly to displace proteins from ssDNA. Moreover, we show that monomers of Pif1 retain some unwinding activity although a dimer is clearly a better helicase, suggesting that regulation of the oligomeric state of Pif1 could play a role in its functioning as a helicase or a translocase. Finally, although we show that Pif1 can translocate on ssDNA, the translocation profiles suggest the presence on ssDNA of two populations of Pif1, both able to translocate with 5′ to 3′ directionality.
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Affiliation(s)
- Roberto Galletto
- 252 McDonnell Science Building, Department of Biochemistry and Molecular Biophysics, Washington University, School of Medicine, 660 South Euclid Avenue, MS8231, Saint Louis, MO 63110,
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20
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Eastlund A, Malik SS, Fischer CJ. Kinetic mechanism of DNA translocation by the RSC molecular motor. Arch Biochem Biophys 2013; 532:73-83. [PMID: 23399434 DOI: 10.1016/j.abb.2013.01.011] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2012] [Revised: 01/21/2013] [Accepted: 01/30/2013] [Indexed: 01/29/2023]
Abstract
ATP-dependent nucleosome repositioning by chromatin remodeling enzymes requires the translocation of these enzymes along the nucleosomal DNA. Using a fluorescence stopped-flow assay we monitored DNA translocation by a minimal RSC motor and through global analysis of these time courses we have determined that this motor has a macroscopic translocation rate of 2.9 bp/s with a step size of 1.24 bp. From the complementary quantitative analysis of the associated time courses of ATP consumption during DNA translocation we have determined that this motor has an efficiency of 3.0 ATP/bp, which is slightly less that the efficiency observed for several genetically related DNA helicases and which likely results from random pausing by the motor during translocation. Nevertheless, this motor is able to exert enough force during translocation to displace streptavidin from biotinylated DNA. Taken together these results are the necessary first step for quantifying both the role of DNA translocation in nucleosome repositioning by RSC and the efficiency at which RSC couples ATP binding and hydrolysis to nucleosome repositioning.
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Affiliation(s)
- Allen Eastlund
- Department of Physics and Astronomy, University of Kansas, 1251 Wescoe Hall Dr., 1082 Malott Hall, Lawrence, KS 66045, USA
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21
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Xie F, Wu CG, Weiland E, Lohman TM. Asymmetric regulation of bipolar single-stranded DNA translocation by the two motors within Escherichia coli RecBCD helicase. J Biol Chem 2012. [PMID: 23192341 DOI: 10.1074/jbc.m112.423384] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Repair of double-stranded DNA breaks in Escherichia coli is initiated by the RecBCD helicase that possesses two superfamily-1 motors, RecB (3' to 5' translocase) and RecD (5' to 3' translocase), that operate on the complementary DNA strands to unwind duplex DNA. However, it is not known whether the RecB and RecD motors act independently or are functionally coupled. Here we show by directly monitoring ATP-driven single-stranded DNA translocation of RecBCD that the 5' to 3' rate is always faster than the 3' to 5' rate on DNA without a crossover hotspot instigator site and that the translocation rates are coupled asymmetrically. That is, RecB regulates both 3' to 5' and 5' to 3' translocation, whereas RecD only regulates 5' to 3' translocation. We show that the recently identified RecBC secondary translocase activity functions within RecBCD and that this contributes to the coupling. This coupling has implications for how RecBCD activity is regulated after it recognizes a crossover hotspot instigator sequence during DNA unwinding.
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Affiliation(s)
- Fuqian Xie
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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22
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Adedeji AO, Marchand B, te Velthuis AJW, Snijder EJ, Weiss S, Eoff RL, Singh K, Sarafianos SG. Mechanism of nucleic acid unwinding by SARS-CoV helicase. PLoS One 2012; 7:e36521. [PMID: 22615777 PMCID: PMC3352918 DOI: 10.1371/journal.pone.0036521] [Citation(s) in RCA: 125] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2011] [Accepted: 04/03/2012] [Indexed: 02/04/2023] Open
Abstract
The non-structural protein 13 (nsp13) of Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) is a helicase that separates double-stranded RNA (dsRNA) or DNA (dsDNA) with a 5′→3′ polarity, using the energy of nucleotide hydrolysis. We determined the minimal mechanism of helicase function by nsp13. We showed a clear unwinding lag with increasing length of the double-stranded region of the nucleic acid, suggesting the presence of intermediates in the unwinding process. To elucidate the nature of the intermediates we carried out transient kinetic analysis of the nsp13 helicase activity. We demonstrated that the enzyme unwinds nucleic acid in discrete steps of 9.3 base-pairs (bp) each, with a catalytic rate of 30 steps per second. Therefore the net unwinding rate is ∼280 base-pairs per second. We also showed that nsp12, the SARS-CoV RNA-dependent RNA polymerase (RdRp), enhances (2-fold) the catalytic efficiency of nsp13 by increasing the step size of nucleic acid (RNA/RNA or DNA/DNA) unwinding. This effect is specific for SARS-CoV nsp12, as no change in nsp13 activity was observed when foot-and-mouth-disease virus RdRp was used in place of nsp12. Our data provide experimental evidence that nsp13 and nsp12 can function in a concerted manner to improve the efficiency of viral replication and enhance our understanding of nsp13 function during SARS-CoV RNA synthesis.
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Affiliation(s)
- Adeyemi O. Adedeji
- Christopher Bond Life Sciences Center, Department of Molecular Microbiology and Immunology, University of Missouri, School of Medicine, Columbia, Missouri, United States of America
| | - Bruno Marchand
- Christopher Bond Life Sciences Center, Department of Molecular Microbiology and Immunology, University of Missouri, School of Medicine, Columbia, Missouri, United States of America
| | - Aartjan J. W. te Velthuis
- Molecular Virology Laboratory, Department of Medical Microbiology, Center of Infectious Diseases, Leiden University Medical Center, Leiden, The Netherlands
| | - Eric J. Snijder
- Molecular Virology Laboratory, Department of Medical Microbiology, Center of Infectious Diseases, Leiden University Medical Center, Leiden, The Netherlands
| | - Susan Weiss
- Department of Microbiology, University of Pennsylvania, School of Medicine, Philadelphia, Pennsylvania, United States of America
| | - Robert L. Eoff
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States of America
| | - Kamalendra Singh
- Christopher Bond Life Sciences Center, Department of Molecular Microbiology and Immunology, University of Missouri, School of Medicine, Columbia, Missouri, United States of America
| | - Stefan G. Sarafianos
- Christopher Bond Life Sciences Center, Department of Molecular Microbiology and Immunology, University of Missouri, School of Medicine, Columbia, Missouri, United States of America
- * E-mail:
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23
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Tomko EJ, Fischer CJ, Lohman TM. Single-stranded DNA translocation of E. coli UvrD monomer is tightly coupled to ATP hydrolysis. J Mol Biol 2012; 418:32-46. [PMID: 22342931 DOI: 10.1016/j.jmb.2012.02.013] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2011] [Revised: 01/31/2012] [Accepted: 02/08/2012] [Indexed: 10/14/2022]
Abstract
Escherichia coli UvrD is an SF1A (superfamily 1 type A) helicase/translocase that functions in several DNA repair pathways. A UvrD monomer is a rapid and processive single-stranded DNA (ssDNA) translocase but is unable to unwind DNA processively in vitro. Based on data at saturating ATP (500 μM), we proposed a nonuniform stepping mechanism in which a UvrD monomer translocates with biased (3' to 5') directionality while hydrolyzing 1 ATP per DNA base translocated, but with a kinetic step size of 4-5 nt/step, suggesting that a pause occurs every 4-5 nt translocated. To further test this mechanism, we examined UvrD translocation over a range of lower ATP concentrations (10-500 μM ATP), using transient kinetic approaches. We find a constant ATP coupling stoichiometry of ∼1 ATP/DNA base translocated even at the lowest ATP concentration examined (10 μM), indicating that ATP hydrolysis is tightly coupled to forward translocation of a UvrD monomer along ssDNA with little slippage or futile ATP hydrolysis during translocation. The translocation kinetic step size remains constant at 4-5 nt/step down to 50 μM ATP but increases to ∼7 nt/step at 10 μM ATP. These results suggest that UvrD pauses more frequently during translocation at low ATP but with little futile ATP hydrolysis.
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Affiliation(s)
- Eric J Tomko
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 South Euclid Avenue, Box 8231, St. Louis, MO 63110-1093, USA
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24
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Fischer CJ, Tomko EJ, Wu CG, Lohman TM. Fluorescence methods to study DNA translocation and unwinding kinetics by nucleic acid motors. Methods Mol Biol 2012; 875:85-104. [PMID: 22573437 DOI: 10.1007/978-1-61779-806-1_5] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Translocation of nucleic acid motor proteins (translocases) along linear nucleic acids can be studied by monitoring either the time course of the arrival of the motor protein at one end of the nucleic acid or the kinetics of ATP hydrolysis by the motor protein during translocation using pre-steady state ensemble kinetic methods in a stopped-flow instrument. Similarly, the unwinding of double-stranded DNA or RNA by helicases can be studied in ensemble experiments by monitoring either the kinetics of the conversion of the double-stranded nucleic acid into its complementary single strands by the helicase or the kinetics of ATP hydrolysis by the helicase during unwinding. Such experiments monitor translocation of the enzyme along or unwinding of a series of nucleic acids labeled at one position (usually the end) with a fluorophore or a pair of fluorophores that undergo changes in fluorescence intensity or efficiency of fluorescence resonance energy transfer (FRET). We discuss how the pre-steady state kinetic data collected in these ensemble experiments can be analyzed by simultaneous global nonlinear least squares (NLLS) analysis using simple sequential "n-step" mechanisms to obtain estimates of the macroscopic rates and processivities of translocation and/or unwinding, the rate-limiting step(s) in these mechanisms, the average "kinetic step-size," and the stoichiometry of coupling ATP binding and hydrolysis to movement along the nucleic acid.
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Affiliation(s)
- Christopher J Fischer
- Department of Physics and Astronomy, Department of Molecular Biosciences, University of Kansas, Lawrence, KS, USA
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25
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Hwang H, Kim H, Myong S. Protein induced fluorescence enhancement as a single molecule assay with short distance sensitivity. Proc Natl Acad Sci U S A 2011; 108:7414-8. [PMID: 21502529 PMCID: PMC3088603 DOI: 10.1073/pnas.1017672108] [Citation(s) in RCA: 188] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Single-molecule FRET has been widely used for monitoring protein-nucleic acids interactions. Direct visualization of the interactions, however, often requires a site-specific labeling of the protein, which can be circuitous and inefficient. In addition, FRET is insensitive to distance changes in the 0-3-nm range. Here, we report a systematic calibration of a single molecule fluorescence assay termed protein induced fluorescence enhancement. This method circumvents protein labeling and displays a marked distance dependence below the 4-nm distance range. The enhancement of fluorescence is based on the photophysical phenomenon whereby the intensity of a fluorophore increases upon proximal binding of a protein. Our data reveals that the method can resolve as small as a single base pair distance at the extreme vicinity of the fluorophore, where the enhancement is maximized. We demonstrate the general applicability and distance sensitivity using (a) a finely spaced DNA ladder carrying a restriction site for BamHI, (b) RNA translocation by DExH enzyme RIG-I, and (c) filament dynamics of RecA on single-stranded DNA. The high spatio-temporal resolution data and sensitivity to short distances combined with the ability to bypass protein labeling makes this assay an effective alternative or a complement to FRET.
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Affiliation(s)
- Helen Hwang
- Bioengineering Department, University of Illinois, Urbana‐Champaign, Urbana, IL 61801
- Medical Scholars Program, University of Illinois, Urbana‐Champaign, Urbana, IL 61801
| | - Hajin Kim
- Physics Department, University of Illinois, Urbana‐Champaign, Urbana, IL 61801; and
| | - Sua Myong
- Bioengineering Department, University of Illinois, Urbana‐Champaign, Urbana, IL 61801
- Institute for Genomic Biology, University of Illinois, Urbana‐Champaign, Urbana, IL 61801
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26
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Patel SS. One motor driving two translocases. Nat Struct Mol Biol 2010; 17:1166-7. [PMID: 20924403 DOI: 10.1038/nsmb1010-1166] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In this issue, Wu et al. show that the RecBC helicase, which is involved in repairing double-strand DNA breaks,uses one ATPase motor to drive two translocases along opposite strands of DNA—much as an all-wheel drive engine controls movement of both front and back wheels. This mechanism may allow RecBC to load onto blunt-end DNA more efficiently and to move through obstacles such as gaps and DNA damage.
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Affiliation(s)
- Smita S Patel
- Department of Biochemistry, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, New Jersey, USA
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27
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5'-Single-stranded/duplex DNA junctions are loading sites for E. coli UvrD translocase. EMBO J 2010; 29:3826-39. [PMID: 20877334 DOI: 10.1038/emboj.2010.242] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2010] [Accepted: 09/06/2010] [Indexed: 01/05/2023] Open
Abstract
Escherichia coli UvrD is a 3'-5' superfamily 1A helicase/translocase involved in a variety of DNA metabolic processes. UvrD can function either as a helicase or only as an single-stranded DNA (ssDNA) translocase. The switch between these activities is controlled in vitro by the UvrD oligomeric state; a monomer has ssDNA translocase activity, whereas at least a dimer is needed for helicase activity. Although a 3'-ssDNA partial duplex provides a high-affinity site for a UvrD monomer, here we show that a monomer also binds with specificity to DNA junctions possessing a 5'-ssDNA flanking region and can initiate translocation from this site. Thus, a 5'-ss-duplex DNA junction can serve as a high-affinity loading site for the monomeric UvrD translocase, whereas a 3'-ss-duplex DNA junction inhibits both translocase and helicase activity of the UvrD monomer. Furthermore, the 2B subdomain of UvrD is important for this junction specificity. This highlights a separation of helicase and translocase function for UvrD and suggests that a monomeric UvrD translocase can be loaded at a 5'-ssDNA junction when translocation activity alone is needed.
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28
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Brosh RM. Special Methods collection on DNA helicases. Methods 2010; 51:257-8. [DOI: 10.1016/j.ymeth.2010.06.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2010] [Accepted: 06/14/2010] [Indexed: 10/19/2022] Open
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