101
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Single-molecule fluorescence reveals the unwinding stepping mechanism of replicative helicase. Cell Rep 2014; 6:1037-1045. [PMID: 24630993 PMCID: PMC3988844 DOI: 10.1016/j.celrep.2014.02.022] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Revised: 01/10/2014] [Accepted: 02/16/2014] [Indexed: 11/21/2022] Open
Abstract
Bacteriophage T7 gp4 serves as a model protein for replicative helicases that couples deoxythymidine triphosphate (dTTP) hydrolysis to directional movement and DNA strand separation. We employed single-molecule fluorescence resonance energy transfer methods to resolve steps during DNA unwinding by T7 helicase. We confirm that the unwinding rate of T7 helicase decreases with increasing base pair stability. For duplexes containing >35% guanine-cytosine (GC) base pairs, we observed stochastic pauses every 2–3 bp during unwinding. The dwells on each pause were distributed nonexponentially, consistent with two or three rounds of dTTP hydrolysis before each unwinding step. Moreover, we observed backward movements of the enzyme on GC-rich DNAs at low dTTP concentrations. Our data suggest a coupling ratio of 1:1 between base pairs unwound and dTTP hydrolysis, and they further support the concept that nucleic acid motors can have a hierarchy of different-sized steps or can accumulate elastic energy before transitioning to a subsequent phase. Single DNA unwinding assay recapitulates sequence-dependent unwinding High-resolution data reveal an unwinding step size of 2–3 bp Two or three hidden steps precede the unwinding step, suggesting 1:1 chemical coupling 1:1 coupling is maintained at low dNTP, but helicase often slips backward
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102
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Lee W, von Hippel PH, Marcus AH. Internally labeled Cy3/Cy5 DNA constructs show greatly enhanced photo-stability in single-molecule FRET experiments. Nucleic Acids Res 2014; 42:5967-77. [PMID: 24627223 PMCID: PMC4027219 DOI: 10.1093/nar/gku199] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
DNA constructs labeled with cyanine fluorescent dyes are important substrates for single-molecule (sm) studies of the functional activity of protein–DNA complexes. We previously studied the local DNA backbone fluctuations of replication fork and primer–template DNA constructs labeled with Cy3/Cy5 donor–acceptor Förster resonance energy transfer (FRET) chromophore pairs and showed that, contrary to dyes linked ‘externally’ to the bases with flexible tethers, direct ‘internal’ (and rigid) insertion of the chromophores into the sugar-phosphate backbones resulted in DNA constructs that could be used to study intrinsic and protein-induced DNA backbone fluctuations by both smFRET and sm Fluorescent Linear Dichroism (smFLD). Here we show that these rigidly inserted Cy3/Cy5 chromophores also exhibit two additional useful properties, showing both high photo-stability and minimal effects on the local thermodynamic stability of the DNA constructs. The increased photo-stability of the internal labels significantly reduces the proportion of false positive smFRET conversion ‘background’ signals, thereby simplifying interpretations of both smFRET and smFLD experiments, while the decreased effects of the internal probes on local thermodynamic stability also make fluctuations sensed by these probes more representative of the unperturbed DNA structure. We suggest that internal probe labeling may be useful in studies of many DNA–protein interaction systems.
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Affiliation(s)
- Wonbae Lee
- Oregon Center for Optics and Department of Chemistry, University of Oregon, Eugene, OR 97403, USA Institute of Molecular Biology and Department of Chemistry, University of Oregon, Eugene, OR 97403, USA
| | - Peter H von Hippel
- Institute of Molecular Biology and Department of Chemistry, University of Oregon, Eugene, OR 97403, USA
| | - Andrew H Marcus
- Oregon Center for Optics and Department of Chemistry, University of Oregon, Eugene, OR 97403, USA Institute of Molecular Biology and Department of Chemistry, University of Oregon, Eugene, OR 97403, USA
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103
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Abstract
A large family of chromatin remodelers that noncovalently modify chromatin is crucial in cell development and differentiation. They are often the targets of cancer, neurological disorders, and other human diseases. These complexes alter nucleosome positioning, higher-order chromatin structure, and nuclear organization. They also assemble chromatin, exchange out histone variants, and disassemble chromatin at defined locations. We review aspects of the structural organization of these complexes, the functional properties of their protein domains, and variation between complexes. We also address the mechanistic details of these complexes in mobilizing nucleosomes and altering chromatin structure. A better understanding of these issues will be vital for further analyses of subunits of these chromatin remodelers, which are being identified as targets in human diseases by NGS (next-generation sequencing).
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Affiliation(s)
- Blaine Bartholomew
- University of Texas MD Anderson Cancer Center, Department of Molecular Carcinogenesis, Smithville, Texas 78957;
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104
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Farooq S, Fijen C, Hohlbein J. Studying DNA-protein interactions with single-molecule Förster resonance energy transfer. PROTOPLASMA 2014; 251:317-32. [PMID: 24374460 DOI: 10.1007/s00709-013-0596-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Accepted: 12/09/2013] [Indexed: 05/21/2023]
Abstract
Single-molecule Förster resonance energy transfer (smFRET) has emerged as a powerful tool for elucidating biological structure and mechanisms on the molecular level. Here, we focus on applications of smFRET to study interactions between DNA and enzymes such as DNA and RNA polymerases. SmFRET, used as a nanoscopic ruler, allows for the detection and precise characterisation of dynamic and rarely occurring events, which are otherwise averaged out in ensemble-based experiments. In this review, we will highlight some recent developments that provide new means of studying complex biological systems either by combining smFRET with force-based techniques or by using data obtained from smFRET experiments as constrains for computer-aided modelling.
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Affiliation(s)
- Shazia Farooq
- Laboratory of Biophysics, Wageningen UR, Wageningen, The Netherlands
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105
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Spies M. Two steps forward, one step back: determining XPD helicase mechanism by single-molecule fluorescence and high-resolution optical tweezers. DNA Repair (Amst) 2014; 20:58-70. [PMID: 24560558 DOI: 10.1016/j.dnarep.2014.01.013] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2013] [Revised: 12/31/2013] [Accepted: 01/13/2014] [Indexed: 11/17/2022]
Abstract
XPD-like helicases constitute a prominent DNA helicase family critical for many aspects of genome maintenance. These enzymes share a unique structural feature, an auxiliary domain stabilized by an iron-sulphur (FeS) cluster, and a 5'-3' polarity of DNA translocation and duplex unwinding. Biochemical analyses alongside two single-molecule approaches, total internal reflection fluorescence microscopy and high-resolution optical tweezers, have shown how the unique structural features of XPD helicase and its specific patterns of substrate interactions tune the helicase for its specific cellular function and shape its molecular mechanism. The FeS domain forms a duplex separation wedge and contributes to an extended DNA binding site. Interactions within this site position the helicase in an orientation to unwind the duplex, control the helicase rate, and verify the integrity of the translocating strand. Consistent with its cellular role, processivity of XPD is limited and is defined by an idiosyncratic stepping kinetics. DNA duplex separation occurs in single base pair steps punctuated by frequent backward steps and conformational rearrangements of the protein-DNA complex. As such, the helicase in isolation mainly stabilizes spontaneous base pair opening and exhibits a limited ability to unwind stable DNA duplexes. The presence of a cognate ssDNA binding protein converts XPD into a vigorous helicase by destabilizing the upstream dsDNA as well as by trapping the unwound strands. Remarkably, the two proteins can co-exist on the same DNA strand without competing for binding. The current model of the XPD unwinding mechanism will be discussed along with possible modifications to this mechanism by the helicase interacting partners and unique features of such bio-medically important XPD-like helicases as FANCJ (BACH1), RTEL1 and CHLR1 (DDX11).
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Affiliation(s)
- Maria Spies
- Department of Biochemistry, University of Iowa Carver College of Medicine, IA 52242, United States.
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106
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Abstract
A prerequisite for DNA replication is the unwinding of duplex DNA catalyzed by a replicative hexameric helicase. Despite a growing body of research, key elements of helicase mechanism remain under substantial debate. In particular, the number of DNA strands encircled by the helicase ring during unwinding and the ring orientation at the replication fork completely contrast in contemporary mechanistic models. Here we use single-molecule and ensemble assays to address these questions for the papillomavirus E1 helicase. We find that E1 unwinds DNA with a strand-exclusion mechanism, with the N-terminal side of the helicase ring facing the replication fork. We show that E1 generates strikingly heterogeneous unwinding patterns stemming from varying degrees of repetitive movements, which is modulated by the DNA-binding domain. Together, our studies reveal previously unrecognized dynamic facets of replicative helicase unwinding mechanisms.
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107
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Single-molecule and single-particle imaging of molecular motors in vitro and in vivo. EXPERIENTIA SUPPLEMENTUM (2012) 2014; 105:131-59. [PMID: 25095994 DOI: 10.1007/978-3-0348-0856-9_7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Motor proteins are multi-potent molecular machines, whose localisation, function and regulation are achieved through tightly controlled processes involving conformational changes and interactions with their tracks, cargos and binding partners. Understanding how these complex machines work requires dissection of these processes both in space and time. Complementing the traditional ensemble measurements, single-molecule assays enable the detection of rare or short-lived intermediates and molecular heterogeneities, and the measurements of subpopulation dynamics. This chapter is focusing on the fluorescence imaging of single motors and their cargo. It discusses what is required in order to achieve single-molecule imaging with high temporal and spatial resolution and how these requirements are met both in vitro and in vivo. It also presents a general overview and applied examples of the major single-molecule imaging techniques and experimental assays which have been used to study motor proteins.
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108
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Klaue D, Kobbe D, Kemmerich F, Kozikowska A, Puchta H, Seidel R. Fork sensing and strand switching control antagonistic activities of RecQ helicases. Nat Commun 2013; 4:2024. [PMID: 23771268 PMCID: PMC3709500 DOI: 10.1038/ncomms3024] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2012] [Accepted: 05/17/2013] [Indexed: 12/16/2022] Open
Abstract
RecQ helicases have essential roles in maintaining genome stability during replication and in controlling double-strand break repair by homologous recombination. Little is known about how the different RecQ helicases found in higher eukaryotes achieve their specialized and partially opposing functions. Here, we investigate the DNA unwinding of RecQ helicases from Arabidopsis thaliana, AtRECQ2 and AtRECQ3 at the single-molecule level using magnetic tweezers. Although AtRECQ2 predominantly unwinds forked DNA substrates in a highly repetitive fashion, AtRECQ3 prefers to rewind, that is, to close preopened DNA forks. For both enzymes, this process is controlled by frequent strand switches and active sensing of the unwinding fork. The relative extent of the strand switches towards unwinding or towards rewinding determines the predominant direction of the enzyme. Our results provide a simple explanation for how different biological activities can be achieved by rather similar members of the RecQ family. RecQ helicases are enzymes that play a central role in maintaining genome stability in the DNA repair cascade. Klaue et al. show that RecQ2 and RecQ3 from Arabidopsis thaliana process DNA by, respectively, unwinding and rewinding forked DNA substrates, using a frequent strand switching mechanism.
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Affiliation(s)
- Daniel Klaue
- Biotechnology Center, Technische Universität Dresden, Dresden 01062, Germany
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109
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Lee KS, Balci H, Jia H, Lohman TM, Ha T. Direct imaging of single UvrD helicase dynamics on long single-stranded DNA. Nat Commun 2013; 4:1878. [PMID: 23695672 PMCID: PMC3674262 DOI: 10.1038/ncomms2882] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2012] [Accepted: 04/12/2013] [Indexed: 12/31/2022] Open
Abstract
Fluorescence imaging of single-protein dynamics on DNA has been largely limited to double-stranded DNA or short single-stranded DNA. We have developed a hybrid approach for observing single proteins moving on laterally stretched kilobase-sized ssDNA. Here we probed the single-stranded DNA translocase activity of Escherichia coli UvrD by single fluorophore tracking, while monitoring DNA unwinding activity with optical tweezers to capture the entire sequence of protein binding, single-stranded DNA translocation and multiple pathways of unwinding initiation. The results directly demonstrate that the UvrD monomer is a highly processive single-stranded DNA translocase that is stopped by a double-stranded DNA, whereas two monomers are required to unwind DNA to a detectable degree. The single-stranded DNA translocation rate does not depend on the force applied and displays a remarkable homogeneity, whereas the unwinding rate shows significant heterogeneity. These findings demonstrate that UvrD assembly state regulates its DNA helicase activity with functional implications for its stepping mechanism, and also reveal a previously unappreciated complexity in the active species during unwinding. Tracking single molecules on long stretches of single-stranded DNA poses technical challenges due to its propensity to form hairpin structures. To solve this problem, the authors combine TIRF microscopy with optical tweezers to stretch the DNA and capture the dynamics of DNA unwinding by UvrD DNA helicase.
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Affiliation(s)
- Kyung Suk Lee
- Department of Physics, Center for Physics in Living Cells and Institute for Genomic Biology, University of Illinois, Urbana-Champaign, Urbana, Illinois 61801-2902, USA
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110
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Parts, assembly and operation of the RIG-I family of motors. Curr Opin Struct Biol 2013; 25:25-33. [PMID: 24878341 DOI: 10.1016/j.sbi.2013.11.011] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2013] [Revised: 11/26/2013] [Accepted: 11/28/2013] [Indexed: 11/21/2022]
Abstract
Host cell invasion is monitored by a series of pattern recognition receptors (PRRs) that activate the innate immune machinery upon detection of a cognate pathogen associated molecular pattern (PAMP). The RIG-I like receptor (RLR) family of PRRs includes three proteins--RIG-I, MDA5, and LGP2--responsible for the detection of intracellular pathogenic RNA. All RLR proteins are built around an ATPase core homologous to those found in canonical Superfamily 2 (SF2) RNA helicases, which has been modified through the addition of novel accessory domains to recognize duplex RNA. This review focuses on the structural bases for pathogen-specific dsRNA binding and ATPase activation in RLRs, differential RNA recognition by RLR family members, and implications for other duplex RNA activated ATPases, such as Dicer.
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111
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Zegeye ED, Balasingham SV, Laerdahl JK, Homberset H, Kristiansen PE, Tønjum T. Effects of conserved residues and naturally occurring mutations on Mycobacterium tuberculosis RecG helicase activity. MICROBIOLOGY-SGM 2013; 160:217-227. [PMID: 24169816 DOI: 10.1099/mic.0.072140-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
RecG is a helicase that is conserved in nearly all bacterial species. The prototypical Escherichia coli RecG promotes regression of stalled replication forks, participates in DNA recombination and DNA repair, and prevents aberrant replication. Mycobacterium tuberculosis RecG (RecGMtb) is a DNA-dependent ATPase that unwinds a variety of DNA substrates, although its preferred substrate is a Holliday junction. Here, we performed site-directed mutagenesis of selected residues in the wedge domain and motifs Q, I, Ib and VI of RecGMtb. Three of the 10 substitution mutations engineered were detected previously as naturally occurring SNPs in the gene encoding RecGMtb. Alanine substitution mutations at residues Q292, F286, K321 and R627 abolished the RecGMtb unwinding activity, whilst RecGMtb F99A, P285S and T408A mutants exhibited ~25-50 % lower unwinding activity than WT. We also found that RecGMtb bound ATP in the absence of a DNA cofactor.
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Affiliation(s)
- Ephrem Debebe Zegeye
- Centre for Molecular Biology and Neuroscience and Department of Microbiology, Oslo University Hospital (Rikshospitalet), Oslo, Norway.,Centre for Molecular Biology and Neuroscience and Department of Microbiology, University of Oslo, Oslo, Norway
| | - Seetha V Balasingham
- Centre for Molecular Biology and Neuroscience and Department of Microbiology, Oslo University Hospital (Rikshospitalet), Oslo, Norway.,Centre for Molecular Biology and Neuroscience and Department of Microbiology, University of Oslo, Oslo, Norway
| | - Jon K Laerdahl
- Bioinformatics Core Facility, Department of Informatics, University of Oslo, Oslo, Norway.,Centre for Molecular Biology and Neuroscience and Department of Microbiology, Oslo University Hospital (Rikshospitalet), Oslo, Norway.,Centre for Molecular Biology and Neuroscience and Department of Microbiology, University of Oslo, Oslo, Norway
| | - Håvard Homberset
- Centre for Molecular Biology and Neuroscience and Department of Microbiology, University of Oslo, Oslo, Norway
| | - Per E Kristiansen
- Department of Molecular Biosciences, University of Oslo, Oslo, Norway
| | - Tone Tønjum
- Centre for Molecular Biology and Neuroscience and Department of Microbiology, Oslo University Hospital (Rikshospitalet), Oslo, Norway.,Centre for Molecular Biology and Neuroscience and Department of Microbiology, University of Oslo, Oslo, Norway
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112
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Holzmeister P, Acuna GP, Grohmann D, Tinnefeld P. Breaking the concentration limit of optical single-molecule detection. Chem Soc Rev 2013; 43:1014-28. [PMID: 24019005 DOI: 10.1039/c3cs60207a] [Citation(s) in RCA: 143] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Over the last decade, single-molecule detection has been successfully utilized in the life sciences and materials science. Yet, single-molecule measurements only yield meaningful results when working in a suitable, narrow concentration range. On the one hand, diffraction limits the minimal size of the observation volume in optical single-molecule measurements and consequently a sample must be adequately diluted so that only one molecule resides within the observation volume. On the other hand, at ultra-low concentrations relevant for sensing, the detection volume has to be increased in order to detect molecules in a reasonable timespan. This in turn results in the loss of an optimal signal-to-noise ratio necessary for single-molecule detection. This review discusses the requirements for effective single-molecule fluorescence applications, reflects on the motivation for the extension of the dynamic concentration range of single-molecule measurements and reviews various approaches that have been introduced recently to solve these issues. For the high-concentration limit, we identify four promising strategies including molecular confinement, optical observation volume reduction, temporal separation of signals and well-conceived experimental designs that specifically circumvent the high concentration limit. The low concentration limit is addressed by increasing the measurement speed, parallelization, signal amplification and preconcentration. The further development of these ideas will expand our possibilities to interrogate research questions with the clarity and precision provided only by the single-molecule approach.
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Affiliation(s)
- Phil Holzmeister
- Braunschweig University of Technology, Institute for Physical & Theoretical Chemistry, Hans-Sommer-Str. 10, 38106 Braunschweig, Germany.
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113
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Yokota H, Chujo YA, Harada Y. Single-molecule imaging of the oligomer formation of the nonhexameric Escherichia coli UvrD helicase. Biophys J 2013; 104:924-33. [PMID: 23442971 DOI: 10.1016/j.bpj.2013.01.014] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2012] [Revised: 12/06/2012] [Accepted: 01/08/2013] [Indexed: 11/18/2022] Open
Abstract
Superfamily I helicases are nonhexameric helicases responsible for the unwinding of nucleic acids. However, whether they unwind DNA in the form of monomers or oligomers remains a controversy. In this study, we addressed this question using direct single-molecule fluorescence visualization of Escherichia coli UvrD, a superfamily I DNA helicase. We performed a photobleaching-step analysis of dye-labeled helicases and determined that the helicase is bound to 18-basepair (bp) double-stranded DNA (dsDNA) with a 3' single-stranded DNA (ssDNA) tail (12, 20, or 40 nt) in a dimeric or trimeric form in the absence of ATP. We also discovered through simultaneous visualization of association/dissociation of the helicase with/from DNA and the DNA unwinding dynamics of the helicase in the presence of ATP that these dimeric and trimeric forms are responsible for the unwinding of DNA. We can therefore propose a new kinetic scheme for the helicase-DNA interaction in which not only a dimeric helicase but also a trimeric helicase can unwind DNA. This is, to our knowledge, the first direct single-molecule nonhexameric helicase quantification study, and it strongly supports a model in which an oligomer is the active form of the helicase, which carries important implications for the DNA unwinding mechanism of all superfamily I helicases.
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Affiliation(s)
- Hiroaki Yokota
- Institute for Integrated Cell-Material Sciences (WPI-iCeMS), Kyoto University, Yoshida-Honmachi, Kyoto, Japan.
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114
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Abstract
Helicases have major roles in genome maintenance by unwinding structured nucleic acids. Their prominence is marked by various cancers and genetic disorders that are linked to helicase defects. Although considerable effort has been made to understand the functions of DNA helicases that are important for genomic stability and cellular homeostasis, the complexity of the DNA damage response leaves us with unanswered questions regarding how helicase-dependent DNA repair pathways are regulated and coordinated with cell cycle checkpoints. Further studies may open the door to targeting helicases in order to improve cancer treatments based on DNA-damaging chemotherapy or radiation.
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Affiliation(s)
- Robert M Brosh
- Laboratory of Molecular Gerontology, National Institute on Aging, National Institutes of Health, NIH Biomedical Research Center, 251 Bayview Boulevard, Baltimore, Maryland 21224, USA.
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115
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Substrate-selective repair and restart of replication forks by DNA translocases. Cell Rep 2013; 3:1958-69. [PMID: 23746452 DOI: 10.1016/j.celrep.2013.05.002] [Citation(s) in RCA: 129] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2013] [Revised: 04/15/2013] [Accepted: 05/01/2013] [Indexed: 11/19/2022] Open
Abstract
Stalled replication forks are sources of genetic instability. Multiple fork-remodeling enzymes are recruited to stalled forks, but how they work to promote fork restart is poorly understood. By combining ensemble biochemical assays and single-molecule studies with magnetic tweezers, we show that SMARCAL1 branch migration and DNA-annealing activities are directed by the single-stranded DNA-binding protein RPA to selectively regress stalled replication forks caused by blockage to the leading-strand polymerase and to restore normal replication forks with a lagging-strand gap. We unveil the molecular mechanisms by which RPA enforces SMARCAL1 substrate preference. E. coli RecG acts similarly to SMARCAL1 in the presence of E. coli SSB, whereas the highly related human protein ZRANB3 has different substrate preferences. Our findings identify the important substrates of SMARCAL1 in fork repair, suggest that RecG and SMARCAL1 are functional orthologs, and provide a comprehensive model of fork repair by these DNA translocases.
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116
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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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117
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Lee W, Jose D, Phelps C, Marcus AH, von Hippel PH. A single-molecule view of the assembly pathway, subunit stoichiometry, and unwinding activity of the bacteriophage T4 primosome (helicase-primase) complex. Biochemistry 2013; 52:3157-70. [PMID: 23578280 DOI: 10.1021/bi400231s] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Single-molecule fluorescence resonance energy transfer (smFRET) methods were used to study the assembly pathway and DNA unwinding activity of the bacteriophage T4 helicase-primase (primosome) complex. The helicase substrates used were surface-immobilized model DNA replication forks "internally" labeled in the duplex region with opposed donor/acceptor (iCy3/iCy5) chromophore pairs in the lagging and leading strands. The time dependence of the smFRET signals was monitored during the unwinding process, and helicase rates and processivities were measured as a function of GTP concentration. This smFRET approach was also used to investigate the subunit stoichiometry of the primosome and the assembly pathway required to form functional and fully active primosome-DNA complexes. We confirmed that gp41 helicase monomer subunits form stable hexameric helicases in the presence of GTP and that the resulting (gp41)(6) complexes bind only weakly at DNA fork junctions. The addition of a single subunit of gp61 primase stabilized the resulting primosome complex at the fork and resulted in fully active and processive primosome helicases with gp41:gp61 subunit ratios of 6:1, while higher and lower subunit ratios substantially reduced the primosome unwinding activity. The use of alternative assembly pathways resulted in a loss of helicase activity and the formation of metastable DNA-protein aggregates, which were easily detected in our smFRET experiments as intense light-scattering foci. These single-molecule experiments provide a detailed real-time visualization of the assembly pathway and duplex DNA unwinding activity of the T4 primosome and are consistent with more indirect equilibrium and steady state results obtained in bulk solution studies.
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Affiliation(s)
- Wonbae Lee
- Oregon Center for Optics and Department of Chemistry, University of Oregon, Eugene, OR 97403, USA
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118
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Schwarz FW, Tóth J, van Aelst K, Cui G, Clausing S, Szczelkun MD, Seidel R. The helicase-like domains of type III restriction enzymes trigger long-range diffusion along DNA. Science 2013; 340:353-6. [PMID: 23599494 PMCID: PMC3646237 DOI: 10.1126/science.1231122] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Helicases are ubiquitous adenosine triphosphatases (ATPases) with widespread roles in genome metabolism. Here, we report a previously undescribed functionality for ATPases with helicase-like domains; namely, that ATP hydrolysis can trigger ATP-independent long-range protein diffusion on DNA in one dimension (1D). Specifically, using single-molecule fluorescence microscopy we show that the Type III restriction enzyme EcoP15I uses its ATPase to switch into a distinct structural state that diffuses on DNA over long distances and long times. The switching occurs only upon binding to the target site and requires hydrolysis of ~30 ATPs. We define the mechanism for these enzymes and show how ATPase activity is involved in DNA target site verification and 1D signaling, roles that are common in DNA metabolism: for example, in nucleotide excision and mismatch repair.
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Affiliation(s)
- Friedrich W. Schwarz
- DNA motors group, Biotechnology Center, Technische Universität Dresden, 01062 Dresden, Germany
| | - Júlia Tóth
- DNA-Protein Interactions Unit, School of Biochemistry, Medical Sciences Building, University of Bristol, Bristol, BS8 1TD, UK
| | - Kara van Aelst
- DNA-Protein Interactions Unit, School of Biochemistry, Medical Sciences Building, University of Bristol, Bristol, BS8 1TD, UK
| | - Guanshen Cui
- DNA-Protein Interactions Unit, School of Biochemistry, Medical Sciences Building, University of Bristol, Bristol, BS8 1TD, UK
| | - Sylvia Clausing
- DNA motors group, Biotechnology Center, Technische Universität Dresden, 01062 Dresden, Germany
| | - Mark D. Szczelkun
- DNA-Protein Interactions Unit, School of Biochemistry, Medical Sciences Building, University of Bristol, Bristol, BS8 1TD, UK
| | - Ralf Seidel
- DNA motors group, Biotechnology Center, Technische Universität Dresden, 01062 Dresden, Germany
- Institute of Molecular Cell Biology, University of Münster, 48149 Münster, Germany
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119
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Gu M, Rice CM. Structures of hepatitis C virus nonstructural proteins required for replicase assembly and function. Curr Opin Virol 2013; 3:129-36. [PMID: 23601958 DOI: 10.1016/j.coviro.2013.03.013] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2012] [Revised: 03/08/2013] [Accepted: 03/20/2013] [Indexed: 02/07/2023]
Abstract
Approximately 3% of the world population is infected with hepatitis C virus (HCV), causing a serious public health burden. Like other positive-strand RNA viruses, HCV assembles replicase complexes in association with cellular membranes and produces progeny RNA genomes through negative-strand intermediates. The viral proteins required for RNA replication are nonstructural (NS) proteins NS3 to NS5B. Owing to many obstacles and limitations in structural characterization of proteins and complexes with multiple transmembrane segments, attempts to understand the assembly and action of the HCV replicase complex have been challenging. Nevertheless, great progress has been made in obtaining structural information for several replicase components, providing insights into some aspects of the viral genome replication machinery.
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Affiliation(s)
- Meigang Gu
- Center for the Study of Hepatitis C, Laboratory of Virology and Infectious Disease, The Rockefeller University, New York, NY 10065, United States.
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120
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Deindl S, Hwang WL, Hota SK, Blosser TR, Prasad P, Bartholomew B, Zhuang X. ISWI remodelers slide nucleosomes with coordinated multi-base-pair entry steps and single-base-pair exit steps. Cell 2013; 152:442-52. [PMID: 23374341 DOI: 10.1016/j.cell.2012.12.040] [Citation(s) in RCA: 122] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2012] [Revised: 10/16/2012] [Accepted: 12/17/2012] [Indexed: 12/27/2022]
Abstract
ISWI-family enzymes remodel chromatin by sliding nucleosomes along DNA, but the nucleosome translocation mechanism remains unclear. Here we use single-molecule FRET to probe nucleosome translocation by ISWI-family remodelers. Distinct ISWI-family members translocate nucleosomes with a similar stepping pattern maintained by the catalytic subunit of the enzyme. Nucleosome remodeling begins with a 7 bp step of DNA translocation followed by 3 bp subsequent steps toward the exit side of nucleosomes. These multi-bp, compound steps are comprised of 1 bp substeps. DNA movement on the entry side of the nucleosome occurs only after 7 bp of exit-side translocation, and each entry-side step draws in a 3 bp equivalent of DNA that allows three additional base pairs to be moved to the exit side. Our results suggest a remodeling mechanism with well-defined coordination at different nucleosomal sites featuring DNA translocation toward the exit side in 1 bp steps preceding multi-bp steps of DNA movement on the entry side.
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Affiliation(s)
- Sebastian Deindl
- Howard Hughes Medical Institute, Harvard University, Cambridge, MA 02138, USA
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121
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Arunajadai SG, Cheng W. Step detection in single-molecule real time trajectories embedded in correlated noise. PLoS One 2013; 8:e59279. [PMID: 23533612 PMCID: PMC3606409 DOI: 10.1371/journal.pone.0059279] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Accepted: 02/13/2013] [Indexed: 11/19/2022] Open
Abstract
Single-molecule real time trajectories are embedded in high noise. To extract kinetic or dynamic information of the molecules from these trajectories often requires idealization of the data in steps and dwells. One major premise behind the existing single-molecule data analysis algorithms is the gaussian 'white' noise, which displays no correlation in time and whose amplitude is independent on data sampling frequency. This so-called 'white' noise is widely assumed but its validity has not been critically evaluated. We show that correlated noise exists in single-molecule real time trajectories collected from optical tweezers. The assumption of white noise during analysis of these data can lead to serious over- or underestimation of the number of steps depending on the algorithms employed. We present a statistical method that quantitatively evaluates the structure of the underlying noise, takes the noise structure into account, and identifies steps and dwells in a single-molecule trajectory. Unlike existing data analysis algorithms, this method uses Generalized Least Squares (GLS) to detect steps and dwells. Under the GLS framework, the optimal number of steps is chosen using model selection criteria such as Bayesian Information Criterion (BIC). Comparison with existing step detection algorithms showed that this GLS method can detect step locations with highest accuracy in the presence of correlated noise. Because this method is automated, and directly works with high bandwidth data without pre-filtering or assumption of gaussian noise, it may be broadly useful for analysis of single-molecule real time trajectories.
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Affiliation(s)
- Srikesh G Arunajadai
- Department of Biostatistics, Columbia University, New York, New York, United States of America.
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122
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Holler TP, Parkinson T, Pryde DC. Targeting the non-structural proteins of hepatitis C virus: beyond hepatitis C virus protease and polymerase. Expert Opin Drug Discov 2013; 4:293-314. [PMID: 23489127 DOI: 10.1517/17460440902762802] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
BACKGROUND Chronic hepatitis C virus (HCV) infection is a main cause of cirrhosis of the liver and hepatocellular carcinoma. The standard of care is a combination of pegylated interferon with ribavirin, a regimen that has undesirable side effects and is frequently ineffective. Compounds targeting HCV protease and polymerase are in late-stage clinical trials and have been extensively reviewed elsewhere. OBJECTIVE To review and evaluate the progress towards finding novel HCV antivirals targeting HCV proteins beyond the already precedented NS3 protease and NS5B polymerase. METHODS Searches of CAplus and Medline databases were combined with information from key conferences. This review focuses on NS2/3 serine protease, NS3 helicase activity and the non-structural proteins 4A, 4B and 5A. CONCLUSIONS Use of the replicon model of HCV replication and biochemical assays of specific targets has allowed screening of vast libraries of compounds, but resulted in clinical candidates from only NS4A and NS5A. The field is hindered by a lack of good chemical matter that inhibits the remaining enzymes from HCV, and a lack of understanding of the functions of non-structural proteins 4A, 4B and 5A in the replication of HCV.
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Affiliation(s)
- Tod P Holler
- Associate Research Fellow Pfizer Global Research and Development, Antiviral Biology, Ramsgate Road, Sandwich, Kent CT13 9NJ, UK +44 130 464 6387 ; +44 130 465 1819 ;
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123
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Jang H, Ryoo S, Kim Y, Yoon S, Kim H, Han SW, Choi B, Kim D, Min D. Discovery of hepatitis C virus NS3 helicase inhibitors by a multiplexed, high-throughput helicase activity assay based on graphene oxide. Angew Chem Int Ed Engl 2013; 52:2340-4. [PMID: 23355441 PMCID: PMC7159783 DOI: 10.1002/anie.201209222] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2012] [Indexed: 01/16/2023]
Affiliation(s)
- Hongje Jang
- Department of Chemistry, KAIST, Daejeon, 305‐701 (Korea)
| | - Soo‐Ryoon Ryoo
- Department of Chemistry, Seoul National University, Seoul, 151‐747 (Korea)
| | - Young‐Kwan Kim
- Department of Chemistry, Seoul National University, Seoul, 151‐747 (Korea)
| | - Soojin Yoon
- Department of Bioscience and Biotechnology, Konkuk University, Seoul, 143‐701 (Korea)
| | - Henna Kim
- Department of Chemistry, KAIST, Daejeon, 305‐701 (Korea)
| | - Sang Woo Han
- Department of Chemistry, KAIST, Daejeon, 305‐701 (Korea)
| | | | - Dong‐Eun Kim
- Department of Bioscience and Biotechnology, Konkuk University, Seoul, 143‐701 (Korea)
| | - Dal‐Hee Min
- Department of Chemistry, Seoul National University, Seoul, 151‐747 (Korea)
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124
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Jang H, Ryoo S, Kim Y, Yoon S, Kim H, Han SW, Choi B, Kim D, Min D. Discovery of Hepatitis C Virus NS3 Helicase Inhibitors by a Multiplexed, High-Throughput Helicase Activity Assay Based on Graphene Oxide. ANGEWANDTE CHEMIE (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2013; 125:2396-2400. [PMID: 32313317 PMCID: PMC7159770 DOI: 10.1002/ange.201209222] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/17/2012] [Indexed: 01/16/2023]
Affiliation(s)
- Hongje Jang
- Department of Chemistry, KAIST, Daejeon, 305‐701 (Korea)
| | - Soo‐Ryoon Ryoo
- Department of Chemistry, Seoul National University, Seoul, 151‐747 (Korea)
| | - Young‐Kwan Kim
- Department of Chemistry, Seoul National University, Seoul, 151‐747 (Korea)
| | - Soojin Yoon
- Department of Bioscience and Biotechnology, Konkuk University, Seoul, 143‐701 (Korea)
| | - Henna Kim
- Department of Chemistry, KAIST, Daejeon, 305‐701 (Korea)
| | - Sang Woo Han
- Department of Chemistry, KAIST, Daejeon, 305‐701 (Korea)
| | | | - Dong‐Eun Kim
- Department of Bioscience and Biotechnology, Konkuk University, Seoul, 143‐701 (Korea)
| | - Dal‐Hee Min
- Department of Chemistry, Seoul National University, Seoul, 151‐747 (Korea)
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125
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Structure-based simulations of the translocation mechanism of the hepatitis C virus NS3 helicase along single-stranded nucleic acid. Biophys J 2013; 103:1343-53. [PMID: 22995507 DOI: 10.1016/j.bpj.2012.08.026] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2012] [Revised: 08/01/2012] [Accepted: 08/06/2012] [Indexed: 01/14/2023] Open
Abstract
The NS3 helicase of Hepatitis C virus is an ATP-fueled molecular motor that can translocate along single-stranded (ss) nucleic acid, and unwind double-stranded nucleic acids. It makes a promising antiviral target and an important prototype system for helicase research. Despite recent progress, the detailed mechanism of NS3 helicase remains unknown. In this study, we have combined coarse-grained (CG) and atomistic simulations to probe the translocation mechanism of NS3 helicase along ssDNA. At the residue level of detail, our CG simulations have captured functionally important interdomain motions of NS3 helicase and reproduced single-base translocation of NS3 helicase along ssDNA in the 3'-5' direction, which is in good agreement with experimental data and the inchworm model. By combining the CG simulations with residue-specific perturbations to protein-DNA interactions, we have identified a number of key residues important to the translocation machinery that agree with previous structural and mutational studies. Additionally, our atomistic simulations with targeted molecular dynamics have corroborated the findings of CG simulations and further revealed key protein-DNA hydrogen bonds that break/form during the transitions. This study offers, to our knowledge, the most detailed and realistic simulations of translocation mechanism of NS3 helicase. The simulation protocol established in this study will be useful for designing inhibitors that target the translocation machinery of NS3 helicase, and for simulations of a variety of nucleic-acid-based molecular motors.
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126
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Kim H, Ha T. Single-molecule nanometry for biological physics. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2013; 76:016601. [PMID: 23249673 PMCID: PMC3549428 DOI: 10.1088/0034-4885/76/1/016601] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Precision measurement is a hallmark of physics but the small length scale (∼nanometer) of elementary biological components and thermal fluctuations surrounding them challenge our ability to visualize their action. Here, we highlight the recent developments in single-molecule nanometry where the position of a single fluorescent molecule can be determined with nanometer precision, reaching the limit imposed by the shot noise, and the relative motion between two molecules can be determined with ∼0.3 nm precision at ∼1 ms time resolution, as well as how these new tools are providing fundamental insights into how motor proteins move on cellular highways. We will also discuss how interactions between three and four fluorescent molecules can be used to measure three and six coordinates, respectively, allowing us to correlate the movements of multiple components. Finally, we will discuss recent progress in combining angstrom-precision optical tweezers with single-molecule fluorescent detection, opening new windows for multi-dimensional single-molecule nanometry for biological physics.
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Affiliation(s)
- Hajin Kim
- Howard Hughes Medical Institute, Urbana, IL 61801, USA
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127
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König SLB, Liyanage PS, Sigel RKO, Rueda D. Helicase-mediated changes in RNA structure at the single-molecule level. RNA Biol 2013; 10:133-48. [PMID: 23353571 DOI: 10.4161/rna.23507] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
RNA helicases are a diverse group of RNA-dependent ATPases known to play a large number of biological roles inside the cell, such as RNA unwinding, remodeling, export and degradation. Understanding how helicases mediate changes in RNA structure is therefore of fundamental interest. The advent of single-molecule spectroscopic techniques has unveiled with unprecedented detail the interplay of RNA helicases with their substrates. In this review, we describe the characterization of helicase-RNA interactions by single-molecule approaches. State-of-the-art techniques are presented, followed by a discussion of recent advancements in this exciting field.
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128
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Abstract
DNA replication requires hexameric ring-shaped helicases that unwind double-stranded DNA. In this issue, Itsathitphaisarn et al. report a high-resolution crystal structure of DnaB in complex with single-stranded DNA and nucleotide triphosphate analogs, revealing a unique mechanism by which DnaB unwinds DNA two base pairs at a time.
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Affiliation(s)
- Michael Schlierf
- B CUBE, Center for Molecular Bioengineering, Technische Universität Dresden, 01062 Dresden, Germany.
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129
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Rezazadeh S. On BLM helicase in recombination-mediated telomere maintenance. Mol Biol Rep 2012; 40:3049-64. [DOI: 10.1007/s11033-012-2379-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Accepted: 12/17/2012] [Indexed: 11/29/2022]
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130
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Lee G, Bratkowski MA, Ding F, Ke A, Ha T. Elastic coupling between RNA degradation and unwinding by an exoribonuclease. Science 2012; 336:1726-9. [PMID: 22745434 DOI: 10.1126/science.1216848] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Rrp44 (Dis3) is a key catalytic subunit of the yeast exosome complex and can processively digest structured RNA one nucleotide at a time in the 3' to 5' direction. Its motor function is powered by the energy released from the hydrolytic nuclease reaction instead of adenosine triphosphate hydrolysis as in conventional helicases. Single-molecule fluorescence analysis revealed that instead of unwinding RNA in single base pair steps, Rrp44 accumulates the energy released by multiple single nucleotide step hydrolysis reactions until about four base pairs are unwound in a burst. Kinetic analyses showed that RNA unwinding, not cleavage or strand release, determines the overall RNA degradation rate and that the unwinding step size is determined by the nonlinear elasticity of the Rrp44/RNA complex, but not by duplex stability.
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Affiliation(s)
- Gwangrog Lee
- Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, IL 61801, USA
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131
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Raney VM, Reynolds KA, Harrison MK, Harrison DK, Cameron CE, Raney KD. Binding by the hepatitis C virus NS3 helicase partially melts duplex DNA. Biochemistry 2012; 51:7596-607. [PMID: 22916835 DOI: 10.1021/bi300654v] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Binding of NS3 helicase to DNA was investigated by footprinting with KMnO(4), which reacts preferentially with thymidine residues in single-stranded DNA (ssDNA) compared to those in double-stranded DNA (dsDNA). A distinct pattern of reactivity was observed on ssDNA, which repeated every 8 nucleotides (nt) and is consistent with the known binding site size of NS3. Binding to a DNA substrate containing a partial duplex was also investigated. The DNA contained a 15 nt overhang made entirely of thymidine residues adjacent to a 22 bp duplex that contained thymidine at every other position. Surprisingly, the KMnO(4) reactivity pattern extended from the ssDNA into the dsDNA region of the substrate. Lengthening the partial duplex to 30 bp revealed a similar pattern extending from the ssDNA into the dsDNA, indicating that NS3 binds within the duplex region. Increasing the length of the ssDNA portion of the partial duplex by 4 nt resulted in a shift in the footprinting pattern for the ssDNA by 4 nt, which is consistent with binding to the 3'-end of the ssDNA. However, the footprinting pattern in the dsDNA region was shifted by only 1-2 bp, indicating that binding to the ssDNA-dsDNA region was preferred. Footprinting performed as a function of time indicated that NS3 binds to the ssDNA rapidly, followed by slower binding to the duplex. Hence, multiple molecules of NS3 can bind along a ssDNA-dsDNA partial duplex by interacting with the ssDNA as well as the duplex DNA.
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Affiliation(s)
- Veronica M Raney
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
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132
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Ode H, Nakashima M, Kitamura S, Sugiura W, Sato H. Molecular dynamics simulation in virus research. Front Microbiol 2012; 3:258. [PMID: 22833741 PMCID: PMC3400276 DOI: 10.3389/fmicb.2012.00258] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2012] [Accepted: 07/02/2012] [Indexed: 01/24/2023] Open
Abstract
Virus replication in the host proceeds by chains of interactions between viral and host proteins. The interactions are deeply influenced by host immune molecules and anti-viral compounds, as well as by mutations in viral proteins. To understand how these interactions proceed mechanically and how they are influenced by mutations, one needs to know the structures and dynamics of the proteins. Molecular dynamics (MD) simulation is a powerful computational method for delineating motions of proteins at an atomic-scale via theoretical and empirical principles in physical chemistry. Recent advances in the hardware and software for biomolecular simulation have rapidly improved the precision and performance of this technique. Consequently, MD simulation is quickly extending the range of applications in biology, helping to reveal unique features of protein structures that would be hard to obtain by experimental methods alone. In this review, we summarize the recent advances in MD simulations in the study of virus–host interactions and evolution, and present future perspectives on this technique.
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Affiliation(s)
- Hirotaka Ode
- Clinical Research Center, National Hospital Organization Nagoya Medical Center Nagoya, Aichi, Japan
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133
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Abstract
RNA helicases unwind their RNA substrates in an ATP-dependent reaction, and are central to all cellular processes involving RNA. They have important roles in viral life cycles, where RNA helicases are either virus-encoded or recruited from the host. Vertebrate RNA helicases sense viral infections, and trigger the innate antiviral immune response. RNA helicases have been implicated in protozoic, bacterial and fungal infections. They are also linked to neurological disorders, cancer, and aging processes. Genome-wide studies continue to identify helicase genes that change their expression patterns after infection or disease outbreak, but the mechanism of RNA helicase action has been defined for only a few diseases. RNA helicases are prognostic and diagnostic markers and suitable drug targets, predominantly for antiviral and anti-cancer therapies. This review summarizes the current knowledge on RNA helicases in infection and disease, and their growing potential as drug targets.
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Affiliation(s)
- Lenz Steimer
- University of Muenster, Institute for Physical Chemistry, Muenster, Germany
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134
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Lee G, Ha T. Single-Molecule Imaging: A Collagenase Pauses before Embarking on a Killing Spree. Curr Biol 2012; 22:R499-501. [DOI: 10.1016/j.cub.2012.04.037] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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135
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Abstract
Superfamily 2 helicases are involved in all aspects of RNA metabolism, and many steps in DNA metabolism. This review focuses on the basic mechanistic, structural and biological properties of each of the families of helicases within superfamily 2. There are ten separate families of helicases within superfamily 2, each playing specific roles in nucleic acid metabolism. The mechanisms of action are diverse, as well as the effect on the nucleic acid. Some families translocate on single-stranded nucleic acid and unwind duplexes, some unwind double-stranded nucleic acids without translocation, and some translocate on double-stranded or single-stranded nucleic acids without unwinding.
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Affiliation(s)
- Alicia K Byrd
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205, USA
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136
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Li Y, Zhang CY. Analysis of microRNA-induced silencing complex-involved microRNA-target recognition by single-molecule fluorescence resonance energy transfer. Anal Chem 2012; 84:5097-102. [PMID: 22545900 DOI: 10.1021/ac300839d] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
MicroRNAs (miRNAs) are important regulators of gene expression that control almost every physiological and pathological process. Although the complementarity between the seed region of a miRNA and its target mRNA is usually deemed as the key determinant in the miRNA-target recognition in animals, the mechanism of their recognition still remains enigmatic as more and more exceptions challenge the seed rule. Herein, we employ single-molecule fluorescence resonance energy transfer (smFRET) to investigate human miRNA-induced silencing complex (miRISC)-involved miRNA-target recognition with either perfect base pairing or poor seed match in real time. Our results demonstrate that the recognition between mammalian miRNA and its target with perfect base pairing proceeds in a two-state model as prokaryotic guide DNA-mediated recognition, suggesting a conserved pattern of guide RNA/DNA strand recognition. In addition to the general rule of miRNA-target recognition, our results reveal that annealing between miRNA and its target with poor seed match proceeds in a stepwise way, which is in accordance with the increase in the number of conformational states of miRNA-target duplex accommodated by the miRISC, suggesting the structural plasticity of human miRISC to conciliate the mismatches in seed region. This new dynamic information revealed by smFRET has an important implication for comprehensive understanding of the role of miRISC in the target recognition in mammals.
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Affiliation(s)
- Ying Li
- Single-molecule Detection and Imaging Laboratory, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Guangdong, 518055, China
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137
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Sun Y, Atas E, Lindqvist L, Sonenberg N, Pelletier J, Meller A. The eukaryotic initiation factor eIF4H facilitates loop-binding, repetitive RNA unwinding by the eIF4A DEAD-box helicase. Nucleic Acids Res 2012; 40:6199-207. [PMID: 22457067 PMCID: PMC3401463 DOI: 10.1093/nar/gks278] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Eukaryotic translation initiation is a highly regulated process in protein synthesis. The principal translation initiation factor eIF4AI displays helicase activity, unwinding secondary structures in the mRNAs 5'-UTR. Single molecule fluorescence resonance energy transfer (sm-FRET) is applied here to directly observe and quantify the helicase activity of eIF4AI in the presence of the ancillary RNA-binding factor eIF4H. Results show that eIF4H can significantly enhance the helicase activity of eIF4AI by strongly binding both to loop structures within the RNA transcript as well as to eIF4AI. In the presence of ATP, the eIF4AI/eIF4H complex exhibits persistent rapid and repetitive cycles of unwinding and re-annealing. ATP titration assays suggest that this process consumes a single ATP molecule per cycle. In contrast, helicase unwinding activity does not occur in the presence of the non-hydrolysable analog ATP-γS. Based on our sm-FRET results, we propose an unwinding mechanism where eIF4AI/eIF4H can bind directly to loop structures to destabilize duplexes. Since eIF4AI is the prototypical example of a DEA(D/H)-box RNA helicase, it is highly likely that this unwinding mechanism is applicable to a myriad of DEAD-box helicases employed in RNA metabolism.
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Affiliation(s)
- Yingjie Sun
- Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA
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138
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Hopfner KP, Gerhold CB, Lakomek K, Wollmann P. Swi2/Snf2 remodelers: hybrid views on hybrid molecular machines. Curr Opin Struct Biol 2012; 22:225-33. [PMID: 22445226 DOI: 10.1016/j.sbi.2012.02.007] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2012] [Accepted: 02/26/2012] [Indexed: 12/14/2022]
Abstract
Swi2/Snf2 (switch/sucrose non-fermentable) enzymes form a large and diverse class of proteins and multiprotein assemblies that remodel nucleic acid:protein complexes, using the energy of ATP hydrolysis. The core Swi2/Snf2 type ATPase domain belongs to the 'helicase and NTP driven nucleic acid translocase' superfamily 2 (SF2). It serves as a motor that functionally and structurally interacts with different targeting domains and functional modules to drive a plethora of remodeling activities in chromatin structure and dynamics, transcription regulation and DNA repair. Recent progress on the interaction of Swi2/Snf2 enzymes and multiprotein assemblies with their substrate nucleic acids and proteins, using hybrid structural biology methods, illuminates mechanisms for complex chemo-mechanical remodeling reactions. For Mot1, a hybrid mechanism of remodeler and chaperone emerged.
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Affiliation(s)
- Karl-Peter Hopfner
- Department of Biochemistry at the Gene Center, Ludwig-Maximilians-University Munich, Feodor-Lynen-Str. 25, 81377 Munich, Germany.
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139
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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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140
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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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141
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Efficient coupling of ATP hydrolysis to translocation by RecQ helicase. Proc Natl Acad Sci U S A 2012; 109:1443-8. [PMID: 22307597 DOI: 10.1073/pnas.1119952109] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Helicases are ubiquitous enzymes that unwind double-stranded DNA (dsDNA) to reveal single-stranded DNA (ssDNA) during essential processes such as replication, transcription, or repair. The Escherichia coli RecQ protein is a 3' to 5' helicase, which functions in the processes of homologous recombination and replication fork restart. Here, we analyzed the relationship between ATP hydrolysis by RecQ and its translocation on ssDNA. We monitored a single round of RecQ translocation on ssDNA by measuring the rates of inorganic phosphate release during translocation, and the dissociation of RecQ from ssDNA. We find that RecQ translocates with a rate of 16( ± 4) nucleotides/s and moves on average only 36( ± 2) nucleotides before dissociating. Fitting to an n-step kinetic model suggests that the helicase displays a nonuniform translocation mechanism in which it moves approximately five nucleotides rapidly before undergoing a rate-limiting kinetic slow step. Unexpectedly, RecQ requires a length of 34( ± 3) nucleotides to bind and translocate on ssDNA. This large site size suggests that several monomers are required to bind DNA prior to translocation. Energetically, the RecQ helicase couples the hydrolysis of one ATP molecule to the translocation of more than one nucleotide (1.6 ± 0.3). Thus, our data show that RecQ translocates on ssDNA by efficiently coupling the hydrolysis of one ATP molecule into structural alterations that result in movement of approximately two nucleotides, presumably by an inchworm mechanism. These attributes are consistent with the function of RecQ in recombination and replication.
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142
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Abstract
Historically, research on RNA helicase and translocation enzymes has seemed like a footnote to the extraordinary progress in studies on DNA-remodeling enzymes. However, during the past decade, the rising wave of activity in RNA science has engendered intense interest in the behaviors of specialized motor enzymes that remodel RNA molecules. Functional, mechanistic, and structural investigations of these RNA enzymes have begun to reveal the molecular basis for their key roles in RNA metabolism and signaling. In this chapter, we highlight the structural and mechanistic similarities among monomeric RNA translocase enzymes, while emphasizing the many divergent characteristics that have caused this enzyme family to become one of the most important in metabolism and gene expression.
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Affiliation(s)
- Steve C. Ding
- Infectious and Inflammatory Disease Center, Sanford-Burnham Medical Research Institute, La Jolla, California, USA
| | - Anna Marie Pyle
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut, USA,Howard Hughes Medical Institute, Yale University, New Haven, Connecticut, USA
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143
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Fairman-Williams ME, Jankowsky E. Unwinding initiation by the viral RNA helicase NPH-II. J Mol Biol 2011; 415:819-32. [PMID: 22155080 DOI: 10.1016/j.jmb.2011.11.045] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2011] [Revised: 11/26/2011] [Accepted: 11/29/2011] [Indexed: 12/27/2022]
Abstract
Viral RNA helicases of the NS3/NPH-II group unwind RNA duplexes by processive, directional translocation on one of the duplex strands. The translocation is preceded by a poorly understood unwinding initiation phase. For NPH-II from vaccinia virus, unwinding initiation is rate limiting for the overall unwinding reaction. To develop a mechanistic understanding of the unwinding initiation, we studied kinetic and thermodynamic aspects of this reaction phase for NPH-II in vitro, using biochemical and single molecule fluorescence approaches. Our data show that NPH-II functions as a monomer and that different stages of the ATP hydrolysis cycle dictate distinct binding preferences of NPH-II for duplex versus single-stranded RNA. We further find that the NPH-II-RNA complex does not adopt a single conformation but rather at least two distinct conformations in each of the analyzed stages of ATP hydrolysis. These conformations interconvert with rate constants that depend on the stage of the ATP hydrolysis cycle. Our data establish a basic mechanistic framework for unwinding initiation by NPH-II and suggest that the various stages of the ATP hydrolysis cycle do not induce single, stage-specific conformations in the NPH-II-RNA complex but primarily control transitions between multiple states.
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Affiliation(s)
- Margaret E Fairman-Williams
- Center for RNA Molecular Biology and Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA
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144
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Abstract
Fluorescent sensors that make use of DNA structures have become widely useful in monitoring enzymatic activities. Early studies focused primarily on enzymes that naturally use DNA or RNA as the substrate. However, recent advances in molecular design have enabled the development of nucleic acid sensors for a wider range of functions, including enzymes that do not normally bind DNA or RNA. Nucleic acid sensors present some potential advantages over classical small-molecule sensors, including water solubility and ease of synthesis. An overview of the multiple strategies under recent development is presented in this critical review, and expected future developments in microarrays, single molecule analysis, and in vivo sensing are discussed (160 references).
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Affiliation(s)
- Nan Dai
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
| | - Eric T. Kool
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
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145
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Ragunathan K, Joo C, Ha T. Real-time observation of strand exchange reaction with high spatiotemporal resolution. Structure 2011; 19:1064-73. [PMID: 21827943 DOI: 10.1016/j.str.2011.06.009] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2011] [Revised: 05/23/2011] [Accepted: 06/07/2011] [Indexed: 11/25/2022]
Abstract
RecA binds to single-stranded (ss) DNA to form a helical filament that catalyzes strand exchange with a homologous double-stranded (ds) DNA. The study of strand exchange in ensemble assays is limited by the diffusion limited homology search process, which masks the subsequent strand exchange reaction. We developed a single-molecule fluorescence assay with a few base-pair and millisecond resolution that can separate initial docking from the subsequent propagation of joint molecule formation. Our data suggest that propagation occurs in 3 bp increments with destabilization of the incoming dsDNA and concomitant pairing with the reference ssDNA. Unexpectedly, we discovered the formation of a dynamic complex between RecA and the displaced DNA that remains bound transiently after joint molecule formation. This finding could have important implications for the irreversibility of strand exchange. Our model for strand exchange links structural models of RecA to its catalytic function.
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Affiliation(s)
- Kaushik Ragunathan
- Center for Biophysics and Computational Biology, Department of Physics, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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146
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Luo D, Ding SC, Vela A, Kohlway A, Lindenbach BD, Pyle AM. Structural insights into RNA recognition by RIG-I. Cell 2011; 147:409-22. [PMID: 22000018 PMCID: PMC3222294 DOI: 10.1016/j.cell.2011.09.023] [Citation(s) in RCA: 311] [Impact Index Per Article: 23.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2011] [Revised: 08/02/2011] [Accepted: 09/16/2011] [Indexed: 12/19/2022]
Abstract
Intracellular RIG-I-like receptors (RLRs, including RIG-I, MDA-5, and LGP2) recognize viral RNAs as pathogen-associated molecular patterns (PAMPs) and initiate an antiviral immune response. To understand the molecular basis of this process, we determined the crystal structure of RIG-I in complex with double-stranded RNA (dsRNA). The dsRNA is sheathed within a network of protein domains that include a conserved "helicase" domain (regions HEL1 and HEL2), a specialized insertion domain (HEL2i), and a C-terminal regulatory domain (CTD). A V-shaped pincer connects HEL2 and the CTD by gripping an α-helical shaft that extends from HEL1. In this way, the pincer coordinates functions of all the domains and couples RNA binding with ATP hydrolysis. RIG-I falls within the Dicer-RIG-I clade of the superfamily 2 helicases, and this structure reveals complex interplay between motor domains, accessory mechanical domains, and RNA that has implications for understanding the nanomechanical function of this protein family and other ATPases more broadly.
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Affiliation(s)
- Dahai Luo
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520
- Howard Hughes Medical Institute, Chevy Chase, Maryland 20815
| | - Steve C. Ding
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520
| | - Adriana Vela
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520
| | - Andrew Kohlway
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, Connecticut 06520
| | - Brett D. Lindenbach
- Section of Microbial Pathogenesis, Yale University, New Haven, Connecticut 06520
| | - Anna Marie Pyle
- Department of Molecular, Cellular, and Developmental Biology, Yale University, New Haven, Connecticut 06520
- Department of Chemistry, Yale University, New Haven, Connecticut 06520
- Howard Hughes Medical Institute, Chevy Chase, Maryland 20815
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147
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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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148
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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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149
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Pyle AM. RNA helicases and remodeling proteins. Curr Opin Chem Biol 2011; 15:636-42. [PMID: 21862383 PMCID: PMC7172669 DOI: 10.1016/j.cbpa.2011.07.019] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2011] [Revised: 07/27/2011] [Accepted: 07/28/2011] [Indexed: 01/21/2023]
Abstract
It is becoming increasingly clear that RNA molecules play a major role in all aspects of metabolism. The conformational state and stability of RNA are controlled by RNA remodeling proteins, which are ubiquitous motor proteins in the cell. Here, we review advances in our understanding of the structure and function of three major structural families of RNA remodeling proteins, the hexameric ring proteins, the processive monomeric RNA translocase/helicases, and the functionally diverse DEAD-box remodeling proteins. New studies have revealed molecular mechanisms for coupling between ATP hydrolysis and unwinding, the physical basis for regulatory control by cofactors, and novel functions for RNA remodeling proteins.
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Affiliation(s)
- Anna Marie Pyle
- Department of Molecular, Cellular and Developmental Biology, Yale University, Howard Hughes Medical Institute, New Haven, CT 0652, USA.
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150
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Flechsig H, Popp D, Mikhailov AS. In silico investigation of conformational motions in superfamily 2 helicase proteins. PLoS One 2011; 6:e21809. [PMID: 21829442 PMCID: PMC3139591 DOI: 10.1371/journal.pone.0021809] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2011] [Accepted: 06/07/2011] [Indexed: 01/31/2023] Open
Abstract
Helicases are motor proteins that play a central role in the metabolism of DNA and RNA in biological cells. Using the energy of ATP molecules, they are able to translocate along the nucleic acids and unwind their duplex structure. They have been extensively characterized in the past and grouped into superfamilies based on structural similarities and sequential motifs. However, their functional aspects and the mechanism of their operation are not yet well understood. Here, we consider three helicases from the major superfamily 2 - Hef, Hel308 and XPD - and study their conformational dynamics by using coarse-grained relaxational elastic network models. Specifically, their responses to mechanical perturbations are analyzed. This enables us to identify robust and ordered conformational motions which may underlie the functional activity of these proteins. As we show, such motions are well-organized and have large amplitudes. Their possible roles in the processing of nucleic substrate are discussed.
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Affiliation(s)
- Holger Flechsig
- Department of Physical Chemistry, Fritz Haber Institute of the Max Planck Society, Berlin, Germany.
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