1
|
Dos Santos Á, Rollins DE, Hari-Gupta Y, McArthur H, Du M, Ru SYZ, Pidlisna K, Stranger A, Lorgat F, Lambert D, Brown I, Howland K, Aaron J, Wang L, Ellis PJI, Chew TL, Martin-Fernandez M, Pyne ALB, Toseland CP. Autophagy receptor NDP52 alters DNA conformation to modulate RNA polymerase II transcription. Nat Commun 2023; 14:2855. [PMID: 37202403 PMCID: PMC10195817 DOI: 10.1038/s41467-023-38572-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2022] [Accepted: 05/09/2023] [Indexed: 05/20/2023] Open
Abstract
NDP52 is an autophagy receptor involved in the recognition and degradation of invading pathogens and damaged organelles. Although NDP52 was first identified in the nucleus and is expressed throughout the cell, to date, there is no clear nuclear functions for NDP52. Here, we use a multidisciplinary approach to characterise the biochemical properties and nuclear roles of NDP52. We find that NDP52 clusters with RNA Polymerase II (RNAPII) at transcription initiation sites and that its overexpression promotes the formation of additional transcriptional clusters. We also show that depletion of NDP52 impacts overall gene expression levels in two model mammalian cells, and that transcription inhibition affects the spatial organisation and molecular dynamics of NDP52 in the nucleus. This directly links NDP52 to a role in RNAPII-dependent transcription. Furthermore, we also show that NDP52 binds specifically and with high affinity to double-stranded DNA (dsDNA) and that this interaction leads to changes in DNA structure in vitro. This, together with our proteomics data indicating enrichment for interactions with nucleosome remodelling proteins and DNA structure regulators, suggests a possible function for NDP52 in chromatin regulation. Overall, here we uncover nuclear roles for NDP52 in gene expression and DNA structure regulation.
Collapse
Affiliation(s)
- Ália Dos Santos
- Department of Oncology and Metabolism, University of Sheffield, Sheffield, S10 2RX, UK
- MRC LMB, Francis Crick Avenue, Cambridge, CB2 0QH, UK
| | - Daniel E Rollins
- Department of Materials Science and Engineering, University of Sheffield, Sheffield, S1 3JD, UK
| | - Yukti Hari-Gupta
- School of Biosciences, University of Kent, Canterbury, CT2 7NJ, UK
- MRC LMCB, University College London, Gower Street, London, WC1E 6BT, UK
| | - Hannah McArthur
- School of Biosciences, University of Kent, Canterbury, CT2 7NJ, UK
| | - Mingxue Du
- Department of Materials Science and Engineering, University of Sheffield, Sheffield, S1 3JD, UK
| | | | - Kseniia Pidlisna
- School of Biosciences, University of Kent, Canterbury, CT2 7NJ, UK
| | - Ane Stranger
- School of Biosciences, University of Kent, Canterbury, CT2 7NJ, UK
| | - Faeeza Lorgat
- Department of Oncology and Metabolism, University of Sheffield, Sheffield, S10 2RX, UK
| | - Danielle Lambert
- Department of Oncology and Metabolism, University of Sheffield, Sheffield, S10 2RX, UK
| | - Ian Brown
- School of Biosciences, University of Kent, Canterbury, CT2 7NJ, UK
| | - Kevin Howland
- School of Biosciences, University of Kent, Canterbury, CT2 7NJ, UK
| | - Jesse Aaron
- Advanced Imaging Center, HHMI Janelia Research Campus, Ashburn, VA, 20147, USA
| | - Lin Wang
- Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell, Didcot, Oxford, OX11 0QX, UK
| | - Peter J I Ellis
- School of Biosciences, University of Kent, Canterbury, CT2 7NJ, UK
| | - Teng-Leong Chew
- Advanced Imaging Center, HHMI Janelia Research Campus, Ashburn, VA, 20147, USA
| | - Marisa Martin-Fernandez
- Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell, Didcot, Oxford, OX11 0QX, UK
| | - Alice L B Pyne
- Department of Materials Science and Engineering, University of Sheffield, Sheffield, S1 3JD, UK
| | | |
Collapse
|
2
|
Jarmoskaite I, Helmers AE, Russell R. Measurement of ATP utilization in RNA unwinding and RNA chaperone activities by DEAD-box helicase proteins. Methods Enzymol 2022; 673:53-76. [PMID: 35965018 PMCID: PMC10040262 DOI: 10.1016/bs.mie.2022.04.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
RNA helicase proteins perform coupled reactions in which cycles of ATP binding and hydrolysis are used to drive local unwinding of double-stranded RNA (dsRNA). For some helicases in the ubiquitous DEAD-box family, these local unwinding events are integral to folding transitions in structured RNAs, and thus these helicases function as RNA chaperones. An important measure of the efficiency of the helicase-catalyzed reaction is the ATP utilization value, which represents the average number of ATP molecules hydrolyzed during RNA unwinding or a chaperone-assisted RNA structural rearrangement. Here we outline procedures that can be used to measure the ATP utilization value in RNA unwinding or folding transitions. As an example of an RNA folding transition, we focus on the refolding of the Tetrahymena thermophila group I intron ribozyme from a long-lived misfolded structure to its native structure, and we outline strategies for adapting this assay to other RNA folding transitions. For a simple dsRNA unwinding event, the ATP utilization value provides a measure of the coupling between the ATPase and RNA unwinding activities, and for a complex RNA structural transition it can give insight into the scope of the rearrangement and the efficiency with which the helicase uses the energy from ATPase cycles to promote the rearrangement.
Collapse
Affiliation(s)
- Inga Jarmoskaite
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, United States
| | - Anna E Helmers
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, United States
| | - Rick Russell
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, United States.
| |
Collapse
|
3
|
Bianco PR. Insight into the biochemical mechanism of DNA helicases provided by bulk-phase and single-molecule assays. Methods 2021; 204:348-360. [PMID: 34896247 PMCID: PMC9534331 DOI: 10.1016/j.ymeth.2021.12.002] [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: 10/18/2021] [Revised: 12/01/2021] [Accepted: 12/03/2021] [Indexed: 10/19/2022] Open
Abstract
There are multiple assays available that can provide insight into the biochemical mechanism of DNA helicases. For the first 22 years since their discovery, bulk-phase assays were used. These include gel-based, spectrophotometric, and spectrofluorometric assays that revealed many facets of these enzymes. From 2001, single-molecule studies have contributed additional insight into these DNA nanomachines to reveal details on energy coupling, step size, processivity as well as unique aspects of individual enzyme behavior that were masked in the averaging inherent in ensemble studies. In this review, important aspects of the study of helicases are discussed including beginning with active, nuclease-free enzyme, followed by several bulk-phase approaches that have been developed and still find widespread use today. Finally, two single-molecule approaches are discussed, and the resulting findings are related to the results obtained in bulk-phase studies.
Collapse
Affiliation(s)
- Piero R Bianco
- Department of Pharmaceutical Sciences, College of Pharmacy, University of Nebraska Medical Center, Omaha, NE 68198-6025, USA.
| |
Collapse
|
4
|
Dos Santos Á, Fili N, Pearson DS, Hari-Gupta Y, Toseland CP. High-throughput mechanobiology: Force modulation of ensemble biochemical and cell-based assays. Biophys J 2021; 120:631-641. [PMID: 33453266 PMCID: PMC7896026 DOI: 10.1016/j.bpj.2020.12.024] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2020] [Revised: 11/25/2020] [Accepted: 12/17/2020] [Indexed: 11/27/2022] Open
Abstract
Mechanobiology is focused on how the physical forces and mechanical properties of proteins, cells, and tissues contribute to physiology and disease. Although the response of proteins and cells to mechanical stimuli is critical for function, the tools to probe these activities are typically restricted to single-molecule manipulations. Here, we have developed a novel microplate reader assay to encompass mechanical measurements with ensemble biochemical and cellular assays, using a microplate lid modified with magnets. This configuration enables multiple static magnetic tweezers to function simultaneously across the microplate, thereby greatly increasing throughput. We demonstrate the broad applicability and versatility through in vitro and in cellulo approaches. Overall, our methodology allows, for the first time (to our knowledge), ensemble biochemical and cell-based assays to be performed under force in high-throughput format. This approach substantially increases the availability of mechanobiology measurements.
Collapse
Affiliation(s)
- Ália Dos Santos
- Department of Oncology and Metabolism, University of Sheffield, Sheffield, United Kingdom
| | - Natalia Fili
- Department of Oncology and Metabolism, University of Sheffield, Sheffield, United Kingdom
| | - David S Pearson
- School of Biosciences, University of Kent, Canterbury, United Kingdom
| | - Yukti Hari-Gupta
- School of Biosciences, University of Kent, Canterbury, United Kingdom
| | - Christopher P Toseland
- Department of Oncology and Metabolism, University of Sheffield, Sheffield, United Kingdom.
| |
Collapse
|
5
|
Cook A, Hari-Gupta Y, Toseland CP. Application of the SSB biosensor to study in vitro transcription. Biochem Biophys Res Commun 2018; 496:820-825. [PMID: 29378185 PMCID: PMC5811048 DOI: 10.1016/j.bbrc.2018.01.147] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2018] [Accepted: 01/24/2018] [Indexed: 01/09/2023]
Abstract
Gene expression, catalysed by RNA polymerases (RNAP), is one of the most fundamental processes in living cells. The majority of methods to quantify mRNA are based upon purification of the nucleic acid which leads to experimental inaccuracies and loss of product, or use of high cost dyes and sensitive spectrophotometers. Here, we describe the use of a fluorescent biosensor based upon the single stranded binding (SSB) protein. In this study, the SSB biosensor showed similar binding properties to mRNA, to that of its native substrate, single-stranded DNA (ssDNA). We found the biosensor to be reproducible with no associated loss of product through purification, or the requirement for expensive dyes. Therefore, we propose that the SSB biosensor is a useful tool for comparative measurement of mRNA yield following in vitro transcription. Single-stranded binding protein can bind mRNA similar to single-stranded DNA. The biosensor MDCC-SSB can be used to quantify mRNA yield from in vitro transcription. Myosin VI motor activity is required for in vitro and in vivo transcription.
Collapse
Affiliation(s)
- Alexander Cook
- School of Biosciences, University of Kent, Canterbury, CT2 7NJ, UK
| | - Yukti Hari-Gupta
- School of Biosciences, University of Kent, Canterbury, CT2 7NJ, UK
| | | |
Collapse
|
6
|
Fili N, Hari-Gupta Y, Dos Santos Á, Cook A, Poland S, Ameer-Beg SM, Parsons M, Toseland CP. NDP52 activates nuclear myosin VI to enhance RNA polymerase II transcription. Nat Commun 2017; 8:1871. [PMID: 29187741 PMCID: PMC5707354 DOI: 10.1038/s41467-017-02050-w] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2017] [Accepted: 10/30/2017] [Indexed: 11/09/2022] Open
Abstract
Myosin VI (MVI) has been found to be overexpressed in ovarian, breast and prostate cancers. Moreover, it has been shown to play a role in regulating cell proliferation and migration, and to interact with RNA Polymerase II (RNAPII). Here, we find that backfolding of MVI regulates its ability to bind DNA and that a putative transcription co-activator NDP52 relieves the auto-inhibition of MVI to enable DNA binding. Additionally, we show that the MVI-NDP52 complex binds RNAPII, which is critical for transcription, and that depletion of NDP52 or MVI reduces steady-state mRNA levels. Lastly, we demonstrate that MVI directly interacts with nuclear receptors to drive expression of target genes, thereby suggesting a link to cell proliferation and migration. Overall, we suggest MVI may function as an auxiliary motor to drive transcription.
Collapse
Affiliation(s)
- Natalia Fili
- School of Biosciences, University of Kent, Canterbury, CT2 7NJ, UK
| | - Yukti Hari-Gupta
- School of Biosciences, University of Kent, Canterbury, CT2 7NJ, UK
| | - Ália Dos Santos
- School of Biosciences, University of Kent, Canterbury, CT2 7NJ, UK
| | - Alexander Cook
- School of Biosciences, University of Kent, Canterbury, CT2 7NJ, UK
| | - Simon Poland
- Randall Division of Cell and Molecular Biophysics, King's College London, Guys Campus, London, SE1 1UL, UK
| | - Simon M Ameer-Beg
- Randall Division of Cell and Molecular Biophysics, King's College London, Guys Campus, London, SE1 1UL, UK
| | - Maddy Parsons
- Randall Division of Cell and Molecular Biophysics, King's College London, Guys Campus, London, SE1 1UL, UK
| | | |
Collapse
|
7
|
Sang S, Wang Y, Feng Q, Wei Y, Ji J, Zhang W. Progress of new label-free techniques for biosensors: a review. Crit Rev Biotechnol 2015; 36:465-81. [DOI: 10.3109/07388551.2014.991270] [Citation(s) in RCA: 91] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
|
8
|
Green M, Gilhooly NS, Abedeen S, Scott DJ, Dillingham MS, Soultanas P. Engineering a reagentless biosensor for single-stranded DNA to measure real-time helicase activity in Bacillus. Biosens Bioelectron 2014; 61:579-86. [PMID: 24953846 PMCID: PMC4103019 DOI: 10.1016/j.bios.2014.06.011] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Revised: 05/28/2014] [Accepted: 06/03/2014] [Indexed: 10/27/2022]
Abstract
Single-stranded DNA-binding protein (SSB) is a well characterized ubiquitous and essential bacterial protein involved in almost all aspects of DNA metabolism. Using the Bacillus subtilis SSB we have generated a reagentless SSB biosensor that can be used as a helicase probe in B. subtilis and closely related gram positive bacteria. We have demonstrated the utility of the probe in a DNA unwinding reaction using a helicase from Bacillus and for the first time, characterized the B. subtilis SSB's DNA binding mode switching and stoichiometry. The importance of SSB in DNA metabolism is not limited to simply binding and protecting ssDNA during DNA replication, as previously thought. It interacts with an array of partner proteins to coordinate many different aspects of DNA metabolism. In most cases its interactions with partner proteins is species-specific and for this reason, knowing how to produce and use cognate reagentless SSB biosensors in different bacteria is critical. Here we explain how to produce a B. subtilis SSB probe that exhibits 9-fold fluorescence increase upon binding to single stranded DNA and can be used in all related gram positive firmicutes which employ drastically different DNA replication and repair systems than the widely studied Escherichia coli. The materials to produce the B. subtilis SSB probe are commercially available, so the methodology described here is widely available unlike previously published methods for the E. coli SSB.
Collapse
Affiliation(s)
- Matthew Green
- School of Chemistry, Centre for Biomolecular Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UK
| | - Neville S Gilhooly
- School of Biochemistry, Medical Sciences Building, University of Bristol, Bristol BS8 1TD, UK
| | - Shahriar Abedeen
- School of Chemistry, Centre for Biomolecular Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UK
| | - David J Scott
- School of Biosciences, University of Nottingham, Sutton Bonington, Leicestershire LE12 5RD, UK
| | - Mark S Dillingham
- School of Biochemistry, Medical Sciences Building, University of Bristol, Bristol BS8 1TD, UK
| | - Panos Soultanas
- School of Chemistry, Centre for Biomolecular Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
| |
Collapse
|
9
|
Abstract
Most biochemical processes occur on sub-second time scales. Relaxation and rapid mixing methods allow reactions from microsecond time scales onwards to be monitored in real time. This chapter describes the instrumentation for these techniques and it discusses general topics of sample excitation and signal detection.
Collapse
|
10
|
Fili N, Toseland CP. Fluorescence and labelling: how to choose and what to do. ACTA ACUST UNITED AC 2014; 105:1-24. [PMID: 25095988 DOI: 10.1007/978-3-0348-0856-9_1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
This chapter provides an overview of fluorescent labelling of different reactants related to the biochemistry of motor proteins. The fluorescent properties of different labels and the advantages and disadvantages of the labelling methods are discussed. This will allow for a careful selection of fluorescent proteins for different applications relating to motor proteins.
Collapse
Affiliation(s)
- Natalia Fili
- Department of Cellular Physiology, Ludwig-Maximilians-Universität München, Schillerstrasse. 44, 80336, Munich, Germany,
| | | |
Collapse
|
11
|
Toseland CP. Fluorescence to study the ATPase mechanism of motor proteins. ACTA ACUST UNITED AC 2014; 105:67-86. [PMID: 25095991 DOI: 10.1007/978-3-0348-0856-9_4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
This chapter provides an overview of different methodologies to dissect the ATPase mechanism of motor proteins. The use of ATP is fundamental to how these molecular engines work and how they can use the energy to perform various cellular roles. Rapid reaction and single-molecule techniques will be discussed to monitor reactions in real time through the application of fluorescence intensity, anisotropy and FRET. These approaches utilise fluorescent nucleotides and biosensors. While not every technique may be suitable for your motor protein, the different ways to determine the ATPase mechanism should allow a good evaluation of the kinetic parameters.
Collapse
Affiliation(s)
- Christopher P Toseland
- Chromosome Organisation and Dynamics, Max-Planck Institute of Biochemistry, Martinsried, 82152, Germany,
| |
Collapse
|
12
|
Real-time fluorescence assays to monitor duplex unwinding and ATPase activities of helicases. Nat Protoc 2014; 9:1645-61. [PMID: 24945382 DOI: 10.1038/nprot.2014.112] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Many physiological functions of helicases are dependent on their ability to unwind nucleic acid duplexes in an ATP-dependent fashion. Determining the kinetic frameworks of these processes is crucial to understanding how these proteins function. We recently developed a fluorescence assay to monitor RNA duplex unwinding by DEAD-box helicases in real time. In this assay, two fluorescently modified short reporter oligonucleotides are annealed to an unmodified RNA loading strand of any length so that the fluorescent moieties of the two reporters find themselves in close proximity to each other and fluorescence is quenched. One reporter is modified with cyanine 3 (Cy3), whereas the other is modified with a spectrally paired black-hole quencher (BHQ). As the helicase unwinds the loading strand, the enzyme displaces the Cy3-modified reporter, which will bind to a capture or competitor DNA strand, permanently separating it from the BHQ-modified reporter. Complete separation of the Cy3-modified reporter strand is thus detected as an increase in total fluorescence. This assay is compatible with reagentless biosensors to monitor ATPase activity so that the coupling between ATP hydrolysis and duplex unwinding can be determined. With the protocol described, obtaining data and analyzing results of unwinding and ATPase assays takes ∼4 h.
Collapse
|
13
|
Toseland CP, Webb MR. ATPase mechanism of the 5'-3' DNA helicase, RecD2: evidence for a pre-hydrolysis conformation change. J Biol Chem 2013; 288:25183-25193. [PMID: 23839989 PMCID: PMC3757182 DOI: 10.1074/jbc.m113.484667] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
The superfamily 1 helicase, RecD2, is a monomeric, bacterial enzyme with a role in DNA repair, but with 5′-3′ activity unlike most enzymes from this superfamily. Rate constants were determined for steps within the ATPase cycle of RecD2 in the presence of ssDNA. The fluorescent ATP analog, mantATP (2′(3′)-O-(N-methylanthraniloyl)ATP), was used throughout to provide a complete set of rate constants and determine the mechanism of the cycle for a single nucleotide species. Fluorescence stopped-flow measurements were used to determine rate constants for adenosine nucleotide binding and release, quenched-flow measurements were used for the hydrolytic cleavage step, and the fluorescent phosphate biosensor was used for phosphate release kinetics. Some rate constants could also be measured using the natural substrate, ATP, and these suggested a similar mechanism to that obtained with mantATP. The data show that a rearrangement linked to Mg2+ coordination, which occurs before the hydrolysis step, is rate-limiting in the cycle and that this step is greatly accelerated by bound DNA. This is also shown here for the PcrA 3′-5′ helicase and so may be a general mechanism governing superfamily 1 helicases. The mechanism accounts for the tight coupling between translocation and ATPase activity.
Collapse
Affiliation(s)
- Christopher P Toseland
- From the MRC National Institute for Medical Research, Mill Hill, London, NW7 1AA, United Kingdom and; Institut für Zelluläre Physiologie and Center for NanoScience, Physiologisches Institut, Ludwig Maximilians Universität, Munich 80336, Germany
| | - Martin R Webb
- From the MRC National Institute for Medical Research, Mill Hill, London, NW7 1AA, United Kingdom and.
| |
Collapse
|
14
|
Ziemniak M, Szabelski M, Lukaszewicz M, Nowicka A, Darzynkiewicz E, Rhoads RE, Wieczorek Z, Jemielity J. Synthesis and evaluation of fluorescent cap analogues for mRNA labelling. RSC Adv 2013; 3. [PMID: 24273643 DOI: 10.1039/c3ra42769b] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
We describe the synthesis and properties of five dinucleotide fluorescent cap analogues labelled at the ribose of the 7-methylguanosine moiety with either anthraniloyl (Ant) or N-methylanthraniloyl (Mant), which have been designed for the preparation of fluorescent mRNAs via transcription in vitro. Two of the analogues bear a methylene modification in the triphosphate bridge, providing resistance against either the Dcp2 or DcpS decapping enzymes. All these compounds were prepared by ZnCl2-mediated coupling of a nucleotide P-imidazolide with a fluorescently labelled mononucleotide. To evaluate the utility of these compounds for studying interactions with cap-binding proteins and cap-related cellular processes, both biological and spectroscopic features of those compounds were determined. The results indicate acceptable quantum yields of fluorescence, pH independence, environmental sensitivity, and photostability. The cap analogues are incorporated by RNA polymerase into mRNA transcripts that are efficiently translated in vitro. Transcripts containing fluorescent caps but unmodified in the triphosphate chain are hydrolysed by Dcp2 whereas those containing a α-β methylene modification are resistant. Model studies exploiting sensitivity of Mant to changes of local environment demonstrated utility of the synthesized compounds for studying cap-related proteins.
Collapse
Affiliation(s)
- Marcin Ziemniak
- Division of Biophysics, Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Zwirki i Wigury 93, 02-089 Warsaw, Poland
| | | | | | | | | | | | | | | |
Collapse
|
15
|
Toseland CP, Powell B, Webb MR. ATPase cycle and DNA unwinding kinetics of RecG helicase. PLoS One 2012; 7:e38270. [PMID: 22701618 PMCID: PMC3368886 DOI: 10.1371/journal.pone.0038270] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2012] [Accepted: 05/07/2012] [Indexed: 11/18/2022] Open
Abstract
The superfamily 2 bacterial helicase, RecG, is a monomeric enzyme with a role in DNA repair by reversing stalled replication forks. The helicase must act specifically and rapidly to prevent replication fork collapse. We have shown that RecG binds tightly and rapidly to four-strand oligonucleotide junctions, which mimic a stalled replication fork. The helicase unwinds such DNA junctions with a step-size of approximately four bases per ATP hydrolyzed. To gain an insight into this mechanism, we used fluorescent stopped-flow and quenched-flow to measure individual steps within the ATPase cycle of RecG, when bound to a DNA junction. The fluorescent ATP analogue, mantATP, was used throughout to determine the rate limiting steps, effects due to DNA and the main states in the cycle. Measurements, when possible, were also performed with unlabeled ATP to confirm the mechanism. The data show that the chemical step of hydrolysis is the rate limiting step in the cycle and that this step is greatly accelerated by bound DNA. The ADP release rate is similar to the cleavage rate, so that bound ATP and ADP would be the main states during the ATP cycle. Evidence is provided that the main structural rearrangements, which bring about DNA unwinding, are linked to these states.
Collapse
Affiliation(s)
| | - Ben Powell
- MRC National Institute for Medical Research, Mill Hill, London, United Kingdom
| | - Martin R. Webb
- MRC National Institute for Medical Research, Mill Hill, London, United Kingdom
- * E-mail: .
| |
Collapse
|
16
|
Duplex unwinding and ATPase activities of the DEAD-box helicase eIF4A are coupled by eIF4G and eIF4B. J Mol Biol 2011; 412:674-87. [PMID: 21840318 DOI: 10.1016/j.jmb.2011.08.004] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Revised: 07/31/2011] [Accepted: 08/01/2011] [Indexed: 01/23/2023]
Abstract
Eukaryotic initiation factor (eIF) 4A is a DEAD-box helicase that stimulates translation initiation by unwinding mRNA secondary structure. The accessory proteins eIF4G, eIF4B, and eIF4H enhance the duplex unwinding activity of eIF4A, but the extent to which they modulate eIF4A activity is poorly understood. Here, we use real-time fluorescence assays to determine the kinetic parameters of duplex unwinding and ATP hydrolysis by these initiation factors. To ensure efficient duplex unwinding, eIF4B and eIF4G cooperatively activate the duplex unwinding activity of eIF4A. Our data reveal that eIF4H is much less efficient at stimulating eIF4A unwinding activity than eIF4B, implying that eIF4H is not able to completely substitute for eIF4B in duplex unwinding. By monitoring unwinding and ATPase assays under identical conditions, we demonstrate that eIF4B couples the ATP hydrolysis cycle of eIF4A with strand separation, thereby minimizing nonproductive unwinding events. Using duplex substrates with altered GC contents but similar predicted thermal stabilities, we further show that the rate of formation of productive unwinding complexes is strongly influenced by the local stability per base pair, in addition to the stability of the entire duplex. This finding explains how a change in the GC content of a hairpin is able to influence translation initiation while maintaining the overall predicted thermal stability.
Collapse
|
17
|
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
|