1
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Tsutakawa SE, Bacolla A, Katsonis P, Bralić A, Hamdan SM, Lichtarge O, Tainer JA, Tsai CL. Decoding Cancer Variants of Unknown Significance for Helicase-Nuclease-RPA Complexes Orchestrating DNA Repair During Transcription and Replication. Front Mol Biosci 2021; 8:791792. [PMID: 34966786 PMCID: PMC8710748 DOI: 10.3389/fmolb.2021.791792] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2021] [Accepted: 11/16/2021] [Indexed: 01/13/2023] Open
Abstract
All tumors have DNA mutations, and a predictive understanding of those mutations could inform clinical treatments. However, 40% of the mutations are variants of unknown significance (VUS), with the challenge being to objectively predict whether a VUS is pathogenic and supports the tumor or whether it is benign. To objectively decode VUS, we mapped cancer sequence data and evolutionary trace (ET) scores onto crystallography and cryo-electron microscopy structures with variant impacts quantitated by evolutionary action (EA) measures. As tumors depend on helicases and nucleases to deal with transcription/replication stress, we targeted helicase–nuclease–RPA complexes: (1) XPB-XPD (within TFIIH), XPF-ERCC1, XPG, and RPA for transcription and nucleotide excision repair pathways and (2) BLM, EXO5, and RPA plus DNA2 for stalled replication fork restart. As validation, EA scoring predicts severe effects for most disease mutations, but disease mutants with low ET scores not only are likely destabilizing but also disrupt sophisticated allosteric mechanisms. For sites of disease mutations and VUS predicted to be severe, we found strong co-localization to ordered regions. Rare discrepancies highlighted the different survival requirements between disease and tumor mutations, as well as the value of examining proteins within complexes. In a genome-wide analysis of 33 cancer types, we found correlation between the number of mutations in each tumor and which pathways or functional processes in which the mutations occur, revealing different mutagenic routes to tumorigenesis. We also found upregulation of ancient genes including BLM, which supports a non-random and concerted cancer process: reversion to a unicellular, proliferation-uncontrolled, status by breaking multicellular constraints on cell division. Together, these genes and global analyses challenge the binary “driver” and “passenger” mutation paradigm, support a gradient impact as revealed by EA scoring from moderate to severe at a single gene level, and indicate reduced regulation as well as activity. The objective quantitative assessment of VUS scoring and gene overexpression in the context of functional interactions and pathways provides insights for biology, oncology, and precision medicine.
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Affiliation(s)
- Susan E Tsutakawa
- Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA, United States
| | - Albino Bacolla
- Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX, United States
| | - Panagiotis Katsonis
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States
| | - Amer Bralić
- Laboratory of DNA Replication and Recombination, Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia
| | - Samir M Hamdan
- Laboratory of DNA Replication and Recombination, Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia
| | - Olivier Lichtarge
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, United States
| | - John A Tainer
- Molecular Biophysics and Integrated Bioimaging, Lawrence Berkeley National Laboratory, Berkeley, CA, United States.,Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX, United States.,Department of Cancer Biology, University of Texas M.D. Anderson Cancer Center, Houston, TX, United States
| | - Chi-Lin Tsai
- Department of Molecular and Cellular Oncology, University of Texas M.D. Anderson Cancer Center, Houston, TX, United States
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2
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Sobhy MA, Tehseen M, Takahashi M, Bralić A, De Biasio A, Hamdan SM. Implementing fluorescence enhancement, quenching, and FRET for investigating flap endonuclease 1 enzymatic reaction at the single-molecule level. Comput Struct Biotechnol J 2021; 19:4456-4471. [PMID: 34471492 PMCID: PMC8385120 DOI: 10.1016/j.csbj.2021.07.029] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Revised: 07/23/2021] [Accepted: 07/25/2021] [Indexed: 11/24/2022] Open
Abstract
Flap endonuclease 1 (FEN1) is an important component of the intricate molecular machinery for DNA replication and repair. FEN1 is a structure-specific 5' nuclease that cleaves nascent single-stranded 5' flaps during the maturation of Okazaki fragments. Here, we review our research primarily applying single-molecule fluorescence to resolve important mechanistic aspects of human FEN1 enzymatic reaction. The methodology presented in this review is aimed as a guide for tackling other biomolecular enzymatic reactions by fluorescence enhancement, quenching, and FRET and their combinations. Using these methods, we followed in real-time the structures of the substrate and product and 5' flap cleavage during catalysis. We illustrate that FEN1 actively bends the substrate to verify its features and continues to mold it to induce a protein disorder-to-order transitioning that controls active site assembly. This mechanism suppresses off-target cleavage of non-cognate substrates and promotes their dissociation with an accuracy that was underestimated from bulk assays. We determined that product release in FEN1 after the 5' flap release occurs in two steps; a brief binding to the bent nicked-product followed by longer binding to the unbent nicked-product before dissociation. Based on our cryo-electron microscopy structure of the human lagging strand replicase bound to FEN1, we propose how this two-step product release mechanism may regulate the final steps during the maturation of Okazaki fragments.
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Affiliation(s)
- Mohamed A Sobhy
- Laboratory of DNA Replication and Recombination, Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
| | - Muhammad Tehseen
- Laboratory of DNA Replication and Recombination, Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
| | - Masateru Takahashi
- Laboratory of DNA Replication and Recombination, Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
| | - Amer Bralić
- Laboratory of DNA Replication and Recombination, Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
| | - Alfredo De Biasio
- Leicester Institute of Structural & Chemical Biology and Department of Molecular & Cell Biology, University of Leicester, Lancaster Rd, Leicester LE1 7HB, UK
| | - Samir M Hamdan
- Laboratory of DNA Replication and Recombination, Biological and Environmental Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
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3
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González-Corrochano R, Ruiz FM, Taylor NMI, Huecas S, Drakulic S, Spínola-Amilibia M, Fernández-Tornero C. The crystal structure of human XPG, the xeroderma pigmentosum group G endonuclease, provides insight into nucleotide excision DNA repair. Nucleic Acids Res 2020; 48:9943-9958. [PMID: 32821917 PMCID: PMC7515719 DOI: 10.1093/nar/gkaa688] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2020] [Revised: 08/04/2020] [Accepted: 08/06/2020] [Indexed: 01/14/2023] Open
Abstract
Nucleotide excision repair (NER) is an essential pathway to remove bulky lesions affecting one strand of DNA. Defects in components of this repair system are at the ground of genetic diseases such as xeroderma pigmentosum (XP) and Cockayne syndrome (CS). The XP complementation group G (XPG) endonuclease cleaves the damaged DNA strand on the 3′ side of the lesion coordinated with DNA re-synthesis. Here, we determined crystal structures of the XPG nuclease domain in the absence and presence of DNA. The overall fold exhibits similarities to other flap endonucleases but XPG harbors a dynamic helical arch that is uniquely oriented and defines a gateway. DNA binding through a helix-2-turn-helix motif, assisted by one flanking α-helix on each side, shows high plasticity, which is likely relevant for DNA scanning. A positively-charged canyon defined by the hydrophobic wedge and β-pin motifs provides an additional DNA-binding surface. Mutational analysis identifies helical arch residues that play critical roles in XPG function. A model for XPG participation in NER is proposed. Our structures and biochemical data represent a valuable tool to understand the atomic ground of XP and CS, and constitute a starting point for potential therapeutic applications.
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Affiliation(s)
| | - Federico M Ruiz
- Centro de Investigaciones Biológicas Margarita Salas, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain
| | - Nicholas M I Taylor
- Centro de Investigaciones Biológicas Margarita Salas, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain
| | - Sonia Huecas
- Centro de Investigaciones Biológicas Margarita Salas, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain
| | - Srdja Drakulic
- Centro de Investigaciones Biológicas Margarita Salas, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain
| | | | - Carlos Fernández-Tornero
- Centro de Investigaciones Biológicas Margarita Salas, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain
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4
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Human XPG nuclease structure, assembly, and activities with insights for neurodegeneration and cancer from pathogenic mutations. Proc Natl Acad Sci U S A 2020; 117:14127-14138. [PMID: 32522879 PMCID: PMC7321962 DOI: 10.1073/pnas.1921311117] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
DNA repair is essential to life and to avoidance of genome instability and cancer. Xeroderma pigmentosum group G (XPG) protein acts in multiple DNA repair pathways, both as an active enzyme and as a scaffold for coordinating with other repair proteins. We present here the structure of the catalytic domain responsible for its DNA binding and nuclease activity. Our analysis provides structure-based hypotheses for how XPG recognizes its bubble DNA substrate and predictions of the structural impacts of XPG disease mutations associated with two phenotypically distinct diseases: xeroderma pigmentosum (XP, skin cancer prone) or Cockayne syndrome (XP/CS, severe progressive developmental defects). Xeroderma pigmentosum group G (XPG) protein is both a functional partner in multiple DNA damage responses (DDR) and a pathway coordinator and structure-specific endonuclease in nucleotide excision repair (NER). Different mutations in the XPG gene ERCC5 lead to either of two distinct human diseases: Cancer-prone xeroderma pigmentosum (XP-G) or the fatal neurodevelopmental disorder Cockayne syndrome (XP-G/CS). To address the enigmatic structural mechanism for these differing disease phenotypes and for XPG’s role in multiple DDRs, here we determined the crystal structure of human XPG catalytic domain (XPGcat), revealing XPG-specific features for its activities and regulation. Furthermore, XPG DNA binding elements conserved with FEN1 superfamily members enable insights on DNA interactions. Notably, all but one of the known pathogenic point mutations map to XPGcat, and both XP-G and XP-G/CS mutations destabilize XPG and reduce its cellular protein levels. Mapping the distinct mutation classes provides structure-based predictions for disease phenotypes: Residues mutated in XP-G are positioned to reduce local stability and NER activity, whereas residues mutated in XP-G/CS have implied long-range structural defects that would likely disrupt stability of the whole protein, and thus interfere with its functional interactions. Combined data from crystallography, biochemistry, small angle X-ray scattering, and electron microscopy unveil an XPG homodimer that binds, unstacks, and sculpts duplex DNA at internal unpaired regions (bubbles) into strongly bent structures, and suggest how XPG complexes may bind both NER bubble junctions and replication forks. Collective results support XPG scaffolding and DNA sculpting functions in multiple DDR processes to maintain genome stability.
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5
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Thompson MJ, Gotham VJB, Ciani B, Grasby JA. A conserved loop-wedge motif moderates reaction site search and recognition by FEN1. Nucleic Acids Res 2019; 46:7858-7872. [PMID: 29878258 PMCID: PMC6125683 DOI: 10.1093/nar/gky506] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2018] [Accepted: 05/23/2018] [Indexed: 12/24/2022] Open
Abstract
DNA replication and repair frequently involve intermediate two-way junction structures with overhangs, or flaps, that must be promptly removed; a task performed by the essential enzyme flap endonuclease 1 (FEN1). We demonstrate a functional relationship between two intrinsically disordered regions of the FEN1 protein, which recognize opposing sides of the junction and order in response to the requisite substrate. Our results inform a model in which short-range translocation of FEN1 on DNA facilitates search for the annealed 3'-terminus of a primer strand, which is recognized by breaking the terminal base pair to generate a substrate with a single nucleotide 3'-flap. This recognition event allosterically signals hydrolytic removal of the 5'-flap through reaction in the opposing junction duplex, by controlling access of the scissile phosphate diester to the active site. The recognition process relies on a highly-conserved 'wedge' residue located on a mobile loop that orders to bind the newly-unpaired base. The unanticipated 'loop-wedge' mechanism exerts control over substrate selection, rate of reaction and reaction site precision, and shares features with other enzymes that recognize irregular DNA structures. These new findings reveal how FEN1 precisely couples 3'-flap verification to function.
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Affiliation(s)
- Mark J Thompson
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Brook Hill, Sheffield S3 7HF, UK
| | - Victoria J B Gotham
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Brook Hill, Sheffield S3 7HF, UK
| | - Barbara Ciani
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Brook Hill, Sheffield S3 7HF, UK
| | - Jane A Grasby
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Brook Hill, Sheffield S3 7HF, UK
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6
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Zaher MS, Rashid F, Song B, Joudeh LI, Sobhy MA, Tehseen M, Hingorani MM, Hamdan SM. Missed cleavage opportunities by FEN1 lead to Okazaki fragment maturation via the long-flap pathway. Nucleic Acids Res 2019; 46:2956-2974. [PMID: 29420814 PMCID: PMC5888579 DOI: 10.1093/nar/gky082] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2017] [Accepted: 01/27/2018] [Indexed: 12/11/2022] Open
Abstract
RNA–DNA hybrid primers synthesized by low fidelity DNA polymerase α to initiate eukaryotic lagging strand synthesis must be removed efficiently during Okazaki fragment (OF) maturation to complete DNA replication. In this process, each OF primer is displaced and the resulting 5′-single-stranded flap is cleaved by structure-specific 5′-nucleases, mainly Flap Endonuclease 1 (FEN1), to generate a ligatable nick. At least two models have been proposed to describe primer removal, namely short- and long-flap pathways that involve FEN1 or FEN1 along with Replication Protein A (RPA) and Dna2 helicase/nuclease, respectively. We addressed the question of pathway choice by studying the kinetic mechanism of FEN1 action on short- and long-flap DNA substrates. Using single molecule FRET and rapid quench-flow bulk cleavage assays, we showed that unlike short-flap substrates, which are bound, bent and cleaved within the first encounter between FEN1 and DNA, long-flap substrates can escape cleavage even after DNA binding and bending. Notably, FEN1 can access both substrates in the presence of RPA, but bending and cleavage of long-flap DNA is specifically inhibited. We propose that FEN1 attempts to process both short and long flaps, but occasional missed cleavage of the latter allows RPA binding and triggers the long-flap OF maturation pathway.
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Affiliation(s)
- Manal S Zaher
- King Abdullah University of Science and Technology, Division of Biological and Environmental Science and Engineering, Thuwal 23955, Saudi Arabia
| | - Fahad Rashid
- King Abdullah University of Science and Technology, Division of Biological and Environmental Science and Engineering, Thuwal 23955, Saudi Arabia
| | - Bo Song
- Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, CT 06459, USA
| | - Luay I Joudeh
- King Abdullah University of Science and Technology, Division of Biological and Environmental Science and Engineering, Thuwal 23955, Saudi Arabia
| | - Mohamed A Sobhy
- King Abdullah University of Science and Technology, Division of Biological and Environmental Science and Engineering, Thuwal 23955, Saudi Arabia
| | - Muhammad Tehseen
- King Abdullah University of Science and Technology, Division of Biological and Environmental Science and Engineering, Thuwal 23955, Saudi Arabia
| | - Manju M Hingorani
- Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, CT 06459, USA
| | - Samir M Hamdan
- King Abdullah University of Science and Technology, Division of Biological and Environmental Science and Engineering, Thuwal 23955, Saudi Arabia
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7
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Bennet IA, Finger LD, Baxter NJ, Ambrose B, Hounslow AM, Thompson MJ, Exell JC, Shahari NNBM, Craggs TD, Waltho JP, Grasby JA. Regional conformational flexibility couples substrate specificity and scissile phosphate diester selectivity in human flap endonuclease 1. Nucleic Acids Res 2019; 46:5618-5633. [PMID: 29718417 PMCID: PMC6009646 DOI: 10.1093/nar/gky293] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2017] [Accepted: 04/09/2018] [Indexed: 02/07/2023] Open
Abstract
Human flap endonuclease-1 (hFEN1) catalyzes the divalent metal ion-dependent removal of single-stranded DNA protrusions known as flaps during DNA replication and repair. Substrate selectivity involves passage of the 5'-terminus/flap through the arch and recognition of a single nucleotide 3'-flap by the α2-α3 loop. Using NMR spectroscopy, we show that the solution conformation of free and DNA-bound hFEN1 are consistent with crystal structures; however, parts of the arch region and α2-α3 loop are disordered without substrate. Disorder within the arch explains how 5'-flaps can pass under it. NMR and single-molecule FRET data show a shift in the conformational ensemble in the arch and loop region upon addition of DNA. Furthermore, the addition of divalent metal ions to the active site of the hFEN1-DNA substrate complex demonstrates that active site changes are propagated via DNA-mediated allostery to regions key to substrate differentiation. The hFEN1-DNA complex also shows evidence of millisecond timescale motions in the arch region that may be required for DNA to enter the active site. Thus, hFEN1 regional conformational flexibility spanning a range of dynamic timescales is crucial to reach the catalytically relevant ensemble.
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Affiliation(s)
- Ian A Bennet
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute for Biomolecular Research, The University of Sheffield, Sheffield S3 7HF, UK
| | - L David Finger
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute for Biomolecular Research, The University of Sheffield, Sheffield S3 7HF, UK
| | - Nicola J Baxter
- Department of Molecular Biology and Biotechnology, Krebs Institute for Biomolecular Research, The University of Sheffield, Sheffield S10 2TN, UK.,Manchester Institute of Biotechnology, School of Chemistry, The University of Manchester, Manchester M1 7DN, UK
| | - Benjamin Ambrose
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute for Biomolecular Research, The University of Sheffield, Sheffield S3 7HF, UK
| | - Andrea M Hounslow
- Department of Molecular Biology and Biotechnology, Krebs Institute for Biomolecular Research, The University of Sheffield, Sheffield S10 2TN, UK
| | - Mark J Thompson
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute for Biomolecular Research, The University of Sheffield, Sheffield S3 7HF, UK
| | - Jack C Exell
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute for Biomolecular Research, The University of Sheffield, Sheffield S3 7HF, UK
| | - Nur Nazihah B Md Shahari
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute for Biomolecular Research, The University of Sheffield, Sheffield S3 7HF, UK
| | - Timothy D Craggs
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute for Biomolecular Research, The University of Sheffield, Sheffield S3 7HF, UK
| | - Jonathan P Waltho
- Department of Molecular Biology and Biotechnology, Krebs Institute for Biomolecular Research, The University of Sheffield, Sheffield S10 2TN, UK.,Manchester Institute of Biotechnology, School of Chemistry, The University of Manchester, Manchester M1 7DN, UK
| | - Jane A Grasby
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute for Biomolecular Research, The University of Sheffield, Sheffield S3 7HF, UK
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8
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Xu H, Shi R, Han W, Cheng J, Xu X, Cheng K, Wang L, Tian B, Zheng L, Shen B, Hua Y, Zhao Y. Structural basis of 5' flap recognition and protein-protein interactions of human flap endonuclease 1. Nucleic Acids Res 2019; 46:11315-11325. [PMID: 30295841 PMCID: PMC6265464 DOI: 10.1093/nar/gky911] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2018] [Accepted: 10/06/2018] [Indexed: 01/30/2023] Open
Abstract
Human flap endonuclease 1 (hFEN1) is a structure-specific nuclease essential for DNA replication and repair processes. hFEN1 has 5′ flap removal activity, as well as gap endonuclease activity that is critical for restarting stalled replication forks. Here, we report the crystal structures of wild-type and mutant hFEN1 proteins in complex with DNA substrates, followed by mutagenesis studies that provide mechanistic insight into the protein–protein interactions of hFEN1. We found that in an α-helix forming the helical gateway of hFEN1 recognizes the 5′ flap prior to its threading into the active site for cleavage. We also found that the β-pin region is rigidified into a short helix in R192F hFEN1–DNA structures, suppressing its gap endonuclease activity and cycle-dependent kinase interactions. Our findings suggest that a single mutation at the primary methylation site can alter the function of hFEN1 and provide insight into the role of the β-pin region in hFEN1 protein interactions that are essential for DNA replication and repair.
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Affiliation(s)
- Hong Xu
- Key Laboratory of Chinese Ministry of Agriculture for Nuclear-Agricultural Sciences, Institute of Nuclear-Agricultural Sciences, Zhejiang University, Hangzhou, Zhejiang 310029, China
| | - Rongyi Shi
- Key Laboratory of Chinese Ministry of Agriculture for Nuclear-Agricultural Sciences, Institute of Nuclear-Agricultural Sciences, Zhejiang University, Hangzhou, Zhejiang 310029, China
| | - Wanchun Han
- Key Laboratory of Chinese Ministry of Agriculture for Nuclear-Agricultural Sciences, Institute of Nuclear-Agricultural Sciences, Zhejiang University, Hangzhou, Zhejiang 310029, China
| | - Jiahui Cheng
- Key Laboratory of Chinese Ministry of Agriculture for Nuclear-Agricultural Sciences, Institute of Nuclear-Agricultural Sciences, Zhejiang University, Hangzhou, Zhejiang 310029, China
| | - Xiaoli Xu
- Key Laboratory of Chinese Ministry of Agriculture for Nuclear-Agricultural Sciences, Institute of Nuclear-Agricultural Sciences, Zhejiang University, Hangzhou, Zhejiang 310029, China
| | - Kaiying Cheng
- Key Laboratory of Chinese Ministry of Agriculture for Nuclear-Agricultural Sciences, Institute of Nuclear-Agricultural Sciences, Zhejiang University, Hangzhou, Zhejiang 310029, China
| | - Liangyan Wang
- Key Laboratory of Chinese Ministry of Agriculture for Nuclear-Agricultural Sciences, Institute of Nuclear-Agricultural Sciences, Zhejiang University, Hangzhou, Zhejiang 310029, China
| | - Bing Tian
- Key Laboratory of Chinese Ministry of Agriculture for Nuclear-Agricultural Sciences, Institute of Nuclear-Agricultural Sciences, Zhejiang University, Hangzhou, Zhejiang 310029, China
| | - Li Zheng
- Department of Cancer Genetics and Epigenetics, City of Hope National Medical Center and Beckman Research Institute, Duarte, CA 91010, USA
| | - Binghui Shen
- Department of Cancer Genetics and Epigenetics, City of Hope National Medical Center and Beckman Research Institute, Duarte, CA 91010, USA
| | - Yuejin Hua
- Key Laboratory of Chinese Ministry of Agriculture for Nuclear-Agricultural Sciences, Institute of Nuclear-Agricultural Sciences, Zhejiang University, Hangzhou, Zhejiang 310029, China
| | - Ye Zhao
- Key Laboratory of Chinese Ministry of Agriculture for Nuclear-Agricultural Sciences, Institute of Nuclear-Agricultural Sciences, Zhejiang University, Hangzhou, Zhejiang 310029, China
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9
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Ka Man Tse C, Xu J, Xu L, Sheong FK, Wang S, Chow HY, Gao X, Li X, Cheung PPH, Wang D, Zhang Y, Huang X. Intrinsic Cleavage of RNA Polymerase II Adopts a Nucleobase-independent Mechanism Assisted by Transcript Phosphate. Nat Catal 2019; 2:228-235. [PMID: 31179024 PMCID: PMC6548511 DOI: 10.1038/s41929-019-0227-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2018] [Accepted: 12/19/2018] [Indexed: 06/09/2023]
Abstract
RNA polymerase II (Pol II) utilises the same active site for polymerization and intrinsic cleavage. Pol II proofreads the nascent transcript by its intrinsic nuclease activity to maintain high transcriptional fidelity critical for cell growth and viability. The detailed catalytic mechanism of intrinsic cleavage remains unknown. Here, we combined ab initio quantum mechanics/molecular mechanics studies and biochemical cleavage assays to show that Pol II utilises downstream phosphate oxygen to activate the attacking nucleophile in hydrolysis, while the newly formed 3'-end is protonated through active-site water without a defined general acid. Experimentally, alteration of downstream phosphate oxygen either by 2'-5' sugar linkage or stereo-specific thio-substitution of phosphate oxygen drastically reduced cleavage rate. We showed by N7-modification that guanine nucleobase does not directly involve as acid-base catalyst. Our proposed mechanism provides important insights into the understanding of intrinsic transcriptional cleavage reaction, an essential step of transcriptional fidelity control.
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Affiliation(s)
- Carmen Ka Man Tse
- Department of Chemistry, Centre of Systems Biology and Human Health, State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Kowloon, Hong Kong
| | - Jun Xu
- Department of Cellular and Molecular Medicine, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California 92093, United States
| | - Liang Xu
- Department of Cellular and Molecular Medicine, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California 92093, United States
- Department of Chemistry, Sun Yat-Sen University, Guangzhou, China
| | - Fu Kit Sheong
- Department of Chemistry, Centre of Systems Biology and Human Health, State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Kowloon, Hong Kong
| | - Shenglong Wang
- Department of Chemistry, New York University, New York, New York 10003 United States
| | - Hoi Yee Chow
- Department of Chemistry, State Key Lab of Synthetic Chemistry, The University of Hong Kong, Hong Kong
| | - Xin Gao
- Computational Bioscience Research Centre (CBRC), CEMSE Division, King Abdullah University of Science and Technology (KAUST), Thuwal, Saudi Arabia
| | - Xuechen Li
- Department of Chemistry, State Key Lab of Synthetic Chemistry, The University of Hong Kong, Hong Kong
| | - Peter Pak-Hang Cheung
- Department of Chemistry, Centre of Systems Biology and Human Health, State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Kowloon, Hong Kong
| | - Dong Wang
- Department of Cellular and Molecular Medicine, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California 92093, United States
| | - Yingkai Zhang
- Department of Chemistry, New York University, New York, New York 10003 United States
- NYU-ECNU Centre for Computational Chemistry at NYU Shanghai, Shanghai 200062, China
| | - Xuhui Huang
- Department of Chemistry, Centre of Systems Biology and Human Health, State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Kowloon, Hong Kong
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10
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Two symmetric arginine residues play distinct roles in Thermus thermophilus Argonaute DNA guide strand-mediated DNA target cleavage. Proc Natl Acad Sci U S A 2018; 116:845-853. [PMID: 30591565 DOI: 10.1073/pnas.1817041116] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Bacterium Thermus thermophilus Argonaute (Ago; TtAgo) is a prokaryotic Ago (pAgo) that acts as the host defense against the uptake and propagation of foreign DNA by catalyzing the DNA cleavage reaction. The TtAgo active site consists of a plugged-in glutamate finger with two arginine residues (R545 and R486) located symmetrically around it. An interesting challenge is to understand how they can collaboratively facilitate enzymatic catalysis. In Kluyveromyces polysporus Ago, a eukaryotic Ago, the evolutionarily symmetrical residues are arginine and histidine, both of which function to stabilize the plugged-in catalytic tetrad conformation. Surprisingly, our simulation results indicated that, in TtAgo, only R545 is involved in the cleavage reaction by serving as a critical structural anchor to stabilize the catalytic tetrad Asp-Glu-Asp-Asp that is completed by the insertion of the glutamate finger, whereas R486 is not involved in target cleavage. The TtAgo-mediated target DNA cleavage occurs in a substrate-assisted mechanism, in which the pro-Rp (Rp, a tetrahedral phosphorus center with "R-type" chirality) oxygen of scissile phosphate acts as a general base to activate the nucleophilic water. Our unexpected theoretical findings on distinct roles played by R545 and R486 in TtAgo catalysis have been validated by single-point site-mutagenesis experiments, wherein the target cleavage is abolished for all mutants of R545. In sharp contrast, the cleavage activity is maintained for all mutants of R486. Our work provides mechanistic insights on the catalytic specificity of Ago proteins and could facilitate the design of new gene-editing tools in the long term.
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11
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Algasaier SI, Finger LD, Bennet IA, Grasby JA. Flap Endonuclease 1 Mutations A159V and E160D Cause Genomic Instability by Slowing Reaction on Double-Flap Substrates. Biochemistry 2018; 57:6838-6847. [DOI: 10.1021/acs.biochem.8b00891] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- Sana I. Algasaier
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, U.K
| | - L. David Finger
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, U.K
| | - Ian A. Bennet
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, U.K
| | - Jane A. Grasby
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, U.K
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12
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Uson ML, Carl A, Goldgur Y, Shuman S. Crystal structure and mutational analysis of Mycobacterium smegmatis FenA highlight active site amino acids and three metal ions essential for flap endonuclease and 5' exonuclease activities. Nucleic Acids Res 2018; 46:4164-4175. [PMID: 29635474 PMCID: PMC5934675 DOI: 10.1093/nar/gky238] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2018] [Revised: 03/19/2018] [Accepted: 03/21/2018] [Indexed: 02/02/2023] Open
Abstract
Mycobacterium smegmatis FenA is a nucleic acid phosphodiesterase with flap endonuclease and 5' exonuclease activities. The 1.8 Å crystal structure of FenA reported here highlights as its closest homologs bacterial FEN-family enzymes ExoIX, the Pol1 exonuclease domain and phage T5 Fen. Mycobacterial FenA assimilates three active site manganese ions (M1, M2, M3) that are coordinated, directly and via waters, to a constellation of eight carboxylate side chains. We find via mutagenesis that the carboxylate contacts to all three manganese ions are essential for FenA's activities. Structures of nuclease-dead FenA mutants D125N, D148N and D208N reveal how they fail to bind one of the three active site Mn2+ ions, in a distinctive fashion for each Asn change. The structure of FenA D208N with a phosphate anion engaged by M1 and M2 in a state mimetic of a product complex suggests a mechanism for metal-catalyzed phosphodiester hydrolysis similar to that proposed for human Exo1. A distinctive feature of FenA is that it does not have the helical arch module found in many other FEN/FEN-like enzymes. Instead, this segment of FenA adopts a unique structure comprising a short 310 helix and surface β-loop that coordinates a fourth manganese ion (M4).
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Affiliation(s)
- Maria Loressa Uson
- Molecular Biology Program, Sloan-Kettering Institute, New York, NY 10065, USA
| | - Ayala Carl
- Molecular Biology Program, Sloan-Kettering Institute, New York, NY 10065, USA
| | - Yehuda Goldgur
- Structural Biology Program, Sloan-Kettering Institute, New York, NY 10065, USA
| | - Stewart Shuman
- Molecular Biology Program, Sloan-Kettering Institute, New York, NY 10065, USA
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13
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Song B, Hamdan SM, Hingorani MM. Positioning the 5'-flap junction in the active site controls the rate of flap endonuclease-1-catalyzed DNA cleavage. J Biol Chem 2018; 293:4792-4804. [PMID: 29462789 DOI: 10.1074/jbc.ra117.001137] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2017] [Revised: 02/08/2018] [Indexed: 12/14/2022] Open
Abstract
Flap endonucleases catalyze cleavage of single-stranded DNA flaps formed during replication, repair, and recombination and are therefore essential for genome processing and stability. Recent crystal structures of DNA-bound human flap endonuclease (hFEN1) offer new insights into how conformational changes in the DNA and hFEN1 may facilitate the reaction mechanism. For example, previous biochemical studies of DNA conformation performed under non-catalytic conditions with Ca2+ have suggested that base unpairing at the 5'-flap:template junction is an important step in the reaction, but the new structural data suggest otherwise. To clarify the role of DNA changes in the kinetic mechanism, we measured a series of transient steps, from substrate binding to product release, during the hFEN1-catalyzed reaction in the presence of Mg2+ We found that whereas hFEN1 binds and bends DNA at a fast, diffusion-limited rate, much slower Mg2+-dependent conformational changes in DNA around the active site are subsequently necessary and rate-limiting for 5'-flap cleavage. These changes are reported overall by fluorescence of 2-aminopurine at the 5'-flap:template junction, indicating that local DNA distortion (e.g. disruption of base stacking observed in structures), associated with positioning the 5'-flap scissile phosphodiester bond in the hFEN1 active site, controls catalysis. hFEN1 residues with distinct roles in the catalytic mechanism, including those binding metal ions (Asp-34 and Asp-181), steering the 5'-flap through the active site and binding the scissile phosphate (Lys-93 and Arg-100), and stacking against the base 5' to the scissile phosphate (Tyr-40), all contribute to these rate-limiting conformational changes, ensuring efficient and specific cleavage of 5'-flaps.
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Affiliation(s)
- Bo Song
- Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459
| | - Samir M Hamdan
- Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955, Saudi Arabia
| | - Manju M Hingorani
- Department of Molecular Biology and Biochemistry, Wesleyan University, Middletown, Connecticut 06459.
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14
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Matelska D, Steczkiewicz K, Ginalski K. Comprehensive classification of the PIN domain-like superfamily. Nucleic Acids Res 2017; 45:6995-7020. [PMID: 28575517 PMCID: PMC5499597 DOI: 10.1093/nar/gkx494] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Accepted: 05/24/2017] [Indexed: 12/21/2022] Open
Abstract
PIN-like domains constitute a widespread superfamily of nucleases, diverse in terms of the reaction mechanism, substrate specificity, biological function and taxonomic distribution. Proteins with PIN-like domains are involved in central cellular processes, such as DNA replication and repair, mRNA degradation, transcription regulation and ncRNA maturation. In this work, we identify and classify the most complete set of PIN-like domains to provide the first comprehensive analysis of sequence–structure–function relationships within the whole PIN domain-like superfamily. Transitive sequence searches using highly sensitive methods for remote homology detection led to the identification of several new families, including representatives of Pfam (DUF1308, DUF4935) and CDD (COG2454), and 23 other families not classified in the public domain databases. Further sequence clustering revealed relationships between individual sequence clusters and showed heterogeneity within some families, suggesting a possible functional divergence. With five structural groups, 70 defined clusters, over 100,000 proteins, and broad biological functions, the PIN domain-like superfamily constitutes one of the largest and most diverse nuclease superfamilies. Detailed analyses of sequences and structures, domain architectures, and genomic contexts allowed us to predict biological function of several new families, including new toxin-antitoxin components, proteins involved in tRNA/rRNA maturation and transcription/translation regulation.
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Affiliation(s)
- Dorota Matelska
- University of Warsaw, CeNT, Laboratory of Bioinformatics and Systems Biology, Zwirki i Wigury 93, 02-089 Warsaw, Poland
| | - Kamil Steczkiewicz
- University of Warsaw, CeNT, Laboratory of Bioinformatics and Systems Biology, Zwirki i Wigury 93, 02-089 Warsaw, Poland
| | - Krzysztof Ginalski
- University of Warsaw, CeNT, Laboratory of Bioinformatics and Systems Biology, Zwirki i Wigury 93, 02-089 Warsaw, Poland
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15
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The DNA Repair Repertoire of Mycobacterium smegmatis FenA Includes the Incision of DNA 5' Flaps and the Removal of 5' Adenylylated Products of Aborted Nick Ligation. J Bacteriol 2017. [PMID: 28630124 DOI: 10.1128/jb.00304-17] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
We characterize Mycobacterium smegmatis FenA as a manganese-dependent 5'-flap endonuclease homologous to the 5'-exonuclease of DNA polymerase I. FenA incises a nicked 5' flap between the first and second nucleotides of the duplex segment to yield a 1-nucleotide gapped DNA, which is then further resected in dinucleotide steps. Initial FenA cleavage at a Y-flap or nick occurs between the first and second nucleotides of the duplex. However, when the template 3' single strand is eliminated to create a 5'-tailed duplex, FenA incision shifts to between the second and third nucleotides. A double-flap substrate with a mobile junction (mimicking limited strand displacement synthesis during gap repair) is preferentially incised as the 1-nucleotide 3'-flap isomer, with the scissile phosphodiester shifted by one nucleotide versus a static double flap. FenA efficiently removes the 5' App(dN) terminus of an aborted nick ligation reaction intermediate, thereby highlighting FenA as an agent of repair of such lesions, which are formed under a variety of circumstances by bacterial NAD+-dependent DNA ligases and especially by mycobacterial DNA ligases D and C.IMPORTANCE Structure-specific DNA endonucleases are implicated in bacterial DNA replication, repair, and recombination, yet there is scant knowledge of the roster and catalytic repertoire of such nucleases in Mycobacteria This study identifies M. smegmatis FenA as a stand-alone endonuclease homologous to the 5'-exonuclease domain of mycobacterial DNA polymerase 1. FenA incises 5' flaps, 5' nicks, and 5' App(dN) intermediates of aborted nick ligation. The isolated N-terminal domain of M. smegmatis Pol1 is also shown to be a flap endonuclease.
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16
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Shaw SJ, Finger LD, Grasby JA. Human Exonuclease 1 Threads 5'-Flap Substrates through Its Helical Arch. Biochemistry 2017; 56:3704-3707. [PMID: 28682061 DOI: 10.1021/acs.biochem.7b00507] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Human exonuclease 1 (hEXO1) is a member of the 5'-nuclease superfamily and plays important roles in DNA repair. Along with acting as a 5'-exonuclease on blunt, gapped, nicked, and 3'-overhang DNAs, hEXO1 can also act as an endonuclease removing protruding 5'-single-stranded flaps from duplex ends. How hEXO1 and related 5'-nuclease human flap endonuclease 1 (hFEN1) are specific for discontinuous DNA substrates like 5'-flaps has been controversial. Here we report the first functional data that imply that hEXO1 threads the 5'-flap through a hole in the protein known as the helical arch, thereby excluding reactions of continuous single strands. Conjugation of bulky 5'-streptavidin that would "block" threading through the arch drastically slowed the hEXO1 reaction. In contrast, addition of streptavidin to a preformed hEXO1 5'-biotin flap DNA complex trapped a portion of the substrate in a highly reactive threaded conformation. However, another fraction behaves as if it were "blocked" and decayed very slowly, implying there were both threaded and unthreaded forms of the substrate present. The reaction of an unmodified hEXO1-flap DNA complex did not exhibit marked biphasic kinetics, suggesting a fast re-equilibration occurs that produces more threaded substrate when some decays. The finding that a threading mechanism like that used by hFEN1 is also used by hEXO1 unifies the mode of operation for members of the 5'-nuclease superfamily that act on discontinuous substrates. As with hFEN1, intrinsic disorder of the arch region of the protein may explain how flaps can be threaded without a need for a coupled energy source.
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Affiliation(s)
- Steven J Shaw
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield , Sheffield S3 7HF, U.K
| | - L David Finger
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield , Sheffield S3 7HF, U.K
| | - Jane A Grasby
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield , Sheffield S3 7HF, U.K
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17
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Phosphate steering by Flap Endonuclease 1 promotes 5'-flap specificity and incision to prevent genome instability. Nat Commun 2017; 8:15855. [PMID: 28653660 PMCID: PMC5490271 DOI: 10.1038/ncomms15855] [Citation(s) in RCA: 65] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Accepted: 05/05/2017] [Indexed: 12/13/2022] Open
Abstract
DNA replication and repair enzyme Flap Endonuclease 1 (FEN1) is vital for genome integrity, and FEN1 mutations arise in multiple cancers. FEN1 precisely cleaves single-stranded (ss) 5′-flaps one nucleotide into duplex (ds) DNA. Yet, how FEN1 selects for but does not incise the ss 5′-flap was enigmatic. Here we combine crystallographic, biochemical and genetic analyses to show that two dsDNA binding sites set the 5′polarity and to reveal unexpected control of the DNA phosphodiester backbone by electrostatic interactions. Via ‘phosphate steering’, basic residues energetically steer an inverted ss 5′-flap through a gateway over FEN1’s active site and shift dsDNA for catalysis. Mutations of these residues cause an 18,000-fold reduction in catalytic rate in vitro and large-scale trinucleotide (GAA)n repeat expansions in vivo, implying failed phosphate-steering promotes an unanticipated lagging-strand template-switch mechanism during replication. Thus, phosphate steering is an unappreciated FEN1 function that enforces 5′-flap specificity and catalysis, preventing genomic instability. Flap Endonuclease 1 is a DNA replication and repair enzyme indispensable for maintaining genomic stability. Here the authors provide mechanistic details on how FEN1 selects for 5′-flaps and promotes catalysis to avoid large-scale repeat expansion by a process termed ‘phosphate steering’.
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18
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Interplay of catalysis, fidelity, threading, and processivity in the exo- and endonucleolytic reactions of human exonuclease I. Proc Natl Acad Sci U S A 2017; 114:6010-6015. [PMID: 28533382 DOI: 10.1073/pnas.1704845114] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Human exonuclease 1 (hExo1) is a member of the RAD2/XPG structure-specific 5'-nuclease superfamily. Its dominant, processive 5'-3' exonuclease and secondary 5'-flap endonuclease activities participate in various DNA repair, recombination, and replication processes. A single active site processes both recessed ends and 5'-flap substrates. By initiating enzyme reactions in crystals, we have trapped hExo1 reaction intermediates that reveal structures of these substrates before and after their exo- and endonucleolytic cleavage, as well as structures of uncleaved, unthreaded, and partially threaded 5' flaps. Their distinctive 5' ends are accommodated by a small, mobile arch in the active site that binds recessed ends at its base and threads 5' flaps through a narrow aperture within its interior. A sequence of successive, interlocking conformational changes guides the two substrate types into a shared reaction mechanism that catalyzes their cleavage by an elaborated variant of the two-metal, in-line hydrolysis mechanism. Coupling of substrate-dependent arch motions to transition-state stabilization suppresses inappropriate or premature cleavage, enhancing processing fidelity. The striking reduction in flap conformational entropy is catalyzed, in part, by arch motions and transient binding interactions between the flap and unprocessed DNA strand. At the end of the observed reaction sequence, hExo1 resets without relinquishing DNA binding, suggesting a structural basis for its processivity.
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19
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Rashid F, Harris PD, Zaher MS, Sobhy MA, Joudeh LI, Yan C, Piwonski H, Tsutakawa SE, Ivanov I, Tainer JA, Habuchi S, Hamdan SM. Single-molecule FRET unveils induced-fit mechanism for substrate selectivity in flap endonuclease 1. eLife 2017; 6. [PMID: 28230529 PMCID: PMC5358979 DOI: 10.7554/elife.21884] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Accepted: 02/20/2017] [Indexed: 12/21/2022] Open
Abstract
Human flap endonuclease 1 (FEN1) and related structure-specific 5’nucleases precisely identify and incise aberrant DNA structures during replication, repair and recombination to avoid genomic instability. Yet, it is unclear how the 5’nuclease mechanisms of DNA distortion and protein ordering robustly mediate efficient and accurate substrate recognition and catalytic selectivity. Here, single-molecule sub-millisecond and millisecond analyses of FEN1 reveal a protein-DNA induced-fit mechanism that efficiently verifies substrate and suppresses off-target cleavage. FEN1 sculpts DNA with diffusion-limited kinetics to test DNA substrate. This DNA distortion mutually ‘locks’ protein and DNA conformation and enables substrate verification with extreme precision. Strikingly, FEN1 never misses cleavage of its cognate substrate while blocking probable formation of catalytically competent interactions with noncognate substrates and fostering their pre-incision dissociation. These findings establish FEN1 has practically perfect precision and that separate control of induced-fit substrate recognition sets up the catalytic selectivity of the nuclease active site for genome stability. DOI:http://dx.doi.org/10.7554/eLife.21884.001 When a cell divides it must copy its genetic information, which is found in the form of strands of DNA. Damage to the DNA may lead to cancer or a number of genetic diseases. However, every time a cell divides more than 10 million toxic “flaps” of excess DNA are generated. A protein called flap endonuclease 1 (FEN1) keeps the DNA in good repair by cutting off the flaps in a highly specific and selective manner. Many proteins that interact with DNA are attracted to specific genetic sequences within the DNA strands. However, this is not the case for FEN1 and several other “structure-specific” proteins that help to repair and replicate DNA strands. So how do these proteins select the correct regions of DNA to interact with? Rashid et al. used single-molecule fluorescence measurements to examine how purified FEN1 proteins interact with DNA flaps. The results show that FEN1 can perfectly recognize and correctly remove flaps through a process called “mutual-induced fit”, where the DNA and FEN1 are shaped by each other to produce a highly specific structure. Further work is now needed to examine whether other proteins that are related to FEN1 use a similar process to ensure that they always cut DNA in the same way. More detailed and direct examination of the structure of FEN1 through other experimental methods may also help to reveal how the mutual-induced fit process enables FEN1 to achieve such high levels of precision. This could increase our understanding of how problems with FEN1 and similar proteins lead to different genetic diseases. DOI:http://dx.doi.org/10.7554/eLife.21884.002
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Affiliation(s)
- Fahad Rashid
- Division of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
| | - Paul D Harris
- Division of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
| | - Manal S Zaher
- Division of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
| | - Mohamed A Sobhy
- Division of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
| | - Luay I Joudeh
- Division of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
| | - Chunli Yan
- Department of Chemistry, Georgia State University, Atlanta, United States.,Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, United States
| | - Hubert Piwonski
- Division of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
| | | | - Ivaylo Ivanov
- Department of Chemistry, Georgia State University, Atlanta, United States.,Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, United States
| | - John A Tainer
- Lawrence Berkeley National Laboratory, Berkeley, United States.,Department of Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, United States
| | - Satoshi Habuchi
- Division of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
| | - Samir M Hamdan
- Division of Biological and Environmental Science and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia
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20
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Exell JC, Thompson MJ, Finger LD, Shaw SJ, Debreczeni J, Ward TA, McWhirter C, Siöberg CLB, Martinez Molina D, Abbott WM, Jones CD, Nissink JWM, Durant ST, Grasby JA. Cellularly active N-hydroxyurea FEN1 inhibitors block substrate entry to the active site. Nat Chem Biol 2016; 12:815-21. [PMID: 27526030 PMCID: PMC5348030 DOI: 10.1038/nchembio.2148] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2015] [Accepted: 05/19/2016] [Indexed: 02/07/2023]
Abstract
The structure-specific nuclease human flap endonuclease-1 (hFEN1) plays a key role in DNA replication and repair and may be of interest as an oncology target. We present the crystal structure of inhibitor-bound hFEN1, which shows a cyclic N-hydroxyurea bound in the active site coordinated to two magnesium ions. Three such compounds had similar IC50 values but differed subtly in mode of action. One had comparable affinity for protein and protein-substrate complex and prevented reaction by binding to active site catalytic metal ions, blocking the necessary unpairing of substrate DNA. Other compounds were more competitive with substrate. Cellular thermal shift data showed that both inhibitor types engaged with hFEN1 in cells, and activation of the DNA damage response was evident upon treatment with inhibitors. However, cellular EC50 values were significantly higher than in vitro inhibition constants, and the implications of this for exploitation of hFEN1 as a drug target are discussed.
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Affiliation(s)
- Jack C Exell
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield, UK
| | - Mark J Thompson
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield, UK
| | - L David Finger
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield, UK
| | - Steven J Shaw
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield, UK
| | - Judit Debreczeni
- Discovery Sciences, Innovative Medicines and Early Development Biotech Unit, AstraZeneca, Cambridge, UK
| | - Thomas A Ward
- Bioscience, Oncology Innovative Medicines and Early Development Biotech Unit, AstraZeneca, Alderley Park, Cheshire, UK
| | - Claire McWhirter
- Discovery Sciences, Innovative Medicines and Early Development Biotech Unit, AstraZeneca, Cambridge, UK
| | | | | | - W Mark Abbott
- Discovery Sciences, Innovative Medicines and Early Development Biotech Unit, AstraZeneca, Cambridge, UK
| | - Clifford D Jones
- Chemistry, Oncology Innovative Medicines and Early Development Biotech Unit, AstraZeneca, Alderley Park, UK
| | - J Willem M Nissink
- Chemistry, Oncology Innovative Medicines and Early Development Biotech Unit, AstraZeneca, Cambridge, UK
| | - Stephen T Durant
- Bioscience, Oncology Innovative Medicines and Early Development Biotech Unit, Cambridge, UK
| | - Jane A Grasby
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield, UK.,Bioscience, Oncology Innovative Medicines and Early Development Biotech Unit, Cambridge, UK
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21
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Direct observation of DNA threading in flap endonuclease complexes. Nat Struct Mol Biol 2016; 23:640-6. [PMID: 27273516 PMCID: PMC4939078 DOI: 10.1038/nsmb.3241] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2016] [Accepted: 05/10/2016] [Indexed: 02/06/2023]
Abstract
Maintenance of genome integrity requires that branched nucleic acid
molecules are accurately processed to produce double-helical DNA. Flap
endonucleases are essential enzymes that trim such branched molecules generated
by Okazaki fragment synthesis during replication. Here, we report crystal
structures of bacteriophage T5 flap endonuclease in complexes with intact DNA
substrates, and products, at resolutions of 1.9–2.2 Å. They reveal
single-stranded DNA threading through a hole in the enzyme enclosed by an
inverted V-shaped helical arch straddling the active site. Residues lining the
hole induce an unusual barb-like conformation in the DNA substrate juxtaposing
the scissile phosphate and essential catalytic metal ions. A series of complexes
and biochemical analyses show how the substrate’s single-stranded branch
approaches, threads through, and finally emerges on the far side of the enzyme.
Our studies suggest that substrate recognition involves an unusual
“fly-casting, thread, bend and barb” mechanism.
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22
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Algasaier SI, Exell JC, Bennet IA, Thompson MJ, Gotham VJB, Shaw SJ, Craggs TD, Finger LD, Grasby JA. DNA and Protein Requirements for Substrate Conformational Changes Necessary for Human Flap Endonuclease-1-catalyzed Reaction. J Biol Chem 2016; 291:8258-68. [PMID: 26884332 PMCID: PMC4825025 DOI: 10.1074/jbc.m115.698993] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Revised: 02/04/2016] [Indexed: 12/02/2022] Open
Abstract
Human flap endonuclease-1 (hFEN1) catalyzes the essential removal of single-stranded flaps arising at DNA junctions during replication and repair processes. hFEN1 biological function must be precisely controlled, and consequently, the protein relies on a combination of protein and substrate conformational changes as a prerequisite for reaction. These include substrate bending at the duplex-duplex junction and transfer of unpaired reacting duplex end into the active site. When present, 5'-flaps are thought to thread under the helical cap, limiting reaction to flaps with free 5'-terminiin vivo Here we monitored DNA bending by FRET and DNA unpairing using 2-aminopurine exciton pair CD to determine the DNA and protein requirements for these substrate conformational changes. Binding of DNA to hFEN1 in a bent conformation occurred independently of 5'-flap accommodation and did not require active site metal ions or the presence of conserved active site residues. More stringent requirements exist for transfer of the substrate to the active site. Placement of the scissile phosphate diester in the active site required the presence of divalent metal ions, a free 5'-flap (if present), a Watson-Crick base pair at the terminus of the reacting duplex, and the intact secondary structure of the enzyme helical cap. Optimal positioning of the scissile phosphate additionally required active site conserved residues Tyr(40), Asp(181), and Arg(100)and a reacting duplex 5'-phosphate. These studies suggest a FEN1 reaction mechanism where junctions are bound and 5'-flaps are threaded (when present), and finally the substrate is transferred onto active site metals initiating cleavage.
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Affiliation(s)
- Sana I Algasaier
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
| | - Jack C Exell
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
| | - Ian A Bennet
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
| | - Mark J Thompson
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
| | - Victoria J B Gotham
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
| | - Steven J Shaw
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
| | - Timothy D Craggs
- the DNA:Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol BS8 1TD,United Kingdom
| | - L David Finger
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
| | - Jane A Grasby
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
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23
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Lee SH, Princz LN, Klügel MF, Habermann B, Pfander B, Biertümpfel C. Human Holliday junction resolvase GEN1 uses a chromodomain for efficient DNA recognition and cleavage. eLife 2015; 4:e12256. [PMID: 26682650 PMCID: PMC5039027 DOI: 10.7554/elife.12256] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2015] [Accepted: 12/17/2015] [Indexed: 12/22/2022] Open
Abstract
Holliday junctions (HJs) are key DNA intermediates in homologous recombination. They link homologous DNA strands and have to be faithfully removed for proper DNA segregation and genome integrity. Here, we present the crystal structure of human HJ resolvase GEN1 complexed with DNA at 3.0 Å resolution. The GEN1 core is similar to other Rad2/XPG nucleases. However, unlike other members of the superfamily, GEN1 contains a chromodomain as an additional DNA interaction site. Chromodomains are known for their chromatin-targeting function in chromatin remodelers and histone(de)acetylases but they have not previously been found in nucleases. The GEN1 chromodomain directly contacts DNA and its truncation severely hampers GEN1's catalytic activity. Structure-guided mutations in vitro and in vivo in yeast validated our mechanistic findings. Our study provides the missing structure in the Rad2/XPG family and insights how a well-conserved nuclease core acquires versatility in recognizing diverse substrates for DNA repair and maintenance.
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Affiliation(s)
- Shun-Hsiao Lee
- Department of Structural Cell Biology, Molecular Mechanisms of DNA Repair, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Lissa Nicola Princz
- Department of Molecular Cell Biology, DNA Replication and Genome Integrity, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Maren Felizitas Klügel
- Department of Structural Cell Biology, Molecular Mechanisms of DNA Repair, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Bianca Habermann
- Computational Biology, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Boris Pfander
- Department of Molecular Cell Biology, DNA Replication and Genome Integrity, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Christian Biertümpfel
- Department of Structural Cell Biology, Molecular Mechanisms of DNA Repair, Max Planck Institute of Biochemistry, Martinsried, Germany
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24
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Tarantino ME, Bilotti K, Huang J, Delaney S. Rate-determining Step of Flap Endonuclease 1 (FEN1) Reflects a Kinetic Bias against Long Flaps and Trinucleotide Repeat Sequences. J Biol Chem 2015; 290:21154-21162. [PMID: 26160176 DOI: 10.1074/jbc.m115.666438] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Indexed: 11/06/2022] Open
Abstract
Flap endonuclease 1 (FEN1) is a structure-specific nuclease responsible for removing 5'-flaps formed during Okazaki fragment maturation and long patch base excision repair. In this work, we use rapid quench flow techniques to examine the rates of 5'-flap removal on DNA substrates of varying length and sequence. Of particular interest are flaps containing trinucleotide repeats (TNR), which have been proposed to affect FEN1 activity and cause genetic instability. We report that FEN1 processes substrates containing flaps of 30 nucleotides or fewer at comparable single-turnover rates. However, for flaps longer than 30 nucleotides, FEN1 kinetically discriminates substrates based on flap length and flap sequence. In particular, FEN1 removes flaps containing TNR sequences at a rate slower than mixed sequence flaps of the same length. Furthermore, multiple-turnover kinetic analysis reveals that the rate-determining step of FEN1 switches as a function of flap length from product release to chemistry (or a step prior to chemistry). These results provide a kinetic perspective on the role of FEN1 in DNA replication and repair and contribute to our understanding of FEN1 in mediating genetic instability of TNR sequences.
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Affiliation(s)
- Mary E Tarantino
- Department of Chemistry, Brown University, Providence, Rhode Island 02912
| | - Katharina Bilotti
- Department of Chemistry, Brown University, Providence, Rhode Island 02912
| | - Ji Huang
- Department of Chemistry, Brown University, Providence, Rhode Island 02912
| | - Sarah Delaney
- Department of Chemistry, Brown University, Providence, Rhode Island 02912.
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25
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Sgrignani J, Magistrato A. QM/MM MD Simulations on the Enzymatic Pathway of the Human Flap Endonuclease (hFEN1) Elucidating Common Cleavage Pathways to RNase H Enzymes. ACS Catal 2015. [DOI: 10.1021/acscatal.5b00178] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Affiliation(s)
- Jacopo Sgrignani
- Institute of Research in Biomedicine (IRB), Via Vincenzo Vela, 6500 Bellinzona, Switzerland
| | - Alessandra Magistrato
- CNR-IOM-Democritos
National Simulation Center c/o International School for Advanced Studies (SISSA/ISAS), Via Bonomea 265, 34136 Trieste, Italy
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26
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Andres SN, Schellenberg MJ, Wallace BD, Tumbale P, Williams RS. Recognition and repair of chemically heterogeneous structures at DNA ends. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2015; 56:1-21. [PMID: 25111769 PMCID: PMC4303525 DOI: 10.1002/em.21892] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2014] [Accepted: 07/28/2014] [Indexed: 05/13/2023]
Abstract
Exposure to environmental toxicants and stressors, radiation, pharmaceutical drugs, inflammation, cellular respiration, and routine DNA metabolism all lead to the production of cytotoxic DNA strand breaks. Akin to splintered wood, DNA breaks are not "clean." Rather, DNA breaks typically lack DNA 5'-phosphate and 3'-hydroxyl moieties required for DNA synthesis and DNA ligation. Failure to resolve damage at DNA ends can lead to abnormal DNA replication and repair, and is associated with genomic instability, mutagenesis, neurological disease, ageing and carcinogenesis. An array of chemically heterogeneous DNA termini arises from spontaneously generated DNA single-strand and double-strand breaks (SSBs and DSBs), and also from normal and/or inappropriate DNA metabolism by DNA polymerases, DNA ligases and topoisomerases. As a front line of defense to these genotoxic insults, eukaryotic cells have accrued an arsenal of enzymatic first responders that bind and protect damaged DNA termini, and enzymatically tailor DNA ends for DNA repair synthesis and ligation. These nucleic acid transactions employ direct damage reversal enzymes including Aprataxin (APTX), Polynucleotide kinase phosphatase (PNK), the tyrosyl DNA phosphodiesterases (TDP1 and TDP2), the Ku70/80 complex and DNA polymerase β (POLβ). Nucleolytic processing enzymes such as the MRE11/RAD50/NBS1/CtIP complex, Flap endonuclease (FEN1) and the apurinic endonucleases (APE1 and APE2) also act in the chemical "cleansing" of DNA breaks to prevent genomic instability and disease, and promote progression of DNA- and RNA-DNA damage response (DDR and RDDR) pathways. Here, we provide an overview of cellular first responders dedicated to the detection and repair of abnormal DNA termini.
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Affiliation(s)
- Sara N Andres
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences, NIH, DHHS, North Carolina
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27
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Shah S, Dunten P, Stiteler A, Park CK, Horton NC. Structure and specificity of FEN-1 from Methanopyrus kandleri. Proteins 2014; 83:188-94. [PMID: 25354467 DOI: 10.1002/prot.24704] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2014] [Revised: 10/06/2014] [Accepted: 10/18/2014] [Indexed: 11/06/2022]
Abstract
DNA repair is fundamental to genome stability and is found in all three domains of life. However many archaeal species, such as Methanopyrus kandleri, contain only a subset of the eukaryotic nucleotide excision repair (NER) homologs, and those present often contain significant differences compared to their eukaryotic homologs. To clarify the role of the NER XPG-like protein Mk0566 from M. kandleri, its biochemical activity and three-dimensional structure were investigated. Both were found to be more similar to human FEN-1 than human XPG, suggesting a biological role in replication and long-patch base excision repair rather than in NER.
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Affiliation(s)
- Santosh Shah
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona, 85721
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28
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Miętus M, Nowak E, Jaciuk M, Kustosz P, Studnicka J, Nowotny M. Crystal structure of the catalytic core of Rad2: insights into the mechanism of substrate binding. Nucleic Acids Res 2014; 42:10762-75. [PMID: 25120270 PMCID: PMC4176360 DOI: 10.1093/nar/gku729] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2014] [Revised: 07/29/2014] [Accepted: 07/29/2014] [Indexed: 12/26/2022] Open
Abstract
Rad2/XPG belongs to the flap nuclease family and is responsible for a key step of the eukaryotic nucleotide excision DNA repair (NER) pathway. To elucidate the mechanism of DNA binding by Rad2/XPG, we solved crystal structures of the catalytic core of Rad2 in complex with a substrate. Rad2 utilizes three structural modules for recognition of the double-stranded portion of DNA substrate, particularly a Rad2-specific α-helix for binding the cleaved strand. The protein does not specifically recognize the single-stranded portion of the nucleic acid. Our data suggest that in contrast to related enzymes (FEN1 and EXO1), the Rad2 active site may be more accessible, which would create an exit route for substrates without a free 5' end.
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Affiliation(s)
- Michał Miętus
- Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, Warsaw 02-109, Poland
| | - Elżbieta Nowak
- Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, Warsaw 02-109, Poland
| | - Marcin Jaciuk
- Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, Warsaw 02-109, Poland
| | - Paweł Kustosz
- Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, Warsaw 02-109, Poland
| | - Justyna Studnicka
- Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, Warsaw 02-109, Poland
| | - Marcin Nowotny
- Laboratory of Protein Structure, International Institute of Molecular and Cell Biology, Warsaw 02-109, Poland
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29
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Mitsunobu H, Zhu B, Lee SJ, Tabor S, Richardson CC. Flap endonuclease of bacteriophage T7: Possible roles in RNA primer removal, recombination and host DNA breakdown. BACTERIOPHAGE 2014; 4:e28507. [PMID: 25105057 PMCID: PMC4124056 DOI: 10.4161/bact.28507] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Revised: 03/10/2014] [Accepted: 03/11/2014] [Indexed: 11/19/2022]
Abstract
Gene 6 protein of bacteriophage T7 has 5′-3′-exonuclease activity specific for duplex DNA. We have found that gene 6 protein also has flap endonuclease activity. The flap endonuclease activity is considerably weaker than the exonuclease activity. Unlike the human homolog of gene 6 protein, the flap endonuclease activity of gene 6 protein is dependent on the length of the 5′-flap. This dependency of activity on the length of the 5′-flap may result from the structured helical gateway region of gene 6 protein which differs from that of human flap endonuclease 1. The flap endonuclease activity provides a mechanism by which RNA-terminated Okazaki fragments, displaced by the lagging strand DNA polymerase, are processed. 3′-extensions generated during degradation of duplex DNA by the exonuclease activity of gene 6 protein are inhibitory to further degradation of the 5′-terminus by the exonuclease activity of gene 6 protein. The single-stranded DNA binding protein of T7 overcomes this inhibition.
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Affiliation(s)
- Hitoshi Mitsunobu
- The Department of Biological Chemistry and Molecular Pharmacology; Harvard Medical School; Boston, MA USA
| | - Bin Zhu
- The Department of Biological Chemistry and Molecular Pharmacology; Harvard Medical School; Boston, MA USA
| | - Seung-Joo Lee
- The Department of Biological Chemistry and Molecular Pharmacology; Harvard Medical School; Boston, MA USA
| | - Stanley Tabor
- The Department of Biological Chemistry and Molecular Pharmacology; Harvard Medical School; Boston, MA USA
| | - Charles C Richardson
- The Department of Biological Chemistry and Molecular Pharmacology; Harvard Medical School; Boston, MA USA
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30
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Dong Y, Liu D, Yang Z. A brief review of methods for terminal functionalization of DNA. Methods 2014; 67:116-22. [DOI: 10.1016/j.ymeth.2013.11.004] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2013] [Revised: 11/06/2013] [Accepted: 11/12/2013] [Indexed: 12/29/2022] Open
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31
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Craggs TD, Hutton RD, Brenlla A, White MF, Penedo JC. Single-molecule characterization of Fen1 and Fen1/PCNA complexes acting on flap substrates. Nucleic Acids Res 2014; 42:1857-72. [PMID: 24234453 PMCID: PMC3919604 DOI: 10.1093/nar/gkt1116] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2013] [Revised: 10/21/2013] [Accepted: 10/22/2013] [Indexed: 11/21/2022] Open
Abstract
Flap endonuclease 1 (Fen1) is a highly conserved structure-specific nuclease that catalyses a specific incision to remove 5' flaps in double-stranded DNA substrates. Fen1 plays an essential role in key cellular processes, such as DNA replication and repair, and mutations that compromise Fen1 expression levels or activity have severe health implications in humans. The nuclease activity of Fen1 and other FEN family members can be stimulated by processivity clamps such as proliferating cell nuclear antigen (PCNA); however, the exact mechanism of PCNA activation is currently unknown. Here, we have used a combination of ensemble and single-molecule Förster resonance energy transfer together with protein-induced fluorescence enhancement to uncouple and investigate the substrate recognition and catalytic steps of Fen1 and Fen1/PCNA complexes. We propose a model in which upon Fen1 binding, a highly dynamic substrate is bent and locked into an open flap conformation where specific Fen1/DNA interactions can be established. PCNA enhances Fen1 recognition of the DNA substrate by further promoting the open flap conformation in a step that may involve facilitated threading of the 5' ssDNA flap. Merging our data with existing crystallographic and molecular dynamics simulations we provide a solution-based model for the Fen1/PCNA/DNA ternary complex.
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Affiliation(s)
- Timothy D. Craggs
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife, KY16 9SS, UK and Biomedical Sciences Research Complex, University of St Andrews, St Andrews, Fife KY16 9SS, UK
| | - Richard D. Hutton
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife, KY16 9SS, UK and Biomedical Sciences Research Complex, University of St Andrews, St Andrews, Fife KY16 9SS, UK
| | - Alfonso Brenlla
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife, KY16 9SS, UK and Biomedical Sciences Research Complex, University of St Andrews, St Andrews, Fife KY16 9SS, UK
| | - Malcolm F. White
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife, KY16 9SS, UK and Biomedical Sciences Research Complex, University of St Andrews, St Andrews, Fife KY16 9SS, UK
| | - J. Carlos Penedo
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife, KY16 9SS, UK and Biomedical Sciences Research Complex, University of St Andrews, St Andrews, Fife KY16 9SS, UK
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32
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Mitsunobu H, Zhu B, Lee SJ, Tabor S, Richardson CC. Flap endonuclease activity of gene 6 exonuclease of bacteriophage T7. J Biol Chem 2014; 289:5860-75. [PMID: 24394415 DOI: 10.1074/jbc.m113.538611] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Flap endonucleases remove flap structures generated during DNA replication. Gene 6 protein of bacteriophage T7 is a 5'-3'-exonuclease specific for dsDNA. Here we show that gene 6 protein also possesses a structure-specific endonuclease activity similar to known flap endonucleases. The flap endonuclease activity is less active relative to its exonuclease activity. The major cleavage by the endonuclease activity occurs at a position one nucleotide into the duplex region adjacent to a dsDNA-ssDNA junction. The efficiency of cleavage of the flap decreases with increasing length of the 5'-overhang. A 3'-single-stranded tail arising from the same end of the duplex as the 5'-tail inhibits gene 6 protein flap endonuclease activity. The released flap is not degraded further, but the exonuclease activity then proceeds to hydrolyze the 5'-terminal strand of the duplex. T7 gene 2.5 single-stranded DNA-binding protein stimulates the exonuclease and also the endonuclease activity. This stimulation is attributed to a specific interaction between the two proteins because Escherichia coli single-stranded DNA binding protein does not produce this stimulatory effect. The ability of gene 6 protein to remove 5'-terminal overhangs as well as to remove nucleotides from the 5'-termini enables it to effectively process the 5'-termini of Okazaki fragments before they are ligated.
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Affiliation(s)
- Hitoshi Mitsunobu
- From the Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115
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33
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Patel N, Exell JC, Jardine E, Ombler B, Finger LD, Ciani B, Grasby JA. Proline scanning mutagenesis reveals a role for the flap endonuclease-1 helical cap in substrate unpairing. J Biol Chem 2013; 288:34239-34248. [PMID: 24126913 PMCID: PMC3837164 DOI: 10.1074/jbc.m113.509489] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2013] [Revised: 10/07/2013] [Indexed: 02/02/2023] Open
Abstract
The prototypical 5'-nuclease, flap endonuclease-1 (FEN1), catalyzes the essential removal of single-stranded flaps during DNA replication and repair. FEN1 hydrolyzes a specific phosphodiester bond one nucleotide into double-stranded DNA. This specificity arises from double nucleotide unpairing that places the scissile phosphate diester on active site divalent metal ions. Also related to FEN1 specificity is the helical arch, through which 5'-flaps, but not continuous DNAs, can thread. The arch contains basic residues (Lys-93 and Arg-100 in human FEN1 (hFEN1)) that are conserved by all 5'-nucleases and a cap region only present in enzymes that process DNAs with 5' termini. Proline mutations (L97P, L111P, L130P) were introduced into the hFEN1 helical arch. Each mutation was severely detrimental to reaction. However, all proteins were at least as stable as wild-type (WT) hFEN1 and bound substrate with comparable affinity. Moreover, all mutants produced complexes with 5'-biotinylated substrate that, when captured with streptavidin, were resistant to challenge with competitor DNA. Removal of both conserved basic residues (K93A/R100A) was no more detrimental to reaction than the single mutation R100A, but much less severe than L97P. The ability of protein-Ca(2+) to rearrange 2-aminopurine-containing substrates was monitored by low energy CD. Although L97P and K93A/R100A retained the ability to unpair substrates, the cap mutants L111P and L130P did not. Taken together, these data challenge current assumptions related to 5'-nuclease family mechanism. Conserved basic amino acids are not required for double nucleotide unpairing and appear to act cooperatively, whereas the helical cap plays an unexpected role in hFEN1-substrate rearrangement.
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Affiliation(s)
- Nikesh Patel
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom
| | - Jack C Exell
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom
| | - Emma Jardine
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom
| | - Ben Ombler
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom
| | - L David Finger
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom.
| | - Barbara Ciani
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom.
| | - Jane A Grasby
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom.
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34
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Anstey-Gilbert CS, Hemsworth GR, Flemming CS, Hodskinson MRG, Zhang J, Sedelnikova SE, Stillman TJ, Sayers JR, Artymiuk PJ. The structure of Escherichia coli ExoIX--implications for DNA binding and catalysis in flap endonucleases. Nucleic Acids Res 2013; 41:8357-67. [PMID: 23821668 PMCID: PMC3783174 DOI: 10.1093/nar/gkt591] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2012] [Revised: 06/10/2013] [Accepted: 06/12/2013] [Indexed: 11/13/2022] Open
Abstract
Escherichia coli Exonuclease IX (ExoIX), encoded by the xni gene, was the first identified member of a novel subfamily of ubiquitous flap endonucleases (FENs), which possess only one of the two catalytic metal-binding sites characteristic of other FENs. We have solved the first structure of one of these enzymes, that of ExoIX itself, at high resolution in DNA-bound and DNA-free forms. In the enzyme-DNA cocrystal, the single catalytic site binds two magnesium ions. The structures also reveal a binding site in the C-terminal domain where a potassium ion is directly coordinated by five main chain carbonyl groups, and we show this site is essential for DNA binding. This site resembles structurally and functionally the potassium sites in the human FEN1 and exonuclease 1 enzymes. Fluorescence anisotropy measurements and the crystal structures of the ExoIX:DNA complexes show that this potassium ion interacts directly with a phosphate diester in the substrate DNA.
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Affiliation(s)
- Christopher S. Anstey-Gilbert
- Department of Molecular Biology and Biotechnology, Krebs Institute, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK and Department of Infection & Immunity, Krebs Institute, University of Sheffield Medical School, Beech Hill Road, Sheffield S10 2RX, UK
| | - Glyn R. Hemsworth
- Department of Molecular Biology and Biotechnology, Krebs Institute, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK and Department of Infection & Immunity, Krebs Institute, University of Sheffield Medical School, Beech Hill Road, Sheffield S10 2RX, UK
| | - Claudia S. Flemming
- Department of Molecular Biology and Biotechnology, Krebs Institute, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK and Department of Infection & Immunity, Krebs Institute, University of Sheffield Medical School, Beech Hill Road, Sheffield S10 2RX, UK
| | - Michael R. G. Hodskinson
- Department of Molecular Biology and Biotechnology, Krebs Institute, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK and Department of Infection & Immunity, Krebs Institute, University of Sheffield Medical School, Beech Hill Road, Sheffield S10 2RX, UK
| | - Jing Zhang
- Department of Molecular Biology and Biotechnology, Krebs Institute, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK and Department of Infection & Immunity, Krebs Institute, University of Sheffield Medical School, Beech Hill Road, Sheffield S10 2RX, UK
| | - Svetlana E. Sedelnikova
- Department of Molecular Biology and Biotechnology, Krebs Institute, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK and Department of Infection & Immunity, Krebs Institute, University of Sheffield Medical School, Beech Hill Road, Sheffield S10 2RX, UK
| | - Timothy J. Stillman
- Department of Molecular Biology and Biotechnology, Krebs Institute, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK and Department of Infection & Immunity, Krebs Institute, University of Sheffield Medical School, Beech Hill Road, Sheffield S10 2RX, UK
| | - Jon R. Sayers
- Department of Molecular Biology and Biotechnology, Krebs Institute, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK and Department of Infection & Immunity, Krebs Institute, University of Sheffield Medical School, Beech Hill Road, Sheffield S10 2RX, UK
| | - Peter J. Artymiuk
- Department of Molecular Biology and Biotechnology, Krebs Institute, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK and Department of Infection & Immunity, Krebs Institute, University of Sheffield Medical School, Beech Hill Road, Sheffield S10 2RX, UK
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35
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Finger LD, Patel N, Beddows A, Ma L, Exell JC, Jardine E, Jones AC, Grasby JA. Observation of unpaired substrate DNA in the flap endonuclease-1 active site. Nucleic Acids Res 2013; 41:9839-47. [PMID: 23975198 PMCID: PMC3834815 DOI: 10.1093/nar/gkt737] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The structure- and strand-specific phosphodiesterase flap endonuclease-1 (FEN1), the prototypical 5′-nuclease, catalyzes the essential removal of 5′-single-stranded flaps during replication and repair. FEN1 achieves this by selectively catalyzing hydrolysis one nucleotide into the duplex region of substrates, always targeting the 5′-strand. This specificity is proposed to arise by unpairing the 5′-end of duplex to permit the scissile phosphate diester to contact catalytic divalent metal ions. Providing the first direct evidence for this, we detected changes induced by human FEN1 (hFEN1) in the low-energy CD spectra and fluorescence lifetimes of 2-aminopurine in substrates and products that were indicative of unpairing. Divalent metal ions were essential for unpairing. However, although 5′-nuclease superfamily-conserved active-site residues K93 and R100 were required to produce unpaired product, they were not necessary to unpair substrates. Nevertheless, a unique arrangement of protein residues around the unpaired DNA was detected only with wild-type protein, suggesting a cooperative assembly of active-site residues that may be triggered by unpaired DNA. The general principles of FEN1 strand and reaction-site selection, which depend on the ability of juxtaposed divalent metal ions to unpair the end of duplex DNA, may also apply more widely to other structure- and strand-specific nucleases.
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Affiliation(s)
- L David Finger
- Department of Chemistry, Centre for Chemical Biology, Krebs Institute, University of Sheffield, Sheffield, S3 7HF, UK and EaStCHEM School of Chemistry and Collaborative Optical Spectroscopy, Micromanipulation and Imaging Centre, The University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, UK
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36
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Sobhy MA, Joudeh LI, Huang X, Takahashi M, Hamdan SM. Sequential and multistep substrate interrogation provides the scaffold for specificity in human flap endonuclease 1. Cell Rep 2013; 3:1785-94. [PMID: 23746444 DOI: 10.1016/j.celrep.2013.05.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2012] [Revised: 04/03/2013] [Accepted: 05/02/2013] [Indexed: 11/30/2022] Open
Abstract
Human flap endonuclease 1 (FEN1), one of the structure-specific 5' nucleases, is integral in replication, repair, and recombination of cellular DNA. The 5' nucleases share significant unifying features yet cleave diverse substrates at similar positions relative to 5' end junctions. Using single-molecule Förster resonance energy transfer, we find a multistep mechanism that verifies all substrate features before inducing the intermediary-DNA bending step that is believed to unify 5' nuclease mechanisms. This is achieved by coordinating threading of the 5' flap of a nick junction into the conserved capped-helical gateway, overseeing the active site, and bending by binding at the base of the junction. We propose that this sequential and multistep substrate recognition process allows different 5' nucleases to recognize different substrates and restrict the induction of DNA bending to the last common step. Such mechanisms would also ensure the protection of DNA junctions from nonspecific bending and cleavage.
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Affiliation(s)
- Mohamed A Sobhy
- Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955, Saudi Arabia
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Abstract
5'-3' Exoribonucleases (XRNs) have important functions in RNA processing, RNA turnover and decay, RNA interference, RNA polymerase transcription, and other cellular processes. Their sequences share two highly conserved regions, CR1 and CR2. The cytoplasmic Xrn1 and the nuclear Xrn2/Rat1 are found in yeast and animals, and XRNs are found in most other eukaryotes. Crystal structures of Xrn1 and Rat1 have been reported recently, offering the first detailed information on these enzymes. The two conserved regions of XRNs form a single, large domain. CR1 has structural homology with the FEN superfamily of nucleases, while CR2 restricts access to the active site, ensuring that XRNs are exclusive exoribonucleases. The structure of Rai1, the protein partner of Rat1, revealed the presence of an active site, and further studies demonstrated that this activity is a novel mechanism for mRNA 5'-end capping quality surveillance.
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Affiliation(s)
- Jeong Ho Chang
- Department of Biological Sciences, Columbia University, New York, NY, USA
| | - Song Xiang
- Department of Biological Sciences, Columbia University, New York, NY, USA; Key Laboratory of Nutrition and Metabolism, Institute for Nutritional Sciences, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, PR China
| | - Liang Tong
- Department of Biological Sciences, Columbia University, New York, NY, USA.
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Gloor JW, Balakrishnan L, Campbell JL, Bambara RA. Biochemical analyses indicate that binding and cleavage specificities define the ordered processing of human Okazaki fragments by Dna2 and FEN1. Nucleic Acids Res 2012; 40:6774-86. [PMID: 22570407 PMCID: PMC3413157 DOI: 10.1093/nar/gks388] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In eukaryotic Okazaki fragment processing, the RNA primer is displaced into a single-stranded flap prior to removal. Evidence suggests that some flaps become long before they are cleaved, and that this cleavage involves the sequential action of two nucleases. Strand displacement characteristics of the polymerase show that a short gap precedes the flap during synthesis. Using biochemical techniques, binding and cleavage assays presented here indicate that when the flap is ∼30 nt long the nuclease Dna2 can bind with high affinity to the flap and downstream double strand and begin cleavage. When the polymerase idles or dissociates the Dna2 can reorient for additional contacts with the upstream primer region, allowing the nuclease to remain stably bound as the flap is further shortened. The DNA can then equilibrate to a double flap that can bind Dna2 and flap endonuclease (FEN1) simultaneously. When Dna2 shortens the flap even more, FEN1 can displace the Dna2 and cleave at the flap base to make a nick for ligation.
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Affiliation(s)
- Jason W Gloor
- Department of Microbiology and Immunology, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
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Finger LD, Atack JM, Tsutakawa S, Classen S, Tainer J, Grasby J, Shen B. The wonders of flap endonucleases: structure, function, mechanism and regulation. Subcell Biochem 2012; 62:301-26. [PMID: 22918592 PMCID: PMC3728657 DOI: 10.1007/978-94-007-4572-8_16] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Processing of Okazaki fragments to complete lagging strand DNA synthesis requires coordination among several proteins. RNA primers and DNA synthesised by DNA polymerase α are displaced by DNA polymerase δ to create bifurcated nucleic acid structures known as 5'-flaps. These 5'-flaps are removed by Flap Endonuclease 1 (FEN), a structure-specific nuclease whose divalent metal ion-dependent phosphodiesterase activity cleaves 5'-flaps with exquisite specificity. FENs are paradigms for the 5' nuclease superfamily, whose members perform a wide variety of roles in nucleic acid metabolism using a similar nuclease core domain that displays common biochemical properties and structural features. A detailed review of FEN structure is undertaken to show how DNA substrate recognition occurs and how FEN achieves cleavage at a single phosphate diester. A proposed double nucleotide unpairing trap (DoNUT) is discussed with regards to FEN and has relevance to the wider 5' nuclease superfamily. The homotrimeric proliferating cell nuclear antigen protein (PCNA) coordinates the actions of DNA polymerase, FEN and DNA ligase by facilitating the hand-off intermediates between each protein during Okazaki fragment maturation to maximise through-put and minimise consequences of intermediates being released into the wider cellular environment. FEN has numerous partner proteins that modulate and control its action during DNA replication and is also controlled by several post-translational modification events, all acting in concert to maintain precise and appropriate cleavage of Okazaki fragment intermediates during DNA replication.
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Affiliation(s)
- L. David Finger
- Department of Chemistry, Centre for Chemical Biology, Krebs Institute, University of Sheffield, Sheffield S3 7HF, UK
| | - John M. Atack
- Department of Chemistry, Centre for Chemical Biology, Krebs Institute, University of Sheffield, Sheffield S3 7HF, UK
| | - Susan Tsutakawa
- Life Sciences Division, Lawrence Berkeley National, Laboratory, Berkeley, CA 94720, USA
| | - Scott Classen
- Physical Biosciences Division, The Scripps Research, Institute, La Jolla, CA 92037, USA
| | - John Tainer
- Life Sciences Division, Lawrence Berkeley, National Laboratory, Berkeley, CA 94720, USA, Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037, USA, Skaggs Institute for Chemical Biology, La Jolla, CA 92037, USA
| | - Jane Grasby
- Department of Chemistry, Centre for Chemical Biology, Krebs Institute, University of Sheffield, Sheffield S3 7HF, UK
| | - Binghui Shen
- Division of Radiation Biology, City of Hope National Medical Center and Beckman Research Institute, Duarte, CA 91010, USA, College of Life Sciences, Zhejiang University, Hangzhou 310058, China
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