1
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Alnajjar K, Wang K, Alvarado-Cruz I, Chavira C, Negahbani A, Nakhjiri M, Minard C, Garcia-Barboza B, Kashemirov BA, McKenna CE, Goodman MF, Sweasy JB. Modifying the Basicity of the dNTP Leaving Group Modulates Precatalytic Conformational Changes of DNA Polymerase β. Biochemistry 2024; 63:1412-1422. [PMID: 38780930 PMCID: PMC11155676 DOI: 10.1021/acs.biochem.4c00065] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2024] [Revised: 05/15/2024] [Accepted: 05/16/2024] [Indexed: 05/25/2024]
Abstract
The catalytic function of DNA polymerase β (pol β) fulfills the gap-filling requirement of the base excision DNA repair pathway by incorporating a single nucleotide into a gapped DNA substrate resulting from the removal of damaged DNA bases. Most importantly, pol β can select the correct nucleotide from a pool of similarly structured nucleotides to incorporate into DNA in order to prevent the accumulation of mutations in the genome. Pol β is likely to employ various mechanisms for substrate selection. Here, we use dCTP analogues that have been modified at the β,γ-bridging group of the triphosphate moiety to monitor the effect of leaving group basicity of the incoming nucleotide on precatalytic conformational changes, which are important for catalysis and selectivity. It has been previously shown that there is a linear free energy relationship between leaving group pKa and the chemical transition state. Our results indicate that there is a similar relationship with the rate of a precatalytic conformational change, specifically, the closing of the fingers subdomain of pol β. In addition, by utilizing analogue β,γ-CHX stereoisomers, we identified that the orientation of the β,γ-bridging group relative to R183 is important for the rate of fingers closing, which directly influences chemistry.
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Affiliation(s)
- Khadijeh
S. Alnajjar
- Department
of Cellular and Molecular Medicine, University
of Arizona Cancer Center, University of Arizona, Tucson, Arizona 85724, United States
| | - Katarina Wang
- Therapeutic
Radiology Department, Yale University, New Haven, Connecticut 06520, United States
| | - Isabel Alvarado-Cruz
- Department
of Cellular and Molecular Medicine, University
of Arizona Cancer Center, University of Arizona, Tucson, Arizona 85724, United States
| | - Cristian Chavira
- Fred
and Pamela Buffett Cancer Center and Eppley Institute for Cancer Research, Omaha, Nebraska 68198, United States
- Department
of Cellular and Molecular Medicine, University
of Arizona Cancer Center, University of Arizona, Tucson, Arizona 85724, United States
| | - Amirsoheil Negahbani
- Department
of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Maryam Nakhjiri
- Department
of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Corinne Minard
- Department
of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Beatriz Garcia-Barboza
- Department
of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Boris A. Kashemirov
- Department
of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Charles E. McKenna
- Department
of Chemistry, University of Southern California, Los Angeles, California 90089, United States
| | - Myron F. Goodman
- Department
of Chemistry, University of Southern California, Los Angeles, California 90089, United States
- Department
of Biological Sciences, University of Southern
California, Los Angeles, California 90089, United States
| | - Joann B. Sweasy
- Fred
and Pamela Buffett Cancer Center and Eppley Institute for Cancer Research, Omaha, Nebraska 68198, United States
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2
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Arslan S, Garcia FJ, Guo M, Kellinger MW, Kruglyak S, LeVieux JA, Mah AH, Wang H, Zhao J, Zhou C, Altomare A, Bailey J, Byrne MB, Chang C, Chen SX, Cho B, Dennler CN, Dien VT, Fuller D, Kelley R, Khandan O, Klein MG, Kim M, Lajoie BR, Lin B, Liu Y, Lopez T, Mains PT, Price AD, Robertson SR, Taylor-Weiner H, Tippana R, Tomaney AB, Zhang S, Abtahi M, Ambroso MR, Bajari R, Bellizzi AM, Benitez CB, Berard DR, Berti L, Blease KN, Blum AP, Boddicker AM, Bondar L, Brown C, Bui CA, Calleja-Aguirre J, Cappa K, Chan J, Chang VW, Charov K, Chen X, Constandse RM, Damron W, Dawood M, DeBuono N, Dimalanta JD, Edoli L, Elango K, Faustino N, Feng C, Ferrari M, Frankie K, Fries A, Galloway A, Gavrila V, Gemmen GJ, Ghadiali J, Ghorbani A, Goddard LA, Guetter AR, Hendricks GL, Hentschel J, Honigfort DJ, Hsieh YT, Hwang Fu YH, Im SK, Jin C, Kabu S, Kincade DE, Levy S, Li Y, Liang VK, Light WH, Lipsher JB, Liu TL, Long G, Ma R, Mailloux JM, Mandla KA, Martinez AR, Mass M, McKean DT, Meron M, Miller EA, Moh CS, Moore RK, Moreno J, Neysmith JM, Niman CS, Nunez JM, Ojeda MT, Ortiz SE, Owens J, Piland G, Proctor DJ, Purba JB, Ray M, Rong D, Saade VM, Saha S, Tomas GS, Scheidler N, Sirajudeen LH, Snow S, Stengel G, Stinson R, Stone MJ, Sundseth KJ, Thai E, Thompson CJ, Tjioe M, Trejo CL, Trieger G, Truong DN, Tse B, Voiles B, Vuong H, Wong JC, Wu CT, Yu H, Yu Y, Yu M, Zhang X, Zhao D, Zheng G, He M, Previte M. Sequencing by avidity enables high accuracy with low reagent consumption. Nat Biotechnol 2024; 42:132-138. [PMID: 37231263 DOI: 10.1038/s41587-023-01750-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2022] [Accepted: 03/15/2023] [Indexed: 05/27/2023]
Abstract
We present avidity sequencing, a sequencing chemistry that separately optimizes the processes of stepping along a DNA template and that of identifying each nucleotide within the template. Nucleotide identification uses multivalent nucleotide ligands on dye-labeled cores to form polymerase-polymer-nucleotide complexes bound to clonal copies of DNA targets. These polymer-nucleotide substrates, termed avidites, decrease the required concentration of reporting nucleotides from micromolar to nanomolar and yield negligible dissociation rates. Avidity sequencing achieves high accuracy, with 96.2% and 85.4% of base calls having an average of one error per 1,000 and 10,000 base pairs, respectively. We show that the average error rate of avidity sequencing remained stable following a long homopolymer.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | - Bill Lin
- Element Biosciences, San Diego, CA, USA
| | - Yu Liu
- Element Biosciences, San Diego, CA, USA
| | | | | | | | | | | | | | | | - Su Zhang
- Element Biosciences, San Diego, CA, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | - Xiyi Chen
- Element Biosciences, San Diego, CA, USA
| | | | | | | | | | | | | | | | | | - Chao Feng
- Element Biosciences, San Diego, CA, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | - Yu Li
- Element Biosciences, San Diego, CA, USA
| | | | | | | | | | | | - Rui Ma
- Element Biosciences, San Diego, CA, USA
| | | | | | | | - Max Mass
- Element Biosciences, San Diego, CA, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | - Ben Tse
- Element Biosciences, San Diego, CA, USA
| | | | | | | | | | - Hua Yu
- Element Biosciences, San Diego, CA, USA
| | | | - Ming Yu
- Element Biosciences, San Diego, CA, USA
| | - Xi Zhang
- Element Biosciences, San Diego, CA, USA
| | - Da Zhao
- Element Biosciences, San Diego, CA, USA
| | | | - Molly He
- Element Biosciences, San Diego, CA, USA
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3
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Xi G, Wu L, Meng H, Li F, Ge Q, Tu J. Discriminating Single Nucleotide Variations in Solid-State Nanopores by Evaluating the Combination Efficiency between DNA Polymerase and Its Substrate. J Phys Chem B 2023. [PMID: 37197998 DOI: 10.1021/acs.jpcb.3c01912] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
A single nucleotide variant present between two otherwise identical nucleic acids will have unexpected functional consequences frequently. Here, a neoteric single nucleotide variation (SNV) detection assay that integrates two complementary nanotechnology systems, nanoassembly technology and an ingenious nanopore biosensing platform, has been applied to this research. Specifically, we set up a detection system to reflect the binding efficiency of the polymerase and nanoprobe through the difference of nanopore signals and then explore the effect of base mutation at the binding site. In addition, machine learning based on support vector machines is used to automatically classify characteristic events mapped by nanopore signals. Our system reliably discriminates single nucleotide variants at binding sites, even possessing the recognition among transitions, transversions, and hypoxanthine (base I). Our results demonstrate the potential of solid-state nanopore detection for SNV and provide some ideas for expanding solid-state nanopore detection platforms.
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Affiliation(s)
- Guohao Xi
- State Key Laboratory of Digital Medical Engineering, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China
| | - Lingzhi Wu
- School of Geographic and Biologic Information, Nanjing University of Posts and Telecommunications, Nanjing 210046, China
| | - Hao Meng
- State Key Laboratory of Digital Medical Engineering, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China
| | - Fuyao Li
- State Key Laboratory of Digital Medical Engineering, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China
| | - Qinyu Ge
- State Key Laboratory of Digital Medical Engineering, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China
| | - Jing Tu
- State Key Laboratory of Digital Medical Engineering, School of Biological Science and Medical Engineering, Southeast University, Nanjing 210096, China
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4
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Bubenik M, Mader P, Mochirian P, Vallée F, Clark J, Truchon JF, Perryman AL, Pau V, Kurinov I, Zahn KE, Leclaire ME, Papp R, Mathieu MC, Hamel M, Duffy NM, Godbout C, Casas-Selves M, Falgueyret JP, Baruah PS, Nicolas O, Stocco R, Poirier H, Martino G, Fortin AB, Roulston A, Chefson A, Dorich S, St-Onge M, Patel P, Pellerin C, Ciblat S, Pinter T, Barabé F, Bakkouri ME, Parikh P, Gervais C, Sfeir A, Mamane Y, Morris SJ, Black WC, Sicheri F, Gallant M. Identification of RP-6685, an Orally Bioavailable Compound that Inhibits the DNA Polymerase Activity of Polθ. J Med Chem 2022; 65:13198-13215. [PMID: 36126059 PMCID: PMC9942948 DOI: 10.1021/acs.jmedchem.2c00998] [Citation(s) in RCA: 25] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
DNA polymerase theta (Polθ) is an attractive synthetic lethal target for drug discovery, predicted to be efficacious against breast and ovarian cancers harboring BRCA-mutant alleles. Here, we describe our hit-to-lead efforts in search of a selective inhibitor of human Polθ (encoded by POLQ). A high-throughput screening campaign of 350,000 compounds identified an 11 micromolar hit, giving rise to the N2-substituted fused pyrazolo series, which was validated by biophysical methods. Structure-based drug design efforts along with optimization of cellular potency and ADME ultimately led to the identification of RP-6685: a potent, selective, and orally bioavailable Polθ inhibitor that showed in vivo efficacy in an HCT116 BRCA2-/- mouse tumor xenograft model.
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Affiliation(s)
- Monica Bubenik
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Pavel Mader
- Lunenfeld-Tanenbaum Research Institute, Sinai Health System, Toronto, Ontario, M5G 1X5, Canada
| | - Philippe Mochirian
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Fréderic Vallée
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Jillian Clark
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Jean-François Truchon
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Alexander L. Perryman
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Victor Pau
- Lunenfeld-Tanenbaum Research Institute, Sinai Health System, Toronto, Ontario, M5G 1X5, Canada
| | - Igor Kurinov
- Department of Chemistry and Chemical Biology, Cornell University, NE-CAT, Argonne, Illinois 60439, USA
| | - Karl E. Zahn
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Marie-Eve Leclaire
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Robert Papp
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Marie-Claude Mathieu
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Martine Hamel
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Nicole M. Duffy
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Claude Godbout
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Matias Casas-Selves
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Jean-Pierre Falgueyret
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Prasamit S. Baruah
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Olivier Nicolas
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Rino Stocco
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Hugo Poirier
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Giovanni Martino
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | | | - Anne Roulston
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Amandine Chefson
- Ventus Therapeutics 7150 Frederick-Banting suite 200, Montréal, Québec, H4S 2A1, Canada
| | - Stéphane Dorich
- Ventus Therapeutics 7150 Frederick-Banting suite 200, Montréal, Québec, H4S 2A1, Canada
| | - Miguel St-Onge
- Ventus Therapeutics 7150 Frederick-Banting suite 200, Montréal, Québec, H4S 2A1, Canada
| | - Purvish Patel
- Ventus Therapeutics 7150 Frederick-Banting suite 200, Montréal, Québec, H4S 2A1, Canada
| | - Charles Pellerin
- Ventus Therapeutics 7150 Frederick-Banting suite 200, Montréal, Québec, H4S 2A1, Canada
| | - Stéphane Ciblat
- Ventus Therapeutics 7150 Frederick-Banting suite 200, Montréal, Québec, H4S 2A1, Canada
- Paraza Pharma Inc., 2525 Ave. Marie Curie, Montréal, Québec, H4S 1Z9, Canada
| | - Thomas Pinter
- Paraza Pharma Inc., 2525 Ave. Marie Curie, Montréal, Québec, H4S 1Z9, Canada
| | - Francis Barabé
- Paraza Pharma Inc., 2525 Ave. Marie Curie, Montréal, Québec, H4S 1Z9, Canada
| | - Majida El Bakkouri
- Paraza Pharma Inc., 2525 Ave. Marie Curie, Montréal, Québec, H4S 1Z9, Canada
- National Research Council of Canada, 6100 Royalmount Ave, Montréal, Québec, H4P 2R2, Canada
| | - Paranjay Parikh
- Piramal Pharma Ltd., Plot No. 18, Village Matoda, Taluka: Sanand, Ahmedabad-382213, Gujarat, India
| | - Christian Gervais
- National Research Council of Canada, 6100 Royalmount Ave, Montréal, Québec, H4P 2R2, Canada
| | - Agnel Sfeir
- Molecular Biology Program, Sloan Kettering Institute, MSKCC, 430 E 67th Street, New York, NY 10065, USA
| | - Yael Mamane
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Stephen J. Morris
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - W. Cameron Black
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
| | - Frank Sicheri
- Lunenfeld-Tanenbaum Research Institute, Sinai Health System, Toronto, Ontario, M5G 1X5, Canada
| | - Michel Gallant
- Repare Therapeutics, 7171 Frederick-Banting, Building 2, H4S 1Z9, Montréal, Québec, Canada
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5
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Evans GW, Craggs T, Kapanidis AN. The Rate-limiting Step of DNA Synthesis by DNA Polymerase Occurs in the Fingers-closed Conformation. J Mol Biol 2022; 434:167410. [PMID: 34929202 PMCID: PMC8783057 DOI: 10.1016/j.jmb.2021.167410] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Revised: 11/22/2021] [Accepted: 12/12/2021] [Indexed: 12/03/2022]
Abstract
DNA polymerases maintain genomic integrity by copying DNA with high fidelity, part of which relies on the polymerase fingers opening-closing transition, a series of conformational changes during the DNA synthesis reaction cycle. Fingers opening and closing has been challenging to study, mainly due to the need to synchronise molecular ensembles. We previously studied fingers opening-closing on single polymerase-DNA complexes using single-molecule FRET; however, our work was limited to pre-chemistry reaction steps. Here, we advance our analysis to extensible substrates, and observe DNA polymerase (Pol) conformational changes across the entire DNA polymerisation reaction in real-time, gaining direct access to an elusive post-chemistry step rate-limiting for DNA synthesis. Our results showed that Pol adopts the fingers-closed conformation during polymerisation, and that the post-chemistry rate-limiting step occurs in the fingers-closed conformation. We found that fingers-opening in the Pol-DNA binary complex in the absence of polymerisation is slow (∼5.3 s-1), and comparable to the rate of fingers-opening after polymerisation (3.4 s-1); this indicates that the fingers-opening step itself could be largely responsible for the slow post-chemistry step, with the residual rate potentially accounted for by pyrophosphase release. We also observed that DNA chain-termination of the 3' end of the primer increases substantially the rate of fingers-opening in the Pol-DNA binary complex (5.3 → 29 s-1), demonstrating that the 3'-OH residue is important for the kinetics of fingers conformational changes. Our observations offer mechanistic insight and tools to offer mechanistic insight for all nucleic acid polymerases.
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Affiliation(s)
- Geraint W Evans
- Department of Physics and Biological Physics Research Group, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom. https://twitter.com/geraintwe
| | - Timothy Craggs
- Department of Physics and Biological Physics Research Group, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom; Sheffield Institute for Nucleic Acids, Department of Chemistry, University of Sheffield, Brook Hill, Sheffield S3 7HF, United Kingdom. https://twitter.com/Craggs_Lab
| | - Achillefs N Kapanidis
- Department of Physics and Biological Physics Research Group, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom.
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6
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DNA Polymerase-Parental DNA Interaction Is Essential for Helicase-Polymerase Coupling during Bacteriophage T7 DNA Replication. Int J Mol Sci 2022; 23:ijms23031342. [PMID: 35163266 PMCID: PMC8835902 DOI: 10.3390/ijms23031342] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 01/19/2022] [Accepted: 01/22/2022] [Indexed: 11/17/2022] Open
Abstract
DNA helicase and polymerase work cooperatively at the replication fork to perform leading-strand DNA synthesis. It was believed that the helicase migrates to the forefront of the replication fork where it unwinds the duplex to provide templates for DNA polymerases. However, the molecular basis of the helicase-polymerase coupling is not fully understood. The recently elucidated T7 replisome structure suggests that the helicase and polymerase sandwich parental DNA and each enzyme pulls a daughter strand in opposite directions. Interestingly, the T7 polymerase, but not the helicase, carries the parental DNA with a positively charged cleft and stacks at the fork opening using a β-hairpin loop. Here, we created and characterized T7 polymerases each with a perturbed β-hairpin loop and positively charged cleft. Mutations on both structural elements significantly reduced the strand-displacement synthesis by T7 polymerase but had only a minor effect on DNA synthesis performed against a linear DNA substrate. Moreover, the aforementioned mutations eliminated synergistic helicase-polymerase binding and unwinding at the DNA fork and processive fork progressions. Thus, our data suggested that T7 polymerase plays a dominant role in helicase-polymerase coupling and replisome progression.
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7
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Li QS, Shu YG, Ou-Yang ZC, Li M. Kinetic assays of DNA polymerase fidelity: A theoretical perspective beyond Michaelis-Menten kinetics. Phys Rev E 2021; 104:014408. [PMID: 34412358 DOI: 10.1103/physreve.104.014408] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2020] [Accepted: 06/23/2021] [Indexed: 11/07/2022]
Abstract
The high fidelity of DNA polymerase (DNAP) is critical for the faithful replication of DNA. There are several quantitative approaches to measure DNAP fidelity. Directly counting the error frequency in the replication products gives the true fidelity but it turns out very hard to implement in practice. Two biochemical kinetic approaches, the steady-state assay and the transient-state assay, were then suggested and widely adopted. In these assays, the error frequency is indirectly estimated by using kinetic theories combined with the measured apparent kinetic rates. However, whether it is equivalent to the true fidelity has never been clarified theoretically, and in particular there are different strategies using these assays to quantify the proofreading efficiency of DNAP but often lead to inconsistent results. In this paper, we make a comprehensive examination on the theoretical foundation of the two kinetic assays, based on the theory of DNAP fidelity recently proposed by us. Our studies show that while the conventional kinetic assays are generally valid to quantify the discrimination efficiency of DNAP, they are valid to quantify the proofreading efficiency of DNAP only when the kinetic parameters satisfy some constraints which will be given explicitly in this paper. These results may inspire more carefully-designed experiments to quantify DNAP fidelity.
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Affiliation(s)
- Qiu-Shi Li
- School of Physical Science, University of Chinese Academy of Sciences, No. 19(A) Yuquan Road, Shijingshan District, Beijing 101400, People's Republic of China
| | - Yao-Gen Shu
- Wenzhou Institute, University of Chinese Academy of Sciences, No 1, Jinlian Road, Longwan District, Wenzhou, Zhejiang 325000, People's Republic of China
| | - Zhong-Can Ou-Yang
- Institute of Theoretical Physics, Chinese Academy of Sciences, Zhong Guan Cun East Street 55, P. O. Box 2735, Beijing 100190, People's Republic of China
| | - Ming Li
- School of Physical Science, University of Chinese Academy of Sciences, No. 19(A) Yuquan Road, Shijingshan District, Beijing 101400, People's Republic of China
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8
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Passow KT, Antczak NM, Sturla SJ, Harki DA. Synthesis of 4-Cyanoindole Nucleosides, 4-Cyanoindole-2'-Deoxyribonucleoside-5'-Triphosphate (4CIN-TP), and Enzymatic Incorporation of 4CIN-TP into DNA. ACTA ACUST UNITED AC 2021; 80:e101. [PMID: 31909864 DOI: 10.1002/cpnc.101] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
4-Cyanoindole-2'-deoxyribonucleoside (4CIN) is a fluorescent isomorphic nucleoside analogue with superior spectroscopic properties in terms of Stokes shift and quantum yield in comparison to the widely utilized isomorphic nucleoside analogue, 2-aminopurine-2'-deoxyribonucleoside (2APN). Notably, when inserted into single- or double-stranded DNA, 4CIN experiences substantially less in-strand fluorescence quenching compared to 2APN. Given the utility of these properties for a spectrum of research applications involving oligonucleotides and oligonucleotide-protein interactions (e.g., enzymatic processes, DNA hybridization, DNA damage), we envision that additional reagents based on 4-cyanoindole nucleosides may be widely utilized. This protocol expands on the previously published synthesis of 4CIN to include synthetic routes to both 4-cyanoindole-ribonucleoside (4CINr) and 4-cyanoindole-2'-deoxyribonucleoside-5'-triphosphate (4CIN-TP), as well as a method for the enzymatic incorporation of 4CIN-TP into DNA by a polymerase. These methods are anticipated to further enable the utilization of 4CIN in diverse applications involving DNA and RNA oligonucleotides. © 2020 by John Wiley & Sons, Inc. Basic Protocol 1: Synthesis of 4-cyanoindole-2'-deoxyribonucleoside (4CIN) and 4CIN phosphoramidite 4 Basic Protocol 2: Synthesis of 4-cyanoindole-ribonucleoside (4CINr) Basic Protocol 3: Synthesis of 4-cyanoindole-2'-deoxyribonucleoside-5'-triphosphate (4CIN-TP) Basic Protocol 4: Steady state incorporation kinetics of 2AP-TP and 4CIN-TP by a DNA polymerase.
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Affiliation(s)
- Kellan T Passow
- Department of Medicinal Chemistry, University of Minnesota, Minneapolis, Minnesota
| | - Nicole M Antczak
- Department of Health Sciences and Technology, ETH Zurich, Zurich, Switzerland
| | - Shana J Sturla
- Department of Health Sciences and Technology, ETH Zurich, Zurich, Switzerland
| | - Daniel A Harki
- Department of Medicinal Chemistry, University of Minnesota, Minneapolis, Minnesota
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9
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Bocanegra R, Ismael Plaza GA, Pulido CR, Ibarra B. DNA replication machinery: Insights from in vitro single-molecule approaches. Comput Struct Biotechnol J 2021; 19:2057-2069. [PMID: 33995902 PMCID: PMC8085672 DOI: 10.1016/j.csbj.2021.04.013] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2021] [Revised: 04/03/2021] [Accepted: 04/03/2021] [Indexed: 11/16/2022] Open
Abstract
The replisome is the multiprotein molecular machinery that replicates DNA. The replisome components work in precise coordination to unwind the double helix of the DNA and replicate the two strands simultaneously. The study of DNA replication using in vitro single-molecule approaches provides a novel quantitative understanding of the dynamics and mechanical principles that govern the operation of the replisome and its components. ‘Classical’ ensemble-averaging methods cannot obtain this information. Here we describe the main findings obtained with in vitro single-molecule methods on the performance of individual replisome components and reconstituted prokaryotic and eukaryotic replisomes. The emerging picture from these studies is that of stochastic, versatile and highly dynamic replisome machinery in which transient protein-protein and protein-DNA associations are responsible for robust DNA replication.
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Affiliation(s)
- Rebeca Bocanegra
- IMDEA Nanociencia, Faraday 9, Campus Cantoblanco, 28049 Madrid, Spain
| | - G A Ismael Plaza
- IMDEA Nanociencia, Faraday 9, Campus Cantoblanco, 28049 Madrid, Spain
| | - Carlos R Pulido
- IMDEA Nanociencia, Faraday 9, Campus Cantoblanco, 28049 Madrid, Spain
| | - Borja Ibarra
- IMDEA Nanociencia, Faraday 9, Campus Cantoblanco, 28049 Madrid, Spain
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10
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Javier GM. Computational insight into the selective allosteric inhibition for PTP1B versus TCPTP: a molecular modelling study. J Biomol Struct Dyn 2020; 39:5399-5410. [PMID: 32643532 DOI: 10.1080/07391102.2020.1790421] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
All over the world, diabetes mellitus type 2 has spread as a problematic pandemic. Despite currently available treatments, approved drugs still show undesirable side effects and loss of efficacy or target symptoms instead of causes. Protein tyrosine phosphatase 1B (PTP1B), since its discovery, has emerged as a very promising target against this disease. Although the information regarding the enzyme is immense, little is known about the selectivity between this enzyme and its closest homologue, lymphocyte T tyrosine phosphatase (TCPTP), which is responsible for complicated side effects. In this study, on the basis of different computational approaches, we are able to highlight the importance of a phenylalanine residue located in PTP1B, but not in TCPTP, as a crucial hotspot that causes selectivity and stability for the whole ligand bound system. These results not only allow to explain the selectivity determinants of PTP1B but also provide a useful guide for the design of new allosteric inhibitors. Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Garcia-Marin Javier
- Facultad de Farmacia, Departamento de Química Orgánica y Química Inorgánica, Universidad de Alcalá, Alcalá de Henares, Spain.,Instituto Ramón y Cajal de Investigación Sanitaria (IRYCIS), Madrid, Spain.,Facultad de Farmacia, Instituto de Investigación Química Andrés M. del Río, Universidad de Alcalá, Alcalá de Henares, Spain
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11
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Alnajjar KS, Krylov IS, Negahbani A, Haratipour P, Kashemirov BA, Huang J, Mahmoud M, McKenna CE, Goodman MF, Sweasy JB. A pre-catalytic non-covalent step governs DNA polymerase β fidelity. Nucleic Acids Res 2020; 47:11839-11849. [PMID: 31732732 PMCID: PMC7145665 DOI: 10.1093/nar/gkz1076] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2019] [Revised: 10/23/2019] [Accepted: 11/07/2019] [Indexed: 12/27/2022] Open
Abstract
DNA polymerase β (pol β) selects the correct deoxyribonucleoside triphosphate for incorporation into the DNA polymer. Mistakes made by pol β lead to mutations, some of which occur within specific sequence contexts to generate mutation hotspots. The adenomatous polyposis coli (APC) gene is mutated within specific sequence contexts in colorectal carcinomas but the underlying mechanism is not fully understood. In previous work, we demonstrated that a somatic colon cancer variant of pol β, K289M, misincorporates deoxynucleotides at significantly increased frequencies over wild-type pol β within a mutation hotspot that is present several times within the APC gene. Kinetic studies provide evidence that the rate-determining step of pol β catalysis is phosphodiester bond formation and suggest that substrate selection is governed at this step. Remarkably, we show that, unlike WT, a pre-catalytic step in the K289M pol β kinetic pathway becomes slower than phosphodiester bond formation with the APC DNA sequence but not with a different DNA substrate. Based on our studies, we propose that pre-catalytic conformational changes are of critical importance for DNA polymerase fidelity within specific DNA sequence contexts.
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Affiliation(s)
- Khadijeh S Alnajjar
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85724, USA
| | - Ivan S Krylov
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
| | - Amirsoheil Negahbani
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
| | - Pouya Haratipour
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
| | - Boris A Kashemirov
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
| | - Ji Huang
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85724, USA
| | - Mariam Mahmoud
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85724, USA
| | - Charles E McKenna
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA
| | - Myron F Goodman
- Department of Chemistry, University of Southern California, Los Angeles, CA 90089, USA.,Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089, USA
| | - Joann B Sweasy
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ 85724, USA.,University of Arizona Cancer Center, Tucson, AZ 85724, USA
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12
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Johnson MK, Kottur J, Nair DT. A polar filter in DNA polymerases prevents ribonucleotide incorporation. Nucleic Acids Res 2020; 47:10693-10705. [PMID: 31544946 PMCID: PMC6846668 DOI: 10.1093/nar/gkz792] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2019] [Revised: 09/02/2019] [Accepted: 09/09/2019] [Indexed: 12/17/2022] Open
Abstract
The presence of ribonucleotides in DNA can lead to genomic instability and cellular lethality. To prevent adventitious rNTP incorporation, the majority of the DNA polymerases (dPols) possess a steric filter. The dPol named MsDpo4 (Mycobacterium smegmatis) naturally lacks this steric filter and hence is capable of rNTP addition. The introduction of the steric filter in MsDpo4 did not result in complete abrogation of the ability of this enzyme to incorporate ribonucleotides. In comparison, DNA polymerase IV (PolIV) from Escherichia coli exhibited stringent selection for deoxyribonucleotides. A comparison of MsDpo4 and PolIV led to the discovery of an additional polar filter responsible for sugar selectivity. Thr43 represents the filter in PolIV and this residue forms interactions with the incoming nucleotide to draw it closer to the enzyme surface. As a result, the 2’-OH in rNTPs will clash with the enzyme surface, and therefore ribonucleotides cannot be accommodated in the active site in a conformation compatible with productive catalysis. The substitution of the equivalent residue in MsDpo4–Cys47, with Thr led to a drastic reduction in the ability of the mycobacterial enzyme to incorporate rNTPs. Overall, our studies evince that the polar filter serves to prevent ribonucleotide incorporation by dPols.
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Affiliation(s)
- Mary K Johnson
- Regional Centre for Biotechnology, NCR Biotech Science Cluster, 3rd Milestone, Faridabad-Gurgaon Expressway, Faridabad 121001, India.,National Centre for Biological Sciences, Tata Institute of Fundamental Research, GKVK Campus, Bangalore 560065, India
| | - Jithesh Kottur
- Regional Centre for Biotechnology, NCR Biotech Science Cluster, 3rd Milestone, Faridabad-Gurgaon Expressway, Faridabad 121001, India
| | - Deepak T Nair
- Regional Centre for Biotechnology, NCR Biotech Science Cluster, 3rd Milestone, Faridabad-Gurgaon Expressway, Faridabad 121001, India
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13
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Liptak C, Mahmoud MM, Eckenroth BE, Moreno MV, East K, Alnajjar KS, Huang J, Towle-Weicksel JB, Doublié S, Loria J, Sweasy JB. I260Q DNA polymerase β highlights precatalytic conformational rearrangements critical for fidelity. Nucleic Acids Res 2019; 46:10740-10756. [PMID: 30239932 PMCID: PMC6237750 DOI: 10.1093/nar/gky825] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Accepted: 09/05/2018] [Indexed: 11/14/2022] Open
Abstract
DNA polymerase β (pol β) fills single nucleotide gaps in DNA during base excision repair and non-homologous end-joining. Pol β must select the correct nucleotide from among a pool of four nucleotides with similar structures and properties in order to maintain genomic stability during DNA repair. Here, we use a combination of X-ray crystallography, fluorescence resonance energy transfer and nuclear magnetic resonance to show that pol β‘s ability to access the appropriate conformations both before and upon binding to nucleotide substrates is integral to its fidelity. Importantly, we also demonstrate that the inability of the I260Q mutator variant of pol β to properly navigate this conformational landscape results in error-prone DNA synthesis. Our work reveals that precatalytic conformational rearrangements themselves are an important underlying mechanism of substrate selection by DNA pol β.
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Affiliation(s)
- Cary Liptak
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
| | - Mariam M Mahmoud
- Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Brian E Eckenroth
- Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, VT 05405, USA
| | - Marcus V Moreno
- Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, VT 05405, USA
| | - Kyle East
- Department of Chemistry, Yale University, New Haven, CT 06520, USA
| | - Khadijeh S Alnajjar
- Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Ji Huang
- Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Jamie B Towle-Weicksel
- Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Sylvie Doublié
- Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, VT 05405, USA
| | - J Patrick Loria
- Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520, USA
- Department of Chemistry, Yale University, New Haven, CT 06520, USA
- To whom correspondence should be addressed. Tel: +203 436 2518; Fax: +203 436 6144; . Correspondence may also be addressed to Joann B. Sweasy. Tel: +203 737 2626; Fax: +203 785 6309;
| | - Joann B Sweasy
- Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520, USA
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06520, USA
- To whom correspondence should be addressed. Tel: +203 436 2518; Fax: +203 436 6144; . Correspondence may also be addressed to Joann B. Sweasy. Tel: +203 737 2626; Fax: +203 785 6309;
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14
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Affiliation(s)
- Vito Genna
- Laboratory of Molecular Modeling and Drug Discovery, Istituto Italiano di Tecnologia, Via Morego 30, 16163, Genoa, Italy
| | - Elisa Donati
- Laboratory of Molecular Modeling and Drug Discovery, Istituto Italiano di Tecnologia, Via Morego 30, 16163, Genoa, Italy
| | - Marco De Vivo
- Laboratory of Molecular Modeling and Drug Discovery, Istituto Italiano di Tecnologia, Via Morego 30, 16163, Genoa, Italy
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15
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Zhao Q, Yang W, Qin T, Huang Z. Moonlighting Phosphatase Activity of Klenow DNA Polymerase in the Presence of RNA. Biochemistry 2018; 57:5127-5135. [PMID: 30059615 DOI: 10.1021/acs.biochem.8b00688] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
RNA is a key player in the cellular central dogma, including RNA transcription and protein synthesis. However, it is unknown whether RNA can directly interfere with DNA synthesis. Recently, we have found in vitro that while binding to DNA polymerase nonspecifically, RNA can transform DNA polymerase to display a moonlighting activity, dNTP phosphatase, in turn interfering with DNA synthesis. This phosphatase activity removes the γ-phosphate from dNTPs (generating dNDPs) and subsequently removes the β-phosphate from the formed dNDPs (generating dNMPs), confirmed by the noncleavable α,β-CH2-dGTP and β,γ-CH2-dGTP analogues. We also found that dGTP is the best substrate for the phosphatase, and the dNTP phosphatase activity is sensitive to the reaction medium. In addition, we have revealed that RNA can tune the activity of closely related proteins and give rise to new catalytic functions with subtle differences. Moreover, we have demonstrated in vitro that at the lower dNTP level, this phosphatase can directly inhibit DNA synthesis by dNTP depletion, though the phosphatase activity is 690-fold slower than the polymerase activity. Our observation in vitro suggests a plausible strategy for RNA to directly interfere with DNA polymerase and DNA synthesis in vivo.
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Affiliation(s)
- Qianwei Zhao
- College of Life Sciences , Sichuan University , Chengdu , China
| | - Wen Yang
- College of Life Sciences , Sichuan University , Chengdu , China
| | - Tong Qin
- College of Life Sciences , Sichuan University , Chengdu , China
| | - Zhen Huang
- College of Life Sciences , Sichuan University , Chengdu , China.,Department of Chemistry , Georgia State University , Atlanta , Georgia 30303 , United States
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16
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Huang J, Alnajjar KS, Mahmoud MM, Eckenroth B, Doublié S, Sweasy JB. The nature of the DNA substrate influences pre-catalytic conformational changes of DNA polymerase β. J Biol Chem 2018; 293:15084-15094. [PMID: 30068550 DOI: 10.1074/jbc.ra118.004564] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Revised: 07/29/2018] [Indexed: 11/06/2022] Open
Abstract
DNA polymerase β (Pol β) is essential for maintaining genomic integrity. During short-patch base excision repair (BER), Pol β incorporates a nucleotide into a single-gapped DNA substrate. Pol β may also function in long-patch BER, where the DNA substrate consists of larger gap sizes or 5'-modified downstream DNA. We have recently shown that Pol β fills small gaps in DNA during microhomology-mediated end-joining as part of a process that increases genomic diversity. Our previous results with single-nucleotide gapped DNA show that Pol β undergoes two pre-catalytic conformational changes upon binding to the correct nucleotide substrate. Here we use FRET to investigate nucleotide incorporation of Pol β with various DNA substrates. The results show that increasing the gap size influences the fingers closing step by increasing its reverse rate. However, the 5'-phosphate group has a more significant effect. The absence of the 5'-phosphate decreases the DNA binding affinity of Pol β and results in a conformationally more open binary complex. Moreover, upon addition of the correct nucleotide in the absence of 5'-phosphate, a slow fingers closing step is observed. Interestingly, either increasing the gap size or removing the 5'-phosphate group results in loss of the noncovalent step. Together, these results suggest that the character of the DNA substrate impacts the nature and rates of pre-catalytic conformational changes of Pol β. Our results also indicate that conformational changes are important for the fidelity of DNA synthesis by Pol β.
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Affiliation(s)
- Ji Huang
- From the Departments of Therapeutic Radiology and
| | | | | | - Brian Eckenroth
- the Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont 05405
| | - Sylvie Doublié
- the Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont 05405
| | - Joann B Sweasy
- From the Departments of Therapeutic Radiology and .,Genetics, Yale University School of Medicine, New Haven, Connecticut 06520 and
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17
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Passow KT, Harki DA. 4-Cyanoindole-2'-deoxyribonucleoside (4CIN): A Universal Fluorescent Nucleoside Analogue. Org Lett 2018; 20:4310-4313. [PMID: 29989830 PMCID: PMC6168291 DOI: 10.1021/acs.orglett.8b01746] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The synthesis and characterization of a universal and fluorescent nucleoside, 4-cyanoindole-2'-deoxyribonucleoside (4CIN), and its incorporation into DNA is described. 4CIN is a highly efficient fluorophore with quantum yields >0.90 in water. When incorporated into duplex DNA, 4CIN pairs equivalently with native nucleobases and has uniquely high quantum yields ranging from 0.15 to 0.31 depending on sequence and hybridization contexts, surpassing that of 2-aminopurine, the prototypical nucleoside fluorophore. 4CIN constitutes a new isomorphic nucleoside for diverse applications.
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Affiliation(s)
- Kellan T. Passow
- Department of Medicinal Chemistry, University of Minnesota, Minneapolis, Minnesota 55455
| | - Daniel A. Harki
- Department of Medicinal Chemistry, University of Minnesota, Minneapolis, Minnesota 55455
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18
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Christian TV, Konigsberg WH. Single-molecule FRET reveals proofreading complexes in the large fragment of Bacillus stearothermophilus DNA polymerase I. AIMS BIOPHYSICS 2018; 5:144-154. [PMID: 29888335 PMCID: PMC5990039 DOI: 10.3934/biophy.2018.2.144] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
There is increasing interest in the use of DNA polymerases (DNA pols) in next-generation sequencing strategies. These methodologies typically rely on members of the A and B family of DNA polymerases that are classified as high-fidelity DNA polymerases. These enzymes possess the ability to selectively incorporate the correct nucleotide opposite a templating base with an error frequency of only 1 in 106 insertion events. How they achieve this remarkable fidelity has been the subject of numerous investigations, yet the mechanism by which these enzymes achieve this level of accuracy remains elusive. Several smFRET assays were designed to monitor the conformational changes associated with the nucleotide selection mechanism(s) employed by DNA pols. smFRET has also been used to monitor the movement of DNA pols along a DNA substrate as well as to observe the formation of proof-reading complexes. One member among this class of enzymes, the large fragment of Bacillus stearothermophilus DNA polymerase I (Bst pol I LF), contains both 5'→3' polymerase and 3'→5' exonuclease domains, but reportedly lacks exonuclease activity. We have designed a smFRET assay showing that Bst pol I LF forms proofreading complexes. The formation of proofreading complexes at the single molecule level is strongly influenced by the presence of the 3' hydroxyl at the primer-terminus of the DNA substrate. Our assays also identify an additional state, observed in the presence of a mismatched primer-template terminus, that may be involved in the transfer of the primer-terminus from the polymerase to the exonuclease active site.
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Affiliation(s)
- Thomas V Christian
- Konigsberg Laboratory, Yale University, 333 Cedar Street, New Haven, CT 06520, USA
| | - William H Konigsberg
- Konigsberg Laboratory, Yale University, 333 Cedar Street, New Haven, CT 06520, USA
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19
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Ralec C, Henry E, Lemor M, Killelea T, Henneke G. Calcium-driven DNA synthesis by a high-fidelity DNA polymerase. Nucleic Acids Res 2017; 45:12425-12440. [PMID: 29040737 PMCID: PMC5716173 DOI: 10.1093/nar/gkx927] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2017] [Accepted: 10/04/2017] [Indexed: 11/14/2022] Open
Abstract
Divalent metal ions, usually Mg2+, are required for both DNA synthesis and proofreading functions by DNA polymerases (DNA Pol). Although used as a non-reactive cofactor substitute for binding and crystallographic studies, Ca2+ supports DNA polymerization by only one DNA Pol, Dpo4. Here, we explore whether Ca2+-driven catalysis might apply to high-fidelity (HiFi) family B DNA Pols. The consequences of replacing Mg2+ by Ca2+ on base pairing at the polymerase active site as well as the editing of terminal nucleotides at the exonuclease active site of the archaeal Pyrococcus abyssi DNA Pol (PabPolB) are characterized and compared to other (families B, A, Y, X, D) DNA Pols. Based on primer extension assays, steady-state kinetics and ion-chased experiments, we demonstrate that Ca2+ (and other metal ions) activates DNA synthesis by PabPolB. While showing a slower rate of phosphodiester bond formation, nucleotide selectivity is improved over that of Mg2+. Further mechanistic studies show that the affinities for primer/template are higher in the presence of Ca2+ and reinforced by a correct incoming nucleotide. Conversely, no exonuclease degradation of the terminal nucleotides occurs with Ca2+. Evolutionary and mechanistic insights among DNA Pols are thus discussed.
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Affiliation(s)
- Céline Ralec
- Ifremer, Centre de Brest, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France.,CNRS, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France.,Université de Brest Occidentale, UBO, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France
| | - Etienne Henry
- Ifremer, Centre de Brest, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France.,CNRS, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France.,Université de Brest Occidentale, UBO, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France
| | - Mélanie Lemor
- Ifremer, Centre de Brest, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France.,CNRS, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France.,Université de Brest Occidentale, UBO, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France
| | - Tom Killelea
- Ifremer, Centre de Brest, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France.,CNRS, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France.,Université de Brest Occidentale, UBO, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France
| | - Ghislaine Henneke
- Ifremer, Centre de Brest, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France.,CNRS, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France.,Université de Brest Occidentale, UBO, LM2E, UMR 6197, Technopole Brest-Iroise, 29280 Plouzané, France
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20
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Mahmoud MM, Schechter A, Alnajjar KS, Huang J, Towle-Weicksel J, Eckenroth BE, Doublié S, Sweasy JB. Defective Nucleotide Release by DNA Polymerase β Mutator Variant E288K Is the Basis of Its Low Fidelity. Biochemistry 2017; 56:5550-5559. [PMID: 28945359 DOI: 10.1021/acs.biochem.7b00869] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
DNA polymerases synthesize new DNA during DNA replication and repair, and their ability to do so faithfully is essential to maintaining genomic integrity. DNA polymerase β (Pol β) functions in base excision repair to fill in single-nucleotide gaps, and variants of Pol β have been associated with cancer. Specifically, the E288K Pol β variant has been found in colon tumors and has been shown to display sequence-specific mutator activity. To probe the mechanism that may underlie E288K's loss of fidelity, a fluorescence resonance energy transfer system that utilizes a fluorophore on the fingers domain of Pol β and a quencher on the DNA substrate was employed. Our results show that E288K utilizes an overall mechanism similar to that of wild type (WT) Pol β when incorporating correct dNTP. However, when inserting the correct dNTP, E288K exhibits a faster rate of closing of the fingers domain combined with a slower rate of nucleotide release compared to those of WT Pol β. We also detect enzyme closure upon mixing with the incorrect dNTP for E288K but not WT Pol β. Taken together, our results suggest that E288K Pol β incorporates all dNTPs more readily than WT because of an inherent defect that results in rapid isomerization of dNTPs within its active site. Structural modeling implies that this inherent defect is due to interaction of E288K with DNA, resulting in a stable closed enzyme structure.
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Affiliation(s)
- Mariam M Mahmoud
- Department of Therapeutic Radiology, Yale University School of Medicine , New Haven, Connecticut 06520, United States
| | - Allison Schechter
- Department of Therapeutic Radiology, Yale University School of Medicine , New Haven, Connecticut 06520, United States
| | - Khadijeh S Alnajjar
- Department of Therapeutic Radiology, Yale University School of Medicine , New Haven, Connecticut 06520, United States
| | - Ji Huang
- Department of Therapeutic Radiology, Yale University School of Medicine , New Haven, Connecticut 06520, United States
| | - Jamie Towle-Weicksel
- Department of Therapeutic Radiology, Yale University School of Medicine , New Haven, Connecticut 06520, United States
| | - Brian E Eckenroth
- Department of Microbiology and Molecular Genetics, University of Vermont , Burlington, Vermont 05405, United States
| | - Sylvie Doublié
- Department of Microbiology and Molecular Genetics, University of Vermont , Burlington, Vermont 05405, United States
| | - Joann B Sweasy
- Department of Therapeutic Radiology, Yale University School of Medicine , New Haven, Connecticut 06520, United States.,Department of Genetics, Yale University School of Medicine , New Haven, Connecticut 06520, United States
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21
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Hoekstra TP, Depken M, Lin SN, Cabanas-Danés J, Gross P, Dame RT, Peterman EJG, Wuite GJL. Switching between Exonucleolysis and Replication by T7 DNA Polymerase Ensures High Fidelity. Biophys J 2017; 112:575-583. [PMID: 28256218 DOI: 10.1016/j.bpj.2016.12.044] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2016] [Revised: 12/02/2016] [Accepted: 12/27/2016] [Indexed: 12/11/2022] Open
Abstract
DNA polymerase catalyzes the accurate transfer of genetic information from one generation to the next, and thus it is vitally important for replication to be faithful. DNA polymerase fulfills the strict requirements for fidelity by a combination of mechanisms: 1) high selectivity for correct nucleotide incorporation, 2) a slowing down of the replication rate after misincorporation, and 3) proofreading by excision of misincorporated bases. To elucidate the kinetic interplay between replication and proofreading, we used high-resolution optical tweezers to probe how DNA-duplex stability affects replication by bacteriophage T7 DNA polymerase. Our data show highly irregular replication dynamics, with frequent pauses and direction reversals as the polymerase cycles through the states that govern the mechanochemistry behind high-fidelity T7 DNA replication. We constructed a kinetic model that incorporates both existing biochemical data and the, to our knowledge, novel states we observed. We fit the model directly to the acquired pause-time and run-time distributions. Our findings indicate that the main pathway for error correction is DNA polymerase dissociation-mediated DNA transfer, followed by biased binding into the exonuclease active site. The number of bases removed by this proofreading mechanism is much larger than the number of erroneous bases that would be expected to be incorporated, ensuring a high-fidelity replication of the bacteriophage T7 genome.
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Affiliation(s)
- Tjalle P Hoekstra
- Department of Physics and Astronomy, Vrije Universiteit, Amsterdam, the Netherlands; LaserLaB Amsterdam, Vrije Universiteit, Amsterdam, the Netherlands
| | - Martin Depken
- Department of Bionanoscience, Kavli Institute of Nanoscience, Delft University of Technology, Delft, the Netherlands
| | - Szu-Ning Lin
- Department of Physics and Astronomy, Vrije Universiteit, Amsterdam, the Netherlands; LaserLaB Amsterdam, Vrije Universiteit, Amsterdam, the Netherlands; Leiden Institute of Chemistry, Leiden University, Leiden, the Netherlands
| | - Jordi Cabanas-Danés
- Department of Physics and Astronomy, Vrije Universiteit, Amsterdam, the Netherlands; LaserLaB Amsterdam, Vrije Universiteit, Amsterdam, the Netherlands
| | - Peter Gross
- Department of Physics and Astronomy, Vrije Universiteit, Amsterdam, the Netherlands; LaserLaB Amsterdam, Vrije Universiteit, Amsterdam, the Netherlands
| | - Remus T Dame
- Leiden Institute of Chemistry, Leiden University, Leiden, the Netherlands
| | - Erwin J G Peterman
- Department of Physics and Astronomy, Vrije Universiteit, Amsterdam, the Netherlands; LaserLaB Amsterdam, Vrije Universiteit, Amsterdam, the Netherlands
| | - Gijs J L Wuite
- Department of Physics and Astronomy, Vrije Universiteit, Amsterdam, the Netherlands; LaserLaB Amsterdam, Vrije Universiteit, Amsterdam, the Netherlands.
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22
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Alnajjar KS, Garcia-Barboza B, Negahbani A, Nakhjiri M, Kashemirov B, McKenna C, Goodman MF, Sweasy JB. A Change in the Rate-Determining Step of Polymerization by the K289M DNA Polymerase β Cancer-Associated Variant. Biochemistry 2017; 56:2096-2105. [PMID: 28326765 DOI: 10.1021/acs.biochem.6b01230] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
K289M is a variant of DNA polymerase β (pol β) that has previously been identified in colorectal cancer. The expression of this variant leads to a 16-fold increase in mutation frequency at a specific site in vivo and a reduction in fidelity in vitro in a sequence context-specific manner. Previous work shows that this reduction in fidelity results from a decreased level of discrimination against incorrect nucleotide incorporation at the level of polymerization. To probe the transition state of the K289M mutator variant of pol β, single-turnover kinetic experiments were performed using β,γ-CXY dGTP analogues with a wide range of leaving group monoacid dissociation constants (pKa4), including a corresponding set of novel β,γ-CXY dCTP analogues. Surprisingly, we found that the values of the log of the catalytic rate constant (kpol) for correct insertion by K289M, in contrast to those of wild-type pol β, do not decrease with increased leaving group pKa4 for analogues with pKa4 values of <11. This suggests that one of the relative rate constants differs for the K289M reaction in comparison to that of the wild type (WT). However, a plot of log(kpol) values for incorrect insertion by K289M versus pKa4 reveals a linear correlation with a negative slope, in this respect resembling kpol values for misincorporation by the WT enzyme. We also show that some of these analogues improve the fidelity of K289M. Taken together, our data show that Lys289 critically influences the catalytic pathway of pol β.
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Affiliation(s)
- Khadijeh S Alnajjar
- Department of Therapeutic Radiology and Department of Genetics, Yale University School of Medicine , New Haven, Connecticut 06520, United States
| | - Beatriz Garcia-Barboza
- Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States
| | - Amirsoheil Negahbani
- Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States
| | - Maryam Nakhjiri
- Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States
| | - Boris Kashemirov
- Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States
| | - Charles McKenna
- Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States
| | - Myron F Goodman
- Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States
| | - Joann B Sweasy
- Department of Therapeutic Radiology and Department of Genetics, Yale University School of Medicine , New Haven, Connecticut 06520, United States
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23
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Moreno A, Knee JL, Mukerji I. Photophysical Characterization of Enhanced 6-Methylisoxanthopterin Fluorescence in Duplex DNA. J Phys Chem B 2016; 120:12232-12248. [PMID: 27934220 DOI: 10.1021/acs.jpcb.6b07369] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The structure and dynamic motions of bases in DNA duplexes and other constructs are important for understanding mechanisms of selectivity and recognition of DNA-binding proteins. The fluorescent guanine analogue, 6-methylisoxanthopterin 6-MI, is well suited to this purpose as it exhibits an unexpected 3- to 4-fold increase in relative quantum yield upon duplex formation when incorporated into the following sequences: ATFAA, AAFTA, or ATFTA (where F represents 6-MI). To better understand some of the factors leading to the 6-MI fluorescence increase upon duplex formation, we characterized the effect of local sequence and structural perturbations on 6-MI photophysics through temperature melts, quantum yield measurements, fluorescence quenching assays, and fluorescence lifetime measurements. By examining 21 sequences we have determined that the duplex-enhanced fluorescence (DEF) depends on the composition of bases adjacent to 6-MI and the presence of adenines at locations n ± 2 from the probe. Investigation of duplex stability and local solvent accessibility measurements support a model in which the DEF arises from a constrained geometry of 6-MI in the duplex, which remains H-bonded to cytosine, stacked with adjacent bases and inaccessible to quenchers. Perturbation of DNA structure through the introduction of an unpaired base 3' to 6-MI or a mismatched basepair increases 6-MI dynamic motion leading to fluorescence quenching and a reduction in quantum yield. Molecular dynamics simulations suggest the enhanced fluorescence results from a greater degree of twist at the X-F step relative to the quenched duplexes examined. These results point to a model where adenine residues located at n ± 2 from 6-MI induce a structural geometry with greater twist in the duplex that hinders local motion reducing dynamic quenching and producing an increase in 6-MI fluorescence.
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Affiliation(s)
- Andrew Moreno
- Departments of Chemistry and ‡Molecular Biology and Biochemistry, Molecular Biophysics Program, Wesleyan University , 52 Lawn Ave, Middletown, Connecticut 06459, United States
| | - J L Knee
- Departments of Chemistry and ‡Molecular Biology and Biochemistry, Molecular Biophysics Program, Wesleyan University , 52 Lawn Ave, Middletown, Connecticut 06459, United States
| | - Ishita Mukerji
- Departments of Chemistry and ‡Molecular Biology and Biochemistry, Molecular Biophysics Program, Wesleyan University , 52 Lawn Ave, Middletown, Connecticut 06459, United States
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24
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Hohlbein J, Kapanidis AN. Probing the Conformational Landscape of DNA Polymerases Using Diffusion-Based Single-Molecule FRET. Methods Enzymol 2016; 581:353-378. [PMID: 27793286 DOI: 10.1016/bs.mie.2016.08.023] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Monitoring conformational changes in DNA polymerases using single-molecule Förster resonance energy transfer (smFRET) has provided new tools for studying fidelity-related mechanisms that promote the rejection of incorrect nucleotides before DNA synthesis. In addition to the previously known open and closed conformations of DNA polymerases, our smFRET assays utilizing doubly labeled variants of Escherichia coli DNA polymerase I were pivotal in identifying and characterizing a partially closed conformation as a primary checkpoint for nucleotide selection. Here, we provide a comprehensive overview of the methods we used for the conformational analysis of wild-type DNA polymerase and some of its low-fidelity derivatives; these methods include strategies for protein labeling and our procedures for solution-based single-molecule fluorescence data acquisition and data analysis. We also discuss alternative single-molecule fluorescence strategies for analyzing the conformations of DNA polymerases in vitro and in vivo.
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Affiliation(s)
- J Hohlbein
- Laboratory of Biophysics, Wageningen University and Research, Wageningen, The Netherlands; Microspectroscopy Centre, Wageningen University and Research, Wageningen, The Netherlands.
| | - A N Kapanidis
- Clarendon Laboratory, University of Oxford, Oxford, United Kingdom.
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25
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Abstract
Extracting kinetic parameters from DNA polymerase-catalyzed processive polymerization data using traditional initial-rate analysis has proven to be problematic for multiple reasons. The first substrate, DNA template, is a heterogeneous polymer and binds tightly to DNA polymerase. Further, the affinity and speed of incorporation of the second substrate, deoxynucleoside triphosphate (dNTP), vary greatly depending on the nature of the templating base and surrounding sequence. Here, we present a mathematical model consisting of the DNA template-binding step and a Michaelis-Menten-type nucleotide incorporation step acting on a DNA template with a finite length. The model was numerically integrated and globally fitted to experimental reaction time courses. The time courses were determined by monitoring the processive synthesis of oligonucleotides of lengths between 50 and 120 nucleotides by DNA polymerase I (Klenow fragment exo-) using the fluorophore PicoGreen. For processive polymerization, we were able to estimate an enzyme-template association rate k1 of 7.4 μM-1 s-1, a disassociation rate k-1 of 0.07 s-1, and a Kd of 10 nM, and the steady-state parameters for correct dNTP incorporation give kcat values of 2.5-3.3 s-1 and Km values of 0.51-0.86 μM. From the analysis of time courses measured between 5 and 25 °C, an activation energy for kcat of 82 kJ mol-1 was calculated, and it was found that up to 73% of Klenow fragment becomes inactivated or involved in unproductive binding at lower temperatures. Finally, a solvent deuterium kinetic isotope effect (KIE) of 3.0-3.2 was observed under processive synthesis conditions, which suggests that either the intrinsic KIE is unusually high, at least 30-40, or previous findings, showing that the phosphoryl transfer step occurs rapidly and is flanked by two slow conformational changes, need to be re-evaluated. We suggest that the numerical integration of rate equations provides a high level of flexibility and generally produces superior results compared to those of initial-rate analysis in the study of DNA polymerase kinetics and, by extension, other complex enzyme systems.
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Affiliation(s)
- Julius Rentergent
- Manchester Institute of Biotechnology, University of Manchester , Manchester M1 7DN, U.K
| | - Max D Driscoll
- Manchester Institute of Biotechnology, University of Manchester , Manchester M1 7DN, U.K
| | - Sam Hay
- Manchester Institute of Biotechnology, University of Manchester , Manchester M1 7DN, U.K
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26
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Milton ME, Choe JY, Honzatko RB, Nelson SW. Crystal Structure of the Apicoplast DNA Polymerase from Plasmodium falciparum: The First Look at a Plastidic A-Family DNA Polymerase. J Mol Biol 2016; 428:3920-3934. [PMID: 27487482 DOI: 10.1016/j.jmb.2016.07.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Revised: 07/19/2016] [Accepted: 07/22/2016] [Indexed: 11/18/2022]
Abstract
Plasmodium falciparum, the primary cause of malaria, contains a non-photosynthetic plastid called the apicoplast. The apicoplast exists in most members of the phylum Apicomplexa and has its own genome along with organelle-specific enzymes for its replication. The only DNA polymerase found in the apicoplast (apPOL) was putatively acquired through horizontal gene transfer from a bacteriophage and is classified as an atypical A-family polymerase. Here, we present its crystal structure at a resolution of 2.9Å. P. falciparum apPOL, the first structural representative of a plastidic A-family polymerase, diverges from typical A-family members in two of three previously identified signature motifs and in a region not implicated by sequence. Moreover, apPOL has an additional N-terminal subdomain, the absence of which severely diminishes its 3' to 5' exonuclease activity. A compound known to be toxic to Plasmodium is a potent inhibitor of apPOL, suggesting that apPOL is a viable drug target. The structure provides new insights into the structural diversity of A-family polymerases and may facilitate structurally guided antimalarial drug design.
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Affiliation(s)
- Morgan E Milton
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA
| | - Jun-Yong Choe
- Department of Biochemistry and Molecular Biology, Rosalind Franklin University of Medicine and Science, North Chicago, IL 60064, USA
| | - Richard B Honzatko
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA.
| | - Scott W Nelson
- Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, IA 50011, USA.
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27
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Gül OT, Pugliese KM, Choi Y, Sims PC, Pan D, Rajapakse AJ, Weiss GA, Collins PG. Single Molecule Bioelectronics and Their Application to Amplification-Free Measurement of DNA Lengths. BIOSENSORS-BASEL 2016; 6:bios6030029. [PMID: 27348011 PMCID: PMC5039648 DOI: 10.3390/bios6030029] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Revised: 06/08/2016] [Accepted: 06/15/2016] [Indexed: 01/17/2023]
Abstract
As biosensing devices shrink smaller and smaller, they approach a scale in which single molecule electronic sensing becomes possible. Here, we review the operation of single-enzyme transistors made using single-walled carbon nanotubes. These novel hybrid devices transduce the motions and catalytic activity of a single protein into an electronic signal for real-time monitoring of the protein’s activity. Analysis of these electronic signals reveals new insights into enzyme function and proves the electronic technique to be complementary to other single-molecule methods based on fluorescence. As one example of the nanocircuit technique, we have studied the Klenow Fragment (KF) of DNA polymerase I as it catalytically processes single-stranded DNA templates. The fidelity of DNA polymerases makes them a key component in many DNA sequencing techniques, and here we demonstrate that KF nanocircuits readily resolve DNA polymerization with single-base sensitivity. Consequently, template lengths can be directly counted from electronic recordings of KF’s base-by-base activity. After measuring as few as 20 copies, the template length can be determined with <1 base pair resolution, and different template lengths can be identified and enumerated in solutions containing template mixtures.
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Affiliation(s)
- O Tolga Gül
- Department of Physics and Astronomy, University of California at Irvine, Irvine, CA 92697, USA
- Department of Physics, Polatlı Faculty of Science and Arts, Gazi University, Polatlı 06900, Turkey
| | - Kaitlin M Pugliese
- Department of Chemistry, University of California at Irvine, Irvine, CA 92697, USA
| | - Yongki Choi
- Department of Physics and Astronomy, University of California at Irvine, Irvine, CA 92697, USA
- Department of Physics, North Dakota State University, Fargo, ND 58108, USA
| | - Patrick C Sims
- Department of Physics and Astronomy, University of California at Irvine, Irvine, CA 92697, USA
| | - Deng Pan
- Department of Physics and Astronomy, University of California at Irvine, Irvine, CA 92697, USA
| | - Arith J Rajapakse
- Department of Physics and Astronomy, University of California at Irvine, Irvine, CA 92697, USA
| | - Gregory A Weiss
- Department of Chemistry, University of California at Irvine, Irvine, CA 92697, USA.
- Department of Molecular Biology and Biochemistry, University of California at Irvine, Irvine, CA 92697, USA.
| | - Philip G Collins
- Department of Physics and Astronomy, University of California at Irvine, Irvine, CA 92697, USA.
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28
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Meli M, Sustarsic M, Craggs TD, Kapanidis AN, Colombo G. DNA Polymerase Conformational Dynamics and the Role of Fidelity-Conferring Residues: Insights from Computational Simulations. Front Mol Biosci 2016; 3:20. [PMID: 27303671 PMCID: PMC4882331 DOI: 10.3389/fmolb.2016.00020] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Accepted: 05/10/2016] [Indexed: 12/11/2022] Open
Abstract
Herein we investigate the molecular bases of DNA polymerase I conformational dynamics that underlie the replication fidelity of the enzyme. Such fidelity is determined by conformational changes that promote the rejection of incorrect nucleotides before the chemical ligation step. We report a comprehensive atomic resolution study of wild type and mutant enzymes in different bound states and starting from different crystal structures, using extensive molecular dynamics (MD) simulations that cover a total timespan of ~5 ms. The resulting trajectories are examined via a combination of novel methods of internal dynamics and energetics analysis, aimed to reveal the principal molecular determinants for the (de)stabilization of a certain conformational state. Our results show that the presence of fidelity-decreasing mutations or the binding of incorrect nucleotides in ternary complexes tend to favor transitions from closed toward open structures, passing through an ensemble of semi-closed intermediates. The latter ensemble includes the experimentally observed ajar conformation which, consistent with previous experimental observations, emerges as a molecular checkpoint for the selection of the correct nucleotide to incorporate. We discuss the implications of our results for the understanding of the relationships between the structure, dynamics, and function of DNA polymerase I at the atomistic level.
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Affiliation(s)
- Massimiliano Meli
- Computational Biochemistry Group, Istituto di Chimica del Riconoscimento Molecolare, National Research Council of Italy Milano, Italy
| | - Marko Sustarsic
- Clarendon Laboratory, Department of Physics, Biological Physics Research Group, University of Oxford Oxford, UK
| | - Timothy D Craggs
- Clarendon Laboratory, Department of Physics, Biological Physics Research Group, University of Oxford Oxford, UK
| | - Achillefs N Kapanidis
- Clarendon Laboratory, Department of Physics, Biological Physics Research Group, University of Oxford Oxford, UK
| | - Giorgio Colombo
- Computational Biochemistry Group, Istituto di Chimica del Riconoscimento Molecolare, National Research Council of Italy Milano, Italy
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29
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Abstract
The machines that decode and regulate genetic information require the translation, transcription and replication pathways essential to all living cells. Thus, it might be expected that all cells share the same basic machinery for these pathways that were inherited from the primordial ancestor cell from which they evolved. A clear example of this is found in the translation machinery that converts RNA sequence to protein. The translation process requires numerous structural and catalytic RNAs and proteins, the central factors of which are homologous in all three domains of life, bacteria, archaea and eukarya. Likewise, the central actor in transcription, RNA polymerase, shows homology among the catalytic subunits in bacteria, archaea and eukarya. In contrast, while some "gears" of the genome replication machinery are homologous in all domains of life, most components of the replication machine appear to be unrelated between bacteria and those of archaea and eukarya. This review will compare and contrast the central proteins of the "replisome" machines that duplicate DNA in bacteria, archaea and eukarya, with an eye to understanding the issues surrounding the evolution of the DNA replication apparatus.
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Affiliation(s)
- Nina Y Yao
- a DNA Replication Laboratory, The Rockefeller University , New York , NY , USA and
| | - Mike E O'Donnell
- a DNA Replication Laboratory, The Rockefeller University , New York , NY , USA and.,b Howard Hughes Medical Institute, The Rockefeller University , New York , NY , USA
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30
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Miller BR, Beese LS, Parish CA, Wu EY. The Closing Mechanism of DNA Polymerase I at Atomic Resolution. Structure 2015. [PMID: 26211612 DOI: 10.1016/j.str.2015.06.016] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
DNA polymerases must quickly and accurately distinguish between similar nucleic acids to form Watson-Crick base pairs and avoid DNA replication errors. Deoxynucleoside triphosphate (dNTP) binding to the DNA polymerase active site induces a large conformational change that is difficult to characterize experimentally on an atomic level. Here, we report an X-ray crystal structure of DNA polymerase I bound to DNA in the open conformation with a dNTP present in the active site. We use this structure to computationally simulate the open to closed transition of DNA polymerase in the presence of a Watson-Crick base pair. Our microsecond simulations allowed us to characterize the key steps involved in active site assembly, and propose the sequence of events involved in the prechemistry steps of DNA polymerase catalysis. They also reveal new features of the polymerase mechanism, such as a conserved histidine as a potential proton acceptor from the primer 3'-hydroxyl.
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Affiliation(s)
- Bill R Miller
- Department of Biology, University of Richmond, 28 Westhampton Way, Richmond, VA 23173, USA; Department of Chemistry, University of Richmond, 28 Westhampton Way, Richmond, VA 23173, USA
| | - Lorena S Beese
- Department of Biochemistry, Duke University Medical Center, 255 Nanaline H. Duke Building, Durham, NC 27710, USA
| | - Carol A Parish
- Department of Chemistry, University of Richmond, 28 Westhampton Way, Richmond, VA 23173, USA.
| | - Eugene Y Wu
- Department of Biology, University of Richmond, 28 Westhampton Way, Richmond, VA 23173, USA; Department of Biochemistry, Duke University Medical Center, 255 Nanaline H. Duke Building, Durham, NC 27710, USA.
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31
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Evans GW, Hohlbein J, Craggs T, Aigrain L, Kapanidis AN. Real-time single-molecule studies of the motions of DNA polymerase fingers illuminate DNA synthesis mechanisms. Nucleic Acids Res 2015; 43:5998-6008. [PMID: 26013816 PMCID: PMC4499156 DOI: 10.1093/nar/gkv547] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Accepted: 05/13/2015] [Indexed: 12/30/2022] Open
Abstract
DNA polymerases maintain genomic integrity by copying DNA with high fidelity. A conformational change important for fidelity is the motion of the polymerase fingers subdomain from an open to a closed conformation upon binding of a complementary nucleotide. We previously employed intra-protein single-molecule FRET on diffusing molecules to observe fingers conformations in polymerase-DNA complexes. Here, we used the same FRET ruler on surface-immobilized complexes to observe fingers-opening and closing of individual polymerase molecules in real time. Our results revealed the presence of intrinsic dynamics in the binary complex, characterized by slow fingers-closing and fast fingers-opening. When binary complexes were incubated with increasing concentrations of complementary nucleotide, the fingers-closing rate increased, strongly supporting an induced-fit model for nucleotide recognition. Meanwhile, the opening rate in ternary complexes with complementary nucleotide was 6 s(-1), much slower than either fingers closing or the rate-limiting step in the forward direction; this rate balance ensures that, after nucleotide binding and fingers-closing, nucleotide incorporation is overwhelmingly likely to occur. Our results for ternary complexes with a non-complementary dNTP confirmed the presence of a state corresponding to partially closed fingers and suggested a radically different rate balance regarding fingers transitions, which allows polymerase to achieve high fidelity.
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Affiliation(s)
- Geraint W Evans
- Department of Physics and Biological Physics Research Group, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - Johannes Hohlbein
- Department of Physics and Biological Physics Research Group, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - Timothy Craggs
- Department of Physics and Biological Physics Research Group, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - Louise Aigrain
- Department of Physics and Biological Physics Research Group, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
| | - Achillefs N Kapanidis
- Department of Physics and Biological Physics Research Group, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom
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32
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Morin JA, Cao FJ, Lázaro JM, Arias-Gonzalez JR, Valpuesta JM, Carrascosa JL, Salas M, Ibarra B. Mechano-chemical kinetics of DNA replication: identification of the translocation step of a replicative DNA polymerase. Nucleic Acids Res 2015; 43:3643-52. [PMID: 25800740 PMCID: PMC4402526 DOI: 10.1093/nar/gkv204] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Revised: 02/14/2015] [Accepted: 02/27/2015] [Indexed: 11/25/2022] Open
Abstract
During DNA replication replicative polymerases move in discrete mechanical steps along the DNA template. To address how the chemical cycle is coupled to mechanical motion of the enzyme, here we use optical tweezers to study the translocation mechanism of individual bacteriophage Phi29 DNA polymerases during processive DNA replication. We determine the main kinetic parameters of the nucleotide incorporation cycle and their dependence on external load and nucleotide (dNTP) concentration. The data is inconsistent with power stroke models for translocation, instead supports a loose-coupling mechanism between chemical catalysis and mechanical translocation during DNA replication. According to this mechanism the DNA polymerase works by alternating between a dNTP/PPi-free state, which diffuses thermally between pre- and post-translocated states, and a dNTP/PPi-bound state where dNTP binding stabilizes the post-translocated state. We show how this thermal ratchet mechanism is used by the polymerase to generate work against large opposing loads (∼50 pN).
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Affiliation(s)
- José A Morin
- Instituto Madrileño de Estudios Avanzados en Nanociencia, IMDEA Nanociencia, 28049 Madrid, Spain
| | - Francisco J Cao
- Departamento Física Atómica, Molecular y Nuclear, Universidad Complutense, 28040 Madrid, Spain
| | - José M Lázaro
- Centro de Biología Molecular 'Severo Ochoa' (CSIC-UAM), Universidad Autónoma, Cantoblanco, 28049 Madrid, Spain
| | - J Ricardo Arias-Gonzalez
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia) & CNB-CSIC-IMDEA Nanociencia Associated Unit 'Unidad de Nanobiotecnología', 28049 Madrid, Spain
| | - José M Valpuesta
- Centro Nacional de Biotecnología (CNB-CSIC), 28049 Madrid, Spain
| | - José L Carrascosa
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia) & CNB-CSIC-IMDEA Nanociencia Associated Unit 'Unidad de Nanobiotecnología', 28049 Madrid, Spain Centro Nacional de Biotecnología (CNB-CSIC), 28049 Madrid, Spain
| | - Margarita Salas
- Centro de Biología Molecular 'Severo Ochoa' (CSIC-UAM), Universidad Autónoma, Cantoblanco, 28049 Madrid, Spain
| | - Borja Ibarra
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia) & CNB-CSIC-IMDEA Nanociencia Associated Unit 'Unidad de Nanobiotecnología', 28049 Madrid, Spain
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33
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Martina CE, Lapenta F, Montón Silva A, Hochkoeppler A. HoLaMa: A Klenow sub-fragment lacking the 3'-5' exonuclease domain. Arch Biochem Biophys 2015; 575:46-53. [PMID: 25906742 DOI: 10.1016/j.abb.2015.04.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2015] [Accepted: 04/14/2015] [Indexed: 11/30/2022]
Abstract
The design, construction, overexpression, and purification of a Klenow sub-fragment lacking the 3'-5' exonuclease domain is presented here. In particular, a synthetic gene coding for the residues 515-928 of Escherichia coli DNA polymerase I was constructed. To improve the solubility and stability of the corresponding protein, the synthetic gene was designed to contain 11 site-specific substitutions. The gene was inserted into the pBADHis expression vector, generating 2 identical Klenow sub-fragments, bearing or not a hexahistidine tag. Both these Klenow sub-fragments, denominated HoLaMa and HoLaMaHis, were purified, and their catalytic properties were compared to those of Klenow enzyme. When DNA polymerase activity was assayed under processive conditions, the Klenow enzyme performed much better than HoLaMa and HoLaMaHis. However, when DNA polymerase activity was assayed under distributive conditions, the initial velocity of the reaction catalyzed by HoLaMa was comparable to that observed in the presence of Klenow enzyme. In particular, under distributive conditions HoLaMa was found to strongly prefer dsDNAs bearing a short template overhang, to the length of which the Klenow enzyme was relatively insensitive. Overall, our observations indicate that the exonuclease domain of the Klenow enzyme, besides its proofreading activity, does significantly contribute to the catalytic efficiency of DNA elongation.
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Affiliation(s)
- Cristina Elisa Martina
- Department of Pharmacy and Biotechnology, University of Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
| | - Fabio Lapenta
- Department of Pharmacy and Biotechnology, University of Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
| | - Alejandro Montón Silva
- Department of Pharmacy and Biotechnology, University of Bologna, Viale Risorgimento 4, 40136 Bologna, Italy
| | - Alejandro Hochkoeppler
- Department of Pharmacy and Biotechnology, University of Bologna, Viale Risorgimento 4, 40136 Bologna, Italy; CSGI, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, FI, Italy.
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34
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Nevin P, Engen JR, Beuning PJ. Steric gate residues of Y-family DNA polymerases DinB and pol kappa are crucial for dNTP-induced conformational change. DNA Repair (Amst) 2015; 29:65-73. [PMID: 25684709 DOI: 10.1016/j.dnarep.2015.01.012] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Revised: 01/22/2015] [Accepted: 01/23/2015] [Indexed: 01/08/2023]
Abstract
Discrimination against ribonucleotides by DNA polymerases is critical to preserve DNA integrity. For many DNA polymerases, including those of the Y family, rNTP discrimination has been attributed to steric clashes between a residue near the active site, the steric gate, and the 2'-hydroxyl of the incoming rNTP. Here we used hydrogen/deuterium exchange (HDX) mass spectrometry (MS) to probe the effects of the steric gate in the Y-family DNA polymerases Escherichia coli DinB and human DNA pol κ. Formation of a ternary complex with a G:dCTP base pair in the active site resulted in slower hydrogen exchange relative to a ternary complex with G:rCTP in the active site. The protection from exchange was localized to regions both distal and proximal to the active site, suggesting that DinB and DNA pol κ adopt different conformations depending on the sugar of the incoming nucleotide. In contrast, when the respective steric gate residues were mutated to alanine, the differences in HDX between the dNTP- and rNTP-bound ternary complexes were attenuated such that for DinB(F13A) and pol κ(Y112A), ternary complexes with either G:dCTP or G:rCTP base pairs had similar HDX profiles. Furthermore, the HDX in these ternary complexes resembled that of the rCTP-bound state rather than the dCTP-bound state of the wild-type enzymes. Primer extension assays confirmed that DinB(F13A) and pol κ(Y112A) do not discriminate against rNTPs to the same extent as the wild-type enzymes. Our observations indicate that the steric gate is crucial for rNTP discrimination because of its role in specifically promoting a dNTP-induced conformational change and that rNTP discrimination occurs in a relatively closed state of the polymerases.
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Affiliation(s)
- Philip Nevin
- Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Avenue, Boston, MA 02115, USA
| | - John R Engen
- Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Avenue, Boston, MA 02115, USA
| | - Penny J Beuning
- Department of Chemistry and Chemical Biology, Northeastern University, 360 Huntington Avenue, Boston, MA 02115, USA.
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35
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Abstract
In all living cells, DNA is the storage medium for genetic information. Being quite stable, DNA is well-suited for its role in storage and propagation of information, but RNA is also covalently included in DNA through various mechanisms. Recent studies also demonstrate useful aspects of including ribonucleotides in the genome during repair. Therefore, our understanding of the consequences of RNA inclusion into bacterial genomic DNA is just beginning, but with its high frequency of occurrence the consequences and potential benefits are likely to be numerous and diverse. In this review, we discuss the processes that cause ribonucleotide inclusion in genomic DNA, the pathways important for ribonucleotide removal and the consequences that arise should ribonucleotides remain nested in genomic DNA.
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Affiliation(s)
- Jeremy W. Schroeder
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Justin R. Randall
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Lindsay A. Matthews
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA
| | - Lyle A. Simmons
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA
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36
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Xu C, Maxwell BA, Suo Z. Conformational dynamics of Thermus aquaticus DNA polymerase I during catalysis. J Mol Biol 2014; 426:2901-2917. [PMID: 24931550 DOI: 10.1016/j.jmb.2014.06.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Revised: 06/02/2014] [Accepted: 06/07/2014] [Indexed: 11/15/2022]
Abstract
Despite the fact that DNA polymerases have been investigated for many years and are commonly used as tools in a number of molecular biology assays, many details of the kinetic mechanism they use to catalyze DNA synthesis remain unclear. Structural and kinetic studies have characterized a rapid, pre-catalytic open-to-close conformational change of the Finger domain during nucleotide binding for many DNA polymerases including Thermus aquaticus DNA polymerase I (Taq Pol), a thermostable enzyme commonly used for DNA amplification in PCR. However, little has been performed to characterize the motions of other structural domains of Taq Pol or any other DNA polymerase during catalysis. Here, we used stopped-flow Förster resonance energy transfer to investigate the conformational dynamics of all five structural domains of the full-length Taq Pol relative to the DNA substrate during nucleotide binding and incorporation. Our study provides evidence for a rapid conformational change step induced by dNTP binding and a subsequent global conformational transition involving all domains of Taq Pol during catalysis. Additionally, our study shows that the rate of the global transition was greatly increased with the truncated form of Taq Pol lacking the N-terminal domain. Finally, we utilized a mutant of Taq Pol containing a de novo disulfide bond to demonstrate that limiting protein conformational flexibility greatly reduced the polymerization activity of Taq Pol.
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Affiliation(s)
- Cuiling Xu
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA
| | - Brian A Maxwell
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA.,Ohio State Biophysics Program, The Ohio State University, Columbus, OH 43210, USA
| | - Zucai Suo
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA.,Ohio State Biophysics Program, The Ohio State University, Columbus, OH 43210, USA
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37
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Lieberman KR, Dahl JM, Wang H. Kinetic mechanism at the branchpoint between the DNA synthesis and editing pathways in individual DNA polymerase complexes. J Am Chem Soc 2014; 136:7117-31. [PMID: 24761828 PMCID: PMC4046759 DOI: 10.1021/ja5026408] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Exonucleolytic editing of incorrectly incorporated nucleotides by replicative DNA polymerases (DNAPs) plays an essential role in the fidelity of DNA replication. Editing requires that the primer strand of the DNA substrate be transferred between the DNAP polymerase and exonuclease sites, separated by a distance that is typically on the order of ~30 Å. Dynamic transitions between functional states can be quantified with single-nucleotide spatial precision and submillisecond temporal resolution from ionic current time traces recorded when individual DNAP complexes are held atop a nanoscale pore in an electric field. In this study, we have exploited this capability to determine the kinetic relationship between the translocation step and primer strand transfer between the polymerase and exonuclease sites in complexes formed between the replicative DNAP from bacteriophage Φ29 and DNA. We demonstrate that the pathway for primer strand transfer from the polymerase to exonuclease site initiates prior to the translocation step, while complexes are in the pre-translocation state. We developed a mathematical method to determine simultaneously the forward and reverse translocation rates and the rates of primer strand transfer in both directions between the polymerase and the exonuclease sites, and we have applied it to determine these rates for Φ29 DNAP complexes formed with a DNA substrate bearing a fully complementary primer-template duplex. This work provides a framework that will be extended to determine the kinetic mechanisms by which incorporation of noncomplementary nucleotides promotes primer strand transfer from the polymerase site to the exonuclease site.
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Affiliation(s)
- Kate R Lieberman
- Department of Biomolecular Engineering, ‡Department of Applied Mathematics and Statistics, Baskin School of Engineering, University of California , Santa Cruz, California 95064, United States
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38
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Towle-Weicksel JB, Dalal S, Sohl CD, Doublié S, Anderson KS, Sweasy JB. Fluorescence resonance energy transfer studies of DNA polymerase β: the critical role of fingers domain movements and a novel non-covalent step during nucleotide selection. J Biol Chem 2014; 289:16541-50. [PMID: 24764311 DOI: 10.1074/jbc.m114.561878] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
During DNA repair, DNA polymerase β (Pol β) is a highly dynamic enzyme that is able to select the correct nucleotide opposite a templating base from a pool of four different deoxynucleoside triphosphates (dNTPs). To gain insight into nucleotide selection, we use a fluorescence resonance energy transfer (FRET)-based system to monitor movement of the Pol β fingers domain during catalysis in the presence of either correct or incorrect dNTPs. By labeling the fingers domain with ((((2-iodoacetyl)amino)ethyl)amino)naphthalene-1-sulfonic acid (IAEDANS) and the DNA substrate with Dabcyl, we are able to observe rapid fingers closing in the presence of correct dNTPs as the IAEDANS comes into contact with a Dabcyl-labeled, one-base gapped DNA. Our findings show that not only do the fingers close after binding to the correct dNTP, but that there is a second conformational change associated with a non-covalent step not previously reported for Pol β. Further analyses suggest that this conformational change corresponds to the binding of the catalytic metal into the polymerase active site. FRET studies with incorrect dNTP result in no changes in fluorescence, indicating that the fingers do not close in the presence of incorrect dNTP. Together, our results show that nucleotide selection initially occurs in an open fingers conformation and that the catalytic pathways of correct and incorrect dNTPs differ from each other. Overall, this study provides new insight into the mechanism of substrate choice by a polymerase that plays a critical role in maintaining genome stability.
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Affiliation(s)
| | | | - Christal D Sohl
- Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520 and
| | - Sylvie Doublié
- the Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont 05405
| | - Karen S Anderson
- Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520 and
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39
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Optimized delivery of fluorescently labeled proteins in live bacteria using electroporation. Histochem Cell Biol 2014; 142:113-24. [PMID: 24696085 PMCID: PMC4072925 DOI: 10.1007/s00418-014-1213-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/13/2014] [Indexed: 10/31/2022]
Abstract
Studying the structure and dynamics of proteins in live cells is essential to understanding their physiological activities and mechanisms, and to validating in vitro characterization. Improvements in labeling and imaging technologies are starting to allow such in vivo studies; however, a number of technical challenges remain. Recently, we developed an electroporation-based protocol for internalization, which allows biomolecules labeled with organic fluorophores to be introduced at high efficiency into live E. coli (Crawford et al. in Biophys J 105 (11):2439-2450, 2013). Here, we address important challenges related to internalization of proteins, and optimize our method in terms of (1) electroporation buffer conditions; (2) removal of dye contaminants from stock protein samples; and (3) removal of non-internalized molecules from cell suspension after electroporation. We illustrate the usability of the optimized protocol by demonstrating high-efficiency internalization of a 10-kDa protein, the ω subunit of RNA polymerase. Provided that suggested control experiments are carried out, any fluorescently labeled protein of up to 60 kDa could be internalized using our method. Further, we probe the effect of electroporation voltage on internalization efficiency and cell viability and demonstrate that, whilst internalization increases with increased voltage, cell viability is compromised. However, due to the low number of damaged cells in our samples, the major fraction of loaded cells always corresponds to non-damaged cells. By taking care to include only viable cells into analysis, our method allows physiologically relevant studies to be performed, including in vivo measurements of protein diffusion, localization and intramolecular dynamics via single-molecule Förster resonance energy transfer.
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40
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Maxwell BA, Xu C, Suo Z. Conformational dynamics of a Y-family DNA polymerase during substrate binding and catalysis as revealed by interdomain Förster resonance energy transfer. Biochemistry 2014; 53:1768-78. [PMID: 24568554 PMCID: PMC3985488 DOI: 10.1021/bi5000146] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
Numerous kinetic, structural, and
theoretical studies have established
that DNA polymerases adjust their domain structures to enclose nucleotides
in their active sites and then rearrange critical active site residues
and substrates for catalysis, with the latter conformational change
acting to kinetically limit the correct nucleotide incorporation rate.
Additionally, structural studies have revealed a large conformational
change between the apoprotein and the DNA–protein binary state
for Y-family DNA polymerases. In previous studies [Xu, C., Maxwell,
B. A., Brown, J. A., Zhang, L., and Suo, Z. (2009) PLoS Biol.7, e1000225], a real-time Förster resonance
energy transfer (FRET) method was developed to monitor the global
conformational transitions of DNA polymerase IV from Sulfolobus
solfataricus (Dpo4), a prototype Y-family enzyme, during
nucleotide binding and incorporation by measuring changes in distance
between locations on the enzyme and the DNA substrate. To elucidate
further details of the conformational transitions of Dpo4 during substrate
binding and catalysis, in this study, the real-time FRET technique
was used to monitor changes in distance between various pairs of locations
in the protein itself. In addition to providing new insight into the
conformational changes as revealed in previous studies, the results
here show that the previously described conformational change between
the apo and DNA-bound states of Dpo4 occurs in a mechanistic step
distinct from initial formation or dissociation of the binary complex
of Dpo4 and DNA.
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Affiliation(s)
- Brian A Maxwell
- Ohio State Biophysics Program and ‡Department of Chemistry and Biochemistry, The Ohio State University , Columbus, Ohio 43210, United States
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41
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Farooq S, Fijen C, Hohlbein J. Studying DNA-protein interactions with single-molecule Förster resonance energy transfer. PROTOPLASMA 2014; 251:317-32. [PMID: 24374460 DOI: 10.1007/s00709-013-0596-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Accepted: 12/09/2013] [Indexed: 05/21/2023]
Abstract
Single-molecule Förster resonance energy transfer (smFRET) has emerged as a powerful tool for elucidating biological structure and mechanisms on the molecular level. Here, we focus on applications of smFRET to study interactions between DNA and enzymes such as DNA and RNA polymerases. SmFRET, used as a nanoscopic ruler, allows for the detection and precise characterisation of dynamic and rarely occurring events, which are otherwise averaged out in ensemble-based experiments. In this review, we will highlight some recent developments that provide new means of studying complex biological systems either by combining smFRET with force-based techniques or by using data obtained from smFRET experiments as constrains for computer-aided modelling.
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Affiliation(s)
- Shazia Farooq
- Laboratory of Biophysics, Wageningen UR, Wageningen, The Netherlands
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42
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Hohlbein J, Aigrain L, Craggs TD, Bermek O, Potapova O, Shoolizadeh P, Grindley NDF, Joyce CM, Kapanidis AN. Conformational landscapes of DNA polymerase I and mutator derivatives establish fidelity checkpoints for nucleotide insertion. Nat Commun 2014; 4:2131. [PMID: 23831915 PMCID: PMC3715850 DOI: 10.1038/ncomms3131] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2012] [Accepted: 06/11/2013] [Indexed: 01/04/2023] Open
Abstract
The fidelity of DNA polymerases depends on conformational changes that promote the rejection of incorrect nucleotides before phosphoryl transfer. Here, we combine single-molecule FRET with the use of DNA polymerase I and various fidelity mutants to highlight mechanisms by which active-site side chains influence the conformational transitions and free-energy landscape that underlie fidelity decisions in DNA synthesis. Ternary complexes of high fidelity derivatives with complementary dNTPs adopt mainly a fully closed conformation, whereas a conformation with a FRET value between those of open and closed is sparsely populated. This intermediate-FRET state, which we attribute to a partially closed conformation, is also predominant in ternary complexes with incorrect nucleotides and, strikingly, in most ternary complexes of low-fidelity derivatives for both correct and incorrect nucleotides. The mutator phenotype of the low-fidelity derivatives correlates well with reduced affinity for complementary dNTPs and highlights the partially closed conformation as a primary checkpoint for nucleotide selection. The fidelity of DNA polymerases depends on conformational changes that promote the rejection of incorrect nucleotides. Here, by using an intramolecular single-molecule FRET assay, the authors establish and characterize the partially closed conformation as a crucial fidelity checkpoint.
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Affiliation(s)
- Johannes Hohlbein
- Biological Physics Research Group, Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK
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43
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Brenlla A, Markiewicz RP, Rueda D, Romano LJ. Nucleotide selection by the Y-family DNA polymerase Dpo4 involves template translocation and misalignment. Nucleic Acids Res 2013; 42:2555-63. [PMID: 24270793 PMCID: PMC3936744 DOI: 10.1093/nar/gkt1149] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Y-family DNA polymerases play a crucial role in translesion DNA synthesis. Here, we have characterized the binding kinetics and conformational dynamics of the Y-family polymerase Sulfolobus solfataricus P2 DNA polymerase IV (Dpo4) using single-molecule fluorescence. We find that in the absence of dNTPs, the binary complex shuttles between two different conformations within ∼1 s. These data are consistent with prior crystal structures in which the nucleotide binding site is either occupied by the terminal base pair (preinsertion conformation) or empty following Dpo4 translocation by 1 base pair (insertion conformation). Most interestingly, on dNTP binding, only the insertion conformation is observed and the correct dNTP stabilizes this complex compared with the binary complex, whereas incorrect dNTPs destabilize it. However, if the n+1 template base is complementary to the incoming dNTP, a structure consistent with a misaligned template conformation is observed, in which the template base at the n position loops out. This structure provides evidence for a Dpo4 mutagenesis pathway involving a transient misalignment mechanism.
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Affiliation(s)
- Alfonso Brenlla
- Department of Chemistry, Wayne State University, Detroit, MI 48202, USA, Department of Medicine, Section of Virology, Imperial College London, London W12 0NN, UK and Single Molecule Imaging, MRC Clinical Sciences Center, Imperial College London, London W12 0NN, UK
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44
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Bermek O, Grindley NDF, Joyce CM. Prechemistry nucleotide selection checkpoints in the reaction pathway of DNA polymerase I and roles of glu710 and tyr766. Biochemistry 2013; 52:6258-74. [PMID: 23937394 PMCID: PMC3770053 DOI: 10.1021/bi400837k] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
![]()
The accuracy of high-fidelity DNA
polymerases such as DNA polymerase
I (Klenow fragment) is governed by conformational changes early in
the reaction pathway that serve as fidelity checkpoints, identifying
inappropriate template–nucleotide pairings. The fingers-closing
transition (detected by a fluorescence resonance energy transfer-based
assay) is the unique outcome of binding a correct incoming nucleotide,
both complementary to the templating base and with a deoxyribose (rather
than ribose) sugar structure. Complexes with mispaired dNTPs or complementary
rNTPs are arrested at an earlier stage, corresponding to a partially
closed fingers conformation, in which weak binding of DNA and nucleotide
promote dissociation and resampling of the substrate pool. A 2-aminopurine
fluorescence probe on the DNA template provides further information
about the steps preceding fingers closing. A characteristic 2-aminopurine
signal is observed on binding a complementary nucleotide, regardless
of whether the sugar is deoxyribose or ribose. However, mispaired
dNTPs show entirely different behavior. Thus, a fidelity checkpoint
ahead of fingers closing is responsible for distinguishing complementary
from noncomplementary nucleotides and routing them toward different
outcomes. The E710A mutator polymerase has a defect in the early fidelity
checkpoint such that some complementary dNTPs are treated as if they
were mispaired. In the Y766A mutant, the early checkpoint functions
normally, but some correctly paired dNTPs do not efficiently undergo
fingers closing. Thus, both mutator alleles cause a blurring of the
distinction between correct and incorrect base pairs and result in
a larger fraction of errors passing through the prechemistry fidelity
checkpoints.
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Affiliation(s)
- Oya Bermek
- Department of Molecular Biophysics and Biochemistry, Yale University , New Haven, Connecticut 06520, United States
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45
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Espinoza-Herrera SJ, Gaur V, Suo Z, Carey PR. Following DNA chain extension and protein conformational changes in crystals of a Y-family DNA polymerase via Raman crystallography. Biochemistry 2013; 52:4881-90. [PMID: 23855392 DOI: 10.1021/bi400524h] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Y-Family DNA polymerases are known to bypass DNA lesions in vitro and in vivo. Sulfolobus solfataricus DNA polymerase (Dpo4) was chosen as a model Y-family enzyme for investigating the mechanism of DNA synthesis in single crystals. Crystals of Dpo4 in complexes with DNA (the binary complex) in the presence or absence of an incoming nucleotide were analyzed by Raman microscopy. (13)C- and (15)N-labeled d*CTP, or unlabeled dCTP, were soaked into the binary crystals with G as the templating base. In the presence of the catalytic metal ions, Mg(2+) and Mn(2+), nucleotide incorporation was detected by the disappearance of the triphosphate band of dCTP and the retention of *C modes in the crystal following soaking out of noncovalently bound C(or *C)TP. The addition of the second coded base, thymine, was observed by adding cognate dTTP to the crystal following a single d*CTP addition. Adding these two bases caused visible damage to the crystal that was possibly caused by protein and/or DNA conformational change within the crystal. When d*CTP is soaked into the Dpo4 crystal in the absence of Mn(2+) or Mg(2+), the primer extension reaction did not occur; instead, a ternary protein·template·d*CTP complex was formed. In the Raman difference spectra of both binary and ternary complexes, in addition to the modes of d(*C)CTP, features caused by ring modes from the template/primer bases being perturbed and from the DNA backbone appear, as well as features from perturbed peptide and amino acid side chain modes. These effects are more pronounced in the ternary complex than in the binary complex. Using standardized Raman intensities followed as a function of time, the C(*C)TP population in the crystal was maximal at ∼20 min. These remained unchanged in the ternary complex but declined in the binary complexes as chain incorporation occurred.
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46
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Wang H, Hurt N, Dunbar WB. Measuring and modeling the kinetics of individual DNA-DNA polymerase complexes on a nanopore. ACS NANO 2013; 7:3876-3886. [PMID: 23565679 PMCID: PMC3682681 DOI: 10.1021/nn401180j] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The assembly of a DNA-DNA polymerase binary complex is the precursory step in genome replication, in which the enzyme binds to the 3' junction created when a primer binds to its complementary substrate. In this study, we use an active control method for observing the binding interaction between Klenow fragment (exo-) (KF) in the bulk-phase chamber above an α-hemolysin (α-HL) nanopore and a single DNA molecule tethered noncovalently in the nanopore. Specifically, the control method regulates the temporal availability of the primer-template DNA to KF binding and unbinding above the nanopore, on millisecond-to-second time scales. Our nanopore measurements support a model that incorporates two mutually exclusive binding states of KF to DNA at the primer-template junction site, termed "weakly bound" and "strongly bound" states. The composite binding affinity constant, the equilibrium constant between the weak and strong states, and the unbound-to-strong association rate are quantified from the data using derived modeling analysis. The results support that the strong state is in the nucleotide incorporation pathway, consistent with other nanopore assays. Surprisingly, the measured unbound-to-strong association process does not fit a model that admits binding of only free (unbound) KF to the tethered DNA but does fit an association rate that is proportional to the total (unbound and DNA-bound) KF concentration in the chamber above the nanopore. Our method provides a tool for measuring pre-equilibrium kinetics one molecule at a time, serially and for tens of thousands of single-molecule events, and can be used for other polynucleotide-binding enzymes.
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Affiliation(s)
- Hongyun Wang
- Department of Applied Mathematics and Statistics, University of California, Santa Cruz, 95064
| | - Nicholas Hurt
- Department of Chemistry and Biochemistry, University of California, Santa Cruz, 95064
| | - William B. Dunbar
- Department of Computer Engineering, University of California, Santa Cruz, 95064
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47
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Lahiri I, Mukherjee P, Pata JD. Kinetic characterization of exonuclease-deficient Staphylococcus aureus PolC, a C-family replicative DNA polymerase. PLoS One 2013; 8:e63489. [PMID: 23696828 PMCID: PMC3656037 DOI: 10.1371/journal.pone.0063489] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2013] [Accepted: 04/03/2013] [Indexed: 11/19/2022] Open
Abstract
PolC is the C-family replicative polymerase in low G+C content Gram-positive bacteria. To date several structures of C-family polymerases have been reported, including a high resolution crystal structure of a ternary complex of PolC with DNA and incoming deoxynucleoside triphosphate (dNTP). However, kinetic information needed to understand the enzymatic mechanism of C-family polymerases is limited. For this study we have performed a detailed steady-state and pre-steady-state kinetic characterization of correct dNTP incorporation by PolC from the Gram-positive pathogen Staphylococcus aureus, using a construct lacking both the non-conserved N-terminal domain and the 3′–5′ exonuclease domain (Sau-PolC-ΔNΔExo). We find that Sau-PolC-ΔNΔExo has a very fast catalytic rate (kpol 330 s−1) but also dissociates from DNA rapidly (koff ∼150 s−1), which explains the low processivity of PolC in the absence of sliding clamp processivity factor. Although Sau-PolC-ΔNΔExo follows the overall enzymatic pathway defined for other polymerases, some significant differences exist. The most striking feature is that the nucleotidyl transfer reaction for Sau-PolC-ΔNΔExo is reversible and is in equilibrium with dNTP binding. Simulation of the reaction pathway suggests that rate of pyrophosphate release, or a conformational change required for pyrophosphate release, is much slower than rate of bond formation. The significance of these findings is discussed in the context of previous data showing that binding of the β-clamp processivity factor stimulates the intrinsic nucleotide incorporation rate of the C-family polymerases, in addition to increasing processivity.
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Affiliation(s)
- Indrajit Lahiri
- Wadsworth Center, New York State Department of Health, Albany, New York, United States of America
- Department of Biomedical Sciences, University at Albany School of Public Health, Albany, New York, United States of America
| | - Purba Mukherjee
- Wadsworth Center, New York State Department of Health, Albany, New York, United States of America
- Department of Biomedical Sciences, University at Albany School of Public Health, Albany, New York, United States of America
| | - Janice D. Pata
- Wadsworth Center, New York State Department of Health, Albany, New York, United States of America
- Department of Biomedical Sciences, University at Albany School of Public Health, Albany, New York, United States of America
- * E-mail:
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48
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Olsen TJ, Choi Y, Sims PC, Gul OT, Corso BL, Dong C, Brown WA, Collins PG, Weiss GA. Electronic measurements of single-molecule processing by DNA polymerase I (Klenow fragment). J Am Chem Soc 2013; 135:7855-60. [PMID: 23631761 DOI: 10.1021/ja311603r] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Bioconjugating single molecules of the Klenow fragment of DNA polymerase I into electronic nanocircuits allowed electrical recordings of enzymatic function and dynamic variability with the resolution of individual nucleotide incorporation events. Continuous recordings of DNA polymerase processing multiple homopolymeric DNA templates extended over 600 s and through >10,000 bond-forming events. An enzymatic processivity of 42 nucleotides for a template of the same length was directly observed. Statistical analysis determined key kinetic parameters for the enzyme's open and closed conformations. Consistent with these nanocircuit-based observations, the enzyme's closed complex forms a phosphodiester bond in a highly efficient process >99.8% of the time, with a mean duration of only 0.3 ms for all four dNTPs. The rate-limiting step for catalysis occurs during the enzyme's open state, but with a nearly 2-fold longer duration for dATP or dTTP incorporation than for dCTP or dGTP into complementary, homopolymeric DNA templates. Taken together, the results provide a wealth of new information complementing prior work on the mechanism and dynamics of DNA polymerase I.
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Affiliation(s)
- Tivoli J Olsen
- Department of Chemistry, University of California, Irvine, California 92697, USA
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Maxwell BA, Suo Z. Single-molecule investigation of substrate binding kinetics and protein conformational dynamics of a B-family replicative DNA polymerase. J Biol Chem 2013; 288:11590-600. [PMID: 23463511 DOI: 10.1074/jbc.m113.459982] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Replicative DNA polymerases use a complex, multistep mechanism for efficient and accurate DNA replication as uncovered by intense kinetic and structural studies. Recently, single-molecule fluorescence spectroscopy has provided new insights into real time conformational dynamics utilized by DNA polymerases during substrate binding and nucleotide incorporation. We have used single-molecule Förster resonance energy transfer techniques to investigate the kinetics and conformational dynamics of Sulfolobus solfataricus DNA polymerase B1 (PolB1) during DNA and nucleotide binding. Our experiments demonstrate that this replicative polymerase can bind to DNA in at least three conformations, corresponding to an open and closed conformation of the finger domain as well as a conformation with the DNA substrate bound to the exonuclease active site of PolB1. Additionally, our results show that PolB1 can transition between these conformations without dissociating from a primer-template DNA substrate. Furthermore, we show that the closed conformation is promoted by a matched incoming dNTP but not by a mismatched dNTP and that mismatches at the primer-template terminus lead to an increase in the binding of the DNA to the exonuclease site. Our analysis has also revealed new details of the biphasic dissociation kinetics of the polymerase-DNA binary complex. Notably, comparison of the results obtained in this study with PolB1 with those from similar single-molecule studies with an A-family DNA polymerase suggests mechanistic differences between these polymerases. In summary, our findings provide novel mechanistic insights into protein conformational dynamics and substrate binding kinetics of a high fidelity B-family DNA polymerase.
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Affiliation(s)
- Brian A Maxwell
- Biophysics Program and the Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA
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Basu RS, Murakami KS. Watching the bacteriophage N4 RNA polymerase transcription by time-dependent soak-trigger-freeze X-ray crystallography. J Biol Chem 2012; 288:3305-11. [PMID: 23235152 DOI: 10.1074/jbc.m112.387712] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The challenge for structural biology is to understand atomic-level macromolecular motions during enzymatic reaction. X-ray crystallography can reveal high resolution structures; however, one perceived limitation is that it reveals only static views. Here we use time-dependent soak-trigger-freeze X-ray crystallography, namely, soaking nucleotide and divalent metal into the bacteriophage RNA polymerase (RNAP)-promoter DNA complex crystals to trigger the nucleotidyl transfer reaction and freezing crystals at different time points, to capture real-time intermediates in the pathway of transcription. In each crystal structure, different intensities and shapes of electron density maps corresponding to the nucleotide and metal were revealed at the RNAP active site which allow watching the nucleotide and metal bindings and the phosphodiester bond formation in a time perspective. Our study provides the temporal order of substrate assembly and metal co-factor binding at the active site of enzyme which completes our understanding of the two-metal-ion mechanism and fidelity mechanism in single-subunit RNAPs. The nucleotide-binding metal (Me(B)) is coordinated at the active site prior to the catalytic metal (Me(A)). Me(A) coordination is only temporal, established just before and dissociated immediately after phosphodiester bond formation. We captured these elusive intermediates exploiting the slow enzymatic reaction in crystallo. These results demonstrate that the simple time-dependent soak-trigger-freeze X-ray crystallography offers a direct means for monitoring enzymatic reactions.
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Affiliation(s)
- Ritwika S Basu
- Department of Biochemistry and Molecular Biology, The Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
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