1
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Figueroa Blanco DR, Vidossich P, De Vivo M. Correct Nucleotide Selection Is Confined at the Binding Site of Polymerase Enzymes. J Chem Inf Model 2024; 64:5285-5294. [PMID: 38901009 DOI: 10.1021/acs.jcim.4c00696] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/22/2024]
Abstract
DNA polymerases (Pols) add incoming nucleotides (deoxyribonucleoside triphosphate (dNTPs)) to growing DNA strands, a crucial step for DNA synthesis. The insertion of correct (vs incorrect) nucleotides relates to Pols' fidelity, which defines Pols' ability to faithfully replicate DNA strands in a template-dependent manner. We and others have demonstrated that reactant alignment and correct base pairing at the Pols catalytic site are crucial structural features to fidelity. Here, we first used equilibrium molecular simulations to demonstrate that the local dynamics at the protein-DNA interface in the proximity of the catalytic site is different when correct vs incorrect dNTPs are bound to polymerase β (Pol β). Formation and dynamic stability of specific interatomic interactions around the incoming nucleotide influence the overall binding site architecture. This explains why certain Pols' mutants can affect the local catalytic environment and influence the selection of correct vs incorrect nucleotides. In particular, this is here demonstrated by analyzing the interaction network formed by the residue R283, whose mutant R283A has an experimentally measured lower capacity of differentiating correct (G:dCTP) vs incorrect (G:dATP) base pairing in Pol β. We also used alchemical free-energy calculations to quantify the G:dCTP →G:dATP transformation in Pol β wild-type and mutant R283A. These results correlate well with the experimental trend, thus corroborating our mechanistic insights. Sequence and structural comparisons with other Pols from the same family suggest that these findings may also be valid in similar enzymes.
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Affiliation(s)
- David Ricardo Figueroa Blanco
- Laboratory of Molecular Modelling & Drug Discovery, Istituto Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy
| | - Pietro Vidossich
- Laboratory of Molecular Modelling & Drug Discovery, Istituto Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy
| | - Marco De Vivo
- Laboratory of Molecular Modelling & Drug Discovery, Istituto Italiano di Tecnologia, Via Morego 30, Genoa 16163, Italy
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2
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Gulkis M, Martinez E, Almohdar D, Çağlayan M. Unfilled gaps by polβ lead to aberrant ligation by LIG1 at the downstream steps of base excision repair pathway. Nucleic Acids Res 2024; 52:3810-3822. [PMID: 38366780 DOI: 10.1093/nar/gkae104] [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: 08/12/2023] [Revised: 01/11/2024] [Accepted: 02/06/2024] [Indexed: 02/18/2024] Open
Abstract
Base excision repair (BER) involves the tightly coordinated function of DNA polymerase β (polβ) and DNA ligase I (LIG1) at the downstream steps. Our previous studies emphasize that defective substrate-product channeling, from gap filling by polβ to nick sealing by LIG1, can lead to interruptions in repair pathway coordination. Yet, the molecular determinants that dictate accurate BER remains largely unknown. Here, we demonstrate that a lack of gap filling by polβ leads to faulty repair events and the formation of deleterious DNA intermediates. We dissect how ribonucleotide challenge and cancer-associated mutations could adversely impact the ability of polβ to efficiently fill the one nucleotide gap repair intermediate which subsequently results in gap ligation by LIG1, leading to the formation of single-nucleotide deletion products. Moreover, we demonstrate that LIG1 is not capable of discriminating against nick DNA containing a 3'-ribonucleotide, regardless of base-pairing potential or damage. Finally, AP-Endonuclease 1 (APE1) shows distinct substrate specificity for the exonuclease removal of 3'-mismatched bases and ribonucleotides from nick repair intermediate. Overall, our results reveal that unfilled gaps result in impaired coordination between polβ and LIG1, defining a possible type of mutagenic event at the downstream steps where APE1 could provide a proofreading role to maintain BER efficiency.
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Affiliation(s)
- Mitchell Gulkis
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA
| | - Ernesto Martinez
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA
| | - Danah Almohdar
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA
| | - Melike Çağlayan
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610, USA
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3
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Abstract
DNA polymerase beta (Pol β) is a 39 kD vertebrate polymerase that lacks proofreading ability, yet still maintains a moderate fidelity of DNA synthesis. Pol β is a key enzyme that functions in the base excision repair and non-homologous end joining pathways of DNA repair. Mechanisms of fidelity for Pol β are still being elucidated but are likely to involve dynamic conformational motions of the enzyme upon its binding to DNA and deoxynucleoside triphosphates. Recent studies have linked germline and somatic variants of Pol β with cancer and autoimmunity. These variants induce genomic instability by a number of mechanisms, including error-prone DNA synthesis and accumulation of single nucleotide gaps that lead to replication stress. Here, we review the structure and function of Pol β, and we provide insights into how structural changes in Pol β variants may contribute to genomic instability, mutagenesis, disease, cancer development, and impacts on treatment outcomes.
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Affiliation(s)
- Danielle L Sawyer
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ
| | - Joann B Sweasy
- Department of Cellular and Molecular Medicine, University of Arizona, Tucson, AZ
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4
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Maffeo C, Chou HY, Aksimentiev A. Molecular Mechanisms of DNA Replication and Repair Machinery: Insights from Microscopic Simulations. ADVANCED THEORY AND SIMULATIONS 2019; 2:1800191. [PMID: 31728433 PMCID: PMC6855400 DOI: 10.1002/adts.201800191] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Indexed: 12/15/2022]
Abstract
Reproduction, the hallmark of biological activity, requires making an accurate copy of the genetic material to allow the progeny to inherit parental traits. In all living cells, the process of DNA replication is carried out by a concerted action of multiple protein species forming a loose protein-nucleic acid complex, the replisome. Proofreading and error correction generally accompany replication but also occur independently, safeguarding genetic information through all phases of the cell cycle. Advances in biochemical characterization of intracellular processes, proteomics and the advent of single-molecule biophysics have brought about a treasure trove of information awaiting to be assembled into an accurate mechanistic model of the DNA replication process. In this review, we describe recent efforts to model elements of DNA replication and repair processes using computer simulations, an approach that has gained immense popularity in many areas of molecular biophysics but has yet to become mainstream in the DNA metabolism community. We highlight the use of diverse computational methods to address specific problems of the fields and discuss unexplored possibilities that lie ahead for the computational approaches in these areas.
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Affiliation(s)
- Christopher Maffeo
- Department of Physics, Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign,1110 W Green St, Urbana, IL 61801, USA
| | - Han-Yi Chou
- Department of Physics, Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign,1110 W Green St, Urbana, IL 61801, USA
| | - Aleksei Aksimentiev
- Department of Physics, Center for the Physics of Living Cells, University of Illinois at Urbana-Champaign,1110 W Green St, Urbana, IL 61801, USA
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5
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Homouz D, Joyce-Tan KH, ShahirShamsir M, Moustafa IM, Idriss HT. Molecular dynamics simulations suggest changes in electrostatic interactions as a potential mechanism through which serine phosphorylation inhibits DNA polymerase β activity. J Mol Graph Model 2018; 84:236-241. [PMID: 30138833 DOI: 10.1016/j.jmgm.2018.08.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
DNA polymerase β is a 39 kDa enzyme that is a major component of Base Excision Repair in human cells. The enzyme comprises two major domains, a 31 kDa domain responsible for the polymerase activity and an 8 kDa domain, which bind ssDNA and has a deoxyribose phosphate (dRP) lyase activity. DNA polymerase β was shown to be phosphorylated in vitro with protein kinase C (PKC) at serines 44 and 55 (S44 and S55), resulting in loss of its polymerase enzymic activity, but not its ability to bind ssDNA. In this study, we investigate the potential phosphorylation-induced structural changes for DNA polymerase β using molecular dynamics simulations. The simulations show drastic conformational changes of the polymerase structure as a result of S44 phosphorylation. Phosphorylation-induced conformational changes transform the closed (active) enzyme structure into an open one. Further analysis of the results points to a key hydrogen bond and newly formed salt bridges as potential drivers of these structural fluctuations. The changes observed with S55/44 and S55 phosphorylation were less dramatic and the integrity of the H-bond was not compromised. Thus the phosphorylation of S44 is the major contributor to structural fluctuations that lead to loss of enzymatic activity.
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Affiliation(s)
- Dirar Homouz
- Department of Statistics and Applied Mathematics Khalifa University, Abu Dhabi, United Arab Emirates; Department of Physics, University of Houston, Houston, TX, USA; Center for Theoretical Biological Physics, Rice University, Houston, TX, USA
| | - Kwee Hong Joyce-Tan
- Faculty of Bioscience and Bioengineering, Universiti Teknologi Malaysia, Johor, Malaysia
| | - Mohd ShahirShamsir
- Faculty of Bioscience and Bioengineering, Universiti Teknologi Malaysia, Johor, Malaysia
| | | | - Haitham T Idriss
- Department of Biology and Biochemistry, Birzeit University, Palestine.
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6
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Homouz D, Joyce-Tan KH, Shahir Shamsir M, Moustafa IM, Idriss H. Molecular dynamics simulations suggest changes in electrostatic interactions as a potential mechanism through which serine phosphorylation inhibits DNA Polymerase β's activity. J Mol Graph Model 2017; 79:192. [PMID: 29223917 DOI: 10.1016/j.jmgm.2017.11.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2017] [Revised: 10/31/2017] [Accepted: 11/02/2017] [Indexed: 11/27/2022]
Abstract
DNA polymerase β is a 39kDa enzyme that is a major component of Base Excision Repair in human cells. The enzyme comprises two major domains, a 31kDa domain responsible for the polymerase activity and an 8kDa domain, which bind ssDNA and has a deoxyribose phosphate (dRP) lyase activity. DNA polymerase β was shown to be phosphorylated in vitro with protein kinase C (PKC) at serines 44 and 55 (S44 and S55), resulting in loss of its polymerase enzymic activity, but not its ability to bind ssDNA. In this study, we investigate the potential phosphorylation-induced structural changes for DNA polymerase β using molecular dynamics. The simulations show drastic conformational changes of the polymerase structure as a result of S44 phosphorylation. Phosphorylation-induced conformational changes transform the closed (active) enzyme structure into an open one. Further analysis of the results points to a key hydrogen bond and newly formed salt bridges as potential drivers of these structural fluctuations. The changes observed with S44/55 and S55 phosphorylation were less dramatic than S44 and the integrity of the H-bond was not compromised. Thus the phosphorylation of S44 is likely the major contributor to structural fluctuations that lead to loss of enzymatic activity.
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Affiliation(s)
- Dirar Homouz
- Department of Physics, Khalifa University of Science and Technology, P.O. Box 127788, Abu Dhabi, United Arab Emirates; Department of Physics, University of Houston, Houston, TX, USA; Center for Theoretical Biological Physics, Rice University, Houston, TX, USA
| | - Kwee Hong Joyce-Tan
- Faculty of Bioscience and Bioengineering, Universiti Teknologi Malaysia, Johor, Malaysia
| | - Mohd Shahir Shamsir
- Faculty of Bioscience and Bioengineering, Universiti Teknologi Malaysia, Johor, Malaysia
| | | | - Haitham Idriss
- Department of Biology and Biochemistry, Birzeit University, Palestine.
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7
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Rozacky J, Nemec AA, Sweasy JB, Kidane D. Gastric cancer associated variant of DNA polymerase beta (Leu22Pro) promotes DNA replication associated double strand breaks. Oncotarget 2016; 6:24474-87. [PMID: 26090616 PMCID: PMC4695199 DOI: 10.18632/oncotarget.4426] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2015] [Accepted: 05/31/2015] [Indexed: 12/14/2022] Open
Abstract
DNA polymerase beta (Pol β) is a key enzymefor the protection against oxidative DNA lesions via itsrole in base excision repair (BER). Approximately 1/3 of tumors studied to date express Pol β variant proteins, and several tumors overexpress Pol β. Pol β possesses DNA polymerase and dRP lyase activities, both of which are known to be important for efficient BER. The dRP lyase activity resides within the 8kDa amino terminal domain of Pol β, is responsible for removal of the 5′ phosphate group (5′-dRP). The DNA polymerase subsequently fills the gaps. Previously, we demonstrated that the human gastric cancer-associated variant of Pol β (Leu22Pro (L22P)) lacks dRP lyase function in vitro. Here, we report that L22P-expressing cells harbor significantly increased replication associated DNA double strand breaks (DSBs) and defective maintenance of the nascent DNA strand (NDS) during replication stress. Moreover, L22P-expressing cells are sensitive to PARP1 inhibitors, which suggests trapped PARP1 binds to the 5′-dRP group and blocks replications forks, resulting in fork collapse and DSBs. Our data suggest that the normal function of the dRP lyase is critical to maintain replication fork integrity and prevent replication fork collapse to DSBs and cellular transformation.
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Affiliation(s)
- Jenna Rozacky
- Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Dell Pediatric Research Institute, Austin, TX, USA
| | - Antoni A Nemec
- Department of Biomedical Sciences, Florida State University College of Medicine, Tallahassee, FL, USA
| | - Joann B Sweasy
- Departments of Therapeutic Radiology and Genetics, The Yale Comprehensive Cancer Center, New Haven CT, USA
| | - Dawit Kidane
- Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Dell Pediatric Research Institute, Austin, TX, USA
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8
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Kim T, Freudenthal BD, Beard WA, Wilson SH, Schlick T. Insertion of oxidized nucleotide triggers rapid DNA polymerase opening. Nucleic Acids Res 2016; 44:4409-24. [PMID: 27034465 PMCID: PMC4872097 DOI: 10.1093/nar/gkw174] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2016] [Accepted: 03/04/2016] [Indexed: 11/21/2022] Open
Abstract
A novel mechanism is unveiled to explain why a pro-mutagenic nucleotide lesion (oxidized guanine, 8-oxoG) causes the mammalian DNA repair polymerase-β (pol-β) to rapidly transition to an inactive open conformation. The mechanism involves unexpected features revealed recently in time-lapse crystallography. Specifically, a delicate water network associated with a lesion-stabilizing auxilliary product ion Mg(p) triggers a cascade of events that leads to poor active site geometry and the rupture of crucial molecular interactions between key residues in both the anti(8-oxoG:C) and syn(8-oxoG:A) systems. Once the base pairs in these lesioned systems are broken, dislocation of both Asp192 (a metal coordinating ligand) and the oxoG phosphate group (PO4) interfere with the hydrogen bonding between Asp192 and Arg258, whose rotation toward Asp192 is crucial to the closed-to-open enzyme transition. Energetically, the lesioned open states are similar in energy to those of the corresponding closed complexes after chemistry, in marked contrast to the unlesioned pol-β anti(G:C) system, whose open state is energetically higher than the closed state. The delicate surveillance system offers a fundamental protective mechanism in the cell that triggers DNA repair events which help deter insertion of oxidized lesions.
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Affiliation(s)
- Taejin Kim
- Department of Chemistry, New York University, 10th Floor Silver Center, 100 Washington Square East, New York, NY 10003, USA
| | - Bret D Freudenthal
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, P.O. Box 12233, Research Triangle Park, NC 27709, USA
| | - William A Beard
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, P.O. Box 12233, Research Triangle Park, NC 27709, USA
| | - Samuel H Wilson
- Genome Integrity and Structural Biology Laboratory, National Institute of Environmental Health Sciences, National Institutes of Health, P.O. Box 12233, Research Triangle Park, NC 27709, USA
| | - Tamar Schlick
- Department of Chemistry, New York University, 10th Floor Silver Center, 100 Washington Square East, New York, NY 10003, USA Courant Institute of Mathematical Sciences, New York University, 251 Mercer Street, New York, NY 10012, USA
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9
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Moscato B, Swain M, Loria JP. Induced Fit in the Selection of Correct versus Incorrect Nucleotides by DNA Polymerase β. Biochemistry 2016; 55:382-95. [PMID: 26678253 PMCID: PMC8259413 DOI: 10.1021/acs.biochem.5b01213] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
DNA polymerase β (Pol β) repairs single-nucleotide gapped DNA (sngDNA) by enzymatic incorporation of the Watson-Crick partner nucleotide at the gapped position opposite the templating nucleotide. The process by which the matching nucleotide is incorporated into a sngDNA sequence has been relatively well-characterized, but the process of discrimination from nucleotide misincorporation remains unclear. We report here NMR spectroscopic characterization of full-length, uniformly labeled Pol β in apo, sngDNA-bound binary, and ternary complexes containing matching and mismatching nucleotide. Our data indicate that, while binding of the correct nucleotide to the binary complex induces chemical shift changes consistent with the process of enzyme closure, the ternary Pol β complex containing a mismatching nucleotide exhibits no such changes and appears to remain in an open, unstable, binary-like conformation. Our findings support an induced-fit mechanism for polymerases in which a closed ternary complex can only be achieved in the presence of matching nucleotide.
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Affiliation(s)
- Beth Moscato
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - Monalisa Swain
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
| | - J. Patrick Loria
- Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, United States
- Department of Molecular Biophysics and Biochemistry, Yale University, 260 Whitney Avenue, New Haven, Connecticut 06520, United States
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10
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Abstract
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DNA
polymerase (pol) β is a small eukaryotic DNA polymerase
composed of two domains. Each domain contributes an enzymatic activity
(DNA synthesis and deoxyribose phosphate lyase) during the repair
of simple base lesions. These domains are termed the polymerase and
lyase domains, respectively. Pol β has been an excellent model
enzyme for studying the nucleotidyl transferase reaction and substrate
discrimination at a molecular level. In this review, recent crystallographic
studies of pol β in various liganded and conformational states
during the insertion of right and wrong nucleotides as well as during
the bypass of damaged DNA (apurinic sites and 8-oxoguanine) are described.
Structures of these catalytic intermediates provide unexpected insights
into mechanisms by which DNA polymerases enhance genome stability.
These structures also provide an improved framework that permits computational
studies to facilitate the interpretation of detailed kinetic analyses
of this model enzyme.
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Affiliation(s)
- William A Beard
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences, National Institutes of Health , 111 T. W. Alexander Drive, P.O. Box 12233, MD F3-01, Research Triangle Park, North Carolina 27709, United States
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11
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Kirby TW, Derose EF, Beard WA, Shock DD, Wilson SH, London RE. Substrate rescue of DNA polymerase β containing a catastrophic L22P mutation. Biochemistry 2014; 53:2413-22. [PMID: 24655288 PMCID: PMC4004254 DOI: 10.1021/bi5001855] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
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DNA polymerase (pol)
β is a multidomain enzyme with two enzymatic
activities that plays a central role in the overlapping base excision
repair and single-strand break repair pathways. The high frequency
of pol β variants identified in tumor-derived tissues suggests
a possible role in the progression of cancer, making the determination
of the functional consequences of these variants of interest. Pol
β containing a proline substitution for leucine 22 in the lyase
domain (LD), identified in gastric tumors, has been reported to exhibit
severe impairment of both lyase and polymerase activities. Nuclear
magnetic resonance (NMR) spectroscopic evaluations of both pol β
and the isolated LD containing the L22P mutation demonstrate destabilization
sufficient to result in LD-selective unfolding with minimal structural
perturbations to the polymerase domain. Unexpectedly, addition of
single-stranded or hairpin DNA resulted in partial refolding of the
mutated lyase domain, both in isolation and for the full-length enzyme.
Further, formation of an abortive ternary complex using Ca2+ and a complementary dNTP indicates that the fraction of pol β(L22P)
containing the folded LD undergoes conformational activation similar
to that of the wild-type enzyme. Kinetic characterization of the polymerase
activity of L22P pol β indicates that the L22P mutation compromises
DNA binding, but nearly wild-type catalytic rates can be observed
at elevated substrate concentrations. The organic osmolyte trimethylamine N-oxide (TMAO) is similarly able to induce folding and kinetic
activation of both polymerase and lyase activities of the mutant.
Kinetic data indicate synergy between the TMAO cosolvent and substrate
binding. NMR data indicate that the effect of the DNA results primarily
from interaction with the folded LD(L22P), while the effect of the
TMAO results primarily from destabilization of the unfolded LD(L22P).
These studies illustrate that substrate-induced catalytic activation
of pol β provides an optimal enzyme conformation even in the
presence of a strongly destabilizing point mutation. Accordingly,
it remains to be determined whether this mutation alters the threshold
of cellular repair activity needed for routine genome maintenance
or whether the “inactive” variant interferes with DNA
repair.
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Affiliation(s)
- Thomas W Kirby
- Laboratory of Structural Biology, National Institute of Environmental Health Sciences , Research Triangle Park, North Carolina 27709, United States
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12
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Li Y, Freudenthal BD, Beard WA, Wilson SH, Schlick T. Optimal and variant metal-ion routes in DNA polymerase β's conformational pathways. J Am Chem Soc 2014; 136:3630-9. [PMID: 24511902 PMCID: PMC7032070 DOI: 10.1021/ja412701f] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To interpret recent structures of the R283K mutant of human DNA repair enzyme DNA polymerase β (pol β) differing in the number of Mg(2+) ions, we apply transition path sampling (TPS) to assess the effect of differing ion placement on the transition from the open one-metal to the closed two-metal state. We find that the closing pathway depends on the initial ion position, both in terms of the individual transition states and associated energies. The energy barrier of the conformational pathway varies from 25 to 58 kJ/mol, compared to the conformational energy barrier of 42 kJ/mol for the wild-type pol β reported previously. Moreover, we find a preferred ion route located in the center of the enzyme, parallel to the DNA. Within this route, the conformational pathway is similar to that of the overall open to closed transition of pol β, but outside it, especially when the ion starts near active site residues Arg258 and Asp190, the conformational pathway diverges significantly. Our findings should apply generally to pol β, since R283K is relatively far from the active site; further experimental and computational work are required to confirm this. Our studies also underscore the common feature that less active mutants have less stable closed states than their open states, in marked contrast to the wild-type enzyme, where the closed state is significantly more stable than the open form.
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Affiliation(s)
- Yunlang Li
- Department of Chemistry and Courant Institute of
Mathematical Sciences, New York University, 251 Mercer Street, New York, NY
10012
| | - Bret D. Freudenthal
- Laboratory of Structural Biology, National
Institute of Environmental Health Sciences, National Institutes of Health, Bethesda,
Research Triangle Park, NC 27709
| | - William A. Beard
- Laboratory of Structural Biology, National
Institute of Environmental Health Sciences, National Institutes of Health, Bethesda,
Research Triangle Park, NC 27709
| | - Samuel H. Wilson
- Laboratory of Structural Biology, National
Institute of Environmental Health Sciences, National Institutes of Health, Bethesda,
Research Triangle Park, NC 27709
| | - Tamar Schlick
- Department of Chemistry and Courant Institute of
Mathematical Sciences, New York University, 251 Mercer Street, New York, NY
10012
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13
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Ray S, Menezes MR, Senejani A, Sweasy JB. Cellular roles of DNA polymerase beta. THE YALE JOURNAL OF BIOLOGY AND MEDICINE 2013; 86:463-9. [PMID: 24348210 PMCID: PMC3848100] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Since its discovery and purification in 1971, DNA polymerase ß (Pol ß) is one of the most well-studied DNA polymerases. Pol ß is a key enzyme in the base excision repair (BER) pathway that functions in gap filling DNA synthesis subsequent to the excision of damaged DNA bases. A major focus of our studies is on the cellular roles of Pol ß. We have shown that germline and tumor-associated variants of Pol ß catalyze aberrant BER that leads to genomic instability and cellular transformation. Our studies suggest that Pol ß is critical for the maintenance of genomic stability and that it is a tumor suppressor. We have also shown that Pol ß functions during Prophase I of meiosis. Pol ß localizes to the synaptonemal complex and is critical for removal of the Spo11 complex from the 5' ends of double-strand breaks. Studies with Pol ß mutant mice are currently being undertaken to more clearly understand the function of Pol ß during meiosis. In this review, we will highlight our contributions from our studies of Pol ß germline and cancer-associated variants.
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Affiliation(s)
| | | | | | - Joann B. Sweasy
- To whom all correspondence should be
addressed: Joann B. Sweasy, Department of Therapeutic Radiology, Yale School of
Medicine, 333 Cedar St., P.O. Box 208040, New Haven, CT 06520; Tele:
203-737-2626; Fax: 203-785-6309;
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14
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Eckenroth BE, Towle-Weicksel JB, Sweasy JB, Doublié S. The E295K cancer variant of human polymerase β favors the mismatch conformational pathway during nucleotide selection. J Biol Chem 2013; 288:34850-60. [PMID: 24133209 DOI: 10.1074/jbc.m113.510891] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
DNA polymerase β (pol β) is responsible for gap filling synthesis during repair of damaged DNA as part of the base excision repair pathway. Human pol β mutations were recently identified in a high percentage (∼30%) of tumors. Characterization of specific cancer variants is particularly useful to further the understanding of the general mechanism of pol β while providing context to disease contribution. We showed that expression of the carcinoma variant E295K induces cellular transformation. The poor polymerase activity exhibited by the variant was hypothesized to be caused by the destabilization of proper active site assembly by the glutamate to lysine mutation. Here, we show that this variant exhibits an unusual preference for binding dCTP opposite a templating adenine over the cognate dTTP. Biochemical studies indicate that the noncognate competes with the cognate nucleotide for binding to the polymerase active site with the noncognate incorporation a function of higher affinity and not increased activity. In the crystal structure of the variant bound to dA:dCTP, the fingers domain closes around the mismatched base pair. Nucleotide incorporation is hindered because key residues in the polymerase active site are not properly positioned for nucleotidyl transfer. In contrast to the noncognate dCTP, neither the cognate dTTP nor its nonhydrolyzable analog induced fingers closure, as isomorphous difference Fourier maps show that the cognate nucleotides are bound to the open state of the polymerase. Comparison with published structures provides insight into the structural rearrangements within pol β that occur during the process of nucleotide discrimination.
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Affiliation(s)
- Brian E Eckenroth
- From the Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont 05405 and
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15
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Schlick T, Arora K, Beard WA, Wilson SH. Perspective: pre-chemistry conformational changes in DNA polymerase mechanisms. Theor Chem Acc 2012; 131:1287. [PMID: 23459563 DOI: 10.1007/s00214-012-1287-7] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
In recent papers, there has been a lively exchange concerning theories for enzyme catalysis, especially the role of protein dynamics/pre-chemistry conformational changes in the catalytic cycle of enzymes. Of particular interest is the notion that substrate-induced conformational changes that assemble the polymerase active site prior to chemistry are required for DNA synthesis and impact fidelity (i.e., substrate specificity). High-resolution crystal structures of DNA polymerase β representing intermediates of substrate complexes prior to the chemical step are available. These structures indicate that conformational adjustments in both the protein and substrates must occur to achieve the requisite geometry of the reactive participants for catalysis. We discuss computational and kinetic methods to examine possible conformational change pathways that lead from the observed crystal structure intermediates to the final structures poised for chemistry. The results, as well as kinetic data from site-directed mutagenesis studies, are consistent with models requiring pre-chemistry conformational adjustments in order to achieve high fidelity DNA synthesis. Thus, substrate-induced conformational changes that assemble the polymerase active site prior to chemistry contribute to DNA synthesis even when they do not represent actual rate-determining steps for chemistry.
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Affiliation(s)
- Tamar Schlick
- Department of Chemistry, New York University, 100 Washington Square East, Silver Building, New York, NY 10003, USA. Courant Institute of Mathematical Sciences, New York, University, 251 Mercer Street, New York, NY 10012, USA
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Ram Prasad B, Kamerlin SCL, Florián J, Warshel A. Prechemistry barriers and checkpoints do not contribute to fidelity and catalysis as long as they are not rate limiting. Theor Chem Acc 2012. [DOI: 10.1007/s00214-012-1288-6] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Affiliation(s)
- Robert W Sobol
- Department of Pharmacology and Chemical Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, United States of America.
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