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Zhao W, Xu W, Tang J, Kaushik S, Chang CEA, Zhao L. Key Amino Acid Residues of Mitochondrial Transcription Factor A Synergize with Abasic (AP) Site Dynamics To Facilitate AP-Lyase Reactions. ACS Chem Biol 2023; 18:1168-1179. [PMID: 36930463 PMCID: PMC10198963 DOI: 10.1021/acschembio.3c00047] [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] [Indexed: 03/18/2023]
Abstract
Human mitochondrial DNA (mtDNA) encodes 37 essential genes and plays a critical role in mitochondrial and cellular functions. mtDNA is susceptible to damage by endogenous and exogenous chemicals. Damaged mtDNA molecules are counteracted by the redundancy, repair, and degradation of mtDNA. In response to difficult-to-repair or excessive amounts of DNA lesions, mtDNA degradation is a crucial mitochondrial genome maintenance mechanism. Nevertheless, the molecular basis of mtDNA degradation remains incompletely understood. Recently, mitochondrial transcription factor A (TFAM) has emerged as a factor in degrading damaged mtDNA containing abasic (AP) sites. TFAM has AP-lyase activity, which cleaves DNA at AP sites. Human TFAM and its homologs contain a higher abundance of Glu than that of the proteome. To decipher the role of Glu in TFAM-catalyzed AP-DNA cleavage, we constructed TFAM variants and used biochemical assays, kinetic simulations, and molecular dynamics (MD) simulations to probe the functional importance of E187 near a key residue K186. Our previous studies showed that K186 is a primary residue to cleave AP-DNA via Schiff base chemistry. Here, we demonstrate that E187 facilitates β-elimination, key to AP-DNA strand scission. MD simulations showed that extrahelical confirmation of the AP lesion and the flexibility of E187 in TFAM-DNA complexes facilitate AP-lyase reactions. Together, highly abundant Lys and Glu residues in TFAM promote AP-DNA strand scission, supporting the role of TFAM in AP-DNA turnover and implying the breadth of this process across different species.
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Affiliation(s)
- Wenxin Zhao
- Department of Chemistry, University of California, Riverside, Riverside, California, 92521, United States
| | - Wenyan Xu
- Department of Chemistry, University of California, Riverside, Riverside, California, 92521, United States
| | - Jin Tang
- Department of Chemistry, University of California, Riverside, Riverside, California, 92521, United States
| | - Shivansh Kaushik
- Department of Chemistry, University of California, Riverside, Riverside, California, 92521, United States
| | - Chia-En A. Chang
- Department of Chemistry, University of California, Riverside, Riverside, California, 92521, United States
- Environmental Toxicology Graduate Program, University of California, Riverside, Riverside, California, 92521, United States
| | - Linlin Zhao
- Department of Chemistry, University of California, Riverside, Riverside, California, 92521, United States
- Environmental Toxicology Graduate Program, University of California, Riverside, Riverside, California, 92521, United States
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2
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Ten TB, Zvoda V, Sarangi MK, Kuznetsov SV, Ansari A. "Flexible hinge" dynamics in mismatched DNA revealed by fluorescence correlation spectroscopy. J Biol Phys 2022; 48:253-272. [PMID: 35451661 PMCID: PMC9411374 DOI: 10.1007/s10867-022-09607-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2021] [Accepted: 03/22/2022] [Indexed: 10/18/2022] Open
Abstract
Altered unwinding/bending fluctuations at DNA lesion sites are implicated as plausible mechanisms for damage sensing by DNA-repair proteins. These dynamics are expected to occur on similar timescales as one-dimensional (1D) diffusion of proteins on DNA if effective in stalling these proteins as they scan DNA. We examined the flexibility and dynamics of DNA oligomers containing 3 base pair (bp) mismatched sites specifically recognized in vitro by nucleotide excision repair protein Rad4 (yeast ortholog of mammalian XPC). A previous Forster resonance energy transfer (FRET) study mapped DNA conformational distributions with cytosine analog FRET pair primarily sensitive to DNA twisting/unwinding deformations (Chakraborty et al. Nucleic Acids Res. 46: 1240-1255 (2018)). These studies revealed B-DNA conformations for nonspecific (matched) constructs but significant unwinding for mismatched constructs specifically recognized by Rad4, even in the absence of Rad4. The timescales of these unwinding fluctuations, however, remained elusive. Here, we labeled DNA with Atto550/Atto647N FRET dyes suitable for fluorescence correlation spectroscopy (FCS). With these probes, we detected higher FRET in specific, mismatched DNA compared with matched DNA, reaffirming unwinding/bending deformations in mismatched DNA. FCS unveiled the dynamics of these spontaneous deformations at ~ 300 µs with no fluctuations detected for matched DNA within the ~ 600 ns-10 ms FCS time window. These studies are the first to visualize anomalous unwinding/bending fluctuations in mismatched DNA on timescales that overlap with the < 500 µs "stepping" times of repair proteins on DNA. Such "flexible hinge" dynamics at lesion sites could arrest a diffusing protein to facilitate damage interrogation and recognition.
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Affiliation(s)
- Timour B Ten
- Department of Physics (M/C 273), University of Illinois at Chicago, Chicago, IL, 60607, USA
| | - Viktoriya Zvoda
- Department of Physics (M/C 273), University of Illinois at Chicago, Chicago, IL, 60607, USA
| | - Manas K Sarangi
- Department of Physics (M/C 273), University of Illinois at Chicago, Chicago, IL, 60607, USA
- Present Address: Department of Physics, Indian Institute of Technology, Patna, 801103, India
| | - Serguei V Kuznetsov
- Department of Physics (M/C 273), University of Illinois at Chicago, Chicago, IL, 60607, USA
| | - Anjum Ansari
- Department of Physics (M/C 273), University of Illinois at Chicago, Chicago, IL, 60607, USA.
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3
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Abstract
Bacteria are continuously exposed to numerous endogenous and exogenous DNA-damaging agents. To maintain genome integrity and ensure cell survival, bacteria have evolved several DNA repair pathways to correct different types of DNA damage and non-canonical bases, including strand breaks, nucleotide modifications, cross-links, mismatches and ribonucleotide incorporations. Recent advances in genome-wide screens, the availability of thousands of whole-genome sequences and advances in structural biology have enabled the rapid discovery and characterization of novel bacterial DNA repair pathways and new enzymatic activities. In this Review, we discuss recent advances in our understanding of base excision repair and nucleotide excision repair, and we discuss several new repair processes including the EndoMS mismatch correction pathway and the MrfAB excision repair system.
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Affiliation(s)
- Katherine J Wozniak
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
| | - Lyle A Simmons
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, USA.
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4
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Tripathi P, Bruner SD. Structural Basis for the Interactions of the Colibactin Resistance Gene Product ClbS with DNA. Biochemistry 2021; 60:1619-1625. [PMID: 33945270 DOI: 10.1021/acs.biochem.1c00201] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The natural product colibactin, along with its associated biosynthetic gene cluster, is an example system for the role microbially derived small molecules play in the human microbiome. This is particularly relevant in the human gut, where host microbiota is involved in various disorders, including colorectal cancer pathogenesis. Bacteria harboring the colibactin gene cluster induce alkylation of nucleobases in host DNA, forming interstrand cross-links both in vivo and in vitro. These lesions can lead to deleterious double-strand breaks and have been identified as the primary mechanism of colibactin-induced cytotoxicity. The gene product ClbS is one of several mechanisms utilized by the producing bacteria to maintain genome integrity. ClbS catalyzes hydrolytic inactivation of colibactin and has been shown to bind DNA, incurring self-resistance. Presented is the molecular basis for ClbS bound to a DNA oligonucleotide. The structure shows the interaction of the protein with the ends of a DNA duplex with terminal nucleotides flipped to the enzyme active site. The structure suggests an additional function for ClbS, the binding to damaged DNA followed by repair. Additionally, our study provides general insight into the function of the widely distributed and largely uncharacterized DUF1706 protein family.
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Affiliation(s)
- Prabhanshu Tripathi
- Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - Steven D Bruner
- Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
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5
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Westwood MN, Ljunggren KD, Boyd B, Becker J, Dwyer TJ, Meints GA. Single-Base Lesions and Mismatches Alter the Backbone Conformational Dynamics in DNA. Biochemistry 2021; 60:873-885. [PMID: 33689312 DOI: 10.1021/acs.biochem.0c00784] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
DNA damage has been implicated in numerous human diseases, particularly cancer, and the aging process. Single-base lesions and mismatches in DNA can be cytotoxic or mutagenic and are recognized by a DNA glycosylase during the process of base excision repair. Altered local dynamics and conformational properties in damaged DNAs have previously been suggested to assist in recognition and specificity. Herein, we use solution nuclear magnetic resonance to quantify changes in BI-BII backbone conformational dynamics due to the presence of single-base lesions in DNA, including uracil, dihydrouracil, 1,N6-ethenoadenine, and T:G mismatches. Stepwise changes to the %BII and ΔG of the BI-BII dynamic equilibrium compared to those of unmodified sequences were observed. Additionally, the equilibrium skews toward endothermicity for the phosphates nearest the lesion/mismatched base pair. Finally, the phosphates with the greatest alterations correlate with those most relevant to the repair of enzyme binding. All of these results suggest local conformational rearrangement of the DNA backbone may play a role in lesion recognition by repair enzymes.
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Affiliation(s)
- M N Westwood
- Department of Chemistry, Missouri State University, 901 South National Avenue, Springfield, Missouri 65897, United States
| | - K D Ljunggren
- Department of Chemistry, Missouri State University, 901 South National Avenue, Springfield, Missouri 65897, United States
| | - Benjamin Boyd
- Department of Chemistry, Missouri State University, 901 South National Avenue, Springfield, Missouri 65897, United States
| | - Jaclyn Becker
- Department of Chemistry, Missouri State University, 901 South National Avenue, Springfield, Missouri 65897, United States
| | - Tammy J Dwyer
- Department of Chemistry and Biochemistry, University of San Diego, San Diego, California 92110, United States
| | - Gary A Meints
- Department of Chemistry, Missouri State University, 901 South National Avenue, Springfield, Missouri 65897, United States
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6
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Baiken Y, Kanayeva D, Taipakova S, Groisman R, Ishchenko AA, Begimbetova D, Matkarimov B, Saparbaev M. Role of Base Excision Repair Pathway in the Processing of Complex DNA Damage Generated by Oxidative Stress and Anticancer Drugs. Front Cell Dev Biol 2021; 8:617884. [PMID: 33553154 PMCID: PMC7862338 DOI: 10.3389/fcell.2020.617884] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2020] [Accepted: 12/17/2020] [Indexed: 01/22/2023] Open
Abstract
Chemical alterations in DNA induced by genotoxic factors can have a complex nature such as bulky DNA adducts, interstrand DNA cross-links (ICLs), and clustered DNA lesions (including double-strand breaks, DSB). Complex DNA damage (CDD) has a complex character/structure as compared to singular lesions like randomly distributed abasic sites, deaminated, alkylated, and oxidized DNA bases. CDD is thought to be critical since they are more challenging to repair than singular lesions. Although CDD naturally constitutes a relatively minor fraction of the overall DNA damage induced by free radicals, DNA cross-linking agents, and ionizing radiation, if left unrepaired, these lesions cause a number of serious consequences, such as gross chromosomal rearrangements and genome instability. If not tightly controlled, the repair of ICLs and clustered bi-stranded oxidized bases via DNA excision repair will either inhibit initial steps of repair or produce persistent chromosomal breaks and consequently be lethal for the cells. Biochemical and genetic evidences indicate that the removal of CDD requires concurrent involvement of a number of distinct DNA repair pathways including poly(ADP-ribose) polymerase (PARP)-mediated DNA strand break repair, base excision repair (BER), nucleotide incision repair (NIR), global genome and transcription coupled nucleotide excision repair (GG-NER and TC-NER, respectively), mismatch repair (MMR), homologous recombination (HR), non-homologous end joining (NHEJ), and translesion DNA synthesis (TLS) pathways. In this review, we describe the role of DNA glycosylase-mediated BER pathway in the removal of complex DNA lesions.
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Affiliation(s)
- Yeldar Baiken
- School of Sciences and Humanities, Nazarbayev University, Nur-Sultan, Kazakhstan.,National Laboratory Astana, Nazarbayev University, Nur-Sultan, Kazakhstan.,School of Engineering and Digital Sciences, Nazarbayev University, Nur-Sultan, Kazakhstan
| | - Damira Kanayeva
- School of Sciences and Humanities, Nazarbayev University, Nur-Sultan, Kazakhstan
| | - Sabira Taipakova
- Department of Molecular Biology and Genetics, Faculty of Biology and Biotechnology, al-Farabi Kazakh National University, Almaty, Kazakhstan
| | - Regina Groisman
- Groupe ≪Mechanisms of DNA Repair and Carcinogenesis≫, Equipe Labellisée LIGUE 2016, CNRS UMR9019, Université Paris-Saclay, Gustave Roussy Cancer Campus, Villejuif, France
| | - Alexander A Ishchenko
- Groupe ≪Mechanisms of DNA Repair and Carcinogenesis≫, Equipe Labellisée LIGUE 2016, CNRS UMR9019, Université Paris-Saclay, Gustave Roussy Cancer Campus, Villejuif, France
| | - Dinara Begimbetova
- National Laboratory Astana, Nazarbayev University, Nur-Sultan, Kazakhstan
| | - Bakhyt Matkarimov
- National Laboratory Astana, Nazarbayev University, Nur-Sultan, Kazakhstan
| | - Murat Saparbaev
- Department of Molecular Biology and Genetics, Faculty of Biology and Biotechnology, al-Farabi Kazakh National University, Almaty, Kazakhstan.,Groupe ≪Mechanisms of DNA Repair and Carcinogenesis≫, Equipe Labellisée LIGUE 2016, CNRS UMR9019, Université Paris-Saclay, Gustave Roussy Cancer Campus, Villejuif, France
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7
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Mullins EA, Rodriguez AA, Bradley NP, Eichman BF. Emerging Roles of DNA Glycosylases and the Base Excision Repair Pathway. Trends Biochem Sci 2019; 44:765-781. [PMID: 31078398 DOI: 10.1016/j.tibs.2019.04.006] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2019] [Revised: 04/09/2019] [Accepted: 04/10/2019] [Indexed: 12/20/2022]
Abstract
The base excision repair (BER) pathway historically has been associated with maintaining genome integrity by eliminating nucleobases with small chemical modifications. In the past several years, however, BER was found to play additional roles in genome maintenance and metabolism, including sequence-specific restriction modification and repair of bulky adducts and interstrand crosslinks. Central to this expanded biological utility are specialized DNA glycosylases - enzymes that selectively excise damaged, modified, or mismatched nucleobases. In this review we discuss the newly identified roles of the BER pathway and examine the structural and mechanistic features of the DNA glycosylases that enable these functions.
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Affiliation(s)
- Elwood A Mullins
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA
| | - Alyssa A Rodriguez
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA
| | - Noah P Bradley
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA
| | - Brandt F Eichman
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA; Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37232, USA.
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8
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Dow BJ, Malik SS, Drohat AC. Defining the Role of Nucleotide Flipping in Enzyme Specificity Using 19F NMR. J Am Chem Soc 2019; 141:4952-4962. [PMID: 30841696 DOI: 10.1021/jacs.9b00146] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A broad range of proteins employ nucleotide flipping to recognize specific sites in nucleic acids, including DNA glycosylases, which remove modified nucleobases to initiate base excision repair. Deamination, a pervasive mode of damage, typically generates lesions that are recognized by glycosylases as being foreign to DNA. However, deamination of 5-methylcytosine (mC) generates thymine, a canonical DNA base, presenting a challenge for damage recognition. Nevertheless, repair of mC deamination is important because the resulting G·T mispairs cause C → T transition mutations, and mC is abundant in all three domains of life. Countering this threat are three types of glycosylases that excise thymine from G·T mispairs, including thymine DNA glycosylase (TDG). These enzymes must minimize excision of thymine that is not generated by mC deamination, in A·T pairs and in polymerase-generated G·T mispairs. TDG preferentially removes thymine from DNA contexts in which cytosine methylation is prevalent, including CG and one non-CG site. This remarkable context specificity could be attained through modulation of nucleotide flipping, a reversible step that precedes base excision. We tested this idea using fluorine NMR and DNA containing 2'-fluoro-substituted nucleotides. We find that dT nucleotide flipping depends on DNA context and is efficient only in contexts known to feature cytosine methylation. We also show that a conserved Ala residue limits thymine excision by hindering nucleotide flipping. A linear free energy correlation reveals that TDG attains context specificity for thymine excision through modulation of nucleotide flipping. Our results provide a framework for characterizing nucleotide flipping in nucleic acids using 19F NMR.
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Affiliation(s)
- Blaine J Dow
- Department of Biochemistry and Molecular Biology , University of Maryland School of Medicine , Baltimore , Maryland 21201 , United States
| | - Shuja S Malik
- Department of Biochemistry and Molecular Biology , University of Maryland School of Medicine , Baltimore , Maryland 21201 , United States
| | - Alexander C Drohat
- Department of Biochemistry and Molecular Biology , University of Maryland School of Medicine , Baltimore , Maryland 21201 , United States
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9
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Votaw KA, McCullagh M. Characterization of the Search Complex and Recognition Mechanism of the AlkD-DNA Glycosylase. J Phys Chem B 2018; 123:95-105. [PMID: 30525620 DOI: 10.1021/acs.jpcb.8b09555] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
DNA damage is a routine problem for cells, and pathways such as base excision repair have evolved to protect the genome by using DNA glycosylases to first recognize and excise lesions. The search mechanism of these enzymes is of particular interest due to the seemingly intractable problem of probing the billions of base pairs in the genome for potential damage. It has been hypothesized that glycosylases form multiple protein-DNA conformational states to efficiently search and recognize DNA lesions, ultimately only flipping out the damaged substrate into the active site. A unique DNA glycosylase, the Bacillus cereus AlkD enzyme, has been shown to excise damaged DNA without flipping the nucleobase into a protein binding pocket following lesion recognition. Here, we use microsecond-scale all-atom molecular dynamics simulations to characterize the AlkD recognition mechanism, putting it in perspective with other DNA glycosylases. We first identify and describe two distinct enzyme-DNA conformations of AlkD: the search complex (SC) and excision complex (EC). The SC is distinguished by the linearity of DNA, changes in four helical parameters in the vicinity of the lesion, and changes in distance between active site residues and the DNA. Free DNA simulations are used to demonstrate that the DNA structural deviations and increased active site interactions present in the EC are initiated by the recognition of a methylation-induced signal in the rises both 5' to the methylation and opposing this base. Our results support the hypothesis that subtle geometric distortions in DNA are recognized by AlkD and are consequently probed to initiate concerted protein and DNA conformational changes which prime excise without additional intermediate states. This mechanism is shown to be consistent among the three methylated DNA sequences that have been crystallized bound to AlkD.
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Affiliation(s)
- Kevin A Votaw
- Department of Chemistry , Colorado State University , Fort Collins , Colorado 80523, United States
| | - Martin McCullagh
- Department of Chemistry , Colorado State University , Fort Collins , Colorado 80523, United States
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10
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Johnson RP, Perera RT, Fleming AM, Burrows CJ, White HS. Energetics of base flipping at a DNA mismatch site confined at the latch constriction of α-hemolysin. Faraday Discuss 2018; 193:471-485. [PMID: 27711888 DOI: 10.1039/c6fd00058d] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Unique, two-state modulating current signatures are observed when a cytosine-cytosine mismatch pair is confined at the 2.4 nm latch constriction of the α-hemolysin (αHL) nanopore. We have previously speculated that the modulation is due to base flipping at the mismatch site. Base flipping is a biologically significant mechanism in which a single base is rotated out of the DNA helical stack by 180°. It is the mechanism by which enzymes are able to access bases for repair operations without disturbing the global structure of the helix. Here, temperature dependent ion channel recordings of individual double-stranded DNA duplexes inside αHL are used to derive thermodynamic (ΔH, ΔS) and kinetic (EA) parameters for base flipping of a cytosine at an unstable cytosine-cytosine mismatch site. The measured activation energy for flipping a cytosine located at the latch of αHL out of the helix (18 ± 1 kcal mol-1) is comparable to that previously reported for base flipping at mismatch sites from NMR measurements and potential mean force calculations. We propose that the αHL nanopore is a useful tool for measuring conformational changes in dsDNA at the single molecule level.
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Affiliation(s)
- Robert P Johnson
- Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, UT 84112-0850, USA.
| | - Rukshan T Perera
- Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, UT 84112-0850, USA.
| | - Aaron M Fleming
- Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, UT 84112-0850, USA.
| | - Cynthia J Burrows
- Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, UT 84112-0850, USA.
| | - Henry S White
- Department of Chemistry, University of Utah, 315 South 1400 East, Salt Lake City, UT 84112-0850, USA.
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11
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Hao W, Qi T, Pan L, Wang R, Zhu B, Aguilera-Aguirre L, Radak Z, Hazra TK, Vlahopoulos SA, Bacsi A, Brasier AR, Ba X, Boldogh I. Effects of the stimuli-dependent enrichment of 8-oxoguanine DNA glycosylase1 on chromatinized DNA. Redox Biol 2018; 18:43-53. [PMID: 29940424 PMCID: PMC6019822 DOI: 10.1016/j.redox.2018.06.002] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2018] [Revised: 06/04/2018] [Accepted: 06/06/2018] [Indexed: 12/16/2022] Open
Abstract
8-Oxoguanine DNA glycosylase 1 (OGG1) initiates the base excision repair pathway by removing one of the most abundant DNA lesions, 8-oxo-7,8-dihydroguanine (8-oxoG). Recent data showed that 8-oxoG not only is a pro-mutagenic genomic base lesion, but also functions as an epigenetic mark and that consequently OGG1 acquire distinct roles in modulation of gene expression. In support, lack of functional OGG1 in Ogg1-/- mice led to an altered expression of genes including those responsible for the aberrant innate and adaptive immune responses and susceptibility to metabolic disorders. Therefore, the present study examined stimulus-driven OGG1-DNA interactions at whole genome level using chromatin immunoprecipitation (ChIP)-coupled sequencing, and the roles of OGG1 enriched on the genome were validated by molecular and system-level approaches. Results showed that signaling levels of cellular ROS generated by TNFα, induced enrichment of OGG1 at specific sites of chromatinized DNA, primarily in the regulatory regions of genes. OGG1-ChIP-ed genes are associated with important cellular and biological processes and OGG1 enrichment was limited to a time scale required for immediate cellular responses. Prevention of OGG1-DNA interactions by siRNA depletion led to modulation of NF-κB's DNA occupancy and differential expression of genes. Taken together these data show TNFα-ROS-driven enrichment of OGG1 at gene regulatory regions in the chromatinized DNA, which is a prerequisite to modulation of gene expression for prompt cellular responses to oxidant stress.
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Affiliation(s)
- Wenjing Hao
- Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA
| | - Tianyang Qi
- Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA
| | - Lang Pan
- Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA
| | - Ruoxi Wang
- Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA; Internal Medicine, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA; Sealy Center for Molecular Medicine, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA
| | - Bing Zhu
- Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA
| | - Leopoldo Aguilera-Aguirre
- Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA
| | - Zsolt Radak
- Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA
| | - Tapas K Hazra
- Internal Medicine, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA; Sealy Center for Molecular Medicine, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA
| | - Spiros A Vlahopoulos
- Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA
| | - Attila Bacsi
- Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA
| | - Allan R Brasier
- Internal Medicine, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA; Sealy Center for Molecular Medicine, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA
| | - Xueqing Ba
- Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA
| | - Istvan Boldogh
- Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA; Sealy Center for Molecular Medicine, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA.
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12
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Ba X, Boldogh I. 8-Oxoguanine DNA glycosylase 1: Beyond repair of the oxidatively modified base lesions. Redox Biol 2017; 14:669-678. [PMID: 29175754 PMCID: PMC5975208 DOI: 10.1016/j.redox.2017.11.008] [Citation(s) in RCA: 160] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Revised: 10/08/2017] [Accepted: 11/08/2017] [Indexed: 12/11/2022] Open
Abstract
Oxidative stress and the resulting damage to genomic DNA are inevitable consequences of endogenous physiological processes, and they are amplified by cellular responses to environmental exposures. One of the most frequent reactions of reactive oxygen species with DNA is the oxidation of guanine to pre-mutagenic 8-oxo-7,8-dihydroguanine (8-oxoG). Despite the vulnerability of guanine to oxidation, vertebrate genes are primarily embedded in GC-rich genomic regions, and over 72% of the promoters of human genes belong to a class with a high GC content. In the promoter, 8-oxoG may serve as an epigenetic mark, and when complexed with the oxidatively inactivated repair enzyme 8-oxoguanine DNA glycosylase 1, provide a platform for the coordination of the initial steps of DNA repair and the assembly of the transcriptional machinery to launch the prompt and preferential expression of redox-regulated genes. Deviations/variations from this artful coordination may be the etiological links between guanine oxidation and various cellular pathologies and diseases during ageing processes.
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Affiliation(s)
- Xueqing Ba
- The Key Laboratory of Molecular Epigenetics of Ministry of Education, Northeast Normal University, Changchun, Jilin 130024, China; School of Life Science, Northeast Normal University, Changchun, Jilin 130024, China.
| | - Istvan Boldogh
- Department of Microbiology and Immunology, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA; Sealy Center for Molecular Medicine, University of Texas Medical Branch at Galveston, Galveston, TX 77555, USA.
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13
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Mullins EA, Shi R, Eichman BF. Toxicity and repair of DNA adducts produced by the natural product yatakemycin. Nat Chem Biol 2017; 13:1002-1008. [PMID: 28759018 PMCID: PMC5657529 DOI: 10.1038/nchembio.2439] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Accepted: 06/20/2017] [Indexed: 12/22/2022]
Abstract
Yatakemycin (YTM) is an extraordinarily toxic DNA alkylating agent with potent antimicrobial and antitumor properties and the most recent addition to the CC-1065 and duocarmycin family of natural products. While bulky DNA lesions the size of those produced by YTM are normally removed from the genome by the nucleotide excision repair (NER) pathway, YTM adducts are also a substrate for the bacterial DNA glycosylases AlkD and YtkR2, unexpectedly implicating base excision repair (BER) in their elimination. The reason for the extreme toxicity of these lesions and the molecular basis for how they are eliminated by BER have been unclear. Here, we describe the structural and biochemical properties of YTM adducts responsible for their toxicity, and define the mechanism by which they are excised by AlkD. These findings delineate an alternative strategy for repair of bulky DNA damage and establish the cellular utility of this pathway relative to that of NER.
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Affiliation(s)
- Elwood A Mullins
- Department of Biological Sciences and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee, USA
| | - Rongxin Shi
- Department of Biological Sciences and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee, USA
| | - Brandt F Eichman
- Department of Biological Sciences and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee, USA
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14
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Ma N, van der Vaart A. Free Energy Coupling between DNA Bending and Base Flipping. J Chem Inf Model 2017; 57:2020-2026. [PMID: 28696686 DOI: 10.1021/acs.jcim.7b00215] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Free energy simulations are presented to probe the energetic coupling between DNA bending and the flipping of a central thymine in double stranded DNA 13mers. The energetics are shown to depend on the neighboring base pairs, and upstream C or T or downstream C tended to make flipping more costly. Flipping to the major groove side was generally preferred. Bending aids flipping, by pushing the system up in free energy, but for small and intermediate bending angles the two were uncorrelated. At higher bending angles, bending and flipping became correlated, and bending primed the system for base flipping toward the major groove. Flipping of the 6-4 pyrimidine-pyrimidone and pyrimidine dimer photoproducts is shown to be more facile than for undamaged DNA. For the damages, major groove flipping was preferred, and DNA bending was much facilitated in the 6-4 pyrimidine-pyrimidone damaged system. Aspects of the calculations were verified by structural analyses of protein-DNA complexes with flipped bases.
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Affiliation(s)
- Ning Ma
- Department of Chemistry, University of South Florida , 4202 East Fowler Avenue CHE 205, Tampa, Florida 33620, United States
| | - Arjan van der Vaart
- Department of Chemistry, University of South Florida , 4202 East Fowler Avenue CHE 205, Tampa, Florida 33620, United States
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15
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Pan L, Hao W, Zheng X, Zeng X, Ahmed Abbasi A, Boldogh I, Ba X. OGG1-DNA interactions facilitate NF-κB binding to DNA targets. Sci Rep 2017; 7:43297. [PMID: 28266569 PMCID: PMC5339705 DOI: 10.1038/srep43297] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Accepted: 01/20/2017] [Indexed: 12/13/2022] Open
Abstract
DNA repair protein counteracting oxidative promoter lesions may modulate gene expression. Oxidative DNA bases modified by reactive oxygen species (ROS), primarily as 7, 8-dihydro-8-oxo-2′-deoxyguanosine (8-oxoG), which is repaired by 8-oxoguanine DNA glycosylase1 (OGG1) during base excision repair (BER) pathway. Because cellular response to oxidative challenge is accompanied by DNA damage repair, we tested whether the repair by OGG1 is compatible with transcription factor binding and gene expression. We performed electrophoretic mobility shift assay (EMSA) using wild-type sequence deriving from Cxcl2 gene promoter and the same sequence bearing a single synthetic 8-oxoG at defined 5′ or 3′ guanine in runs of guanines to mimic oxidative effects. We showed that DNA occupancy of NF-κB present in nuclear extracts from tumour necrosis factor alpha (TNFα) exposed cells is OGG1 and 8-oxoG position dependent, importantly, OGG1 counteracting 8-oxoG outside consensus motif had a profound influence on purified NF-κB binding to DNA. Furthermore, OGG1 is essential for NF-κB dependent gene expression, prior to 8-oxoG excised from DNA. These observations imply that pre-excision step(s) during OGG1 initiated BER evoked by ROS facilitates NF-κB DNA occupancy and gene expression.
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Affiliation(s)
- Lang Pan
- The Key Laboratory of Molecular Epigenetics of the Ministry of Education, Northeast Normal University, Changchun, Jilin 130024, China.,Institute of Genetics and Cytology, Northeast Normal University, Changchun, Jilin 130024, China
| | - Wenjing Hao
- The Key Laboratory of Molecular Epigenetics of the Ministry of Education, Northeast Normal University, Changchun, Jilin 130024, China.,Institute of Genetics and Cytology, Northeast Normal University, Changchun, Jilin 130024, China
| | - Xu Zheng
- The Key Laboratory of Molecular Epigenetics of the Ministry of Education, Northeast Normal University, Changchun, Jilin 130024, China.,Institute of Genetics and Cytology, Northeast Normal University, Changchun, Jilin 130024, China
| | - Xianlu Zeng
- The Key Laboratory of Molecular Epigenetics of the Ministry of Education, Northeast Normal University, Changchun, Jilin 130024, China.,Institute of Genetics and Cytology, Northeast Normal University, Changchun, Jilin 130024, China
| | - Adeel Ahmed Abbasi
- The Key Laboratory of Molecular Epigenetics of the Ministry of Education, Northeast Normal University, Changchun, Jilin 130024, China
| | - Istvan Boldogh
- Department of Microbiology and Immunology, Sealy Center for Molecular Medicine, University of Texas Medical Branch at Galveston, Galveston, Texas 77555, USA
| | - Xueqing Ba
- The Key Laboratory of Molecular Epigenetics of the Ministry of Education, Northeast Normal University, Changchun, Jilin 130024, China.,Institute of Genetics and Cytology, Northeast Normal University, Changchun, Jilin 130024, China
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16
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Li H, Endutkin AV, Bergonzo C, Fu L, Grollman A, Zharkov DO, Simmerling C. DNA Deformation-Coupled Recognition of 8-Oxoguanine: Conformational Kinetic Gating in Human DNA Glycosylase. J Am Chem Soc 2017; 139:2682-2692. [PMID: 28098999 DOI: 10.1021/jacs.6b11433] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
8-Oxoguanine (8-oxoG), a mutagenic DNA lesion generated under oxidative stress, differs from its precursor guanine by only two substitutions (O8 and H7). Human 8-oxoguanine glycosylase 1 (OGG1) can locate and remove 8-oxoG through extrusion and excision. To date, it remains unclear how OGG1 efficiently distinguishes 8-oxoG from a large excess of undamaged DNA bases. We recently showed that formamidopyrimidine-DNA glycosylase (Fpg), a bacterial functional analog of OGG1, can selectively facilitate eversion of oxoG by stabilizing several intermediate states, and it is intriguing whether OGG1 also employs a similar mechanism in lesion recognition. Here, we use molecular dynamics simulations to explore the mechanism by which OGG1 discriminates between 8-oxoG and guanine along the base-eversion pathway. The MD results suggest an important role for kinking of the DNA by the glycosylase, which positions DNA phosphates in a way that assists lesion recognition during base eversion. The computational predictions were validated through experimental enzyme assays on phosphorothioate substrate analogs. Our simulations suggest that OGG1 distinguishes between 8-oxoG and G using their chemical dissimilarities not only at the active site but also at earlier stages during base eversion, and this mechanism is at least partially conserved in Fpg despite a lack of structural homology. The similarity also suggests that lesion recognition through multiple gating steps may be a common theme in DNA repair. Our results provide new insight into how enzymes can exploit kinetics and DNA conformational changes to probe the chemical modifications present in DNA lesions.
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Affiliation(s)
| | - Anton V Endutkin
- Novosibirsk State University , 2 Pirogova Street, Novosibirsk 630090, Russia.,SB RAS Institute of Chemical Biology and Fundamental Medicine , 8 Lavrentieva Avenue, Novosibirsk 630090, Russia
| | | | - Lin Fu
- School of Pharmaceutical Sciences, Wenzhou Medical University , Wenzhou 325035, P. R. China
| | | | - Dmitry O Zharkov
- Novosibirsk State University , 2 Pirogova Street, Novosibirsk 630090, Russia.,SB RAS Institute of Chemical Biology and Fundamental Medicine , 8 Lavrentieva Avenue, Novosibirsk 630090, Russia
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17
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Miyazono KI, Furuta Y, Watanabe-Matsui M, Miyakawa T, Ito T, Kobayashi I, Tanokura M. A sequence-specific DNA glycosylase mediates restriction-modification in Pyrococcus abyssi. Nat Commun 2016; 5:3178. [PMID: 24458096 DOI: 10.1038/ncomms4178] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Accepted: 12/23/2013] [Indexed: 11/09/2022] Open
Abstract
Restriction-modification systems consist of genes that encode a restriction enzyme and a cognate methyltransferase. Thus far, it was believed that restriction enzymes are sequence-specific endonucleases that introduce double-strand breaks at specific sites by catalysing the cleavages of phosphodiester bonds. Here we report that based on the crystal structure and enzymatic activity, one of the restriction enzymes, R.PabI, is not an endonuclease but a sequence-specific adenine DNA glycosylase. The structure of the R.PabI-DNA complex shows that R.PabI unwinds DNA at a 5'-GTAC-3' site and flips the guanine and adenine bases out of the DNA helix to recognize the sequence. R.PabI catalyses the hydrolysis of the N-glycosidic bond between the adenine base and the sugar in the DNA and produces two opposing apurinic/apyrimidinic (AP) sites. The opposing AP sites are cleaved by heat-promoted β elimination and/or by endogenous AP endonucleases of host cells to introduce a double-strand break.
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Affiliation(s)
- Ken-ichi Miyazono
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
| | - Yoshikazu Furuta
- 1] Department of Medical Genome Sciences, Graduate School of Frontier Science, The University of Tokyo, Tokyo 108-8639, Japan [2] Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan
| | - Miki Watanabe-Matsui
- 1] Department of Medical Genome Sciences, Graduate School of Frontier Science, The University of Tokyo, Tokyo 108-8639, Japan [2]
| | - Takuya Miyakawa
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
| | - Tomoko Ito
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
| | - Ichizo Kobayashi
- 1] Department of Medical Genome Sciences, Graduate School of Frontier Science, The University of Tokyo, Tokyo 108-8639, Japan [2] Institute of Medical Science, The University of Tokyo, Tokyo 108-8639, Japan [3] Graduate Program in Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, Tokyo 108-8639, Japan
| | - Masaru Tanokura
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan
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18
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Mullins EA, Shi R, Parsons ZD, Yuen PK, David SS, Igarashi Y, Eichman BF. The DNA glycosylase AlkD uses a non-base-flipping mechanism to excise bulky lesions. Nature 2015; 527:254-8. [PMID: 26524531 DOI: 10.1038/nature15728] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2015] [Accepted: 09/18/2015] [Indexed: 01/10/2023]
Abstract
Threats to genomic integrity arising from DNA damage are mitigated by DNA glycosylases, which initiate the base excision repair pathway by locating and excising aberrant nucleobases. How these enzymes find small modifications within the genome is a current area of intensive research. A hallmark of these and other DNA repair enzymes is their use of base flipping to sequester modified nucleotides from the DNA helix and into an active site pocket. Consequently, base flipping is generally regarded as an essential aspect of lesion recognition and a necessary precursor to base excision. Here we present the first, to our knowledge, DNA glycosylase mechanism that does not require base flipping for either binding or catalysis. Using the DNA glycosylase AlkD from Bacillus cereus, we crystallographically monitored excision of an alkylpurine substrate as a function of time, and reconstructed the steps along the reaction coordinate through structures representing substrate, intermediate and product complexes. Instead of directly interacting with the damaged nucleobase, AlkD recognizes aberrant base pairs through interactions with the phosphoribose backbone, while the lesion remains stacked in the DNA duplex. Quantum mechanical calculations revealed that these contacts include catalytic charge-dipole and CH-π interactions that preferentially stabilize the transition state. We show in vitro and in vivo how this unique means of recognition and catalysis enables AlkD to repair large adducts formed by yatakemycin, a member of the duocarmycin family of antimicrobial natural products exploited in bacterial warfare and chemotherapeutic trials. Bulky adducts of this or any type are not excised by DNA glycosylases that use a traditional base-flipping mechanism. Hence, these findings represent a new model for DNA repair and provide insights into catalysis of base excision.
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Affiliation(s)
- Elwood A Mullins
- Department of Biological Sciences and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37232, USA
| | - Rongxin Shi
- Department of Biological Sciences and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37232, USA
| | - Zachary D Parsons
- Department of Biological Sciences and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37232, USA
| | - Philip K Yuen
- Department of Chemistry, University of California, Davis, California 95616, USA
| | - Sheila S David
- Department of Chemistry, University of California, Davis, California 95616, USA
| | - Yasuhiro Igarashi
- Biotechnology Research Center, Toyama Prefectural University, 5180 Kurokawa, Imizu, Toyama 939-0398, Japan
| | - Brandt F Eichman
- Department of Biological Sciences and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37232, USA
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19
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Pedersen HL, Johnson KA, McVey CE, Leiros I, Moe E. Structure determination of uracil-DNA N-glycosylase from Deinococcus radiodurans in complex with DNA. ACTA ACUST UNITED AC 2015; 71:2137-49. [PMID: 26457437 DOI: 10.1107/s1399004715014157] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Accepted: 07/27/2015] [Indexed: 11/10/2022]
Abstract
Uracil-DNA N-glycosylase (UNG) is a DNA-repair enzyme in the base-excision repair (BER) pathway which removes uracil from DNA. Here, the crystal structure of UNG from the extremophilic bacterium Deinococcus radiodurans (DrUNG) in complex with DNA is reported at a resolution of 1.35 Å. Prior to the crystallization experiments, the affinity between DrUNG and different DNA oligonucleotides was tested by electrophoretic mobility shift assays (EMSAs). As a result of this analysis, two 16 nt double-stranded DNAs were chosen for the co-crystallization experiments, one of which (16 nt AU) resulted in well diffracting crystals. The DNA in the co-crystal structure contained an abasic site (substrate product) flipped into the active site of the enzyme, with no uracil in the active-site pocket. Despite the high resolution, it was not possible to fit all of the terminal nucleotides of the DNA complex into electron density owing to disorder caused by a lack of stabilizing interactions. However, the DNA which was in contact with the enzyme, close to the active site, was well ordered and allowed detailed analysis of the enzyme-DNA interaction. The complex revealed that the interaction between DrUNG and DNA is similar to that in the previously determined crystal structure of human UNG (hUNG) in complex with DNA [Slupphaug et al. (1996). Nature (London), 384, 87-92]. Substitutions in a (here defined) variable part of the leucine loop result in a shorter loop (eight residues instead of nine) in DrUNG compared with hUNG; regardless of this, it seems to fulfil its role and generate a stabilizing force with the minor groove upon flipping out of the damaged base into the active site. The structure also provides a rationale for the previously observed high catalytic efficiency of DrUNG caused by high substrate affinity by demonstrating an increased number of long-range electrostatic interactions between the enzyme and the DNA. Interestingly, specific interactions between residues in the N-terminus of a symmetry-related molecule and the complementary DNA strand facing away from the active site were also observed which seem to stabilize the enzyme-DNA complex. However, the significance of this observation remains to be investigated. The results provide new insights into the current knowledge about DNA damage recognition and repair by uracil-DNA glycosylases.
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Affiliation(s)
- Hege Lynum Pedersen
- The Norwegian Structural Biology Center (NorStruct), Department of Chemistry, UiT - The Arctic University of Norway, 9037 Tromsø, Norway
| | - Kenneth A Johnson
- The Norwegian Structural Biology Center (NorStruct), Department of Chemistry, UiT - The Arctic University of Norway, 9037 Tromsø, Norway
| | - Colin E McVey
- Instituto de Tecnologia Química e Biológica (ITQB), Universidade Nova de Lisboa, 2780-157 Oeiras, Portugal
| | - Ingar Leiros
- The Norwegian Structural Biology Center (NorStruct), Department of Chemistry, UiT - The Arctic University of Norway, 9037 Tromsø, Norway
| | - Elin Moe
- The Norwegian Structural Biology Center (NorStruct), Department of Chemistry, UiT - The Arctic University of Norway, 9037 Tromsø, Norway
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20
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Mullins EA, Shi R, Kotsch LA, Eichman BF. A New Family of HEAT-Like Repeat Proteins Lacking a Critical Substrate Recognition Motif Present in Related DNA Glycosylases. PLoS One 2015; 10:e0127733. [PMID: 25978435 PMCID: PMC4433238 DOI: 10.1371/journal.pone.0127733] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Accepted: 04/20/2015] [Indexed: 12/21/2022] Open
Abstract
DNA glycosylases are important repair enzymes that eliminate a diverse array of aberrant nucleobases from the genomes of all organisms. Individual bacterial species often contain multiple paralogs of a particular glycosylase, yet the molecular and functional distinctions between these paralogs are not well understood. The recently discovered HEAT-like repeat (HLR) DNA glycosylases are distributed across all domains of life and are distinct in their specificity for cationic alkylpurines and mechanism of damage recognition. Here, we describe a number of phylogenetically diverse bacterial species with two orthologs of the HLR DNA glycosylase AlkD. One ortholog, which we designate AlkD2, is substantially less conserved. The crystal structure of Streptococcus mutans AlkD2 is remarkably similar to AlkD but lacks the only helix present in AlkD that penetrates the DNA minor groove. We show that AlkD2 possesses only weak DNA binding affinity and lacks alkylpurine excision activity. Mutational analysis of residues along this DNA binding helix in AlkD substantially reduced binding affinity for damaged DNA, for the first time revealing the importance of this structural motif for damage recognition by HLR glycosylases.
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Affiliation(s)
- Elwood A. Mullins
- Department of Biological Sciences and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee, United States of America
| | - Rongxin Shi
- Department of Biological Sciences and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee, United States of America
| | - Lyle A. Kotsch
- Department of Biological Sciences and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee, United States of America
| | - Brandt F. Eichman
- Department of Biological Sciences and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee, United States of America
- * E-mail:
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21
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Szulik M, Pallan PS, Nocek B, Voehler M, Banerjee S, Brooks S, Joachimiak A, Egli M, Eichman BF, Stone MP. Differential stabilities and sequence-dependent base pair opening dynamics of Watson-Crick base pairs with 5-hydroxymethylcytosine, 5-formylcytosine, or 5-carboxylcytosine. Biochemistry 2015; 54:1294-305. [PMID: 25632825 PMCID: PMC4325598 DOI: 10.1021/bi501534x] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
5-Hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC) form during active demethylation of 5-methylcytosine (5mC) and are implicated in epigenetic regulation of the genome. They are differentially processed by thymine DNA glycosylase (TDG), an enzyme involved in active demethylation of 5mC. Three modified Dickerson-Drew dodecamer (DDD) sequences, amenable to crystallographic and spectroscopic analyses and containing the 5'-CG-3' sequence associated with genomic cytosine methylation, containing 5hmC, 5fC, or 5caC placed site-specifically into the 5'-T(8)X(9)G(10)-3' sequence of the DDD, were compared. The presence of 5caC at the X(9) base increased the stability of the DDD, whereas 5hmC or 5fC did not. Both 5hmC and 5fC increased imino proton exchange rates and calculated rate constants for base pair opening at the neighboring base pair A(5):T(8), whereas 5caC did not. At the oxidized base pair G(4):X(9), 5fC exhibited an increase in the imino proton exchange rate and the calculated kop. In all cases, minimal effects to imino proton exchange rates occurred at the neighboring base pair C(3):G(10). No evidence was observed for imino tautomerization, accompanied by wobble base pairing, for 5hmC, 5fC, or 5caC when positioned at base pair G(4):X(9); each favored Watson-Crick base pairing. However, both 5fC and 5caC exhibited intranucleobase hydrogen bonding between their formyl or carboxyl oxygens, respectively, and the adjacent cytosine N(4) exocyclic amines. The lesion-specific differences observed in the DDD may be implicated in recognition of 5hmC, 5fC, or 5caC in DNA by TDG. However, they do not correlate with differential excision of 5hmC, 5fC, or 5caC by TDG, which may be mediated by differences in transition states of the enzyme-bound complexes.
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Affiliation(s)
- Marta
W. Szulik
- Department
of Chemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt
Ingram Cancer Center, and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Pradeep S. Pallan
- Department
of Biochemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt
Ingram Cancer Center, and Center for Structural Biology, School of
Medicine, Vanderbilt University, Nashville, Tennessee 37232, United States
| | - Boguslaw Nocek
- Bioscience
Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - Markus Voehler
- Department
of Chemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt
Ingram Cancer Center, and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37235, United States
| | - Surajit Banerjee
- Northeastern
Collaborative Access Team and Department of Chemistry and Chemical
Biology, Cornell University, Argonne National
Laboratory, Argonne, Illinois 60439, United
States
| | - Sonja Brooks
- Department
of Biological Sciences, Vanderbilt Institute of Chemical Biology,
and Center for Structural Biology, Vanderbilt
University, Nashville, Tennessee 37235, United States
| | - Andrzej Joachimiak
- Bioscience
Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - Martin Egli
- Department
of Biochemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt
Ingram Cancer Center, and Center for Structural Biology, School of
Medicine, Vanderbilt University, Nashville, Tennessee 37232, United States
| | - Brandt F. Eichman
- Department
of Biological Sciences, Vanderbilt Institute of Chemical Biology,
and Center for Structural Biology, Vanderbilt
University, Nashville, Tennessee 37235, United States
| | - Michael P. Stone
- Department
of Chemistry, Vanderbilt Institute of Chemical Biology, Vanderbilt
Ingram Cancer Center, and Center for Structural Biology, Vanderbilt University, Nashville, Tennessee 37235, United States,(M.P.S.) Tel.: 615-322-2589; E-mail:
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22
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Abstract
Recent applications of solid-state NMR spectroscopy to studies of nucleic acids and their components.
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Affiliation(s)
- Martin Dračínský
- Institute of Organic Chemistry and Biochemistry
- Prague
- Czech Republic
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23
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Hendershot JM, O'Brien PJ. Critical role of DNA intercalation in enzyme-catalyzed nucleotide flipping. Nucleic Acids Res 2014; 42:12681-90. [PMID: 25324304 PMCID: PMC4227769 DOI: 10.1093/nar/gku919] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Revised: 09/21/2014] [Accepted: 09/22/2014] [Indexed: 11/14/2022] Open
Abstract
Nucleotide flipping is a common feature of DNA-modifying enzymes that allows access to target sites within duplex DNA. Structural studies have identified many intercalating amino acid side chains in a wide variety of enzymes, but the functional contribution of these intercalating residues is poorly understood. We used site-directed mutagenesis and transient kinetic approaches to dissect the energetic contribution of intercalation for human alkyladenine DNA glycosylase, an enzyme that initiates repair of alkylation damage. When AAG flips out a damaged nucleotide, the void in the duplex is filled by a conserved tyrosine (Y162). We find that tyrosine intercalation confers 140-fold stabilization of the extrahelical specific recognition complex, and that Y162 functions as a plug to slow the rate of unflipping by 6000-fold relative to the Y162A mutant. Surprisingly, mutation to the smaller alanine side chain increases the rate of nucleotide flipping by 50-fold relative to the wild-type enzyme. This provides evidence against the popular model that DNA intercalation accelerates nucleotide flipping. In the case of AAG, DNA intercalation contributes to the specific binding of a damaged nucleotide, but this enhanced specificity comes at the cost of reduced speed of nucleotide flipping.
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Affiliation(s)
- Jenna M Hendershot
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Patrick J O'Brien
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, MI 48109, USA
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24
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Beuck C, Weinhold E. Reversibly locked thionucleobase pairs in DNA to study base flipping enzymes. Beilstein J Org Chem 2014; 10:2293-306. [PMID: 25298797 PMCID: PMC4187101 DOI: 10.3762/bjoc.10.239] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2014] [Accepted: 08/28/2014] [Indexed: 12/16/2022] Open
Abstract
Covalently interstrand cross-linked DNA is an interesting tool to study DNA binding proteins that locally open up the DNA duplex by flipping single bases out of the DNA helix or melting whole stretches of base pairs to perform their function. The ideal DNA cross-link to study protein–DNA interactions should be specific and easy to synthesize, be stable during protein binding experiments, have a short covalent linker to avoid steric hindrance of protein binding, and should be available as a mimic for both A/T and G/C base pairs to cover all possible binding specificities. Several covalent interstrand cross-links have been described in the literature, but most of them fall short of at least one of the above criteria. We developed an efficient method to site-specifically and reversibly cross-link thionucleoside base pairs in synthetic duplex oligodeoxynucleotides by bisalkylation with 1,2-diiodoethane resulting in an ethylene-bridged base pair. Both linked A/T and G/C base pair analogs can conveniently be prepared which allows studying any base pair-opening enzyme regardless of its sequence specificity. The cross-link is stable in the absence of reducing agents but the linker can be quickly and tracelessly removed by the addition of thiol reagents like dithiothreitol. This property makes the cross-linking reaction fully reversible and allows for a switching of the linked base pair from locked to unlocked during biochemical experiments. Using the DNA methyltransferase from Thermus aquaticus (M.TaqI) as example, we demonstrate that the presented cross-linked DNA with an ethylene-linked A/T base pair analog at the target position is a useful tool to determine the base-flipping equilibrium constant of a base-flipping enzyme which lies mostly on the extrahelical side for M.TaqI.
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Affiliation(s)
- Christine Beuck
- Department of Structural & Medicinal Biochemistry, University of Duisburg-Essen, Universitätsstr. 2-5, D-45141 Essen, Germany
| | - Elmar Weinhold
- Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, D-52056 Aachen, Germany
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25
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Cao L, Lv C, Yang W. Hidden Conformation Events in DNA Base Extrusions: A Generalized Ensemble Path Optimization and Equilibrium Simulation Study. J Chem Theory Comput 2013; 9:10.1021/ct400198q. [PMID: 24250279 PMCID: PMC3829643 DOI: 10.1021/ct400198q] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
DNA base extrusion is a crucial component of many biomolecular processes. Elucidating how bases are selectively extruded from the interiors of double-strand DNAs is pivotal to accurately understanding and efficiently sampling this general type of conformational transitions. In this work, the on-the-path random walk (OTPRW) method, which is the first generalized ensemble sampling scheme designed for finite-temperature-string path optimizations, was improved and applied to obtain the minimum free energy path (MFEP) and the free energy profile of a classical B-DNA major-groove base extrusion pathway. Along the MFEP, an intermediate state and the corresponding transition state were located and characterized. The MFEP result suggests that a base-plane-elongation event rather than the commonly focused base-flipping event is dominant in the transition state formation portion of the pathway; and the energetic penalty at the transition state is mainly introduced by the stretching of the Watson-Crick base pair. Moreover to facilitate the essential base-plane-elongation dynamics, the surrounding environment of the flipped base needs to be intimately involved. Further taking the advantage of the extended-dynamics nature of the OTPRW Hamiltonian, an equilibrium generalized ensemble simulation was performed along the optimized path; and based on the collected samples, several base-flipping (opening) angle collective variables were evaluated. In consistence with the MFEP result, the collective variable analysis result reveals that none of these commonly employed flipping (opening) angles alone can adequately represent the base extrusion pathway, especially in the pre-transition-state portion. As further revealed by the collective variable analysis, the base-pairing partner of the extrusion target undergoes a series of in-plane rotations to facilitate the base-plane-elongation dynamics. A base-plane rotation angle is identified to be a possible reaction coordinate to represent these in-plane rotations. Notably, these in-plane rotation motions may play a pivotal role in determining the base extrusion selectivity.
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Affiliation(s)
- Liaoran Cao
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL, 32306
| | - Chao Lv
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL, 32306
| | - Wei Yang
- Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL, 32306
- Institute of Molecular Biophysics, Florida State University, Tallahassee, FL, 32306
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26
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Matje DM, Zhou H, Smith DA, Neely RK, Dryden DTF, Jones AC, Dahlquist FW, Reich NO. Enzyme-promoted base flipping controls DNA methylation fidelity. Biochemistry 2013; 52:1677-85. [PMID: 23409782 DOI: 10.1021/bi3012912] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A quantitative understanding of how conformational transitions contribute to enzyme catalysis and specificity remains a fundamental challenge. A suite of biophysical approaches was used to reveal several transient states of the enzyme-substrate complexes of the model DNA cytosine methyltransferase M.HhaI. Multidimensional, transverse relaxation-optimized nuclear magnetic resonance (NMR) experiments show that M.HhaI has the same conformation with noncognate and cognate DNA sequences. The high-affinity cognatelike mode requires the formation of a subset of protein-DNA interactions that drive the flipping of the target base from the helix to the active site. Noncognate substrates lacking these interactions undergo slow base flipping, and fluorescence tracking of the catalytic loop corroborates the NMR evidence of a loose, nonspecific binding mode prior to base flipping and subsequent closure of the catalytic loop. This slow flipping transition defines the rate-limiting step for the methylation of noncognate sequences. Additionally, we present spectroscopic evidence of an intermediate along the base flipping pathway that has been predicted but never previously observed. These findings provide important details of how conformational rearrangements are used to balance specificity with catalytic efficiency.
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Affiliation(s)
- Douglas M Matje
- Department of Chemistry and Biochemistry, University of California , Santa Barbara, California 93106, United States
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27
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Adhikary S, Cato MC, McGary KL, Rokas A, Eichman BF. Non-productive DNA damage binding by DNA glycosylase-like protein Mag2 from Schizosaccharomyces pombe. DNA Repair (Amst) 2012; 12:196-204. [PMID: 23273506 DOI: 10.1016/j.dnarep.2012.12.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2012] [Revised: 12/03/2012] [Accepted: 12/03/2012] [Indexed: 11/15/2022]
Abstract
Schizosaccharomyces pombe contains two paralogous proteins, Mag1 and Mag2, related to the helix-hairpin-helix (HhH) superfamily of alkylpurine DNA glycosylases from yeast and bacteria. Phylogenetic analysis of related proteins from four Schizosaccharomyces and other fungal species shows that the Mag1/Mag2 duplication is unique to the genus Schizosaccharomyces and most likely occurred in its ancestor. Mag1 excises N3- and N7-alkylguanines and 1,N(6)-ethenoadenine from DNA, whereas Mag2 has been reported to have no detectible alkylpurine base excision activity despite high sequence and active site similarity to Mag1. To understand this discrepancy we determined the crystal structure of Mag2 bound to abasic DNA and compared it to our previously determined Mag1-DNA structure. In contrast to Mag1, Mag2 does not flip the abasic moiety into the active site or stabilize the DNA strand 5' to the lesion, suggesting that it is incapable of forming a catalytically competent protein-DNA complex. Subtle differences in Mag1 and Mag2 interactions with the DNA duplex illustrate how Mag2 can stall at damage sites without fully engaging the lesion. We tested our structural predictions by mutational analysis of base excision and found a single amino acid responsible at least in part for Mag2's lack of activity. Substitution of Mag2 Asp56, which caps the helix at the base of the DNA intercalation loop, with the corresponding serine residue in Mag1 endows Mag2 with ɛA excision activity comparable to Mag1. This work provides novel insight into the chemical and physical determinants by which the HhH glycosylases engage DNA in a catalytically productive manner.
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Affiliation(s)
- Suraj Adhikary
- Department of Biological Sciences, Vanderbilt University, Nashville, TN 37232, USA
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28
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Gouge J, Ralec C, Henneke G, Delarue M. Molecular recognition of canonical and deaminated bases by P. abyssi family B DNA polymerase. J Mol Biol 2012; 423:315-36. [PMID: 22902479 DOI: 10.1016/j.jmb.2012.07.025] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Revised: 07/27/2012] [Accepted: 07/30/2012] [Indexed: 10/28/2022]
Abstract
Euryarchaeal polymerase B can recognize deaminated bases on the template strand, effectively stalling the replication fork 4nt downstream the modified base. Using Pyrococcus abyssi DNA B family polymerase (PabPolB), we investigated the discrimination between deaminated and natural nucleotide(s) by primer extension assays, electrophoretic mobility shift assays, and X-ray crystallography. Structures of complexes between the protein and DNA duplexes with either a dU or a dH in position +4 were solved at 2.3Å and 2.9Å resolution, respectively. The PabPolB is found in the editing mode. A new metal binding site has been uncovered below the base-checking cavity where the +4 base is flipped out; it is fully hydrated in an octahedral fashion and helps guide the strongly kinked template strand. Four other crystal structures with each of the canonical bases were also solved in the editing mode, and the presence of three nucleotides in the exonuclease site caused a shift in the coordination state of its metal A from octahedral to tetrahedral. Surprisingly, we find that all canonical bases also enter the base-checking pocket with very small differences in the binding geometry and in the calculated binding free energy compared to deaminated ones. To explain how this can lead to stalling of the replication fork, the full catalytic pathway and its branches must be taken into account, during which the base is checked several times. Our results strongly suggest a switch from elongation to editing modes right after nucleotide insertion when the modified base is at position +5.
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Affiliation(s)
- Jérôme Gouge
- Unité de Dynamique Structurale des Macromolécules, UMR 3528 du CNRS, Institut Pasteur, 25 rue du Dr Roux, 75015 Paris, France
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29
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Adhikary S, Eichman BF. Analysis of substrate specificity of Schizosaccharomyces pombe Mag1 alkylpurine DNA glycosylase. EMBO Rep 2011; 12:1286-92. [PMID: 21960007 DOI: 10.1038/embor.2011.189] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2011] [Revised: 08/26/2011] [Accepted: 08/29/2011] [Indexed: 11/09/2022] Open
Abstract
DNA glycosylases specialized for the repair of alkylation damage must identify, with fine specificity, a diverse array of subtle modifications within DNA. The current mechanism involves damage sensing through interrogation of the DNA duplex, followed by more specific recognition of the target base inside the active site pocket. To better understand the physical basis for alkylpurine detection, we determined the crystal structure of Schizosaccharomyces pombe Mag1 (spMag1) in complex with DNA and performed a mutational analysis of spMag1 and the close homologue from Saccharomyces cerevisiae (scMag). Despite strong homology, spMag1 and scMag differ in substrate specificity and cellular alkylation sensitivity, although the enzymological basis for their functional differences is unknown. We show that Mag preference for 1,N(6)-ethenoadenine (ɛA) is influenced by a minor groove-interrogating residue more than the composition of the nucleobase-binding pocket. Exchanging this residue between Mag proteins swapped their ɛA activities, providing evidence that residues outside the extrahelical base-binding pocket have a role in identification of a particular modification in addition to sensing damage.
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Affiliation(s)
- Suraj Adhikary
- Department of Biological Sciences and Center for Structural Biology, Vanderbilt University, 465 21st Avenue South, Box 351634 Station B, 5270A MRBIII, Nashville, Tennessee 37235, USA
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30
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An unprecedented nucleic acid capture mechanism for excision of DNA damage. Nature 2010; 468:406-11. [PMID: 20927102 DOI: 10.1038/nature09428] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2009] [Accepted: 08/17/2010] [Indexed: 01/22/2023]
Abstract
DNA glycosylases that remove alkylated and deaminated purine nucleobases are essential DNA repair enzymes that protect the genome, and at the same time confound cancer alkylation therapy, by excising cytotoxic N3-methyladenine bases formed by DNA-targeting anticancer compounds. The basis for glycosylase specificity towards N3- and N7-alkylpurines is believed to result from intrinsic instability of the modified bases and not from direct enzyme functional group chemistry. Here we present crystal structures of the recently discovered Bacillus cereus AlkD glycosylase in complex with DNAs containing alkylated, mismatched and abasic nucleotides. Unlike other glycosylases, AlkD captures the extrahelical lesion in a solvent-exposed orientation, providing an illustration for how hydrolysis of N3- and N7-alkylated bases may be facilitated by increased lifetime out of the DNA helix. The structures and supporting biochemical analysis of base flipping and catalysis reveal how the HEAT repeats of AlkD distort the DNA backbone to detect non-Watson-Crick base pairs without duplex intercalation.
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31
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Fadda E, Pomès R. On the molecular basis of uracil recognition in DNA: comparative study of T-A versus U-A structure, dynamics and open base pair kinetics. Nucleic Acids Res 2010; 39:767-80. [PMID: 20876689 PMCID: PMC3025553 DOI: 10.1093/nar/gkq812] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Uracil (U) can be found in DNA as a mismatch paired either to adenine (A) or to guanine (G). Removal of U from DNA is performed by a class of enzymes known as uracil–DNA–glycosylases (UDG). Recent studies suggest that recognition of U–A and U–G mismatches by UDG takes place via an extra-helical mechanism. In this work, we use molecular dynamics simulations to analyze the structure, dynamics and open base pair kinetics of U–A base pairs relative to their natural T–A counterpart in 12 dodecamers. Our results show that the presence of U does not alter the local conformation of B-DNA. Breathing dynamics and base pair closing kinetics are only weakly dependent on the presence of U versus T, with open T–A and U–A pairs lifetimes in the nanosecond timescale. Additionally, we observed spontaneous base flipping in U–A pairs. We analyze the structure and dynamics for this event and compare the results to available crystallographic data of open base pair conformations. Our results are in agreement with both structural and kinetic data derived from NMR imino proton exchange measurements, providing the first detailed description at the molecular level of elusive events such as spontaneous base pair opening and flipping in mismatched U–A sequences in DNA. Based on these results, we propose that base pair flipping can occur spontaneously at room temperature via a 3-step mechanism with an open base pair intermediate. Implications for the molecular basis of U recognition by UDG are discussed.
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Affiliation(s)
- Elisa Fadda
- School of Chemistry, National University of Ireland, Galway (NUIG), Galway, Ireland.
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32
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Kinde-Carson MN, Ferguson C, Oyler NA, Harbison GS, Meints GA. Solid state 2H NMR analysis of furanose ring dynamics in DNA containing uracil. J Phys Chem B 2010; 114:3285-93. [PMID: 20151717 DOI: 10.1021/jp9091656] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
DNA damage has been implicated in numerous human diseases, particularly cancer, and the aging process. Single-base lesions, such as uracil, in DNA can be cytotoxic or mutagenic and are recognized by a DNA glycosylase during the process of base excision repair. Increased dynamic properties in lesion-containing DNAs have been suggested to assist recognition and specificity. Deuterium solid-state nuclear magnetic resonance (SSNMR) has been used to directly observe local dynamics of the furanose ring within a uracil:adenine (U:A) base pair and compared to a normal thymine:adenine (T:A) base pair. Quadrupole echo lineshapes, <T(1Z)>, and <T(2e)> relaxation data were collected, and computer modeling was performed. The results indicate that the relaxation times are identical within the experimental error, the solid lineshapes are essentially indistinguishable above the noise level, and our lineshapes are best fit with a model that does not have significant local motions. Therefore, U:A base pair furanose rings appear to have essentially identical dynamic properties as a normal T:A base pair, and the local dynamics of the furanose ring are unlikely to be the sole arbiter for uracil recognition and specificity in U:A base pairs.
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33
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Naômé A, Schyman P, Laaksonen A, Vercauteren DP. Molecular Dynamics Simulation of 8-Oxoguanine Containing DNA Fragments Reveals Altered Hydration and Ion Binding Patterns. J Phys Chem B 2010; 114:4789-801. [DOI: 10.1021/jp1000539] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Aymeric Naômé
- Laboratoire de Physico-Chimie Informatique, Unité de Chimie Physique Théorique et Structurale, University of Namur (FUNDP), Namur, Belgium, and Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden
| | - Patric Schyman
- Laboratoire de Physico-Chimie Informatique, Unité de Chimie Physique Théorique et Structurale, University of Namur (FUNDP), Namur, Belgium, and Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden
| | - Aatto Laaksonen
- Laboratoire de Physico-Chimie Informatique, Unité de Chimie Physique Théorique et Structurale, University of Namur (FUNDP), Namur, Belgium, and Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden
| | - Daniel P. Vercauteren
- Laboratoire de Physico-Chimie Informatique, Unité de Chimie Physique Théorique et Structurale, University of Namur (FUNDP), Namur, Belgium, and Division of Physical Chemistry, Arrhenius Laboratory, Stockholm University, Stockholm, Sweden
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34
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Brolich MA, Wang L, O'Neill MA. Folding kinetics of recognition loop peptides from a photolyase and cryptochrome-DASH. Biochem Biophys Res Commun 2009; 391:874-8. [PMID: 19945437 DOI: 10.1016/j.bbrc.2009.11.155] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2009] [Accepted: 11/21/2009] [Indexed: 11/16/2022]
Abstract
Cryptochromes (CRY) and photolyases (PL) use a common flavin adenine dinucleotide cofactor and homologous protein scaffold to accomplish numerous, seemingly dissimilar functions. PL repairs UV-damaged DNA in a mechanism requiring light and DNA base flipping. CRY cannot repair DNA, and instead function in core biological processes including plant photomorphogenesis, circadian rhythm, and magnetoreception. One subclass, CRY-DASH, does catalyze repair of single-stranded DNA; compromised base flipping may deactivate its tight binding to duplex DNA substrates. We recently demonstrated that the a "recognition loop" involved in DNA binding by both PL and CRY-DASH is among the most flexible regions in the two proteins, and exhibits especially heightened dynamics in CRY-DASH. Here, we establish that these distinct dynamics are encoded by the loop sequences: we quantify the flexibility of the isolated loop peptides through the kinetics and activation parameters for their folding. Mirroring the dynamics within the proteins, the CRY-DASH recognition loop peptide folds 2.5-fold faster than its counterpart in PL, predominantly due to a lower enthalpy of activation. We propose that these distinct dynamics are functionally significant in DNA recognition. Binding duplex DNA in the catalytically-active base-flipped conformation imposes significant order on the recognition loop, and a corresponding entropic penalty. This may be surmounted by the more preorganized PL recognition loop, but may impose too large a barrier for the more dynamic loop in CRY-DASH. These results suggest that evolution of protein dynamics, through local sequence tuning in the recognition loop, may be an important mechanism for functional diversification in PL and CRY.
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Affiliation(s)
- Matthew A Brolich
- Department of Chemistry, Simon Fraser University, Burnaby, BC, Canada
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35
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Base flipping in V(D)J recombination: insights into the mechanism of hairpin formation, the 12/23 rule, and the coordination of double-strand breaks. Mol Cell Biol 2009; 29:5889-99. [PMID: 19720743 DOI: 10.1128/mcb.00187-09] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Tn5 transposase cleaves the transposon end using a hairpin intermediate on the transposon end. This involves a flipped base that is stacked against a tryptophan residue in the protein. However, many other members of the cut-and-paste transposase family, including the RAG1 protein, produce a hairpin on the flanking DNA. We have investigated the reversed polarity of the reaction for RAG recombination. Although the RAG proteins appear to employ a base-flipping mechanism using aromatic residues, the putatively flipped base is not at the expected location and does not appear to stack against any of the said aromatic residues. We propose an alternative model in which a flipped base is accommodated in a nonspecific pocket or cleft within the recombinase. This is consistent with the location of the flipped base at position -1 in the coding flank, which can be occupied by purine or pyrimidine bases that would be difficult to stabilize using a single, highly specific, interaction. Finally, during this work we noticed that the putative base-flipping events on either side of the 12/23 recombination signal sequence paired complex are coupled to the nicking steps and serve to coordinate the double-strand breaks on either side of the complex.
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36
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Bischerour J, Chalmers R. Base flipping in tn10 transposition: an active flip and capture mechanism. PLoS One 2009; 4:e6201. [PMID: 19593448 PMCID: PMC2705183 DOI: 10.1371/journal.pone.0006201] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2009] [Accepted: 05/25/2009] [Indexed: 11/19/2022] Open
Abstract
The bacterial Tn5 and Tn10 transposases have a single active site that cuts both strands of DNA at their respective transposon ends. This is achieved using a hairpin intermediate that requires the DNA to change conformation during the reaction. In Tn5 these changes are controlled in part by a flipped nucleoside that is stacked on a tryptophan residue in a hydrophobic pocket of the transposase. Here we have investigated the base flipping mechanism in Tn10 transposition. As in Tn5 transposition, we find that base flipping takes place after the first nick and is required for efficient hairpin formation and resolution. Experiments with an abasic substrate show that the role of base flipping in hairpin formation is to remove the base from the DNA helix. Specific interactions between the flipped base and the stacking tryptophan residue are required for hairpin resolution later in the reaction. We show that base flipping in Tn10 transposition is not a passive reaction in which a spontaneously flipped base is captured and retained by the protein. Rather, it is driven in part by a methionine probe residue that helps to force the flipped base from the base stack. Overall, it appears that base flipping in Tn10 transposition is similar to that in Tn5 transposition.
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Affiliation(s)
- Julien Bischerour
- University of Nottingham, School of Biomedical Sciences, The Medical School, Queens Medical Centre (QMC), Nottingham, United Kingdom
| | - Ronald Chalmers
- University of Nottingham, School of Biomedical Sciences, The Medical School, Queens Medical Centre (QMC), Nottingham, United Kingdom
- * E-mail:
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37
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Distinct recognition loop dynamics in cryptochrome-DASH and photolyase revealed by limited proteolysis. Biochem Biophys Res Commun 2009; 385:424-9. [DOI: 10.1016/j.bbrc.2009.05.087] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2009] [Accepted: 05/20/2009] [Indexed: 11/23/2022]
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38
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Banavali NK, MacKerell AD. Characterizing structural transitions using localized free energy landscape analysis. PLoS One 2009; 4:e5525. [PMID: 19436759 PMCID: PMC2678196 DOI: 10.1371/journal.pone.0005525] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2008] [Accepted: 03/27/2009] [Indexed: 11/24/2022] Open
Abstract
BACKGROUND Structural changes in molecules are frequently observed during biological processes like replication, transcription and translation. These structural changes can usually be traced to specific distortions in the backbones of the macromolecules involved. Quantitative energetic characterization of such distortions can greatly advance the atomic-level understanding of the dynamic character of these biological processes. METHODOLOGY/PRINCIPAL FINDINGS Molecular dynamics simulations combined with a variation of the Weighted Histogram Analysis Method for potential of mean force determination are applied to characterize localized structural changes for the test case of cytosine (underlined) base flipping in a GTCAGCGCATGG DNA duplex. Free energy landscapes for backbone torsion and sugar pucker degrees of freedom in the DNA are used to understand their behavior in response to the base flipping perturbation. By simplifying the base flipping structural change into a two-state model, a free energy difference of upto 14 kcal/mol can be attributed to the flipped state relative to the stacked Watson-Crick base paired state. This two-state classification allows precise evaluation of the effect of base flipping on local backbone degrees of freedom. CONCLUSIONS/SIGNIFICANCE The calculated free energy landscapes of individual backbone and sugar degrees of freedom expectedly show the greatest change in the vicinity of the flipping base itself, but specific delocalized effects can be discerned upto four nucleotide positions away in both 5' and 3' directions. Free energy landscape analysis thus provides a quantitative method to pinpoint the determinants of structural change on the atomic scale and also delineate the extent of propagation of the perturbation along the molecule. In addition to nucleic acids, this methodology is anticipated to be useful for studying conformational changes in all macromolecules, including carbohydrates, lipids, and proteins.
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Affiliation(s)
- Nilesh K. Banavali
- Laboratory of Computational and Structural Biology, Division of Genetics, Wadsworth Center, New York State Department of Health, Albany, New York, United States of America
- Department of Biomedical Sciences, The State University of New York at Albany, Albany, New York, United States of America
| | - Alexander D. MacKerell
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, Maryland, United States of America
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39
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Baute J, Depicker A. Base excision repair and its role in maintaining genome stability. Crit Rev Biochem Mol Biol 2008; 43:239-76. [PMID: 18756381 DOI: 10.1080/10409230802309905] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
For all living organisms, genome stability is important, but is also under constant threat because various environmental and endogenous damaging agents can modify the structural properties of DNA bases. As a defense, organisms have developed different DNA repair pathways. Base excision repair (BER) is the predominant pathway for coping with a broad range of small lesions resulting from oxidation, alkylation, and deamination, which modify individual bases without large effect on the double helix structure. As, in mammalian cells, this damage is estimated to account daily for 10(4) events per cell, the need for BER pathways is unquestionable. The damage-specific removal is carried out by a considerable group of enzymes, designated as DNA glycosylases. Each DNA glycosylase has its unique specificity and many of them are ubiquitous in microorganisms, mammals, and plants. Here, we review the importance of the BER pathway and we focus on the different roles of DNA glycosylases in various organisms.
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Affiliation(s)
- Joke Baute
- Department of Plant Systems Biology, Flanders Institute for Biotechnology, Gent, Belgium
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40
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Mura C, McCammon JA. Molecular dynamics of a kappaB DNA element: base flipping via cross-strand intercalative stacking in a microsecond-scale simulation. Nucleic Acids Res 2008; 36:4941-55. [PMID: 18653524 PMCID: PMC2528173 DOI: 10.1093/nar/gkn473] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The sequence-dependent structural variability and conformational dynamics of DNA play pivotal roles in many biological milieus, such as in the site-specific binding of transcription factors to target regulatory elements. To better understand DNA structure, function, and dynamics in general, and protein···DNA recognition in the ‘κB’ family of genetic regulatory elements in particular, we performed molecular dynamics simulations of a 20-bp DNA encompassing a cognate κB site recognized by the proto-oncogenic ‘c-Rel’ subfamily of NF-κB transcription factors. Simulations of the κB DNA in explicit water were extended to microsecond duration, providing a broad, atomically detailed glimpse into the structural and dynamical behavior of double helical DNA over many timescales. Of particular note, novel (and structurally plausible) conformations of DNA developed only at the long times sampled in this simulation—including a peculiar state arising at ≈0.7 μs and characterized by cross-strand intercalative stacking of nucleotides within a longitudinally sheared base pair, followed (at ≈1 μs) by spontaneous base flipping of a neighboring thymine within the A-rich duplex. Results and predictions from the microsecond-scale simulation include implications for a dynamical NF-κB recognition motif, and are amenable to testing and further exploration via specific experimental approaches that are suggested herein.
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Affiliation(s)
- Cameron Mura
- Department of Chemistry and Biochemistry and Center for Theoretical Biological Physics, University of California, San Diego, La Jolla, CA 92093-0365, USA.
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41
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Lee S, Radom CT, Verdine GL. Trapping and structural elucidation of a very advanced intermediate in the lesion-extrusion pathway of hOGG1. J Am Chem Soc 2008; 130:7784-5. [PMID: 18507380 PMCID: PMC2878488 DOI: 10.1021/ja800821t] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Here we present the first structure of a very advanced intermediate in the lesion-extrusion pathway of a DNA glycosylase, human 8-oxoguanine DNA glycosylase (hOGG1), and a substrate DNA containing a mutagenic lesion, 8-oxoguanine (oxoG). The structure was obtained by irradiation and flash-freezing of a disulfide-cross-linked (DXLed) complex of hOgg1 bound to DNA containing a novel photocaged derivative of oxoG. The X-ray structure reveals that, upon irradiation, the oxoG lesion has transited from the exosite to the active site pocket, but has not undergone cleavage by the enzyme. Furthermore, all but one of the specificity-determining interactions between the lesion and the enzyme are unformed in the flashed complex (FC), because active site functionality and elements of the DNA backbone are mispositioned. This structure thus provides a first glimpse into the structure of a very late-stage intermediate in the lesion-extrusion pathway--the latest observed to date for any glycosylase--in which the oxoG has undergone insertion into the enzyme active site following photodeprotection, but the enzyme and DNA have not yet completed the slower process of adjusting to the presence of the lesion in the active site.
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Affiliation(s)
- Seongmin Lee
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138
| | - Christopher T. Radom
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138
| | - Gregory L. Verdine
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138
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42
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Firbank SJ, Wardle J, Heslop P, Lewis RJ, Connolly BA. Uracil recognition in archaeal DNA polymerases captured by X-ray crystallography. J Mol Biol 2008; 381:529-39. [PMID: 18614176 DOI: 10.1016/j.jmb.2008.06.004] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2008] [Revised: 05/29/2008] [Accepted: 06/02/2008] [Indexed: 11/26/2022]
Abstract
Archaeal family B DNA polymerases bind tightly to template-strand uracil and stall replication on encountering the pro-mutagenic base. This article describes an X-ray crystal structure, at 2.8 A resolution, of Thermococcus gorgonarius polymerase in complex with a DNA primer-template containing uracil in the single-stranded region. The DNA backbone is distorted to position the uracil deeply within a pocket, located in the amino-terminal domain of the polymerase. Specificity arises from a combination of hydrogen bonds between the protein backbone and uracil, with the pocket shaped to prevent the stable binding of the four standard DNA bases. Strong interactions are seen with the two phosphates that flank the uracil and the structure gives clues concerning the coupling of uracil binding to the halting of replication. The importance of key amino acids, identified by the analysis of the structure and their conservation between archaeal polymerases, was confirmed by site-directed mutagenesis. The crystal structure of V93Q, a polymerase variant that no longer recognises uracil, is also reported, explaining the V93Q phenotype by the steric exclusion of uracil from the pocket.
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Affiliation(s)
- Susan J Firbank
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
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43
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Abstract
The efficient enzymatic detection of damaged bases concealed in the DNA double helix is an essential step during DNA repair in all cells. Emergent structural and mechanistic approaches have provided glimpses into this enigmatic molecular recognition event in several systems. A ubiquitous feature of these essential reactions is the binding of the damaged base in an extrahelical binding mode. The reaction pathway by which this remarkable extrahelical state is achieved is of great interest and even more debate.
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Affiliation(s)
- James T Stivers
- Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, 725 North Wolfe St., WBS 314, Baltimore, MD 21205, USA.
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44
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Abstract
A fundamental question in DNA repair is how a lesion is detected when embedded in millions to billions of normal base pairs. Extensive structural and functional studies reveal atomic details of DNA repair protein and nucleic acid interactions. This review summarizes seemingly diverse structural motifs used in lesion recognition and suggests a general mechanism to recognize DNA lesion by the poor base stacking. After initial recognition of this shared structural feature of lesions, different DNA repair pathways use unique verification mechanisms to ensure correct lesion identification and removal.
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45
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Krishnamurthy N, Muller JG, Burrows CJ, David SS. Unusual structural features of hydantoin lesions translate into efficient recognition by Escherichia coli Fpg. Biochemistry 2007; 46:9355-65. [PMID: 17655276 PMCID: PMC2442889 DOI: 10.1021/bi602459v] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Oxidation of guanine (G) and 8-oxoguanine (OG) with a wide variety of oxidants yields the hydantoin lesions, guanidinohydantoin (Gh) and spiroiminodihydantoin (Sp). These two lesions have garnered much recent attention due to their unusual structures and high mutagenic potential. We have previously shown that duplexes containing Gh and Sp are substrates for the base excision repair glycosylase Escherichia coli Fpg (EcFpg). To evaluate the recognition features of these unusual lesions, binding and footprinting experiments were performed using a glycosylase inactive variant, E3Q EcFpg, and 30 bp duplexes containing the embedded lesions. Surprisingly, E3Q EcFpg was found to bind significantly more tightly ( approximately 1000-fold) to duplexes containing Gh or Sp over the corresponding duplexes containing OG. This may be a consequence of the helix-destabilizing nature of the hydantoin lesions that facilitates their recognition within duplex DNA. Though DNA binding affinities of E3Q EcFpg with Gh- and Sp-containing duplexes were found to be similar to each other, hydroxyl radical footprinting using methidium-propyl-EDTA (MPE)-Fe(II) revealed subtle differences between binding of E3Q EcFpg to the two lesions. Most notably, in the presence of E3Q EcFpg, the Sp nucleotide (nt) is hyperreactive toward cleavage by MPE-Fe(II)-generated hydroxyl radicals, suggestive of the formation of an intercalation site for the MPE-Fe(II) reagent at the Sp nt. Interestingly, increasing the duplex length from 18 to 30 bp enhanced the excision efficiency of Gh and Sp paired with C, G, or T by EcFpg such that these substrates are processed as efficiently as the signature substrate lesion, OG. Moreover, the base removal activity with these two lesions was more efficient than removal of OG when in a base pairing context opposite A. The high affinity and efficient activity of EcFpg toward the hydantoin lesions suggest that EcFpg mediates repair of the lesions in vivo. Notably, the facile activity of EcFpg toward Gh and Sp in base pairing contexts with G and A, which are likely to be present after DNA replication, would be detrimental and enhance mutagenesis.
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Affiliation(s)
| | | | | | - Sheila S. David
- *Corresponding Author: SSD: telephone: (530)-752-4830; fax: (530)-752-8995, Email address:
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46
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Abstract
Maintaining the chemical integrity of DNA in the face of assault by oxidizing agents is a constant challenge for living organisms. Base-excision repair has an important role in preventing mutations associated with a common product of oxidative damage to DNA, 8-oxoguanine. Recent structural studies have shown that 8-oxoguanine DNA glycosylases use an intricate series of steps to locate and excise 8-oxoguanine lesions efficiently against a high background of undamaged bases. The importance of preventing mutations associated with 8-oxoguanine is shown by a direct association between defects in the DNA glycosylase MUTYH and colorectal cancer. The properties of other guanine oxidation products and the associated DNA glycosylases that remove them are now also being revealed.
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Affiliation(s)
- Sheila S David
- Department of Chemistry, University of California at Davis, 1 Shields Avenue, Davis, California 95616, USA.
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47
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Bouvier B, Grubmüller H. A molecular dynamics study of slow base flipping in DNA using conformational flooding. Biophys J 2007; 93:770-86. [PMID: 17496048 PMCID: PMC1913169 DOI: 10.1529/biophysj.106.091751] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Individual DNA bases are known to be able to flip out of the helical stack, providing enzymes with access to the genetic information otherwise hidden inside the helix. Consequently, base flipping is a necessary first step to many more complex biological processes such as DNA transcription or replication. Much remains unknown about this elementary step, despite a wealth of experimental and theoretical studies. From the theoretical point of view, the involved timescale of milliseconds or longer requires the use of enhanced sampling techniques. In contrast to previous theoretical studies employing umbrella sampling along a predefined flipping coordinate, this study attempts to induce flipping without prior knowledge of the pathway, using information from a molecular dynamics simulation of a B-DNA fragment and the conformational flooding method. The relevance to base flipping of the principal components of the simulation is assayed, and a combination of modes optimally related to the flipping of the base through either helical groove is derived for each of the two bases of the central guanine-cytosine basepair. By applying an artificial flooding potential along these collective coordinates, the flipping mechanism is accelerated to within the scope of molecular dynamics simulations. The associated free energy surface is found to feature local minima corresponding to partially flipped states, particularly relevant to flipping in isolated DNA; further transitions from these minima to the fully flipped conformation are accelerated by additional flooding potentials. The associated free energy profiles feature similar barrier heights for both bases and pathways; the flipped state beyond is a broad and rugged attraction basin, only a few kcal/mol higher in energy than the closed conformation. This result diverges from previous works but echoes some aspects of recent experimental findings, justifying the need for novel approaches to this difficult problem: this contribution represents a first step in this direction. Important structural factors involved in flipping, both local (sugar-phosphate backbone dihedral angles) and global (helical axis bend), are also identified.
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Affiliation(s)
- Benjamin Bouvier
- Theoretical and Computational Biophysics Department, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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48
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Abstract
Many enzymes that repair or modify bases in double-stranded DNA gain access to their substrates by base flipping. Although crystal structures provide stunning snap shots, biochemical approaches addressing the dynamics have proven difficult, particularly in complicated multi-step reactions. Here, we use protein-DNA crosslinking and potassium permanganate reactivity to explore the base-flipping step in Tn5 transposition. We present a model to suggest that base flipping is driven by a combination of factors including DNA bending and the intrusion of a probe residue. The forces are postulated to act early in the reaction to create a state of tension, relieved by base flipping after cleavage of the first strand of DNA at the transposon end. Elimination of the probe residue retards the kinetics of nicking and reduces base flipping by 50%. Unexpectedly, the probe residue is even more important during the hairpin resolution step. Overall, base flipping is pivotal to the hairpin processing reaction because it performs two opposite but closely related functions. On one hand it disrupts the double helix, providing the necessary strand separation and steric freedom. While on the other, transposase appears to position the second DNA strand in the active site for cleavage using the flipped base as a handle.
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Affiliation(s)
- Julien Bischerour
- University of Oxford, Department of Biochemistry, South Parks Road, Oxford, OX1 3QU, UK
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49
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Estabrook RA, Reich N. Observing an Induced-fit Mechanism during Sequence-specific DNA Methylation. J Biol Chem 2006; 281:37205-14. [PMID: 17005571 DOI: 10.1074/jbc.m607538200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The characterization of conformational changes that drive induced-fit mechanisms and their quantitative importance to enzyme specificity are essential for a full understanding of enzyme function. Here, we report on M.HhaI, a sequence-specific DNA cytosine C(5) methyltransferase that reorganizes a flexible loop (residues 80-100) upon binding cognate DNA as part of an induced-fit mechanism. To directly observe this approximately 26A conformational rearrangement and provide a basis for understanding its importance to specificity, we replaced loop residues Lys-91 and Glu-94 with tryptophans. The double mutants W41F/K91W and W41F/E94W are relatively unperturbed in kinetic and thermodynamic properties. W41F/E94W shows DNA sequence-dependent changes in fluorescence: significant changes in equilibrium and transient state fluorescence that occur when the enzyme binds cognate DNA are absent with nonspecific DNA. These real-time, solution-based results provide direct evidence that binding to cognate DNA induces loop reorganization into the closed conformer, resulting in the correct assembly of the active site. We propose that M.HhaI scans nonspecific DNA in the loop-open conformer and rearranges to the closed form once the cognate site is recognized. The fluorescence data exclude mechanisms in which loop motion precedes base flipping, and we show loop rearrangements are directly coupled to base flipping, because the sequential removal of single hydrogen bonds within the target guanosine:cytosine base pair results in corresponding changes in loop motion.
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Affiliation(s)
- R August Estabrook
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, USA
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50
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Cao C, Jiang YL, Krosky DJ, Stivers JT. The catalytic power of uracil DNA glycosylase in the opening of thymine base pairs. J Am Chem Soc 2006; 128:13034-5. [PMID: 17017766 PMCID: PMC2529456 DOI: 10.1021/ja062978n] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Uracil DNA glycosylase (UNG) locates uracil and its structural congener thymine in the context of duplex DNA using a base flipping mechanism. NMR imino proton exchange measurements were performed on free and UNG-bound DNA duplexes in which a single thymine (T) was paired with a series of adenine analogues (X) capable of forming one, two, or three hydrogen bonds. The base pair opening equilibrium for the free DNA increased 55-fold as the number of hydrogen bonds decreased, but the opening rate constants were nearly the same in the absence and presence of UNG. In contrast, UNG was found to slow the base pair closing rate constants (kcl) compared to each free duplex by a factor of 3- to 23-fold. These findings indicate that regardless of the inherent thermodynamic stability of the TX pair, UNG does not alter the spontaneous opening rate. Instead, the enzyme holds the spontaneously expelled thymine (or uracil) in a transient extrahelical sieving site where it may partition forward into the enzyme active site (uracil) or back into the DNA base stack (thymine).
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Affiliation(s)
- Chunyang Cao
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore Maryland, 21205
| | - Yu Lin Jiang
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore Maryland, 21205
| | - Daniel J. Krosky
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore Maryland, 21205
| | - James T. Stivers
- Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore Maryland, 21205
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