scholarly journals Structure of human apurinic/apyrimidinic endonuclease 1 with the essential Mg2+cofactor

2013 ◽  
Vol 69 (12) ◽  
pp. 2555-2562 ◽  
Author(s):  
Brittney A. Manvilla ◽  
Edwin Pozharski ◽  
Eric A. Toth ◽  
Alexander C. Drohat
Keyword(s):  
Active Site ◽  
Excision Repair ◽  
Strand Break ◽  
Dnase I ◽  
Dna Lesions ◽  
Water Molecules ◽  
Repair Synthesis ◽  
Phosphodiester Bond ◽  
Abasic Sites ◽  
Catalytic Function

Apurinic/apyrimidinic endonuclease 1 (APE1) mediates the repair of abasic sites and other DNA lesions and is essential for base-excision repair and strand-break repair pathways. APE1 hydrolyzes the phosphodiester bond at abasic sites, producing 5′-deoxyribose phosphate and the 3′-OH primer needed for repair synthesis. It also has additional repair activities, including the removal of 3′-blocking groups. APE1 is a powerful enzyme that absolutely requires Mg2+, but the stoichiometry and catalytic function of the divalent cation remain unresolved for APE1 and for other enzymes in the DNase I superfamily. Previously reported structures of DNA-free APE1 contained either Sm3+or Pb2+in the active site. However, these are poor surrogates for Mg2+because Sm3+is not a cofactor and Pb2+inhibits APE1, and their coordination geometry is expected to differ from that of Mg2+. A crystal structure of human APE1 was solved at 1.92 Å resolution with a single Mg2+ion in the active site. The structure reveals ideal octahedral coordination of Mg2+viatwo carboxylate groups and four water molecules. One residue that coordinates Mg2+directly and two that bind inner-sphere water molecules are strictly conserved in the DNase I superfamily. This structure, together with a recent structure of the enzyme–product complex, inform on the stoichiometry and the role of Mg2+in APE1-catalyzed reactions.

scholarly journals Structural intermediates of a DNA–ligase complex illuminate the role of the catalytic metal ion and mechanism of phosphodiester bond formation

2019 ◽  
Vol 47 (14) ◽  
pp. 7147-7162 ◽  
Author(s):  
Adele Williamson ◽  
Hanna-Kirsti S Leiros
Keyword(s):  
Active Site ◽  
Metal Ion ◽  
Bond Formation ◽  
Strand Break ◽  
Nucleophilic Attack ◽  
Dna Ligase ◽  
Phosphodiester Bond ◽  
Dna Ligases ◽  
Catalytic Metal ◽  
Ternary Structure

Abstract DNA ligases join adjacent 5′ phosphate (5′P) and 3′ hydroxyl (3′OH) termini of double-stranded DNA via a three-step mechanism requiring a nucleotide cofactor and divalent metal ion. Although considerable structural detail is available for the first two steps, less is known about step 3 where the DNA-backbone is joined or about the cation role at this step. We have captured high-resolution structures of an adenosine triphosphate (ATP)-dependent DNA ligase from Prochlorococcus marinus including a Mn-bound pre-ternary ligase–DNA complex poised for phosphodiester bond formation, and a post-ternary intermediate retaining product DNA and partially occupied AMP in the active site. The pre-ternary structure unambiguously identifies the binding site of the catalytic metal ion and confirms both its role in activating the 3′OH terminus for nucleophilic attack on the 5′P group and stabilizing the pentavalent transition state. The post-ternary structure indicates that DNA distortion and most enzyme-AMP contacts remain after phosphodiester bond formation, implying loss of covalent linkage to the DNA drives release of AMP, rather than active site rearrangement. Additionally, comparisons of this cyanobacterial DNA ligase with homologs from bacteria and bacteriophage pose interesting questions about the structural origin of double-strand break joining activity and the evolution of these ATP-dependent DNA ligase enzymes.

scholarly journals Structure of the endonuclease IV homologue fromThermotoga maritimain the presence of active-site divalent metal ions

2010 ◽  
Vol 66 (9) ◽  
pp. 1003-1012 ◽  
Author(s):  
Stephen J. Tomanicek ◽  
Ronny C. Hughes ◽  
Joseph D. Ng ◽  
Leighton Coates
Keyword(s):  
Metal Ions ◽  
Active Site ◽  
Excision Repair ◽  
Divalent Metal ◽  
Hydroxyl Group ◽  
Divalent Metal Ions ◽  
Ap Endonuclease ◽  
Phosphodiester Bond ◽  
Dna Base ◽  
Ap Site

The most frequent lesion in DNA is at apurinic/apyrimidinic (AP) sites resulting from DNA-base losses. These AP-site lesions can stall DNA replication and lead to genome instability if left unrepaired. The AP endonucleases are an important class of enzymes that are involved in the repair of AP-site intermediates during damage-general DNA base-excision repair pathways. These enzymes hydrolytically cleave the 5′-phosphodiester bond at an AP site to generate a free 3′-hydroxyl group and a 5′-terminal sugar phosphate using their AP nuclease activity. Specifically,Thermotoga maritimaendonuclease IV is a member of the second conserved AP endonuclease family that includesEscherichia coliendonuclease IV, which is the archetype of the AP endonuclease superfamily. In order to more fully characterize the AP endonuclease family of enzymes, two X-ray crystal structures of theT. maritimaendonuclease IV homologue were determined in the presence of divalent metal ions bound in the active-site region. These structures of theT. maritimaendonuclease IV homologue further revealed the use of the TIM-barrel fold and the trinuclear metal binding site as important highly conserved structural elements that are involved in DNA-binding and AP-site repair processes in the AP endonuclease superfamily.

scholarly journals ERCC1-XPF Endonuclease Facilitates DNA Double-Strand Break Repair

2008 ◽  
Vol 28 (16) ◽  
pp. 5082-5092 ◽  
Author(s):  
Anwaar Ahmad ◽  
Andria Rasile Robinson ◽  
Anette Duensing ◽  
Ellen van Drunen ◽  
H. Berna Beverloo ◽  
...  
Keyword(s):  
Gamma Irradiation ◽  
Excision Repair ◽  
Strand Break ◽  
Dna Lesions ◽  
End Joining ◽  
Dsb Repair ◽  
Large Deletions ◽  
Mutant Cells

ABSTRACT ERCC1-XPF endonuclease is required for nucleotide excision repair (NER) of helix-distorting DNA lesions. However, mutations in ERCC1 or XPF in humans or mice cause a more severe phenotype than absence of NER, prompting a search for novel repair activities of the nuclease. In Saccharomyces cerevisiae, orthologs of ERCC1-XPF (Rad10-Rad1) participate in the repair of double-strand breaks (DSBs). Rad10-Rad1 contributes to two error-prone DSB repair pathways: microhomology-mediated end joining (a Ku86-independent mechanism) and single-strand annealing. To determine if ERCC1-XPF participates in DSB repair in mammals, mutant cells and mice were screened for sensitivity to gamma irradiation. ERCC1-XPF-deficient fibroblasts were hypersensitive to gamma irradiation, and γH2AX foci, a marker of DSBs, persisted in irradiated mutant cells, consistent with a defect in DSB repair. Mutant mice were also hypersensitive to irradiation, establishing an essential role for ERCC1-XPF in protecting against DSBs in vivo. Mice defective in both ERCC1-XPF and Ku86 were not viable. However, Ercc1 −/− Ku86 −/− fibroblasts were hypersensitive to gamma irradiation compared to single mutants and accumulated significantly greater chromosomal aberrations. Finally, in vitro repair of DSBs with 3′ overhangs led to large deletions in the absence of ERCC1-XPF. These data support the conclusion that, as in yeast, ERCC1-XPF facilitates DSB repair via an end-joining mechanism that is Ku86 independent.

scholarly journals Role of Base Excision Repair Pathway in the Processing of Complex DNA Damage Generated by Oxidative Stress and Anticancer Drugs

2021 ◽  
Vol 8 ◽  
Author(s):  
Yeldar Baiken ◽  
Damira Kanayeva ◽  
Sabira Taipakova ◽  
Regina Groisman ◽  
Alexander A. Ishchenko ◽  
...  
Keyword(s):  
Dna Damage ◽  
Base Excision Repair ◽  
Genome Instability ◽  
Excision Repair ◽  
Chromosomal Rearrangements ◽  
Strand Break ◽  
Dna Lesions ◽  
Complex Nature ◽  
Base Excision

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.

scholarly journals Mitochondrial DNA Repair in an Arabidopsis thaliana Uracil N-Glycosylase Mutant

2018 ◽  
Author(s):  
Emily Wynn ◽  
Emma Purfeerst ◽  
Alan Christensen
Keyword(s):  
Excision Repair ◽  
Plant Mitochondria ◽  
Strand Break ◽  
Double Strand Break ◽  
Dna Lesions ◽  
Double Strand Break Repair ◽  
Nucleotide Polymorphisms ◽  
Cytosine Deamination ◽  
Repair Pathways ◽  
Break Repair

AbstractSubstitution rates in plant mitochondrial genes are extremely low, indicating strong selective pressure as well as efficient repair. Plant mitochondria possess base excision repair pathways, however, many repair pathways such as nucleotide excision repair and mismatch repair appear to be absent. In the absence of these pathways, many DNA lesions must be repaired by a different mechanism. To test the hypothesis that double-strand break repair (DSBR) is that mechanism, we maintained independent self-crossing lineages of plants deficient in uracil-N-glycosylase (UNG) for 11 generations to determine the repair outcomes when that pathway is missing. Surprisingly, no single nucleotide polymorphisms (SNPs) were fixed in any line in generation 11. The pattern of heteroplasmic SNPs was also unaltered through 11 generations. When the rate of cytosine deamination was increased by mitochondrial expression of the cytosine deaminase APOBEC3G, there was an increase in heteroplasmic SNPs, but only in mature leaves. Clearly DNA maintenance in reproductive meristem mitochondria is very effective in the absence of UNG, while mitochondrial genomes in differentiated tissue are maintained through a different mechanism, or not at all. Several genes involved in DSBR are upregulated in the absence of UNG, indicating that double strand break repair is a general system of repair in plant mitochondria. It is important to note that the developmental stage of tissues is critically important for these types of experiments.

scholarly journals Imbalanced Base Excision Repair Increases Spontaneous Mutation and Alkylation Sensitivity inEscherichia coli

1999 ◽  
Vol 181 (21) ◽  
pp. 6763-6771 ◽  
Author(s):  
Lauren M. Posnick ◽  
Leona D. Samson
Keyword(s):  
Base Excision Repair ◽  
Mammalian Cells ◽  
Excision Repair ◽  
Spontaneous Mutation ◽  
Dna Lesions ◽  
Dna Glycosylases ◽  
E Coli ◽  
Abasic Sites ◽  
Base Excision ◽  
Harmful Effects

ABSTRACT Inappropriate expression of 3-methyladenine (3MeA) DNA glycosylases has been shown to have harmful effects on microbial and mammalian cells. To understand the underlying reasons for this phenomenon, we have determined how DNA glycosylase activity and substrate specificity modulate glycosylase effects in Escherichia coli. We compared the effects of two 3MeA DNA glycosylases with very different substrate ranges, namely, the Saccharomyces cerevisiae Mag1 and the E. coli Tag glycosylases. Both glycosylases increased spontaneous mutation, decreased cell viability, and sensitized E. coli to killing by the alkylating agent methyl methanesulfonate. However, Tag had much less harmful effects than Mag1. The difference between the two enzymes’ effects may be accounted for by the fact that Tag almost exclusively excises 3MeA lesions, whereas Mag1 excises a broad range of alkylated and other purines. We infer that the DNA lesions responsible for changes in spontaneous mutation, viability, and alkylation sensitivity are abasic sites and secondary lesions resulting from processing abasic sites via the base excision repair pathway.

scholarly journals Mitochondrial DNA Repair in an Arabidopsis thaliana Uracil N-Glycosylase Mutant

Plants ◽  
2020 ◽  
Vol 9 (2) ◽  
pp. 261 ◽  
Author(s):  
Emily Wynn ◽  
Emma Purfeerst ◽  
Alan Christensen
Keyword(s):  
Excision Repair ◽  
Plant Mitochondria ◽  
Strand Break ◽  
Double Strand Break ◽  
Dna Lesions ◽  
Double Strand Break Repair ◽  
Nucleotide Polymorphisms ◽  
Cytosine Deamination ◽  
Repair Pathways ◽  
Break Repair

Substitution rates in plant mitochondrial genes are extremely low, indicating strong selective pressure as well as efficient repair. Plant mitochondria possess base excision repair pathways; however, many repair pathways such as nucleotide excision repair and mismatch repair appear to be absent. In the absence of these pathways, many DNA lesions must be repaired by a different mechanism. To test the hypothesis that double-strand break repair (DSBR) is that mechanism, we maintained independent self-crossing lineages of plants deficient in uracil-N-glycosylase (UNG) for 11 generations to determine the repair outcomes when that pathway is missing. Surprisingly, no single nucleotide polymorphisms (SNPs) were fixed in any line in generation 11. The pattern of heteroplasmic SNPs was also unaltered through 11 generations. When the rate of cytosine deamination was increased by mitochondrial expression of the cytosine deaminase APOBEC3G, there was an increase in heteroplasmic SNPs but only in mature leaves. Clearly, DNA maintenance in reproductive meristem mitochondria is very effective in the absence of UNG while mitochondrial genomes in differentiated tissue are maintained through a different mechanism or not at all. Several genes involved in DSBR are upregulated in the absence of UNG, indicating that double-strand break repair is a general system of repair in plant mitochondria. It is important to note that the developmental stage of tissues is critically important for these types of experiments.

scholarly journals Replication protein A safeguards genome integrity by controlling NER incision events

2011 ◽  
Vol 192 (3) ◽  
pp. 401-415 ◽  
Author(s):  
René M. Overmeer ◽  
Jill Moser ◽  
Marcel Volker ◽  
Hanneke Kool ◽  
Alan E. Tomkinson ◽  
...  
Keyword(s):  
Excision Repair ◽  
Protein A ◽  
Replication Protein A ◽  
Dna Lesions ◽  
Replication Protein ◽  
Genome Integrity ◽  
Repair Synthesis ◽  
Dna Strand ◽  
Dna Repair Synthesis

Single-stranded DNA gaps that might arise by futile repair processes can lead to mutagenic events and challenge genome integrity. Nucleotide excision repair (NER) is an evolutionarily conserved repair mechanism, essential for removal of helix-distorting DNA lesions. In the currently prevailing model, NER operates through coordinated assembly of repair factors into pre- and post-incision complexes; however, its regulation in vivo is poorly understood. Notably, the transition from dual incision to repair synthesis should be rigidly synchronized as it might lead to accumulation of unprocessed repair intermediates. We monitored NER regulatory events in vivo using sequential UV irradiations. Under conditions that allow incision yet prevent completion of repair synthesis or ligation, preincision factors can reassociate with new damage sites. In contrast, replication protein A remains at the incomplete NER sites and regulates a feedback loop from completion of DNA repair synthesis to subsequent damage recognition, independently of ATR signaling. Our data reveal an important function for replication protein A in averting further generation of DNA strand breaks that could lead to mutagenic and recombinogenic events.

scholarly journals Loss of DNA repair capacity during successive subcultures of primary rat fibroblasts.

1977 ◽  
Vol 74 (2) ◽  
pp. 365-370 ◽  
Author(s):  
A C Chan ◽  
I G Walker
Keyword(s):  
Dna Repair ◽  
Excision Repair ◽  
Strand Break ◽  
Single Strand ◽  
Velocity Sedimentation ◽  
Early Passage ◽  
Repair Capacity ◽  
Repair Synthesis ◽  
Single Strand Break ◽  
Passage Cells

Cultures of fibroblasts from newborn rats and successive subcultures of these cells were treated with 4-nitroquinoline-1-oxide to induce DNA repair. DNA from the cultures was examined by velocity sedimentation in alkaline sucrose gradients immediately after drug treatment and after a post-treatment incubation period of 3 h. Early passage cells were able to repair the damage that appeared as single strand breaks, however, by the seventh subculture this activity was not apparent. Measurements of repair synthesis showed a partial loss of this capacity with successive subculture. The results fit a model in which 4NQO causes two kinds of DNA modification, one of which is alkali labile and appears as a single-strand break. Both modifications are subject to excision repair, but each is recognized initially by a specific endonuclease. In the late passage cells, the endonuclease specific for the alkali labile modification is absent.

scholarly journals Diastereomeric Recognition of 5',8-cyclo-2'-deoxyadenosine Lesions by Human poly(ADP-ribose) Polymerase 1 in Biomimetic Model

2018 ◽  
Author(s):  
Annalisa Masi ◽  
Arianna Sabbia ◽  
Carla Ferreri ◽  
Francesco Manoli ◽  
Yanhao Lai ◽  
...  
Keyword(s):  
Excision Repair ◽  
Strand Break ◽  
Dna Lesions ◽  
Affinity Constant ◽  
Mobility Shift ◽  
New Finding ◽  
Mobility Shift Assay ◽  
Low Efficiency ◽  
Gel Mobility Shift

Abstract5′,8-Cyclo-2′-deoxyadenosine (cdA), in the 5′R and 5′Sdiastereomeric forms, are typical non strand-break oxidative DNA lesions, induced by hydroxyl radicals, with emerging importance as a molecular marker. These lesions are exclusively repaired by nucleotide excision repair (NER) mechanism with a low efficiency, thus readily accumulating in the genome. Poly(ADP-ribose) polymerase1 (PARP1) acts as an early responder to DNA damage and plays a key role as a nick sensor in the maintenance of the integrity of the genome by recognizing nicked DNA. So far, it was unknown whether the diastereomeric cdA lesions could induce specific PARP1 binding. Here we provide the first evidence of PARP1 to selectively recognize the diastereomeric lesions 5′S-cdA and 5′R-cdA in vitro as compared to deoxyadenosine in model DNA substrates (23-mers) by using circular dichroism,fluorescence spectroscopy, immunoblotting analysis and gel mobility shift assay. Several features of the recognition of the damaged and undamaged oligonucleotides by PARP1were characterized. Remarkably, PARP1 efficiently binds to both cdA lesions in the double stranded (ds)-oligonucleotides. In particular, PARP1 proved to bind 5′S-cdAwith a higher affinity constant for the 5'S lesion in a model of ds DNA than 5′R-cdA, showing different recognition patterns, also compared with undamaged dA. This new finding highlights the ability of PARP1 to recognize and differentiate the distorted DNA backbone in a biomimetic system caused by different diastereomeric forms of a cdA lesion.

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