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Human DNA polymerase η accommodates RNA for strand extension.
Su Y, Egli M, Guengerich FP
(2017) J Biol Chem 292: 18044-18051
MeSH Terms: Base Pair Mismatch, DNA Primers, DNA Replication, DNA-Directed DNA Polymerase, Deoxyguanosine, Electrophoretic Mobility Shift Assay, Humans, Kinetics, Nucleic Acid Heteroduplexes, Nucleic Acid Hybridization, Oligodeoxyribonucleotides, Oligoribonucleotides, Pyrimidine Dimers, RNA, Recombinant Proteins, Reverse Transcription, Substrate Specificity, Transcription Elongation, Genetic
Show Abstract · Added March 14, 2018
Ribonucleotides are the natural analogs of deoxyribonucleotides, which can be misinserted by DNA polymerases, leading to the most abundant DNA lesions in genomes. During replication, DNA polymerases tolerate patches of ribonucleotides on the parental strands to different extents. The majority of human DNA polymerases have been reported to misinsert ribonucleotides into genomes. However, only PrimPol, DNA polymerase α, telomerase, and the mitochondrial human DNA polymerase (hpol) γ have been shown to tolerate an entire RNA strand. Y-family hpol η is known for translesion synthesis opposite the UV-induced DNA lesion cyclobutane pyrimidine dimer and was recently found to incorporate ribonucleotides into DNA. Here, we report that hpol η is able to bind DNA/DNA, RNA/DNA, and DNA/RNA duplexes with similar affinities. In addition, hpol η, as well as another Y-family DNA polymerase, hpol κ, accommodates RNA as one of the two strands during primer extension, mainly by inserting dNMPs opposite unmodified templates or DNA lesions, such as 8-oxo-2'-deoxyguanosine or cyclobutane pyrimidine dimer, even in the presence of an equal amount of the DNA/DNA substrate. The discovery of this RNA-accommodating ability of hpol η redefines the traditional concept of human DNA polymerases and indicates potential new functions of hpol η .
© 2017 by The American Society for Biochemistry and Molecular Biology, Inc.
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18 MeSH Terms
Molecular basis for PrimPol recruitment to replication forks by RPA.
Guilliam TA, Brissett NC, Ehlinger A, Keen BA, Kolesar P, Taylor EM, Bailey LJ, Lindsay HD, Chazin WJ, Doherty AJ
(2017) Nat Commun 8: 15222
MeSH Terms: Amino Acid Motifs, Amino Acid Sequence, Animals, Chickens, Chromatin, Crystallography, X-Ray, DNA Primase, DNA Replication, DNA-Directed DNA Polymerase, HEK293 Cells, Humans, Models, Biological, Multifunctional Enzymes, Protein Binding, Protein Domains, Replication Protein A, Xenopus
Show Abstract · Added March 24, 2018
DNA damage and secondary structures can stall the replication machinery. Cells possess numerous tolerance mechanisms to complete genome duplication in the presence of such impediments. In addition to translesion synthesis (TLS) polymerases, most eukaryotic cells contain a multifunctional replicative enzyme called primase-polymerase (PrimPol) that is capable of directly bypassing DNA damage by TLS, as well as repriming replication downstream of impediments. Here, we report that PrimPol is recruited to reprime through its interaction with RPA. Using biophysical and crystallographic approaches, we identify that PrimPol possesses two RPA-binding motifs and ascertained the key residues required for these interactions. We demonstrate that one of these motifs is critical for PrimPol's recruitment to stalled replication forks in vivo. In addition, biochemical analysis reveals that RPA serves to stimulate the primase activity of PrimPol. Together, these findings provide significant molecular insights into PrimPol's mode of recruitment to stalled forks to facilitate repriming and restart.
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17 MeSH Terms
Formation of S-[2-(N-Deoxyadenosinyl)ethyl]glutathione in DNA and Replication Past the Adduct by Translesion DNA Polymerases.
Sedgeman CA, Su Y, Guengerich FP
(2017) Chem Res Toxicol 30: 1188-1196
MeSH Terms: Animals, Cattle, Chromatography, Liquid, DNA Adducts, DNA Replication, DNA-Directed DNA Polymerase, Ethylene Dibromide, Glutathione, Tandem Mass Spectrometry
Show Abstract · Added March 14, 2018
1,2-Dibromoethane (DBE, ethylene dibromide) is a potent carcinogen due at least in part to its DNA cross-linking effects. DBE cross-links glutathione (GSH) to DNA, notably to sites on 2'-deoxyadenosine and 2'-deoxyguanosine ( Cmarik , J. L. , et al. ( 1991 ) J. Biol. Chem. 267 , 6672 - 6679 ). Adduction at the N6 position of 2'-deoxyadenosine (dA) had not been detected, but this is a site for the linkage of O-alkylguanine DNA alkyltransferase ( Chowdhury , G. , et al. ( 2013 ) Angew. Chem. Int. Ed. 52 , 12879 - 12882 ). We identified and quantified a new adduct, S-[2-(N-deoxyadenosinyl)ethyl]GSH, in calf thymus DNA using LC-MS/MS. Replication studies were performed in duplex oligonucleotides containing this adduct with human DNA polymerases (hPols) η, ι, and κ, as well as with Sulfolobus solfataricus Dpo4, Escherichia coli polymerase I Klenow fragment, and bacteriophage T7 polymerase. hPols η and ι, Dpo4, and Klenow fragment were able to bypass the adduct with only slight impedance; hPol η and ι showed increased misincorporation opposite the adduct compared to that of unmodified 2'-deoxyadenosine. LC-MS/MS analysis of full-length primer extension products by hPol η confirmed the incorporation of dC opposite S-[2-(N-deoxyadenosinyl)ethyl]GSH and also showed the production of a -1 frameshift. These results reveal the significance of N-dA GSH-DBE adducts in blocking replication, as well as producing mutations, by human translesion synthesis DNA polymerases.
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9 MeSH Terms
Mechanisms of Insertion of dCTP and dTTP Opposite the DNA Lesion O6-Methyl-2'-deoxyguanosine by Human DNA Polymerase η.
Patra A, Zhang Q, Guengerich FP, Egli M
(2016) J Biol Chem 291: 24304-24313
MeSH Terms: Bacterial Proteins, Crystallography, X-Ray, DNA, DNA Polymerase beta, DNA-Directed DNA Polymerase, Deoxycytosine Nucleotides, Humans, Sulfolobus solfataricus, Thymine Nucleotides
Show Abstract · Added March 14, 2018
O-Methyl-2'-deoxyguanosine (O-MeG) is a ubiquitous DNA lesion, formed not only by xenobiotic carcinogens but also by the endogenous methylating agent S-adenosylmethionine. It can introduce mutations during DNA replication, with different DNA polymerases displaying different ratios of correct or incorrect incorporation opposite this nucleoside. Of the "translesion" Y-family human DNA polymerases (hpols), hpol η is most efficient in incorporating equal numbers of correct and incorrect C and T bases. However, the mechanistic basis for this specific yet indiscriminate activity is not known. To explore this question, we report biochemical and structural analysis of the catalytic core of hpol η. Activity assays showed the truncated form displayed similar misincorporation properties as the full-length enzyme, incorporating C and T equally and extending from both. X-ray crystal structures of both dC and dT paired with O-MeG were solved in both insertion and extension modes. The structures revealed a Watson-Crick-like pairing between O-MeG and 2"-deoxythymidine-5"-[(α, β)-imido]triphosphate (approximating dT) at both the insertion and extension stages with formation of two H-bonds. Conversely, both the structures with O- MeG opposite dCTP and dC display sheared configuration of base pairs but to different degrees, with formation of two bifurcated H-bonds and two single H-bonds in the structures trapped in the insertion and extension states, respectively. The structural data are consistent with the observed tendency of hpol η to insert both dC and dT opposite the O-MeG lesion with similar efficiencies. Comparison of the hpol η active site configurations with either O-MeG:dC or O-MeG:dT bound compared with the corresponding situations in structures of complexes of Sulfolobus solfataricus Dpo4, a bypass pol that favors C relative to T by a factor of ∼4, helps rationalize the more error-prone synthesis opposite the lesion by hpol η.
© 2016 by The American Society for Biochemistry and Molecular Biology, Inc.
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9 MeSH Terms
Bypass of DNA-Protein Cross-links Conjugated to the 7-Deazaguanine Position of DNA by Translesion Synthesis Polymerases.
Wickramaratne S, Ji S, Mukherjee S, Su Y, Pence MG, Lior-Hoffmann L, Fu I, Broyde S, Guengerich FP, Distefano M, Schärer OD, Sham YY, Tretyakova N
(2016) J Biol Chem 291: 23589-23603
MeSH Terms: Amination, Amino Acid Sequence, Base Sequence, DNA Adducts, DNA Replication, DNA-Directed DNA Polymerase, Guanine, Humans, Molecular Dynamics Simulation, Oxidation-Reduction, Peptides, Proteins, Recombinant Proteins
Show Abstract · Added March 14, 2018
DNA-protein cross-links (DPCs) are bulky DNA lesions that form both endogenously and following exposure to bis-electrophiles such as common antitumor agents. The structural and biological consequences of DPCs have not been fully elucidated due to the complexity of these adducts. The most common site of DPC formation in DNA following treatment with bis-electrophiles such as nitrogen mustards and cisplatin is the N7 position of guanine, but the resulting conjugates are hydrolytically labile and thus are not suitable for structural and biological studies. In this report, hydrolytically stable structural mimics of N7-guanine-conjugated DPCs were generated by reductive amination reactions between the Lys and Arg side chains of proteins/peptides and aldehyde groups linked to 7-deazaguanine residues in DNA. These model DPCs were subjected to in vitro replication in the presence of human translesion synthesis DNA polymerases. DPCs containing full-length proteins (11-28 kDa) or a 23-mer peptide blocked human polymerases η and κ. DPC conjugates to a 10-mer peptide were bypassed with nucleotide insertion efficiency 50-100-fold lower than for native G. Both human polymerase (hPol) κ and hPol η inserted the correct base (C) opposite the 10-mer peptide cross-link, although small amounts of T were added by hPol η. Molecular dynamics simulation of an hPol κ ternary complex containing a template-primer DNA with dCTP opposite the 10-mer peptide DPC revealed that this bulky lesion can be accommodated in the polymerase active site by aligning with the major groove of the adducted DNA within the ternary complex of polymerase and dCTP.
© 2016 by The American Society for Biochemistry and Molecular Biology, Inc.
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13 MeSH Terms
Pfh1 Is an Accessory Replicative Helicase that Interacts with the Replisome to Facilitate Fork Progression and Preserve Genome Integrity.
McDonald KR, Guise AJ, Pourbozorgi-Langroudi P, Cristea IM, Zakian VA, Capra JA, Sabouri N
(2016) PLoS Genet 12: e1006238
MeSH Terms: Binding Sites, DNA Helicases, DNA Replication, DNA-Directed DNA Polymerase, Genomic Instability, Multienzyme Complexes, Protein Binding, S Phase, Schizosaccharomyces, Schizosaccharomyces pombe Proteins
Show Abstract · Added April 18, 2017
Replicative DNA helicases expose the two strands of the double helix to the replication apparatus, but accessory helicases are often needed to help forks move past naturally occurring hard-to-replicate sites, such as tightly bound proteins, RNA/DNA hybrids, and DNA secondary structures. Although the Schizosaccharomyces pombe 5'-to-3' DNA helicase Pfh1 is known to promote fork progression, its genomic targets, dynamics, and mechanisms of action are largely unknown. Here we address these questions by integrating genome-wide identification of Pfh1 binding sites, comprehensive analysis of the effects of Pfh1 depletion on replication and DNA damage, and proteomic analysis of Pfh1 interaction partners by immunoaffinity purification mass spectrometry. Of the 621 high confidence Pfh1-binding sites in wild type cells, about 40% were sites of fork slowing (as marked by high DNA polymerase occupancy) and/or DNA damage (as marked by high levels of phosphorylated H2A). The replication and integrity of tRNA and 5S rRNA genes, highly transcribed RNA polymerase II genes, and nucleosome depleted regions were particularly Pfh1-dependent. The association of Pfh1 with genomic integrity at highly transcribed genes was S phase dependent, and thus unlikely to be an artifact of high transcription rates. Although Pfh1 affected replication and suppressed DNA damage at discrete sites throughout the genome, Pfh1 and the replicative DNA polymerase bound to similar extents to both Pfh1-dependent and independent sites, suggesting that Pfh1 is proximal to the replication machinery during S phase. Consistent with this interpretation, Pfh1 co-purified with many key replisome components, including the hexameric MCM helicase, replicative DNA polymerases, RPA, and the processivity clamp PCNA in an S phase dependent manner. Thus, we conclude that Pfh1 is an accessory DNA helicase that interacts with the replisome and promotes replication and suppresses DNA damage at hard-to-replicate sites. These data provide insight into mechanisms by which this evolutionarily conserved helicase helps preserve genome integrity.
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10 MeSH Terms
Six Germline Genetic Variations Impair the Translesion Synthesis Activity of Human DNA Polymerase κ.
Kim JK, Yeom M, Hong JK, Song I, Lee YS, Guengerich FP, Choi JY
(2016) Chem Res Toxicol 29: 1741-1754
MeSH Terms: DNA-Directed DNA Polymerase, Genetic Variation, Humans, Models, Molecular, Molecular Conformation
Show Abstract · Added March 14, 2018
DNA polymerase (pol) κ efficiently catalyzes error-free translesion DNA synthesis (TLS) opposite bulky N-guanyl lesions induced by carcinogens such as polycyclic aromatic hydrocarbons. We investigated the biochemical effects of nine human nonsynonymous germline POLK variations on the TLS properties of pol κ, utilizing recombinant pol κ (residues 1-526) enzymes and DNA templates containing an N-CH(9-anthracenyl)G (N-AnthG), 8-oxo-7,8-dihydroguanine (8-oxoG), O-methyl(Me)G, or an abasic site. In steady-state kinetic analyses, the R246X, R298H, T473A, and R512W variants displayed 7- to 18-fold decreases in k/K for dCTP insertion opposite G and N-AnthG, with 2- to 3-fold decreases in DNA binding affinity, compared to that of the wild-type, and further showed 5- to 190-fold decreases in k/K for next-base extension from C paired with N-AnthG. The A471V variant showed 2- to 4-fold decreases in k/K for correct nucleotide insertion opposite and beyond G (or N-AnthG) compared to that of the wild-type. These five hypoactive variants also showed similar patterns of attenuation of TLS activity opposite 8-oxoG, O-MeG, and abasic lesions. By contrast, the T44M variant exhibited 7- to 11-fold decreases in k/K for dCTP insertion opposite N-AnthG and O-MeG (as well as for dATP insertion opposite an abasic site) but not opposite both G and 8-oxoG, nor beyond N-AnthG, compared to that of the wild-type. These results suggest that the R246X, R298H, T473A, R512W, and A471V variants cause a general catalytic impairment of pol κ opposite G and all four lesions, whereas the T44M variant induces opposite lesion-dependent catalytic impairment, i.e., only opposite O-MeG, abasic, and bulky N-G lesions but not opposite G and 8-oxoG, in pol κ, which might indicate that these hypoactive pol κ variants are genetic factors in modifying individual susceptibility to genotoxic carcinogens in certain subsets of populations.
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5 MeSH Terms
Kinetic and Structural Impact of Metal Ions and Genetic Variations on Human DNA Polymerase ι.
Choi JY, Patra A, Yeom M, Lee YS, Zhang Q, Egli M, Guengerich FP
(2016) J Biol Chem 291: 21063-21073
MeSH Terms: Amino Acid Substitution, Crystallography, X-Ray, DNA-Directed DNA Polymerase, Deoxycytosine Nucleotides, Humans, Hydrogen Bonding, Kinetics, Magnesium, Manganese, Mutation, Missense, Protein Domains
Show Abstract · Added March 14, 2018
DNA polymerase (pol) ι is a Y-family polymerase involved in translesion synthesis, exhibiting higher catalytic activity with Mn than Mg The human germline R96G variant impairs both Mn-dependent and Mg-dependent activities of pol ι, whereas the Δ1-25 variant selectively enhances its Mg-dependent activity. We analyzed pre-steady-state kinetic and structural effects of these two metal ions and genetic variations on pol ι using pol ι core (residues 1-445) proteins. The presence of Mn (0.15 mm) instead of Mg (2 mm) caused a 770-fold increase in efficiency (k/K) of pol ι for dCTP insertion opposite G, mainly due to a 450-fold decrease in K The R96G and Δ1-25 variants displayed a 53-fold decrease and a 3-fold increase, respectively, in k/K for dCTP insertion opposite G with Mg when compared with wild type, substantially attenuated by substitution with Mn Crystal structures of pol ι ternary complexes, including the primer terminus 3'-OH and a non-hydrolyzable dCTP analogue opposite G with the active-site Mg or Mn, revealed that Mn achieves more optimal octahedral coordination geometry than Mg, with lower values in average coordination distance geometry in the catalytic metal A-site. Crystal structures of R96G revealed the loss of three H-bonds of residues Gly-96 and Tyr-93 with an incoming dNTP, due to the lack of an arginine, as well as a destabilized Tyr-93 side chain secondary to the loss of a cation-π interaction between both side chains. These results provide a mechanistic basis for alteration in pol ι catalytic function with coordinating metals and genetic variation.
© 2016 by The American Society for Biochemistry and Molecular Biology, Inc.
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11 MeSH Terms
Mechanisms of mutagenesis: DNA replication in the presence of DNA damage.
Liu B, Xue Q, Tang Y, Cao J, Guengerich FP, Zhang H
(2016) Mutat Res Rev Mutat Res 768: 53-67
MeSH Terms: Animals, DNA Adducts, DNA Damage, DNA Repair, DNA Replication, DNA-Directed DNA Polymerase, Environmental Exposure, Genetic Predisposition to Disease, Humans, Mutagenesis, Mutagens, Mutation, Protein Binding
Show Abstract · Added March 14, 2018
Environmental mutagens cause DNA damage that disturbs replication and produces mutations, leading to cancer and other diseases. We discuss mechanisms of mutagenesis resulting from DNA damage, from the level of DNA replication by a single polymerase to the complex DNA replisome of some typical model organisms (including bacteriophage T7, T4, Sulfolobus solfataricus, Escherichia coli, yeast and human). For a single DNA polymerase, DNA damage can affect replication in three major ways: reducing replication fidelity, causing frameshift mutations, and blocking replication. For the DNA replisome, protein interactions and the functions of accessory proteins can yield rather different results even with a single DNA polymerase. The mechanism of mutation during replication performed by the DNA replisome is a long-standing question. Using new methods and techniques, the replisomes of certain organisms and human cell extracts can now be investigated with regard to the bypass of DNA damage. In this review, we consider the molecular mechanism of mutagenesis resulting from DNA damage in replication at the levels of single DNA polymerases and complex DNA replisomes, including translesion DNA synthesis.
Copyright © 2016 Elsevier B.V. All rights reserved.
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13 MeSH Terms
Structural and Kinetic Analysis of Miscoding Opposite the DNA Adduct 1,N6-Ethenodeoxyadenosine by Human Translesion DNA Polymerase η.
Patra A, Su Y, Zhang Q, Johnson KM, Guengerich FP, Egli M
(2016) J Biol Chem 291: 14134-45
MeSH Terms: Adenosine, Crystallography, X-Ray, DNA Adducts, DNA-Directed DNA Polymerase, Humans, Mass Spectrometry, Protein Structure, Tertiary
Show Abstract · Added March 14, 2018
1,N(6)-Ethenodeoxyadenosine (1,N(6)-ϵdA) is the major etheno lesion formed in the reaction of DNA with epoxides substituted with good leaving groups (e.g. vinyl chloride epoxide). This lesion is also formed endogenously in DNA from lipid oxidation. Recombinant human DNA polymerase η (hpol η) can replicate oligonucleotide templates containing 1,N(6)-ϵdA. In steady-state kinetic analysis, hpol η preferred to incorporate dATP and dGTP, compared with dTTP. Mass spectral analysis of incorporation products also showed preferred purine (A, G) incorporation and extensive -1 frameshifts, suggesting pairing of the inserted purine and slippage before further replication. Five x-ray crystal structures of hpol η ternary complexes were determined, three at the insertion and two at the extension stage. Two insertion complexes revealed incoming non-hydrolyzable dATP or dGTP analogs not pairing with but instead in a staggered configuration relative to 1,N(6)-ϵdA in the anti conformation, thus opposite the 5'-T in the template, explaining the proclivity for frameshift misincorporation. In another insertion complex, dTTP was positioned opposite 1,N(6)-ϵdA, and the adduct base was in the syn conformation, with formation of two hydrogen bonds. At the extension stage, with either an incorporated dA or dT opposite 1,N(6)-ϵdA and 2'-deoxythymidine-5'-[(α,β)-imido]triphosphate opposite the 5'-A, the 3'-terminal nucleoside of the primer was disordered, consistent with the tendency not to incorporate dTTP opposite 1,N(6)-ϵdA. Collectively, the results show a preference for purine pairing opposite 1,N(6)-ϵdA and for -1 frameshifts.
© 2016 by The American Society for Biochemistry and Molecular Biology, Inc.
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7 MeSH Terms