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Structural Biology of the HEAT-Like Repeat Family of DNA Glycosylases.
Shi R, Shen XX, Rokas A, Eichman BF
(2018) Bioessays 40: e1800133
MeSH Terms: Archaea, Bacteria, Crystallography, X-Ray, DNA, DNA Damage, DNA Glycosylases, DNA Repair, Eukaryota, Protein Conformation
Show Abstract · Added August 26, 2019
DNA glycosylases remove aberrant DNA nucleobases as the first enzymatic step of the base excision repair (BER) pathway. The alkyl-DNA glycosylases AlkC and AlkD adopt a unique structure based on α-helical HEAT repeats. Both enzymes identify and excise their substrates without a base-flipping mechanism used by other glycosylases and nucleic acid processing proteins to access nucleobases that are otherwise stacked inside the double-helix. Consequently, these glycosylases act on a variety of cationic nucleobase modifications, including bulky adducts, not previously associated with BER. The related non-enzymatic HEAT-like repeat (HLR) proteins, AlkD2, and AlkF, have unique nucleic acid binding properties that expand the functions of this relatively new protein superfamily beyond DNA repair. Here, we review the phylogeny, biochemistry, and structures of the HLR proteins, which have helped broaden our understanding of the mechanisms by which DNA glycosylases locate and excise chemically modified DNA nucleobases.
© 2018 WILEY Periodicals, Inc.
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Perspective on Oncogenic Processes at the End of the Beginning of Cancer Genomics.
Ding L, Bailey MH, Porta-Pardo E, Thorsson V, Colaprico A, Bertrand D, Gibbs DL, Weerasinghe A, Huang KL, Tokheim C, Cortés-Ciriano I, Jayasinghe R, Chen F, Yu L, Sun S, Olsen C, Kim J, Taylor AM, Cherniack AD, Akbani R, Suphavilai C, Nagarajan N, Stuart JM, Mills GB, Wyczalkowski MA, Vincent BG, Hutter CM, Zenklusen JC, Hoadley KA, Wendl MC, Shmulevich L, Lazar AJ, Wheeler DA, Getz G, Cancer Genome Atlas Research Network
(2018) Cell 173: 305-320.e10
MeSH Terms: Carcinogenesis, DNA Repair, Databases, Genetic, Genes, Neoplasm, Genomics, Humans, Metabolic Networks and Pathways, Microsatellite Instability, Mutation, Neoplasms, Transcriptome, Tumor Microenvironment
Show Abstract · Added October 30, 2019
The Cancer Genome Atlas (TCGA) has catalyzed systematic characterization of diverse genomic alterations underlying human cancers. At this historic junction marking the completion of genomic characterization of over 11,000 tumors from 33 cancer types, we present our current understanding of the molecular processes governing oncogenesis. We illustrate our insights into cancer through synthesis of the findings of the TCGA PanCancer Atlas project on three facets of oncogenesis: (1) somatic driver mutations, germline pathogenic variants, and their interactions in the tumor; (2) the influence of the tumor genome and epigenome on transcriptome and proteome; and (3) the relationship between tumor and the microenvironment, including implications for drugs targeting driver events and immunotherapies. These results will anchor future characterization of rare and common tumor types, primary and relapsed tumors, and cancers across ancestry groups and will guide the deployment of clinical genomic sequencing.
Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.
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Genomic and Molecular Landscape of DNA Damage Repair Deficiency across The Cancer Genome Atlas.
Knijnenburg TA, Wang L, Zimmermann MT, Chambwe N, Gao GF, Cherniack AD, Fan H, Shen H, Way GP, Greene CS, Liu Y, Akbani R, Feng B, Donehower LA, Miller C, Shen Y, Karimi M, Chen H, Kim P, Jia P, Shinbrot E, Zhang S, Liu J, Hu H, Bailey MH, Yau C, Wolf D, Zhao Z, Weinstein JN, Li L, Ding L, Mills GB, Laird PW, Wheeler DA, Shmulevich I, Cancer Genome Atlas Research Network, Monnat RJ, Xiao Y, Wang C
(2018) Cell Rep 23: 239-254.e6
MeSH Terms: Cell Line, Tumor, DNA Damage, Gene Silencing, Genome, Human, Humans, Loss of Heterozygosity, Machine Learning, Mutation, Neoplasms, Recombinational DNA Repair, Tumor Suppressor Proteins
Show Abstract · Added October 30, 2019
DNA damage repair (DDR) pathways modulate cancer risk, progression, and therapeutic response. We systematically analyzed somatic alterations to provide a comprehensive view of DDR deficiency across 33 cancer types. Mutations with accompanying loss of heterozygosity were observed in over 1/3 of DDR genes, including TP53 and BRCA1/2. Other prevalent alterations included epigenetic silencing of the direct repair genes EXO5, MGMT, and ALKBH3 in ∼20% of samples. Homologous recombination deficiency (HRD) was present at varying frequency in many cancer types, most notably ovarian cancer. However, in contrast to ovarian cancer, HRD was associated with worse outcomes in several other cancers. Protein structure-based analyses allowed us to predict functional consequences of rare, recurrent DDR mutations. A new machine-learning-based classifier developed from gene expression data allowed us to identify alterations that phenocopy deleterious TP53 mutations. These frequent DDR gene alterations in many human cancers have functional consequences that may determine cancer progression and guide therapy.
Copyright © 2018 The Author(s). Published by Elsevier Inc. All rights reserved.
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Selective base excision repair of DNA damage by the non-base-flipping DNA glycosylase AlkC.
Shi R, Mullins EA, Shen XX, Lay KT, Yuen PK, David SS, Rokas A, Eichman BF
(2018) EMBO J 37: 63-74
MeSH Terms: Adenine, Alkylation, Amino Acid Sequence, Bacillus cereus, Catalytic Domain, Crystallography, X-Ray, DNA Adducts, DNA Damage, DNA Glycosylases, DNA Repair, Models, Molecular, Protein Conformation, Sequence Homology
Show Abstract · Added March 21, 2018
DNA glycosylases preserve genome integrity and define the specificity of the base excision repair pathway for discreet, detrimental modifications, and thus, the mechanisms by which glycosylases locate DNA damage are of particular interest. Bacterial AlkC and AlkD are specific for cationic alkylated nucleobases and have a distinctive HEAT-like repeat (HLR) fold. AlkD uses a unique non-base-flipping mechanism that enables excision of bulky lesions more commonly associated with nucleotide excision repair. In contrast, AlkC has a much narrower specificity for small lesions, principally N3-methyladenine (3mA). Here, we describe how AlkC selects for and excises 3mA using a non-base-flipping strategy distinct from that of AlkD. A crystal structure resembling a catalytic intermediate complex shows how AlkC uses unique HLR and immunoglobulin-like domains to induce a sharp kink in the DNA, exposing the damaged nucleobase to active site residues that project into the DNA This active site can accommodate and excise N3-methylcytosine (3mC) and N1-methyladenine (1mA), which are also repaired by AlkB-catalyzed oxidative demethylation, providing a potential alternative mechanism for repair of these lesions in bacteria.
© 2017 The Authors.
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13 MeSH Terms
Improved base excision repair inhibition and bacteriophage Mu Gam protein yields C:G-to-T:A base editors with higher efficiency and product purity.
Komor AC, Zhao KT, Packer MS, Gaudelli NM, Waterbury AL, Koblan LW, Kim YB, Badran AH, Liu DR
(2017) Sci Adv 3: eaao4774
MeSH Terms: Bacteriophage mu, Base Pairing, Cell Line, DNA Repair, DNA-Binding Proteins, Enzyme Activation, Gene Frequency, Gene Order, Humans, INDEL Mutation, Uracil-DNA Glycosidase, Viral Proteins
Show Abstract · Added March 21, 2018
We recently developed base editing, the programmable conversion of target C:G base pairs to T:A without inducing double-stranded DNA breaks (DSBs) or requiring homology-directed repair using engineered fusions of Cas9 variants and cytidine deaminases. Over the past year, the third-generation base editor (BE3) and related technologies have been successfully used by many researchers in a wide range of organisms. The product distribution of base editing-the frequency with which the target C:G is converted to mixtures of undesired by-products, along with the desired T:A product-varies in a target site-dependent manner. We characterize determinants of base editing outcomes in human cells and establish that the formation of undesired products is dependent on uracil N-glycosylase (UNG) and is more likely to occur at target sites containing only a single C within the base editing activity window. We engineered CDA1-BE3 and AID-BE3, which use cytidine deaminase homologs that increase base editing efficiency for some sequences. On the basis of these observations, we engineered fourth-generation base editors (BE4 and SaBE4) that increase the efficiency of C:G to T:A base editing by approximately 50%, while halving the frequency of undesired by-products compared to BE3. Fusing BE3, BE4, SaBE3, or SaBE4 to Gam, a bacteriophage Mu protein that binds DSBs greatly reduces indel formation during base editing, in most cases to below 1.5%, and further improves product purity. BE4, SaBE4, BE4-Gam, and SaBE4-Gam represent the state of the art in C:G-to-T:A base editing, and we recommend their use in future efforts.
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12 MeSH Terms
Analysis of DNA binding by human factor xeroderma pigmentosum complementation group A (XPA) provides insight into its interactions with nucleotide excision repair substrates.
Sugitani N, Voehler MW, Roh MS, Topolska-Woś AM, Chazin WJ
(2017) J Biol Chem 292: 16847-16857
MeSH Terms: Amino Acid Substitution, DNA Repair, DNA Repair Enzymes, DNA, Single-Stranded, Humans, Mutation, Missense, Nuclear Magnetic Resonance, Biomolecular, Protein Binding, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, Structural Homology, Protein, Xeroderma Pigmentosum, Xeroderma Pigmentosum Group A Protein
Show Abstract · Added March 24, 2018
Xeroderma pigmentosum (XP) complementation group A (XPA) is an essential scaffolding protein in the multiprotein nucleotide excision repair (NER) machinery. The interaction of XPA with DNA is a core function of this protein; a number of mutations in the DNA-binding domain (DBD) are associated with XP disease. Although structures of the central globular domain of human XPA and data on binding of DNA substrates have been reported, the structural basis for XPA's DNA-binding activity remains unknown. X-ray crystal structures of the central globular domain of yeast XPA (Rad14) with lesion-containing DNA duplexes have provided valuable insights, but the DNA substrates used for this study do not correspond to the substrates of XPA as it functions within the NER machinery. To better understand the DNA-binding activity of human XPA in NER, we used NMR to investigate the interaction of its DBD with a range of DNA substrates. We found that XPA binds different single-stranded/double-stranded junction DNA substrates with a common surface. Comparisons of our NMR-based mapping of binding residues with the previously reported Rad14-DNA crystal structures revealed similarities and differences in substrate binding between XPA and Rad14. This includes direct evidence for DNA contacts to the residues extending C-terminally from the globular core, which are lacking in the Rad14 construct. Moreover, mutation of the XPA residue corresponding to Phe-262 in Rad14, previously reported as being critical for DNA binding, had only a moderate effect on the DNA-binding activity of XPA. The DNA-binding properties of several disease-associated mutations in the DBD were investigated. These results suggest that for XPA mutants exhibiting altered DNA-binding properties, a correlation exists between the extent of reduction in DNA-binding affinity and the severity of symptoms in XP patients.
© 2017 by The American Society for Biochemistry and Molecular Biology, Inc.
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13 MeSH Terms
Toxicity and repair of DNA adducts produced by the natural product yatakemycin.
Mullins EA, Shi R, Eichman BF
(2017) Nat Chem Biol 13: 1002-1008
MeSH Terms: Biological Products, DNA Adducts, DNA Damage, DNA Repair, Drug Resistance, Bacterial, Indoles, Molecular Structure, Pyrroles
Show Abstract · Added August 26, 2019
Yatakemycin (YTM) is an extraordinarily toxic DNA alkylating agent with potent antimicrobial and antitumor properties and is the most recent addition to the CC-1065 and duocarmycin family of natural products. Though 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 the way they are eliminated by BER have been unclear. Here, we describe the structural and biochemical properties of YTM adducts that are 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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RADX Promotes Genome Stability and Modulates Chemosensitivity by Regulating RAD51 at Replication Forks.
Dungrawala H, Bhat KP, Le Meur R, Chazin WJ, Ding X, Sharan SK, Wessel SR, Sathe AA, Zhao R, Cortez D
(2017) Mol Cell 67: 374-386.e5
MeSH Terms: A549 Cells, Animals, BRCA2 Protein, CRISPR-Cas Systems, DNA Breaks, Double-Stranded, DNA Repair, DNA, Neoplasm, Dose-Response Relationship, Drug, Drug Resistance, Neoplasm, Gene Expression Regulation, Neoplastic, Genomic Instability, HEK293 Cells, Humans, Mice, Models, Molecular, Mutation, Neoplasms, Poly(ADP-ribose) Polymerase Inhibitors, Protein Binding, RNA Interference, Rad51 Recombinase, Replication Origin, Transfection
Show Abstract · Added March 24, 2018
RAD51 promotes homology-directed repair (HDR), replication fork reversal, and stalled fork protection. Defects in these functions cause genomic instability and tumorigenesis but also generate hypersensitivity to cancer therapeutics. Here we describe the identification of RADX as an RPA-like, single-strand DNA binding protein. RADX is recruited to replication forks, where it prevents fork collapse by regulating RAD51. When RADX is inactivated, excessive RAD51 activity slows replication elongation and causes double-strand breaks. In cancer cells lacking BRCA2, RADX deletion restores fork protection without restoring HDR. Furthermore, RADX inactivation confers chemotherapy and PARP inhibitor resistance to cancer cells with reduced BRCA2/RAD51 pathway function. By antagonizing RAD51 at forks, RADX allows cells to maintain a high capacity for HDR while ensuring that replication functions of RAD51 are properly regulated. Thus, RADX is essential to achieve the proper balance of RAD51 activity to maintain genome stability.
Copyright © 2017 Elsevier Inc. All rights reserved.
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23 MeSH Terms
Preface.
Eichman BF
(2017) Methods Enzymol 592: xvii-xx
MeSH Terms: Animals, Biochemistry, DNA, DNA Damage, DNA Repair, DNA Repair Enzymes, Humans
Added August 26, 2019
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Preface.
Eichman BF
(2017) Methods Enzymol 591: xv-xviii
MeSH Terms: DNA Damage, DNA Repair, DNA Repair Enzymes, Methods
Added August 26, 2019
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