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Chen L, Hong M, Luan C, Gao H, Ru G, Guo X, Zhang D, Zhang S, Li C, Wu J, Randolph PB, Sousa AA, Qu C, Zhu Y, Guan Y, Wang L, Liu M, Feng B, Song G, Liu DR, Li D. Adenine transversion editors enable precise, efficient A•T-to-C•G base editing in mammalian cells and embryos. Nat Biotechnol 2024; 42:638-650. [PMID: 37322276 DOI: 10.1038/s41587-023-01821-9] [Citation(s) in RCA: 33] [Impact Index Per Article: 33.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Accepted: 05/08/2023] [Indexed: 06/17/2023]
Abstract
Base editors have substantial promise in basic research and as therapeutic agents for the correction of pathogenic mutations. The development of adenine transversion editors has posed a particular challenge. Here we report a class of base editors that enable efficient adenine transversion, including precise A•T-to-C•G editing. We found that a fusion of mouse alkyladenine DNA glycosylase (mAAG) with nickase Cas9 and deaminase TadA-8e catalyzed adenosine transversion in specific sequence contexts. Laboratory evolution of mAAG significantly increased A-to-C/T conversion efficiency up to 73% and expanded the targeting scope. Further engineering yielded adenine-to-cytosine base editors (ACBEs), including a high-accuracy ACBE-Q variant, that precisely install A-to-C transversions with minimal Cas9-independent off-targeting effects. ACBEs mediated high-efficiency installation or correction of five pathogenic mutations in mouse embryos and human cell lines. Founder mice showed 44-56% average A-to-C edits and allelic frequencies of up to 100%. Adenosine transversion editors substantially expand the capabilities and possible applications of base editing technology.
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Affiliation(s)
- Liang Chen
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - Mengjia Hong
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - Changming Luan
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - Hongyi Gao
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - Gaomeng Ru
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - Xinyuan Guo
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - Dujuan Zhang
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - Shun Zhang
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - Changwei Li
- Department of Orthopedics, Shanghai Key Laboratory for Prevention and Treatment of Bone and Joint Diseases with Integrated Chinese-Western Medicine, Shanghai Institute of Traumatology and Orthopedics, Ruijin Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China
| | - Jun Wu
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - Peyton B Randolph
- Merkin Institute of Transformative Technologies in Healthcare, Broad Institute of MIT and Harvard, Cambridge, MA, USA
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
- Howard Hughes Medical Institute, Cambridge, MA, USA
| | - Alexander A Sousa
- Merkin Institute of Transformative Technologies in Healthcare, Broad Institute of MIT and Harvard, Cambridge, MA, USA
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
- Howard Hughes Medical Institute, Cambridge, MA, USA
| | - Chao Qu
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - Yifan Zhu
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - Yuting Guan
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - Liren Wang
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - Mingyao Liu
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
- BRL Medicine, Inc., Shanghai, China
| | - Bo Feng
- School of Biomedical Sciences, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, China
| | - Gaojie Song
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China
| | - David R Liu
- Merkin Institute of Transformative Technologies in Healthcare, Broad Institute of MIT and Harvard, Cambridge, MA, USA
- Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA
- Howard Hughes Medical Institute, Cambridge, MA, USA
| | - Dali Li
- Shanghai Frontiers Science Center of Genome Editing and Cell Therapy, Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences and School of Life Sciences, East China Normal University, Shanghai, China.
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2
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Xu F, Zheng C, Xu W, Zhang S, Liu S, Chen X, Yao K. Breaking genetic shackles: The advance of base editing in genetic disorder treatment. Front Pharmacol 2024; 15:1364135. [PMID: 38510648 PMCID: PMC10953296 DOI: 10.3389/fphar.2024.1364135] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2024] [Accepted: 02/26/2024] [Indexed: 03/22/2024] Open
Abstract
The rapid evolution of gene editing technology has markedly improved the outlook for treating genetic diseases. Base editing, recognized as an exceptionally precise genetic modification tool, is emerging as a focus in the realm of genetic disease therapy. We provide a comprehensive overview of the fundamental principles and delivery methods of cytosine base editors (CBE), adenine base editors (ABE), and RNA base editors, with a particular focus on their applications and recent research advances in the treatment of genetic diseases. We have also explored the potential challenges faced by base editing technology in treatment, including aspects such as targeting specificity, safety, and efficacy, and have enumerated a series of possible solutions to propel the clinical translation of base editing technology. In conclusion, this article not only underscores the present state of base editing technology but also envisions its tremendous potential in the future, providing a novel perspective on the treatment of genetic diseases. It underscores the vast potential of base editing technology in the realm of genetic medicine, providing support for the progression of gene medicine and the development of innovative approaches to genetic disease therapy.
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Affiliation(s)
- Fang Xu
- Institute of Visual Neuroscience and Stem Cell Engineering, Wuhan University of Science and Technology, Wuhan, China
- College of Life Sciences and Health, Wuhan University of Science and Technology, Wuhan, China
| | - Caiyan Zheng
- Institute of Visual Neuroscience and Stem Cell Engineering, Wuhan University of Science and Technology, Wuhan, China
- College of Life Sciences and Health, Wuhan University of Science and Technology, Wuhan, China
| | - Weihui Xu
- Institute of Visual Neuroscience and Stem Cell Engineering, Wuhan University of Science and Technology, Wuhan, China
- College of Life Sciences and Health, Wuhan University of Science and Technology, Wuhan, China
| | - Shiyao Zhang
- Institute of Visual Neuroscience and Stem Cell Engineering, Wuhan University of Science and Technology, Wuhan, China
- College of Life Sciences and Health, Wuhan University of Science and Technology, Wuhan, China
| | - Shanshan Liu
- Institute of Visual Neuroscience and Stem Cell Engineering, Wuhan University of Science and Technology, Wuhan, China
- College of Life Sciences and Health, Wuhan University of Science and Technology, Wuhan, China
| | - Xiaopeng Chen
- Institute of Visual Neuroscience and Stem Cell Engineering, Wuhan University of Science and Technology, Wuhan, China
- College of Life Sciences and Health, Wuhan University of Science and Technology, Wuhan, China
| | - Kai Yao
- Institute of Visual Neuroscience and Stem Cell Engineering, Wuhan University of Science and Technology, Wuhan, China
- College of Life Sciences and Health, Wuhan University of Science and Technology, Wuhan, China
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3
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Liu B, Qi Y, Wang X, Gao X, Yao Y, Zhang L. Investigation of the Flipping Dynamics of 1, N6-Ethenoadenine in Alkyladenine DNA Glycosylase. J Phys Chem B 2024; 128:1606-1617. [PMID: 38331753 DOI: 10.1021/acs.jpcb.3c06853] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2024]
Abstract
Alkyladenine DNA glycosylase (AAG) is an essential enzyme responsible for maintaining genome integrity by repairing several DNA lesions damaged by alkylation or deamination. Understanding how it can recognize and excise the lesions thus lays the foundation for therapeutic treatment against lesion-associated diseases or cancers. However, the molecular details of how the lesion can be distinguished from the matched base by AAG and how it enters the cleavage site, ready for excision, are not fully elucidated. In this study, we have revealed the molecular details of the flipping dynamics of 1, N6-ethenoadenine (εA) not only in the form of free double-stranded DNA (dsDNA) but also in the form of the AAG-dsDNA complex. Our MD simulations and PMF calculations have shown that the flipping of εA and dA is thermodynamically disfavored in the free dsDNA, even though εA has a lower flipping energy barrier than dA. By sharp contrast, the flipping of εA is thermodynamically favored in AAG with an obvious free energy drop, while dA is equally stabilized before and after the flipping. Moreover, a comparison of the PMFs in the forms of free dsDNA and the AAG-dsDNA complex has pinpointed the role of AAG in discriminating εA against dA and facilitating the flipping of εA. Besides, the flipping process is simulated along the major and minor grooves, and our results have additionally demonstrated that the flipping is not directional in the free dsDNA while flipping along the major groove is kinetically more favorable than the minor groove in the AAG-dsDNA complex. Overall, our study has offered molecular insights into the flipping dynamics of εA and revealed its discrimination mechanism by AAG, which is expected to guide further enzyme engineering for therapeutic applications.
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Affiliation(s)
- Bin Liu
- State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yanping Qi
- State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China
- University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xiaowei Wang
- Department of Chemical and Biological Engineering and Department of Mathematics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon 999077, Hong Kong
| | - Xin Gao
- Computational Bioscience Research Center, King Abdullah University of Science and Technology (KAUST), Thuwal 23955, Saudi Arabia
- Computer, Electrical and Mathematical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955, Saudi Arabia
| | - Yuan Yao
- Department of Chemical and Biological Engineering and Department of Mathematics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon 999077, Hong Kong
| | - Lu Zhang
- State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China
- University of Chinese Academy of Sciences, Beijing 100049, China
- Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, Fuzhou, Fujian 361005, China
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4
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Tong H, Wang X, Liu Y, Liu N, Li Y, Luo J, Ma Q, Wu D, Li J, Xu C, Yang H. Programmable A-to-Y base editing by fusing an adenine base editor with an N-methylpurine DNA glycosylase. Nat Biotechnol 2023; 41:1080-1084. [PMID: 36624150 DOI: 10.1038/s41587-022-01595-6] [Citation(s) in RCA: 47] [Impact Index Per Article: 47.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Accepted: 11/01/2022] [Indexed: 01/11/2023]
Abstract
Here we developed an adenine transversion base editor, AYBE, for A-to-C and A-to-T transversion editing in mammalian cells by fusing an adenine base editor (ABE) with hypoxanthine excision protein N-methylpurine DNA glycosylase (MPG). We also engineered AYBE variants enabling targeted editing at genomic loci with higher transversion editing activity (up to 72% for A-to-C or A-to-T editing).
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Affiliation(s)
- Huawei Tong
- HuiGene Therapeutics Co., Ltd., Shanghai, China.
| | - Xuchen Wang
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Key Laboratory of Primate Neurobiology, Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai, China
- College of Life Sciences, University of Chinese Academy of Sciences, Beijing, China
| | - Yuanhua Liu
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Key Laboratory of Primate Neurobiology, Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai, China
| | - Nana Liu
- HuiGene Therapeutics Co., Ltd., Shanghai, China
| | - Yun Li
- HuiGene Therapeutics Co., Ltd., Shanghai, China
| | - Jiamin Luo
- HuiGene Therapeutics Co., Ltd., Shanghai, China
| | - Qian Ma
- HuiGene Therapeutics Co., Ltd., Shanghai, China
| | - Danni Wu
- HuiGene Therapeutics Co., Ltd., Shanghai, China
| | - Jiyong Li
- HuiGene Therapeutics Co., Ltd., Shanghai, China
| | | | - Hui Yang
- HuiGene Therapeutics Co., Ltd., Shanghai, China.
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Key Laboratory of Primate Neurobiology, Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai, China.
- Shanghai Research Center for Brain Science and Brain-Inspired Intelligence, Shanghai, China.
- HuiEdit Therapeutics Co., Ltd., Shanghai, China.
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5
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Tong H, Liu N, Wei Y, Zhou Y, Li Y, Wu D, Jin M, Cui S, Li H, Li G, Zhou J, Yuan Y, Zhang H, Shi L, Yao X, Yang H. Programmable deaminase-free base editors for G-to-Y conversion by engineered glycosylase. Natl Sci Rev 2023; 10:nwad143. [PMID: 37404457 PMCID: PMC10317176 DOI: 10.1093/nsr/nwad143] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Revised: 05/13/2023] [Accepted: 05/13/2023] [Indexed: 07/06/2023] Open
Abstract
Current DNA base editors contain nuclease and DNA deaminase that enables deamination of cytosine (C) or adenine (A), but no method for guanine (G) or thymine (T) editing is available at present. Here we developed a deaminase-free glycosylase-based guanine base editor (gGBE) with G editing ability, by fusing Cas9 nickase with engineered N-methylpurine DNA glycosylase protein (MPG). By several rounds of MPG mutagenesis via unbiased and rational screening using an intron-split EGFP reporter, we demonstrated that gGBE with engineered MPG could increase G editing efficiency by more than 1500 fold. Furthermore, this gGBE exhibited high base editing efficiency (up to 81.2%) and high G-to-T or G-to-C (i.e. G-to-Y) conversion ratio (up to 0.95) in both cultured human cells and mouse embryos. Thus, we have provided a proof-of-concept of a new base editing approach by endowing the engineered DNA glycosylase the capability to selectively excise a new type of substrate.
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Affiliation(s)
| | | | | | | | | | | | - Ming Jin
- Department of Neurology and Institute of Neurology of First Affiliated Hospital, Institute of Neuroscience, and Fujian Key Laboratory of Molecular Neurology, Fujian Medical University, Fuzhou 350004, China
| | - Shuna Cui
- HuidaGene Therapeutics Co., Ltd., Shanghai 200131, China
| | - Hengbin Li
- HuidaGene Therapeutics Co., Ltd., Shanghai 200131, China
| | - Guoling Li
- HuidaGene Therapeutics Co., Ltd., Shanghai 200131, China
| | - Jingxing Zhou
- HuidaGene Therapeutics Co., Ltd., Shanghai 200131, China
| | - Yuan Yuan
- HuidaGene Therapeutics Co., Ltd., Shanghai 200131, China
| | - Hainan Zhang
- HuidaGene Therapeutics Co., Ltd., Shanghai 200131, China
| | - Linyu Shi
- HuidaGene Therapeutics Co., Ltd., Shanghai 200131, China
| | - Xuan Yao
- HuidaGene Therapeutics Co., Ltd., Shanghai 200131, China
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Zheng L, Tsai B, Gao N. Structural and mechanistic insights into the DNA glycosylase AAG-mediated base excision in nucleosome. Cell Discov 2023; 9:62. [PMID: 37339965 DOI: 10.1038/s41421-023-00560-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Accepted: 05/06/2023] [Indexed: 06/22/2023] Open
Abstract
The engagement of a DNA glycosylase with a damaged DNA base marks the initiation of base excision repair. Nucleosome-based packaging of eukaryotic genome obstructs DNA accessibility, and how DNA glycosylases locate the substrate site on nucleosomes is currently unclear. Here, we report cryo-electron microscopy structures of nucleosomes bearing a deoxyinosine (DI) in various geometric positions and structures of them in complex with the DNA glycosylase AAG. The apo nucleosome structures show that the presence of a DI alone perturbs nucleosomal DNA globally, leading to a general weakening of the interface between DNA and the histone core and greater flexibility for the exit/entry of the nucleosomal DNA. AAG makes use of this nucleosomal plasticity and imposes further local deformation of the DNA through formation of the stable enzyme-substrate complex. Mechanistically, local distortion augmentation, translation/rotational register shift and partial opening of the nucleosome are employed by AAG to cope with substrate sites in fully exposed, occluded and completely buried positions, respectively. Our findings reveal the molecular basis for the DI-induced modification on the structural dynamics of the nucleosome and elucidate how the DNA glycosylase AAG accesses damaged sites on the nucleosome with different solution accessibility.
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Affiliation(s)
- Lvqin Zheng
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China
- Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, China
| | - Bin Tsai
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China
| | - Ning Gao
- State Key Laboratory of Membrane Biology, Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China.
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Burroughs A, Aravind L. New biochemistry in the Rhodanese-phosphatase superfamily: emerging roles in diverse metabolic processes, nucleic acid modifications, and biological conflicts. NAR Genom Bioinform 2023; 5:lqad029. [PMID: 36968430 PMCID: PMC10034599 DOI: 10.1093/nargab/lqad029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 02/10/2023] [Accepted: 03/09/2023] [Indexed: 03/25/2023] Open
Abstract
The protein-tyrosine/dual-specificity phosphatases and rhodanese domains constitute a sprawling superfamily of Rossmannoid domains that use a conserved active site with a cysteine to catalyze a range of phosphate-transfer, thiotransfer, selenotransfer and redox activities. While these enzymes have been extensively studied in the context of protein/lipid head group dephosphorylation and various thiotransfer reactions, their overall diversity and catalytic potential remain poorly understood. Using comparative genomics and sequence/structure analysis, we comprehensively investigate and develop a natural classification for this superfamily. As a result, we identified several novel clades, both those which retain the catalytic cysteine and those where a distinct active site has emerged in the same location (e.g. diphthine synthase-like methylases and RNA 2' OH ribosyl phosphate transferases). We also present evidence that the superfamily has a wider range of catalytic capabilities than previously known, including a set of parallel activities operating on various sugar/sugar alcohol groups in the context of NAD+-derivatives and RNA termini, and potential phosphate transfer activities involving sugars and nucleotides. We show that such activities are particularly expanded in the RapZ-C-DUF488-DUF4326 clade, defined here for the first time. Some enzymes from this clade are predicted to catalyze novel DNA-end processing activities as part of nucleic-acid-modifying systems that are likely to function in biological conflicts between viruses and their hosts.
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Affiliation(s)
- A Maxwell Burroughs
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA
| | - L Aravind
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, MD 20894, USA
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8
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Liu C, Ren Y, Gao XQ, Du X, Yang ZZ. Development of QM/MM (ABEEM polarizable force field) method to simulate the excision reaction mechanism of damaged cytosine. J Comput Chem 2022; 43:2139-2153. [PMID: 36151878 DOI: 10.1002/jcc.27008] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2022] [Revised: 07/25/2022] [Accepted: 09/05/2022] [Indexed: 11/06/2022]
Abstract
DNA damages are regarded as having harmful effects on cell. The base excision repair mechanism combats these effects by removing damaged bases. The deglycosylation mechanism of excising damaged bases by DNA glycosylase and the state of the leaving base have been controversial. The enzymatic reaction of DNA glycosylase to remove the damaged bases involves not only the formation and breaking of chemical bonds, but also complex polarization effect and charge transfer, which cannot be accurately simulated by the QM/MM method combined with the fixed charge force field. This work has developed the ABEEM fluctuating polarizable force field combining with the QM method, that is (QM/MM[ABEEM]), to accurately simulate the proton transfer, charge transfer and the charge distribution. The piecewise function is used as the valence-state electronegativity in the QM/MM (ABEEM) to realize the accurate fitting of the charge distribution in reaction. And the charge transfer is accurately simulated by the local charge conservation conditions. Four deglycosylation mechanisms including the monofunctional and difunctional mechanisms of four neutral and protonated cytosine derivatives are explored. It is confirmed that the monofunctional mechanism of Asp-activated nucleophile water is a better deglycosylation mechanism and the base is protonated before the reaction occurs. Protonization of the base reduced the activation energy by 10.00-17.00 kcal/mol. Asp provides the necessary charge for the reaction, and DNA glycosylase preferentially cleaves ɛC. This work provides a theoretical basis for the research of excising damaged bases by DNA glycosylase.
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Affiliation(s)
- Cui Liu
- School of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian, People's Republic of China
| | - Yang Ren
- School of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian, People's Republic of China
| | - Xiao-Qin Gao
- School of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian, People's Republic of China
| | - Xue Du
- School of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian, People's Republic of China
| | - Zhong-Zhi Yang
- School of Chemistry and Chemical Engineering, Liaoning Normal University, Dalian, People's Republic of China
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Wang L, Xi K, Zhu L, Da LT. DNA Deformation Exerted by Regulatory DNA-Binding Motifs in Human Alkyladenine DNA Glycosylase Promotes Base Flipping. J Chem Inf Model 2022; 62:3213-3226. [PMID: 35708296 DOI: 10.1021/acs.jcim.2c00091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Human alkyladenine DNA glycosylase (AAG) is a key enzyme that corrects a broad range of alkylated and deaminated nucleobases to maintain genomic integrity. When encountering the lesions, AAG adopts a base-flipping strategy to extrude the target base from the DNA duplex to its active site, thereby cleaving the glycosidic bond. Despite its functional importance, the detailed mechanism of such base extrusion and how AAG distinguishes the lesions from an excess of normal bases both remain elusive. Here, through the Markov state model constructed on extensive all-atom molecular dynamics simulations, we find that the alkylated nucleobase (N3-methyladenine, 3MeA) everts through the DNA major groove. Two key AAG motifs, the intercalation and E131-N146 motifs, play active roles in bending/pressing the DNA backbone and widening the DNA minor groove during 3MeA eversion. In particular, the intercalated residue Y162 is involved in buckling the target site at the early stage of 3MeA eversion. Our traveling-salesman based automated path searching algorithm further revealed that a non-target normal adenine tends to be trapped in an exo site near the active site, which however barely exists for a target base 3MeA. Collectively, these results suggest that the Markov state model combined with traveling-salesman based automated path searching acts as a promising approach for studying complex conformational changes of biomolecules and dissecting the elaborate mechanism of target recognition by this unique enzyme.
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Affiliation(s)
- Lingyan Wang
- Key Laboratory of Systems Biomedicine (Ministry of Education), Shanghai Center for Systems Biomedicine, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
| | - Kun Xi
- Warshel Institute for Computational Biology, School of Life and Health Sciences, The Chinese University of Hong Kong (Shenzhen), Shenzhen, Guangdong 518172, P. R. China
| | - Lizhe Zhu
- Warshel Institute for Computational Biology, School of Life and Health Sciences, The Chinese University of Hong Kong (Shenzhen), Shenzhen, Guangdong 518172, P. R. China
| | - Lin-Tai Da
- Key Laboratory of Systems Biomedicine (Ministry of Education), Shanghai Center for Systems Biomedicine, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
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Wang L, Song K, Yu J, Da LT. Computational investigations on target-site searching and recognition mechanisms by thymine DNA glycosylase during DNA repair process. Acta Biochim Biophys Sin (Shanghai) 2022; 54:796-806. [PMID: 35593467 PMCID: PMC9828053 DOI: 10.3724/abbs.2022050] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
DNA glycosylase, as one member of DNA repair machineries, plays an essential role in correcting mismatched/damaged DNA nucleotides by cleaving the N-glycosidic bond between the sugar and target nucleobase through the base excision repair (BER) pathways. Efficient corrections of these DNA lesions are critical for maintaining genome integrity and preventing premature aging and cancers. The target-site searching/recognition mechanisms and the subsequent conformational dynamics of DNA glycosylase, however, remain challenging to be characterized using experimental techniques. In this review, we summarize our recent studies of sequential structural changes of thymine DNA glycosylase (TDG) during the DNA repair process, achieved mostly by molecular dynamics (MD) simulations. Computational simulations allow us to reveal atomic-level structural dynamics of TDG as it approaches the target-site, and pinpoint the key structural elements responsible for regulating the translocation of TDG along DNA. Subsequently, upon locating the lesions, TDG adopts a base-flipping mechanism to extrude the mispaired nucleobase into the enzyme active-site. The constructed kinetic network model elucidates six metastable states during the base-extrusion process and suggests an active role of TDG in flipping the intrahelical nucleobase. Finally, the molecular mechanism of product release dynamics after catalysis is also summarized. Taken together, we highlight to what extent the computational simulations advance our knowledge and understanding of the molecular mechanism underlying the conformational dynamics of TDG, as well as the limitations of current theoretical work.
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Affiliation(s)
- Lingyan Wang
- Key Laboratory of Systems Biomedicine (Ministry of Education)Shanghai Center for Systems BiomedicineShanghai Jiao Tong UniversityShanghai200240China
| | - Kaiyuan Song
- Key Laboratory of Systems Biomedicine (Ministry of Education)Shanghai Center for Systems BiomedicineShanghai Jiao Tong UniversityShanghai200240China
| | - Jin Yu
- Department of Physics and AstronomyDepartment of ChemistryNSF-Simons Center for Multiscale Cell Fate ResearchUniversity of CaliforniaIrvineCA92697USA
| | - Lin-Tai Da
- Key Laboratory of Systems Biomedicine (Ministry of Education)Shanghai Center for Systems BiomedicineShanghai Jiao Tong UniversityShanghai200240China,Correspondence address. Tel: +86-21-34207348; E-mail:
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11
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Insights into the substrate discrimination mechanisms of methyl-CpG-binding domain 4. Biochem J 2021; 478:1985-1997. [PMID: 33960375 DOI: 10.1042/bcj20210017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Revised: 05/05/2021] [Accepted: 05/07/2021] [Indexed: 11/17/2022]
Abstract
G:T mismatches, the major mispairs generated during DNA metabolism, are repaired in part by mismatch-specific DNA glycosylases such as methyl-CpG-binding domain 4 (MBD4) and thymine DNA glycosylase (TDG). Mismatch-specific DNA glycosylases must discriminate the mismatches against million-fold excess correct base pairs. MBD4 efficiently removes thymine opposite guanine but not opposite adenine. Previous studies have revealed that the substrate thymine is flipped out and enters the catalytic site of the enzyme, while the estranged guanine is stabilized by Arg468 of MBD4. To gain further insights into the mismatch discrimination mechanism of MBD4, we assessed the glycosylase activity of MBD4 toward various base pairs. In addition, we determined a crystal structure of MBD4 bound to T:O6-methylguanine-containing DNA, which suggests the O6 and N2 of purine and the O4 of pyrimidine are required to be a substrate for MBD4. To understand the role of the Arg468 finger in catalysis, we evaluated the glycosylase activity of MBD4 mutants, which revealed the guanidinium moiety of Arg468 may play an important role in catalysis. D560N/R468K MBD4 bound to T:G mismatched DNA shows that the side chain amine moiety of the Lys stabilizes the flipped-out thymine by a water-mediated phosphate pinching, while the backbone carbonyl oxygen of the Lys engages in hydrogen bonds with N2 of the estranged guanine. Comparison of various DNA glycosylase structures implies the guanidinium and amine moieties of Arg and Lys, respectively, may involve in discriminating between substrate mismatches and nonsubstrate base pairs.
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12
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Catalytic mechanism of the mismatch-specific DNA glycosylase methyl-CpG-binding domain 4. Biochem J 2020; 477:1601-1612. [PMID: 32297632 DOI: 10.1042/bcj20200125] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Revised: 04/09/2020] [Accepted: 04/14/2020] [Indexed: 12/15/2022]
Abstract
Thymine:guanine base pairs are major promutagenic mismatches occurring in DNA metabolism. If left unrepaired, these mispairs can cause C to T transition mutations. In humans, T:G mismatches are repaired in part by mismatch-specific DNA glycosylases such as methyl-CpG-binding domain 4 (hMBD4) and thymine-DNA glycosylase. Unlike lesion-specific DNA glycosylases, T:G-mismatch-specific DNA glycosylases specifically recognize both bases of the mismatch and remove the thymine but only from mispairs with guanine. Despite the advances in biochemical and structural characterizations of hMBD4, the catalytic mechanism of hMBD4 remains elusive. Herein, we report two structures of hMBD4 processing T:G-mismatched DNA. A high-resolution crystal structure of Asp560Asn hMBD4-T:G complex suggests that hMBD4-mediated glycosidic bond cleavage occurs via a general base catalysis mechanism assisted by Asp560. A structure of wild-type hMBD4 encountering T:G-containing DNA shows the generation of an apurinic/apyrimidinic (AP) site bearing the C1'-(S)-OH. The inversion of the stereochemistry at the C1' of the AP-site indicates that a nucleophilic water molecule approaches from the back of the thymine substrate, suggesting a bimolecular displacement mechanism (SN2) for hMBD4-catalyzed thymine excision. The AP-site is stabilized by an extensive hydrogen bond network in the MBD4 catalytic site, highlighting the role of MBD4 in protecting the genotoxic AP-site.
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13
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Muruzabal D, Collins A, Azqueta A. The enzyme-modified comet assay: Past, present and future. Food Chem Toxicol 2020; 147:111865. [PMID: 33217526 DOI: 10.1016/j.fct.2020.111865] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2020] [Revised: 11/08/2020] [Accepted: 11/13/2020] [Indexed: 12/17/2022]
Abstract
The enzyme-modified comet assay was developed in order to detect DNA lesions other than those detected by the standard version (single and double strand breaks and alkali-labile sites). Various lesion-specific enzymes, from the DNA repair machinery of bacteria and humans, have been combined with the comet assay, allowing detection of different oxidized and alkylated bases as well as cyclobutane pyrimidine dimers, mis-incorporated uracil and apurinic/apyrimidinic sites. The enzyme-modified comet assay has been applied in different fields - human biomonitoring, environmental toxicology, and genotoxicity testing (both in vitro and in vivo) - as well as in basic research. Up to now, twelve enzymes have been employed; here we describe the enzymes and give examples of studies in which they have been applied. The bacterial formamidopyrimidine DNA glycosylase (Fpg) and endonuclease III (EndoIII) have been extensively used while others have been used only rarely. Adding further enzymes to the comet assay toolbox could potentially increase the variety of DNA lesions that can be detected. The enzyme-modified comet assay can play a crucial role in the elucidation of the mechanism of action of both direct and indirect genotoxins, thus increasing the value of the assay in the regulatory context.
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Affiliation(s)
- Damián Muruzabal
- Universidad de Navarra, Department of Pharmacology and Toxicology, Faculty of Pharmacy and Nutrition, Irunlarrea 1, 310008, Pamplona, Spain
| | - Andrew Collins
- Department of Nutrition, Institute for Basic Medical Sciences, University of Oslo, Sognsvannsveien 9, 0372, Oslo, Norway
| | - Amaya Azqueta
- Universidad de Navarra, Department of Pharmacology and Toxicology, Faculty of Pharmacy and Nutrition, Irunlarrea 1, 310008, Pamplona, Spain; IdiSNA, Navarra Institute for Health Research, Pamplona, Spain.
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14
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Abstract
Genomic DNA is chemically reactive and therefore susceptible to damage by many exogenous and endogenous sources. Lesions produced from these damaging events can have various mutagenic and genotoxic consequences. This Perspective follows the journey of one particular lesion, 1,N6-ethenoadenine (εA), from its formation to replication and repair, and its role in cancerous tissues and inflammatory diseases. εA is generated by the reaction of adenine (A) with vinyl chloride or lipid peroxidation products. We present the miscoding properties of εA with an emphasis on how bacterial and mammalian cells can process lesions differently, leading to varied mutational spectra. But with information from these assays, we can better understand how the miscoding properties of εA lead to biological consequences and how genomic stability can be maintained via DNA repair mechanisms. We discuss how base excision repair (BER) and direct reversal repair (DRR) can minimize the biological consequences of εA lesions. Kinetic parameters of glycosylases and AlkB family enzymes are described, along with a discussion of the relative contributions of the BER and DRR pathways in the repair of εA. Because eukaryotic DNA is packaged in chromatin, we also discuss the impact of this packaging on BER and DRR, specifically in regards to repair of εA. Studying DNA lesions like εA in this context, from origin to biological implications, can provide crucial information to better understand prevention of mutagenesis and cancer.
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Affiliation(s)
- Katelyn L Rioux
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Sarah Delaney
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
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15
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Kot W, Olsen NS, Nielsen TK, Hutinet G, de Crécy-Lagard V, Cui L, Dedon PC, Carstens AB, Moineau S, Swairjo MA, Hansen LH. Detection of preQ0 deazaguanine modifications in bacteriophage CAjan DNA using Nanopore sequencing reveals same hypermodification at two distinct DNA motifs. Nucleic Acids Res 2020; 48:10383-10396. [PMID: 32941607 PMCID: PMC7544227 DOI: 10.1093/nar/gkaa735] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Revised: 08/19/2020] [Accepted: 08/26/2020] [Indexed: 12/22/2022] Open
Abstract
In the constant evolutionary battle against mobile genetic elements (MGEs), bacteria have developed several defense mechanisms, some of which target the incoming, foreign nucleic acids e.g. restriction-modification (R-M) or CRISPR-Cas systems. Some of these MGEs, including bacteriophages, have in turn evolved different strategies to evade these hurdles. It was recently shown that the siphophage CAjan and 180 other viruses use 7-deazaguanine modifications in their DNA to evade bacterial R-M systems. Among others, phage CAjan genome contains a gene coding for a DNA-modifying homolog of a tRNA-deazapurine modification enzyme, together with four 7-cyano-7-deazaguanine synthesis genes. Using the CRISPR-Cas9 genome editing tool combined with the Nanopore Sequencing (ONT) we showed that the 7-deazaguanine modification in the CAjan genome is dependent on phage-encoded genes. The modification is also site-specific and is found mainly in two separate DNA sequence contexts: GA and GGC. Homology modeling of the modifying enzyme DpdA provides insight into its probable DNA binding surface and general mode of DNA recognition.
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Affiliation(s)
- Witold Kot
- Department of Plant and Environmental Science, University of Copenhagen, Denmark
| | - Nikoline S Olsen
- Department of Environmental Science, Aarhus University, Roskilde, Denmark
| | - Tue K Nielsen
- Department of Plant and Environmental Science, University of Copenhagen, Denmark
| | - Geoffrey Hutinet
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL USA
| | - Valérie de Crécy-Lagard
- Department of Microbiology and Cell Science, University of Florida, Gainesville, FL USA.,Genetics Institute, University of Florida, Gainesville, FL, USA
| | - Liang Cui
- Antimicrobial Resistance Interdisciplinary Research Group, Singapore-MIT Alliance for Research and Technology, Singapore
| | - Peter C Dedon
- Antimicrobial Resistance Interdisciplinary Research Group, Singapore-MIT Alliance for Research and Technology, Singapore.,Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Alexander B Carstens
- Department of Plant and Environmental Science, University of Copenhagen, Denmark
| | - Sylvain Moineau
- Département de biochimie, de microbiologie et de bio-informatique, Université Laval, Québec City, PQ, Canada.,Groupe de recherche en écologie buccale, Faculté de médecine dentaire, Université Laval, Québec City, PQ, Canada.,Félix d'Hérelle Reference Center for Bacterial Viruses, Université Laval, Québec City, PQ, Canada
| | - Manal A Swairjo
- Department of Chemistry and Biochemistry and the Viral Information Institute, San Diego State University, San Diego, CA, USA
| | - Lars H Hansen
- Department of Plant and Environmental Science, University of Copenhagen, Denmark
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16
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Kotandeniya D, Rogers MS, Fernandez J, Kanugula S, Hudson RHE, Rodriguez F, Lipscomb JD, Tretyakova N. 6-phenylpyrrolocytosine as a fluorescent probe to examine nucleotide flipping catalyzed by a DNA repair protein. Biopolymers 2020; 112:e23405. [PMID: 33098572 DOI: 10.1002/bip.23405] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2020] [Revised: 09/30/2020] [Accepted: 09/30/2020] [Indexed: 11/05/2022]
Abstract
Cellular exposure to tobacco-specific nitrosamines causes formation of promutagenic O6 -[4-oxo-4-(3-pyridyl)but-1-yl]guanine (O6 -POB-G) and O6 -methylguanine (O6 -Me-G) adducts in DNA. These adducts can be directly repaired by O6 -alkylguanine-DNA alkyltransferase (AGT). Repair begins by flipping the damaged base out of the DNA helix. AGT binding and base-flipping have been previously studied using pyrrolocytosine as a fluorescent probe paired to the O6 -alkylguanine lesion, but low fluorescence yield limited the resolution of steps in the repair process. Here, we utilize the highly fluorescent 6-phenylpyrrolo-2'-deoxycytidine (6-phenylpyrrolo-C) to investigate AGT-DNA interactions. Synthetic oligodeoxynucleotide duplexes containing O6 -POB-G and O6 -Me-G adducts were placed within the CpG sites of codons 158, 245, and 248 of the p53 tumor suppressor gene and base-paired to 6-phenylpyrrolo-C in the opposite strand. Neighboring cytosine was either unmethylated or methylated. Stopped-flow fluorescence measurements were performed by mixing the DNA duplexes with C145A or R128G AGT variants. We observe a rapid, two-step, nearly irreversible binding of AGT to DNA followed by two slower steps, one of which is base-flipping. Placing 5-methylcytosine immediately 5' to the alkylated guanosine causes a reduction in rate constant of nucleotide flipping. O6 -POB-G at codon 158 decreased the base flipping rate constant by 3.5-fold compared with O6 -Me-G at the same position. A similar effect was not observed at other codons.
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Affiliation(s)
- Delshanee Kotandeniya
- Department of Medicinal Chemistry and the Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota, USA
| | - Melanie S Rogers
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota, USA
| | - Jenna Fernandez
- Department of Medicinal Chemistry and the Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota, USA
| | - Sreenivas Kanugula
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA
| | - Robert H E Hudson
- Department of Chemistry, University of Western Ontario, London, Ontario, Canada
| | - Freddys Rodriguez
- Department of Medicinal Chemistry and the Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota, USA
| | - John D Lipscomb
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota, USA
| | - Natalia Tretyakova
- Department of Medicinal Chemistry and the Masonic Cancer Center, University of Minnesota, Minneapolis, Minnesota, USA
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17
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Verma P, Tandon R, Yadav G, Gaur V. Structural Aspects of DNA Repair and Recombination in Crop Improvement. Front Genet 2020; 11:574549. [PMID: 33024442 PMCID: PMC7516265 DOI: 10.3389/fgene.2020.574549] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2020] [Accepted: 08/25/2020] [Indexed: 12/18/2022] Open
Abstract
The adverse effects of global climate change combined with an exponentially increasing human population have put substantial constraints on agriculture, accelerating efforts towards ensuring food security for a sustainable future. Conventional plant breeding and modern technologies have led to the creation of plants with better traits and higher productivity. Most crop improvement approaches (conventional breeding, genome modification, and gene editing) primarily rely on DNA repair and recombination (DRR). Studying plant DRR can provide insights into designing new strategies or improvising the present techniques for crop improvement. Even though plants have evolved specialized DRR mechanisms compared to other eukaryotes, most of our insights about plant-DRRs remain rooted in studies conducted in animals. DRR mechanisms in plants include direct repair, nucleotide excision repair (NER), base excision repair (BER), mismatch repair (MMR), non-homologous end joining (NHEJ) and homologous recombination (HR). Although each DRR pathway acts on specific DNA damage, there is crosstalk between these. Considering the importance of DRR pathways as a tool in crop improvement, this review focuses on a general description of each DRR pathway, emphasizing on the structural aspects of key DRR proteins. The review highlights the gaps in our understanding and the importance of studying plant DRR in the context of crop improvement.
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Affiliation(s)
- Prabha Verma
- National Institute of Plant Genome Research, New Delhi, India
| | - Reetika Tandon
- National Institute of Plant Genome Research, New Delhi, India
| | - Gitanjali Yadav
- National Institute of Plant Genome Research, New Delhi, India
| | - Vineet Gaur
- National Institute of Plant Genome Research, New Delhi, India
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18
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Pinthong N, Limudomporn P, Vasuvat J, Adisakwattana P, Rattaprasert P, Chavalitshewinkoon-Petmitr P. Molecular characterization of Plasmodium falciparum DNA-3-methyladenine glycosylase. Malar J 2020; 19:284. [PMID: 32762689 PMCID: PMC7409487 DOI: 10.1186/s12936-020-03355-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Accepted: 07/28/2020] [Indexed: 11/10/2022] Open
Abstract
Background The emergence of artemisinin-resistant malaria parasites highlights the need for novel drugs and their targets. Alkylation of purine bases can hinder DNA replication and if unresolved would eventually result in cell death. DNA-3-methyladenine glycosylase (MAG) is responsible for the repair of those alkylated bases. Plasmodium falciparum (Pf) MAG was characterized for its potential for development as an anti-malarial candidate. Methods Native PfMAG from crude extract of chloroquine- and pyrimethamine-resistant P. falciparum K1 strain was partially purified using three chromatographic procedures. From bio-informatics analysis, primers were designed for amplification, insertion into pBAD202/D-TOPO and heterologous expression in Escherichia coli of recombinant PfMAG. Functional and biochemical properties of the recombinant enzyme were characterized. Results PfMAG activity was most prominent in parasite schizont stages, with a specific activity of 147 U/mg (partially purified) protein. K1 PfMAG contained an insertion of AAT (coding for asparagine) compared to 3D7 strain and 16% similarity to the human enzyme. Recombinant PfMAG (74 kDa) was twice as large as the human enzyme, preferred double-stranded DNA substrate, and demonstrated glycosylase activity over a pH range of 4–9, optimal salt concentration of 100–200 mM NaCl but reduced activity at 250 mM NaCl, no requirement for divalent cations, which were inhibitory in a dose-dependent manner. Conclusion PfMAG activity increased with parasite development being highest in the schizont stages. K1 PfMAG contained an indel AAT (asparagine) not present in 3D7 strain and the recombinant enzyme was twice as large as the human enzyme. Recombinant PfMAG had a wide range of optimal pH activity, and was inhibited at high (250 mM) NaCl concentration as well as by divalent cations. The properties of PfMAG provide basic data that should be of assistance in developing anti-malarials against this potential parasite target.
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Affiliation(s)
- Nattapon Pinthong
- Department of Protozoology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Paviga Limudomporn
- Department of Zoology, Faculty of Science, Kasetsart University, Bangkok, Thailand
| | - Jitlada Vasuvat
- Department of Protozoology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Poom Adisakwattana
- Department of Helminthology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
| | - Pongruj Rattaprasert
- Department of Protozoology, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand
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19
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An aza-nucleoside, fragment-like inhibitor of the DNA repair enzyme alkyladenine glycosylase (AAG). Bioorg Med Chem 2020; 28:115507. [PMID: 32327352 DOI: 10.1016/j.bmc.2020.115507] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Revised: 04/06/2020] [Accepted: 04/09/2020] [Indexed: 11/21/2022]
Abstract
The DNA repair enzyme AAG has been shown in mice to promote tissue necrosis in response to ischaemic reperfusion or treatment with alkylating agents. A chemical probe inhibitor is required for investigations of the biological mechanism causing this phenomenon and as a lead for drugs that are potentially protective against tissue damage from organ failure and transplantation, and alkylative chemotherapy. Herein, we describe the rationale behind the choice of arylmethylpyrrolidines as appropriate aza-nucleoside mimics for an inhibitor followed by their synthesis and the first use of a microplate-based assay for quantification of their inhibition of AAG. We finally report the discovery of an imidazol-4-ylmethylpyrrolidine as a fragment-sized, weak inhibitor of AAG.
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20
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Muruzabal D, Sanz-Serrano J, Sauvaigo S, Gützkow KB, López de Cerain A, Vettorazzi A, Azqueta A. Novel approach for the detection of alkylated bases using the enzyme-modified comet assay. Toxicol Lett 2020; 330:108-117. [PMID: 32380118 DOI: 10.1016/j.toxlet.2020.04.021] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2020] [Revised: 04/06/2020] [Accepted: 04/24/2020] [Indexed: 12/26/2022]
Abstract
The enzyme-modified comet assay is widely used for the detection of oxidized DNA lesions. Here we describe for the first time the use of the human alkyladenine DNA glycosylase (hAAG) for the detection of alkylated bases. hAAG was titrated using untreated and methyl methanesulfonate (MMS)-treated TK-6 cells. The hAAG-modified comet assay was compared to the formamidopyrimidine DNA glycosylase (Fpg)-modified comet assay, widely used to detect oxidized lesions but that also detects ring-opened purines derived from some alkylated lesions, using cells treated with potassium bromate (oxidizing agent) or MMS. Moreover, neutral and alkaline lysis conditions were used to determine the nature of detected lesions. When alkaline lysis was employed (condition normally used), the level of hAAG-sensitive sites was higher than the Fpg-sensitive sites in MMS-treated cells and hAAG, unlike Fpg, did not detect oxidized bases. After neutral lysis, Fpg did not detect MMS-induced lesions; however, results obtained with hAAG remained unchanged. As expected, Fpg detected oxidized purines and imidazole ring-opened purines, derived from N7-methylguanines under alkaline conditions. It seems that hAAG detected N7-methylguanines, the ring-opened purines derived at high pH, and 3-methlyladenines. Specificity of hAAG towards different DNA lesions was evaluated using a multiplex oligonucleotide-cleavage assay, confirming the ability of hAAG to detect ethenoadenines and hypoxanthine. The hAAG-modified comet assay is a new tool for the detection of alkylated bases.
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Affiliation(s)
- Damián Muruzabal
- Department of Pharmacology and Toxicology, University of Navarra, C/Irunlarrea 1, 31009 Pamplona, Spain
| | - Julen Sanz-Serrano
- Department of Pharmacology and Toxicology, University of Navarra, C/Irunlarrea 1, 31009 Pamplona, Spain
| | - Sylvie Sauvaigo
- LXRepair, Biopolis, 5 avenue du Grand Sablon, 38700 La Tronche, France
| | - Kristine B Gützkow
- Section of Molecular Toxicology, Department of Environmental Health, Norwegian Institute of Public Health, P.O. Box 222, Skøyen, 0213 Oslo, Norway
| | - Adela López de Cerain
- Department of Pharmacology and Toxicology, University of Navarra, C/Irunlarrea 1, 31009 Pamplona, Spain; IdiSNA, Navarra Institute for Health Research, Spain
| | - Ariane Vettorazzi
- Department of Pharmacology and Toxicology, University of Navarra, C/Irunlarrea 1, 31009 Pamplona, Spain; IdiSNA, Navarra Institute for Health Research, Spain
| | - Amaya Azqueta
- Department of Pharmacology and Toxicology, University of Navarra, C/Irunlarrea 1, 31009 Pamplona, Spain; IdiSNA, Navarra Institute for Health Research, Spain.
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21
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Caffrey PJ, Kher R, Bian K, Li D, Delaney S. Comparison of the Base Excision and Direct Reversal Repair Pathways for Correcting 1, N6-Ethenoadenine in Strongly Positioned Nucleosome Core Particles. Chem Res Toxicol 2020; 33:1888-1896. [PMID: 32293880 PMCID: PMC7374743 DOI: 10.1021/acs.chemrestox.0c00089] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
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1,N6-ethenoadenine (εA) is a
mutagenic lesion and biomarker observed in numerous cancerous tissues.
Two pathways are responsible for its repair: base excision repair
(BER) and direct reversal repair (DRR). Alkyladenine DNA glycosylase
(AAG) is the primary enzyme that excises εA in BER, generating
stable intermediates that are processed by downstream enzymes. For
DRR, the Fe(II)/α-ketoglutarate-dependent ALKBH2 enzyme repairs
εA by direct conversion of εA to A. While the molecular
mechanism of each enzyme is well understood on unpackaged duplex DNA,
less is known about their actions on packaged DNA. The nucleosome
core particle (NCP) forms the minimal packaging unit of DNA in eukaryotic
organisms and is composed of 145–147 base pairs wrapped around
a core of eight histone proteins. In this work, we investigated the
activity of AAG and ALKBH2 on εA lesions globally distributed
at positions throughout a strongly positioned NCP. Overall, we examined
the repair of εA at 23 unique locations in packaged DNA. We
observed a strong correlation between rotational positioning of εA
and AAG activity but not ALKBH2 activity. ALKBH2 was more effective
than AAG at repairing occluded εA lesions, but only AAG was
capable of full repair of any εA in the NCP. However, notable
exceptions to these trends were observed, highlighting the complexity
of the NCP as a substrate for DNA repair. Modeling of binding of the
repair enzymes to NCPs revealed that some of these observations can
be explained by steric interference caused by DNA packaging. Specifically,
interactions between ALKBH2 and the histone proteins obstruct binding
to DNA, which leads to diminished activity. Taken together, these
results support in vivo observations of alkylation
damage profiles and contribute to our understanding of mutational
hotspots.
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Affiliation(s)
- Paul J Caffrey
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Raadhika Kher
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Ke Bian
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, Rhode Island 02881, United States
| | - Deyu Li
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, Rhode Island 02881, United States
| | - Sarah Delaney
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
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Kladova OA, Kuznetsova AA, Barthes NPF, Michel BY, Burger A, Fedorova OS, Kuznetsov NA. New Fluorescent Analogs of Nucleotides Based on 3-Hydroxychromone for Recording Conformational Changes of DNA. RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY 2020. [DOI: 10.1134/s1068162019060220] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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23
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Abstract
In every cell from bacteria to mammals, NusG-like proteins bind transcribing RNA polymerase to modulate the rate of nascent RNA synthesis and to coordinate it with numerous cotranscriptional processes that ultimately determine the transcript fate. Housekeeping NusG factors regulate expression of the bulk of the genome, whereas their highly specialized paralogs control just a few targets. In every cell from bacteria to mammals, NusG-like proteins bind transcribing RNA polymerase to modulate the rate of nascent RNA synthesis and to coordinate it with numerous cotranscriptional processes that ultimately determine the transcript fate. Housekeeping NusG factors regulate expression of the bulk of the genome, whereas their highly specialized paralogs control just a few targets. In Escherichia coli, NusG stimulates silencing of horizontally acquired genes, while its paralog RfaH counters NusG action by activating a subset of these genes. Acting alone or as part of regulatory complexes, NusG factors can promote uninterrupted RNA synthesis, bring about transcription pausing or premature termination, modulate RNA processing, and facilitate translation. Recent structural and mechanistic studies of NusG homologs from all domains of life reveal molecular details of multifaceted interactions that underpin their unexpectedly diverse regulatory roles. NusG proteins share conserved binding sites on RNA polymerase and many effects on the transcription elongation complex but differ in their mechanisms of recruitment, interactions with nucleic acids and secondary partners, and regulatory outcomes. Strikingly, some can alternate between autoinhibited and activated states that possess dramatically different secondary structures to achieve exquisite target specificity.
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24
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Shi R, Shen XX, Rokas A, Eichman BF. Structural Biology of the HEAT-Like Repeat Family of DNA Glycosylases. Bioessays 2018; 40:e1800133. [PMID: 30264543 DOI: 10.1002/bies.201800133] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Revised: 08/27/2018] [Indexed: 11/08/2022]
Abstract
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.
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Affiliation(s)
- Rongxin Shi
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37232, USA
| | - Xing-Xing Shen
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37232, USA
| | - Antonis Rokas
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37232, USA
| | - Brandt F Eichman
- Department of Biological Sciences, Vanderbilt University, Nashville, TN, 37232, USA
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25
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Abstract
The base excision repair (BER) pathway removes modified nucleobases that can be deleterious to an organism. BER is initiated by a glycosylase, which finds and removes these modified nucleobases. Most of the characterization of glycosylase activity has been conducted in the context of DNA oligomer substrates. However, DNA within eukaryotic organisms exists in a packaged environment with the basic unit of organization being the nucleosome core particle (NCP). The NCP is a complex substrate for repair in which a variety of factors can influence glycosylase activity. In this Review, we focus on the geometric positioning of modified nucleobases in an NCP and the consequences on glycosylase activity and initiating BER.
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Affiliation(s)
- Erin E Kennedy
- Department of Molecular Biology, Cell Biology, and Biochemistry, Brown University, Providence, RI 02912, United States
| | - Paul J Caffrey
- Department of Chemistry, Brown University, Providence, RI 02912, United States
| | - Sarah Delaney
- Department of Chemistry, Brown University, Providence, RI 02912, United States.
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26
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Taylor EL, Kesavan PM, Wolfe AE, O'Brien PJ. Distinguishing Specific and Nonspecific Complexes of Alkyladenine DNA Glycosylase. Biochemistry 2018; 57:4440-4454. [PMID: 29940097 DOI: 10.1021/acs.biochem.8b00531] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Human alkyladenine DNA glycosylase (AAG) recognizes many alkylated and deaminated purine lesions and excises them to initiate the base excision DNA repair pathway. AAG employs facilitated diffusion to rapidly scan nonspecific sites and locate rare sites of damage. Nonspecific DNA binding interactions are critical to the efficiency of this search for damage, but little is known about the binding footprint or the affinity of AAG for nonspecific sites. We used biochemical and biophysical approaches to characterize the binding of AAG to both undamaged and damaged DNA. Although fluorescence anisotropy is routinely used to study DNA binding, we found unexpected complexities in the data for binding of AAG to DNA. Systematic comparison of different fluorescent labels and different lengths of DNA allowed binding models to be distinguished and demonstrated that AAG can bind with high affinity and high density to nonspecific DNA. Fluorescein-labeled DNA gave the most complex behavior but also showed the greatest potential to distinguish specific and nonspecific binding modes. We suggest a unified model that is expected to apply to many DNA binding proteins that exhibit affinity for nonspecific DNA. Although AAG strongly prefers to excise lesions from duplex DNA, nonspecific binding is comparable for single- and double-stranded nonspecific sites. The electrostatically driven binding of AAG to small DNA sites (∼5 nucleotides of single-stranded and ∼6 base pairs of duplex) facilitates the search for DNA damage in chromosomal DNA, which is bound by nucleosomes and other proteins.
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Affiliation(s)
- Erin L Taylor
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Preethi M Kesavan
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Abigail E Wolfe
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Patrick J O'Brien
- Department of Biological Chemistry , University of Michigan , Ann Arbor , Michigan 48109 , United States
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27
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Zuber PK, Artsimovitch I, NandyMazumdar M, Liu Z, Nedialkov Y, Schweimer K, Rösch P, Knauer SH. The universally-conserved transcription factor RfaH is recruited to a hairpin structure of the non-template DNA strand. eLife 2018; 7:36349. [PMID: 29741479 PMCID: PMC5995543 DOI: 10.7554/elife.36349] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Accepted: 05/05/2018] [Indexed: 12/31/2022] Open
Abstract
RfaH, a transcription regulator of the universally conserved NusG/Spt5 family, utilizes a unique mode of recruitment to elongating RNA polymerase to activate virulence genes. RfaH function depends critically on an ops sequence, an exemplar of a consensus pause, in the non-template DNA strand of the transcription bubble. We used structural and functional analyses to elucidate the role of ops in RfaH recruitment. Our results demonstrate that ops induces pausing to facilitate RfaH binding and establishes direct contacts with RfaH. Strikingly, the non-template DNA forms a hairpin in the RfaH:ops complex structure, flipping out a conserved T residue that is specifically recognized by RfaH. Molecular modeling and genetic evidence support the notion that ops hairpin is required for RfaH recruitment. We argue that both the sequence and the structure of the non-template strand are read out by transcription factors, expanding the repertoire of transcriptional regulators in all domains of life.
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Affiliation(s)
- Philipp K Zuber
- Lehrstuhl Biopolymere und Forschungszentrum für Bio-Makromoleküle, Universität Bayreuth, Bayreuth, Germany
| | - Irina Artsimovitch
- Department of Microbiology, The Ohio State University, Columbus, United States.,The Center for RNA Biology, The Ohio State University, Columbus, United States
| | - Monali NandyMazumdar
- Department of Microbiology, The Ohio State University, Columbus, United States.,The Center for RNA Biology, The Ohio State University, Columbus, United States
| | - Zhaokun Liu
- Department of Microbiology, The Ohio State University, Columbus, United States.,The Center for RNA Biology, The Ohio State University, Columbus, United States
| | - Yuri Nedialkov
- Department of Microbiology, The Ohio State University, Columbus, United States.,The Center for RNA Biology, The Ohio State University, Columbus, United States
| | - Kristian Schweimer
- Lehrstuhl Biopolymere und Forschungszentrum für Bio-Makromoleküle, Universität Bayreuth, Bayreuth, Germany
| | - Paul Rösch
- Lehrstuhl Biopolymere und Forschungszentrum für Bio-Makromoleküle, Universität Bayreuth, Bayreuth, Germany
| | - Stefan H Knauer
- Lehrstuhl Biopolymere und Forschungszentrum für Bio-Makromoleküle, Universität Bayreuth, Bayreuth, Germany
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28
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Lenz SAP, Wetmore SD. QM/MM Study of the Reaction Catalyzed by Alkyladenine DNA Glycosylase: Examination of the Substrate Specificity of a DNA Repair Enzyme. J Phys Chem B 2017; 121:11096-11108. [PMID: 29148771 DOI: 10.1021/acs.jpcb.7b09646] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Human alkyladenine DNA glycosylase (AAG) functions as part of the base excision repair pathway to excise structurally diverse oxidized and alkylated DNA purines. Specifically, AAG uses a water molecule activated by a general base and a nonspecific active site lined with aromatic residues to cleave the N-glycosidic bond. Despite broad substrate specificity, AAG does not target the natural purines (adenine (A) and guanine (G)). Using the ONIOM(QM:MM) methodology, we provide fundamental atomic level details of AAG bound to DNA-containing a neutral substrate (hypoxanthine (Hx)), a nonsubstrate (G), or a cationic substrate (7-methylguanine (7MeG)) and probe changes in the reaction pathway that occur when AAG targets different nucleotides. We reveal that subtle differences in protein-DNA contacts upon binding different substrates within the flexible AAG active site can significantly affect the deglycosylation reaction. Notably, we predict that AAG excises Hx in a concerted mechanism that is facilitated through correct alignment of the (E125) general base due to hydrogen bonding with a neighboring aromatic amino acid (Y127). Hx departure is further stabilized by π-π interactions with aromatic amino acids and hydrogen bonds with active site water. Despite possessing a similar structure to Hx, G is not excised since the additional exocyclic amino group leads to misalignment of the general base due to disruption of the key E125-Y127 hydrogen bond, the catalytically unfavorable placement of water within the active site, and weakened π-contacts between aromatic amino acids and the nucleobase. In contrast, cationic 7MeG does not occupy the same position within the AAG active site as G due to steric clashes with the additional N7 methyl group, which results in the correct alignment of the general base and permits nucleobase excision as observed for neutral Hx. Overall, our structural data rationalizes the observed substrate specificity of AAG and contributes to our fundamental understanding of enzymes with flexible active sites and broad substrate specificities.
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Affiliation(s)
- Stefan A P Lenz
- Department of Chemistry and Biochemistry, University of Lethbridge , 4401 University Drive West, Lethbridge, Alberta T1K 3M4, Canada
| | - Stacey D Wetmore
- Department of Chemistry and Biochemistry, University of Lethbridge , 4401 University Drive West, Lethbridge, Alberta T1K 3M4, Canada
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29
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Hendershot JM, O'Brien PJ. Search for DNA damage by human alkyladenine DNA glycosylase involves early intercalation by an aromatic residue. J Biol Chem 2017; 292:16070-16080. [PMID: 28747435 PMCID: PMC5625039 DOI: 10.1074/jbc.m117.782813] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2017] [Revised: 07/19/2017] [Indexed: 01/22/2023] Open
Abstract
DNA repair enzymes recognize and remove damaged bases that are embedded in the duplex. To gain access, most enzymes use nucleotide flipping, whereby the target nucleotide is rotated 180° into the active site. In human alkyladenine DNA glycosylase (AAG), the enzyme that initiates base excision repair of alkylated bases, the flipped-out nucleotide is stabilized by intercalation of the side chain of tyrosine 162 that replaces the lesion nucleobase. Previous kinetic studies provided evidence for the formation of a transient complex that precedes the stable flipped-out complex, but it is not clear how this complex differs from nonspecific complexes. We used site-directed mutagenesis and transient-kinetic approaches to investigate the timing of Tyr162 intercalation for AAG. The tryptophan substitution (Y162W) appeared to be conservative, because the mutant protein retained a highly favorable equilibrium constant for flipping the 1,N6-ethenoadenine (ϵA) lesion, and the rate of N-glycosidic bond cleavage was identical to that of the wild-type enzyme. We assigned the tryptophan fluorescence signal from Y162W by removing two native tryptophan residues (W270A/W284A). Stopped-flow experiments then demonstrated that the change in tryptophan fluorescence of the Y162W mutant is extremely rapid upon binding to either damaged or undamaged DNA, much faster than the lesion-recognition and nucleotide flipping steps that were independently determined by monitoring the ϵA fluorescence. These observations suggest that intercalation by this aromatic residue is one of the earliest steps in the search for DNA damage and that this interaction is important for the progression of AAG from nonspecific searching to specific-recognition complexes.
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Affiliation(s)
- Jenna M Hendershot
- From the Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109-0600
| | - Patrick J O'Brien
- From the Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, Michigan 48109-0600
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30
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D'Errico M, Parlanti E, Pascucci B, Fortini P, Baccarini S, Simonelli V, Dogliotti E. Single nucleotide polymorphisms in DNA glycosylases: From function to disease. Free Radic Biol Med 2017; 107:278-291. [PMID: 27932076 DOI: 10.1016/j.freeradbiomed.2016.12.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/04/2016] [Revised: 11/25/2016] [Accepted: 12/02/2016] [Indexed: 02/08/2023]
Abstract
Oxidative stress is associated with a growing number of diseases that span from cancer to neurodegeneration. Most oxidatively induced DNA base lesions are repaired by the base excision repair (BER) pathway which involves the action of various DNA glycosylases. There are numerous genome wide studies attempting to associate single-nucleotide polymorphisms (SNPs) with predispositions to various types of disease; often, these common variants do not have significant alterations in their biochemical function and do not exhibit a convincing phenotype. Nevertheless several lines of evidence indicate that SNPs in DNA repair genes may modulate DNA repair capacity and contribute to risk of disease. This overview provides a convincing picture that SNPs of DNA glycosylases that remove oxidatively generated DNA lesions are susceptibility factors for a wide disease spectrum that includes besides cancer (particularly lung, breast and gastrointestinal tract), cochlear/ocular disorders, myocardial infarction and neurodegenerative disorders which can be all grouped under the umbrella of oxidative stress-related pathologies.
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Affiliation(s)
- Mariarosaria D'Errico
- Department of Environment and Primary Prevention, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy.
| | - Eleonora Parlanti
- Department of Environment and Primary Prevention, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy
| | - Barbara Pascucci
- Department of Environment and Primary Prevention, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy; Istituto di Cristallografia, Consiglio Nazionale delle Ricerche, Via Salaria, Km 29,300, 00016 Monterotondo Stazione, Rome, Italy
| | - Paola Fortini
- Department of Environment and Primary Prevention, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy
| | - Sara Baccarini
- Department of Environment and Primary Prevention, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy
| | - Valeria Simonelli
- Department of Environment and Primary Prevention, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy
| | - Eugenia Dogliotti
- Department of Environment and Primary Prevention, Istituto Superiore di Sanità, Viale Regina Elena 299, 00161 Rome, Italy.
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31
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Boiteux S, Coste F, Castaing B. Repair of 8-oxo-7,8-dihydroguanine in prokaryotic and eukaryotic cells: Properties and biological roles of the Fpg and OGG1 DNA N-glycosylases. Free Radic Biol Med 2017; 107:179-201. [PMID: 27903453 DOI: 10.1016/j.freeradbiomed.2016.11.042] [Citation(s) in RCA: 103] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Revised: 11/22/2016] [Accepted: 11/25/2016] [Indexed: 01/23/2023]
Abstract
Oxidatively damaged DNA results from the attack of sugar and base moieties by reactive oxygen species (ROS), which are formed as byproducts of normal cell metabolism and during exposure to endogenous or exogenous chemical or physical agents. Guanine, having the lowest redox potential, is the DNA base the most susceptible to oxidation, yielding products such as 8-oxo-7,8-dihydroguanine (8-oxoG) and 2-6-diamino-4-hydroxy-5-formamidopyrimidine (FapyG). In DNA, 8-oxoG was shown to be mutagenic yielding GC to TA transversions upon incorporation of dAMP opposite this lesion by replicative DNA polymerases. In prokaryotic and eukaryotic cells, 8-oxoG is primarily repaired by the base excision repair pathway (BER) initiated by a DNA N-glycosylase, Fpg and OGG1, respectively. In Escherichia coli, Fpg cooperates with MutY and MutT to prevent 8-oxoG-induced mutations, the "GO-repair system". In Saccharomyces cerevisiae, OGG1 cooperates with nucleotide excision repair (NER), mismatch repair (MMR), post-replication repair (PRR) and DNA polymerase η to prevent mutagenesis. Human and mouse cells mobilize all these pathways using OGG1, MUTYH (MutY-homolog also known as MYH), MTH1 (MutT-homolog also known as NUDT1), NER, MMR, NEILs and DNA polymerases η and λ, to prevent 8-oxoG-induced mutations. In fact, mice deficient in both OGG1 and MUTYH develop cancer in different organs at adult age, which points to the critical impact of 8-oxoG repair on genetic stability in mammals. In this review, we will focus on Fpg and OGG1 proteins, their biochemical and structural properties as well as their biological roles. Other DNA N-glycosylases able to release 8-oxoG from damaged DNA in various organisms will be discussed. Finally, we will report on the role of OGG1 in human disease and the possible use of 8-oxoG DNA N-glycosylases as therapeutic targets.
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Affiliation(s)
- Serge Boiteux
- Centre de Biophysique Moléculaire, CNRS, UPR4301, rue Charles Sadron, 45072 Orléans, France.
| | - Franck Coste
- Centre de Biophysique Moléculaire, CNRS, UPR4301, rue Charles Sadron, 45072 Orléans, France
| | - Bertrand Castaing
- Centre de Biophysique Moléculaire, CNRS, UPR4301, rue Charles Sadron, 45072 Orléans, France.
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32
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Hendershot JM, O'Brien PJ. Transient Kinetic Methods for Mechanistic Characterization of DNA Binding and Nucleotide Flipping. Methods Enzymol 2017; 592:377-415. [PMID: 28668128 DOI: 10.1016/bs.mie.2017.04.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Enzymes that modify nucleobases in double-stranded genomic DNA, either as part of a DNA repair pathway or as an epigenetic modifying pathway, adopt a multistep pathway to locate target sites and reconfigure the DNA to gain access. Work on several different enzymes has shown that in almost all cases base flipping, also known as nucleotide flipping, is a key feature of specific site recognition. In this chapter, we discuss some of the strategies that can be used to perform a kinetic characterization for DNA binding and nucleotide flipping. The resulting kinetic and thermodynamic framework provides a platform for understanding substrate specificity, mechanisms of inhibition, and the roles of important amino acids. We use a human DNA repair glycosylase called alkyladenine DNA glycosylase as a case study, because this is one of the best-characterized nucleotide-flipping enzymes. However, the approaches that are described can be readily adapted to study other enzymes, and future studies are needed to understand the mechanism of substrate recognition in each individual case. As more enzymes are characterized, we can hope to uncover which features of DNA searching and nucleotide flipping are fundamental features shared by many different families of DNA modifying enzymes, and which features are specific to a particular enzyme. Such an understanding provides reasonable models for less characterized enzymes that are important for epigenetic DNA modification and DNA repair pathways.
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Affiliation(s)
| | - Patrick J O'Brien
- University of Michigan Medical School, Ann Arbor, MI, United States.
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33
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Wilson KA, Wetmore SD. Combining crystallographic and quantum chemical data to understand DNA-protein π-interactions in nature. Struct Chem 2017. [DOI: 10.1007/s11224-017-0954-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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34
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Yang Z, Nejad MI, Varela JG, Price NE, Wang Y, Gates KS. A role for the base excision repair enzyme NEIL3 in replication-dependent repair of interstrand DNA cross-links derived from psoralen and abasic sites. DNA Repair (Amst) 2017; 52:1-11. [PMID: 28262582 PMCID: PMC5424475 DOI: 10.1016/j.dnarep.2017.02.011] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2017] [Accepted: 02/13/2017] [Indexed: 12/23/2022]
Abstract
Interstrand DNA-DNA cross-links are highly toxic lesions that are important in medicinal chemistry, toxicology, and endogenous biology. In current models of replication-dependent repair, stalling of a replication fork activates the Fanconi anemia pathway and cross-links are "unhooked" by the action of structure-specific endonucleases such as XPF-ERCC1 that make incisions flanking the cross-link. This process generates a double-strand break, which must be subsequently repaired by homologous recombination. Recent work provided evidence for a new, incision-independent unhooking mechanism involving intrusion of a base excision repair (BER) enzyme, NEIL3, into the world of cross-link repair. The evidence suggests that the glycosylase action of NEIL3 unhooks interstrand cross-links derived from an abasic site or the psoralen derivative trioxsalen. If the incision-independent NEIL3 pathway is blocked, repair reverts to the incision-dependent route. In light of the new model invoking participation of NEIL3 in cross-link repair, we consider the possibility that various BER glycosylases or other DNA-processing enzymes might participate in the unhooking of chemically diverse interstrand DNA cross-links.
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Affiliation(s)
- Zhiyu Yang
- University of Missouri Department of Chemistry, 125 Chemistry Building Columbia, MO 65211, United States
| | - Maryam Imani Nejad
- University of Missouri Department of Chemistry, 125 Chemistry Building Columbia, MO 65211, United States
| | - Jacqueline Gamboa Varela
- University of Missouri Department of Chemistry, 125 Chemistry Building Columbia, MO 65211, United States
| | - Nathan E Price
- University of California-Riverside, Department of Chemistry, 501 Big Springs Road Riverside, CA 92521-0403, United States
| | - Yinsheng Wang
- University of California-Riverside, Department of Chemistry, 501 Big Springs Road Riverside, CA 92521-0403, United States
| | - Kent S Gates
- University of Missouri Department of Chemistry, 125 Chemistry Building Columbia, MO 65211, United States; University of Missouri Department of Biochemistry, 125 Chemistry Building Columbia, MO 65211, United States.
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35
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Repair of oxidatively induced DNA damage by DNA glycosylases: Mechanisms of action, substrate specificities and excision kinetics. MUTATION RESEARCH-REVIEWS IN MUTATION RESEARCH 2017; 771:99-127. [PMID: 28342455 DOI: 10.1016/j.mrrev.2017.02.001] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Indexed: 02/07/2023]
Abstract
Endogenous and exogenous reactive species cause oxidatively induced DNA damage in living organisms by a variety of mechanisms. As a result, a plethora of mutagenic and/or cytotoxic products are formed in cellular DNA. This type of DNA damage is repaired by base excision repair, although nucleotide excision repair also plays a limited role. DNA glycosylases remove modified DNA bases from DNA by hydrolyzing the glycosidic bond leaving behind an apurinic/apyrimidinic (AP) site. Some of them also possess an accompanying AP-lyase activity that cleaves the sugar-phosphate chain of DNA. Since the first discovery of a DNA glycosylase, many studies have elucidated the mechanisms of action, substrate specificities and excision kinetics of these enzymes present in all living organisms. For this purpose, most studies used single- or double-stranded oligodeoxynucleotides with a single DNA lesion embedded at a defined position. High-molecular weight DNA with multiple base lesions has been used in other studies with the advantage of the simultaneous investigation of many DNA base lesions as substrates. Differences between the substrate specificities and excision kinetics of DNA glycosylases have been found when these two different substrates were used. Some DNA glycosylases possess varying substrate specificities for either purine-derived lesions or pyrimidine-derived lesions, whereas others exhibit cross-activity for both types of lesions. Laboratory animals with knockouts of the genes of DNA glycosylases have also been used to provide unequivocal evidence for the substrates, which had previously been found in in vitro studies, to be the actual substrates in vivo as well. On the basis of the knowledge gained from the past studies, efforts are being made to discover small molecule inhibitors of DNA glycosylases that may be used as potential drugs in cancer therapy.
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36
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Lenz SAP, Kohout JD, Wetmore SD. Hydrolytic Glycosidic Bond Cleavage in RNA Nucleosides: Effects of the 2'-Hydroxy Group and Acid-Base Catalysis. J Phys Chem B 2016; 120:12795-12806. [PMID: 27933981 DOI: 10.1021/acs.jpcb.6b09620] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Despite the inherent stability of glycosidic linkages in nucleic acids that connect the nucleobases to sugar-phosphate backbones, cleavage of these bonds is often essential for organism survival. The current study uses DFT (B3LYP) to provide a fundamental understanding of the hydrolytic deglycosylation of the natural RNA nucleosides (A, C, G, and U), offers a comparison to DNA hydrolysis, and examines the effects of acid, base, or simultaneous acid-base catalysis on RNA deglycosylation. By initially examining HCOO-···H2O mediated deglycosylation, the barriers for RNA hydrolysis were determined to be 30-38 kJ mol-1 higher than the corresponding DNA barriers, indicating that the 2'-OH group stabilizes the glycosidic bond. Although the presence of HCOO- as the base (i.e., to activate the water nucleophile) reduces the barrier for uncatalyzed RNA hydrolysis (i.e., unactivated H2O nucleophile) by ∼15-20 kJ mol-1, the extreme of base catalysis as modeled using a fully deprotonated water molecule (i.e., OH- nucleophile) decreases the uncatalyzed barriers by up to 65 kJ mol-1. Acid catalysis was subsequently examined by selectively protonating the hydrogen-bond acceptor sites of the RNA nucleobases, which results in an up to ∼80 kJ mol-1 barrier reduction relative to the corresponding uncatalyzed pathway. Interestingly, the nucleobase proton acceptor sites that result in the greatest barrier reductions match sites typically targeted in enzyme-catalyzed reactions. Nevertheless, simultaneous acid and base catalysis is the most beneficial way to enhance the reactivity of the glycosidic bonds in RNA, with the individual effects of each catalytic approach being weakened, additive, or synergistic depending on the strength of the base (i.e., degree of water nucleophile activation), the nucleobase, and the hydrogen-bonding acceptor site on the nucleobase. Together, the current contribution provides a greater understanding of the reactivity of the glycosidic bond in natural RNA nucleosides, and has fundamental implications for the function of RNA-targeting enzymes.
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Affiliation(s)
- Stefan A P Lenz
- Department of Chemistry and Biochemistry, University of Lethbridge , 4401 University Drive West, Lethbridge, Alberta T1K 3M4, Canada
| | - Johnathan D Kohout
- Department of Chemistry and Biochemistry, University of Lethbridge , 4401 University Drive West, Lethbridge, Alberta T1K 3M4, Canada
| | - Stacey D Wetmore
- Department of Chemistry and Biochemistry, University of Lethbridge , 4401 University Drive West, Lethbridge, Alberta T1K 3M4, Canada
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37
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Wickramaratne S, Banda DM, Ji S, Manlove AH, Malayappan B, Nuñez NN, Samson L, Campbell C, David SS, Tretyakova N. Base Excision Repair of N 6-Deoxyadenosine Adducts of 1,3-Butadiene. Biochemistry 2016; 55:6070-6081. [PMID: 27552084 DOI: 10.1021/acs.biochem.6b00553] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The important industrial and environmental carcinogen 1,3-butadiene (BD) forms a range of adenine adducts in DNA, including N6-(2-hydroxy-3-buten-1-yl)-2'-deoxyadenosine (N6-HB-dA), 1,N6-(2-hydroxy-3-hydroxymethylpropan-1,3-diyl)-2'-deoxyadenosine (1,N6-HMHP-dA), and N6,N6-(2,3-dihydroxybutan-1,4-diyl)-2'-deoxyadenosine (N6,N6-DHB-dA). If not removed prior to DNA replication, these lesions can contribute to A → T and A → G mutations commonly observed following exposure to BD and its metabolites. In this study, base excision repair of BD-induced 2'-deoxyadenosine (BD-dA) lesions was investigated. Synthetic DNA duplexes containing site-specific and stereospecific (S)-N6-HB-dA, (R,S)-1,N6-HMHP-dA, and (R,R)-N6,N6-DHB-dA adducts were prepared by a postoligomerization strategy. Incision assays with nuclear extracts from human fibrosarcoma (HT1080) cells have revealed that BD-dA adducts were recognized and cleaved by a BER mechanism, with the relative excision efficiency decreasing in the following order: (S)-N6-HB-dA > (R,R)-N6,N6-DHB-dA > (R,S)-1,N6-HMHP-dA. The extent of strand cleavage at the adduct site was decreased in the presence of BER inhibitor methoxyamine and by competitor duplexes containing known BER substrates. Similar strand cleavage assays conducted using several eukaryotic DNA glycosylases/lyases (AAG, Mutyh, hNEIL1, and hOGG1) have failed to observe correct incision products at the BD-dA lesion sites, suggesting that a different BER enzyme may be involved in the removal of BD-dA adducts in human cells.
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Affiliation(s)
- Susith Wickramaratne
- Masonic Cancer Center and Departments of Chemistry and Medicinal Chemistry, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Douglas M Banda
- Department of Chemistry, University of California , Davis, California 95616, United States
| | - Shaofei Ji
- Masonic Cancer Center and Departments of Chemistry and Medicinal Chemistry, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Amelia H Manlove
- Department of Chemistry, University of California , Davis, California 95616, United States
| | - Bhaskar Malayappan
- Masonic Cancer Center and Departments of Chemistry and Medicinal Chemistry, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Nicole N Nuñez
- Department of Chemistry, University of California , Davis, California 95616, United States
| | - Leona Samson
- Division of Biological Engineering, Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States
| | - Colin Campbell
- Department of Pharmacology, University of Minnesota , Minneapolis, Minnesota 55455, United States
| | - Sheila S David
- Department of Chemistry, University of California , Davis, California 95616, United States
| | - Natalia Tretyakova
- Masonic Cancer Center and Departments of Chemistry and Medicinal Chemistry, University of Minnesota , Minneapolis, Minnesota 55455, United States
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Kuznetsov NA, Kiryutin AS, Kuznetsova AA, Panov MS, Barsukova MO, Yurkovskaya AV, Fedorova OS. The formation of catalytically competent enzyme-substrate complex is not a bottleneck in lesion excision by human alkyladenine DNA glycosylase. J Biomol Struct Dyn 2016; 35:950-967. [PMID: 27025273 DOI: 10.1080/07391102.2016.1171800] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Human alkyladenine DNA glycosylase (AAG) protects DNA from alkylated and deaminated purine lesions. AAG flips out the damaged nucleotide from the double helix of DNA and catalyzes the hydrolysis of the N-glycosidic bond to release the damaged base. To understand better, how the step of nucleotide eversion influences the overall catalytic process, we performed a pre-steady-state kinetic analysis of AAG interaction with specific DNA-substrates, 13-base pair duplexes containing in the 7th position 1-N6-ethenoadenine (εA), hypoxanthine (Hx), and the stable product analogue tetrahydrofuran (F). The combination of the fluorescence of tryptophan, 2-aminopurine, and 1-N6-ethenoadenine was used to record conformational changes of the enzyme and DNA during the processes of DNA lesion recognition, damaged base eversion, excision of the N-glycosidic bond, and product release. The thermal stability of the duplexes characterized by the temperature of melting, Tm, and the rates of spontaneous opening of individual nucleotide base pairs were determined by NMR spectroscopy. The data show that the relative thermal stability of duplexes containing a particular base pair in position 7, (Tm(F/T) < Tm(εA/T) < Tm(Hx/T) < Tm(A/T)) correlates with the rate of reversible spontaneous opening of the base pair. However, in contrast to that, the catalytic lesion excision rate is two orders of magnitude higher for Hx-containing substrates than for substrates containing εA, proving that catalytic activity is not correlated with the stability of the damaged base pair. Our study reveals that the formation of the catalytically competent enzyme-substrate complex is not the bottleneck controlling the catalytic activity of AAG.
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Affiliation(s)
- N A Kuznetsov
- a Institute of Chemical Biology and Fundamental Medicine , Lavrentyev Ave. 8, Novosibirsk 630090 , Russia.,c Department of Natural Sciences , Novosibirsk State University , Pirogova St. 2, Novosibirsk 630090 , Russia
| | - A S Kiryutin
- b International Tomography Center SB RAS, Institutskaya 3a , Novosibirsk 630090 , Russia.,c Department of Natural Sciences , Novosibirsk State University , Pirogova St. 2, Novosibirsk 630090 , Russia
| | - A A Kuznetsova
- a Institute of Chemical Biology and Fundamental Medicine , Lavrentyev Ave. 8, Novosibirsk 630090 , Russia
| | - M S Panov
- b International Tomography Center SB RAS, Institutskaya 3a , Novosibirsk 630090 , Russia.,c Department of Natural Sciences , Novosibirsk State University , Pirogova St. 2, Novosibirsk 630090 , Russia
| | - M O Barsukova
- c Department of Natural Sciences , Novosibirsk State University , Pirogova St. 2, Novosibirsk 630090 , Russia
| | - A V Yurkovskaya
- b International Tomography Center SB RAS, Institutskaya 3a , Novosibirsk 630090 , Russia.,c Department of Natural Sciences , Novosibirsk State University , Pirogova St. 2, Novosibirsk 630090 , Russia
| | - O S Fedorova
- a Institute of Chemical Biology and Fundamental Medicine , Lavrentyev Ave. 8, Novosibirsk 630090 , Russia
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Structures of human ADAR2 bound to dsRNA reveal base-flipping mechanism and basis for site selectivity. Nat Struct Mol Biol 2016; 23:426-33. [PMID: 27065196 PMCID: PMC4918759 DOI: 10.1038/nsmb.3203] [Citation(s) in RCA: 138] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2016] [Accepted: 03/11/2016] [Indexed: 12/20/2022]
Abstract
ADARs (adenosine deaminases acting on RNA) are editing enzymes that convert adenosine (A) to inosine (I) in duplex RNA, a modification reaction with wide-ranging consequences on RNA function. Our understanding of the ADAR reaction mechanism, origin of editing site selectivity and effect of mutations is limited by the lack of high-resolution structural data for complexes of ADARs bound to substrate RNAs. Here we describe four crystal structures of the deaminase domain of human ADAR2 bound to RNA duplexes bearing a mimic of the deamination reaction intermediate. These structures, together with structure-guided mutagenesis and RNA-modification experiments, explain the basis for ADAR deaminase domain’s dsRNA specificity, its base-flipping mechanism, and nearest neighbor preferences. In addition, an ADAR2-specific RNA-binding loop was identified near the enzyme active site rationalizing differences in selectivity observed between different ADARs. Finally, our results provide a structural framework for understanding the effects of ADAR mutations associated with human disease.
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40
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Prakash A, Doublié S. Base Excision Repair in the Mitochondria. J Cell Biochem 2016; 116:1490-9. [PMID: 25754732 DOI: 10.1002/jcb.25103] [Citation(s) in RCA: 94] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2015] [Accepted: 01/23/2015] [Indexed: 01/01/2023]
Abstract
The 16.5 kb human mitochondrial genome encodes for 13 polypeptides, 22 tRNAs and 2 rRNAs involved in oxidative phosphorylation. Mitochondrial DNA (mtDNA), unlike its nuclear counterpart, is not packaged into nucleosomes and is more prone to the adverse effects of reactive oxygen species (ROS) generated during oxidative phosphorylation. The past few decades have witnessed an increase in the number of proteins observed to translocate to the mitochondria for the purposes of mitochondrial genome maintenance. The mtDNA damage produced by ROS, if not properly repaired, leads to instability and can ultimately manifest in mitochondrial dysfunction and disease. The base excision repair (BER) pathway is employed for the removal and consequently the repair of deaminated, oxidized, and alkylated DNA bases. Specialized enzymes called DNA glycosylases, which locate and cleave the damaged base, catalyze the first step of this highly coordinated repair pathway. This review focuses on members of the four human BER DNA glycosylase superfamilies and their subcellular localization in the mitochondria and/or the nucleus, as well as summarizes their structural features, biochemical properties, and functional role in the excision of damaged bases.
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Affiliation(s)
- Aishwarya Prakash
- Department of Microbiology and Molecular Genetics, The Markey Center for Molecular Genetics, University of Vermont, Stafford Hall, 95 Carrigan Drive, Burlington, Vermont
| | - Sylvie Doublié
- Department of Microbiology and Molecular Genetics, The Markey Center for Molecular Genetics, University of Vermont, Stafford Hall, 95 Carrigan Drive, Burlington, Vermont
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41
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Lenz SAP, Wetmore SD. Evaluating the Substrate Selectivity of Alkyladenine DNA Glycosylase: The Synergistic Interplay of Active Site Flexibility and Water Reorganization. Biochemistry 2016; 55:798-808. [PMID: 26765542 DOI: 10.1021/acs.biochem.5b01179] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Human alkyladenine DNA glycosylase (AAG) functions as part of the base excision repair (BER) pathway by cleaving the N-glycosidic bond that connects nucleobases to the sugar-phosphate backbone in DNA. AAG targets a range of structurally diverse purine lesions using nonspecific DNA-protein π-π interactions. Nevertheless, the enzyme discriminates against the natural purines and is inhibited by pyrimidine lesions. This study uses molecular dynamics simulations and seven different neutral or charged substrates, inhibitors, or canonical purines to probe how the bound nucleotide affects the conformation of the AAG active site, and the role of active site residues in dictating substrate selectivity. The neutral substrates form a common DNA-protein hydrogen bond, which results in a consistent active site conformation that maximizes π-π interactions between the aromatic residues and the nucleobase required for catalysis. Nevertheless, subtle differences in DNA-enzyme contacts for different neutral substrates explain observed differential catalytic efficiencies. In contrast, the exocyclic amino groups of the natural purines clash with active site residues, which leads to catalytically incompetent DNA-enzyme complexes due to significant reorganization of active site water. Specifically, water resides between the A nucleobase and the active site aromatic amino acids required for catalysis, while a shift in the position of the general base (E125) repositions (potentially nucleophilic) water away from G. Despite sharing common amino groups, the methyl substituents in cationic purine lesions (3MeA and 7MeG) exhibit repulsion with active site residues, which repositions the damaged bases in the active site in a manner that promotes their excision. Overall, we provide a structural explanation for the diverse yet discriminatory substrate selectivity of AAG and rationalize key kinetic data available for the enzyme. Specifically, our results highlight the complex interplay of many different DNA-protein interactions used by AAG to facilitate BER, as well as the crucial role of the general base and water (nucleophile) positioning. The insights gained from our work will aid the understanding of the function of other enzymes that use flexible active sites to exhibit diverse substrate specificity.
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Affiliation(s)
- Stefan A P Lenz
- Department of Chemistry and Biochemistry, University of Lethbridge , 4401 University Drive West, Lethbridge, Alberta, Canada T1K 3M4
| | - Stacey D Wetmore
- Department of Chemistry and Biochemistry, University of Lethbridge , 4401 University Drive West, Lethbridge, Alberta, Canada T1K 3M4
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42
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Trasviña-Arenas CH, Lopez-Castillo LM, Sanchez-Sandoval E, Brieba LG. Dispensability of the [4Fe-4S] cluster in novel homologues of adenine glycosylase MutY. FEBS J 2016; 283:521-40. [PMID: 26613369 DOI: 10.1111/febs.13608] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2015] [Revised: 11/15/2015] [Accepted: 11/24/2015] [Indexed: 01/31/2023]
Abstract
7,8-Dihydro-8-deoxyguanine (8oG) is one of the most common oxidative lesions in DNA. DNA polymerases misincorporate an adenine across from this lesion. Thus, 8oG is a highly mutagenic lesion responsible for G:C→T:A transversions. MutY is an adenine glycosylase, part of the base excision repair pathway that removes adenines, when mispaired with 8oG or guanine. Its catalytic domain includes a [4Fe-4S] cluster motif coordinated by cysteinyl ligands. When this cluster is absent, MutY activity is depleted and several studies concluded that the [4Fe-4S] cluster motif is an indispensable component for DNA binding, substrate recognition and enzymatic activity. In the present study, we identified 46 MutY homologues that lack the canonical cysteinyl ligands, suggesting an absence of the [4Fe-4S] cluster. A phylogenetic analysis groups these novel MutYs into two different clades. One clade is exclusive of the order Lactobacillales and another clade has a mixed composition of anaerobic and microaerophilic bacteria and species from the protozoan genus Entamoeba. Structural modeling and sequence analysis suggests that the loss of the [4Fe-4S] cluster is compensated by a convergent solution in which bulky amino acids substitute the [4Fe-4S] cluster. We functionally characterized MutYs from Lactobacillus brevis and Entamoeba histolytica as representative members from each clade and found that both enzymes are active adenine glycosylases. Furthermore, chimeric glycosylases, in which the [4Fe-4S] cluster of Escherichia coli MutY is replaced by the corresponding amino acids of LbY and EhY, are also active. Our data indicates that the [4Fe-4S] cluster plays a structural role in MutYs and evidences the existence of alternative functional solutions in nature.
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Affiliation(s)
- Carlos H Trasviña-Arenas
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Irapuato, Guanajuato, México
| | - Laura M Lopez-Castillo
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Irapuato, Guanajuato, México
| | - Eugenia Sanchez-Sandoval
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Irapuato, Guanajuato, México
| | - Luis G Brieba
- Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Irapuato, Guanajuato, México
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43
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Lenz SAP, Kellie JL, Wetmore SD. Glycosidic Bond Cleavage in DNA Nucleosides: Effect of Nucleobase Damage and Activation on the Mechanism and Barrier. J Phys Chem B 2015; 119:15601-12. [PMID: 26618397 DOI: 10.1021/acs.jpcb.5b10337] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Stefan A. P. Lenz
- Department of Chemistry and
Biochemistry, University of Lethbridge, 4401 University Drive West, Lethbridge, Alberta T1K 3M4, Canada
| | - Jennifer L. Kellie
- Department of Chemistry and
Biochemistry, University of Lethbridge, 4401 University Drive West, Lethbridge, Alberta T1K 3M4, Canada
| | - Stacey D. Wetmore
- Department of Chemistry and
Biochemistry, University of Lethbridge, 4401 University Drive West, Lethbridge, Alberta T1K 3M4, Canada
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44
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Zhang Y, O’Brien PJ. Repair of Alkylation Damage in Eukaryotic Chromatin Depends on Searching Ability of Alkyladenine DNA Glycosylase. ACS Chem Biol 2015; 10:2606-15. [PMID: 26317160 DOI: 10.1021/acschembio.5b00409] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Human alkyladenine DNA glycosylase (AAG) initiates the base excision repair pathway by excising alkylated and deaminated purine lesions. In vitro biochemical experiments demonstrate that AAG uses facilitated diffusion to efficiently search DNA to find rare sites of damage and suggest that electrostatic interactions are critical to the searching process. However, it remains an open question whether DNA searching limits the rate of DNA repair in vivo. We constructed AAG mutants with altered searching ability and measured their ability to protect yeast from alkylation damage in order to address this question. Each of the conserved arginine and lysine residues that are near the DNA binding interface were mutated, and the functional impacts were evaluated using kinetic and thermodynamic analysis. These mutations do not perturb catalysis of N-glycosidic bond cleavage, but they decrease the ability to capture rare lesion sites. Nonspecific and specific DNA binding properties are closely correlated, suggesting that the electrostatic interactions observed in the specific recognition complex are similarly important for DNA searching complexes. The ability of the mutant proteins to complement repair-deficient yeast cells is positively correlated with the ability of the proteins to search DNA in vitro, suggesting that cellular resistance to DNA alkylation is governed by the ability to find and efficiently capture cytotoxic lesions. It appears that chromosomal access is not restricted and toxic sites of alkylation damage are readily accessible to a searching protein.
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Affiliation(s)
- Yaru Zhang
- Chemical
Biology Program, University of Michigan, 210 Washtenaw Avenue, Ann Arbor, Michigan 48109-2216, United States
| | - Patrick J. O’Brien
- Chemical
Biology Program, University of Michigan, 210 Washtenaw Avenue, Ann Arbor, Michigan 48109-2216, United States
- Department
of Biological Chemistry, University of Michigan Medical School, 1150
W. Medical Center Dr., Ann Arbor, Michigan 48109-0600, United States
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45
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Bae B, Feklistov A, Lass-Napiorkowska A, Landick R, Darst SA. Structure of a bacterial RNA polymerase holoenzyme open promoter complex. eLife 2015; 4. [PMID: 26349032 PMCID: PMC4593229 DOI: 10.7554/elife.08504] [Citation(s) in RCA: 149] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2015] [Accepted: 09/03/2015] [Indexed: 01/17/2023] Open
Abstract
Initiation of transcription is a primary means for controlling gene expression. In bacteria, the RNA polymerase (RNAP) holoenzyme binds and unwinds promoter DNA, forming the transcription bubble of the open promoter complex (RPo). We have determined crystal structures, refined to 4.14 Å-resolution, of RPo containing Thermus aquaticus RNAP holoenzyme and promoter DNA that includes the full transcription bubble. The structures, combined with biochemical analyses, reveal key features supporting the formation and maintenance of the double-strand/single-strand DNA junction at the upstream edge of the −10 element where bubble formation initiates. The results also reveal RNAP interactions with duplex DNA just upstream of the −10 element and potential protein/DNA interactions that direct the DNA template strand into the RNAP active site. Addition of an RNA primer to yield a 4 base-pair post-translocated RNA:DNA hybrid mimics an initially transcribing complex at the point where steric clash initiates abortive initiation and σA dissociation. DOI:http://dx.doi.org/10.7554/eLife.08504.001 Inside cells, molecules of double-stranded DNA encode the instructions needed to make proteins. To make a protein, the two strands of DNA that make up a gene are separated and one strand acts as a template to make molecules of messenger ribonucleic acid (or mRNA for short). This process is called transcription. The mRNA is then used as a template to assemble the protein. An enzyme called RNA polymerase carries out transcription and is found in all cells ranging from bacteria to humans and other animals. Bacteria have the simplest form of RNA polymerase and provide an excellent system to study how it controls transcription. It is made up of several proteins that work together to make RNA using DNA as a template. However, it requires the help of another protein called sigma factor to direct it to regions of DNA called promoters, which are just before the start of the gene. When RNA polymerase and the sigma factor interact the resulting group of proteins is known as the RNA polymerase ‘holoenzyme’. Transcription takes place in several stages. To start with, the RNA polymerase holoenzyme locates and binds to promoter DNA. Next, it separates the two strands of DNA and exposes a portion of the template strand. At this point, the DNA and the holoenzyme are said to be in an ‘open promoter complex’ and the section of promoter DNA that is within it is known as a ‘transcription bubble’. However, it is not clear how RNA polymerase holoenzyme interacts with DNA in the open promoter complex. Bae, Feklistov et al. have now used X-ray crystallography to reveal the three-dimensional structure of the open promoter complex with an entire transcription bubble from a bacterium called Thermus aquaticus. The experiments show that there are several important interactions between RNA polymerase holoenzyme and promoter DNA. In particular, the sigma factor inserts into a region of the DNA at the start of the transcription bubble. This rearranges the DNA in a manner that allows the DNA to be exposed and contact the main part of the RNA polymerase. If the holoenyzyme fails to contact the DNA in this way, the holoenzyme does not bind properly to the promoter and transcription does not start. These findings build on previous work to provide a detailed structural framework for understanding how the RNA polymerase holoenzyme and DNA interact to form the open promoter complex. Another study by Bae et al.—which involved some of the same researchers as this study—reveals how another protein called CarD also binds to DNA at the start of the transcription bubble to stabilize the open promoter complex. DOI:http://dx.doi.org/10.7554/eLife.08504.002
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Affiliation(s)
- Brian Bae
- Laboratory for Molecular Biophysics, The Rockefeller University, New York, United States
| | - Andrey Feklistov
- Laboratory for Molecular Biophysics, The Rockefeller University, New York, United States
| | - Agnieszka Lass-Napiorkowska
- Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, St Louis, United States
| | - Robert Landick
- Department of Biochemistry, University of Wisconsin-madison, Madison, United States.,Department of Bacteriology, University of Wisconsin-Madison, Madison, United States
| | - Seth A Darst
- Laboratory for Molecular Biophysics, The Rockefeller University, New York, United States
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Li M, Ko T, Li S. High-resolution Digital Mapping of N-Methylpurines in Human Cells Reveals Modulation of Their Induction and Repair by Nearest-neighbor Nucleotides. J Biol Chem 2015; 290:23148-61. [PMID: 26240148 DOI: 10.1074/jbc.m115.676296] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2015] [Indexed: 11/06/2022] Open
Abstract
N-Methylpurines (NMPs), including N(7)-methylguanine (7MeG) and N(3)-methyladenine (3MeA), can be induced by environmental methylating agents, chemotherapeutics, and natural cellular methyl donors. In human cells, NMPs are repaired by the multi-step base excision repair pathway initiated by human alkyladenine glycosylase. Repair of NMPs has been shown to be affected by DNA sequence contexts. However, the nature of the sequence contexts has been poorly understood. We developed a sensitive method, LAF-Seq (Lesion-Adjoining Fragment Sequencing), which allows nucleotide-resolution digital mapping of DNA damage and repair in multiple genomic fragments of interest in human cells. We also developed a strategy that allows accurate measurement of the excision kinetics of NMP bases in vitro. We demonstrate that 3MeAs are induced to a much lower level by the SN2 methylating agent dimethyl sulfate and repaired much faster than 7MeGs in human fibroblasts. Induction of 7MeGs by dimethyl sulfate is affected by nearest-neighbor nucleotides, being enhanced at sites neighbored by a G or T on the 3' side, but impaired at sites neighbored by a G on the 5' side. Repair of 7MeGs is also affected by nearest-neighbor nucleotides, being slow if the lesions are between purines, especially Gs, and fast if the lesions are between pyrimidines, especially Ts. Excision of 7MeG bases from the DNA backbone by human alkyladenine glycosylase in vitro is similarly affected by nearest-neighbor nucleotides, suggesting that the effect of nearest-neighbor nucleotides on repair of 7MeGs in the cells is primarily achieved by modulating the initial step of the base excision repair process.
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Affiliation(s)
- Mingyang Li
- From the Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana 70803
| | - Tengyu Ko
- From the Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana 70803
| | - Shisheng Li
- From the Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana 70803
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47
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Chou WC, Hu LY, Hsiung CN, Shen CY. Initiation of the ATM-Chk2 DNA damage response through the base excision repair pathway. Carcinogenesis 2015; 36:832-40. [DOI: 10.1093/carcin/bgv079] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2015] [Accepted: 05/22/2015] [Indexed: 11/13/2022] Open
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48
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Admiraal SJ, O'Brien PJ. Base excision repair enzymes protect abasic sites in duplex DNA from interstrand cross-links. Biochemistry 2015; 54:1849-57. [PMID: 25679877 DOI: 10.1021/bi501491z] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Hydrolysis of the N-glycosyl bond between a nucleobase and deoxyribose leaves an abasic site within duplex DNA. The abasic site can react with exocyclic amines of nucleobases on the complementary strand to form interstrand DNA-DNA cross-links (ICLs). We find that several enzymes from the base excision repair (BER) pathway protect an abasic site on one strand of a DNA duplex from cross-linking with an amine on the opposing strand. Human alkyladenine DNA glycosylase (AAG) and Escherichia coli 3-methyladenine DNA glycosylase II (AlkA) accomplish this by binding tightly to the abasic site and sequestering it. AAG protects an abasic site opposite T, the product of its canonical glycosylase reaction, by a factor of ∼10-fold, as estimated from its inhibition of the reaction of an exogenous amine with the damaged DNA. Human apurinic/apyrimidinic site endonuclease 1 and E. coli endonuclease III both decrease the amount of ICL at equilibrium by generating a single-strand DNA nick at the abasic position as it is liberated from the cross-link. The reversibility of the reaction between amines and abasic sites allows BER enzymes to counter the potentially disruptive effects of this type of cross-link on DNA transactions.
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Affiliation(s)
- Suzanne J Admiraal
- Department of Biological Chemistry, University of Michigan Medical School , Ann Arbor, Michigan 48109-5606, United States
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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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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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