1
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Zhang J, Li Y, Huang W, Sun G, Ren H, Tang M. An ultrasensitive DNA-enhanced amplification method for detecting cfDNA drug-resistant mutations in non-small cell lung cancer with selective FEN-assisted degradation of dominant somatic fragments. Clin Chem Lab Med 2024:cclm-2024-0614. [PMID: 39089988 DOI: 10.1515/cclm-2024-0614] [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: 05/17/2024] [Accepted: 07/18/2024] [Indexed: 08/04/2024]
Abstract
OBJECTIVES Blood cell-free DNA (cfDNA) can be a new reliable tool for detecting epidermal growth factor receptor (EGFR) mutations in non-small cell lung cancer (NSCLC) patients. However, the currently reported cfDNA assays have a limited role in detecting drug-resistant mutations due to their deficiencies in sensitivity, stability, or mutation detection rate. METHODS We developed an Archaeoglobus fulgidus-derived flap endonuclease (Afu FEN)-based DNA-enhanced amplification system of mutated cfDNA by designing a pair of hairpin probes to anneal with wild-type cfDNA to form two 5'-flaps, allowing for the specific cleavage of wild-type cfDNA by Afu FEN. When the dominant wild-type somatic cfDNA fragments were cleaved by structure-recognition-specific Afu FEN, the proportion of mutated cfDNA in the reaction system was greatly enriched. As the amount of mutated cfDNA in the system was further increased by PCR amplification, the mutation status could be easily detected through first-generation sequencing. RESULTS In a mixture of synthetic wild-type and T790M EGFR DNA fragments, our new assay still could detect T790M mutation at the fg level with remarkably high sensitivity. We also tested its performance in detecting low variant allele frequency (VAF) mutations in clinical samples from NSCLC patients. The plasma cfDNA samples with low VAF (0.1 and 0.5 %) could be easily detected by DNA-enhanced amplification. CONCLUSIONS This system with enhanced amplification of mutated cfDNA is an effective tool used for the early screening and individualized targeted therapy of NSCLC by providing a rapid, sensitive, and economical way for the detection of drug-resistant mutations in tumors.
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Affiliation(s)
- Junhua Zhang
- The Key Laboratory of Geriatrics, Beijing Institute of Geriatrics, Institute of Geriatric Medicine, Chinese Academy of Medical Sciences, 117555 Beijing Hospital/National Center of Gerontology of National Health Commission , Beijing, P.R. China
| | - Yifei Li
- Clinical Biobank, Beijing Hospital, National Center of Gerontology, National Health Commission, Institute of Geriatric Medicine, Chinese Academy of Medical Sciences, Beijing, P.R. China
| | - Wei Huang
- The Key Laboratory of Geriatrics, Beijing Institute of Geriatrics, Institute of Geriatric Medicine, Chinese Academy of Medical Sciences, 117555 Beijing Hospital/National Center of Gerontology of National Health Commission , Beijing, P.R. China
| | - Gaoyuan Sun
- Clinical Biobank, Beijing Hospital, National Center of Gerontology, National Health Commission, Institute of Geriatric Medicine, Chinese Academy of Medical Sciences, Beijing, P.R. China
| | - Hongjun Ren
- Advanced Research Institute and Department of Chemistry, Taizhou University, Jiaojiang 318000, P.R. China
| | - Min Tang
- Department of Oncology, Beijing Hospital, National Center of Gerontology, Institute of Geriatric Medicine, Chinese Academy of Medical Sciences, Beijing, P.R. China
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2
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Krasikova YS, Maltseva EA, Khodyreva SN, Evdokimov AN, Rechkunova NI, Lavrik OI. Does the XPA-FEN1 Interaction Concern to Nucleotide Excision Repair or Beyond? Biomolecules 2024; 14:814. [PMID: 39062528 PMCID: PMC11274875 DOI: 10.3390/biom14070814] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2024] [Revised: 06/28/2024] [Accepted: 07/04/2024] [Indexed: 07/28/2024] Open
Abstract
Nucleotide excision repair (NER) is the most universal repair pathway, which removes a wide range of DNA helix-distorting lesions caused by chemical or physical agents. The final steps of this repair process are gap-filling repair synthesis and subsequent ligation. XPA is the central NER scaffolding protein factor and can be involved in post-incision NER stages. Replication machinery is loaded after the first incision of the damaged strand that is performed by the XPF-ERCC1 nuclease forming a damaged 5'-flap processed by the XPG endonuclease. Flap endonuclease I (FEN1) is a critical component of replication machinery and is absolutely indispensable for the maturation of newly synthesized strands. FEN1 also contributes to the long-patch pathway of base excision repair. Here, we use a set of DNA substrates containing a fluorescently labeled 5'-flap and different size gap to analyze possible repair factor-replication factor interactions. Ternary XPA-FEN1-DNA complexes with each tested DNA are detected. Furthermore, we demonstrate XPA-FEN1 complex formation in the absence of DNA due to protein-protein interaction. Functional assays reveal that XPA moderately inhibits FEN1 catalytic activity. Using fluorescently labeled XPA, formation of ternary RPA-XPA-FEN1 complex, where XPA accommodates FEN1 and RPA contacts simultaneously, can be proposed. We discuss possible functional roles of the XPA-FEN1 interaction in NER related DNA resynthesis and/or other DNA metabolic processes where XPA can be involved in the complex with FEN1.
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Affiliation(s)
- Yuliya S. Krasikova
- Institute of Chemical Biology and Fundamental Medicine, 630090 Novosibirsk, Russia; (Y.S.K.); (E.A.M.); (S.N.K.); (A.N.E.); (N.I.R.)
| | - Ekaterina A. Maltseva
- Institute of Chemical Biology and Fundamental Medicine, 630090 Novosibirsk, Russia; (Y.S.K.); (E.A.M.); (S.N.K.); (A.N.E.); (N.I.R.)
| | - Svetlana N. Khodyreva
- Institute of Chemical Biology and Fundamental Medicine, 630090 Novosibirsk, Russia; (Y.S.K.); (E.A.M.); (S.N.K.); (A.N.E.); (N.I.R.)
| | - Alexey N. Evdokimov
- Institute of Chemical Biology and Fundamental Medicine, 630090 Novosibirsk, Russia; (Y.S.K.); (E.A.M.); (S.N.K.); (A.N.E.); (N.I.R.)
| | - Nadejda I. Rechkunova
- Institute of Chemical Biology and Fundamental Medicine, 630090 Novosibirsk, Russia; (Y.S.K.); (E.A.M.); (S.N.K.); (A.N.E.); (N.I.R.)
| | - Olga I. Lavrik
- Institute of Chemical Biology and Fundamental Medicine, 630090 Novosibirsk, Russia; (Y.S.K.); (E.A.M.); (S.N.K.); (A.N.E.); (N.I.R.)
- Department of Natural Sciences, Novosibirsk State University, 630090 Novosibirsk, Russia
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3
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Lowder FC, Simmons LA. Bacillus subtilis encodes a discrete flap endonuclease that cleaves RNA-DNA hybrids. PLoS Genet 2023; 19:e1010585. [PMID: 37146086 PMCID: PMC10191290 DOI: 10.1371/journal.pgen.1010585] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Revised: 05/17/2023] [Accepted: 04/18/2023] [Indexed: 05/07/2023] Open
Abstract
The current model for Okazaki fragment maturation in bacteria invokes RNA cleavage by RNase H, followed by strand displacement synthesis and 5' RNA flap removal by DNA polymerase I (Pol I). RNA removal by Pol I is thought to occur through the 5'-3' flap endo/exonuclease (FEN) domain, located in the N-terminus of the protein. In addition to Pol I, many bacteria encode a second, Pol I-independent FEN. The contribution of Pol I and Pol I-independent FENs to DNA replication and genome stability remains unclear. In this work we purified Bacillus subtilis Pol I and FEN, then assayed these proteins on a variety of RNA-DNA hybrid and DNA-only substrates. We found that FEN is far more active than Pol I on nicked double-flap, 5' single flap, and nicked RNA-DNA hybrid substrates. We show that the 5' nuclease activity of B. subtilis Pol I is feeble, even during DNA synthesis when a 5' flapped substrate is formed modeling an Okazaki fragment intermediate. Examination of Pol I and FEN on DNA-only substrates shows that FEN is more active than Pol I on most substrates tested. Further experiments show that ΔpolA phenotypes are completely rescued by expressing the C-terminal polymerase domain while expression of the N-terminal 5' nuclease domain fails to complement ΔpolA. Cells lacking FEN (ΔfenA) show a phenotype in conjunction with an RNase HIII defect, providing genetic evidence for the involvement of FEN in Okazaki fragment processing. With these results, we propose a model where cells remove RNA primers using FEN while upstream Okazaki fragments are extended through synthesis by Pol I. Our model resembles Okazaki fragment processing in eukaryotes, where Pol δ catalyzes strand displacement synthesis followed by 5' flap cleavage using FEN-1. Together our work highlights the conservation of ordered steps for Okazaki fragment processing in cells ranging from bacteria to human.
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Affiliation(s)
- Frances Caroline Lowder
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Lyle A. Simmons
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan, United States of America
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4
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Zeng S, Chen J, Chai Q, Zhu T, Mao G. Label-free and low-background FEN1 sensing based on cleavage-induced ligation of bifunctional dumbbell DNA and in-situ signal readout. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2023; 290:122295. [PMID: 36603277 DOI: 10.1016/j.saa.2022.122295] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2022] [Revised: 12/25/2022] [Accepted: 12/28/2022] [Indexed: 06/17/2023]
Abstract
Flap endonuclease 1 (FEN1) is overexpressed in various types of human tumor cells and has been recognized as a promising biomarker for cancer diagnosis in recent years. In this work, a label-free fluorescent nanosensor for FEN1 detection was developed based on cleavage-induced ligation of bifunctional dumbbell DNA and in-situ signal readout by copper nanoparticles (CuNPs). The dumbbell DNA was rationally designed with a FEN1 cleavable 5' flap for target recognition and AT-riched stem-loop template for CuNPs formation. In the presence of FEN1, 5' overhanging DNA flap of dumbbell DNA was effectively removed to form a linkable nick site. After the ligation by T4 DNA ligase, the dumbbell DNA changed to exonuclease-resisted closed structure which enabled in-situ generation of fluorescent CuNPs that served as signal source for target quantification. The low background attributed to synergic digestion by exonucleases facilitated the highly sensitive detection of FEN1 with limit of detection of 0.007 U/mL. Additionally, the sensor was extended to the assay of FEN1 inhibitor (aurintricarboxylic acid) with reasonable results. Last but not least, the normal cells and tumor cells were distinguished unambiguously by this sensor according to the detected concentration difference of cellular FEN1, which indicates the robustness and practicability of this nanosensor.
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Affiliation(s)
- Shasha Zeng
- Hubei Key Laboratory of Pollutant Analysis & Reuse Technology, College of Chemistry and Chemical Engineering, Hubei Normal University, Huangshi 435002, Hubei, China
| | - Jinyang Chen
- Hubei Key Laboratory of Pollutant Analysis & Reuse Technology, College of Chemistry and Chemical Engineering, Hubei Normal University, Huangshi 435002, Hubei, China.
| | - Qingli Chai
- Hubei Key Laboratory of Pollutant Analysis & Reuse Technology, College of Chemistry and Chemical Engineering, Hubei Normal University, Huangshi 435002, Hubei, China
| | - Ting Zhu
- Hubei Key Laboratory of Pollutant Analysis & Reuse Technology, College of Chemistry and Chemical Engineering, Hubei Normal University, Huangshi 435002, Hubei, China
| | - Guobin Mao
- Institute of Synthetic Biology, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen 518055, Guangdong, China
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5
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Zhu Y, Zhu J, Gao Y, Shi J, Miao P. Electrochemical Determination of Flap Endonuclease 1 Activity Amplified by CRISPR/Cas12a Trans‐Cleavage**. ChemElectroChem 2023. [DOI: 10.1002/celc.202300020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/19/2023]
Affiliation(s)
- Yulin Zhu
- University of Science and Technology of China 230026 Hefei P. R. China
- Suzhou Institute of Biomedical Engineering and Technology Chinese Academy of Sciences 215163 Suzhou P. R. China
| | - Jinwen Zhu
- University of Science and Technology of China 230026 Hefei P. R. China
- Suzhou Institute of Biomedical Engineering and Technology Chinese Academy of Sciences 215163 Suzhou P. R. China
| | - Yan Gao
- Suzhou Institute of Biomedical Engineering and Technology Chinese Academy of Sciences 215163 Suzhou P. R. China
- Jinan Guoke Medical Technology Development Co., Ltd. 250103 Jinan P. R. China
| | - Jiayue Shi
- Suzhou Institute of Biomedical Engineering and Technology Chinese Academy of Sciences 215163 Suzhou P. R. China
| | - Peng Miao
- University of Science and Technology of China 230026 Hefei P. R. China
- Suzhou Institute of Biomedical Engineering and Technology Chinese Academy of Sciences 215163 Suzhou P. R. China
- Jinan Guoke Medical Technology Development Co., Ltd. 250103 Jinan P. R. China
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6
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Ma Y, Ma X, Bu L, Shan J, Liu D, Zhang L, Qi X, Chu Y, Wu H, Zou B, Zhou G. Flap Endonuclease-Induced Steric Hindrance Change Enables the Construction of Multiplex and Versatile Lateral Flow Strips for DNA Detection. Anal Chem 2022; 94:14725-14733. [PMID: 36223239 DOI: 10.1021/acs.analchem.2c03143] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A lateral flow strip (LFS) is an ideal tool for point-of-care testing (POCT), but traditional LFSs cannot be used for multiplex detection. Herein, a multiplex and versatile LFS based on flap endonuclease 1 (FEN1)-induced steric hindrance change (FISH-LFS) is proposed. In this method, multiplex PCR coupled with cascade invasive reactions was employed to yield single-stranded flaps, which were target-specific but independent of target sequences. Then, the amplicons were applied for FISH-LFS, and the single-stranded flaps would be efficiently captured by the complementary LFS-probes at different test lines. As flaps were cleaved from the specially designed hairpin probes, competition among flaps and hairpin probes would occur in capturing the probes at test lines. We enabled the hairpin probes to flow through the test lines while the flaps to stay at the test lines by making use of the difference in steric hindrance between hairpin probes and flaps. The assay is able to detect as low as two copies of blood pathogens (HBV, HCV, and HIV), to pick up as low as 0.1% mutants from wild-type gDNA, and to genotype 200 copies of SARS-CoV-2 variants α and β within 75 min at a conventional PCR engine. As the method is free of dye, a portable PCR engine could be used for a cost-effective multiplex detection on site. Results using an ultrafast mobile PCR system for FISH-LFS showed that as fast as 30 min was achieved for detecting three pathogens (HBV, HCV, and HIV) in blood, very suitable for POCT of pathogen screening. The method is convenient in operation, simple in instrumentation, specific in genotyping, and very easy in setting up multiplex POCT assays.
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Affiliation(s)
- Yi Ma
- Department of Clinical Pharmacy, State Key Laboratory of Analytical Chemistry for Life Science and Jiangsu Key Laboratory of Molecular Medicine, Affiliated Jinling Hospital, Medical School of Nanjing University, Nanjing 210002, China
| | - Xueping Ma
- Department of Clinical Pharmacy, State Key Laboratory of Analytical Chemistry for Life Science and Jiangsu Key Laboratory of Molecular Medicine, Affiliated Jinling Hospital, Medical School of Nanjing University, Nanjing 210002, China
| | - Li Bu
- Department of Clinical Pharmacy, State Key Laboratory of Analytical Chemistry for Life Science and Jiangsu Key Laboratory of Molecular Medicine, Affiliated Jinling Hospital, Medical School of Nanjing University, Nanjing 210002, China
| | - Jingwen Shan
- School of Pharmaceutical Sciences, Southern Medical University, Guangzhou 510515, China
| | - Danni Liu
- School of Life Science and Technology, China Pharmaceutical University, Nanjing 210009, China
| | - Likun Zhang
- Department of Clinical Pharmacy, State Key Laboratory of Analytical Chemistry for Life Science and Jiangsu Key Laboratory of Molecular Medicine, Affiliated Jinling Hospital, Medical School of Nanjing University, Nanjing 210002, China
| | - Xiemin Qi
- Department of Clinical Pharmacy, State Key Laboratory of Analytical Chemistry for Life Science and Jiangsu Key Laboratory of Molecular Medicine, Affiliated Jinling Hospital, Medical School of Nanjing University, Nanjing 210002, China
| | - Yanan Chu
- Department of Clinical Pharmacy, State Key Laboratory of Analytical Chemistry for Life Science and Jiangsu Key Laboratory of Molecular Medicine, Affiliated Jinling Hospital, Medical School of Nanjing University, Nanjing 210002, China
| | - Haiping Wu
- Department of Clinical Pharmacy, State Key Laboratory of Analytical Chemistry for Life Science and Jiangsu Key Laboratory of Molecular Medicine, Affiliated Jinling Hospital, Medical School of Nanjing University, Nanjing 210002, China.,School of Pharmaceutical Sciences, Southern Medical University, Guangzhou 510515, China
| | - Bingjie Zou
- Key Laboratory of Drug Quality Control and Pharmacovigilance of Ministry of Education, School of Pharmacy, China Pharmaceutical University, Nanjing 210009, China
| | - Guohua Zhou
- Department of Clinical Pharmacy, State Key Laboratory of Analytical Chemistry for Life Science and Jiangsu Key Laboratory of Molecular Medicine, Affiliated Jinling Hospital, Medical School of Nanjing University, Nanjing 210002, China.,School of Pharmaceutical Sciences, Southern Medical University, Guangzhou 510515, China.,School of Life Science and Technology, China Pharmaceutical University, Nanjing 210009, China.,School of Pharmacy, Nanjing Medical University, Nanjing 211166, China
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7
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Zhao Y, Fang X, Yu H, Fu Y, Zhao Y. Universal Exponential Amplification Confers Multilocus Detection of Mutation-Prone Virus. Anal Chem 2022; 94:927-933. [PMID: 34983181 DOI: 10.1021/acs.analchem.1c03702] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yue Zhao
- Institute of Analytical Chemistry and Instrument for Life Science, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi’an Jiaotong University, Xianning West Road, Xi’an, Shaanxi 710049, P. R. China
| | - Xiaoxing Fang
- Institute of Analytical Chemistry and Instrument for Life Science, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi’an Jiaotong University, Xianning West Road, Xi’an, Shaanxi 710049, P. R. China
| | - Huahang Yu
- Institute of Analytical Chemistry and Instrument for Life Science, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi’an Jiaotong University, Xianning West Road, Xi’an, Shaanxi 710049, P. R. China
| | - Youlan Fu
- Institute of Analytical Chemistry and Instrument for Life Science, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi’an Jiaotong University, Xianning West Road, Xi’an, Shaanxi 710049, P. R. China
| | - Yongxi Zhao
- Institute of Analytical Chemistry and Instrument for Life Science, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi’an Jiaotong University, Xianning West Road, Xi’an, Shaanxi 710049, P. R. China
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8
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Tang Y, Wei W, Liu Y, Liu S. Fluorescent Assay of FEN1 Activity with Nicking Enzyme-Assisted Signal Amplification Based on ZIF-8 for Imaging in Living Cells. Anal Chem 2021; 93:4960-4966. [PMID: 33687192 DOI: 10.1021/acs.analchem.0c05473] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Flap endonuclease 1 (FEN1) participates in both DNA replication and repair to maintain the stability and integrity of the genome. As a potential tumor marker, detecting FEN1 activity could be an effective strategy for cancer diagnosis. In this work, a fluorescence assay was developed for sensitive detection of FEN1 using biomineralized metal-organic framework nanoparticles (ZIF-8 NPs) to codeliver the encapsulated proteins and DNA probes to living cells. After uptake into cells, the biomineralized ZIF-8 NPs were biodegraded to release proteins and DNA probes under an acid environment. In the presence of FEN1, the cleaved flap triggered by FEN1 hybridized with a hairpin probe to fabricate a double-stranded DNA structure which had a cleavage site of the nicking enzyme, causing the fluorophore to move away from the quencher. Assisting the nicking enzyme, an amplified fluorescence signal was obtained after several recycling. Confocal imaging indicated that this fluorescence assay could distinguish cancer cells from normal cells. Therefore, this strategy would contribute to the prediction and diagnosis in early-stage cancer.
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Affiliation(s)
- Yunfei Tang
- Jiangsu Engineering Laboratory of Smart Carbon-Rich Materials and Device, Jiangsu Province Hi-Tech Key Laboratory for Bio-medical Research, School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, China
| | - Wei Wei
- Jiangsu Engineering Laboratory of Smart Carbon-Rich Materials and Device, Jiangsu Province Hi-Tech Key Laboratory for Bio-medical Research, School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, China
| | - Yong Liu
- Henan Key Laboratory of Polyoxometalate Chemistry, College of Chemistry and Chemical Engineering, Henan University, Kaifeng 475004, P. R. China
| | - Songqin Liu
- Jiangsu Engineering Laboratory of Smart Carbon-Rich Materials and Device, Jiangsu Province Hi-Tech Key Laboratory for Bio-medical Research, School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, China
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9
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Ye X, Fang X, Li Y, Wang L, Li X, Kong J. Sequence-Specific Probe-Mediated Isothermal Amplification for the Single-Copy Sensitive Detection of Nucleic Acid. Anal Chem 2019; 91:6738-6745. [PMID: 31046251 DOI: 10.1021/acs.analchem.9b00812] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
There is currently the lack of a method for precisely monitoring the progress of isothermal amplification reactions by means of sequence-specific fluorescent probes like the TaqMan probe used in the PCR system. Here, we created a circular fluorescent probe-mediated isothermal amplification (CFPA) method. This novel method uses two circular fluorescent probes and Bst DNA polymerase to construct an overlapping structure that can be cut off by flap structure-specific endonuclease 1, separating the fluorescence and quenching groups on the probes. The results showed single-copy sensitivity, ultrahigh specificity, stability (C.V. < 0.1), and anti-interference ability in detecting nucleic acid samples. A clinical trial demonstrated the perfect effectiveness of this method in the diagnosis of rotavirus infection and consistency with the gold standard method used in the clinic ( p > 0.05). In summary, we present a new, reliable, and precise isothermal amplification approach for applications in biomedical research and the clinical accurate diagnosis of pathogen infections.
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Affiliation(s)
- Xin Ye
- Department of Chemistry and Institutes of Biomedical Sciences , Fudan University , Shanghai 200433 , P. R. China
| | - Xueen Fang
- Department of Chemistry and Institutes of Biomedical Sciences , Fudan University , Shanghai 200433 , P. R. China
| | - Yang Li
- Shanghai Suchuang Diagnostic Products Co., Ltd, Shanghai 201318 , P. R. China.,Shanghai Suxin Biotechnology Co. Ltd, Shanghai 201318 , P. R. China
| | - Lijuan Wang
- Shanghai Suchuang Diagnostic Products Co., Ltd, Shanghai 201318 , P. R. China.,Shanghai Suxin Biotechnology Co. Ltd, Shanghai 201318 , P. R. China
| | - Xinxin Li
- Shanghai Suchuang Diagnostic Products Co., Ltd, Shanghai 201318 , P. R. China.,Shanghai Suxin Biotechnology Co. Ltd, Shanghai 201318 , P. R. China
| | - Jilie Kong
- Department of Chemistry and Institutes of Biomedical Sciences , Fudan University , Shanghai 200433 , P. R. China
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10
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Stodola JL, Burgers PM. Mechanism of Lagging-Strand DNA Replication in Eukaryotes. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1042:117-133. [PMID: 29357056 DOI: 10.1007/978-981-10-6955-0_6] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
This chapter focuses on the enzymes and mechanisms involved in lagging-strand DNA replication in eukaryotic cells. Recent structural and biochemical progress with DNA polymerase α-primase (Pol α) provides insights how each of the millions of Okazaki fragments in a mammalian cell is primed by the primase subunit and further extended by its polymerase subunit. Rapid kinetic studies of Okazaki fragment elongation by Pol δ illuminate events when the polymerase encounters the double-stranded RNA-DNA block of the preceding Okazaki fragment. This block acts as a progressive molecular break that provides both time and opportunity for the flap endonuclease 1 (FEN1) to access the nascent flap and cut it. The iterative action of Pol δ and FEN1 is coordinated by the replication clamp PCNA and produces a regulated degradation of the RNA primer, thereby preventing the formation of long-strand displacement flaps. Occasional long flaps are further processed by backup nucleases including Dna2.
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Affiliation(s)
- Joseph L Stodola
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, Saint Louis, MO, USA
| | - Peter M Burgers
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, Saint Louis, MO, USA.
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11
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Krzywkowski T, Nilsson M. Fidelity of RNA templated end-joining by chlorella virus DNA ligase and a novel iLock assay with improved direct RNA detection accuracy. Nucleic Acids Res 2017; 45:e161. [PMID: 29048593 PMCID: PMC5737725 DOI: 10.1093/nar/gkx708] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2017] [Accepted: 08/01/2017] [Indexed: 11/29/2022] Open
Abstract
Ligation-based nucleic acid detection methods are primarily limited to DNA, since they exhibit poor performance on RNA. This is attributed to reduced end-joining efficiency and/or fidelity of ligases. Interestingly, chlorella virus DNA ligase (PBCV-1 DNA ligase) has recently been shown to possess high RNA-templated DNA end-joining activity; however, its fidelity has not yet been systematically evaluated. Herein, we characterized PBCV-1 ligase for its RNA-templated end-joining fidelity at single base mismatches in 3′ and 5′ DNA probe termini and found an overall limited end-joining fidelity. To improve the specificity in PBCV-1 ligase-driven RNA detection assays, we utilized structure-specific 5′ exonucleolytic activity of Thermus aquaticus DNA polymerase, used in the invader assay. In the iLock (invader padLock) probe assay, padlock probe molecules are activated prior ligation thus the base at the probe ligation junction is read twice in order to aid successful DNA ligation: first, during structure-specific invader cleavage and then during sequence-specific DNA ligation. We report two distinct iLock probe activation mechanisms and systematically evaluate the assay specificity, including single nucleotide polymorphisms on RNA, mRNA and miRNA. We show significant increase in PBCV-1 ligation fidelity in the iLock probe assay configuration for RNA detection.
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Affiliation(s)
- Tomasz Krzywkowski
- Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, SE-171 65 Solna, Sweden
| | - Mats Nilsson
- Science for Life Laboratory, Department of Biochemistry and Biophysics, Stockholm University, SE-171 65 Solna, Sweden
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12
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Lyu Z, Whitman WB. Evolution of the archaeal and mammalian information processing systems: towards an archaeal model for human disease. Cell Mol Life Sci 2017; 74:183-212. [PMID: 27261368 PMCID: PMC11107668 DOI: 10.1007/s00018-016-2286-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2016] [Revised: 05/05/2016] [Accepted: 05/27/2016] [Indexed: 12/22/2022]
Abstract
Current evolutionary models suggest that Eukaryotes originated from within Archaea instead of being a sister lineage. To test this model of ancient evolution, we review recent studies and compare the three major information processing subsystems of replication, transcription and translation in the Archaea and Eukaryotes. Our hypothesis is that if the Eukaryotes arose within the archaeal radiation, their information processing systems will appear to be one of kind and not wholly original. Within the Eukaryotes, the mammalian or human systems are emphasized because of their importance in understanding health. Biochemical as well as genetic studies provide strong evidence for the functional similarity of archaeal homologs to the mammalian information processing system and their dissimilarity to the bacterial systems. In many independent instances, a simple archaeal system is functionally equivalent to more elaborate eukaryotic homologs, suggesting that evolution of complexity is likely an central feature of the eukaryotic information processing system. Because fewer components are often involved, biochemical characterizations of the archaeal systems are often easier to interpret. Similarly, the archaeal cell provides a genetically and metabolically simpler background, enabling convenient studies on the complex information processing system. Therefore, Archaea could serve as a parsimonious and tractable host for studying human diseases that arise in the information processing systems.
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Affiliation(s)
- Zhe Lyu
- Department of Microbiology, University of Georgia, Athens, GA, 30602, USA
| | - William B Whitman
- Department of Microbiology, University of Georgia, Athens, GA, 30602, USA.
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13
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Xu S, Cao S, Zou B, Yue Y, Gu C, Chen X, Wang P, Dong X, Xiang Z, Li K, Zhu M, Zhao Q, Zhou G. An alternative novel tool for DNA editing without target sequence limitation: the structure-guided nuclease. Genome Biol 2016; 17:186. [PMID: 27634179 PMCID: PMC5025552 DOI: 10.1186/s13059-016-1038-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Accepted: 08/05/2016] [Indexed: 01/31/2023] Open
Abstract
Engineered endonucleases are a powerful tool for editing DNA. However, sequence preferences may limit their application. We engineer a structure-guided endonuclease (SGN) composed of flap endonuclease-1 (FEN-1), which recognizes the 3′ flap structure, and the cleavage domain of Fok I (Fn1), which cleaves DNA strands. The SGN recognizes the target DNA on the basis of the 3′ flap structure formed between the target and the guide DNA (gDNA) and cut the target through its Fn1 dimerization. Our results show that the SGN, guided by a pair of gDNAs, cleaves transgenic reporter gene and endogenous genes in zebrafish embryonic genome.
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Affiliation(s)
- Shu Xu
- Department of Pharmacology, Jinling Hospital, School of Medicine, Nanjing University, No. 305 Zhongshan East Road, Nanjing, 210002, People's Republic of China
| | - Shasha Cao
- MOE Key Laboratory of Model Animal for Disease Study, State Key Laboratory of Pharmaceutical Biotechnology, Model Animal Research Center, Nanjing University, 12 Xuefu Road, Pukou High-tech Development Zone, Nanjing, 210061, People's Republic of China
| | - Bingjie Zou
- Department of Pharmacology, Jinling Hospital, School of Medicine, Nanjing University, No. 305 Zhongshan East Road, Nanjing, 210002, People's Republic of China
| | - Yunyun Yue
- MOE Key Laboratory of Model Animal for Disease Study, State Key Laboratory of Pharmaceutical Biotechnology, Model Animal Research Center, Nanjing University, 12 Xuefu Road, Pukou High-tech Development Zone, Nanjing, 210061, People's Republic of China
| | - Chun Gu
- MOE Key Laboratory of Model Animal for Disease Study, State Key Laboratory of Pharmaceutical Biotechnology, Model Animal Research Center, Nanjing University, 12 Xuefu Road, Pukou High-tech Development Zone, Nanjing, 210061, People's Republic of China
| | - Xin Chen
- MOE Key Laboratory of Model Animal for Disease Study, State Key Laboratory of Pharmaceutical Biotechnology, Model Animal Research Center, Nanjing University, 12 Xuefu Road, Pukou High-tech Development Zone, Nanjing, 210061, People's Republic of China
| | - Pei Wang
- MOE Key Laboratory of Model Animal for Disease Study, State Key Laboratory of Pharmaceutical Biotechnology, Model Animal Research Center, Nanjing University, 12 Xuefu Road, Pukou High-tech Development Zone, Nanjing, 210061, People's Republic of China
| | - Xiaohua Dong
- MOE Key Laboratory of Model Animal for Disease Study, State Key Laboratory of Pharmaceutical Biotechnology, Model Animal Research Center, Nanjing University, 12 Xuefu Road, Pukou High-tech Development Zone, Nanjing, 210061, People's Republic of China
| | - Zheng Xiang
- Department of Pharmacology, Jinling Hospital, School of Medicine, Nanjing University, No. 305 Zhongshan East Road, Nanjing, 210002, People's Republic of China
| | - Kai Li
- College of Pharmaceutical Science, Soochow University, No. 199, Renai Road, Suzhou, 215123, People's Republic of China
| | - Minsheng Zhu
- MOE Key Laboratory of Model Animal for Disease Study, State Key Laboratory of Pharmaceutical Biotechnology, Model Animal Research Center, Nanjing University, 12 Xuefu Road, Pukou High-tech Development Zone, Nanjing, 210061, People's Republic of China.
| | - Qingshun Zhao
- MOE Key Laboratory of Model Animal for Disease Study, State Key Laboratory of Pharmaceutical Biotechnology, Model Animal Research Center, Nanjing University, 12 Xuefu Road, Pukou High-tech Development Zone, Nanjing, 210061, People's Republic of China.
| | - Guohua Zhou
- Department of Pharmacology, Jinling Hospital, School of Medicine, Nanjing University, No. 305 Zhongshan East Road, Nanjing, 210002, People's Republic of China.
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14
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Resolving individual steps of Okazaki-fragment maturation at a millisecond timescale. Nat Struct Mol Biol 2016; 23:402-8. [PMID: 27065195 PMCID: PMC4857878 DOI: 10.1038/nsmb.3207] [Citation(s) in RCA: 80] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Accepted: 03/18/2016] [Indexed: 11/08/2022]
Abstract
DNA polymerase delta (Pol δ) is responsible for elongation and maturation of Okazaki fragments. Pol δ and the flap endonuclease FEN1, coordinated by the PCNA clamp, remove RNA primers and produce ligatable nicks. We studied this process in the Saccharomyces cerevisiae machinery at millisecond resolution. During elongation, PCNA increased the Pol δ catalytic rate by >30-fold. When Pol δ invaded double-stranded RNA-DNA representing unmatured Okazaki fragments, the incorporation rate of each nucleotide decreased successively to 10-20% that of the preceding nucleotide. Thus, the nascent flap acts as a progressive molecular brake on the polymerase, and consequently FEN1 cuts predominantly single-nucleotide flaps. Kinetic and enzyme-trapping experiments support a model in which a stable PCNA-DNA-Pol δ-FEN1 complex moves processively through iterative steps of nick translation, ultimately completely removing primer RNA. Finally, whereas elongation rates are under dynamic dNTP control, maturation rates are buffered against changes in dNTP concentrations.
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15
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Algasaier SI, Exell JC, Bennet IA, Thompson MJ, Gotham VJB, Shaw SJ, Craggs TD, Finger LD, Grasby JA. DNA and Protein Requirements for Substrate Conformational Changes Necessary for Human Flap Endonuclease-1-catalyzed Reaction. J Biol Chem 2016; 291:8258-68. [PMID: 26884332 PMCID: PMC4825025 DOI: 10.1074/jbc.m115.698993] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Revised: 02/04/2016] [Indexed: 12/02/2022] Open
Abstract
Human flap endonuclease-1 (hFEN1) catalyzes the essential removal of single-stranded flaps arising at DNA junctions during replication and repair processes. hFEN1 biological function must be precisely controlled, and consequently, the protein relies on a combination of protein and substrate conformational changes as a prerequisite for reaction. These include substrate bending at the duplex-duplex junction and transfer of unpaired reacting duplex end into the active site. When present, 5'-flaps are thought to thread under the helical cap, limiting reaction to flaps with free 5'-terminiin vivo Here we monitored DNA bending by FRET and DNA unpairing using 2-aminopurine exciton pair CD to determine the DNA and protein requirements for these substrate conformational changes. Binding of DNA to hFEN1 in a bent conformation occurred independently of 5'-flap accommodation and did not require active site metal ions or the presence of conserved active site residues. More stringent requirements exist for transfer of the substrate to the active site. Placement of the scissile phosphate diester in the active site required the presence of divalent metal ions, a free 5'-flap (if present), a Watson-Crick base pair at the terminus of the reacting duplex, and the intact secondary structure of the enzyme helical cap. Optimal positioning of the scissile phosphate additionally required active site conserved residues Tyr(40), Asp(181), and Arg(100)and a reacting duplex 5'-phosphate. These studies suggest a FEN1 reaction mechanism where junctions are bound and 5'-flaps are threaded (when present), and finally the substrate is transferred onto active site metals initiating cleavage.
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Affiliation(s)
- Sana I Algasaier
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
| | - Jack C Exell
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
| | - Ian A Bennet
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
| | - Mark J Thompson
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
| | - Victoria J B Gotham
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
| | - Steven J Shaw
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
| | - Timothy D Craggs
- the DNA:Protein Interactions Unit, School of Biochemistry, University of Bristol, Bristol BS8 1TD,United Kingdom
| | - L David Finger
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
| | - Jane A Grasby
- From the Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, United Kingdom and
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16
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Understanding DNA Repair in Hyperthermophilic Archaea: Persistent Gaps and Other Reasons to Focus on the Fork. ARCHAEA-AN INTERNATIONAL MICROBIOLOGICAL JOURNAL 2015; 2015:942605. [PMID: 26146487 PMCID: PMC4471258 DOI: 10.1155/2015/942605] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/26/2015] [Accepted: 05/21/2015] [Indexed: 11/17/2022]
Abstract
Although hyperthermophilic archaea arguably have a great need for efficient DNA repair, they lack members of several DNA repair protein families broadly conserved among bacteria and eukaryotes. Conversely, the putative DNA repair genes that do occur in these archaea often do not generate the expected phenotype when deleted. The prospect that hyperthermophilic archaea have some unique strategies for coping with DNA damage and replication errors has intellectual and technological appeal, but resolving this question will require alternative coping mechanisms to be proposed and tested experimentally. This review evaluates a combination of four enigmatic properties that distinguishes the hyperthermophilic archaea from all other organisms: DNA polymerase stalling at dU, apparent lack of conventional NER, lack of MutSL homologs, and apparent essentiality of homologous recombination proteins. Hypothetical damage-coping strategies that could explain this set of properties may provide new starting points for efforts to define how archaea differ from conventional models of DNA repair and replication fidelity.
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17
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Shah S, Dunten P, Stiteler A, Park CK, Horton NC. Structure and specificity of FEN-1 from Methanopyrus kandleri. Proteins 2014; 83:188-94. [PMID: 25354467 DOI: 10.1002/prot.24704] [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: 09/02/2014] [Revised: 10/06/2014] [Accepted: 10/18/2014] [Indexed: 11/06/2022]
Abstract
DNA repair is fundamental to genome stability and is found in all three domains of life. However many archaeal species, such as Methanopyrus kandleri, contain only a subset of the eukaryotic nucleotide excision repair (NER) homologs, and those present often contain significant differences compared to their eukaryotic homologs. To clarify the role of the NER XPG-like protein Mk0566 from M. kandleri, its biochemical activity and three-dimensional structure were investigated. Both were found to be more similar to human FEN-1 than human XPG, suggesting a biological role in replication and long-patch base excision repair rather than in NER.
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Affiliation(s)
- Santosh Shah
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona, 85721
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18
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Xu C, Maxwell BA, Suo Z. Conformational dynamics of Thermus aquaticus DNA polymerase I during catalysis. J Mol Biol 2014; 426:2901-2917. [PMID: 24931550 DOI: 10.1016/j.jmb.2014.06.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Revised: 06/02/2014] [Accepted: 06/07/2014] [Indexed: 11/15/2022]
Abstract
Despite the fact that DNA polymerases have been investigated for many years and are commonly used as tools in a number of molecular biology assays, many details of the kinetic mechanism they use to catalyze DNA synthesis remain unclear. Structural and kinetic studies have characterized a rapid, pre-catalytic open-to-close conformational change of the Finger domain during nucleotide binding for many DNA polymerases including Thermus aquaticus DNA polymerase I (Taq Pol), a thermostable enzyme commonly used for DNA amplification in PCR. However, little has been performed to characterize the motions of other structural domains of Taq Pol or any other DNA polymerase during catalysis. Here, we used stopped-flow Förster resonance energy transfer to investigate the conformational dynamics of all five structural domains of the full-length Taq Pol relative to the DNA substrate during nucleotide binding and incorporation. Our study provides evidence for a rapid conformational change step induced by dNTP binding and a subsequent global conformational transition involving all domains of Taq Pol during catalysis. Additionally, our study shows that the rate of the global transition was greatly increased with the truncated form of Taq Pol lacking the N-terminal domain. Finally, we utilized a mutant of Taq Pol containing a de novo disulfide bond to demonstrate that limiting protein conformational flexibility greatly reduced the polymerization activity of Taq Pol.
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Affiliation(s)
- Cuiling Xu
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA
| | - Brian A Maxwell
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA.,Ohio State Biophysics Program, The Ohio State University, Columbus, OH 43210, USA
| | - Zucai Suo
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210, USA.,Ohio State Biophysics Program, The Ohio State University, Columbus, OH 43210, USA
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19
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Nucleases in homologous recombination as targets for cancer therapy. FEBS Lett 2014; 588:2446-56. [DOI: 10.1016/j.febslet.2014.06.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Revised: 06/02/2014] [Accepted: 06/02/2014] [Indexed: 11/21/2022]
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20
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Archaeal genome guardians give insights into eukaryotic DNA replication and damage response proteins. ARCHAEA-AN INTERNATIONAL MICROBIOLOGICAL JOURNAL 2014; 2014:206735. [PMID: 24701133 PMCID: PMC3950489 DOI: 10.1155/2014/206735] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/21/2013] [Revised: 09/27/2013] [Accepted: 11/29/2013] [Indexed: 12/28/2022]
Abstract
As the third domain of life, archaea, like the eukarya and bacteria, must have robust DNA replication and repair complexes to ensure genome fidelity. Archaea moreover display a breadth of unique habitats and characteristics, and structural biologists increasingly appreciate these features. As archaea include extremophiles that can withstand diverse environmental stresses, they provide fundamental systems for understanding enzymes and pathways critical to genome integrity and stress responses. Such archaeal extremophiles provide critical data on the periodic table for life as well as on the biochemical, geochemical, and physical limitations to adaptive strategies allowing organisms to thrive under environmental stress relevant to determining the boundaries for life as we know it. Specifically, archaeal enzyme structures have informed the architecture and mechanisms of key DNA repair proteins and complexes. With added abilities to temperature-trap flexible complexes and reveal core domains of transient and dynamic complexes, these structures provide insights into mechanisms of maintaining genome integrity despite extreme environmental stress. The DNA damage response protein structures noted in this review therefore inform the basis for genome integrity in the face of environmental stress, with implications for all domains of life as well as for biomanufacturing, astrobiology, and medicine.
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21
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Matsui E, Urushibata Y, Abe J, Matsui I. Serial intermediates with a 1 nt 3'-flap and 5' variable-length flaps are formed by cooperative functioning of Pyrococcus horikoshii FEN-1 with either B or D DNA polymerases. Extremophiles 2014; 18:415-27. [PMID: 24509689 DOI: 10.1007/s00792-014-0627-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2013] [Accepted: 01/02/2014] [Indexed: 11/28/2022]
Abstract
Flap endonuclease-1 (FEN-1) plays important roles with DNA polymerases in DNA replication, repair and recombination. FEN-1 activity is elevated by the presence of a 1 nucleotide expansion at the 3' end in the upstream primer of substrates called "structures with a 1 nt 3'-flap", which appear to be the most preferable substrates for FEN-1; however, it is unclear how such substrates are generated in vivo. Here, we show that substrate production occurred by the cooperative function of FEN-1(phFEN-1) and Pyrococcus horikoshii DNA polymerase B (phPol B) or D (phPol D). Using various substrates, the activities of several phFEN-1 F79 mutants were compared with those of the wild type. Analysis of the activity profiles of these mutants led us to discriminate "structures with a 1 nt 3'-flap" from substrates with a 3' -projection longer than 2 nt or from those without a 3'-projection. When phFEN-1 processed a gap substrate with phPol B or phPol D, "structures with a 1 nt 3'-flap" were assumed the reaction intermediates. Furthermore, the phFEN-1 cleavage products with phPol B or D were from 1mer to 7mer, corresponding to the sizes of the strand-displacement products of these polymerases. This suggests that a series of 1 nt 3'-flap with 5'-variable length-flap configurations were generated as transient intermediates, in which the length of the 5'-flaps depended on the displacement distance of the downstream strand by phPol B or D. Therefore, phFEN-1 might act successively on displaced 5'-variable flaps.
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Affiliation(s)
- Eriko Matsui
- Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1 Central 6-9, Tsukuba, Ibaraki, 305-8566, Japan,
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Craggs TD, Hutton RD, Brenlla A, White MF, Penedo JC. Single-molecule characterization of Fen1 and Fen1/PCNA complexes acting on flap substrates. Nucleic Acids Res 2014; 42:1857-72. [PMID: 24234453 PMCID: PMC3919604 DOI: 10.1093/nar/gkt1116] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2013] [Revised: 10/21/2013] [Accepted: 10/22/2013] [Indexed: 11/21/2022] Open
Abstract
Flap endonuclease 1 (Fen1) is a highly conserved structure-specific nuclease that catalyses a specific incision to remove 5' flaps in double-stranded DNA substrates. Fen1 plays an essential role in key cellular processes, such as DNA replication and repair, and mutations that compromise Fen1 expression levels or activity have severe health implications in humans. The nuclease activity of Fen1 and other FEN family members can be stimulated by processivity clamps such as proliferating cell nuclear antigen (PCNA); however, the exact mechanism of PCNA activation is currently unknown. Here, we have used a combination of ensemble and single-molecule Förster resonance energy transfer together with protein-induced fluorescence enhancement to uncouple and investigate the substrate recognition and catalytic steps of Fen1 and Fen1/PCNA complexes. We propose a model in which upon Fen1 binding, a highly dynamic substrate is bent and locked into an open flap conformation where specific Fen1/DNA interactions can be established. PCNA enhances Fen1 recognition of the DNA substrate by further promoting the open flap conformation in a step that may involve facilitated threading of the 5' ssDNA flap. Merging our data with existing crystallographic and molecular dynamics simulations we provide a solution-based model for the Fen1/PCNA/DNA ternary complex.
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Affiliation(s)
- Timothy D. Craggs
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife, KY16 9SS, UK and Biomedical Sciences Research Complex, University of St Andrews, St Andrews, Fife KY16 9SS, UK
| | - Richard D. Hutton
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife, KY16 9SS, UK and Biomedical Sciences Research Complex, University of St Andrews, St Andrews, Fife KY16 9SS, UK
| | - Alfonso Brenlla
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife, KY16 9SS, UK and Biomedical Sciences Research Complex, University of St Andrews, St Andrews, Fife KY16 9SS, UK
| | - Malcolm F. White
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife, KY16 9SS, UK and Biomedical Sciences Research Complex, University of St Andrews, St Andrews, Fife KY16 9SS, UK
| | - J. Carlos Penedo
- SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, Fife, KY16 9SS, UK and Biomedical Sciences Research Complex, University of St Andrews, St Andrews, Fife KY16 9SS, UK
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23
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Kutyavin IV. Use of extremely short Förster resonance energy transfer probes in real-time polymerase chain reaction. Nucleic Acids Res 2013; 41:e191. [PMID: 24013564 PMCID: PMC3814350 DOI: 10.1093/nar/gkt782] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Described in the article is a new approach for the sequence-specific detection of nucleic acids in real-time polymerase chain reaction (PCR) using fluorescently labeled oligonucleotide probes. The method is based on the production of PCR amplicons, which fold into dumbbell-like secondary structures carrying a specially designed ‘probe-luring’ sequence at their 5′ ends. Hybridization of this sequence to a complementary ‘anchoring’ tail introduced at the 3′ end of a fluorescent probe enables the probe to bind to its target during PCR, and the subsequent probe cleavage results in the florescence signal. As it has been shown in the study, this amplicon-endorsed and guided formation of the probe-target duplex allows the use of extremely short oligonucleotide probes, up to tetranucleotides in length. In particular, the short length of the fluorescent probes makes possible the development of a ‘universal’ probe inventory that is relatively small in size but represents all possible sequence variations. The unparalleled cost-effectiveness of the inventory approach is discussed. Despite the short length of the probes, this new method, named Angler real-time PCR, remains highly sequence specific, and the results of the study indicate that it can be effectively used for quantitative PCR and the detection of polymorphic variations.
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24
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Kazak L, Reyes A, He J, Wood SR, Brea-Calvo G, Holen TT, Holt IJ. A cryptic targeting signal creates a mitochondrial FEN1 isoform with tailed R-Loop binding properties. PLoS One 2013; 8:e62340. [PMID: 23675412 PMCID: PMC3652857 DOI: 10.1371/journal.pone.0062340] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Accepted: 03/20/2013] [Indexed: 11/19/2022] Open
Abstract
A growing number of DNA transacting proteins is found in the nucleus and in mitochondria, including the DNA repair and replication protein Flap endonuclease 1, FEN1. Here we show a truncated FEN1 isoform is generated by alternative translation initiation, exposing a mitochondrial targeting signal. The shortened form of FEN1, which we term FENMIT, localizes to mitochondria, based on import into isolated organelles, immunocytochemistry and subcellular fractionation. In vitro FENMIT binds to flap structures containing a 5' RNA flap, and prefers such substrates to single-stranded RNA. FENMIT can also bind to R-loops, and to a lesser extent to D-loops. Exposing human cells to ethidium bromide results in the generation of RNA/DNA hybrids near the origin of mitochondrial DNA replication. FENMIT is recruited to the DNA under these conditions, and is released by RNase treatment. Moreover, high levels of recombinant FENMIT expression inhibit mtDNA replication, following ethidium bromide treatment. These findings suggest FENMIT interacts with RNA/DNA hybrids in mitochondrial DNA, such as those found at the origin of replication.
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Affiliation(s)
- Lawrence Kazak
- MRC-Mitochondrial Biology Unit, Wellcome Trust-MRC Building, Cambridge, United Kingdom
| | - Aurelio Reyes
- MRC-Mitochondrial Biology Unit, Wellcome Trust-MRC Building, Cambridge, United Kingdom
| | - Jiuya He
- MRC-Mitochondrial Biology Unit, Wellcome Trust-MRC Building, Cambridge, United Kingdom
| | - Stuart R. Wood
- MRC-Mitochondrial Biology Unit, Wellcome Trust-MRC Building, Cambridge, United Kingdom
| | - Gloria Brea-Calvo
- MRC-Mitochondrial Biology Unit, Wellcome Trust-MRC Building, Cambridge, United Kingdom
| | | | - Ian J. Holt
- MRC-National Institute for Medical Research, Mill Hill, London, United Kingdom
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25
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Abstract
First discovered as a structure-specific endonuclease that evolved to cut at the base of single-stranded flaps, flap endonuclease (FEN1) is now recognized as a central component of cellular DNA metabolism. Substrate specificity allows FEN1 to process intermediates of Okazaki fragment maturation, long-patch base excision repair, telomere maintenance, and stalled replication fork rescue. For Okazaki fragments, the RNA primer is displaced into a 5' flap and then cleaved off. FEN1 binds to the flap base and then threads the 5' end of the flap through its helical arch and active site to create a configuration for cleavage. The threading requirement prevents this active nuclease from cutting the single-stranded template between Okazaki fragments. FEN1 efficiency and specificity are critical to the maintenance of genome fidelity. Overall, recent advances in our knowledge of FEN1 suggest that it was an ancient protein that has been fine-tuned over eons to coordinate many essential DNA transactions.
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Affiliation(s)
- Lata Balakrishnan
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA.
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26
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Abstract
Although many approaches based on template replication were developed and applied in DNA detection, cross-contamination from amplicons is always a vexing problem. Thus, signal amplification is preferable for DNA detection due to its low risk of cross-contamination from amplicons. Here, we proposed a cascade enzymatic signal amplification (termed as CESA) by coupling Afu flap endonuclease with nicking endonuclease, including three steps: invasive signal amplification, flap ligation, and nicking endonuclease signal amplification. Because of the advantages of low risk of contamination, no sequence requirement of target DNA, and the universal reaction conditions for any target detection, CESA has a great potential in clinical diagnosis.
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Affiliation(s)
- Bingjie Zou
- Department of Pharmacology, Jinling Hospital, Nanjing University School of Medicine, Nanjing, China
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27
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Zou B, Ma Y, Wu H, Zhou G. Signal amplification by rolling circle amplification on universal flaps yielded from target-specific invasive reaction. Analyst 2012; 137:729-34. [DOI: 10.1039/c1an15886d] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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28
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Grasby JA, Finger LD, Tsutakawa SE, Atack JM, Tainer JA. Unpairing and gating: sequence-independent substrate recognition by FEN superfamily nucleases. Trends Biochem Sci 2011; 37:74-84. [PMID: 22118811 DOI: 10.1016/j.tibs.2011.10.003] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2011] [Revised: 10/07/2011] [Accepted: 10/14/2011] [Indexed: 01/13/2023]
Abstract
Structure-specific 5'-nucleases form a superfamily of evolutionarily conserved phosphodiesterases that catalyse a precise incision of a diverse range of DNA and RNA substrates in a sequence-independent manner. Superfamily members, such as flap endonucleases, exonuclease 1, DNA repair protein XPG, endonuclease GEN1 and the 5'-3'-exoribonucleases, play key roles in many cellular processes such as DNA replication and repair, recombination, transcription, RNA turnover and RNA interference. In this review, we discuss recent results that highlight the conserved architectures and active sites of the structure-specific 5'-nucleases. Despite substrate diversity, a common gating mechanism for sequence-independent substrate recognition and incision emerges, whereby double nucleotide unpairing of substrates is required to access the active site.
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Affiliation(s)
- Jane A Grasby
- Centre for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield, Sheffield S3 7HF, UK.
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29
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Structure and function of a novel endonuclease acting on branched DNA substrates. Biochem Soc Trans 2011; 39:145-9. [PMID: 21265762 DOI: 10.1042/bst0390145] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Branched DNA structures that occur during DNA repair and recombination must be efficiently processed by structure-specific endonucleases in order to avoid cell death. In the present paper, we summarize our screen for new interaction partners for the archaeal replication clamp that led to the functional characterization of a novel endonuclease family, dubbed NucS. Structural analyses of Pyrococcus abyssi NucS revealed an unexpected binding site for ssDNA (single-stranded DNA) that directs, together with the replication clamp, the nuclease activity of this protein towards ssDNA-dsDNA (double-stranded DNA) junctions. Our studies suggest that understanding the detailed architecture and dynamic behaviour of the NucS (nuclease specific for ssDNA)-PCNA (proliferating-cell nuclear antigen) complex with DNA will be crucial for identification of its physiologically relevant activities.
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30
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Mase T, Kubota K, Miyazono KI, Kawarabayasi Y, Tanokura M. Structure of flap endonuclease 1 from the hyperthermophilic archaeon Desulfurococcus amylolyticus. Acta Crystallogr Sect F Struct Biol Cryst Commun 2011; 67:209-13. [PMID: 21301087 PMCID: PMC3034609 DOI: 10.1107/s1744309110053030] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2010] [Accepted: 12/17/2010] [Indexed: 11/10/2022]
Abstract
Flap endonuclease 1 (FEN1) is a key enzyme in DNA repair and DNA replication. It is a structure-specific nuclease that removes 5'-overhanging flaps and the RNA/DNA primer during maturation of the Okazaki fragment. Homologues of FEN1 exist in a wide range of bacteria, archaea and eukaryotes. In order to further understand the structural basis of the DNA recognition, binding and cleavage mechanism of FEN1, the structure of FEN1 from the hyperthermophilic archaeon Desulfurococcus amylolyticus (DaFEN1) was determined at 2.00 Å resolution. The overall fold of DaFEN1 was similar to those of other archaeal FEN1 proteins; however, the helical clamp and the flexible loop exhibited a putative substrate-binding pocket with a unique conformation.
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Affiliation(s)
- Tomoko Mase
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Keiko Kubota
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Ken-ichi Miyazono
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
| | - Yutaka Kawarabayasi
- National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan
| | - Masaru Tanokura
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
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31
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Zou B, Ma Y, Wu H, Zhou G. Ultrasensitive DNA Detection by Cascade Enzymatic Signal Amplification Based on Afu Flap Endonuclease Coupled with Nicking Endonuclease. Angew Chem Int Ed Engl 2010; 50:7395-8. [DOI: 10.1002/anie.201001529] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2010] [Revised: 09/03/2010] [Indexed: 01/12/2023]
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32
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Zou B, Ma Y, Wu H, Zhou G. Ultrasensitive DNA Detection by Cascade Enzymatic Signal Amplification Based on Afu Flap Endonuclease Coupled with Nicking Endonuclease. Angew Chem Int Ed Engl 2010. [DOI: 10.1002/ange.201001529] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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33
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Dorjsuren D, Kim D, Maloney DJ, Wilson DM, Simeonov A. Complementary non-radioactive assays for investigation of human flap endonuclease 1 activity. Nucleic Acids Res 2010; 39:e11. [PMID: 21062821 PMCID: PMC3025571 DOI: 10.1093/nar/gkq1082] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
FEN1, a key participant in DNA replication and repair, is the major human flap endonuclease that recognizes and cleaves flap DNA structures. Deficiencies in FEN1 function or deletion of the fen1 gene have profound biological effects, including the suppression of repair of DNA damage incurred from the action of various genotoxic agents. Given the importance of FEN1 in resolving abnormal DNA structures, inhibitors of the enzyme carry a potential as enhancers of DNA-interactive anticancer drugs. To facilitate the studies of FEN1 activity and the search for novel inhibitors, we developed a pair of complementary-readout homogeneous assays utilizing fluorogenic donor/quencher and AlphaScreen chemiluminescence strategies. A previously reported FEN1 inhibitor 3-hydroxy-5-methyl-1-phenylthieno[2,3-d]pyrimidine-2,4(1H,3H)-dione displayed equal potency in the new assays, in agreement with its published IC50. The assays were optimized to a low 4 µl volume and used to investigate a set of small molecules, leading to the identification of previously-unreported FEN1 inhibitors, among which aurintricarboxylic acid and NSC-13755 (an arylstibonic derivative) displayed submicromolar potency (average IC50 of 0.59 and 0.93 µM, respectively). The availability of these simple complementary assays obviates the need for undesirable radiotracer-based assays and should facilitate efforts to develop novel inhibitors for this key biological target.
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Affiliation(s)
- Dorjbal Dorjsuren
- NIH Chemical Genomics Center, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD 20892-3370, USA
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34
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Morita R, Nakane S, Shimada A, Inoue M, Iino H, Wakamatsu T, Fukui K, Nakagawa N, Masui R, Kuramitsu S. Molecular mechanisms of the whole DNA repair system: a comparison of bacterial and eukaryotic systems. J Nucleic Acids 2010; 2010:179594. [PMID: 20981145 PMCID: PMC2957137 DOI: 10.4061/2010/179594] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Accepted: 07/27/2010] [Indexed: 11/20/2022] Open
Abstract
DNA is subjected to many endogenous and exogenous damages. All organisms have developed a complex network of DNA repair mechanisms. A variety of different DNA repair pathways have been reported: direct reversal, base excision repair, nucleotide excision repair, mismatch repair, and recombination repair pathways. Recent studies of the fundamental mechanisms for DNA repair processes have revealed a complexity beyond that initially expected, with inter- and intrapathway complementation as well as functional interactions between proteins involved in repair pathways. In this paper we give a broad overview of the whole DNA repair system and focus on the molecular basis of the repair machineries, particularly in Thermus thermophilus HB8.
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Affiliation(s)
- Rihito Morita
- Department of Biological Sciences, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan
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35
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Zheng L, Jia J, Finger LD, Guo Z, Zer C, Shen B. Functional regulation of FEN1 nuclease and its link to cancer. Nucleic Acids Res 2010; 39:781-94. [PMID: 20929870 PMCID: PMC3035468 DOI: 10.1093/nar/gkq884] [Citation(s) in RCA: 154] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Flap endonuclease-1 (FEN1) is a member of the Rad2 structure-specific nuclease family. FEN1 possesses FEN, 5′-exonuclease and gap-endonuclease activities. The multiple nuclease activities of FEN1 allow it to participate in numerous DNA metabolic pathways, including Okazaki fragment maturation, stalled replication fork rescue, telomere maintenance, long-patch base excision repair and apoptotic DNA fragmentation. Here, we summarize the distinct roles of the different nuclease activities of FEN1 in these pathways. Recent biochemical and genetic studies indicate that FEN1 interacts with more than 30 proteins and undergoes post-translational modifications. We discuss how FEN1 is regulated via these mechanisms. Moreover, FEN1 interacts with five distinct groups of DNA metabolic proteins, allowing the nuclease to be recruited to a specific DNA metabolic complex, such as the DNA replication machinery for RNA primer removal or the DNA degradosome for apoptotic DNA fragmentation. Some FEN1 interaction partners also stimulate FEN1 nuclease activities to further ensure efficient action in processing of different DNA structures. Post-translational modifications, on the other hand, may be critical to regulate protein–protein interactions and cellular localizations of FEN1. Lastly, we also review the biological significance of FEN1 as a tumor suppressor, with an emphasis on studies of human mutations and mouse models.
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Affiliation(s)
- Li Zheng
- Institute of Cell Biology and Genetics, College of Life Sciences, Zhejiang University, Hangzhou, China
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36
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Sengerová B, Tomlinson C, Atack JM, Williams R, Sayers JR, Williams NH, Grasby JA. Brønsted analysis and rate-limiting steps for the T5 flap endonuclease catalyzed hydrolysis of exonucleolytic substrates. Biochemistry 2010; 49:8085-93. [PMID: 20698567 DOI: 10.1021/bi100895j] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
During replication and repair flap endonucleases (FENs) catalyze endonucleolytic and exonucleolytic (EXO) DNA hydrolyses. Altering the leaving group pK(a), by replacing the departing nucleoside with analogues, had minimal effect on k(cat)/K(M) in a T5FEN-catalyzed EXO reaction, producing a very low Brønsted coefficient, β(lg). Investigation of the viscosity dependence of k(cat)/K(M) revealed that reactions of EXO substrates are rate limited by diffusional encounter of enzyme and substrate, explaining the small β(lg). However, the maximal single turnover rate of the FEN EXO reaction also yields a near zero β(lg). A low β(lg) was also observed when evaluating k(cat)/K(M) for D201I/D204S FEN-catalyzed reactions, even though these reactions were not affected by added viscogen. But an active site K83A mutant produced a β(lg) = -1.2 ± 0.10, closer to the value observed for solution hydrolysis of phosphate diesters. The pH-maximal rate profiles of the WT and K83A FEN reactions both reach a maximum at high pH and do not support an explanation of the data that involves catalysis of leaving group departure by Lys 83 functioning as a general acid. Instead, a rate-limiting physical step, such as substrate unpairing or helical arch ordering, that occurs after substrate association must kinetically hide an inherent large β(lg). It is suggested that K83 acts as an electrostatic catalyst that stabilizes the transition state for phosphate diester hydrolysis. When K83 is removed from the active site, chemistry becomes rate limiting and the leaving group sensitivity of the FEN-catalyzed reaction is revealed.
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Affiliation(s)
- Blanka Sengerová
- Centre for Chemical Biology, Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK
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Di Francia R, Frigeri F, Berretta M, Cecchin E, Orlando C, Pinto A, Pinzani P. Decision criteria for rational selection of homogeneous genotyping platforms for pharmacogenomics testing in clinical diagnostics. Clin Chem Lab Med 2010; 48:447-59. [PMID: 20192881 DOI: 10.1515/cclm.2010.112] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
BACKGROUND Genotyping is crucial for the identification of genetic markers underlying the development of neoplastic diseases and for determining individual variations in response to specific drugs. Technologies which can accurately identify genetic polymorphisms will dramatically affect routine diagnostic processes and future therapeutic developments in personalized medicine. However, such methods need to fulfill the principles of analytical validation to determine their suitability to assess nucleotide polymorphisms in target genes. APPROACH This article reviews recent developments in homogeneous technologies for the genotyping of single nucleotide polymorphisms. Here, homogeneous methods essentially refer to "single-tube" assays performed in a liquid phase. For the appropriate choice of any method, several criteria must be considered: 1) detection of known genetic variations; 2) analytical performance including specificity, sensitivity and robustness of the method; 3) availability of large platforms and required equipment; 4) suitability of platforms and tests for routine diagnostics; 5) suitability for high throughput implementation. CONTENT This review is intended to provide the reader with an understanding of these various technologies for pharmacogenomic testing in the routine clinical laboratory. A brief overview is provided on the available technologies for the detection of known mutations, a specific description of the homogeneous platforms currently employed in genotyping analysis, and considerations regarding the proper assessment of the analytical performance of these methods. Based on the criteria proposed here, potential users may evaluate advantages and limitations of the various analytical platforms and identify the most appropriate platform according to their specific setting and diagnostic needs.
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Affiliation(s)
- Raffaele Di Francia
- Hematology-Oncology and Stem Cell Transplantation Unit, National Cancer Institute, Fondazione G. Pascale IRCCS, Naples, Italy.
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38
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Substrate recognition and catalysis by flap endonucleases and related enzymes. Biochem Soc Trans 2010; 38:433-7. [DOI: 10.1042/bst0380433] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
FENs (flap endonucleases) and related FEN-like enzymes [EXO-1 (exonuclease-1), GEN-1 (gap endonuclease 1) and XPG (xeroderma pigmentosum complementation group G)] are a family of bivalent-metal-ion-dependent nucleases that catalyse structure-specific hydrolysis of DNA duplex-containing nucleic acid structures during DNA replication, repair and recombination. In the case of FENs, the ability to catalyse reactions on a variety of substrates has been rationalized as a result of combined functional and structural studies. Analyses of FENs also exemplify controversies regarding the two-metal-ion mechanism. However, kinetic studies of T5FEN (bacteriophage T5 FEN) reveal that a two-metal-ion-like mechanism for chemical catalysis is plausible. Consideration of the metallobiochemistry and the positioning of substrate in metal-free structures has led to the proposal that the duplex termini of substrates are unpaired in the catalytically active form and that FENs and related enzymes may recognize breathing duplex termini within more complex structures. An outstanding issue in FEN catalysis is the role played by the intermediate (I) domain arch or clamp. It has been proposed that FENs thread the 5′-portion of their substrates through this arch, which is wide enough to accommodate single-stranded, but not double-stranded, DNA. However, FENs exhibit gap endonuclease activity acting upon substrates that have a region of 5′-duplex. Moreover, the action of other FEN family members such as GEN-1, proposed to target Holliday junctions without termini, appears incompatible with a threading mechanism. An alterative is that the I domain is used as a clamp. A future challenge is to clarify the role of this domain in FENs and related enzymes.
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39
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Schomacher L, Schürer KA, Ciirdaeva E, McDermott P, Chong JPJ, Kramer W, Fritz HJ. Archaeal DNA uracil repair via direct strand incision: A minimal system reconstituted from purified components. DNA Repair (Amst) 2010; 9:438-47. [PMID: 20129830 DOI: 10.1016/j.dnarep.2010.01.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2009] [Revised: 12/21/2009] [Accepted: 01/05/2010] [Indexed: 11/19/2022]
Abstract
Hydrolytic deamination of DNA cytosine residues results in U/G mispairs, pre-mutagenic lesions threatening long-term genetic stability. Hence, DNA uracil repair is ubiquitous throughout all extant life forms and base excision repair, triggered by a uracil DNA glycosylase (UDG), is the mechanistic paradigm adopted, as it seems, by all bacteria and eukaryotes and a large fraction of archaea. However, members of the UDG superfamily of enzymes are absent from the extremely thermophilic archaeon Methanothermobacter thermautotrophicus DeltaH. This organism, as a hitherto unique case, initiates repair by direct strand incision next to the DNA-U residue, a reaction catalyzed by the DNA uridine endonuclease Mth212, an ExoIII homologue. To elucidate the detailed mechanism, in particular to identify the molecular partners contributing to this repair process, we reconstituted DNA uracil repair in vitro from only four purified enzymes of M. thermautotrophicus DeltaH. After incision at the 5'-side of a 2'-d-uridine residue by Mth212 DNA polymerase B (mthPolB) is able to take over the 3'-OH terminus and carry out repair synthesis generating a 5'-flap structure that is resolved by mthFEN, a 5'-flap endonuclease. Finally, DNA ligase seals the resulting nick. This defines mechanism and minimal enzymatic requirements of DNA-U repair in this organism.
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Affiliation(s)
- Lars Schomacher
- Institut für Mikrobiologie und Genetik, Georg-August-Universität Göttingen, Germany
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40
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Kutyavin IV. New approach to real-time nucleic acids detection: folding polymerase chain reaction amplicons into a secondary structure to improve cleavage of Forster resonance energy transfer probes in 5'-nuclease assays. Nucleic Acids Res 2009; 38:e29. [PMID: 19969535 PMCID: PMC2836566 DOI: 10.1093/nar/gkp1138] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
The article describes a new technology for real-time polymerase chain reaction (PCR) detection of nucleic acids. Similar to Taqman, this new method, named Snake, utilizes the 5′-nuclease activity of Thermus aquaticus (Taq) DNA polymerase that cleaves dual-labeled Förster resonance energy transfer (FRET) probes and generates a fluorescent signal during PCR. However, the mechanism of the probe cleavage in Snake is different. In this assay, PCR amplicons fold into stem–loop secondary structures. Hybridization of FRET probes to one of these structures leads to the formation of optimal substrates for the 5′-nuclease activity of Taq. The stem–loop structures in the Snake amplicons are introduced by the unique design of one of the PCR primers, which carries a special 5′-flap sequence. It was found that at a certain length of these 5′-flap sequences the folded Snake amplicons have very little, if any, effect on PCR yield but benefit many aspects of the detection process, particularly the signal productivity. Unlike Taqman, the Snake system favors the use of short FRET probes with improved fluorescence background. The head-to-head comparison study of Snake and Taqman revealed that these two technologies have more differences than similarities with respect to their responses to changes in PCR protocol, e.g. the variations in primer concentration, annealing time, PCR asymmetry. The optimal PCR protocol for Snake has been identified. The technology’s real-time performance was compared to a number of conventional assays including Taqman, 3′-MGB-Taqman, Molecular Beacon and Scorpion primers. The test trial showed that Snake supersedes the conventional assays in the signal productivity and detection of sequence variations as small as single nucleotide polymorphisms. Due to the assay’s cost-effectiveness and simplicity of design, the technology is anticipated to quickly replace all known conventional methods currently used for real-time nucleic acid detection.
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Affiliation(s)
- Igor V Kutyavin
- Perpetual Genomics, 18943 203rd Avenue NE, Woodinville, WA 98077, USA.
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41
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Molecular diversity and catalytic activity of Thermus DNA polymerases. Extremophiles 2009; 13:817-26. [PMID: 19597696 DOI: 10.1007/s00792-009-0269-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2009] [Accepted: 06/25/2009] [Indexed: 01/11/2023]
Abstract
Thermus aquaticus DNA polymerase (Taq polymerase) made the polymerase chain reaction feasible and led to a paradigm shift in genomic analysis. Other Thermus polymerases were reported to have comparable performance in PCR and there was an analysis of their properties in the 1990s. We re-evaluated our earlier phylogeny of Thermus species on the basis of 16S rDNA sequences and concluded that the genus could be divided into eight clades. We examined 22 representative isolates and isolated their DNA polymerase I genes. The eight most diverse polymerase genes were selected to represent the eight clades and cloned into an expression vector coding for a His-tag. Six of the eight polymerases were expressed so that there was sufficient protein for purification. The proteins were purified to homogeneity and examination of the biochemical characteristics showed that although they were competent to perform PCR, none was as thermostable as commercially available Taq polymerase; all had similar error-frequencies to Taq polymerase and all showed the expected 5'-3' exonuclease activity. We conclude that the initial selection of T. aquaticus for DNA polymerase purification was a far-reaching and fortuitous choice but simple mutagenesis procedures on other Thermus-derived polymerases should provide comparable thermostability for the PCR reaction.
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Finger LD, Blanchard MS, Theimer CA, Sengerová B, Singh P, Chavez V, Liu F, Grasby JA, Shen B. The 3'-flap pocket of human flap endonuclease 1 is critical for substrate binding and catalysis. J Biol Chem 2009; 284:22184-22194. [PMID: 19525235 DOI: 10.1074/jbc.m109.015065] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Flap endonuclease 1 (FEN1) proteins, which are present in all kingdoms of life, catalyze the sequence-independent hydrolysis of the bifurcated nucleic acid intermediates formed during DNA replication and repair. How FEN1s have evolved to preferentially cleave flap structures is of great interest especially in light of studies wherein mice carrying a catalytically deficient FEN1 were predisposed to cancer. Structural studies of FEN1s from phage to human have shown that, although they share similar folds, the FEN1s of higher organisms contain a 3'-extrahelical nucleotide (3'-flap) binding pocket. When presented with 5'-flap substrates having a 3'-flap, archaeal and eukaryotic FEN1s display enhanced reaction rates and cleavage site specificity. To investigate the role of this interaction, a kinetic study of human FEN1 (hFEN1) employing well defined DNA substrates was conducted. The presence of a 3'-flap on substrates reduced Km and increased multiple- and single turnover rates of endonucleolytic hydrolysis at near physiological salt concentrations. Exonucleolytic and fork-gap-endonucleolytic reactions were also stimulated by the presence of a 3'-flap, and the absence of a 3'-flap from a 5'-flap substrate was more detrimental to hFEN1 activity than removal of the 5'-flap or introduction of a hairpin into the 5'-flap structure. hFEN1 reactions were predominantly rate-limited by product release regardless of the presence or absence of a 3'-flap. Furthermore, the identity of the stable enzyme product species was deduced from inhibition studies to be the 5'-phosphorylated product. Together the results indicate that the presence of a 3'-flap is the critical feature for efficient hFEN1 substrate recognition and catalysis.
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Affiliation(s)
| | | | - Carla A Theimer
- Department of Chemistry, University at Albany, State University of New York, Albany, New York 12222
| | - Blanka Sengerová
- Centre for Chemical Biology, Department of Chemistry Krebs Institute, University of Sheffield, Sheffield, S3 7HF, United Kingdom
| | - Purnima Singh
- Division of Radiation Biology, Duarte, California 91010
| | - Valerie Chavez
- Division of Radiation Biology, Duarte, California 91010; Graduate School of Biological Sciences, City of Hope National Medical Center and Beckman Research Institute, Duarte, California 91010
| | - Fei Liu
- Department of Chemistry, University at Albany, State University of New York, Albany, New York 12222
| | - Jane A Grasby
- Centre for Chemical Biology, Department of Chemistry Krebs Institute, University of Sheffield, Sheffield, S3 7HF, United Kingdom
| | - Binghui Shen
- Division of Radiation Biology, Duarte, California 91010
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43
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Huang Q, Li Q. Characterization of the 5′ to 3′ nuclease activity of Thermus aquaticus DNA polymerase on fluorogenic double-stranded probes. Mol Cell Probes 2009; 23:188-94. [DOI: 10.1016/j.mcp.2009.04.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2008] [Revised: 03/25/2009] [Accepted: 04/09/2009] [Indexed: 11/27/2022]
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44
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Schomacher L, Chong JPJ, McDermott P, Kramer W, Fritz HJ. DNA uracil repair initiated by the archaeal ExoIII homologue Mth212 via direct strand incision. Nucleic Acids Res 2009; 37:2283-93. [PMID: 19240141 PMCID: PMC2673441 DOI: 10.1093/nar/gkp102] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2008] [Revised: 01/29/2009] [Accepted: 02/04/2009] [Indexed: 12/02/2022] Open
Abstract
No genes for any of the known uracil DNA glycosylases of the UDG superfamily are present in the genome of Methanothermobacter thermautotrophicus DeltaH, making it difficult to imagine how DNA-U repair might be initiated in this organism. Recently, Mth212, the ExoIII homologue of M. thermautotrophicus DeltaH has been characterized as a DNA uridine endonuclease, which suggested the possibility of a novel endonucleolytic entry mechanism for DNA uracil repair. With no system of genetic experimentation available, the problem was approached biochemically. Assays of DNA uracil repair in vitro, promoted by crude cellular extracts, provide unequivocal confirmation that this mechanism does indeed operate in M. thermautotrophicus DeltaH.
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Affiliation(s)
- Lars Schomacher
- Abteilung Molekulare Genetik und Präparative Molekularbiologie, Institut für Mikrobiologie und Genetik, Georg-August-Universität Göttingen, Grisebachstr. 8, 37077 Göttingen, Germany and Department of Biology (Area 5), P.O. Box 373, University of York, York YO10 5YW, UK
| | - James P. J. Chong
- Abteilung Molekulare Genetik und Präparative Molekularbiologie, Institut für Mikrobiologie und Genetik, Georg-August-Universität Göttingen, Grisebachstr. 8, 37077 Göttingen, Germany and Department of Biology (Area 5), P.O. Box 373, University of York, York YO10 5YW, UK
| | - Paul McDermott
- Abteilung Molekulare Genetik und Präparative Molekularbiologie, Institut für Mikrobiologie und Genetik, Georg-August-Universität Göttingen, Grisebachstr. 8, 37077 Göttingen, Germany and Department of Biology (Area 5), P.O. Box 373, University of York, York YO10 5YW, UK
| | - Wilfried Kramer
- Abteilung Molekulare Genetik und Präparative Molekularbiologie, Institut für Mikrobiologie und Genetik, Georg-August-Universität Göttingen, Grisebachstr. 8, 37077 Göttingen, Germany and Department of Biology (Area 5), P.O. Box 373, University of York, York YO10 5YW, UK
| | - Hans-Joachim Fritz
- Abteilung Molekulare Genetik und Präparative Molekularbiologie, Institut für Mikrobiologie und Genetik, Georg-August-Universität Göttingen, Grisebachstr. 8, 37077 Göttingen, Germany and Department of Biology (Area 5), P.O. Box 373, University of York, York YO10 5YW, UK
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Ehmsen KT, Heyer WD. A junction branch point adjacent to a DNA backbone nick directs substrate cleavage by Saccharomyces cerevisiae Mus81-Mms4. Nucleic Acids Res 2009; 37:2026-36. [PMID: 19211663 PMCID: PMC2665226 DOI: 10.1093/nar/gkp038] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The DNA structure-selective endonuclease Mus81-Mms4/Eme1 incises a number of nicked joint molecule substrates in vitro. 3′-flaps are an excellent in vitro substrate for Mus81-Mms4/Eme1. Mutants in MUS81 are synthetically lethal with mutations in the 5′-flap endonuclease FEN1/Rad27 in Saccharomyces cerevisiae and Schizosaccharomyces pombe. Considering the possibility for isoenergetic interconversion between 3′- and 5′- flaps, these data are consistent with the hypothesis that Mus81-Mms4/Eme1 acts on 3′-flaps in vivo. FEN1/Rad27 prefers dually flapped substrates and cleaves in a way that allows direct ligation of the resulting nick in the product duplex. Here we test the activity of Mus81-Mms4 on dually flapped substrates and find that in contrast to FEN1/Rad27, Mus81-Mms4 activity is impaired on such substrates, resulting in cleavage products that do not allow direct religation. We conclude that Mus81-Mms4, unlike FEN1/Rad27, does not prefer dually flapped substrates and is unlikely to function as a 3′-flapase counterpart to the 5′-flapase activity of FEN1/Rad27. We further find that joint molecule incision by Mus81-Mms4 occurs in a fashion determined by the branch point, regardless of the position of an upstream duplex end. These findings underscore the significance of a nick adjacent to a branch point for Mus81-Mms4 incision.
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Orchestration of Haemophilus influenzae RecJ Exonuclease by Interaction with Single-Stranded DNA-Binding Protein. J Mol Biol 2009; 385:1375-96. [DOI: 10.1016/j.jmb.2008.11.041] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2008] [Revised: 11/17/2008] [Accepted: 11/18/2008] [Indexed: 11/19/2022]
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Quantification of microRNAs, splicing isoforms, and homologous mRNAs with the invader assay. Methods Mol Biol 2009; 488:279-318. [PMID: 18982299 DOI: 10.1007/978-1-60327-475-3_20] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2023]
Abstract
The understanding of physiology and pathology requires accurate quantification of intracellular concentrations of important molecules such as unique RNA species. Accurate quantification of highly homologous messenger RNAs (mRNAs) (1-3), alternatively spliced mRNAs (4), and the short microRNAs (miRNAs) (5,6) has been successfully achieved using the Invader assay. This method directly detects specific RNA molecules in preparations of pure total cellular RNA (1- 100 ng) or in crude cell lysate (10(3)-10(4) cells) samples using an isothermal signal amplification process with a fluorescence resonance energy transfer (FRET)-based fluorescence readout. Features of the Invader assay include the ability to detect 1-10 RNA molecules per cell, to discriminate between RNAs that differ by a single base, and to precisely measure 1.2-fold changes in RNA expression. Further, an isothermal format and the ability to detect two different RNA molecules with a biplex format make the Invader assay suitable for high-throughput screening applications.
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Hutton RD, Roberts JA, Penedo JC, White MF. PCNA stimulates catalysis by structure-specific nucleases using two distinct mechanisms: substrate targeting and catalytic step. Nucleic Acids Res 2008; 36:6720-7. [PMID: 18948279 PMCID: PMC2588518 DOI: 10.1093/nar/gkn745] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The sliding clamp Proliferating Cell Nuclear Antigen (PCNA) functions as a recruiter and organizer of a wide variety of DNA modifying enzymes including nucleases, helicases, polymerases and glycosylases. The 5'-flap endonuclease Fen-1 is essential for Okazaki fragment processing in eukaryotes and archaea, and is targeted to the replication fork by PCNA. Crenarchaeal XPF, a 3'-flap endonuclease, is also stimulated by PCNA in vitro. Using a novel continuous fluorimetric assay, we demonstrate that PCNA activates these two nucleases by fundamentally different mechanisms. PCNA stimulates Fen-1 by increasing the enzyme's binding affinity for substrates, as suggested previously. However, PCNA activates XPF by increasing the catalytic rate constant by four orders of magnitude without affecting the K(M). PCNA may function as a platform upon which XPF exerts force to distort DNA substrates, destabilizing the substrate and/or stabilizing the transition state structure. This suggests that PCNA can function directly in supporting catalysis as an essential cofactor in some circumstances, a new role for a protein that is generally assumed to perform a passive targeting and organizing function in molecular biology. This could provide a mechanism for the exquisite control of nuclease activity targeted to specific circumstances, such as replication forks or damaged DNA with pre-loaded PCNA.
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Affiliation(s)
- Richard D Hutton
- Centre for Biomolecular Sciences and School of Physics, University of St Andrews, Fife, UK
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Nazarkina ZK, Lavrik OI, Khodyreva SN. Flap endonuclease 1 and its role in eukaryotic DNA metabolism. Mol Biol 2008. [DOI: 10.1134/s0026893308030035] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Nucleolar localization and dynamic roles of flap endonuclease 1 in ribosomal DNA replication and damage repair. Mol Cell Biol 2008; 28:4310-9. [PMID: 18443037 DOI: 10.1128/mcb.00200-08] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Despite the wealth of information available on the biochemical functions and our recent findings of its roles in genome stability and cancer avoidance of the structure-specific flap endonuclease 1 (FEN1), its cellular compartmentalization and dynamics corresponding to its involvement in various DNA metabolic pathways are not yet elucidated. Several years ago, we demonstrated that FEN1 migrates into the nucleus in response to DNA damage and under certain cell cycle conditions. In the current paper, we found that FEN1 is superaccumulated in the nucleolus and plays a role in the resolution of stalled DNA replication forks formed at the sites of natural replication fork barriers. In response to UV irradiation and upon phosphorylation, FEN1 migrates to nuclear plasma to participate in the resolution of UV cross-links on DNA, most likely employing its concerted action of exonuclease and gap-dependent endonuclease activities. Based on yeast complementation experiments, the mutation of Ser(187)Asp, mimicking constant phosphorylation, excludes FEN1 from nucleolar accumulation. The replacement of Ser(187) by Ala, eliminating the only phosphorylation site, retains FEN1 in nucleoli. Both of the mutations cause UV sensitivity, impair cellular UV damage repair capacity, and decline overall cellular survivorship.
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