1
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Alvaro-Aranda L, Petitalot A, Djeghmoum Y, Panigada D, Singh J, Ehlén Å, Vugic D, Martin C, Miron S, Contreras-Perez A, Nhiri N, Boucherit V, Lafitte P, Dumoulin I, Quiles F, Rouleau E, Jacquet E, Feliubadaló L, del Valle J, Sharan SK, Stoppa-Lyonnet D, Zinn-Justin S, Lázaro C, Caputo S, Carreira A. The BRCA2 R2645G variant increases DNA binding and induces hyper-recombination. Nucleic Acids Res 2024; 52:6964-6976. [PMID: 38142462 PMCID: PMC11229362 DOI: 10.1093/nar/gkad1222] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Revised: 11/30/2023] [Accepted: 12/12/2023] [Indexed: 12/26/2023] Open
Abstract
BRCA2 tumor suppressor protein ensures genome integrity by mediating DNA repair via homologous recombination (HR). This function is executed in part by its canonical DNA binding domain located at the C-terminus (BRCA2CTD), the only folded domain of the protein. Most germline pathogenic missense variants are located in this highly conserved region which binds to single-stranded DNA (ssDNA) and to the acidic protein DSS1. These interactions are essential for the HR function of BRCA2. Here, we report that the variant R2645G, identified in breast cancer and located at the DSS1 interface, unexpectedly increases the ssDNA binding activity of BRCA2CTDin vitro. Human cells expressing this variant display a hyper-recombination phenotype, chromosomal instability in the form of chromatid gaps when exposed to DNA damage, and increased PARP inhibitor sensitivity. In mouse embryonic stem cells (mES), this variant alters viability and confers sensitivity to cisplatin and Mitomycin C. These results suggest that BRCA2 interaction with ssDNA needs to be tightly regulated to limit HR and prevent chromosomal instability and we propose that this control mechanism involves DSS1. Given that several missense variants located within this region have been identified in breast cancer patients, these findings might have clinical implications for carriers.
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Affiliation(s)
- Lucia Alvaro-Aranda
- Genome Instability and Cancer Predisposition Laboratory, Centro de Biologia Molecular Severo Ochoa (CBMSO), CSIC-UAM, Madrid 28049, Spain
| | - Ambre Petitalot
- Department of Genetics, Institut Curie, Paris 75005, France
- PSL Research University, Paris 75005, France
| | - Yasmina Djeghmoum
- Institut Curie, PSL Research University, CNRS, UMR3348, F-91405 Orsay, France
- Paris-Saclay University CNRS, UMR3348, F-91405 Orsay, France
| | - Davide Panigada
- Institut Curie, PSL Research University, CNRS, UMR3348, F-91405 Orsay, France
- Paris-Saclay University CNRS, UMR3348, F-91405 Orsay, France
| | - Jenny Kaur Singh
- Institut Curie, PSL Research University, CNRS, UMR3348, F-91405 Orsay, France
- Paris-Saclay University CNRS, UMR3348, F-91405 Orsay, France
| | - Åsa Ehlén
- Institut Curie, PSL Research University, CNRS, UMR3348, F-91405 Orsay, France
- Paris-Saclay University CNRS, UMR3348, F-91405 Orsay, France
| | - Domagoj Vugic
- Institut Curie, PSL Research University, CNRS, UMR3348, F-91405 Orsay, France
- Paris-Saclay University CNRS, UMR3348, F-91405 Orsay, France
| | - Charlotte Martin
- Institut Curie, PSL Research University, CNRS, UMR3348, F-91405 Orsay, France
- Paris-Saclay University CNRS, UMR3348, F-91405 Orsay, France
| | - Simona Miron
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Paris-Saclay University, 91190 Gif-sur-Yvette, France
| | - Aida Contreras-Perez
- Genome Instability and Cancer Predisposition Laboratory, Centro de Biologia Molecular Severo Ochoa (CBMSO), CSIC-UAM, Madrid 28049, Spain
| | - Naima Nhiri
- Institut de Chimie des Substances Naturelles, Paris-Saclay University, CNRS, 91190 Gif-sur-Yvette, France
| | - Virginie Boucherit
- Institut Curie, PSL Research University, CNRS, UMR3348, F-91405 Orsay, France
- Paris-Saclay University CNRS, UMR3348, F-91405 Orsay, France
| | - Philippe Lafitte
- Department of Genetics, Institut Curie, Paris 75005, France
- PSL Research University, Paris 75005, France
| | - Isaac Dumoulin
- Institut Curie, PSL Research University, CNRS, UMR3348, F-91405 Orsay, France
- Paris-Saclay University CNRS, UMR3348, F-91405 Orsay, France
| | - Francisco Quiles
- Hereditary Cancer Program, Catalan Institute of Oncology (ICO), Hereditary Cancer Group, Molecular Mechanisms and Experimental Therapy in Oncology Program, Institut d’Investigació Biomèdica de Bellvitge (IDIBELL), L’Hospitalet de Llobregat, Spain
- Ciber Oncología (CIBERONC), Instituto Salud Carlos III, Madrid, Spain
| | - Etienne Rouleau
- Department of Genetics, Institut Curie, Paris 75005, France
- PSL Research University, Paris 75005, France
| | - Eric Jacquet
- Institut de Chimie des Substances Naturelles, Paris-Saclay University, CNRS, 91190 Gif-sur-Yvette, France
| | - Lidia Feliubadaló
- Hereditary Cancer Program, Catalan Institute of Oncology (ICO), Hereditary Cancer Group, Molecular Mechanisms and Experimental Therapy in Oncology Program, Institut d’Investigació Biomèdica de Bellvitge (IDIBELL), L’Hospitalet de Llobregat, Spain
- Ciber Oncología (CIBERONC), Instituto Salud Carlos III, Madrid, Spain
| | - Jesús del Valle
- Hereditary Cancer Program, Catalan Institute of Oncology (ICO), Hereditary Cancer Group, Molecular Mechanisms and Experimental Therapy in Oncology Program, Institut d’Investigació Biomèdica de Bellvitge (IDIBELL), L’Hospitalet de Llobregat, Spain
- Ciber Oncología (CIBERONC), Instituto Salud Carlos III, Madrid, Spain
| | - Shyam K Sharan
- Mouse Cancer Genetics Program, Center for Cancer Research, National Cancer Institute, Frederick, Maryland 21702, USA
| | - Dominique Stoppa-Lyonnet
- Department of Genetics, Institut Curie, Paris 75005, France
- Paris-Cité University, Paris, France
- INSERM U830, Institut Curie, Paris 75005, France
| | - Sophie Zinn-Justin
- Institute for Integrative Biology of the Cell (I2BC), CEA, CNRS, Paris-Saclay University, 91190 Gif-sur-Yvette, France
| | - Conxi Lázaro
- Hereditary Cancer Program, Catalan Institute of Oncology (ICO), Hereditary Cancer Group, Molecular Mechanisms and Experimental Therapy in Oncology Program, Institut d’Investigació Biomèdica de Bellvitge (IDIBELL), L’Hospitalet de Llobregat, Spain
- Ciber Oncología (CIBERONC), Instituto Salud Carlos III, Madrid, Spain
| | - Sandrine M Caputo
- Department of Genetics, Institut Curie, Paris 75005, France
- PSL Research University, Paris 75005, France
| | - Aura Carreira
- Genome Instability and Cancer Predisposition Laboratory, Centro de Biologia Molecular Severo Ochoa (CBMSO), CSIC-UAM, Madrid 28049, Spain
- Institut Curie, PSL Research University, CNRS, UMR3348, F-91405 Orsay, France
- Paris-Saclay University CNRS, UMR3348, F-91405 Orsay, France
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2
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Le HP, Heyer WD, Liu J. Guardians of the Genome: BRCA2 and Its Partners. Genes (Basel) 2021; 12:genes12081229. [PMID: 34440403 PMCID: PMC8394001 DOI: 10.3390/genes12081229] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Revised: 08/04/2021] [Accepted: 08/06/2021] [Indexed: 12/28/2022] Open
Abstract
The tumor suppressor BRCA2 functions as a central caretaker of genome stability, and individuals who carry BRCA2 mutations are predisposed to breast, ovarian, and other cancers. Recent research advanced our mechanistic understanding of BRCA2 and its various interaction partners in DNA repair, DNA replication support, and DNA double-strand break repair pathway choice. In this review, we discuss the biochemical and structural properties of BRCA2 and examine how these fundamental properties contribute to DNA repair and replication fork stabilization in living cells. We highlight selected BRCA2 binding partners and discuss their role in BRCA2-mediated homologous recombination and fork protection. Improved mechanistic understanding of how BRCA2 functions in genome stability maintenance can enable experimental evidence-based evaluation of pathogenic BRCA2 mutations and BRCA2 pseudo-revertants to support targeted therapy.
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Affiliation(s)
- Hang Phuong Le
- Department of Microbiology and Molecular Genetics, University of California, Davis, CA 95616, USA; (H.P.L.); (W.-D.H.)
| | - Wolf-Dietrich Heyer
- Department of Microbiology and Molecular Genetics, University of California, Davis, CA 95616, USA; (H.P.L.); (W.-D.H.)
- Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
| | - Jie Liu
- Department of Microbiology and Molecular Genetics, University of California, Davis, CA 95616, USA; (H.P.L.); (W.-D.H.)
- Correspondence: ; Tel.: +1-530-752-3016
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3
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Le HP, Ma X, Vaquero J, Brinkmeyer M, Guo F, Heyer WD, Liu J. DSS1 and ssDNA regulate oligomerization of BRCA2. Nucleic Acids Res 2020; 48:7818-7833. [PMID: 32609828 PMCID: PMC7641332 DOI: 10.1093/nar/gkaa555] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Revised: 06/16/2020] [Accepted: 06/19/2020] [Indexed: 01/27/2023] Open
Abstract
The tumor suppressor BRCA2 plays a key role in initiating homologous recombination by facilitating RAD51 filament formation on single-stranded DNA. The small acidic protein DSS1 is a crucial partner to BRCA2 in this process. In vitro and in cells (1,2), BRCA2 associates into oligomeric complexes besides also existing as monomers. A dimeric structure was further characterized by electron microscopic analysis (3), but the functional significance of the different BRCA2 assemblies remains to be determined. Here, we used biochemistry and electron microscopic imaging to demonstrate that the multimerization of BRCA2 is counteracted by DSS1 and ssDNA. When validating the findings, we identified three self-interacting regions and two types of self-association, the N-to-C terminal and the N-to-N terminal interactions. The N-to-C terminal self-interaction of BRCA2 is sensitive to DSS1 and ssDNA. The N-to-N terminal self-interaction is modulated by ssDNA. Our results define a novel role of DSS1 to regulate BRCA2 in an RPA-independent fashion. Since DSS1 is required for BRCA2 function in recombination, we speculate that the monomeric and oligomeric forms of BRCA2 might be active for different cellular events in recombinational DNA repair and replication fork stabilization.
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Affiliation(s)
- Hang Phuong Le
- Department of Microbiology and Molecular Genetics, University of California, Davis, Davis, CA 95616-8665, USA
| | - Xiaoyan Ma
- Department of Microbiology and Molecular Genetics, University of California, Davis, Davis, CA 95616-8665, USA
| | - Jorge Vaquero
- Department of Microbiology and Molecular Genetics, University of California, Davis, Davis, CA 95616-8665, USA
| | - Megan Brinkmeyer
- Department of Microbiology and Molecular Genetics, University of California, Davis, Davis, CA 95616-8665, USA
| | - Fei Guo
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616-8665, USA
| | - Wolf-Dietrich Heyer
- Department of Microbiology and Molecular Genetics, University of California, Davis, Davis, CA 95616-8665, USA.,Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA 95616-8665, USA
| | - Jie Liu
- Department of Microbiology and Molecular Genetics, University of California, Davis, Davis, CA 95616-8665, USA
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4
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Zhou Q, Holloman WK, Kojic M. Approaches to Understanding the Mediator Function of Brh2 in Ustilago maydis. Methods Enzymol 2018; 600:513-525. [PMID: 29458772 DOI: 10.1016/bs.mie.2017.11.019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Primary components of the homologous recombination pathway in eukaryotes include Rad51 whose function is to search for DNA sequence homology and promote strand exchange, its mediator BRCA2, and Dss1, a key regulator of BRCA2. We seek to understand the role of BRCA2 in governing the activity of Rad51 and to learn how BRCA2 function is regulated by Dss1. We use the microbe Ustilago maydis as a model system for experimentation because it has a well-conserved BRCA2-homolog, Brh2, and is amenable to biochemical and molecular genetic manipulations and analysis. The powerful attributes of this system open the way for gaining insight into BRCA2's molecular mechanism through avenues not immediately approachable in the vertebrate systems. Here we provide protocols for preparing Brh2, Dss1, and Rad51 as reagents for use in biochemical assays to monitor function and present methods for transposon-based mutational analysis of Brh2 for use in genetic dissection of function.
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Affiliation(s)
- Qingwen Zhou
- Weill Cornell Medical College, New York, NY, United States
| | | | - Milorad Kojic
- Weill Cornell Medical College, New York, NY, United States
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5
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Abstract
Brh2, the BRCA2 ortholog in the fungus Ustilago maydis, mediates delivery of Rad51 to DNA during the course of homology-directed DNA repair. Rad51 interacts with Brh2 through the highly conserved BRC element and through a second region termed CRE located at the extreme carboxy terminus. Dss1, a small intrinsically unstructured protein that interacts with Brh2, is crucial for its activity in DNA repair, but the mechanism of this regulation is uncertain. In previous studies, we found that interaction of Brh2 with DNA was strongly modulated by association with Dss1. Here we report that CRE influences interaction of Dss1 with Brh2 and that Dss1 status markedly alters interaction of Brh2 with Rad51. While it appears that a single Rad51 protomer associates with Brh2 in complex with Dss1, loss of Dss1 is accompanied by a large increase in the number of Rad51 protomers that can associate with Brh2. Concomitant with this buildup of Rad51, Brh2 loses its ability to bind DNA. These observations suggest a feedback circuit in which release of Dss1 from Brh2 as it binds DNA triggers nucleation of a short Rad51 oligomer on Brh2, which in turn promotes dissociation of Brh2 from the DNA.
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Affiliation(s)
- Qingwen Zhou
- Department of Microbiology and Immunology, Weill Cornell Medical College , New York, New York 10065, United States
| | - William K Holloman
- Department of Microbiology and Immunology, Weill Cornell Medical College , New York, New York 10065, United States
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6
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Kragelund BB, Schenstrøm SM, Rebula CA, Panse VG, Hartmann-Petersen R. DSS1/Sem1, a Multifunctional and Intrinsically Disordered Protein. Trends Biochem Sci 2016; 41:446-459. [PMID: 26944332 DOI: 10.1016/j.tibs.2016.02.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Revised: 02/01/2016] [Accepted: 02/04/2016] [Indexed: 01/24/2023]
Abstract
DSS1/Sem1 is a versatile intrinsically disordered protein. Besides being a bona fide subunit of the 26S proteasome, DSS1 associates with other protein complexes, including BRCA2-RPA, involved in homologous recombination; the Csn12-Thp3 complex, involved in RNA splicing; the integrator, involved in transcription; and the TREX-2 complex, involved in nuclear export of mRNA and transcription elongation. As a subunit of the proteasome, DSS1 functions both in complex assembly and possibly as a ubiquitin receptor. Here, we summarise structural and functional aspects of DSS1/Sem1 with particular emphasis on its multifunctional and disordered properties. We suggest that DSS1/Sem1 can act as a polyanionic adhesive to prevent nonproductive interactions during construction of protein assemblies, uniquely employing different structures when associating with the diverse multisubunit complexes.
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Affiliation(s)
- Birthe B Kragelund
- Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200 Copenhagen N, Denmark
| | - Signe M Schenstrøm
- Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200 Copenhagen N, Denmark
| | - Caio A Rebula
- Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200 Copenhagen N, Denmark
| | - Vikram Govind Panse
- Institute of Biochemistry, Department of Biology, ETH Zürich, Zürich, Switzerland.
| | - Rasmus Hartmann-Petersen
- Department of Biology, University of Copenhagen, Ole Maaløes Vej 5, DK-2200 Copenhagen N, Denmark.
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7
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Zhao W, Vaithiyalingam S, San Filippo J, Maranon DG, Jimenez-Sainz J, Fontenay GV, Kwon Y, Leung SG, Lu L, Jensen RB, Chazin WJ, Wiese C, Sung P. Promotion of BRCA2-Dependent Homologous Recombination by DSS1 via RPA Targeting and DNA Mimicry. Mol Cell 2015; 59:176-87. [PMID: 26145171 PMCID: PMC4506714 DOI: 10.1016/j.molcel.2015.05.032] [Citation(s) in RCA: 137] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Revised: 04/21/2015] [Accepted: 05/22/2015] [Indexed: 10/23/2022]
Abstract
The tumor suppressor BRCA2 is thought to facilitate the handoff of ssDNA from replication protein A (RPA) to the RAD51 recombinase during DNA break and replication fork repair by homologous recombination. However, we find that RPA-RAD51 exchange requires the BRCA2 partner DSS1. Biochemical, structural, and in vivo analyses reveal that DSS1 allows the BRCA2-DSS1 complex to physically and functionally interact with RPA. Mechanistically, DSS1 acts as a DNA mimic to attenuate the affinity of RPA for ssDNA. A mutation in the solvent-exposed acidic domain of DSS1 compromises the efficacy of RPA-RAD51 exchange. Thus, by targeting RPA and mimicking DNA, DSS1 functions with BRCA2 in a two-component homologous recombination mediator complex in genome maintenance and tumor suppression. Our findings may provide a paradigm for understanding the roles of DSS1 in other biological processes.
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Affiliation(s)
- Weixing Zhao
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Sivaraja Vaithiyalingam
- Departments of Biochemistry and Chemistry, and Center for Structural Biology, Vanderbilt University, Nashville, TN 37232, USA
| | - Joseph San Filippo
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06520, USA
| | - David G Maranon
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523, USA
| | - Judit Jimenez-Sainz
- Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Gerald V Fontenay
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Youngho Kwon
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Stanley G Leung
- Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Lucy Lu
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Ryan B Jensen
- Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Walter J Chazin
- Departments of Biochemistry and Chemistry, and Center for Structural Biology, Vanderbilt University, Nashville, TN 37232, USA.
| | - Claudia Wiese
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523, USA; Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Patrick Sung
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06520, USA.
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8
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Liu Q, Hu G, Cao Z, Wang J, Chen H. Conformational stability of PCID2 upon DSS1 binding with molecular dynamics simulation. J Mol Model 2015; 21:127. [PMID: 25914122 DOI: 10.1007/s00894-015-2664-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2014] [Accepted: 03/23/2015] [Indexed: 11/26/2022]
Abstract
DSS1 is a small acidic intrinsically disordered protein (IDP) that can fold upon binding with PCID2 TREX-2. The resulting complex plays a key role in mRNA export. However, the binding mechanism between DSS1 and PCID2 is unsolved. Here, three independent 500-ns molecular dynamics (MD) simulations were performed to study the DSS1-PCID2 binding mechanism by comparing apo-PCID2 and bound PCID2. The results show that the conformational variation of bound PCID2 is smaller than that of apo-PCID2, especially in the binding domain of two helices (helix IV and VIII). The probability of coil formation between helix III and helix IV of bound PCID2 increases, and a short anti-parallel β-sheet forms upon DSS1 binding. The decomposition of binding free energy into protein and residue pairs suggests that electrostatic and hydrophobic interactions play key roles in the recognition between DSS1 and PCID2. There is a hydrophobic core of seven residues in DSS1 favorable to the binding of PCID2. These analytical methods can be used to reveal the recognition mechanisms of other IDPs and their partners.
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Affiliation(s)
- Qianjun Liu
- Shandong Provincial Key Laboratory of Functional Macromolecular Biophysics, College of Physics and Electronic Information, Dezhou University, Dezhou, 253023, China
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9
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Dual DNA-binding domains shape the interaction of Brh2 with DNA. DNA Repair (Amst) 2014; 22:104-11. [PMID: 25128760 DOI: 10.1016/j.dnarep.2014.07.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2014] [Revised: 07/01/2014] [Accepted: 07/22/2014] [Indexed: 11/24/2022]
Abstract
Brh2, the BRCA2 ortholog in the fungus Ustilago maydis, harbors two different DNA-binding domains, one located in the N-terminal region and the other located in the C-terminal region. Here we were interested in comparing the biochemical properties of Brh2 fragments, Brh2(NT) and Brh2(CT), respectively, harboring the two different DNA-binding regions to understand the mechanistic purpose of dual DNA-interaction domains. With oligonucleotide substrates to model different DNA conformations, it was found that the substrate specificity of Brh2(NT) and Brh2(CT) was almost indistinguishable although avidity was different depending on salt concentration. DNA annealing activity inherent in Brh2 was found to be attributable to Brh2(NT). Likewise, activity responsible for a second-end capture reaction modeling a later step in repair of DNA double-strand breaks was found attributable to Brh2(NT). Efficient annealing of DNA strands coated with RPA required full length Brh2 rather than Brh2(NT) suggesting Brh2(CT) contributes to the activity when RPA is present. Brh2(NT) and Brh2(CT) were both found capable of physically interacting with RPA. The results suggest that while the two DNA-binding regions of Brh2 appear functionally redundant in certain aspects of DNA repair, they differ in fundamental properties, and likely contribute in different ways to repair processes involving or arising from stalled DNA replication forks.
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