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Zhang X, Xia F, Zhang X, Blumenthal RM, Cheng X. C2H2 Zinc Finger Transcription Factors Associated with Hemoglobinopathies. J Mol Biol 2024; 436:168343. [PMID: 37924864 PMCID: PMC11185177 DOI: 10.1016/j.jmb.2023.168343] [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: 09/04/2023] [Revised: 10/23/2023] [Accepted: 10/30/2023] [Indexed: 11/06/2023]
Abstract
In humans, specific aberrations in β-globin results in sickle cell disease and β-thalassemia, symptoms of which can be ameliorated by increased expression of fetal globin (HbF). Two recent CRISPR-Cas9 screens, centered on ∼1500 annotated sequence-specific DNA binding proteins and performed in a human erythroid cell line that expresses adult hemoglobin, uncovered four groups of candidate regulators of HbF gene expression. They are (1) members of the nucleosome remodeling and deacetylase (NuRD) complex proteins that are already known for HbF control; (2) seven C2H2 zinc finger (ZF) proteins, including some (ZBTB7A and BCL11A) already known for directly silencing the fetal γ-globin genes in adult human erythroid cells; (3) a few other transcription factors of different structural classes that might indirectly influence HbF gene expression; and (4) DNA methyltransferase 1 (DNMT1) that maintains the DNA methylation marks that attract the MBD2-associated NuRD complex to DNA as well as associated histone H3 lysine 9 methylation. Here we briefly discuss the effects of these regulators, particularly C2H2 ZFs, in inducing HbF expression for treating β-hemoglobin disorders, together with recent advances in developing safe and effective small-molecule therapeutics for the regulation of this well-conserved hemoglobin switch.
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Affiliation(s)
- Xing Zhang
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
| | - Fangfang Xia
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Xiaotian Zhang
- Department of Biochemistry and Molecular Biology, The University of Texas Health Science Center Houston, McGovern Medical School, Houston, TX 77030, USA
| | - Robert M Blumenthal
- Department of Medical Microbiology and Immunology, and Program in Bioinformatics, The University of Toledo College of Medicine and Life Sciences, Toledo, OH 43614, USA
| | - Xiaodong Cheng
- Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
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Balakrishnan S, Adolph M, Tsai MS, Akizuki T, Gallagher K, Cortez D, Chazin WJ. Structure of RADX and mechanism for regulation of RAD51 nucleofilaments. Proc Natl Acad Sci U S A 2024; 121:e2316491121. [PMID: 38466836 PMCID: PMC10962997 DOI: 10.1073/pnas.2316491121] [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: 09/27/2023] [Accepted: 02/07/2024] [Indexed: 03/13/2024] Open
Abstract
Replication fork reversal is a fundamental process required for resolution of encounters with DNA damage. A key step in the stabilization and eventual resolution of reversed forks is formation of RAD51 nucleoprotein filaments on exposed single strand DNA (ssDNA). To avoid genome instability, RAD51 filaments are tightly controlled by a variety of positive and negative regulators. RADX (RPA-related RAD51-antagonist on the X chromosome) is a recently discovered negative regulator that binds tightly to ssDNA, directly interacts with RAD51, and regulates replication fork reversal and stabilization in a context-dependent manner. Here, we present a structure-based investigation of RADX's mechanism of action. Mass photometry experiments showed that RADX forms multiple oligomeric states in a concentration-dependent manner, with a predominance of trimers in the presence of ssDNA. The structure of RADX, which has no structurally characterized orthologs, was determined ab initio by cryo-electron microscopy (cryo-EM) from maps in the 2 to 4 Å range. The structure reveals the molecular basis for RADX oligomerization and the coupled multi-valent binding of ssDNA binding. The interaction of RADX with RAD51 filaments was imaged by negative stain EM, which showed a RADX oligomer at the end of filaments. Based on these results, we propose a model in which RADX functions by capping and restricting the end of RAD51 filaments.
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Affiliation(s)
- Swati Balakrishnan
- Center for Structural Biology, Vanderbilt University, Nashville, TN37240
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN37237
| | - Madison Adolph
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN37237
| | - Miaw-Sheue Tsai
- Biological Systems and Bioengineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA94720
| | - Tae Akizuki
- Center for Structural Biology, Vanderbilt University, Nashville, TN37240
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN37237
| | - Kaitlyn Gallagher
- Center for Structural Biology, Vanderbilt University, Nashville, TN37240
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN37237
| | - David Cortez
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN37237
| | - Walter J. Chazin
- Center for Structural Biology, Vanderbilt University, Nashville, TN37240
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN37237
- Department of Chemistry, Vanderbilt University, Nashville, TN37235
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Balakrishnan S, Adolph M, Tsai MS, Gallagher K, Cortez D, Chazin WJ. Structure of RADX and mechanism for regulation of RAD51 nucleofilaments. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.09.19.558089. [PMID: 37786681 PMCID: PMC10541619 DOI: 10.1101/2023.09.19.558089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/04/2023]
Abstract
Replication fork reversal is a fundamental process required for resolution of encounters with DNA damage. A key step in the stabilization and eventual resolution of reversed forks is formation of RAD51 nucleoprotein filaments on exposed ssDNA. To avoid genome instability, RAD51 filaments are tightly controlled by a variety of positive and negative regulators. RADX is a recently discovered negative regulator that binds tightly to ssDNA, directly interacts with RAD51, and regulates replication fork reversal and stabilization in a context-dependent manner. Here we present a structure-based investigation of RADX's mechanism of action. Mass photometry experiments showed that RADX forms multiple oligomeric states in a concentration dependent manner, with a predominance of trimers in the presence of ssDNA. The structure of RADX, which has no structurally characterized orthologs, was determined ab initio by cryo-electron microscopy (EM) from maps in the 2-3 Å range. The structure reveals the molecular basis for RADX oligomerization and binding of ssDNA binding. The binding of RADX to RAD51 filaments was imaged by negative stain EM, which showed a RADX oligomer at the end of filaments. Based on these results, we propose a model in which RADX functions by capping and restricting the growing end of RAD51 filaments.
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Affiliation(s)
- Swati Balakrishnan
- Center for Structural Biology, Vanderbilt University, Nashville, TN 37240, USA
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37237, USA
| | - Madison Adolph
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37237, USA
| | - Miaw-Sheue Tsai
- Biological Systems and Bioengineering Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
| | - Kaitlyn Gallagher
- Center for Structural Biology, Vanderbilt University, Nashville, TN 37240, USA
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37237, USA
| | - David Cortez
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37237, USA
| | - Walter J. Chazin
- Center for Structural Biology, Vanderbilt University, Nashville, TN 37240, USA
- Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, TN 37237, USA
- Department of Chemistry, Vanderbilt University, Nashville, TN 37235, USA
- Lead contact
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