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Stinson BM, Carney SM, Walter JC, Loparo JJ. Structural role for DNA Ligase IV in promoting the fidelity of non-homologous end joining. Nat Commun 2024; 15:1250. [PMID: 38341432 PMCID: PMC10858965 DOI: 10.1038/s41467-024-45553-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Accepted: 01/25/2024] [Indexed: 02/12/2024] Open
Abstract
Nonhomologous end joining (NHEJ), the primary pathway of vertebrate DNA double-strand-break (DSB) repair, directly re-ligates broken DNA ends. Damaged DSB ends that cannot be immediately re-ligated are modified by NHEJ processing enzymes, including error-prone polymerases and nucleases, to enable ligation. However, DSB ends that are initially compatible for re-ligation are typically joined without end processing. As both ligation and end processing occur in the short-range (SR) synaptic complex that closely aligns DNA ends, it remains unclear how ligation of compatible ends is prioritized over end processing. In this study, we identify structural interactions of the NHEJ-specific DNA Ligase IV (Lig4) within the SR complex that prioritize ligation and promote NHEJ fidelity. Mutational analysis demonstrates that Lig4 must bind DNA ends to form the SR complex. Furthermore, single-molecule experiments show that a single Lig4 binds both DNA ends at the instant of SR synapsis. Thus, Lig4 is poised to ligate compatible ends upon initial formation of the SR complex before error-prone processing. Our results provide a molecular basis for the fidelity of NHEJ.
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Affiliation(s)
- Benjamin M Stinson
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, MA, 02115, USA
- Howard Hughes Medical Institute, Boston, MA, 02115, USA
| | - Sean M Carney
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, MA, 02115, USA
| | - Johannes C Walter
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, MA, 02115, USA.
- Howard Hughes Medical Institute, Boston, MA, 02115, USA.
| | - Joseph J Loparo
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical School, Boston, MA, 02115, USA.
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Carney SM, Moreno AT, Piatt SC, Cisneros-Aguirre M, Lopezcolorado FW, Stark JM, Loparo JJ. XLF acts as a flexible connector during non-homologous end joining. eLife 2020; 9:e61920. [PMID: 33289484 PMCID: PMC7744095 DOI: 10.7554/elife.61920] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2020] [Accepted: 12/07/2020] [Indexed: 01/01/2023] Open
Abstract
Non-homologous end joining (NHEJ) is the predominant pathway that repairs DNA double-strand breaks in vertebrates. During NHEJ DNA ends are held together by a multi-protein synaptic complex until they are ligated. Here, we use Xenopus laevis egg extract to investigate the role of the intrinsically disordered C-terminal tail of the XRCC4-like factor (XLF), a critical factor in end synapsis. We demonstrate that the XLF tail along with the Ku-binding motif (KBM) at the extreme C-terminus are required for end joining. Although the underlying sequence of the tail can be varied, a minimal tail length is required for NHEJ. Single-molecule FRET experiments that observe end synapsis in real-time show that this defect is due to a failure to closely align DNA ends. Our data supports a model in which a single C-terminal tail tethers XLF to Ku, while allowing XLF to form interactions with XRCC4 that enable synaptic complex formation.
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Affiliation(s)
- Sean M Carney
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical SchoolBostonUnited States
| | - Andrew T Moreno
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical SchoolBostonUnited States
| | - Sadie C Piatt
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical SchoolBostonUnited States
- Harvard Graduate Program in Biophysics, Harvard Medical SchoolBostonUnited States
| | - Metztli Cisneros-Aguirre
- Department of Cancer Genetics and Epigenetics, Beckman Research Institute of the City of HopeDuarteUnited States
- Irell and Manella Graduate School of Biological Sciences, Beckman Research Institute of the City of HopeDuarteUnited States
| | | | - Jeremy M Stark
- Department of Cancer Genetics and Epigenetics, Beckman Research Institute of the City of HopeDuarteUnited States
- Irell and Manella Graduate School of Biological Sciences, Beckman Research Institute of the City of HopeDuarteUnited States
| | - Joseph J Loparo
- Department of Biological Chemistry and Molecular Pharmacology, Blavatnik Institute, Harvard Medical SchoolBostonUnited States
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Carney SM, Gomathinayagam S, Leuba SH, Trakselis MA. Bacterial DnaB helicase interacts with the excluded strand to regulate unwinding. J Biol Chem 2017; 292:19001-19012. [PMID: 28939774 DOI: 10.1074/jbc.m117.814178] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2017] [Revised: 09/19/2017] [Indexed: 11/06/2022] Open
Abstract
Replicative hexameric helicases are thought to unwind duplex DNA by steric exclusion (SE) where one DNA strand is encircled by the hexamer and the other is excluded from the central channel. However, interactions with the excluded strand on the exterior surface of hexameric helicases have also been shown to be important for DNA unwinding, giving rise to the steric exclusion and wrapping (SEW) model. For example, the archaeal Sulfolobus solfataricus minichromosome maintenance (SsoMCM) helicase has been shown to unwind DNA via a SEW mode to enhance unwinding efficiency. Using single-molecule FRET, we now show that the analogous Escherichia coli (Ec) DnaB helicase also interacts specifically with the excluded DNA strand during unwinding. Mutation of several conserved and positively charged residues on the exterior surface of EcDnaB resulted in increased interaction dynamics and states compared with wild type. Surprisingly, these mutations also increased the DNA unwinding rate, suggesting that electrostatic contacts with the excluded strand act as a regulator for unwinding activity. In support of this, experiments neutralizing the charge of the excluded strand with a morpholino substrate instead of DNA also dramatically increased the unwinding rate. Of note, although the stability of the excluded strand was nearly identical for EcDnaB and SsoMCM, these enzymes are from different superfamilies and unwind DNA with opposite polarities. These results support the SEW model of unwinding for EcDnaB that expands on the existing SE model of hexameric helicase unwinding to include contributions from the excluded strand to regulate the DNA unwinding rate.
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Affiliation(s)
- Sean M Carney
- From the Molecular Biophysics and Structural Biology Program, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | | | - Sanford H Leuba
- From the Molecular Biophysics and Structural Biology Program, University of Pittsburgh, Pittsburgh, Pennsylvania 15260.,Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261
| | - Michael A Trakselis
- From the Molecular Biophysics and Structural Biology Program, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, .,Department of Chemistry and Biochemistry, Baylor University, Waco, Texas 76798, and
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Khan I, Crouch JD, Bharti SK, Sommers JA, Carney SM, Yakubovskaya E, Garcia-Diaz M, Trakselis MA, Brosh RM. Biochemical Characterization of the Human Mitochondrial Replicative Twinkle Helicase: SUBSTRATE SPECIFICITY, DNA BRANCH MIGRATION, AND ABILITY TO OVERCOME BLOCKADES TO DNA UNWINDING. J Biol Chem 2016; 291:14324-14339. [PMID: 27226550 DOI: 10.1074/jbc.m115.712026] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Indexed: 01/08/2023] Open
Abstract
Mutations in the c10orf2 gene encoding the human mitochondrial DNA replicative helicase Twinkle are linked to several rare genetic diseases characterized by mitochondrial defects. In this study, we have examined the catalytic activity of Twinkle helicase on model replication fork and DNA repair structures. Although Twinkle behaves as a traditional 5' to 3' helicase on conventional forked duplex substrates, the enzyme efficiently dissociates D-loop DNA substrates irrespective of whether it possesses a 5' or 3' single-stranded tailed invading strand. In contrast, we report for the first time that Twinkle branch-migrates an open-ended mobile three-stranded DNA structure with a strong 5' to 3' directionality preference. To determine how well Twinkle handles potential roadblocks to mtDNA replication, we tested the ability of the helicase to unwind substrates with site-specific oxidative DNA lesions or bound by the mitochondrial transcription factor A. Twinkle helicase is inhibited by DNA damage in a unique manner that is dependent on the type of oxidative lesion and the strand in which it resides. Novel single molecule FRET binding and unwinding assays show an interaction of the excluded strand with Twinkle as well as events corresponding to stepwise unwinding and annealing. TFAM inhibits Twinkle unwinding, suggesting other replisome proteins may be required for efficient removal. These studies shed new insight on the catalytic functions of Twinkle on the key DNA structures it would encounter during replication or possibly repair of the mitochondrial genome and how well it tolerates potential roadblocks to DNA unwinding.
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Affiliation(s)
- Irfan Khan
- Laboratory of Molecular Gerontology, NIA, National Institutes of Health, Baltimore, Maryland 21224
| | - Jack D Crouch
- Laboratory of Molecular Gerontology, NIA, National Institutes of Health, Baltimore, Maryland 21224
| | - Sanjay Kumar Bharti
- Laboratory of Molecular Gerontology, NIA, National Institutes of Health, Baltimore, Maryland 21224
| | - Joshua A Sommers
- Laboratory of Molecular Gerontology, NIA, National Institutes of Health, Baltimore, Maryland 21224
| | - Sean M Carney
- Molecular Biophysics and Structural Biology Program, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - Elena Yakubovskaya
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, New York 11794-8651
| | - Miguel Garcia-Diaz
- Department of Pharmacological Sciences, Stony Brook University, Stony Brook, New York 11794-8651
| | - Michael A Trakselis
- Molecular Biophysics and Structural Biology Program, University of Pittsburgh, Pittsburgh, Pennsylvania 15260,; Department of Chemistry and Biochemistry, Baylor University, Waco, Texas 76798
| | - Robert M Brosh
- Laboratory of Molecular Gerontology, NIA, National Institutes of Health, Baltimore, Maryland 21224,.
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Carney SM, Leuba S, Trakselis M. Mechanistic Insights of Hexameric Helicase Function Provided by Single-Molecule FRET. Biophys J 2015. [DOI: 10.1016/j.bpj.2014.11.401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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Leuba SH, Carney SM, Dahlburg EM, Eells RJ, Ghodke H, Yanamala N, Schauer G, Klein-Seetharaman J. Early integration of the individual student in academic activities: a novel classroom concept for graduate education in molecular biophysics and structural biology. BMC Biophys 2014; 7:6. [PMID: 25132964 PMCID: PMC4134111 DOI: 10.1186/2046-1682-7-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Accepted: 07/09/2014] [Indexed: 11/10/2022]
Abstract
BACKGROUND A key challenge in interdisciplinary research is choosing the best approach from a large number of techniques derived from different disciplines and their interfaces. RESULTS To address this challenge in the area of Biophysics and Structural Biology, we have designed a graduate level course to teach students insightful use of experimental biophysical approaches in relationship to addressing biological questions related to biomolecular interactions and dynamics. A weekly seminar and data and literature club are used to compliment the training in class. The course contains wet-laboratory experimental demonstration and real-data analysis as well as lectures, grant proposal preparation and assessment, and student presentation components. Active student participation is mandatory in all aspects of the class. Students prepare materials for the class receiving individual and iterative feedback from course directors and local experts generating high quality classroom presentations. CONCLUSIONS The ultimate goal of the course is to teach students the skills needed to weigh different experimental approaches against each other in addressing a specific biological question by thinking and executing academic tasks like faculty.
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Affiliation(s)
- Sanford H Leuba
- Graduate Program in Molecular Biophysics and Structural Biology, University of Pittsburgh and Carnegie Mellon University, Pittsburgh, PA 15260, USA ; Department of Cell Biology, University of Pittsburgh School of Medicine, UPCI, Hillman Cancer Center, 5117 Centre Avenue, Pittsburgh, PA 15213, USA
| | - Sean M Carney
- Graduate Program in Molecular Biophysics and Structural Biology, University of Pittsburgh and Carnegie Mellon University, Pittsburgh, PA 15260, USA
| | - Elizabeth M Dahlburg
- Graduate Program in Molecular Biophysics and Structural Biology, University of Pittsburgh and Carnegie Mellon University, Pittsburgh, PA 15260, USA
| | - Rebecca J Eells
- Graduate Program in Molecular Biophysics and Structural Biology, University of Pittsburgh and Carnegie Mellon University, Pittsburgh, PA 15260, USA
| | - Harshad Ghodke
- Graduate Program in Molecular Biophysics and Structural Biology, University of Pittsburgh and Carnegie Mellon University, Pittsburgh, PA 15260, USA ; Presently at: Single Molecule Biophysics Group, Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Naveena Yanamala
- Department of Structural Biology, University of Pittsburgh, Pittsburgh, USA
| | - Grant Schauer
- Graduate Program in Molecular Biophysics and Structural Biology, University of Pittsburgh and Carnegie Mellon University, Pittsburgh, PA 15260, USA
| | - Judith Klein-Seetharaman
- Graduate Program in Molecular Biophysics and Structural Biology, University of Pittsburgh and Carnegie Mellon University, Pittsburgh, PA 15260, USA ; Department of Structural Biology, University of Pittsburgh, Pittsburgh, USA ; Presently at: Department of Biomedicine and Systems Biology, Division of Metabolic and Vascular Health, Warwick Medical School, University of Warwick, Coventry CV4 7AL, UK
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Abstract
OBJECTIVE To review the literature on the use of lithium in the treatment of bipolar disorder and highlight the evidence base supporting its efficacy and safety. METHOD A selective literature review. RESULTS Lithium is widely believed to be effective against acute mania, acute bipolar depression and in relapse prevention to either mania or depression. In fact, the data supporting efficacy in acute treatment are less impressive than is often claimed, whereas for relapse prevention and suicide prevention no other agent has comparable depth of support. Lithium is best described as the bench mark treatment for bipolar disorder, rather than the gold standard, because only a minority of patients show major clinical benefit. There is a developing need for further trials against new alternatives and in combination studies. CONCLUSION Lithium has a continuing important role in the clinical management of bipolar disorder. Its under-utilization in North America reflects opinion rather than evidence and the demonstrated anti-suicide effects should help to reignite interest in its use.
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Affiliation(s)
- S M Carney
- University Department of Psychiatry, Warnford Hospital, Oxford, UK
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Carney SM, Underwood BA, Loerch JD. Effects of zinc and vitamin A deficient diets on the hepatic mobilization and urinary excretion of vitamin A in rats. J Nutr 1976; 106:1773-81. [PMID: 993857 DOI: 10.1093/jn/106.12.1773] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Weanling rats were fed diets deficient in zinc (ZD), vitamin A (AD), or both (ZAD) for 3 weeks. Each then received 20 mug of 11,12-3H-retinyl acetate. Plasma retinol was monitored for radioactivity for 5 hours and urine for 6 days. Rats were killed and measurements made of plasma and liver vitamin A and plasma zinc. Plasma vitamin A was depressed but growth was not affected in AD rats compared to pair-fed controls. Radioactivity appeared most rapidly in the plasma retinol fractions of the two vitamin A-depleted groups (AD and ZAD) and was excreted most rapidly in the urine of these same groups. Zinc-deficient diets (ZD and ZAD) caused depressed plasma levels of zinc and vitamin A and growth retardation greater than in pair-fed controls. However zinc deficiency had no effect on mobilization of newly-ingested vitamin A or urinary excretion of labeled metabolites. Liver stores of vitamin A were lower for ZD rats than for controls. The data indicate that zinc deficiency is not a limiting factor in hepatic vitamin A release except as it influences growth and body demand for the vitamin. The data also suggest that newly-absorbed vitamin A is mobilized and utilized in preference to that previously stored in the liver.
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