1
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Smith KP, Chakravarthy S, Rahi A, Chakraborty M, Vosberg KM, Tonelli M, Plach MG, Grigorescu AA, Curtis JE, Varma D. SAXS/MC studies of the mixed-folded protein Cdt1 reveal monomeric, folded over conformations. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.03.573975. [PMID: 38260441 PMCID: PMC10802334 DOI: 10.1101/2024.01.03.573975] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
Cdt1 is a protein critical for DNA replication licensing and is well-established to be a binding partner of the minichromosome maintenance (MCM) complex. Cdt1 has also been demonstrated to have an emerging, "moonlighting" role at the kinetochore via direct binding to microtubules and to the Ndc80 complex. However, it is not known how the structure and conformations of Cdt1 could allow for these multiple, completely unique sets of protein complexes. And while there exist multiple robust methods to study entirely folded or entirely unfolded proteins, structure-function studies of combined, mixed folded/disordered proteins remain challenging. It this work, we employ multiple orthogonal biophysical and computational techniques to provide a detailed structural characterization of human Cdt1 92-546. DSF and DSCD show both folded winged helix (WH) domains of Cdt1 are relatively unstable. CD and NMR show the N-terminal and the linker regions are intrinsically disordered. Using DLS and SEC-MALS, we show that Cdt1 is polydisperse, monomeric at high concentrations, and without any apparent inter-molecular self-association. SEC-SAXS of the monomer in solution enabled computational modeling of the protein in silico. Using the program SASSIE, we performed rigid body Monte Carlo simulations to generate a conformational ensemble. Using experimental SAXS data, we filtered for conformations which did and did not fit our data. We observe that neither fully extended nor extremely compact Cdt1 conformations are consistent with our SAXS data. The best fit models have the N-terminal and linker regions extended into solution and the two folded domains close to each other in apparent "folded over" conformations. The best fit Cdt1 conformations are consistent with a function as a scaffold protein which may be sterically blocked without the presence of binding partners. Our studies also provide a template for combining experimental and computational biophysical techniques to study mixed-folded proteins.
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Affiliation(s)
- Kyle P Smith
- Department of Cell & Developmental Biology, Northwestern University Feinberg School of Medicine, Chicago, IL, 60611, USA
- Present Address, Xylia Therapeutics, Waltham, MA, 02451, USA
| | - Srinivas Chakravarthy
- Biophysics Collaborative Access Team, Argonne National Laboratory, Argonne, IL, 60439, USA
| | - Amit Rahi
- Department of Cell & Developmental Biology, Northwestern University Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Manas Chakraborty
- Department of Cell & Developmental Biology, Northwestern University Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Kristen M Vosberg
- Department of Cell & Developmental Biology, Northwestern University Feinberg School of Medicine, Chicago, IL, 60611, USA
| | - Marco Tonelli
- National Magnetic Resonance Facility at Madison, Department of Biochemistry, University of Wisconsin, Madison, WI, 53706, USA
| | | | - Arabela A Grigorescu
- Keck Biophysics Facility, Department of Molecular Biosciences, Northwestern University, Evanston, IL, 60201, USA
| | - Joseph E Curtis
- NIST Center for Neutron Research, National Institute of Standards and Technology, 100 Bureau Drive, Mail Stop 6102, Gaithersburg, MD, 20899, United States
| | - Dileep Varma
- Department of Cell & Developmental Biology, Northwestern University Feinberg School of Medicine, Chicago, IL, 60611, USA
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2
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Marnik EA, Almeida MV, Cipriani PG, Chung G, Caspani E, Karaulanov E, Gan HH, Zinno J, Isolehto IJ, Kielisch F, Butter F, Sharp CS, Flanagan RM, Bonnet FX, Piano F, Ketting RF, Gunsalus KC, Updike DL. The Caenorhabditis elegans TDRD5/7-like protein, LOTR-1, interacts with the helicase ZNFX-1 to balance epigenetic signals in the germline. PLoS Genet 2022; 18:e1010245. [PMID: 35657999 PMCID: PMC9200344 DOI: 10.1371/journal.pgen.1010245] [Citation(s) in RCA: 6] [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: 07/20/2021] [Revised: 06/15/2022] [Accepted: 05/09/2022] [Indexed: 11/24/2022] Open
Abstract
LOTUS and Tudor domain containing proteins have critical roles in the germline. Proteins that contain these domains, such as Tejas/Tapas in Drosophila, help localize the Vasa helicase to the germ granules and facilitate piRNA-mediated transposon silencing. The homologous proteins in mammals, TDRD5 and TDRD7, are required during spermiogenesis. Until now, proteins containing both LOTUS and Tudor domains in Caenorhabditis elegans have remained elusive. Here we describe LOTR-1 (D1081.7), which derives its name from its LOTUS and Tudor domains. Interestingly, LOTR-1 docks next to P granules to colocalize with the broadly conserved Z-granule helicase, ZNFX-1. The Tudor domain of LOTR-1 is required for its Z-granule retention. Like znfx-1 mutants, lotr-1 mutants lose small RNAs from the 3’ ends of WAGO and mutator targets, reminiscent of the loss of piRNAs from the 3’ ends of piRNA precursor transcripts in mouse Tdrd5 mutants. Our work shows that LOTR-1 acts with ZNFX-1 to bring small RNA amplifying mechanisms towards the 3’ ends of its RNA templates. Germ granules are protein and RNA complexes that are critical for maintaining an animal’s fertility. Central to the composition of germ granules are their small RNAs, which have the capacity to convey a memory of germline-licensed expression from one generation to the next. Here we describe and characterize a new germ-granule protein in C. elegans that we’ve named LOTR-1, after its LOTUS and Tudor domains. This combination of LOTUS and Tudor domains can be found in the mammalian proteins TDRD5 and TDRD7, which are required during spermatogenesis. During C. elegans embryogenesis, germ granules demix or partition into subgranules with refined functions. We show that LOTR-1 partitions with a specific class of subgranules called Z granules, interacting with a Z-granule helicase called ZNFX-1. Here, LOTR-1 functions with ZNFX-1 to position small RNA amplification from RNA templates, ensuring a memory of germline expression across generations. These findings may provide new insight into the function of TDRD5 and TDRD7 during human germline development.
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Affiliation(s)
- Elisabeth A. Marnik
- The MDI Biological Laboratory, Bar Harbor, Maine, United States of America
- Husson University, Bangor, Maine, United States of America
| | - Miguel V. Almeida
- Institute of Molecular Biology, Mainz, Germany
- International PhD Programme on Gene Regulation, Epigenetics & Genome Stability, Mainz, Germany
| | - P. Giselle Cipriani
- Center for Genomics & Systems Biology, New York University, New York, New York, United States of America
- Center for Genomics & Systems Biology, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
| | - George Chung
- Center for Genomics & Systems Biology, New York University, New York, New York, United States of America
| | - Edoardo Caspani
- Institute of Molecular Biology, Mainz, Germany
- International PhD Programme on Gene Regulation, Epigenetics & Genome Stability, Mainz, Germany
| | | | - Hin Hark Gan
- Center for Genomics & Systems Biology, New York University, New York, New York, United States of America
| | - John Zinno
- Center for Genomics & Systems Biology, New York University, New York, New York, United States of America
| | - Ida J. Isolehto
- Institute of Molecular Biology, Mainz, Germany
- International PhD Programme on Gene Regulation, Epigenetics & Genome Stability, Mainz, Germany
| | | | - Falk Butter
- Institute of Molecular Biology, Mainz, Germany
| | - Catherine S. Sharp
- The MDI Biological Laboratory, Bar Harbor, Maine, United States of America
| | - Roisin M. Flanagan
- Center for Genomics & Systems Biology, New York University, New York, New York, United States of America
| | - Frederic X. Bonnet
- The MDI Biological Laboratory, Bar Harbor, Maine, United States of America
| | - Fabio Piano
- Center for Genomics & Systems Biology, New York University, New York, New York, United States of America
- Center for Genomics & Systems Biology, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
| | - René F. Ketting
- Institute of Molecular Biology, Mainz, Germany
- * E-mail: (RFK); (KCG); (DLU)
| | - Kristin C. Gunsalus
- Center for Genomics & Systems Biology, New York University, New York, New York, United States of America
- Center for Genomics & Systems Biology, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
- * E-mail: (RFK); (KCG); (DLU)
| | - Dustin L. Updike
- The MDI Biological Laboratory, Bar Harbor, Maine, United States of America
- * E-mail: (RFK); (KCG); (DLU)
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3
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Zhou Y, Pozo PN, Oh S, Stone HM, Cook JG. Distinct and sequential re-replication barriers ensure precise genome duplication. PLoS Genet 2020; 16:e1008988. [PMID: 32841231 PMCID: PMC7473519 DOI: 10.1371/journal.pgen.1008988] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2020] [Revised: 09/04/2020] [Accepted: 07/12/2020] [Indexed: 01/19/2023] Open
Abstract
Achieving complete and precise genome duplication requires that each genomic segment be replicated only once per cell division cycle. Protecting large eukaryotic genomes from re-replication requires an overlapping set of molecular mechanisms that prevent the first DNA replication step, the DNA loading of MCM helicase complexes to license replication origins, after S phase begins. Previous reports have defined many such origin licensing inhibition mechanisms, but the temporal relationships among them are not clear, particularly with respect to preventing re-replication in G2 and M phases. Using a combination of mutagenesis, biochemistry, and single cell analyses in human cells, we define a new mechanism that prevents re-replication through hyperphosphorylation of the essential MCM loading protein, Cdt1. We demonstrate that Cyclin A/CDK1 can hyperphosphorylate Cdt1 to inhibit MCM re-loading in G2 phase. The mechanism of inhibition is to block Cdt1 binding to MCM independently of other known Cdt1 inactivation mechanisms such as Cdt1 degradation during S phase or Geminin binding. Moreover, our findings suggest that Cdt1 dephosphorylation at the mitosis-to-G1 phase transition re-activates Cdt1. We propose that multiple distinct, non-redundant licensing inhibition mechanisms act in a series of sequential relays through each cell cycle phase to ensure precise genome duplication. The initial step of DNA replication is loading the DNA helicase, MCM, onto DNA during the first phase of the cell division cycle. If MCM loading occurs inappropriately onto DNA that has already been replicated, then cells risk DNA re-replication, a source of endogenous DNA damage and genome instability. How mammalian cells prevent any sections of their very large genomes from re-replicating is still not fully understood. We found that the Cdt1 protein, one of the critical MCM loading factors, is inhibited specifically in late cell cycle stages through a mechanism involving protein phosphorylation. This phosphorylation prevents Cdt1 from binding MCM; when Cdt1 cannot be phosphorylated MCM is inappropriately re-loaded onto DNA and cells are prone to re-replication. When cells divide and transition into G1 phase, Cdt1 is then dephosphorylated to re-activate it for MCM loading. Based on these findings we assert that the different mechanisms that cooperate to avoid re-replication are not redundant. Instead, different cell cycle phases are dominated by different re-replication control mechanisms. These findings have implications for understanding how genomes are duplicated precisely once per cell cycle and shed light on how that process is perturbed by changes in Cdt1 levels or phosphorylation activity.
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Affiliation(s)
- Yizhuo Zhou
- Department of Biochemistry and Biophysics, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United State of America
| | - Pedro N. Pozo
- Curriculum in Genetics and Molecular Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, United State of America
| | - Seeun Oh
- F. Widjaja Foundation Inflammatory Bowel and Immunobiology Research Institute and the Research Division of Immunology, Department of Biomedical Sciences, Cedars-Sinai Medical Center, Los Angeles, CA, United State of America
| | - Haley M. Stone
- Department of Biochemistry and Biophysics, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United State of America
| | - Jeanette Gowen Cook
- Department of Biochemistry and Biophysics, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United State of America
- Curriculum in Genetics and Molecular Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC, United State of America
- Lineberger Comprehensive Cancer, The University of North Carolina at Chapel Hill, Chapel Hill, NC, United State of America
- * E-mail:
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4
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Liu H, Jeffery CJ. Moonlighting Proteins in the Fuzzy Logic of Cellular Metabolism. Molecules 2020; 25:molecules25153440. [PMID: 32751110 PMCID: PMC7435893 DOI: 10.3390/molecules25153440] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2020] [Revised: 07/09/2020] [Accepted: 07/23/2020] [Indexed: 12/15/2022] Open
Abstract
The numerous interconnected biochemical pathways that make up the metabolism of a living cell comprise a fuzzy logic system because of its high level of complexity and our inability to fully understand, predict, and model the many activities, how they interact, and their regulation. Each cell contains thousands of proteins with changing levels of expression, levels of activity, and patterns of interactions. Adding more layers of complexity is the number of proteins that have multiple functions. Moonlighting proteins include a wide variety of proteins where two or more functions are performed by one polypeptide chain. In this article, we discuss examples of proteins with variable functions that contribute to the fuzziness of cellular metabolism.
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Affiliation(s)
- Haipeng Liu
- Center for Biomolecular Sciences, College of Pharmacy, University of Illinois at Chicago, 900 South Ashland Avenue, Chicago, IL 60607, USA;
| | - Constance J. Jeffery
- Department of Biological Sciences, University of Illinois at Chicago, 900 South Ashland Avenue, Chicago, IL 60607, USA
- Correspondence: ; Tel.: +1-312-996-3168
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5
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Matthews LA, Simmons LA. Cryptic protein interactions regulate DNA replication initiation. Mol Microbiol 2018; 111:118-130. [PMID: 30285297 DOI: 10.1111/mmi.14142] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2018] [Revised: 09/25/2018] [Accepted: 09/26/2018] [Indexed: 12/13/2022]
Abstract
DNA replication is a fundamental biological process that is tightly regulated in all cells. In bacteria, DnaA controls when and where replication begins by building a step-wise complex that loads the replicative helicase onto chromosomal DNA. In many low-GC Gram-positive species, DnaA recruits the DnaD and DnaB proteins to function as adaptors to assist in helicase loading. How DnaA, its adaptors and the helicase form a complex at the origin is unclear. We addressed this question using the bacterial two-hybrid assay to determine how the initiation proteins from Bacillus subtilis interact with each other. We show that cryptic interaction sites play a key role in this process and we map these regions for the entire pathway. In addition, we found that the SirA regulator that blocks initiation in sporulating cells binds to a surface on DnaA that overlaps with DnaD. The interaction between DnaA and DnaD was also mapped to the same DnaA surface in the human pathogen Staphylococcus aureus, demonstrating the broad conservation of this surface. Therefore, our study has unveiled key protein interactions essential for initiation and our approach is widely applicable for mapping interactions in other signaling pathways that are governed by cryptic binding surfaces.
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Affiliation(s)
- Lindsay A Matthews
- Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, 48109-1048, USA
| | - Lyle A Simmons
- Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, 48109-1048, USA
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6
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Pozo PN, Matson JP, Cole Y, Kedziora KM, Grant GD, Temple B, Cook JG. Cdt1 variants reveal unanticipated aspects of interactions with cyclin/CDK and MCM important for normal genome replication. Mol Biol Cell 2018; 29:2989-3002. [PMID: 30281379 PMCID: PMC6333176 DOI: 10.1091/mbc.e18-04-0242] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The earliest step in DNA replication is origin licensing, which is the DNA loading of minichromosome maintenance (MCM) helicase complexes. The Cdc10-dependent transcript 1 (Cdt1) protein is essential for MCM loading during the G1 phase of the cell cycle, but the mechanism of Cdt1 function is still incompletely understood. We examined a collection of rare Cdt1 variants that cause a form of primordial dwarfism (the Meier-Gorlin syndrome) plus one hypomorphic Drosophila allele to shed light on Cdt1 function. Three hypomorphic variants load MCM less efficiently than wild-type (WT) Cdt1, and their lower activity correlates with impaired MCM binding. A structural homology model of the human Cdt1-MCM complex positions the altered Cdt1 residues at two distinct interfaces rather than the previously described single MCM interaction domain. Surprisingly, one dwarfism allele (Cdt1-A66T) is more active than WT Cdt1. This hypermorphic variant binds both cyclin A and SCFSkp2 poorly relative to WT Cdt1. Detailed quantitative live-cell imaging analysis demonstrated no change in the stability of this variant, however. Instead, we propose that cyclin A/CDK inhibits the Cdt1 licensing function independent of the creation of the SCFSkp2 phosphodegron. Together, these findings identify key Cdt1 interactions required for both efficient origin licensing and tight Cdt1 regulation to ensure normal cell proliferation and genome stability.
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Affiliation(s)
- Pedro N Pozo
- Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Jacob P Matson
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Yasemin Cole
- Department of Genetics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Katarzyna M Kedziora
- Department of Genetics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Gavin D Grant
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.,Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Brenda Temple
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.,R. L. Juliano Structural Bioinformatics Core Facility, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.,Center for Structural Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Jeanette Gowen Cook
- Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.,Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.,Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
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7
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Hernández-Carralero E, Cabrera E, Alonso-de Vega I, Hernández-Pérez S, Smits VAJ, Freire R. Control of DNA Replication Initiation by Ubiquitin. Cells 2018; 7:E146. [PMID: 30241373 PMCID: PMC6211026 DOI: 10.3390/cells7100146] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Revised: 09/18/2018] [Accepted: 09/19/2018] [Indexed: 01/07/2023] Open
Abstract
Eukaryotic cells divide by accomplishing a program of events in which the replication of the genome is a fundamental part. To ensure all cells have an accurate copy of the genome, DNA replication occurs only once per cell cycle and is controlled by numerous pathways. A key step in this process is the initiation of DNA replication in which certain regions of DNA are marked as competent to replicate. Moreover, initiation of DNA replication needs to be coordinated with other cell cycle processes. At the molecular level, initiation of DNA replication relies, among other mechanisms, upon post-translational modifications, including the conjugation and hydrolysis of ubiquitin. An example is the precise control of the levels of the DNA replication initiation protein Cdt1 and its inhibitor Geminin by ubiquitin-mediated proteasomal degradation. This control ensures that DNA replication occurs with the right timing during the cell cycle, thereby avoiding re-replication events. Here, we review the events that involve ubiquitin signalling during DNA replication initiation, and how they are linked to human disease.
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Affiliation(s)
- Esperanza Hernández-Carralero
- Unidad de Investigación, Hospital Universitario de Canarias, Instituto de Tecnologías Biomédicas, Ofra s/n, 38320 La Laguna, Tenerife, Spain.
| | - Elisa Cabrera
- Unidad de Investigación, Hospital Universitario de Canarias, Instituto de Tecnologías Biomédicas, Ofra s/n, 38320 La Laguna, Tenerife, Spain.
| | - Ignacio Alonso-de Vega
- Unidad de Investigación, Hospital Universitario de Canarias, Instituto de Tecnologías Biomédicas, Ofra s/n, 38320 La Laguna, Tenerife, Spain.
| | - Santiago Hernández-Pérez
- Unidad de Investigación, Hospital Universitario de Canarias, Instituto de Tecnologías Biomédicas, Ofra s/n, 38320 La Laguna, Tenerife, Spain.
- Division of Oncogenomics, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
| | - Veronique A J Smits
- Unidad de Investigación, Hospital Universitario de Canarias, Instituto de Tecnologías Biomédicas, Ofra s/n, 38320 La Laguna, Tenerife, Spain.
| | - Raimundo Freire
- Unidad de Investigación, Hospital Universitario de Canarias, Instituto de Tecnologías Biomédicas, Ofra s/n, 38320 La Laguna, Tenerife, Spain.
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8
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Agarwal S, Smith KP, Zhou Y, Suzuki A, McKenney RJ, Varma D. Cdt1 stabilizes kinetochore-microtubule attachments via an Aurora B kinase-dependent mechanism. J Cell Biol 2018; 217:3446-3463. [PMID: 30154187 PMCID: PMC6168275 DOI: 10.1083/jcb.201705127] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2017] [Revised: 02/06/2018] [Accepted: 07/17/2018] [Indexed: 12/03/2022] Open
Abstract
Cdt1 is a novel kinetochore–microtubule binding protein. The middle and the C-terminal winged-helix domains of Cdt1 are involved in microtubule binding. Aurora B kinase phosphorylation of Cdt1 influences its microtubule binding in vitro and is necessary for kinetochore–microtubule stability and mitotic progression in cells. Robust kinetochore–microtubule (kMT) attachment is critical for accurate chromosome segregation. G2/M-specific depletion of human Cdt1 that localizes to kinetochores in an Ndc80 complex–dependent manner leads to abnormal kMT attachments and mitotic arrest. This indicates an independent mitotic role for Cdt1 in addition to its prototypic function in DNA replication origin licensing. Here, we show that Cdt1 directly binds to microtubules (MTs). Endogenous or transiently expressed Cdt1 localizes to both mitotic spindle MTs and kinetochores. Deletion mapping of Cdt1 revealed that the regions comprising the middle and C-terminal winged-helix domains but lacking the N-terminal unstructured region were required for efficient MT binding. Mitotic kinase Aurora B interacts with and phosphorylates Cdt1. Aurora B–phosphomimetic Cdt1 exhibited attenuated MT binding, and its cellular expression induced defective kMT attachments with a concomitant delay in mitotic progression. Thus we provide mechanistic insight into how Cdt1 affects overall kMT stability in an Aurora B kinase phosphorylation-dependent manner; which is envisioned to augment the MT-binding of the Ndc80 complex.
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Affiliation(s)
- Shivangi Agarwal
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL
| | - Kyle Paul Smith
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL
| | - Yizhuo Zhou
- Department of Biochemistry and Biophysics, The University of North Carolina at Chapel Hill, Chapel Hill, NC
| | - Aussie Suzuki
- Department of Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC
| | - Richard J McKenney
- Department of Molecular and Cellular Biology, University of California, Davis, Davis, CA
| | - Dileep Varma
- Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL
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9
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The Temporal Regulation of S Phase Proteins During G 1. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1042:335-369. [PMID: 29357066 DOI: 10.1007/978-981-10-6955-0_16] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Successful DNA replication requires intimate coordination with cell-cycle progression. Prior to DNA replication initiation in S phase, a series of essential preparatory events in G1 phase ensures timely, complete, and precise genome duplication. Among the essential molecular processes are regulated transcriptional upregulation of genes that encode replication proteins, appropriate post-transcriptional control of replication factor abundance and activity, and assembly of DNA-loaded protein complexes to license replication origins. In this chapter we describe these critical G1 events necessary for DNA replication and their regulation in the context of both cell-cycle entry and cell-cycle progression.
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10
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Rv0004 is a new essential member of the mycobacterial DNA replication machinery. PLoS Genet 2017; 13:e1007115. [PMID: 29176877 PMCID: PMC5720831 DOI: 10.1371/journal.pgen.1007115] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Revised: 12/07/2017] [Accepted: 11/14/2017] [Indexed: 11/30/2022] Open
Abstract
DNA replication is fundamental for life, yet a detailed understanding of bacterial DNA replication is limited outside the organisms Escherichia coli and Bacillus subtilis. Many bacteria, including mycobacteria, encode no identified homologs of helicase loaders or regulators of the initiator protein DnaA, despite these factors being essential for DNA replication in E. coli and B. subtilis. In this study we discover that a previously uncharacterized protein, Rv0004, from the human pathogen Mycobacterium tuberculosis is essential for bacterial viability and that depletion of Rv0004 leads to a block in cell cycle progression. Using a combination of genetic and biochemical approaches, we found that Rv0004 has a role in DNA replication, interacts with DNA and the replicative helicase DnaB, and affects DnaB-DnaA complex formation. We also identify a conserved domain in Rv0004 that is predicted to structurally resemble the N-terminal protein-protein interaction domain of DnaA. Mutation of a single conserved tryptophan within Rv0004’s DnaA N-terminal-like domain leads to phenotypes similar to those observed upon Rv0004 depletion and can affect the association of Rv0004 with DnaB. In addition, using live cell imaging during depletion of Rv0004, we have uncovered a previously unappreciated role for DNA replication in coordinating mycobacterial cell division and cell size. Together, our data support that Rv0004 encodes a homolog of the recently identified DciA family of proteins found in most bacteria that lack the DnaC-DnaI helicase loaders in E. coli and B. subtilis. Therefore, the mechanisms of Rv0004 elucidated here likely apply to other DciA homologs and reveal insight into the diversity of bacterial strategies in even the most conserved biological processes. DNA is the molecule that encodes all of the genetic information of an organism. In order to pass genes onto the next generation, DNA has to first be copied through a process called DNA replication. Most of the initial studies on bacterial DNA replication were performed in Escherichia coli and Bacillus subtilis. While these studies were very informative, there is an increasing appreciation that more distantly related bacteria have diverged from these organisms in even the most fundamental processes. Mycobacteria, a group of bacteria that includes the human pathogen Mycobacterium tuberculosis, are distantly related to E. coli and B. subtilis and lack some of the proteins used for DNA replication in those model organisms. In this study, we discover that a previously uncharacterized protein in Mycobacteria, named Rv0004, is essential for bacterial viability and involved in DNA replication. Rv0004 is conserved in most bacteria but is absent from E. coli and B. subtilis. Since Rv0004 is essential for mycobacterial viability, this study both identifies a future target for antibiotic therapy and expands our knowledge on the diversity of bacterial DNA replication strategies, which may be applicable to other organisms.
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Frigola J, He J, Kinkelin K, Pye VE, Renault L, Douglas ME, Remus D, Cherepanov P, Costa A, Diffley JFX. Cdt1 stabilizes an open MCM ring for helicase loading. Nat Commun 2017; 8:15720. [PMID: 28643783 PMCID: PMC5490006 DOI: 10.1038/ncomms15720] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Accepted: 04/24/2017] [Indexed: 11/09/2022] Open
Abstract
ORC, Cdc6 and Cdt1 act together to load hexameric MCM, the motor of the eukaryotic replicative helicase, into double hexamers at replication origins. Here we show that Cdt1 interacts with MCM subunits Mcm2, 4 and 6, which both destabilizes the Mcm2-5 interface and inhibits MCM ATPase activity. Using X-ray crystallography, we show that Cdt1 contains two winged-helix domains in the C-terminal half of the protein and a catalytically inactive dioxygenase-related N-terminal domain, which is important for MCM loading, but not for subsequent replication. We used these structures together with single-particle electron microscopy to generate three-dimensional models of MCM complexes. These show that Cdt1 stabilizes MCM in a left-handed spiral open at the Mcm2-5 gate. We propose that Cdt1 acts as a brace, holding MCM open for DNA entry and bound to ATP until ORC-Cdc6 triggers ATP hydrolysis by MCM, promoting both Cdt1 ejection and MCM ring closure.
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Affiliation(s)
- Jordi Frigola
- Chromosome Replication Laboratory, The Francis Crick Institute, 1 Midland Road, London
NW1 1AT, UK
| | - Jun He
- Chromosome Replication Laboratory, The Francis Crick Institute, 1 Midland Road, London
NW1 1AT, UK
- Chromatin Structure and Mobile DNA Laboratory, The Francis Crick Institute, 1 Midland Road, London
NW1 1AT, UK
| | - Kerstin Kinkelin
- Chromosome Replication Laboratory, The Francis Crick Institute, 1 Midland Road, London
NW1 1AT, UK
| | - Valerie E. Pye
- Chromatin Structure and Mobile DNA Laboratory, The Francis Crick Institute, 1 Midland Road, London
NW1 1AT, UK
| | - Ludovic Renault
- Macromolecular Machines Laboratory, The Francis Crick Institute, 1 Midland Road, London
NW1 1AT, UK
| | - Max E. Douglas
- Chromosome Replication Laboratory, The Francis Crick Institute, 1 Midland Road, London
NW1 1AT, UK
| | - Dirk Remus
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, New York
10065, USA
| | - Peter Cherepanov
- Chromatin Structure and Mobile DNA Laboratory, The Francis Crick Institute, 1 Midland Road, London
NW1 1AT, UK
| | - Alessandro Costa
- Macromolecular Machines Laboratory, The Francis Crick Institute, 1 Midland Road, London
NW1 1AT, UK
| | - John F. X. Diffley
- Chromosome Replication Laboratory, The Francis Crick Institute, 1 Midland Road, London
NW1 1AT, UK
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12
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Abstract
The accurate and complete replication of genomic DNA is essential for all life. In eukaryotic cells, the assembly of the multi-enzyme replisomes that perform replication is divided into stages that occur at distinct phases of the cell cycle. Replicative DNA helicases are loaded around origins of DNA replication exclusively during G1 phase. The loaded helicases are then activated during S phase and associate with the replicative DNA polymerases and other accessory proteins. The function of the resulting replisomes is monitored by checkpoint proteins that protect arrested replisomes and inhibit new initiation when replication is inhibited. The replisome also coordinates nucleosome disassembly, assembly, and the establishment of sister chromatid cohesion. Finally, when two replisomes converge they are disassembled. Studies in Saccharomyces cerevisiae have led the way in our understanding of these processes. Here, we review our increasingly molecular understanding of these events and their regulation.
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13
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Zhai Y, Cheng E, Wu H, Li N, Yung PYK, Gao N, Tye BK. Open-ringed structure of the Cdt1-Mcm2-7 complex as a precursor of the MCM double hexamer. Nat Struct Mol Biol 2017; 24:300-308. [PMID: 28191894 DOI: 10.1038/nsmb.3374] [Citation(s) in RCA: 70] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2016] [Accepted: 01/09/2017] [Indexed: 12/17/2022]
Abstract
The minichromosome maintenance complex (MCM) hexameric complex (Mcm2-7) forms the core of the eukaryotic replicative helicase. During G1 phase, two Cdt1-Mcm2-7 heptamers are loaded onto each replication origin by the origin-recognition complex (ORC) and Cdc6 to form an inactive MCM double hexamer (DH), but the detailed loading mechanism remains unclear. Here we examine the structures of the yeast MCM hexamer and Cdt1-MCM heptamer from Saccharomyces cerevisiae. Both complexes form left-handed coil structures with a 10-15-Å gap between Mcm5 and Mcm2, and a central channel that is occluded by the C-terminal domain winged-helix motif of Mcm5. Cdt1 wraps around the N-terminal regions of Mcm2, Mcm6 and Mcm4 to stabilize the whole complex. The intrinsic coiled structures of the precursors provide insights into the DH formation, and suggest a spring-action model for the MCM during the initial origin melting and the subsequent DNA unwinding.
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Affiliation(s)
- Yuanliang Zhai
- Division of Life Science, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.,Institute for Advanced Study, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Erchao Cheng
- Ministry of Education Key Laboratory of Protein Sciences, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing, China
| | - Hao Wu
- Ministry of Education Key Laboratory of Protein Sciences, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing, China
| | - Ningning Li
- Peking-Tsinghua Center for Life Sciences, School of Life Sciences, Peking University, Beijing, China
| | - Philip Yuk Kwong Yung
- Division of Life Science, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
| | - Ning Gao
- Ministry of Education Key Laboratory of Protein Sciences, Beijing Advanced Innovation Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing, China
| | - Bik-Kwoon Tye
- Division of Life Science, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.,Department of Molecular Biology and Genetics, College of Agriculture and Life Sciences, Cornell University, Ithaca, New York, USA
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14
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Parker MW, Botchan MR, Berger JM. Mechanisms and regulation of DNA replication initiation in eukaryotes. Crit Rev Biochem Mol Biol 2017; 52:107-144. [PMID: 28094588 DOI: 10.1080/10409238.2016.1274717] [Citation(s) in RCA: 117] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Cellular DNA replication is initiated through the action of multiprotein complexes that recognize replication start sites in the chromosome (termed origins) and facilitate duplex DNA melting within these regions. In a typical cell cycle, initiation occurs only once per origin and each round of replication is tightly coupled to cell division. To avoid aberrant origin firing and re-replication, eukaryotes tightly regulate two events in the initiation process: loading of the replicative helicase, MCM2-7, onto chromatin by the origin recognition complex (ORC), and subsequent activation of the helicase by its incorporation into a complex known as the CMG. Recent work has begun to reveal the details of an orchestrated and sequential exchange of initiation factors on DNA that give rise to a replication-competent complex, the replisome. Here, we review the molecular mechanisms that underpin eukaryotic DNA replication initiation - from selecting replication start sites to replicative helicase loading and activation - and describe how these events are often distinctly regulated across different eukaryotic model organisms.
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Affiliation(s)
- Matthew W Parker
- a Department of Biophysics and Biophysical Chemistry , Johns Hopkins University School of Medicine , Baltimore , MD , USA
| | - Michael R Botchan
- b Department of Molecular and Cell Biology , University of California Berkeley , Berkeley , CA , USA
| | - James M Berger
- a Department of Biophysics and Biophysical Chemistry , Johns Hopkins University School of Medicine , Baltimore , MD , USA
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15
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Pozo PN, Cook JG. Regulation and Function of Cdt1; A Key Factor in Cell Proliferation and Genome Stability. Genes (Basel) 2016; 8:genes8010002. [PMID: 28025526 PMCID: PMC5294997 DOI: 10.3390/genes8010002] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2016] [Revised: 12/13/2016] [Accepted: 12/14/2016] [Indexed: 12/30/2022] Open
Abstract
Successful cell proliferation requires efficient and precise genome duplication followed by accurate chromosome segregation. The Cdc10-dependent transcript 1 protein (Cdt1) is required for the first step in DNA replication, and in human cells Cdt1 is also required during mitosis. Tight cell cycle controls over Cdt1 abundance and activity are critical to normal development and genome stability. We review here recent advances in elucidating Cdt1 molecular functions in both origin licensing and kinetochore–microtubule attachment, and we describe the current understanding of human Cdt1 regulation.
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Affiliation(s)
- Pedro N Pozo
- Curriculum in Genetics and Molecular Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
| | - Jeanette Gowen Cook
- Curriculum in Genetics and Molecular Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
- Department of Biochemistry and Biophysics, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
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16
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Usachev KS, Efimov SV, Kolosova OA, Klochkova EA, Aganov AV, Klochkov VV. Antimicrobial peptide protegrin-3 adopt an antiparallel dimer in the presence of DPC micelles: a high-resolution NMR study. JOURNAL OF BIOMOLECULAR NMR 2015; 62:71-79. [PMID: 25786621 DOI: 10.1007/s10858-015-9920-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Accepted: 03/14/2015] [Indexed: 06/04/2023]
Abstract
A tendency to dimerize in the presence of lipids was found for the protegrin. The dimer formation by the protegrin-1 (PG-1) is the first step for further oligomeric membrane pore formation. Generally there are two distinct model of PG-1 dimerization in either a parallel or antiparallel β-sheet. But despite the wealth of data available today, protegrin dimer structure and pore formation is still not completely understood. In order to investigate a more detailed dimerization process of PG-1 and if it will be the same for another type of protegrins, in this work we used a high-resolution NMR spectroscopy for structure determination of protegrin-3 (RGGGL-CYCRR-RFCVC-VGR) in the presence of perdeuterated DPC micelles and demonstrate that PG-3 forms an antiparallel NCCN dimer with a possible association of these dimers. This structural study complements previously published solution, solid state and computational studies of PG-1 in various environments and validate the potential of mean force simulations of PG-1 dimers and association of dimers to form octameric or decameric β-barrels.
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Affiliation(s)
- K S Usachev
- NMR Laboratory, Institute of Physics, Kazan Federal University, Kremlevskaya, 18, Kazan, 420008, Russian Federation,
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17
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Schuetz A, Murakawa Y, Rosenbaum E, Landthaler M, Heinemann U. Roquin binding to target mRNAs involves a winged helix-turn-helix motif. Nat Commun 2014; 5:5701. [PMID: 25504471 DOI: 10.1038/ncomms6701] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Accepted: 10/29/2014] [Indexed: 01/31/2023] Open
Abstract
Roquin proteins mediate mRNA deadenylation by recognizing a conserved class of stem-loop RNA degradation motifs via their Roquin domain. Here we present the crystal structure of a Roquin domain, revealing a mostly helical protein fold bearing a winged helix-turn-helix motif. By combining structural, biochemical and mutation analyses, we gain insight into the mode of RNA binding. We show that the winged helix-turn-helix motif is involved in the binding of constitutive decay elements-containing stem-loop mRNAs. Moreover, we provide biochemical evidence that Roquin proteins are additionally able to bind to duplex RNA and have the potential to be functional in different oligomeric states.
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Affiliation(s)
- Anja Schuetz
- Helmholtz Protein Sample Production Facility, Max Delbrück Center for Molecular Medicine, 13092 Berlin, Germany
| | - Yasuhiro Murakawa
- Laboratory for RNA Biology and Posttranscriptional Regulation, Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, 13092 Berlin, Germany
| | - Eva Rosenbaum
- Structure and Membrane Interaction of G-Proteins, Max Delbrück Center for Molecular Medicine, 13092 Berlin, Germany
| | - Markus Landthaler
- Laboratory for RNA Biology and Posttranscriptional Regulation, Berlin Institute for Medical Systems Biology, Max Delbrück Center for Molecular Medicine, 13092 Berlin, Germany
| | - Udo Heinemann
- 1] Helmholtz Protein Sample Production Facility, Max Delbrück Center for Molecular Medicine, 13092 Berlin, Germany [2] Chemistry and Biochemistry Institute, Freie Universität Berlin, 14195 Berlin, Germany
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18
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Sun J, Evrin C, Samel SA, Fernández-Cid A, Riera A, Kawakami H, Stillman B, Speck C, Li H. Cryo-EM structure of a helicase loading intermediate containing ORC-Cdc6-Cdt1-MCM2-7 bound to DNA. Nat Struct Mol Biol 2013; 20:944-51. [PMID: 23851460 PMCID: PMC3735830 DOI: 10.1038/nsmb.2629] [Citation(s) in RCA: 110] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2013] [Accepted: 05/29/2013] [Indexed: 01/08/2023]
Abstract
In eukaryotes, the Cdt1-bound replicative helicase core MCM2-7 is loaded onto DNA by the ORC-Cdc6 ATPase to form a prereplicative complex (pre-RC) with an MCM2-7 double hexamer encircling DNA. Using purified components in the presence of ATP-γS, we have captured in vitro an intermediate in pre-RC assembly that contains a complex between the ORC-Cdc6 and Cdt1-MCM2-7 heteroheptamers called the OCCM. Cryo-EM studies of this 14-subunit complex reveal that the two separate heptameric complexes are engaged extensively, with the ORC-Cdc6 N-terminal AAA+ domains latching onto the C-terminal AAA+ motor domains of the MCM2-7 hexamer. The conformation of ORC-Cdc6 undergoes a concerted change into a right-handed spiral with helical symmetry that is identical to that of the DNA double helix. The resulting ORC-Cdc6 helicase loader shows a notable structural similarity to the replication factor C clamp loader, suggesting a conserved mechanism of action.
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Affiliation(s)
- Jingchuan Sun
- Biosciences Department, Brookhaven National Laboratory, Upton, New York, USA
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19
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Bell SP, Kaguni JM. Helicase loading at chromosomal origins of replication. Cold Spring Harb Perspect Biol 2013; 5:cshperspect.a010124. [PMID: 23613349 DOI: 10.1101/cshperspect.a010124] [Citation(s) in RCA: 93] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Loading of the replicative DNA helicase at origins of replication is of central importance in DNA replication. As the first of the replication fork proteins assemble at chromosomal origins of replication, the loaded helicase is required for the recruitment of the rest of the replication machinery. In this work, we review the current knowledge of helicase loading at Escherichia coli and eukaryotic origins of replication. In each case, this process requires both an origin recognition protein as well as one or more additional proteins. Comparison of these events shows intriguing similarities that suggest a similar underlying mechanism, as well as critical differences that likely reflect the distinct processes that regulate helicase loading in bacterial and eukaryotic cells.
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Affiliation(s)
- Stephen P Bell
- Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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20
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Dynamic association of ORCA with prereplicative complex components regulates DNA replication initiation. Mol Cell Biol 2012; 32:3107-20. [PMID: 22645314 DOI: 10.1128/mcb.00362-12] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
In eukaryotes, initiation of DNA replication requires the assembly of a multiprotein prereplicative complex (pre-RC) at the origins. We recently reported that a WD repeat-containing protein, origin recognition complex (ORC)-associated (ORCA/LRWD1), plays a crucial role in stabilizing ORC to chromatin. Here, we find that ORCA is required for the G(1)-to-S-phase transition in human cells. In addition to binding to ORC, ORCA associates with Cdt1 and its inhibitor, geminin. Single-molecule pulldown experiments demonstrate that each molecule of ORCA can bind to one molecule of ORC, one molecule of Cdt1, and two molecules of geminin. Further, ORCA directly interacts with the N terminus of Orc2, and the stability of ORCA is dependent on its association with Orc2. ORCA associates with Orc2 throughout the cell cycle, with Cdt1 during mitosis and G(1), and with geminin in post-G(1) cells. Overexpression of geminin results in the loss of interaction between ORCA and Cdt1, suggesting that increased levels of geminin in post-G(1) cells titrate Cdt1 away from ORCA. We propose that the dynamic association of ORCA with pre-RC components modulates the assembly of its interacting partners on chromatin and facilitates DNA replication initiation.
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21
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Liu C, Wu R, Zhou B, Wang J, Wei Z, Tye BK, Liang C, Zhu G. Structural insights into the Cdt1-mediated MCM2-7 chromatin loading. Nucleic Acids Res 2012; 40:3208-17. [PMID: 22140117 PMCID: PMC3326298 DOI: 10.1093/nar/gkr1118] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2011] [Revised: 10/31/2011] [Accepted: 11/07/2011] [Indexed: 12/23/2022] Open
Abstract
Initiation of DNA replication in eukaryotes is exquisitely regulated to ensure that DNA replication occurs exactly once in each cell division. A conserved and essential step for the initiation of eukaryotic DNA replication is the loading of the mini-chromosome maintenance 2-7 (MCM2-7) helicase onto chromatin at replication origins by Cdt1. To elucidate the molecular mechanism of this event, we determined the structure of the human Cdt1-Mcm6 binding domains, the Cdt1(410-440)/MCM6(708-821) complex by NMR. Our structural and site-directed mutagenesis studies showed that charge complementarity is a key determinant for the specific interaction between Cdt1 and Mcm2-7. When this interaction was interrupted by alanine substitutions of the conserved interacting residues, the corresponding yeast Cdt1 and Mcm6 mutants were defective in DNA replication and the chromatin loading of Mcm2, resulting in cell death. Having shown that Cdt1 and Mcm6 interact through their C-termini, and knowing that Cdt1 is tethered to Orc6 during the loading of MCM2-7, our results suggest that the MCM2-7 hexamer is loaded with its C terminal end facing the ORC complex. These results provide a structural basis for the Cdt1-mediated MCM2-7 chromatin loading.
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Affiliation(s)
- Changdong Liu
- Division of Life Science and State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China and Department of Molecular Biology & Genetics, Cornell University, USA
| | - Rentian Wu
- Division of Life Science and State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China and Department of Molecular Biology & Genetics, Cornell University, USA
| | - Bo Zhou
- Division of Life Science and State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China and Department of Molecular Biology & Genetics, Cornell University, USA
| | - Jiafeng Wang
- Division of Life Science and State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China and Department of Molecular Biology & Genetics, Cornell University, USA
| | - Zhun Wei
- Division of Life Science and State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China and Department of Molecular Biology & Genetics, Cornell University, USA
| | - Bik K. Tye
- Division of Life Science and State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China and Department of Molecular Biology & Genetics, Cornell University, USA
| | - Chun Liang
- Division of Life Science and State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China and Department of Molecular Biology & Genetics, Cornell University, USA
| | - Guang Zhu
- Division of Life Science and State Key Laboratory of Molecular Neuroscience, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China and Department of Molecular Biology & Genetics, Cornell University, USA
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22
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Abstract
One of the mechanisms controlling the initiation of DNA replication is the dynamic interaction between Cdt1, which promotes assembly of the pre-replication license complex, and Geminin, which inhibits it. Specifically, Cdt1 cooperates with the cell cycle protein Cdc6 to promote loading of the minichromosome maintenance helicases (MCM) onto the chromatin-bound origin recognition complex (ORC), by directly interacting with the MCM complex, and by modulating histone acetylation and inducing chromatin unfolding. Geminin, on the other hand, prevents the loading of the MCM onto the ORC both by directly binding to Cdt1, and by modulating Cdt1 stability and activity. Protein levels of Geminin and Cdt1 are tightly regulated through the cell cycle, and the Cdt1-Geminin complex likely acts as a molecular switch that can enable or disable the firing of each origin of replication. In this review we summarize structural studies of Cdt1 and Geminin and subsequent insights into how this molecular switch may function to ensure DNA is faithfully replicated only once during S phase of each cell cycle.
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Affiliation(s)
- Christophe Caillat
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX, Amsterdam, The Netherlands
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23
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Abstract
Minichromosome maintenance (MCM) complexes have been identified as the primary replicative helicases responsible for unwinding DNA for genome replication. The focus of this chapter is to discuss the current structural and functional understanding of MCMs and their role at origins of replication, which are based mostly on the studies of MCM proteins and MCM complexes from archaeal genomes.
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Affiliation(s)
- Ian M Slaymaker
- Molecular and Computational Biology, University of Southern California, Los Angeles, CA, 90089, USA
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24
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Multiple Cdt1 molecules act at each origin to load replication-competent Mcm2-7 helicases. EMBO J 2011; 30:4885-96. [PMID: 22045335 DOI: 10.1038/emboj.2011.394] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2011] [Accepted: 10/06/2011] [Indexed: 11/08/2022] Open
Abstract
Eukaryotic origins of replication are selected by loading a head-to-head double hexamer of the Mcm2-7 replicative helicase around origin DNA. Cdt1 plays an essential but transient role during this event; however, its mechanism of action is unknown. Through analysis of Cdt1 mutations, we demonstrate that Cdt1 performs multiple functions during helicase loading. The C-terminus of Cdt1 binds Mcm2-7, and this interaction is required for efficient origin recruitment of both proteins. We show that origin recognition complex (ORC) and Cdc6 recruit multiple Cdt1 molecules to the origin during helicase loading, and disruption of this multi-Cdt1 intermediate prevents helicase loading. Although dispensable for loading Mcm2-7 double hexamers that are topologically linked to DNA, the essential N-terminal domain of Cdt1 is required to load Mcm2-7 complexes that are competent for association with the Cdc45 and GINS helicase-activating proteins and replication initiation. Our data support a model in which origin-bound ORC and Cdc6 recruit two Cdt1 molecules to initiate double-hexamer formation prior to helicase loading and demonstrate that Cdt1 influences the replication competence of loaded Mcm2-7 helicases.
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25
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Stress-stimulated mitogen-activated protein kinases control the stability and activity of the Cdt1 DNA replication licensing factor. Mol Cell Biol 2011; 31:4405-16. [PMID: 21930785 DOI: 10.1128/mcb.06163-11] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
DNA replication is tightly coordinated both with cell cycle cues and with responses to extracellular signals to maintain genome stability. We discovered that human Cdt1, an essential origin licensing protein whose activity must be restricted to G(1) phase, is a substrate of the stress-activated mitogen-activated protein (MAP) kinases p38 and c-Jun N-terminal kinase (JNK). These MAP kinases phosphorylate Cdt1 both during unperturbed G(2) phase and during an acute stress response. Phosphorylation renders Cdt1 resistant to ubiquitin-mediated degradation during S phase and after DNA damage by blocking Cdt1 binding to the Cul4 adaptor, Cdt2. Mutations that block normal cell cycle-regulated MAP kinase-mediated phosphorylation interfere with rapid Cdt1 reaccumulation at the end of S phase. Phosphomimetic mutations recapitulate the stabilizing effects of Cdt1 phosphorylation but also reduce the ability of Cdt1 to support origin licensing. Two other CRL4(Cdt2) targets, the cyclin-dependent kinase (CDK) inhibitor p21 and the methyltransferase PR-Set7/Set8, are similarly stabilized by MAP kinase activity. These findings support a model in which MAP kinase activity in G(2) promotes reaccumulation of a low-activity Cdt1 isoform after replication is complete.
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26
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Abstract
DNA replication is a highly regulated process involving a number of licensing and replication factors that function in a carefully orchestrated manner to faithfully replicate DNA during every cell cycle. Loss of proper licensing control leads to deregulated DNA replication including DNA re-replication, which can cause genome instability and tumorigenesis. Eukaryotic organisms have established several conserved mechanisms to prevent DNA re-replication and to counteract its potentially harmful effects. These mechanisms include tightly controlled regulation of licensing factors and activation of cell cycle and DNA damage checkpoints. Deregulated licensing control and its associated compromised checkpoints have both been observed in tumor cells, indicating that proper functioning of these pathways is essential for maintaining genome stability. In this review, we discuss the regulatory mechanisms of licensing control, the deleterious consequences when both licensing and checkpoints are compromised, and present possible mechanisms to prevent re-replication in order to maintain genome stability.
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Affiliation(s)
- Lan N Truong
- Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA
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27
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Jee J, Mizuno T, Kamada K, Tochio H, Chiba Y, Yanagi KI, Yasuda G, Hiroaki H, Hanaoka F, Shirakawa M. Structure and mutagenesis studies of the C-terminal region of licensing factor Cdt1 enable the identification of key residues for binding to replicative helicase Mcm proteins. J Biol Chem 2010; 285:15931-40. [PMID: 20335175 DOI: 10.1074/jbc.m109.075333] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
In eukaryotes, DNA replication is fired once in a single cell cycle before cell division starts to maintain stability of the genome. This event is tightly controlled by a series of proteins. Cdt1 is one of the licensing factors and is involved in recruiting replicative DNA helicase Mcm2-7 proteins into the pre-replicative complex together with Cdc6. In Cdt1, the C-terminal region serves as a binding site for Mcm2-7 proteins, although the details of these interactions remain largely unknown. Here, we report the structure of the region and the key residues for binding to Mcm proteins. We determined the solution structure of the C-terminal fragment, residues 450-557, of mouse Cdt1 by NMR. The structure consists of a winged-helix domain and shows unexpected similarity to those of the C-terminal domain of Cdc6 and the central fragment of Cdt1, thereby implying functional and evolutionary relationships. Structure-based mutagenesis and an in vitro binding assay enabled us to pinpoint the region that interacts with Mcm proteins. Moreover, by performing in vitro binding and budding yeast viability experiments, we showed that approximately 45 residues located in the N-terminal direction of the structural region are equally crucial for recognizing Mcm proteins. Our data suggest the possibility that winged-helix domain plays a role as a common module to interact with replicative helicase in the DNA replication-licensing process.
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Affiliation(s)
- Jungoo Jee
- Center for Priority Areas, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo 192-0397, Japan.
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