1
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Nickens DG, Feng Z, Shen J, Gray SJ, Simmons RH, Niu H, Bochman ML. Cdc13 exhibits dynamic DNA strand exchange in the presence of telomeric DNA. Nucleic Acids Res 2024:gkae265. [PMID: 38613387 DOI: 10.1093/nar/gkae265] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Revised: 03/22/2024] [Accepted: 04/01/2024] [Indexed: 04/14/2024] Open
Abstract
Telomerase is the enzyme that lengthens telomeres and is tightly regulated by a variety of means to maintain genome integrity. Several DNA helicases function at telomeres, and we previously found that the Saccharomyces cerevisiae helicases Hrq1 and Pif1 directly regulate telomerase. To extend these findings, we are investigating the interplay between helicases, single-stranded DNA (ssDNA) binding proteins (ssBPs), and telomerase. The yeast ssBPs Cdc13 and RPA differentially affect Hrq1 and Pif1 helicase activity, and experiments to measure helicase disruption of Cdc13/ssDNA complexes instead revealed that Cdc13 can exchange between substrates. Although other ssBPs display dynamic binding, this was unexpected with Cdc13 due to the reported in vitro stability of the Cdc13/telomeric ssDNA complex. We found that the DNA exchange by Cdc13 occurs rapidly at physiological temperatures, requires telomeric repeat sequence DNA, and is affected by ssDNA length. Cdc13 truncations revealed that the low-affinity binding site (OB1), which is distal from the high-affinity binding site (OB3), is required for this intermolecular dynamic DNA exchange (DDE). We hypothesize that DDE by Cdc13 is the basis for how Cdc13 'moves' at telomeres to alternate between modes where it regulates telomerase activity and assists in telomere replication.
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Affiliation(s)
- David G Nickens
- Molecular & Cellular Biochemistry Department, Indiana University, Bloomington, IN 47405, USA
| | - Zhitong Feng
- Molecular & Cellular Biochemistry Department, Indiana University, Bloomington, IN 47405, USA
| | - Jiangchuan Shen
- Molecular & Cellular Biochemistry Department, Indiana University, Bloomington, IN 47405, USA
| | - Spencer J Gray
- Molecular & Cellular Biochemistry Department, Indiana University, Bloomington, IN 47405, USA
| | - Robert H Simmons
- Molecular & Cellular Biochemistry Department, Indiana University, Bloomington, IN 47405, USA
| | - Hengyao Niu
- Molecular & Cellular Biochemistry Department, Indiana University, Bloomington, IN 47405, USA
| | - Matthew L Bochman
- Molecular & Cellular Biochemistry Department, Indiana University, Bloomington, IN 47405, USA
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2
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Nickens DG, Feng Z, Shen J, Gray SJ, Simmons RH, Niu H, Bochman ML. Cdc13 exhibits dynamic DNA strand exchange in the presence of telomeric DNA. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.12.04.569902. [PMID: 38105973 PMCID: PMC10723391 DOI: 10.1101/2023.12.04.569902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
Telomerase is the enzyme that lengthens telomeres and is tightly regulated by a variety of means to maintain genome integrity. Several DNA helicases function at telomeres, and we previously found that the Saccharomyces cerevisiae helicases Hrq1 and Pif1 directly regulate telomerase. To extend these findings, we are investigating the interplay between helicases, single-stranded DNA (ssDNA) binding proteins (ssBPs), and telomerase. The yeast ssBPs Cdc13 and RPA differentially affect Hrq1 and Pif1 helicase activity, and experiments to measure helicase disruption of Cdc13/ssDNA complexes instead revealed that Cdc13 can exchange between substrates. Although other ssBPs display dynamic binding, this was unexpected with Cdc13 due to the reported in vitro stability of the Cdc13/telomeric ssDNA complex. We found that the DNA exchange by Cdc13 occurs rapidly at physiological temperatures, requires telomeric repeat sequence DNA, and is affected by ssDNA length. Cdc13 truncations revealed that the low-affinity binding site (OB1), which is distal from the high-affinity binding site (OB3), is required for this intermolecular dynamic DNA exchange (DDE). We hypothesize that DDE by Cdc13 is the basis for how Cdc13 'moves' at telomeres to alternate between modes where it regulates telomerase activity and assists in telomere replication.
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3
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Coloma J, Gonzalez-Rodriguez N, Balaguer FA, Gmurczyk K, Aicart-Ramos C, Nuero ÓM, Luque-Ortega JR, Calugaru K, Lue NF, Moreno-Herrero F, Llorca O. Molecular architecture and oligomerization of Candida glabrata Cdc13 underpin its telomeric DNA-binding and unfolding activity. Nucleic Acids Res 2023; 51:668-686. [PMID: 36629261 PMCID: PMC9881146 DOI: 10.1093/nar/gkac1261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2022] [Revised: 12/14/2022] [Accepted: 12/19/2022] [Indexed: 01/12/2023] Open
Abstract
The CST complex is a key player in telomere replication and stability, which in yeast comprises Cdc13, Stn1 and Ten1. While Stn1 and Ten1 are very well conserved across species, Cdc13 does not resemble its mammalian counterpart CTC1 either in sequence or domain organization, and Cdc13 but not CTC1 displays functions independently of the rest of CST. Whereas the structures of human CTC1 and CST have been determined, the molecular organization of Cdc13 remains poorly understood. Here, we dissect the molecular architecture of Candida glabrata Cdc13 and show how it regulates binding to telomeric sequences. Cdc13 forms dimers through the interaction between OB-fold 2 (OB2) domains. Dimerization stimulates binding of OB3 to telomeric sequences, resulting in the unfolding of ssDNA secondary structure. Once bound to DNA, Cdc13 prevents the refolding of ssDNA by mechanisms involving all domains. OB1 also oligomerizes, inducing higher-order complexes of Cdc13 in vitro. OB1 truncation disrupts these complexes, affects ssDNA unfolding and reduces telomere length in C. glabrata. Together, our results reveal the molecular organization of C. glabrata Cdc13 and how this regulates the binding and the structure of DNA, and suggest that yeast species evolved distinct architectures of Cdc13 that share some common principles.
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Affiliation(s)
- Javier Coloma
- Correspondence may also be addressed to Javier Coloma. Tel: +34 91 732 8000 (Ext 3033);
| | | | - Francisco A Balaguer
- Department of Macromolecular Structures, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas, Madrid, Spain
| | - Karolina Gmurczyk
- Department of Macromolecular Structures, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas, Madrid, Spain
| | - Clara Aicart-Ramos
- Department of Macromolecular Structures, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Científicas, Madrid, Spain
| | - Óscar M Nuero
- Molecular Interactions Facility, Centro de Investigaciones Biológicas Margarita Salas (CSIC), Madrid, Spain
| | - Juan Román Luque-Ortega
- Molecular Interactions Facility, Centro de Investigaciones Biológicas Margarita Salas (CSIC), Madrid, Spain
| | - Kimberly Calugaru
- Department of Microbiology and Immunology, W. R. Hearst Microbiology Research Center, Weill Cornell Medicine, New York, NY, USA
| | - Neal F Lue
- Department of Microbiology and Immunology, W. R. Hearst Microbiology Research Center, Weill Cornell Medicine, New York, NY, USA
| | | | - Oscar Llorca
- To whom correspondence should be addressed. Tel: +34 91 732 8000 (Ext 3000);
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4
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Rocha da Silva C, Sá LGDAV, Dos Santos EV, Ferreira TL, Coutinho TDNP, Moreira LEA, de Sousa Campos R, de Andrade CR, Barbosa da Silva WM, de Sá Carneiro I, Silva J, Dos Santos HS, Marinho ES, Cavalcanti BC, de Moraes MO, Júnior HVN, Andrade Neto JB. Evaluation of the antifungal effect of chlorogenic acid against strains of Candida spp. resistant to fluconazole: apoptosis induction and in silico analysis of the possible mechanisms of action. J Med Microbiol 2022; 71. [PMID: 35575783 DOI: 10.1099/jmm.0.001526] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Introduction. Candida spp. are commensal fungal pathogens of humans, but when there is an imbalance in the microbiota, or weak host immunity, these yeasts can become pathogenic, generating high medical costs.Gap Statement. With the increase in resistance to conventional antifungals, the development of new therapeutic strategies is necessary. This study evaluated the in vitro antifungal activity of chlorogenic acid against fluconazole-resistant strains of Candida spp. Mechanism of action through flow cytometry and in silico analyses, as well as molecular docking assays with ALS3 and SAP5, important proteins in the pathogenesis of Candida albicans associated with the adhesion process and biofilm formation.Results. The chlorogenic acid showed in vitro antifungal activity against the strains tested, causing reduced cell viability, increased potential for mitochondrial depolarization and production of reactive oxygen species, DNA fragmentation and phosphatidylserine externalization, indicating an apoptotic process. Concerning the analysis through docking, the complexes formed between chlorogenic acid and the targets Thymidylate Kinase, CYP51, 1Yeast Cytochrome BC1 Complex e Exo-B-(1,3)-glucanase demonstrated more favourable binding energy. In addition, chlorogenic acid presented significant interactions with the ALS3 active site residues of C. albicans, important in the adhesion process and resistance to fluconazole. Regarding molecular docking with SAP5, no significant interactions were found between chlorogenic acid and the active site of the enzyme.Conclusion. We concluded that chlorogenic acid has potential use as an adjuvant in antifungal therapies, due to its anti-Candida activity and ability to interact with important drug targets.
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Affiliation(s)
- Cecília Rocha da Silva
- School of Pharmacy, Laboratory of Bioprospection in Antimicrobial Molecules (LABIMAN), Federal University of Ceará, Fortaleza, CE, Brazil.,Drug Research and Development Center, Federal University of Ceará, Fortaleza, CE, Brazil
| | - Lívia Gurgel do Amaral Valente Sá
- School of Pharmacy, Laboratory of Bioprospection in Antimicrobial Molecules (LABIMAN), Federal University of Ceará, Fortaleza, CE, Brazil.,Drug Research and Development Center, Federal University of Ceará, Fortaleza, CE, Brazil.,Christus University Center (UNICHRISTUS), Fortaleza, CE, Brazil
| | | | | | | | - Lara Elloyse Almeida Moreira
- School of Pharmacy, Laboratory of Bioprospection in Antimicrobial Molecules (LABIMAN), Federal University of Ceará, Fortaleza, CE, Brazil.,Drug Research and Development Center, Federal University of Ceará, Fortaleza, CE, Brazil
| | - Rosana de Sousa Campos
- School of Pharmacy, Laboratory of Bioprospection in Antimicrobial Molecules (LABIMAN), Federal University of Ceará, Fortaleza, CE, Brazil.,Christus University Center (UNICHRISTUS), Fortaleza, CE, Brazil
| | | | | | - Igor de Sá Carneiro
- School of Pharmacy, Laboratory of Bioprospection in Antimicrobial Molecules (LABIMAN), Federal University of Ceará, Fortaleza, CE, Brazil
| | - Jacilene Silva
- Department of Chemistry, Group of Theoretical Chemistry and Electrochemistry (GQTE), State University of Ceará, Limoeiro do Norte, Ceará, Brazil
| | - Hélcio Silva Dos Santos
- Science and Technology Centre, Course of Chemistry, State University Vale do Acaraú, Sobral, CE, Brazil
| | - Emmanuel Silva Marinho
- Department of Chemistry, Group of Theoretical Chemistry and Electrochemistry (GQTE), State University of Ceará, Limoeiro do Norte, Ceará, Brazil
| | - Bruno Coelho Cavalcanti
- Drug Research and Development Center, Federal University of Ceará, Fortaleza, CE, Brazil.,Department of Physiology and Pharmacology, Federal University of Ceará, Fortaleza, CE, Brazil
| | - Manoel Odorico de Moraes
- Drug Research and Development Center, Federal University of Ceará, Fortaleza, CE, Brazil.,Department of Physiology and Pharmacology, Federal University of Ceará, Fortaleza, CE, Brazil
| | - Hélio Vitoriano Nobre Júnior
- School of Pharmacy, Laboratory of Bioprospection in Antimicrobial Molecules (LABIMAN), Federal University of Ceará, Fortaleza, CE, Brazil.,Drug Research and Development Center, Federal University of Ceará, Fortaleza, CE, Brazil
| | - João Batista Andrade Neto
- School of Pharmacy, Laboratory of Bioprospection in Antimicrobial Molecules (LABIMAN), Federal University of Ceará, Fortaleza, CE, Brazil.,Drug Research and Development Center, Federal University of Ceará, Fortaleza, CE, Brazil.,Christus University Center (UNICHRISTUS), Fortaleza, CE, Brazil
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5
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Telomeres and Cancer. Life (Basel) 2021; 11:life11121405. [PMID: 34947936 PMCID: PMC8704776 DOI: 10.3390/life11121405] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2021] [Revised: 12/01/2021] [Accepted: 12/06/2021] [Indexed: 12/18/2022] Open
Abstract
Telomeres cap the ends of eukaryotic chromosomes and are indispensable chromatin structures for genome protection and replication. Telomere length maintenance has been attributed to several functional modulators, including telomerase, the shelterin complex, and the CST complex, synergizing with DNA replication, repair, and the RNA metabolism pathway components. As dysfunctional telomere maintenance and telomerase activation are associated with several human diseases, including cancer, the molecular mechanisms behind telomere length regulation and protection need particular emphasis. Cancer cells exhibit telomerase activation, enabling replicative immortality. Telomerase reverse transcriptase (TERT) activation is involved in cancer development through diverse activities other than mediating telomere elongation. This review describes the telomere functions, the role of functional modulators, the implications in cancer development, and the future therapeutic opportunities.
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6
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Spivakovsky-Gonzalez E, Polleys EJ, Masnovo C, Cebrian J, Molina-Vargas AM, Freudenreich CH, Mirkin SM. Rad9-mediated checkpoint activation is responsible for elevated expansions of GAA repeats in CST-deficient yeast. Genetics 2021; 219:6343461. [PMID: 34849883 DOI: 10.1093/genetics/iyab125] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2021] [Accepted: 07/26/2021] [Indexed: 11/13/2022] Open
Abstract
Large-scale expansion of (GAA)n repeats in the first intron of the FXN gene is responsible for the severe neurodegenerative disease, Friedreich's ataxia in humans. We have previously conducted an unbiased genetic screen for GAA repeat instability in a yeast experimental system. The majority of genes that came from this screen encoded the components of DNA replication machinery, strongly implying that replication irregularities are at the heart of GAA repeat expansions. This screen, however, also produced two unexpected hits: members of the CST complex, CDC13 and TEN1 genes, which are required for telomere maintenance. To understand how the CST complex could affect intra-chromosomal GAA repeats, we studied the well-characterized temperature-sensitive cdc13-1 mutation and its effects on GAA repeat instability in yeast. We found that in-line with the screen results, this mutation leads to ∼10-fold increase in the rate of large-scale expansions of the (GAA)100 repeat at semi-permissive temperature. Unexpectedly, the hyper-expansion phenotype of the cdc13-1 mutant largely depends on activation of the G2/M checkpoint, as deletions of individual genes RAD9, MEC1, RAD53, and EXO1 belonging to this pathway rescued the increased GAA expansions. Furthermore, the hyper-expansion phenotype of the cdc13-1 mutant depended on the subunit of DNA polymerase δ, Pol32. We hypothesize, therefore, that increased repeat expansions in the cdc13-1 mutant happen during post-replicative repair of nicks or small gaps within repetitive tracts during the G2 phase of the cell cycle upon activation of the G2/M checkpoint.
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Affiliation(s)
| | - Erica J Polleys
- Department of Biology, Tufts University, Medford, MA 02155, USA
| | - Chiara Masnovo
- Department of Biology, Tufts University, Medford, MA 02155, USA
| | - Jorge Cebrian
- Department of Biology, Tufts University, Medford, MA 02155, USA.,Department of Pharmacology and Toxicology, School of Medicine, Universidad Complutense de Madrid, Instituto de Investigación Sanitaria Gregorio Marañón, CIBERCV, Madrid 28040, Spain
| | - Adrian M Molina-Vargas
- Department of Biology, Tufts University, Medford, MA 02155, USA.,Department of Biomedical Genetics, University of Rochester Medical Center, Rochester, NY 14642, USA
| | | | - Sergei M Mirkin
- Department of Biology, Tufts University, Medford, MA 02155, USA
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7
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Structural insights into telomere protection and homeostasis regulation by yeast CST complex. Nat Struct Mol Biol 2020; 27:752-762. [PMID: 32661422 DOI: 10.1038/s41594-020-0459-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2019] [Accepted: 05/22/2020] [Indexed: 01/29/2023]
Abstract
Budding yeast Cdc13-Stn1-Ten1 (CST) complex plays an essential role in telomere protection and maintenance. Despite extensive studies, only structural information of individual domains of CST is available; the architecture of CST still remains unclear. Here, we report crystal structures of Kluyveromyces lactis Cdc13-telomeric-DNA, Cdc13-Stn1 and Stn1-Ten1 complexes and propose an integrated model depicting how CST assembles and plays its roles at telomeres. Surprisingly, two oligonucleotide/oligosaccharide-binding (OB) folds of Cdc13 (OB2 and OB4), previously believed to mediate Cdc13 homodimerization, actually form a stable intramolecular interaction. This OB2-OB4 module of Cdc13 is required for the Cdc13-Stn1 interaction that assembles CST into an architecture with a central ring-like core and multiple peripheral modules in a 2:2:2 stoichiometry. Functional analyses indicate that this unique CST architecture is essential for both telomere capping and homeostasis regulation. Overall, our results provide fundamentally valuable structural information regarding the CST complex and its roles in telomere biology.
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8
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Abstract
Telomeres are special structures at the ends of chromosomes that play an
important role in the protection of the genetic material. Telomere composition
is very diverse; noticeable differences can often be observed even among
closely related species. Here, we identify the homolog of telomeric protein
Cdc13 in the thermotolerant yeast Hansenula polymorpha. We
show that it can specifically bind single-stranded telomeric DNA, as well as
interact with the Stn1 protein. In addition, we have uncovered an interaction
between Cdc13 and TERT (one of the core components of the telomerase complex),
which suggests that Cdc13 is potentially involved in telomerase recruitment to
telomeres in H. polymorpha.
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Affiliation(s)
- A. N. Malyavko
- Faculty of Chemistry and Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119991 Russia
| | - O. A. Dontsova
- Faculty of Chemistry and Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119991 Russia
- Skolkovo Institute of Science and Technology, Moscow, 121205 Russia
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry of the Russian Academy of Sciences, Moscow, 117997 Russia
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9
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Mersaoui SY, Bonnell E, Wellinger RJ. Nuclear import of Cdc13 limits chromosomal capping. Nucleic Acids Res 2019; 46:2975-2989. [PMID: 29432594 PMCID: PMC5887288 DOI: 10.1093/nar/gky085] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Accepted: 01/30/2018] [Indexed: 12/15/2022] Open
Abstract
Cdc13 is an essential protein involved in telomere maintenance and chromosome capping. Individual domain analyses on Cdc13 suggest the presence of four distinct OB-fold domains and one recruitment domain. However, it remained unclear how these sub-domains function in the context of the whole protein in vivo. Here, we use individual single domain deletions to address their roles in telomere capping. We find that the OB2 domain contains a nuclear localization signal that is essential for nuclear import of Cdc13 and therefore is required for chromosome capping. The karyopherin Msn5 is important for nuclear localization, and retention of Cdc13 in the nucleus also requires its binding to telomeres. Moreover, Cdc13 homodimerization occurs even if the protein is not bound to DNA and is in the cytoplasm. Hence, Cdc13 abundance in the nucleus and, in consequence, its capping function is strongly affected by nucleo-cytoplasmic transport as well as nuclear retention by DNA binding.
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Affiliation(s)
- Sofiane Y Mersaoui
- Department of Microbiology and Infectiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201 Rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada
| | - Erin Bonnell
- Department of Microbiology and Infectiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201 Rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada
| | - Raymund J Wellinger
- Department of Microbiology and Infectiology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201 Rue Jean Mignault, Sherbrooke, QC J1E 4K8, Canada
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10
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Shastrula PK, Rice CT, Wang Z, Lieberman PM, Skordalakes E. Structural and functional analysis of an OB-fold in human Ctc1 implicated in telomere maintenance and bone marrow syndromes. Nucleic Acids Res 2019; 46:972-984. [PMID: 29228254 PMCID: PMC5778599 DOI: 10.1093/nar/gkx1213] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Accepted: 11/23/2017] [Indexed: 12/18/2022] Open
Abstract
The human CST (Ctc1, Stn1 and Ten1) complex binds the telomeric overhang and regulates telomere length by promoting C-strand replication and inhibiting telomerase-dependent G-strand synthesis. Structural and biochemical studies on the human Stn1 and Ten1 complex revealed its mechanism of assembly and nucleic acid binding. However, little is known about the structural organization of the multi-domain Ctc1 protein and how each of these domains contribute to telomere length regulation. Here, we report the structure of a central domain of human Ctc1. The structure reveals a canonical OB-fold with the two identified disease mutations (R840W and V871M) contributing to the fold of the protein. In vitro assays suggest that although this domain is not contributing directly to Ctc1’s substrate binding properties, it affects full-length Ctc1 localization to telomeres and Stn1-Ten1 binding. Moreover, functional assays show that deletion of the entire OB-fold domain leads to significant increase in telomere length, frequency of internal single G-strands and fragile telomeres. Our findings demonstrate that a previously unknown OB-fold domain contributes to efficient Ctc1 telomere localization and chromosome end maintenance.
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Affiliation(s)
- Prashanth K Shastrula
- The Wistar Institute, Gene expression and regulation program, 3601 Spruce Street, Philadelphia, PA 19104, USA
| | - Cory T Rice
- The Wistar Institute, Gene expression and regulation program, 3601 Spruce Street, Philadelphia, PA 19104, USA
| | - Zhuo Wang
- The Wistar Institute, Gene expression and regulation program, 3601 Spruce Street, Philadelphia, PA 19104, USA
| | - Paul M Lieberman
- The Wistar Institute, Gene expression and regulation program, 3601 Spruce Street, Philadelphia, PA 19104, USA
| | - Emmanuel Skordalakes
- The Wistar Institute, Gene expression and regulation program, 3601 Spruce Street, Philadelphia, PA 19104, USA
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11
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Mersaoui SY, Wellinger RJ. Fine tuning the level of the Cdc13 telomere-capping protein for maximal chromosome stability performance. Curr Genet 2018; 65:109-118. [PMID: 30066139 DOI: 10.1007/s00294-018-0871-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2018] [Revised: 07/24/2018] [Accepted: 07/25/2018] [Indexed: 10/28/2022]
Abstract
Chromosome stability relies on an adequate length and complete replication of telomeres, the physical ends of chromosomes. Telomeres are composed of short direct repeat DNA and the associated nucleoprotein complex is essential for providing end-stability. In addition, the so-called end-replication problem of the conventional replication requires that telomeres be elongated by a special mechanism which, in virtually all organisms, is based by a reverse transcriptase, called telomerase. Although, at the conceptual level, telomere functions are highly similar in most organisms, the telomeric nucleoprotein composition appears to diverge significantly, in particular if it is compared between mammalian and budding yeast cells. However, over the last years, the CST complex has emerged as a central hub for telomere replication in most systems. Composed of three proteins, it is related to the highly conserved replication protein A complex, and in all systems studied, it coordinates telomerase-based telomere elongation with lagging-strand DNA synthesis. In budding yeast, the Cdc13 protein of this complex also is essential for telomerase recruitment and this specialisation is accompanied by additional regulatory adaptations. Based on recent results obtained in yeast, here, we review these issues and present an updated telomere replication hypothesis. We speculate that the similarities between systems far outweigh the differences, once we detach ourselves from the historic descriptions of the mechanisms in the various organisms.
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Affiliation(s)
- Sofiane Y Mersaoui
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201 Rue Jean Mignault, Sherbrooke, QC, J1E 4K8, Canada
| | - Raymund J Wellinger
- Department of Microbiology and Infectious Diseases, Faculty of Medicine and Health Sciences, Université de Sherbrooke, 3201 Rue Jean Mignault, Sherbrooke, QC, J1E 4K8, Canada.
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12
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Stewart JA, Wang Y, Ackerson SM, Schuck PL. Emerging roles of CST in maintaining genome stability and human disease. Front Biosci (Landmark Ed) 2018; 23:1564-1586. [PMID: 29293451 DOI: 10.2741/4661] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The human CTC1-STN1-TEN1 (CST) complex is a single-stranded DNA binding protein that shares homology with RPA and interacts with DNA polymerase alpha/primase. CST complexes are conserved from yeasts to humans and function in telomere maintenance. A common role of CST across species is in the regulation of telomere extension by telomerase and C-strand fill-in synthesis. However, recent studies also indicate that CST promotes telomere duplex replication as well the rescue of stalled DNA replication at non-telomeric sites. Furthermore, CST dysfunction and mutation is associated with several genetic diseases and cancers. In this review, we will summarize what is known about CST with a particular focus on the emerging roles of CST in DNA replication and human disease.
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Affiliation(s)
- Jason A Stewart
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA,
| | - Yilin Wang
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
| | - Stephanie M Ackerson
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
| | - Percy Logan Schuck
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
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13
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Lin H, Gong L, Zhan S, Wang Y, Liu A. Novel biallelic missense mutations in CTC1 gene identified in a Chinese family with Coats plus syndrome. J Neurol Sci 2017; 382:142-145. [DOI: 10.1016/j.jns.2017.09.041] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Revised: 09/26/2017] [Accepted: 09/27/2017] [Indexed: 01/01/2023]
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14
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Scott H, Kim JK, Yu C, Huang L, Qiao F, Taylor DJ. Spatial Organization and Molecular Interactions of the Schizosaccharomyces pombe Ccq1-Tpz1-Poz1 Shelterin Complex. J Mol Biol 2017; 429:2863-2872. [PMID: 28807855 DOI: 10.1016/j.jmb.2017.08.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2017] [Revised: 07/31/2017] [Accepted: 08/05/2017] [Indexed: 12/18/2022]
Abstract
The shelterin complex is a macromolecular assembly of proteins that binds to and protects telomeric DNA, which composes the ends of all linear chromosomes. Shelterin proteins prevent chromosome ends from fusing together and from eliciting erroneous induction of DNA damage response pathways. In addition, shelterin proteins play key roles in regulating the recruitment and activation of telomerase, an enzyme that extends telomeric DNA. In fission yeast, Schizosaccharomyces pombe, interactions between the shelterin proteins Ccq1, Tpz1, and Poz1 are important for regulating telomerase-mediated telomere synthesis and thus telomere length homeostasis. Here, we used electron microscopy combined with genetic labeling to define the three-dimensional arrangement of the S. pombe Ccq1-Tpz1-Poz1 (CTP) complex. Crosslinking mass spectrometry was used to identify individual residues that are in proximity to the protein-protein interfaces of the assembled CTP complex. Together, our data provide a first glimpse into the architectural design of the CTP complex and reveals unique interactions that are important in maintaining the S. pombe telomere in a non-extendible state.
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Affiliation(s)
- Harry Scott
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, United States
| | - Jin-Kwang Kim
- Department of Biological Chemistry, University of California Irvine, Irvine, CA 92697, United States
| | - Clinton Yu
- Department of Physiology and Biophysics, University of California Irvine, Irvine, CA 92697, United States
| | - Lan Huang
- Department of Physiology and Biophysics, University of California Irvine, Irvine, CA 92697, United States
| | - Feng Qiao
- Department of Biological Chemistry, University of California Irvine, Irvine, CA 92697, United States.
| | - Derek J Taylor
- Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, United States; Department of Biochemistry, Case Western Reserve University, Cleveland, OH 44106, United States.
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15
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Strecker J, Stinus S, Caballero MP, Szilard RK, Chang M, Durocher D. A sharp Pif1-dependent threshold separates DNA double-strand breaks from critically short telomeres. eLife 2017; 6:23783. [PMID: 28826474 PMCID: PMC5595431 DOI: 10.7554/elife.23783] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Accepted: 07/26/2017] [Indexed: 11/25/2022] Open
Abstract
DNA double-strand breaks (DSBs) and short telomeres are structurally similar, yet they have diametrically opposed fates. Cells must repair DSBs while blocking the action of telomerase on these ends. Short telomeres must avoid recognition by the DNA damage response while promoting telomerase recruitment. In Saccharomyces cerevisiae, the Pif1 helicase, a telomerase inhibitor, lies at the interface of these end-fate decisions. Using Pif1 as a sensor, we uncover a transition point in which 34 bp of telomeric (TG1-3)n repeat sequence renders a DNA end insensitive to Pif1 action, thereby enabling extension by telomerase. A similar transition point exists at natural chromosome ends, where telomeres shorter than ~40 bp are inefficiently extended by telomerase. This phenomenon is not due to known Pif1 modifications and we instead propose that Cdc13 renders TG34+ ends insensitive to Pif1 action. We contend that the observed threshold of Pif1 activity defines a dividing line between DSBs and telomeres.
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Affiliation(s)
- Jonathan Strecker
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Canada
| | - Sonia Stinus
- European Research Institute for the Biology of Ageing, University of Groningen, University Medical Center Groningen, Groningen, Netherlands
| | - Mariana Pliego Caballero
- European Research Institute for the Biology of Ageing, University of Groningen, University Medical Center Groningen, Groningen, Netherlands
| | - Rachel K Szilard
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Canada
| | - Michael Chang
- European Research Institute for the Biology of Ageing, University of Groningen, University Medical Center Groningen, Groningen, Netherlands
| | - Daniel Durocher
- Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, Toronto, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Canada
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16
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Abstract
Telomerase is an RNA-protein complex that extends the 3' ends of linear chromosomes, using a unique telomerase reverse transcriptase (TERT) and template in the telomerase RNA (TR), thereby helping to maintain genome integrity. TR assembles with TERT and species-specific proteins, and telomerase function in vivo requires interaction with telomere-associated proteins. Over the past two decades, structures of domains of TR and TERT as well as other telomerase- and telomere-interacting proteins have provided insights into telomerase function. A recently reported 9-Å cryo-electron microscopy map of the Tetrahymena telomerase holoenzyme has provided a framework for understanding how TR, TERT, and other proteins from ciliate as well as vertebrate telomerase fit and function together as well as unexpected insight into telomerase interaction at telomeres. Here we review progress in understanding the structural basis of human and Tetrahymena telomerase activity, assembly, and interactions.
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Affiliation(s)
- Henry Chan
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569; , ,
| | - Yaqiang Wang
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569; , ,
| | - Juli Feigon
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569; , ,
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17
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Lloyd NR, Dickey TH, Hom RA, Wuttke DS. Tying up the Ends: Plasticity in the Recognition of Single-Stranded DNA at Telomeres. Biochemistry 2016; 55:5326-40. [PMID: 27575340 PMCID: PMC5656232 DOI: 10.1021/acs.biochem.6b00496] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Telomeres terminate nearly exclusively in single-stranded DNA (ssDNA) overhangs comprised of the G-rich 3' end. This overhang varies widely in length from species to species, ranging from just a few bases to several hundred nucleotides. These overhangs are not merely a remnant of DNA replication but rather are the result of complex further processing. Proper management of the telomeric overhang is required both to deter the action of the DNA damage machinery and to present the ends properly to the replicative enzyme telomerase. This Current Topic addresses the biochemical and structural features used by the proteins that manage these variable telomeric overhangs. The Pot1 protein tightly binds the single-stranded overhang, preventing DNA damage sensors from binding. Pot1 also orchestrates the access of telomerase to that same substrate. The remarkable plasticity of the binding interface exhibited by the Schizosaccharomyces pombe Pot1 provides mechanistic insight into how these roles may be accomplished, and disease-associated mutations clustered around the DNA-binding interface in the hPOT1 highlight the importance of this function. The budding yeast Cdc13-Stn1-Ten1, a telomeric RPA complex closely associated with telomere function, also interacts with ssDNA in a fashion that allows degenerate sequences to be recognized. A related human complex composed of hCTC1, hSTN1, and hTEN1 has recently emerged with links to both telomere maintenance and general DNA replication and also exhibits mutations associated with telomere pathologies. Overall, these sequence-specific ssDNA binders exhibit a range of recognition properties that allow them to perform their unique biological functions.
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Affiliation(s)
- Neil R. Lloyd
- Department of Chemistry and Biochemistry, 596 UCB, University of Colorado Boulder, Boulder, CO 80309-0596, USADepartment of Chemistry and Biochemistry, 596 UCB, University of Colorado Boulder, Boulder, CO 80309, USA
| | | | - Robert A. Hom
- Department of Chemistry and Biochemistry, 596 UCB, University of Colorado Boulder, Boulder, CO 80309-0596, USADepartment of Chemistry and Biochemistry, 596 UCB, University of Colorado Boulder, Boulder, CO 80309, USA
| | - Deborah S. Wuttke
- Department of Chemistry and Biochemistry, 596 UCB, University of Colorado Boulder, Boulder, CO 80309-0596, USADepartment of Chemistry and Biochemistry, 596 UCB, University of Colorado Boulder, Boulder, CO 80309, USA
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18
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Abstract
Telomeres are nucleoprotein complexes that maintain the ends of our chromosomes thus providing genomic stability. Telomerase is a ribonucleoprotein reverse transcriptase that replicates the short tandem repeats of DNA known as telomeres. The telomeric DNA is specifically associated with two major complexes, the shelterin and CST complexes both of which are involved in telomere length regulation and maintenance along with telomerase. Obtaining structural information on these nucleoprotein complexes has been a major bottleneck in fully understanding the mechanism of action of telomeric nucleoproteins for over two decades. The recent advances in molecular and structural biology have enabled us to obtain atomic resolution structures of telomeric proteins alone and in complex with their nucleic acid substrates transforming the field and our understanding and interpretation of this unique biological pathway. Here we report our approach to obtain the structure of the Triobolium castaneum catalytic subunit of telomerase TERT (tcTERT) in its apo- and substrate-bound states.
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Affiliation(s)
- H Hoffman
- The Wistar Institute, Philadelphia, PA, United States
| | - E Skordalakes
- The Wistar Institute, Philadelphia, PA, United States.
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19
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Rice C, Skordalakes E. Structure and function of the telomeric CST complex. Comput Struct Biotechnol J 2016; 14:161-7. [PMID: 27239262 PMCID: PMC4872678 DOI: 10.1016/j.csbj.2016.04.002] [Citation(s) in RCA: 78] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Revised: 04/06/2016] [Accepted: 04/07/2016] [Indexed: 11/25/2022] Open
Abstract
Telomeres comprise the ends of eukaryotic chromosomes and are essential for cell proliferation and genome maintenance. Telomeres are replicated by telomerase, a ribonucleoprotein (RNP) reverse transcriptase, and are maintained primarily by nucleoprotein complexes such as shelterin (TRF1, TRF2, TIN2, RAP1, POT1, TPP1) and CST (Cdc13/Ctc1, Stn1, Ten1). The focus of this review is on the CST complex and its role in telomere maintenance. Although initially thought to be unique to yeast, it is now evident that the CST complex is present in a diverse range of organisms where it contributes to genome maintenance. The CST accomplishes these tasks via telomere capping and by regulating telomerase and DNA polymerase alpha-primase (polα-primase) access to telomeres, a process closely coordinated with the shelterin complex in most organisms. The goal of this review is to provide a brief but comprehensive account of the diverse, and in some cases organism-dependent, functions of the CST complex and how it contributes to telomere maintenance and cell proliferation.
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20
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Greetham M, Skordalakes E, Lydall D, Connolly BA. The Telomere Binding Protein Cdc13 and the Single-Stranded DNA Binding Protein RPA Protect Telomeric DNA from Resection by Exonucleases. J Mol Biol 2015; 427:3023-30. [PMID: 26264873 PMCID: PMC4580210 DOI: 10.1016/j.jmb.2015.08.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2015] [Revised: 07/30/2015] [Accepted: 08/04/2015] [Indexed: 11/30/2022]
Abstract
The telomere is present at the ends of all eukaryotic chromosomes and usually consists of repetitive TG-rich DNA that terminates in a single-stranded 3' TG extension and a 5' CA-rich recessed strand. A biochemical assay that allows the in vitro observation of exonuclease-catalyzed degradation (resection) of telomeres has been developed. The approach uses an oligodeoxynucleotide that folds to a stem-loop with a TG-rich double-stranded region and a 3' single-stranded extension, typical of telomeres. Cdc13, the major component of the telomere-specific CST complex, strongly protects the recessed strand from the 5'→3' exonuclease activity of the model exonuclease from bacteriophage λ. The isolated DNA binding domain of Cdc13 is less effective at shielding telomeres. Protection is specific, not being observed in control DNA lacking the specific TG-rich telomere sequence. RPA, the eukaryotic single-stranded DNA binding protein, also inhibits telomere resection. However, this protein is non-specific, equally hindering the degradation of non-telomere controls.
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Affiliation(s)
- Matthew Greetham
- Institute for Cell and Molecular Biology, The University of Newcastle, Newcastle upon Tyne NE2 4HH, United Kingdom
| | | | - David Lydall
- Institute for Cell and Molecular Biology, The University of Newcastle, Newcastle upon Tyne NE2 4HH, United Kingdom
| | - Bernard A Connolly
- Institute for Cell and Molecular Biology, The University of Newcastle, Newcastle upon Tyne NE2 4HH, United Kingdom.
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21
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Steinberg-Neifach O, Wellington K, Vazquez L, Lue NF. Combinatorial recognition of a complex telomere repeat sequence by the Candida parapsilosis Cdc13AB heterodimer. Nucleic Acids Res 2015; 43:2164-76. [PMID: 25662607 PMCID: PMC4344524 DOI: 10.1093/nar/gkv092] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The telomere repeat units of Candida species are substantially longer and more complex than those in other organisms, raising interesting questions concerning the recognition mechanisms of telomere-binding proteins. Herein we characterized the properties of Candida parapsilosis Cdc13A and Cdc13B, two paralogs that are responsible for binding and protecting the telomere G-strand tails. We found that Cdc13A and Cdc13B can each form complexes with itself and a heterodimeric complex with each other. However, only the heterodimer exhibits high-affinity and sequence-specific binding to the telomere G-tail. EMSA and crosslinking analysis revealed a combinatorial mechanism of DNA recognition, which entails the A and B subunit making contacts to the 3′ and 5′ region of the repeat unit. While both the DBD and OB4 domain of Cdc13A can bind to the equivalent domain in Cdc13B, only the OB4 complex behaves as a stable heterodimer. The unstable Cdc13ABDBD complex binds G-strand with greatly reduced affinity but the same sequence specificity. Thus the OB4 domains evidently contribute to binding by promoting dimerization of the DBDs. Our investigation reveals a rare example of combinatorial recognition of single-stranded DNA and offers insights into the co-evolution of telomere DNA and cognate binding proteins.
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Affiliation(s)
- Olga Steinberg-Neifach
- Department of Microbiology & Immunology, W. R. Hearst Microbiology Research Center, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, USA
- Hostos Community College, City University of New York, 500 Grand Concourse, Bronx, NY 10451, USA
| | - Kemar Wellington
- Hostos Community College, City University of New York, 500 Grand Concourse, Bronx, NY 10451, USA
| | - Leslie Vazquez
- Hostos Community College, City University of New York, 500 Grand Concourse, Bronx, NY 10451, USA
| | - Neal F. Lue
- Department of Microbiology & Immunology, W. R. Hearst Microbiology Research Center, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10065, USA
- To whom correspondence should be addressed. Tel: +1 212 746 6506; Fax: +1 212 746 8587;
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22
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Steinberg-Neifach O, Lue NF. Telomere DNA recognition in Saccharomycotina yeast: potential lessons for the co-evolution of ssDNA and dsDNA-binding proteins and their target sites. Front Genet 2015; 6:162. [PMID: 25983743 PMCID: PMC4416457 DOI: 10.3389/fgene.2015.00162] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2015] [Accepted: 04/10/2015] [Indexed: 01/22/2023] Open
Abstract
In principle, alterations in the telomere repeat sequence would be expected to disrupt the protective nucleoprotein complexes that confer stability to chromosome ends, and hence relatively rare events in evolution. Indeed, numerous organisms in diverse phyla share a canonical 6 bp telomere repeat unit (5'-TTAGGG-3'/5'-CCCTAA-3'), suggesting common descent from an ancestor that carries this particular repeat. All the more remarkable, then, are the extraordinarily divergent telomere sequences that populate the Saccharomycotina subphylum of budding yeast. These sequences are distinguished from the canonical telomere repeat in being long, occasionally degenerate, and frequently non-G/C-rich. Despite the divergent telomere repeat sequences, studies to date indicate that the same families of single-strand and double-strand telomere binding proteins (i.e., the Cdc13 and Rap1 families) are responsible for telomere protection in Saccharomycotina yeast. The recognition mechanisms of the protein family members therefore offer an informative paradigm for understanding the co-evolution of DNA-binding proteins and the cognate target sequences. Existing data suggest three potential, inter-related solutions to the DNA recognition problem: (i) duplication of the recognition protein and functional modification; (ii) combinatorial recognition of target site; and (iii) flexibility of the recognition surfaces of the DNA-binding proteins to adopt alternative conformations. Evidence in support of these solutions and the relevance of these solutions to other DNA-protein regulatory systems are discussed.
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Affiliation(s)
- Olga Steinberg-Neifach
- Department of Microbiology and Immunology, W. R. Hearst Microbiology Research Center, Weill Medical College, Cornell University , New York, NY, USA ; Hostos Community College, City University of New York , Bronx, NY, USA
| | - Neal F Lue
- Department of Microbiology and Immunology, W. R. Hearst Microbiology Research Center, Weill Medical College, Cornell University , New York, NY, USA
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23
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Rajavel M, Mullins MR, Taylor DJ. Multiple facets of TPP1 in telomere maintenance. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2014; 1844:1550-9. [PMID: 24780581 DOI: 10.1016/j.bbapap.2014.04.014] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2014] [Revised: 04/01/2014] [Accepted: 04/18/2014] [Indexed: 11/30/2022]
Abstract
Telomeres are nucleoprotein complexes that cap the ends of all linear chromosomes and function to prevent aberrant repair and end-to-end chromosome fusions. In somatic cells, telomere shortening is a natural part of the aging process as it occurs with each round of cell division. In germ and stem cells, however, the enzyme telomerase synthesizes telomere DNA to counter-balance telomere shortening and help maintain cellular proliferation. Of the primary telomere end-binding proteins, TPP1 has recently emerged as a primary contributor in protecting telomere DNA and in recruiting telomerase to the telomere ends. In this review, we summarize the current knowledge regarding the role of TPP1 in telomere maintenance.
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Affiliation(s)
- Malligarjunan Rajavel
- Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland OH 44106, USA
| | - Michael R Mullins
- Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland OH 44106, USA
| | - Derek J Taylor
- Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland OH 44106, USA; Department of Biochemistry, Case Western Reserve University, School of Medicine, Cleveland OH 44106, USA.
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24
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Gu P, Chang S. Functional characterization of human CTC1 mutations reveals novel mechanisms responsible for the pathogenesis of the telomere disease Coats plus. Aging Cell 2013; 12:1100-9. [PMID: 23869908 DOI: 10.1111/acel.12139] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/10/2013] [Indexed: 11/29/2022] Open
Abstract
Coats plus is a rare recessive disorder characterized by intracranial calcifications, hematological abnormalities, and retinal vascular defects. This disease results from mutations in CTC1, a member of the CTC1-STN1-TEN1 (CST) complex critical for telomere replication. Telomeres are specialized DNA/protein structures essential for the maintenance of genome stability. Several patients with Coats plus display critically shortened telomeres, suggesting that telomere dysfunction plays an important role in disease pathogenesis. These patients inherit CTC1 mutations in a compound heterozygous manner, with one allele encoding a frameshift mutant and the other a missense mutant. How these mutations impact upon telomere function is unknown. We report here the first biochemical characterization of human CTC1 mutations. We found that all CTC1 frameshift mutations generated truncated or unstable protein products, none of which were able to form a complex with STN1-TEN1 on telomeres, resulting in progressive telomere shortening and formation of fused chromosomes. Missense mutations are able to form the CST complex at telomeres, but their expression levels are often repressed by the frameshift mutants. Our results also demonstrate for the first time that CTC1 mutations promote telomere dysfunction by decreasing the stability of STN1 to reduce its ability to interact with DNA Polα, thus highlighting a previously unknown mechanism to induce telomere dysfunction.
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Affiliation(s)
- Peili Gu
- Department of Laboratory Medicine; Yale University School of Medicine; 330 Cedar Street New Haven CT 06520 USA
| | - Sandy Chang
- Department of Laboratory Medicine; Yale University School of Medicine; 330 Cedar Street New Haven CT 06520 USA
- Department of Pathology; Yale University School of Medicine; 330 Cedar Street New Haven CT 06520 USA
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25
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Lewis KA, Pfaff DA, Earley JN, Altschuler SE, Wuttke DS. The tenacious recognition of yeast telomere sequence by Cdc13 is fully exerted by a single OB-fold domain. Nucleic Acids Res 2013; 42:475-84. [PMID: 24057216 PMCID: PMC3874162 DOI: 10.1093/nar/gkt843] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Cdc13, the telomere end-binding protein from Saccharomyces cerevisiae, is a multidomain protein that specifically binds telomeric single-stranded DNA (ssDNA) with exquisitely high affinity to coordinate telomere maintenance. Recent structural and genetic data have led to the proposal that Cdc13 is the paralog of RPA70 within a telomere-specific RPA complex. Our understanding of Cdc13 structure and biochemistry has been largely restricted to studies of individual domains, precluding analysis of how each domain influences the activity of the others. To better facilitate a comparison to RPA70, we evaluated the ssDNA binding of full-length S. cerevisiae Cdc13 to its minimal substrate, Tel11. We found that, unlike RPA70 and the other known telomere end-binding proteins, the core Cdc13 ssDNA-binding activity is wholly contained within a single tight-binding oligosaccharide/oligonucleotide/oligopeptide binding (OB)-fold. Because two OB-folds are implicated in dimerization, we also evaluated the relationship between dimerization and ssDNA-binding activity and found that the two activities are independent. We also find that Cdc13 binding exhibits positive cooperativity that is independent of dimerization. This study reveals that, while Cdc13 and RPA70 share similar domain topologies, the corresponding domains have evolved different and specialized functions.
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Affiliation(s)
- Karen A Lewis
- Department of Chemistry and Biochemistry, UCB 543, University of Colorado Boulder, Boulder, CO 80309, USA
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26
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Lue NF, Chan J. Duplication and functional specialization of the telomere-capping protein Cdc13 in Candida species. J Biol Chem 2013; 288:29115-23. [PMID: 23965999 DOI: 10.1074/jbc.m113.506519] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The budding yeast G-tail binding complex CST (Cdc13-Stn1-Ten1) is crucial for both telomere protection and replication. Previous studies revealed a family of Cdc13 orthologues (Cdc13A) in Candida species that are unusually small but are nevertheless responsible for G-tail binding and the regulation of telomere lengths and structures. Here we report the identification and characterization of a second family of Cdc13-like proteins in the Candida clade, named Cdc13B. Phylogenetic analysis and sequence alignment indicate that Cdc13B probably arose through gene duplication prior to Candida speciation. Like Cdc13A, Cdc13B appears to be essential. Deleting one copy each of the CDC13A and CDC13B genes caused a synergistic effect on aberrant telomere elongation and t-circle accumulation, suggesting that the two paralogues mediate overlapping and nonredundant functions in telomere regulation. Interestingly, Cdc13B utilizes its C-terminal OB-fold domain (OB4) to mediate self-association and binding to Cdc13A. Moreover, the stability of the heterodimer is evidently greater than that of either homodimer. Both the Cdc13 A/A homodimer and A/B heterodimer, but not the B/B homodimer, recognized the telomere G-tail repeat with high affinity and sequence specificity. Our results reveal novel evolutionary elaborations of the G-tail-binding protein in Saccharomycotina yeast, suggesting a drastic remodeling of CDC13 that entails gene duplication, fusion, and functional specialization. The repeated and independent duplication of G-tail-binding proteins such as Cdc13 and Pot1 hints at the evolutionary advantage of having multiple G-tail-binding proteins.
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Affiliation(s)
- Neal F Lue
- From the Department of Microbiology and Immunology, W. R. Hearst Microbiology Research Center, Weill Medical College of Cornell University, New York, New York 10065
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27
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Abstract
The essential Cdc13 protein is part of the trimeric CST complex that confers genome stability by binding to and protecting yeast telomeres. In this issue of Structure, Mason and colleagues characterize an OB fold domain of Cdc13 (named OB2) and propose that homo-dimerization of OB2 is required for proper assembly of the CST complex and telomere maintenance.
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