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Wan L, Toland S, Robinson-McCarthy LR, Lee N, Schaich MA, Hengel SR, Li X, Bernstein KA, Van Houten B, Chang Y, Moore PS. Unlicensed origin DNA melting by MCV and SV40 polyomavirus LT proteins is independent of ATP-dependent helicase activity. Proc Natl Acad Sci U S A 2023; 120:e2308010120. [PMID: 37459531 PMCID: PMC10372695 DOI: 10.1073/pnas.2308010120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Accepted: 06/21/2023] [Indexed: 07/20/2023] Open
Abstract
Cellular eukaryotic replication initiation helicases are first loaded as head-to-head double hexamers on double-stranded (ds) DNA origins and then initiate S-phase DNA melting during licensed (once per cell cycle) replication. Merkel cell polyomavirus (MCV) large T (LT) helicase oncoprotein similarly binds and melts its own 98-bp origin but replicates multiple times in a single cell cycle. To examine the actions of this unlicensed viral helicase, we quantitated multimerization of MCV LT molecules as they assembled on MCV DNA origins using real-time single-molecule microscopy. MCV LT formed highly stable double hexamers having 17-fold longer mean lifetime (τ, >1,500 s) on DNA than single hexamers. Unexpectedly, partial MCV LT assembly without double-hexamer formation was sufficient to melt origin dsDNA as measured by RAD51, RPA70, or S1 nuclease cobinding. DNA melting also occurred with truncated MCV LT proteins lacking the helicase domain, but was lost from a protein without the multimerization domain that could bind only as a monomer to DNA. SV40 polyomavirus LT also multimerized to the MCV origin without forming a functional hexamer but still melted origin DNA. MCV origin melting did not require ATP hydrolysis and occurred for both MCV and SV40 LT proteins using the nonhydrolyzable ATP analog, adenylyl-imidodiphosphate (AMP-PNP). LT double hexamers formed in AMP-PNP, and melted DNA, consistent with direct LT hexamer assembly around single-stranded (ss) DNA without the energy-dependent dsDNA-to-ssDNA melting and remodeling steps used by cellular helicases. These results indicate that LT multimerization rather than helicase activity is required for origin DNA melting during unlicensed virus replication.
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Affiliation(s)
- Li Wan
- Cancer Virology Program, Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA15213
| | - Sabrina Toland
- Cancer Virology Program, Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA15213
| | | | - Nara Lee
- Department of Microbiology and Molecular Genetics, University of Pittsburgh, Pittsburgh, PA15219
| | - Matthew A. Schaich
- Genome Stability Program, Hillman Cancer Center, Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA15232
| | - Sarah R. Hengel
- Department of Pharmacology, Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA15232
| | - Xiaochen Li
- Cancer Virology Program, Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA15213
- School of Medicine, Tsinghua University, Beijing100084, China
| | - Kara A. Bernstein
- Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia, PA19104
| | - Bennett Van Houten
- Genome Stability Program, Hillman Cancer Center, Department of Pharmacology and Chemical Biology, University of Pittsburgh, Pittsburgh, PA15232
| | - Yuan Chang
- Cancer Virology Program, Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA15213
| | - Patrick S. Moore
- Cancer Virology Program, Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA15213
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2
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Rzechorzek NJ, Hardwick SW, Jatikusumo VA, Chirgadze D, Pellegrini L. CryoEM structures of human CMG-ATPγS-DNA and CMG-AND-1 complexes. Nucleic Acids Res 2020; 48:6980-6995. [PMID: 32453425 PMCID: PMC7337937 DOI: 10.1093/nar/gkaa429] [Citation(s) in RCA: 49] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Revised: 05/05/2020] [Accepted: 05/11/2020] [Indexed: 11/25/2022] Open
Abstract
DNA unwinding in eukaryotic replication is performed by the Cdc45-MCM-GINS (CMG) helicase. Although the CMG architecture has been elucidated, its mechanism of DNA unwinding and replisome interactions remain poorly understood. Here we report the cryoEM structure at 3.3 Å of human CMG bound to fork DNA and the ATP-analogue ATPγS. Eleven nucleotides of single-stranded (ss) DNA are bound within the C-tier of MCM2-7 AAA+ ATPase domains. All MCM subunits contact DNA, from MCM2 at the 5'-end to MCM5 at the 3'-end of the DNA spiral, but only MCM6, 4, 7 and 3 make a full set of interactions. DNA binding correlates with nucleotide occupancy: five MCM subunits are bound to either ATPγS or ADP, whereas the apo MCM2-5 interface remains open. We further report the cryoEM structure of human CMG bound to the replisome hub AND-1 (CMGA). The AND-1 trimer uses one β-propeller domain of its trimerisation region to dock onto the side of the helicase assembly formed by Cdc45 and GINS. In the resulting CMGA architecture, the AND-1 trimer is closely positioned to the fork DNA while its CIP (Ctf4-interacting peptide)-binding helical domains remain available to recruit partner proteins.
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Affiliation(s)
- Neil J Rzechorzek
- Department of Biochemistry, Tennis Court Road, Cambridge CB2 1GA, UK
| | - Steven W Hardwick
- Department of Biochemistry, Tennis Court Road, Cambridge CB2 1GA, UK
| | | | | | - Luca Pellegrini
- Department of Biochemistry, Tennis Court Road, Cambridge CB2 1GA, UK
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3
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Perera HM, Behrmann MS, Hoang JM, Griffin WC, Trakselis MA. Contacts and context that regulate DNA helicase unwinding and replisome progression. Enzymes 2019; 45:183-223. [PMID: 31627877 DOI: 10.1016/bs.enz.2019.08.001] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Hexameric DNA helicases involved in the separation of duplex DNA at the replication fork have a universal architecture but have evolved from two separate protein families. The consequences are that the regulation, translocation polarity, strand specificity, and architectural orientation varies between phage/bacteria to that of archaea/eukaryotes. Once assembled and activated for single strand DNA translocation and unwinding, the DNA polymerase couples tightly to the helicase forming a robust replisome complex. However, this helicase-polymerase interaction can be challenged by various forms of endogenous or exogenous agents that can stall the entire replisome or decouple DNA unwinding from synthesis. The consequences of decoupling can be severe, leading to a build-up of ssDNA requiring various pathways for replication fork restart. All told, the hexameric helicase sits prominently at the front of the replisome constantly responding to a variety of obstacles that require transient unwinding/reannealing, traversal of more stable blocks, and alternations in DNA unwinding speed that regulate replisome progression.
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Affiliation(s)
- Himasha M Perera
- Department of Chemistry and Biochemistry, Baylor University, Waco, TX, United States
| | - Megan S Behrmann
- Department of Chemistry and Biochemistry, Baylor University, Waco, TX, United States
| | - Joy M Hoang
- Department of Chemistry and Biochemistry, Baylor University, Waco, TX, United States
| | - Wezley C Griffin
- Department of Chemistry and Biochemistry, Baylor University, Waco, TX, United States
| | - Michael A Trakselis
- Department of Chemistry and Biochemistry, Baylor University, Waco, TX, United States.
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4
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Meagher M, Epling LB, Enemark EJ. DNA translocation mechanism of the MCM complex and implications for replication initiation. Nat Commun 2019; 10:3117. [PMID: 31308367 PMCID: PMC6629641 DOI: 10.1038/s41467-019-11074-3] [Citation(s) in RCA: 47] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Accepted: 06/18/2019] [Indexed: 12/12/2022] Open
Abstract
The DNA translocation activity of the minichromosome maintenance (MCM) complex powers DNA strand separation of the replication forks of eukaryotes and archaea. Here we illustrate an atomic level mechanism for this activity with a crystal structure of an archaeal MCM hexamer bound to single-stranded DNA and nucleotide cofactors. Sequence conservation indicates this rotary mechanism is fully possible for all eukaryotes and archaea. The structure definitively demonstrates the ring orients during translocation with the N-terminal domain leading, indicating that the translocation activity could also provide the physical basis of replication initiation where a double-hexamer idly encircling double-stranded DNA transforms to single-hexamers that encircle only one strand. In this mechanism, each strand binds to the N-terminal tier of one hexamer and the AAA+ tier of the other hexamer such that one ring pulls on the other, aligning equivalent interfaces to enable each hexamer to pull its translocation strand outside of the opposing hexamer.
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Affiliation(s)
- Martin Meagher
- Department of Structural Biology, St Jude Children's Research Hospital, 262 Danny Thomas Place, Mail Stop 311, Memphis, TN, 38105, USA
| | - Leslie B Epling
- Department of Structural Biology, St Jude Children's Research Hospital, 262 Danny Thomas Place, Mail Stop 311, Memphis, TN, 38105, USA.,Incyte Research Institute, 1801 Augustine Cut-off, Wilmington, DE, 19803, USA
| | - Eric J Enemark
- Department of Structural Biology, St Jude Children's Research Hospital, 262 Danny Thomas Place, Mail Stop 311, Memphis, TN, 38105, USA.
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5
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Gai D, Wang D, Li SX, Chen XS. The structure of SV40 large T hexameric helicase in complex with AT-rich origin DNA. eLife 2016; 5. [PMID: 27921994 PMCID: PMC5140265 DOI: 10.7554/elife.18129] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Accepted: 11/03/2016] [Indexed: 12/12/2022] Open
Abstract
DNA replication is a fundamental biological process. The initial step in eukaryotic DNA replication is the assembly of the pre-initiation complex, including the formation of two head-to-head hexameric helicases around the replication origin. How these hexameric helicases interact with their origin dsDNA remains unknown. Here, we report the co-crystal structure of the SV40 Large-T Antigen (LT) hexameric helicase bound to its origin dsDNA. The structure shows that the six subunits form a near-planar ring that interacts with the origin, so that each subunit makes unique contacts with the DNA. The origin dsDNA inside the narrower AAA+ domain channel shows partial melting due to the compression of the two phosphate backbones, forcing Watson-Crick base-pairs within the duplex to flip outward. This structure provides the first snapshot of a hexameric helicase binding to origin dsDNA, and suggests a possible mechanism of origin melting by LT during SV40 replication in eukaryotic cells.
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Affiliation(s)
- Dahai Gai
- Departments of Biological Sciences and Chemistry, Molecular and Computational Biology Program, University of Southern California, Los Angeles, United States
| | - Damian Wang
- Department of Biological Sciences, Genetic, Molecular and Cellular Biology Program, Keck School of Medicine, University of Southern California, Los Angeles, United States
| | - Shu-Xing Li
- Center of Excellence in NanoBiophysics, University of Southern California, Los Angeles, United States
| | - Xiaojiang S Chen
- Departments of Biological Sciences and Chemistry, Molecular and Computational Biology Program, University of Southern California, Los Angeles, United States.,Department of Biological Sciences, Genetic, Molecular and Cellular Biology Program, Keck School of Medicine, University of Southern California, Los Angeles, United States.,Center of Excellence in NanoBiophysics, University of Southern California, Los Angeles, United States.,Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, United States
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6
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A conserved regulatory module at the C terminus of the papillomavirus E1 helicase domain controls E1 helicase assembly. J Virol 2014; 89:1129-42. [PMID: 25378487 DOI: 10.1128/jvi.01903-14] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED Viruses frequently combine multiple activities into one polypeptide to conserve coding capacity. This strategy creates regulatory challenges to ascertain that the combined activities are compatible and do not interfere with each other. The papillomavirus E1 protein, as many other helicases, has the intrinsic ability to form hexamers and double hexamers (DH) that serve as the replicative DNA helicase. However, E1 also has the more unusual ability to generate local melting by forming a double trimer (DT) complex that can untwist the double-stranded origin of DNA replication (ori) DNA in preparation for DH formation. Here we describe a switching mechanism that allows the papillomavirus E1 protein to form these two different kinds of oligomers and to transition between them. We show that a conserved regulatory module attached to the E1 helicase domain blocks hexamer and DH formation and promotes DT formation. In the presence of the appropriate trigger, the inhibitory effect of the regulatory module is relieved and the transition to DH formation can occur. IMPORTANCE This study provides a mechanistic understanding into how a multifunctional viral polypeptide can provide different, seemingly incompatible activities. A conserved regulatory sequence module attached to the AAA+ helicase domain in the papillomavirus E1 protein allows the formation of different oligomers with different biochemical activities.
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7
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Di Maro A, Citores L, Russo R, Iglesias R, Ferreras JM. Sequence comparison and phylogenetic analysis by the Maximum Likelihood method of ribosome-inactivating proteins from angiosperms. PLANT MOLECULAR BIOLOGY 2014; 85:575-88. [PMID: 24880476 DOI: 10.1007/s11103-014-0204-y] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2014] [Accepted: 05/16/2014] [Indexed: 05/16/2023]
Abstract
Ribosome-inactivating proteins (RIPs) from angiosperms are rRNA N-glycosidases that have been proposed as defence proteins against virus and fungi. They have been classified as type 1 RIPs, consisting of single-chain proteins, and type 2 RIPs, consisting of an A chain with RIP properties covalently linked to a B chain with lectin properties. In this work we have carried out a broad search of RIP sequence data banks from angiosperms in order to study their main structural characteristics and phylogenetic evolution. The comparison of the sequences revealed the presence, outside of the active site, of a novel structure that might be involved in the internal protein dynamics linked to enzyme catalysis. Also the B-chains presented another conserved structure that might function either supporting the beta-trefoil structure or in the communication between both sugar-binding sites. A systematic phylogenetic analysis of RIP sequences revealed that the most primitive type 1 RIPs were similar to that of the actual monocots (Poaceae and Asparagaceae). The primitive RIPs evolved to the dicot type 1 related RIPs (like those from Caryophyllales, Lamiales and Euphorbiales). The gene of a type 1 RIP related with the actual Euphorbiaceae type 1 RIPs fused with a double beta trefoil lectin gene similar to the actual Cucurbitaceae lectins to generate the type 2 RIPs and finally this gene underwent deletions rendering either type 1 RIPs (like those from Cucurbitaceae, Rosaceae and Iridaceae) or lectins without A chain (like those from Adoxaceae).
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Affiliation(s)
- Antimo Di Maro
- Department of Environmental, Biological and Pharmaceutical Sciences and Technologies, Second University of Naples, 81100, Caserta, Italy
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8
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Abstract
E1, an ATP-dependent DNA helicase, is the only enzyme encoded by papillomaviruses (PVs). It is essential for replication and amplification of the viral episome in the nucleus of infected cells. To do so, E1 assembles into a double-hexamer at the viral origin, unwinds DNA at the origin and ahead of the replication fork and interacts with cellular DNA replication factors. Biochemical and structural studies have revealed the assembly pathway of E1 at the origin and how the enzyme unwinds DNA using a spiral escalator mechanism. E1 is tightly regulated in vivo, in particular by post-translational modifications that restrict its accumulation in the nucleus. Here we review how different functional domains of E1 orchestrate viral DNA replication, with an emphasis on their interactions with substrate DNA, host DNA replication factors and modifying enzymes. These studies have made E1 one of the best characterized helicases and provided unique insights on how PVs usurp different host-cell machineries to replicate and amplify their genome in a tightly controlled manner.
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9
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Mutations in DNA binding and transactivation domains affect the dynamics of parvovirus NS1 protein. J Virol 2013; 87:11762-74. [PMID: 23986577 DOI: 10.1128/jvi.01678-13] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The multifunctional replication protein of autonomous parvoviruses, NS1, is vital for viral genome replication and for the control of viral protein production. Two DNA-interacting domains of NS1, the N-terminal and helicase domains, are necessary for these functions. In addition, the N and C termini of NS1 are required for activation of viral promoter P38. By comparison with the structural and biochemical data from other parvoviruses, we identified potential DNA-interacting amino acid residues from canine parvovirus NS1. The role of the identified amino acids in NS1 binding dynamics was studied by mutagenesis, fluorescence recovery after photobleaching, and computer simulations. Mutations in the predicted DNA-interacting amino acids of the N-terminal and helicase domains increased the intranuclear binding dynamics of NS1 dramatically. A substantial increase in binding dynamics was also observed for NS1 mutants that targeted the metal ion coordination site in the N terminus. Interestingly, contrary to other mutants, deletion of the C terminus resulted in slower binding dynamics of NS1. P38 transactivation was severely reduced in both N-terminal DNA recognition and in C-terminal deletion mutants. These data suggest that the intranuclear dynamics of NS1 are largely characterized by its sequence-specific and -nonspecific binding to double-stranded DNA. Moreover, binding of NS1 is equally dependent on the N-terminal domain and conserved β-loop of the helicase domain.
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10
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CK2 phosphorylation inactivates DNA binding by the papillomavirus E1 and E2 proteins. J Virol 2013; 87:7668-79. [PMID: 23637413 DOI: 10.1128/jvi.00345-13] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Papillomaviruses have complex life cycles that are understood only superficially. Although it is well established that the viral E1 and E2 proteins play key roles in controlling viral transcription and DNA replication, how these factors are regulated is not well understood. Here, we demonstrate that phosphorylation by the protein kinase CK2 controls the biochemical activities of the bovine papillomavirus E1 and E2 proteins by modifying their DNA binding activity. Phosphorylation at multiple sites in the N-terminal domain in E1 results in the loss of sequence-specific DNA binding activity, a feature that is also conserved in human papillomavirus (HPV) E1 proteins. The bovine papillomavirus (BPV) E2 protein, when phosphorylated by CK2 on two specific sites in the hinge, also loses its site-specific DNA binding activity. Mutation of these sites in E2 results in greatly increased levels of latent viral DNA replication, indicating that CK2 phosphorylation of E2 is a negative regulator of viral DNA replication during latent viral replication. In contrast, mutation of the N-terminal phosphorylation sites in E1 has no effect on latent viral DNA replication. We propose that the phosphorylation of the N terminus of E1 plays a role only in vegetative viral DNA replication, and consistent with such a role, caspase 3 cleavage of E1, which has been shown to be necessary for vegetative viral DNA replication, restores the DNA binding activity to phosphorylated E1.
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11
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Chang YP, Xu M, Machado ACD, Yu XJ, Rohs R, Chen XS. Mechanism of origin DNA recognition and assembly of an initiator-helicase complex by SV40 large tumor antigen. Cell Rep 2013; 3:1117-27. [PMID: 23545501 DOI: 10.1016/j.celrep.2013.03.002] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2012] [Revised: 01/10/2013] [Accepted: 03/01/2013] [Indexed: 10/27/2022] Open
Abstract
The DNA tumor virus Simian virus 40 (SV40) is a model system for studying eukaryotic replication. SV40 large tumor antigen (LTag) is the initiator/helicase that is essential for genome replication. LTag recognizes and assembles at the viral replication origin. We determined the structure of two multidomain LTag subunits bound to origin DNA. The structure reveals that the origin binding domains (OBDs) and Zn and AAA+ domains are involved in origin recognition and assembly. Notably, the OBDs recognize the origin in an unexpected manner. The histidine residues of the AAA+ domains insert into a narrow minor groove region with enhanced negative electrostatic potential. Computational analysis indicates that this region is intrinsically narrow, demonstrating the role of DNA shape readout in origin recognition. Our results provide important insights into the assembly of the LTag initiator/helicase at the replication origin and suggest that histidine contacts with the minor groove serve as a mechanism of DNA shape readout.
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Affiliation(s)
- Y Paul Chang
- Molecular and Computational Biology Program, Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089, USA
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12
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Engagement of the ATR-dependent DNA damage response at the human papillomavirus 18 replication centers during the initial amplification. J Virol 2012; 87:951-64. [PMID: 23135710 DOI: 10.1128/jvi.01943-12] [Citation(s) in RCA: 109] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
We have previously demonstrated that the human papillomavirus (HPV) genome replicates effectively in U2OS cells after transfection using electroporation. The transient extrachromosomal replication, stable maintenance, and late amplification of the viral genome could be studied for high- and low-risk mucosal and cutaneous papillomaviruses. Recent findings indicate that the cellular DNA damage response (DDR) is activated during the HPV life cycle and that the viral replication protein E1 might play a role in this process. We used a U2OS cell-based system to study E1-dependent DDR activation and the involvement of these pathways in viral transient replication. We demonstrated that the E1 protein could cause double-strand DNA breaks in the host genome by directly interacting with DNA. This activity leads to the induction of an ATM-dependent signaling cascade and cell cycle arrest in the S and G(2) phases. However, the transient replication of HPV genomes in U2OS cells induces the ATR-dependent pathway, as shown by the accumulation of γH2AX, ATR-interacting protein (ATRIP), and topoisomerase IIβ-binding protein 1 (TopBP1) in viral replication centers. Viral oncogenes do not play a role in this activation, which is induced only through DNA replication or by replication proteins E1 and E2. The ATR pathway in viral replication centers is likely activated through DNA replication stress and might play an important role in engaging cellular DNA repair/recombination machinery for effective replication of the viral genome upon active amplification.
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13
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Schuck S, Stenlund A. Mechanistic analysis of local ori melting and helicase assembly by the papillomavirus E1 protein. Mol Cell 2011; 43:776-87. [PMID: 21884978 DOI: 10.1016/j.molcel.2011.06.026] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2011] [Revised: 05/22/2011] [Accepted: 06/28/2011] [Indexed: 11/16/2022]
Abstract
Preparation of DNA templates for replication requires opening of the duplex to expose single-stranded (ss) DNA. The locally melted DNA is required for replicative DNA helicases to initiate unwinding. How local melting is generated in eukaryotic replicons is unknown, but initiator proteins from a handful of eukaryotic viruses can perform this function. Here we dissect the local melting process carried out by the papillomavirus E1 protein. We characterize the melting process kinetically and identify mutations in the E1 helicase and in the ori that arrest the local melting process. We show that a subset of these mutants have specific defects for melting of the center of the ori containing the binding sites for E1 and demonstrate that these mutants fail to untwist the ori DNA. This understanding of how E1 generates local melting suggests possible mechanisms for local melting in other replicons.
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Affiliation(s)
- Stephen Schuck
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA
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14
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Duderstadt KE, Chuang K, Berger JM. DNA stretching by bacterial initiators promotes replication origin opening. Nature 2011; 478:209-13. [PMID: 21964332 PMCID: PMC3192921 DOI: 10.1038/nature10455] [Citation(s) in RCA: 151] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2011] [Accepted: 08/12/2011] [Indexed: 11/10/2022]
Abstract
Many replication initiators form higher-order oligomers that process host replication origins to promote replisome formation. In addition to dedicated duplex-DNA-binding domains, cellular initiators possess AAA+ (ATPases associated with various cellular activities) elements that drive functions ranging from protein assembly to origin recognition. In bacteria, the AAA+ domain of the initiator DnaA has been proposed to assist in single-stranded DNA formation during origin melting. Here we show crystallographically and in solution that the ATP-dependent assembly of Aquifex aeolicus DnaA into a spiral oligomer creates a continuous surface that allows successive AAA+ domains to bind and extend single-stranded DNA segments. The mechanism of binding is unexpectedly similar to that of RecA, a homologous recombination factor, but it differs in that DnaA promotes a nucleic acid conformation that prevents pairing of a complementary strand. These findings, combined with strand-displacement assays, indicate that DnaA opens replication origins by a direct ATP-dependent stretching mechanism. Comparative studies reveal notable commonalities between the approach used by DnaA to engage DNA substrates and other, nucleic-acid-dependent, AAA+ systems.
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Affiliation(s)
- Karl E. Duderstadt
- Biophysics Graduate Group, University of California, Berkeley, Berkeley, CA 94720, USA
| | - Kevin Chuang
- Department of Molecular and Cell Biology, California Institute for Quantitative Biology, University of California, Berkeley, Berkeley, CA 94720, USA
| | - James M. Berger
- Biophysics Graduate Group, University of California, Berkeley, Berkeley, CA 94720, USA
- Department of Molecular and Cell Biology, California Institute for Quantitative Biology, University of California, Berkeley, Berkeley, CA 94720, USA
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15
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Gai D, Chang YP, Chen XS. Origin DNA melting and unwinding in DNA replication. Curr Opin Struct Biol 2010; 20:756-62. [PMID: 20870402 DOI: 10.1016/j.sbi.2010.08.009] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2010] [Revised: 08/25/2010] [Accepted: 08/31/2010] [Indexed: 02/04/2023]
Abstract
Genomic DNA replication is a necessary step in the life cycles of all organisms. To initiate DNA replication, the double-stranded DNA (dsDNA) at the origin of replication must be separated or melted; this melted region is propagated and a mature replication fork is formed. To accomplish origin recognition, initial DNA melting, and the eventual formation of a replication fork, coordinated activity of initiators, helicases, and other cellular factors are required. In this review, we focus on recent advances in the structural and biochemical studies of the initiators and the replicative helicases in multiple replication systems, with emphasis on the systems in archaeal and eukaryotic cells. These studies have yielded insights into the plausible mechanisms of the early stages of DNA replication.
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Affiliation(s)
- Dahai Gai
- Molecular and Computational Biology, University of Southern California, 1050 Childs Way, Los Angeles, CA 90089, USA
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16
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Yoshimoto K, Arora K, Brooks CL. Hexameric helicase deconstructed: interplay of conformational changes and substrate coupling. Biophys J 2010; 98:1449-57. [PMID: 20409463 DOI: 10.1016/j.bpj.2009.12.4315] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2009] [Revised: 12/22/2009] [Accepted: 12/23/2009] [Indexed: 12/15/2022] Open
Abstract
Hexameric helicases are molecular motor proteins that utilize energy obtained from ATP hydrolysis to translocate along and/or unwind nucleic acids. In this study, we investigate the dynamic behavior of the Simian Virus 40 hexameric helicase bound to DNA by performing molecular dynamics simulations employing a coarse-grained model. Our results elucidate the two most important molecular features of the helicase motion. First, the attractive interactions between the DNA-binding domain of the helicase and the DNA backbone are essential for the helicase to exhibit a unidirectional motion along the DNA strand. Second, the sequence of ATP binding at multiple binding pockets affects the helicase motion. Specifically, concerted ATP binding does not generate a unidirectional motion of the helicase. It is only when the binding of ATP occurs sequentially from one pocket to the next that the helicase moves unidirectionally along the DNA. Interestingly, in the reverse order of sequential ATP binding, the helicase also moves unidirectionally but in the opposite direction. These observations suggest that in nature ATP molecules must distinguish between different available ATP binding pockets of the hexameric helicase in order to function efficiently. To this end, simulations reveal that the binding of ATP in one pocket induces an opening of the next ATP-binding pocket and such an asymmetric deformation may coordinate the sequential ATP binding in a unidirectional manner. Overall, these findings may provide clues toward understanding the mechanism of substrate translocation in other motor proteins.
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Affiliation(s)
- Kenji Yoshimoto
- Department of Molecular Biology, The Scripps Research Institute, La Jolla, California, USA
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Residues in the central beta-hairpin of the DNA helicase of bacteriophage T7 are important in DNA unwinding. Proc Natl Acad Sci U S A 2010; 107:6782-7. [PMID: 20351255 DOI: 10.1073/pnas.1002734107] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The ring-shaped helicase of bacteriophage T7 (gp4), the product of gene 4, has basic beta-hairpin loops lining its central core where they are postulated to be the major sites of DNA interaction. We have altered multiple residues within the beta-hairpin loop to determine their role during dTTPase-driven DNA unwinding. Residues His-465, Leu-466, and Asn-468 are essential for both DNA unwinding and DNA synthesis mediated by T7 DNA polymerase during leading-strand DNA synthesis. Gp4-K467A, gp4-K471A, and gp4-K473A form fewer hexamers than heptamers compared to wild-type helicase and alone are deficient in DNA unwinding. However, they complement for the growth of T7 bacteriophage lacking gene 4. Single-molecule studies show that these three altered helicases support rates of leading-strand DNA synthesis comparable to that observed with wild-type gp4. Gp4-K467A, devoid of unwinding activity alone, supports leading-strand synthesis in the presence of T7 DNA polymerase. We propose that DNA polymerase limits the backward movement of the helicase during unwinding as well as assisting the forward movement necessary for strand separation.
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Abstract
The Mcm2-7 complex serves as the eukaryotic replicative helicase, the molecular motor that both unwinds duplex DNA and powers fork progression during DNA replication. Consistent with its central role in this process, much prior work has illustrated that Mcm2-7 loading and activation are landmark events in the regulation of DNA replication. Unlike any other hexameric helicase, Mcm2-7 is composed of six unique and essential subunits. Although the unusual oligomeric nature of this complex has long hampered biochemical investigations, recent advances with both the eukaryotic as well as the simpler archaeal Mcm complexes provide mechanistic insight into their function. In contrast to better-studied homohexameric helicases, evidence suggests that the six Mcm2-7 complex ATPase active sites are functionally distinct and are likely specialized to accommodate the regulatory constraints of the eukaryotic process.
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Structure-based mutational analysis of the bovine papillomavirus E1 helicase domain identifies residues involved in the nonspecific DNA binding activity required for double trimer formation. J Virol 2010; 84:4264-76. [PMID: 20147403 DOI: 10.1128/jvi.02214-09] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The papillomavirus E1 protein is a multifunctional initiator protein responsible for preparing the viral DNA template for initiation of DNA replication. The E1 protein encodes two DNA binding activities that are required for initiation of DNA replication. A well-characterized sequence-specific DNA binding activity resides in the E1 DBD and is used to tether E1 to the papillomavirus ori. A non-sequence-specific DNA binding activity is also required for formation of the E1 double trimer (DT) complex, which is responsible for the local template melting that precedes loading of the E1 helicase. This DNA binding activity is very poorly understood. We use a structure-based mutagenesis approach to identify residues in the E1 helicase domain that are required for the non-sequence-specific DNA binding and DT formation. We found that three groups of residues are involved in nonspecific DNA binding: the E1 beta-hairpin structure containing R505, K506, and H507; a hydrophobic loop containing F464; and a charged loop containing K461 together generate the binding surface involved in nonspecific DNA binding. These residues are well conserved in the T antigens from the polyomaviruses, indicating that the polyomaviruses share this nonspecific DNA binding activity.
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Mutations in Sensor 1 and Walker B in the bovine papillomavirus E1 initiator protein mimic the nucleotide-bound state. J Virol 2009; 84:1912-9. [PMID: 19939914 DOI: 10.1128/jvi.01756-09] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Viral replication initiator proteins are multifunctional proteins that utilize ATP binding and hydrolysis by their AAA+ modules for multiple functions in the replication of their viral genomes. These proteins are therefore of particular interest for understanding how AAA+ proteins carry out multiple ATP driven functions. We have performed a comprehensive mutational analysis of the residues involved in ATP binding and hydrolysis in the papillomavirus E1 initiator protein based on the recent structural data. Ten of the eleven residues that were targeted were defective for ATP hydrolysis, and seven of these were also defective for ATP binding. The three mutants that could still bind nucleotide represent the Walker B motif (D478 and D479) and Sensor 1 (N523), three residues that are in close proximity to each other and generally are considered to be involved in ATP hydrolysis. Surprisingly, however, two of these mutants, D478A and N523A, mimicked the nucleotide bound state and were capable of binding DNA in the absence of nucleotide. However, these mutants could not form the E1 double trimer in the absence of nucleotide, demonstrating that there are two qualitatively different consequences of ATP binding by E1, one that can be mimicked by D478A and N523A and one which cannot.
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Papillomavirus DNA replication — From initiation to genomic instability. Virology 2009; 384:360-8. [DOI: 10.1016/j.virol.2008.11.032] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2008] [Accepted: 11/18/2008] [Indexed: 12/25/2022]
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Bae B, Chen YH, Costa A, Onesti S, Brunzelle JS, Lin Y, Cann IK, Nair SK. Insights into the Architecture of the Replicative Helicase from the Structure of an Archaeal MCM Homolog. Structure 2009; 17:211-22. [DOI: 10.1016/j.str.2008.11.010] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2008] [Revised: 11/13/2008] [Accepted: 11/13/2008] [Indexed: 10/21/2022]
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Abstract
Papillomaviruses establish persistent infection in the dividing, basal epithelial cells of the host. The viral genome is maintained as a circular, double-stranded DNA, extrachromosomal element within these cells. Viral genome amplification occurs only when the epithelial cells differentiate and viral particles are shed in squames that are sloughed from the surface of the epithelium. There are three modes of replication in the papillomavirus life cycle. Upon entry, in the establishment phase, the viral genome is amplified to a low copy number. In the second maintenance phase, the genome replicates in dividing cells at a constant copy number, in synchrony with the cellular DNA. And finally, in the vegetative or productive phase, the viral DNA is amplified to a high copy number in differentiated cells and is destined to be packaged in viral capsids. This review discusses the cis elements and protein factors required for each stage of papillomavirus replication.
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Affiliation(s)
- Alison A McBride
- Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA
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Duderstadt KE, Berger JM. AAA+ ATPases in the initiation of DNA replication. Crit Rev Biochem Mol Biol 2008; 43:163-87. [PMID: 18568846 DOI: 10.1080/10409230802058296] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
All cellular organisms and many viruses rely on large, multi-subunit molecular machines, termed replisomes, to ensure that genetic material is accurately duplicated for transmission from one generation to the next. Replisome assembly is facilitated by dedicated initiator proteins, which serve to both recognize replication origins and recruit requisite replisomal components to the DNA in a cell-cycle coordinated manner. Exactly how imitators accomplish this task, and the extent to which initiator mechanisms are conserved among different organisms have remained outstanding issues. Recent structural and biochemical findings have revealed that all cellular initiators, as well as the initiators of certain classes of double-stranded DNA viruses, possess a common adenine nucleotide-binding fold belonging to the ATPases Associated with various cellular Activities (AAA+) family. This review focuses on how the AAA+ domain has been recruited and adapted to control the initiation of DNA replication, and how the use of this ATPase module underlies a common set of initiator assembly states and functions. How biochemical and structural properties correlate with initiator activity, and how species-specific modifications give rise to unique initiator functions, are also discussed.
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Affiliation(s)
- Karl E Duderstadt
- Department Molecular and Cell Biology and Biophysics Graduate Group, California Institute for Quantitative Biology, University of California, Berkeley, California 94720-3220, USA.
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Enemark EJ, Joshua-Tor L. On helicases and other motor proteins. Curr Opin Struct Biol 2008; 18:243-57. [PMID: 18329872 DOI: 10.1016/j.sbi.2008.01.007] [Citation(s) in RCA: 160] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2007] [Revised: 01/17/2008] [Accepted: 01/21/2008] [Indexed: 01/30/2023]
Abstract
Helicases are molecular machines that utilize energy derived from ATP hydrolysis to move along nucleic acids and to separate base-paired nucleotides. The movement of the helicase can also be described as a stationary helicase that pumps nucleic acid. Recent structural data for the hexameric E1 helicase of papillomavirus in complex with single-stranded DNA and MgADP has provided a detailed atomic and mechanistic picture of its ATP-driven DNA translocation. The structural and mechanistic features of this helicase are compared with the hexameric helicase prototypes T7gp4 and SV40 T-antigen. The ATP-binding site architectures of these proteins are structurally similar to the sites of other prototypical ATP-driven motors such as F1-ATPase, suggesting related roles for the individual site residues in the ATPase activity.
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Affiliation(s)
- Eric J Enemark
- W.M. Keck Structural Biology Laboratory, Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, NY 11724, United States
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