1
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Łazowski K, Woodgate R, Fijalkowska IJ. Escherichia coli DNA replication: the old model organism still holds many surprises. FEMS Microbiol Rev 2024; 48:fuae018. [PMID: 38982189 PMCID: PMC11253446 DOI: 10.1093/femsre/fuae018] [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: 05/09/2024] [Revised: 06/26/2024] [Accepted: 07/08/2024] [Indexed: 07/11/2024] Open
Abstract
Research on Escherichia coli DNA replication paved the groundwork for many breakthrough discoveries with important implications for our understanding of human molecular biology, due to the high level of conservation of key molecular processes involved. To this day, it attracts a lot of attention, partially by virtue of being an important model organism, but also because the understanding of factors influencing replication fidelity might be important for studies on the emergence of antibiotic resistance. Importantly, the wide access to high-resolution single-molecule and live-cell imaging, whole genome sequencing, and cryo-electron microscopy techniques, which were greatly popularized in the last decade, allows us to revisit certain assumptions about the replisomes and offers very detailed insight into how they work. For many parts of the replisome, step-by-step mechanisms have been reconstituted, and some new players identified. This review summarizes the latest developments in the area, focusing on (a) the structure of the replisome and mechanisms of action of its components, (b) organization of replisome transactions and repair, (c) replisome dynamics, and (d) factors influencing the base and sugar fidelity of DNA synthesis.
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Affiliation(s)
- Krystian Łazowski
- Laboratory of DNA Replication and Genome Stability, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, Poland
| | - Roger Woodgate
- Laboratory of Genomic Integrity, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-3371, United States
| | - Iwona J Fijalkowska
- Laboratory of DNA Replication and Genome Stability, Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5a, 02-106 Warsaw, Poland
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2
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Simonsen S, Søgaard CK, Olsen JG, Otterlei M, Kragelund BB. The bacterial DNA sliding clamp, β-clamp: structure, interactions, dynamics and drug discovery. Cell Mol Life Sci 2024; 81:245. [PMID: 38814467 PMCID: PMC11139829 DOI: 10.1007/s00018-024-05252-w] [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: 03/14/2024] [Revised: 04/22/2024] [Accepted: 04/23/2024] [Indexed: 05/31/2024]
Abstract
DNA replication is a tightly coordinated event carried out by a multiprotein replication complex. An essential factor in the bacterial replication complex is the ring-shaped DNA sliding clamp, β-clamp, ensuring processive DNA replication and DNA repair through tethering of polymerases and DNA repair proteins to DNA. β -clamp is a hub protein with multiple interaction partners all binding through a conserved clamp binding sequence motif. Due to its central role as a DNA scaffold protein, β-clamp is an interesting target for antimicrobial drugs, yet little effort has been put into understanding the functional interactions of β-clamp. In this review, we scrutinize the β-clamp structure and dynamics, examine how its interactions with a plethora of binding partners are regulated through short linear binding motifs and discuss how contexts play into selection. We describe the dynamic process of clamp loading onto DNA and cover the recent advances in drug development targeting β-clamp. Despite decades of research in β-clamps and recent landmark structural insight, much remains undisclosed fostering an increased focus on this very central protein.
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Affiliation(s)
- Signe Simonsen
- Linderstrøm-Lang Centre for Protein Science, University of Copenhagen, Ole Maaløes Vej 5, 2200, Copenhagen N, Denmark
- Structural Biology and NMR Laboratory, University of Copenhagen, Ole Maaløes Vej 5, 2200, Copenhagen N, Denmark
| | - Caroline K Søgaard
- Department of Clinical and Molecular Medicine, Norwegian University of Science and Technology (NTNU), Trondheim, Norway
| | - Johan G Olsen
- Linderstrøm-Lang Centre for Protein Science, University of Copenhagen, Ole Maaløes Vej 5, 2200, Copenhagen N, Denmark
- Structural Biology and NMR Laboratory, University of Copenhagen, Ole Maaløes Vej 5, 2200, Copenhagen N, Denmark
- Department of Biology, REPIN, University of Copenhagen, Ole Maaløes Vej 5, 2200, Copenhagen N, Denmark
| | - Marit Otterlei
- Department of Clinical and Molecular Medicine, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
| | - Birthe B Kragelund
- Linderstrøm-Lang Centre for Protein Science, University of Copenhagen, Ole Maaløes Vej 5, 2200, Copenhagen N, Denmark.
- Structural Biology and NMR Laboratory, University of Copenhagen, Ole Maaløes Vej 5, 2200, Copenhagen N, Denmark.
- Department of Biology, REPIN, University of Copenhagen, Ole Maaløes Vej 5, 2200, Copenhagen N, Denmark.
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3
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Mulye M, Singh MI, Jain V. From Processivity to Genome Maintenance: The Many Roles of Sliding Clamps. Genes (Basel) 2022; 13:2058. [PMID: 36360296 PMCID: PMC9690074 DOI: 10.3390/genes13112058] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2022] [Revised: 11/03/2022] [Accepted: 11/04/2022] [Indexed: 07/30/2023] Open
Abstract
Sliding clamps play a pivotal role in the process of replication by increasing the processivity of the replicative polymerase. They also serve as an interacting platform for a plethora of other proteins, which have an important role in other DNA metabolic processes, including DNA repair. In other words, clamps have evolved, as has been correctly referred to, into a mobile "tool-belt" on the DNA, and provide a platform for several proteins that are involved in maintaining genome integrity. Because of the central role played by the sliding clamp in various processes, its study becomes essential and relevant in understanding these processes and exploring the protein as an important drug target. In this review, we provide an updated report on the functioning, interactions, and moonlighting roles of the sliding clamps in various organisms and its utilization as a drug target.
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Affiliation(s)
- Meenakshi Mulye
- Correspondence: (M.M.); (V.J.); Tel.: +91-755-269-1425 (V.J.); Fax: +91-755-269-2392 (V.J.)
| | | | - Vikas Jain
- Correspondence: (M.M.); (V.J.); Tel.: +91-755-269-1425 (V.J.); Fax: +91-755-269-2392 (V.J.)
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4
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Schrecker M, Castaneda JC, Devbhandari S, Kumar C, Remus D, Hite RK. Multistep loading of a DNA sliding clamp onto DNA by replication factor C. eLife 2022; 11:e78253. [PMID: 35939393 PMCID: PMC9359705 DOI: 10.7554/elife.78253] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Accepted: 07/07/2022] [Indexed: 11/13/2022] Open
Abstract
The DNA sliding clamp proliferating cell nuclear antigen (PCNA) is an essential co-factor for many eukaryotic DNA metabolic enzymes. PCNA is loaded around DNA by the ATP-dependent clamp loader replication factor C (RFC), which acts at single-stranded (ss)/double-stranded DNA (dsDNA) junctions harboring a recessed 3' end (3' ss/dsDNA junctions) and at DNA nicks. To illuminate the loading mechanism we have investigated the structure of RFC:PCNA bound to ATPγS and 3' ss/dsDNA junctions or nicked DNA using cryogenic electron microscopy. Unexpectedly, we observe open and closed PCNA conformations in the RFC:PCNA:DNA complex, revealing that PCNA can adopt an open, planar conformation that allows direct insertion of dsDNA, and raising the question of whether PCNA ring closure is mechanistically coupled to ATP hydrolysis. By resolving multiple DNA-bound states of RFC:PCNA we observe that partial melting facilitates lateral insertion into the central channel formed by RFC:PCNA. We also resolve the Rfc1 N-terminal domain and demonstrate that its single BRCT domain participates in coordinating DNA prior to insertion into the central RFC channel, which promotes PCNA loading on the lagging strand of replication forks in vitro. Combined, our data suggest a comprehensive and fundamentally revised model for the RFC-catalyzed loading of PCNA onto DNA.
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Affiliation(s)
- Marina Schrecker
- Structural Biology Program, Memorial Sloan Kettering Cancer CenterNew YorkUnited States
| | - Juan C Castaneda
- Weill Cornell Medicine Graduate School, Weill Cornell MedicineNew YorkUnited States
- Molecular Biology Program, Memorial Sloan Kettering Cancer CenterNew YorkUnited States
| | - Sujan Devbhandari
- Molecular Biology Program, Memorial Sloan Kettering Cancer CenterNew YorkUnited States
| | - Charanya Kumar
- Molecular Biology Program, Memorial Sloan Kettering Cancer CenterNew YorkUnited States
| | - Dirk Remus
- Molecular Biology Program, Memorial Sloan Kettering Cancer CenterNew YorkUnited States
| | - Richard K Hite
- Structural Biology Program, Memorial Sloan Kettering Cancer CenterNew YorkUnited States
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5
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Potassium Glutamate and Glycine Betaine Induce Self-Assembly of the PCNA and β-Sliding Clamps. Biophys J 2020; 120:73-85. [PMID: 33221249 DOI: 10.1016/j.bpj.2020.11.013] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 11/06/2020] [Accepted: 11/10/2020] [Indexed: 12/11/2022] Open
Abstract
Sliding clamps are oligomeric ring-shaped proteins that increase the efficiency of DNA replication. The stability of the Escherichia coli β-clamp, a homodimer, is particularly remarkable. The dissociation equilibrium constant of the β-clamp is of the order of 10 pM in buffers of moderate ionic strength. Coulombic electrostatic interactions have been shown to contribute to this remarkable stability. Increasing NaCl concentration in the assay buffer results in decreased dimer stability and faster subunit dissociation kinetics in a way consistent with simple charge-screening models. Here, we examine non-Coulombic ionic effects on the oligomerization properties of sliding clamps. We determined relative diffusion coefficients of two sliding clamps using fluorescence correlation spectroscopy. Replacing NaCl by KGlu, the primary cytoplasmic salt in E. coli, results in a decrease of the diffusion coefficient of these proteins consistent with the formation of protein assemblies. The UV-vis spectrum of the β-clamp labeled with tetramethylrhodamine shows the characteristic absorption band of dimers of rhodamine when KGlu is present in the buffer. This suggests that KGlu induces the formation of assemblies that involve two or more rings stacked face-to-face. Results can be quantitatively explained on the basis of unfavorable interactions between KGlu and the functional groups on the protein surface, which drive biomolecular processes that bury exposed surface. Similar results were obtained with the Saccharomyces cerevisiae PCNA sliding clamp, suggesting that KGlu effects are not specific to the β-clamp. Clamp association is also promoted by glycine betaine, a zwitterionic compound that accumulates intracellularly when E. coli is exposed to high concentrations of extracellular solute. Possible biological implications are discussed.
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6
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Dynamics of the E. coli β-Clamp Dimer Interface and Its Influence on DNA Loading. Biophys J 2019; 117:587-601. [PMID: 31349986 DOI: 10.1016/j.bpj.2019.06.035] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Revised: 06/21/2019] [Accepted: 06/27/2019] [Indexed: 01/17/2023] Open
Abstract
The ring-shaped sliding clamp proteins have crucial roles in the regulation of DNA replication, recombination, and repair in all organisms. We previously showed that the Escherichia coli β-clamp is dynamic in solution, transiently visiting conformational states in which Domain 1 at the dimer interface is more flexible and prone to unfolding. This work aims to understand how the stability of the dimer interface influences clamp-opening dynamics and clamp loading by designing and characterizing stabilizing and destabilizing mutations in the clamp. The variants with stabilizing mutations conferred similar or increased thermostability and had similar quaternary structure as compared to the wild type. These variants stimulated the ATPase function of the clamp loader, complemented cell growth of a temperature-sensitive strain, and were successfully loaded onto a DNA substrate. The L82D and L82E I272A variants with purported destabilizing mutations had decreased thermostability, did not complement the growth of a temperature-sensitive strain, and had weakened dimerization as determined by native trapped ion mobility spectrometry-mass spectrometry. The β L82E variant had a reduced melting temperature but dimerized and complemented growth of a temperature-sensitive strain. All three clamps with destabilizing mutations had perturbed loading on DNA. Molecular dynamics simulations indicate altered hydrogen-bonding patterns at the dimer interface, and cross-correlation analysis showed the largest perturbations in the destabilized variants, consistent with the observed change in the conformations and functions of these clamps.
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7
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Perumal SK, Xu X, Yan C, Ivanov I, Benkovic SJ. Recognition of a Key Anchor Residue by a Conserved Hydrophobic Pocket Ensures Subunit Interface Integrity in DNA Clamps. J Mol Biol 2019; 431:2493-2510. [PMID: 31051173 DOI: 10.1016/j.jmb.2019.04.035] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2018] [Revised: 04/22/2019] [Accepted: 04/22/2019] [Indexed: 10/26/2022]
Abstract
Sliding clamp proteins encircle duplex DNA and are involved in processive DNA replication and the DNA damage response. Clamp proteins are ring-shaped oligomers (dimers or trimers) and are loaded onto DNA by an ATP-dependent clamp loader complex that ruptures the interface between two adjacent subunits. Here we measured the solution dynamics of the human clamp protein, proliferating cell nuclear antigen, by monitoring the change in the fluorescence of a site-specifically labeled. To unravel the origins of clamp subunit interface stability, we carried out comprehensive comparative analysis of the interfaces of seven sliding clamps. We used computational modeling (molecular dynamic simulations and MM/GBSA binding energy decomposition analyses) to identify conserved networks of hydrophobic residues critical for clamp stability and ring-opening dynamics. The hydrophobic network is shared among clamp proteins and exhibits a "key in a keyhole" pattern where a bulky aromatic residue from one clamp subunit is anchored into a hydrophobic pocket of the opposing subunit. Bioinformatics and dynamic network analyses showed that this oligomeric latch is conserved across DNA sliding clamps from all domains of life and dictates the dynamics of clamp opening and closing.
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Affiliation(s)
- Senthil K Perumal
- Department of Chemistry, 414 Wartik Laboratory, The Pennsylvania State University, University Park, PA 16802, USA
| | - Xiaojun Xu
- Department of Chemistry and Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, GA 30302, USA
| | - Chunli Yan
- Department of Chemistry and Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, GA 30302, USA
| | - Ivaylo Ivanov
- Department of Chemistry and Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, GA 30302, USA.
| | - Stephen J Benkovic
- Department of Chemistry, 414 Wartik Laboratory, The Pennsylvania State University, University Park, PA 16802, USA.
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8
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McGrath AE, Martyn AP, Whittell LR, Dawes FE, Beck JL, Dixon NE, Kelso MJ, Oakley AJ. Crystal structures and biochemical characterization of DNA sliding clamps from three Gram-negative bacterial pathogens. J Struct Biol 2018; 204:396-405. [DOI: 10.1016/j.jsb.2018.10.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2018] [Revised: 10/20/2018] [Accepted: 10/22/2018] [Indexed: 12/19/2022]
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9
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Donaphon B, Bloom LB, Levitus M. Photophysical characterization of interchromophoric interactions between rhodamine dyes conjugated to proteins. Methods Appl Fluoresc 2018; 6:045004. [PMID: 29985159 DOI: 10.1088/2050-6120/aad20f] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Rhodamine dyes in aqueous solution form non-fluorescent dimers with a plane-to-plane stacking geometry (H-dimers). The self-quenching properties of these dimers have been exploited to probe the conformation and dynamics of proteins using a variety of fluorescence approaches that require the interpretation of fluorescence intensities, lifetimes and fluctuations. Here, we report on a systematic study of the photophysical properties of three rhodamine dyes (tetramethylrhodamine, Alexa 488 and Alexa 546) covalently bound to the E. coli sliding clamp (β clamp) with emphasis on the properties of the H-dimers that form when the dimeric protein is labeled with one dye at each side of the dimer interface. Overall, results are consistent with an equilibrium between non-emissive dimers and unstacked monomers that experience efficient dynamic quenching Protein constructs labeled with tetramethylrhodamine show the characteristic features of H-dimers in their absorption spectra and a c.a. 40-fold quenching of fluorescence intensity. The degree of quenching decreases when samples are labeled with a tetramethylrhodamine derivative bearing a six-carbon linker. H-dimers do not form in samples labeled with Alexa 488 and A546, but fluorescence is still quenched in these samples through a dynamic mechanism. These results should help researchers design and interpret fluorescence experiments that take advantage of the properties of rhodamine dimers in protein research.
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Affiliation(s)
- Bryan Donaphon
- School of Molecular Sciences and Biodesign Institute, Arizona State University, Tempe, AZ 85287, United States of America
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10
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Douma LG, Yu KK, England JK, Levitus M, Bloom LB. Mechanism of opening a sliding clamp. Nucleic Acids Res 2017; 45:10178-10189. [PMID: 28973453 PMCID: PMC5737080 DOI: 10.1093/nar/gkx665] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2016] [Accepted: 07/20/2017] [Indexed: 11/29/2022] Open
Abstract
Clamp loaders load ring-shaped sliding clamps onto DNA where the clamps serve as processivity factors for DNA polymerases. In the first stage of clamp loading, clamp loaders bind and stabilize clamps in an open conformation, and in the second stage, clamp loaders place the open clamps around DNA so that the clamps encircle DNA. Here, the mechanism of the initial clamp opening stage is investigated. Mutations were introduced into the Escherichia coli β-sliding clamp that destabilize the dimer interface to determine whether the formation of an open clamp loader–clamp complex is dependent on spontaneous clamp opening events. In other work, we showed that mutation of a positively charged Arg residue at the β-dimer interface and high NaCl concentrations destabilize the clamp, but neither facilitates the formation of an open clamp loader–clamp complex in experiments presented here. Clamp opening reactions could be fit to a minimal three-step ‘bind-open-lock’ model in which the clamp loader binds a closed clamp, the clamp opens, and subsequent conformational rearrangements ‘lock’ the clamp loader–clamp complex in a stable open conformation. Our results support a model in which the E. coli clamp loader actively opens the β-sliding clamp.
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Affiliation(s)
- Lauren G Douma
- Department of Biochemistry & Molecular Biology and the Genetics Institute, University of Florida, Gainesville, FL 32610, USA
| | - Kevin K Yu
- Department of Biochemistry & Molecular Biology and the Genetics Institute, University of Florida, Gainesville, FL 32610, USA
| | - Jennifer K England
- School of Molecular Sciences and Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA
| | - Marcia Levitus
- School of Molecular Sciences and Biodesign Institute, Arizona State University, Tempe, AZ 85287, USA
| | - Linda B Bloom
- Department of Biochemistry & Molecular Biology and the Genetics Institute, University of Florida, Gainesville, FL 32610, USA
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11
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Purohit A, England JK, Douma LG, Tondnevis F, Bloom LB, Levitus M. Electrostatic Interactions at the Dimer Interface Stabilize the E. coli β Sliding Clamp. Biophys J 2017; 113:794-804. [PMID: 28834716 DOI: 10.1016/j.bpj.2017.06.057] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2017] [Revised: 06/28/2017] [Accepted: 06/30/2017] [Indexed: 11/25/2022] Open
Abstract
Sliding clamps are ring-shaped oligomeric proteins that encircle DNA and associate with DNA polymerases for processive DNA replication. The dimeric Escherichia coli β-clamp is closed in solution but must adopt an open conformation to be assembled onto DNA by a clamp loader. To determine what factors contribute to the stability of the dimer interfaces in the closed conformation and how clamp dynamics contribute to formation of the open conformation, we identified conditions that destabilized the dimer and measured the effects of these conditions on clamp dynamics. We characterized the role of electrostatic interactions in stabilizing the β-clamp interface. Increasing salt concentration results in decreased dimer stability and faster subunit dissociation kinetics. The equilibrium dissociation constant of the dimeric clamp varies with salt concentration as predicted by simple charge-screening models, indicating that charged amino acids contribute to the remarkable stability of the interface at physiological salt concentrations. Mutation of a charged residue at the interface (Arg-103) weakens the interface significantly, whereas effects are negligible when a hydrophilic (Ser-109) or a hydrophobic (Ile-305) amino acid is mutated instead. It has been suggested that clamp opening by the clamp loader takes advantage of spontaneous opening-closing fluctuations at the clamp's interface, but our time-resolved fluorescence and fluorescence correlation experiments rule out conformational fluctuations that lead to a significant fraction of open states.
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Affiliation(s)
- Anirban Purohit
- School of Molecular Sciences and Biodesign Institute, Arizona State University, Tempe, Arizona
| | - Jennifer K England
- School of Molecular Sciences and Biodesign Institute, Arizona State University, Tempe, Arizona
| | - Lauren G Douma
- Department of Biochemistry and Molecular Biology, The Genetics Institute, University of Florida, Gainesville, Florida
| | - Farzaneh Tondnevis
- Department of Biochemistry and Molecular Biology, The Genetics Institute, University of Florida, Gainesville, Florida
| | - Linda B Bloom
- Department of Biochemistry and Molecular Biology, The Genetics Institute, University of Florida, Gainesville, Florida.
| | - Marcia Levitus
- School of Molecular Sciences and Biodesign Institute, Arizona State University, Tempe, Arizona.
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12
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Kelch BA. Review: The lord of the rings: Structure and mechanism of the sliding clamp loader. Biopolymers 2017; 105:532-46. [PMID: 26918303 DOI: 10.1002/bip.22827] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Revised: 02/15/2016] [Accepted: 02/23/2016] [Indexed: 12/15/2022]
Abstract
Sliding clamps are ring-shaped polymerase processivity factors that act as master regulators of cellular replication by coordinating multiple functions on DNA to ensure faithful transmission of genetic and epigenetic information. Dedicated AAA+ ATPase machines called clamp loaders actively place clamps on DNA, thereby governing clamp function by controlling when and where clamps are used. Clamp loaders are also important model systems for understanding the basic principles of AAA+ mechanism and function. After nearly 30 years of study, the ATP-dependent mechanism of opening and loading of clamps is now becoming clear. Here I review the structural and mechanistic aspects of the clamp loading process, as well as comment on questions that will be addressed by future studies. © 2016 Wiley Periodicals, Inc. Biopolymers 105: 532-546, 2016.
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Affiliation(s)
- Brian A Kelch
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA, 01605
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13
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Abstract
A range of enzymes in DNA replication and repair bind to DNA-clamps: torus-shaped proteins that encircle double-stranded DNA and act as mobile tethers. Clamps from viruses (such as gp45 from the T4 bacteriophage) and eukaryotes (PCNAs) are homotrimers, each protomer containing two repeats of the DNA-clamp motif, while bacterial clamps (pol III β) are homodimers, each protomer containing three DNA-clamp motifs. Clamps need to be flexible enough to allow opening and loading onto primed DNA by clamp loader complexes. Equilibrium and steered molecular dynamics simulations have been used to study DNA-clamp conformation in open and closed forms. The E. coli and PCNA clamps appear to prefer closed, planar conformations. Remarkably, gp45 appears to prefer an open right-handed spiral conformation in solution, in agreement with previously reported biophysical data. The structural preferences of DNA clamps in solution have implications for understanding the duty cycle of clamp-loaders.
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14
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Benke S, Roderer D, Wunderlich B, Nettels D, Glockshuber R, Schuler B. The assembly dynamics of the cytolytic pore toxin ClyA. Nat Commun 2015; 6:6198. [PMID: 25652783 PMCID: PMC4347018 DOI: 10.1038/ncomms7198] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Accepted: 01/05/2015] [Indexed: 12/15/2022] Open
Abstract
Pore-forming toxins are protein assemblies used by many organisms to disrupt the membranes of target cells. They are expressed as soluble monomers that assemble spontaneously into multimeric pores. However, owing to their complexity, the assembly processes have not been resolved in detail for any pore-forming toxin. To determine the assembly mechanism for the ring-shaped, homododecameric pore of the bacterial cytolytic toxin ClyA, we collected a diverse set of kinetic data using single-molecule spectroscopy and complementary techniques on timescales from milliseconds to hours, and from picomolar to micromolar ClyA concentrations. The entire range of experimental results can be explained quantitatively by a surprisingly simple mechanism. First, addition of the detergent n-dodecyl-β-D-maltopyranoside to the soluble monomers triggers the formation of assembly-competent toxin subunits, accompanied by the transient formation of a molten-globule-like intermediate. Then, all sterically compatible oligomers contribute to assembly, which greatly enhances the efficiency of pore formation compared with simple monomer addition.
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Affiliation(s)
- Stephan Benke
- University of Zurich, Department of Biochemistry, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Daniel Roderer
- ETH Zurich, Institute of Molecular Biology and Biophysics, Otto-Stern-Weg 5, 8093 Zurich, Switzerland
| | - Bengt Wunderlich
- University of Zurich, Department of Biochemistry, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Daniel Nettels
- University of Zurich, Department of Biochemistry, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Rudi Glockshuber
- ETH Zurich, Institute of Molecular Biology and Biophysics, Otto-Stern-Weg 5, 8093 Zurich, Switzerland
| | - Benjamin Schuler
- University of Zurich, Department of Biochemistry, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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15
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Kinetic analysis of PCNA clamp binding and release in the clamp loading reaction catalyzed by Saccharomyces cerevisiae replication factor C. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2014; 1854:31-8. [PMID: 25450506 DOI: 10.1016/j.bbapap.2014.09.019] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Revised: 09/17/2014] [Accepted: 09/23/2014] [Indexed: 11/22/2022]
Abstract
DNA polymerases require a sliding clamp to achieve processive DNA synthesis. The toroidal clamps are loaded onto DNA by clamp loaders, members of the AAA+family of ATPases. These enzymes utilize the energy of ATP binding and hydrolysis to perform a variety of cellular functions. In this study, a clamp loader-clamp binding assay was developed to measure the rates of ATP-dependent clamp binding and ATP-hydrolysis-dependent clamp release for the Saccharomyces cerevisiae clamp loader (RFC) and clamp (PCNA). Pre-steady-state kinetics of PCNA binding showed that although ATP binding to RFC increases affinity for PCNA, ATP binding rates and ATP-dependent conformational changes in RFC are fast relative to PCNA binding rates. Interestingly, RFC binds PCNA faster than the Escherichia coli γ complex clamp loader binds the β-clamp. In the process of loading clamps on DNA, RFC maintains contact with PCNA while PCNA closes, as the observed rate of PCNA closing is faster than the rate of PCNA release, precluding the possibility of an open clamp dissociating from DNA. Rates of clamp closing and release are not dependent on the rate of the DNA binding step and are also slower than reported rates of ATP hydrolysis, showing that these rates reflect unique intramolecular reaction steps in the clamp loading pathway.
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16
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Kanno DM, Levitus M. Protein Oligomerization Equilibria and Kinetics Investigated by Fluorescence Correlation Spectroscopy: A Mathematical Treatment. J Phys Chem B 2014; 118:12404-15. [DOI: 10.1021/jp507741r] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- David M. Kanno
- Department
of Chemistry and Biochemistry and the Biodesign Institute, Arizona State University, PO Box 875601, Tempe, Arizona 85287, United States
| | - Marcia Levitus
- Department
of Chemistry and Biochemistry and the Biodesign Institute, Arizona State University, PO Box 875601, Tempe, Arizona 85287, United States
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