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Dodd T, Botto M, Paul F, Fernandez-Leiro R, Lamers MH, Ivanov I. Polymerization and editing modes of a high-fidelity DNA polymerase are linked by a well-defined path. Nat Commun 2020; 11:5379. [PMID: 33097731 PMCID: PMC7584608 DOI: 10.1038/s41467-020-19165-2] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2020] [Accepted: 10/02/2020] [Indexed: 12/27/2022] Open
Abstract
Proofreading by replicative DNA polymerases is a fundamental mechanism ensuring DNA replication fidelity. In proofreading, mis-incorporated nucleotides are excised through the 3'-5' exonuclease activity of the DNA polymerase holoenzyme. The exonuclease site is distal from the polymerization site, imposing stringent structural and kinetic requirements for efficient primer strand transfer. Yet, the molecular mechanism of this transfer is not known. Here we employ molecular simulations using recent cryo-EM structures and biochemical analyses to delineate an optimal free energy path connecting the polymerization and exonuclease states of E. coli replicative DNA polymerase Pol III. We identify structures for all intermediates, in which the transitioning primer strand is stabilized by conserved Pol III residues along the fingers, thumb and exonuclease domains. We demonstrate switching kinetics on a tens of milliseconds timescale and unveil a complete pol-to-exo switching mechanism, validated by targeted mutational experiments.
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Affiliation(s)
- Thomas Dodd
- Department of Chemistry, Georgia State University, Atlanta, GA, USA
- Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, GA, USA
| | - Margherita Botto
- Department of Cell and Chemical Biology, Leiden University Medical Center, Leiden, The Netherlands
| | - Fabian Paul
- Department of Biochemistry & Molecular Biology, University of Chicago, Chicago, IL, USA
| | | | - Meindert H Lamers
- Department of Cell and Chemical Biology, Leiden University Medical Center, Leiden, The Netherlands.
| | - Ivaylo Ivanov
- Department of Chemistry, Georgia State University, Atlanta, GA, USA.
- Center for Diagnostics and Therapeutics, Georgia State University, Atlanta, GA, USA.
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Principles for enhancing virus capsid capacity and stability from a thermophilic virus capsid structure. Nat Commun 2019; 10:4471. [PMID: 31578335 PMCID: PMC6775164 DOI: 10.1038/s41467-019-12341-z] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2019] [Accepted: 08/31/2019] [Indexed: 12/21/2022] Open
Abstract
The capsids of double-stranded DNA viruses protect the viral genome from the harsh extracellular environment, while maintaining stability against the high internal pressure of packaged DNA. To elucidate how capsids maintain stability in an extreme environment, we use cryoelectron microscopy to determine the capsid structure of thermostable phage P74-26 to 2.8-Å resolution. We find P74-26 capsids exhibit an overall architecture very similar to those of other tailed bacteriophages, allowing us to directly compare structures to derive the structural basis for enhanced stability. Our structure reveals lasso-like interactions that appear to function like catch bonds. This architecture allows the capsid to expand during genome packaging, yet maintain structural stability. The P74-26 capsid has T = 7 geometry despite being twice as large as mesophilic homologs. Capsid capacity is increased with a larger, flatter major capsid protein. Given these results, we predict decreased icosahedral complexity (i.e. T ≤ 7) leads to a more stable capsid assembly. Viral capsids need to protect the genome against harsh environmental conditions and cope with high internal pressure from the packaged genome. Here, the authors determine the structure of the thermostable phage P74-26 capsid at 2.8-Å resolution and identify features underlying enhanced capsid capacity and structural stability.
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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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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: 52] [Impact Index Per Article: 7.4] [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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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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Binder JK, Douma LG, Ranjit S, Kanno DM, Chakraborty M, Bloom LB, Levitus M. Intrinsic stability and oligomerization dynamics of DNA processivity clamps. Nucleic Acids Res 2014; 42:6476-86. [PMID: 24728995 PMCID: PMC4041429 DOI: 10.1093/nar/gku255] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2014] [Revised: 03/14/2014] [Accepted: 03/17/2014] [Indexed: 11/29/2022] Open
Abstract
Sliding clamps are ring-shaped oligomeric proteins that are essential for processive deoxyribonucleic acid replication. Although crystallographic structures of several clamps have been determined, much less is known about clamp structure and dynamics in solution. Here, we characterized the intrinsic solution stability and oligomerization dynamics of the homodimeric Escherichia coli β and the homotrimeric Saccharomyces cerevisiae proliferating cell nuclear antigen (PCNA) clamps using single-molecule approaches. We show that E. coli β is stable in solution as a closed ring at concentrations three orders of magnitude lower than PCNA. The trimeric structure of PCNA results in slow subunit association rates and is largely responsible for the lower solution stability. Despite this large difference, the intrinsic lifetimes of the rings differ by only one order of magnitude. Our results show that the longer lifetime of the E. coli β dimer is due to more prominent electrostatic interactions that stabilize the subunit interfaces.
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Affiliation(s)
- Jennifer K Binder
- Department of Chemistry and Biochemistry and Biodesign Institute, Arizona State University, Tempe, AZ 85287-5601, USA
| | - Lauren G Douma
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610-0245, USA
| | - Suman Ranjit
- Department of Chemistry and Biochemistry and Biodesign Institute, Arizona State University, Tempe, AZ 85287-5601, USA
| | - David M Kanno
- Department of Chemistry and Biochemistry and Biodesign Institute, Arizona State University, Tempe, AZ 85287-5601, USA
| | - Manas Chakraborty
- Department of Chemistry and Biochemistry and Biodesign Institute, Arizona State University, Tempe, AZ 85287-5601, USA
| | - Linda B Bloom
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL 32610-0245, USA
| | - Marcia Levitus
- Department of Chemistry and Biochemistry and Biodesign Institute, Arizona State University, Tempe, AZ 85287-5601, USA
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Xu X, Guardiani C, Yan C, Ivanov I. Opening pathways of the DNA clamps proliferating cell nuclear antigen and Rad9-Rad1-Hus1. Nucleic Acids Res 2013; 41:10020-31. [PMID: 24038358 PMCID: PMC3905852 DOI: 10.1093/nar/gkt810] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Proliferating cell nuclear antigen and the checkpoint clamp Rad9-Rad1-Hus1 topologically encircle DNA and act as mobile platforms in the recruitment of proteins involved in DNA damage response and cell cycle regulation. To fulfill these vital cellular functions, both clamps need to be opened and loaded onto DNA by a clamp loader complex—a process, which involves disruption of the DNA clamp’s subunit interfaces. Herein, we compare the relative stabilities of the interfaces using the molecular mechanics Poisson−Boltzmann solvent accessible surface method. We identify the Rad9-Rad1 interface as the weakest and, therefore, most likely to open during clamp loading. We also delineate the dominant interface disruption pathways under external forces in multiple-trajectory steered molecular dynamics runs. We show that, similar to the case of protein folding, clamp opening may not proceed through a single interface breakdown mechanism. Instead, we identify an ensemble of opening pathways, some more prevalent than others, characterized by specific groups of contacts that differentially stabilize the regions of the interface and determine the spatial and temporal patterns of breakdown. In Rad9-Rad1-Hus1, the Rad9-Rad1 and Rad9-Hus1 interfaces share the same dominant unzipping pathway, whereas the Hus1-Rad1 interface is disrupted concertedly with no preferred directionality.
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Affiliation(s)
- Xiaojun Xu
- Department of Chemistry, Center for Diagnostics and Therapeutics, Georgia State University, GA 30302, USA
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