1
|
Feng X, Spiering MM, de Luna Almeida Santos R, Benkovic SJ, Li H. Structural basis of the T4 bacteriophage primosome assembly and primer synthesis. Nat Commun 2023; 14:4396. [PMID: 37474605 PMCID: PMC10359460 DOI: 10.1038/s41467-023-40106-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2022] [Accepted: 07/11/2023] [Indexed: 07/22/2023] Open
Abstract
The T4 bacteriophage gp41 helicase and gp61 primase assemble into a primosome to couple DNA unwinding with RNA primer synthesis for DNA replication. How the primosome is assembled and how the primer length is defined are unclear. Here we report a series of cryo-EM structures of T4 primosome assembly intermediates. We show that gp41 alone is an open spiral, and ssDNA binding triggers a large-scale scissor-like conformational change that drives the ring closure and activates the helicase. Helicase activation exposes a cryptic hydrophobic surface to recruit the gp61 primase. The primase binds the helicase in a bipartite mode in which the N-terminal Zn-binding domain and the C-terminal RNA polymerase domain each contain a helicase-interacting motif that bind to separate gp41 N-terminal hairpin dimers, leading to the assembly of one primase on the helicase hexamer. Our study reveals the T4 primosome assembly process and sheds light on the RNA primer synthesis mechanism.
Collapse
Affiliation(s)
- Xiang Feng
- Department of Structural Biology, Van Andel Institute, Grand Rapids, MI, USA
| | - Michelle M Spiering
- Department of Chemistry, The Pennsylvania State University, University Park, PA, USA
| | | | - Stephen J Benkovic
- Department of Chemistry, The Pennsylvania State University, University Park, PA, USA.
| | - Huilin Li
- Department of Structural Biology, Van Andel Institute, Grand Rapids, MI, USA.
| |
Collapse
|
2
|
Radford HM, Toft CJ, Sorenson AE, Schaeffer PM. Inhibition of Replication Fork Formation and Progression: Targeting the Replication Initiation and Primosomal Proteins. Int J Mol Sci 2023; 24:ijms24108802. [PMID: 37240152 DOI: 10.3390/ijms24108802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 05/02/2023] [Accepted: 05/09/2023] [Indexed: 05/28/2023] Open
Abstract
Over 1.2 million deaths are attributed to multi-drug-resistant (MDR) bacteria each year. Persistence of MDR bacteria is primarily due to the molecular mechanisms that permit fast replication and rapid evolution. As many pathogens continue to build resistance genes, current antibiotic treatments are being rendered useless and the pool of reliable treatments for many MDR-associated diseases is thus shrinking at an alarming rate. In the development of novel antibiotics, DNA replication is still a largely underexplored target. This review summarises critical literature and synthesises our current understanding of DNA replication initiation in bacteria with a particular focus on the utility and applicability of essential initiation proteins as emerging drug targets. A critical evaluation of the specific methods available to examine and screen the most promising replication initiation proteins is provided.
Collapse
Affiliation(s)
- Holly M Radford
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia
| | - Casey J Toft
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia
| | - Alanna E Sorenson
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia
| | - Patrick M Schaeffer
- Molecular and Cell Biology, College of Public Health, Medical and Veterinary Sciences, James Cook University, Douglas, QLD 4811, Australia
| |
Collapse
|
3
|
Feng X, Spiering MM, de Luna Almeida Santos R, Benkovic SJ, Li H. Structural basis of the T4 bacteriophage primosome assembly and primer synthesis. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.03.539249. [PMID: 37205424 PMCID: PMC10187150 DOI: 10.1101/2023.05.03.539249] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The T4 bacteriophage gp41 helicase and gp61 primase assemble into a primosome complex to couple DNA unwinding with RNA primer synthesis for DNA replication. How a primosome is assembled and how the length of the RNA primer is defined in the T4 bacteriophage, or in any model system, are unclear. Here we report a series of cryo-EM structures of T4 primosome assembly intermediates at resolutions up to 2.7 Å. We show that the gp41 helicase is an open spiral in the absence of ssDNA, and ssDNA binding triggers a large-scale scissor-like conformational change that drives the open spiral to a closed ring that activates the helicase. We found that the activation of the gp41 helicase exposes a cryptic hydrophobic primase-binding surface allowing for the recruitment of the gp61 primase. The primase binds the gp41 helicase in a bipartite mode in which the N-terminal Zn-binding domain (ZBD) and the C-terminal RNA polymerase domain (RPD) each contain a helicase-interacting motif (HIM1 and HIM2, respectively) that bind to separate gp41 N-terminal hairpin dimers, leading to the assembly of one primase on the helicase hexamer. Based on two observed primosome conformations - one in a DNA-scanning mode and the other in a post RNA primer-synthesis mode - we suggest that the linker loop between the gp61 ZBD and RPD contributes to the T4 pentaribonucleotide primer. Our study reveals T4 primosome assembly process and sheds light on RNA primer synthesis mechanism.
Collapse
|
4
|
Blaine HC, Simmons LA, Stallings CL. Diverse Mechanisms of Helicase Loading during DNA Replication Initiation in Bacteria. J Bacteriol 2023; 205:e0048722. [PMID: 36877032 PMCID: PMC10128896 DOI: 10.1128/jb.00487-22] [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] [Indexed: 03/07/2023] Open
Abstract
Initiation of DNA replication is required for cell viability and passage of genetic information to the next generation. Studies in Escherichia coli and Bacillus subtilis have established ATPases associated with diverse cellular activities (AAA+) as essential proteins required for loading of the replicative helicase at replication origins. AAA+ ATPases DnaC in E. coli and DnaI in B. subtilis have long been considered the paradigm for helicase loading during replication in bacteria. Recently, it has become increasingly clear that most bacteria lack DnaC/DnaI homologs. Instead, most bacteria express a protein homologous to the newly described DciA (dnaC/dnaI antecedent) protein. DciA is not an ATPase, and yet it serves as a helicase operator, providing a function analogous to that of DnaC and DnaI across diverse bacterial species. The recent discovery of DciA and of other alternative mechanisms of helicase loading in bacteria has changed our understanding of DNA replication initiation. In this review, we highlight recent discoveries, detailing what is currently known about the replicative helicase loading process across bacterial species, and we discuss the critical questions that remain to be investigated.
Collapse
Affiliation(s)
- Helen C. Blaine
- Department of Molecular Microbiology, Washington University School of Medicine, Saint Louis, Missouri, USA
- Center for Women’s Infectious Disease Research, Washington University School of Medicine, Saint Louis, Missouri, USA
| | - Lyle A. Simmons
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, Michigan, USA
| | - Christina L. Stallings
- Department of Molecular Microbiology, Washington University School of Medicine, Saint Louis, Missouri, USA
- Center for Women’s Infectious Disease Research, Washington University School of Medicine, Saint Louis, Missouri, USA
| |
Collapse
|
5
|
Periago J, Mason C, Griep MA. Theoretical Development of DnaG Primase as a Novel Narrow-Spectrum Antibiotic Target. ACS OMEGA 2022; 7:8420-8428. [PMID: 35309427 PMCID: PMC8928506 DOI: 10.1021/acsomega.1c05928] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Accepted: 02/01/2022] [Indexed: 06/01/2023]
Abstract
The widespread use of antibiotics to treat infections is one of the reasons that global mortality rates have fallen over the past 80 years. However, antibiotic use is also responsible for the concomitant rise in antibiotic resistance because it results in dysbiosis in which commensal and pathogenic bacteria are both greatly reduced. Therefore, narrow-range antibiotics are a promising direction for reducing antibiotic resistance because they are more discriminate. As a step toward addressing this problem, the goal of this study was to identify sites on DnaG primase that are conserved within Gram-positive bacteria and different from the equivalent sites in Gram-negative bacteria. Based on sequence and structural analysis, the primase C-terminal helicase-binding domain (CTD) was identified as most promising. Although the primase CTD sequences are very poorly conserved, they have highly conserved protein folds, and Gram-positive bacterial primases fold into a compact state that creates a small molecule binding site adjacent to a groove. The small molecule would stabilize the protein in its compact state, which would interfere with the helicase binding. This is important because primase CTD must be in its open conformation to bind to its cognate helicase at the replication fork.
Collapse
|
6
|
Single-molecule studies of helicases and translocases in prokaryotic genome-maintenance pathways. DNA Repair (Amst) 2021; 108:103229. [PMID: 34601381 DOI: 10.1016/j.dnarep.2021.103229] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2021] [Revised: 09/13/2021] [Accepted: 09/16/2021] [Indexed: 11/22/2022]
Abstract
Helicases involved in genomic maintenance are a class of nucleic-acid dependent ATPases that convert the energy of ATP hydrolysis into physical work to execute irreversible steps in DNA replication, repair, and recombination. Prokaryotic helicases provide simple models to understand broadly conserved molecular mechanisms involved in manipulating nucleic acids during genome maintenance. Our understanding of the catalytic properties, mechanisms of regulation, and roles of prokaryotic helicases in DNA metabolism has been assembled through a combination of genetic, biochemical, and structural methods, further refined by single-molecule approaches. Together, these investigations have constructed a framework for understanding the mechanisms that maintain genomic integrity in cells. This review discusses recent single-molecule insights into molecular mechanisms of prokaryotic helicases and translocases.
Collapse
|
7
|
The alarmone (p)ppGpp regulates primer extension by bacterial primase. J Mol Biol 2021; 433:167189. [PMID: 34389317 DOI: 10.1016/j.jmb.2021.167189] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2021] [Revised: 07/22/2021] [Accepted: 08/02/2021] [Indexed: 11/21/2022]
Abstract
Primase is an essential component of the DNA replication machinery, responsible for synthesizing RNA primers that initiate leading and lagging strand DNA synthesis. Bacterial primase activity can be regulated by the starvation-inducible nucleotide (p)ppGpp. This regulation contributes to a timely inhibition of DNA replication upon amino acid starvation in the Gram-positive bacterium Bacillus subtilis. Here, we characterize the effect of (p)ppGpp on B. subtilis DnaG primase activity in vitro. Using a single-nucleotide resolution primase assay, we dissected the effect of ppGpp on the initiation, extension, and fidelity of B. subtilis primase. We found that ppGpp has a mild effect on initiation, but strongly inhibits primer extension and reduces primase processivity, promoting termination of primer extension. High (p)ppGpp concentration, together with low GTP concentration, additively inhibit primase activity. This explains the strong inhibition of replication elongation during starvation which induces high levels of (p)ppGpp and depletion of GTP in B. subtilis. Finally, we found that lowering GTP concentration results in mismatches in primer base pairing that allow priming readthrough, and that ppGpp reduces readthrough to protect priming fidelity. These results highlight the importance of (p)ppGpp in protecting replisome integrity and genome stability in fluctuating nucleotide concentrations upon onset of environmental stress.
Collapse
|
8
|
Single-Molecule Dynamics at a Bacterial Replication Fork after Nutritional Downshift or Chemically Induced Block in Replication. mSphere 2021; 6:6/1/e00948-20. [PMID: 33504660 PMCID: PMC7885319 DOI: 10.1128/msphere.00948-20] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Replication forks must respond to changes in nutrient conditions, especially in bacterial cells. By investigating the single-molecule dynamics of replicative helicase DnaC, DNA primase DnaG, and lagging-strand polymerase DnaE in the model bacterium Bacillus subtilis, we show that proteins react differently to stress conditions in response to transient replication blocks due to DNA damage, to inhibition of the replicative polymerase, or to downshift of serine availability. DnaG appears to be recruited to the forks by a diffusion and capture mechanism, becomes more statically associated after the arrest of polymerase, but binds less frequently after fork blocks due to DNA damage or to nutritional downshift. These results indicate that binding of the alarmone (p)ppGpp due to stringent response prevents DnaG from binding to forks rather than blocking bound primase. Dissimilar behavior of DnaG and DnaE suggests that both proteins are recruited independently to the forks rather than jointly. Turnover of all three proteins was increased during replication block after nutritional downshift, different from the situation due to DNA damage or polymerase inhibition, showing high plasticity of forks in response to different stress conditions. Forks persisted during all stress conditions, apparently ensuring rapid return to replication extension.IMPORTANCE All cells need to adjust DNA replication, which is achieved by a well-orchestrated multiprotein complex, in response to changes in physiological and environmental conditions. For replication forks, it is extremely challenging to meet with conditions where amino acids are rapidly depleted from cells, called the stringent response, to deal with the inhibition of one of the centrally involved proteins or with DNA modifications that arrest the progression of forks. By tracking helicase (DnaC), primase (DnaG), and polymerase (DnaE), central proteins of Bacillus subtilis replication forks, at a single molecule level in real time, we found that interactions of the three proteins with replication forks change in different manners under different stress conditions, revealing an intriguing plasticity of replication forks in dealing with replication obstacles. We have devised a new tool to determine rates of exchange between static movement (binding to a much larger complex) and free diffusion, showing that during stringent response, all proteins have highly increased exchange rates, slowing down overall replication, while inactivation of polymerase or replication roadblocks leaves forks largely intact, allowing rapid restart once obstacles are removed.
Collapse
|
9
|
Monachino E, Jergic S, Lewis JS, Xu ZQ, Lo ATY, O'Shea VL, Berger JM, Dixon NE, van Oijen AM. A Primase-Induced Conformational Switch Controls the Stability of the Bacterial Replisome. Mol Cell 2020; 79:140-154.e7. [PMID: 32464091 DOI: 10.1016/j.molcel.2020.04.037] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Revised: 03/12/2020] [Accepted: 04/20/2020] [Indexed: 12/16/2022]
Abstract
Recent studies of bacterial DNA replication have led to a picture of the replisome as an entity that freely exchanges DNA polymerases and displays intermittent coupling between the helicase and polymerase(s). Challenging the textbook model of the polymerase holoenzyme acting as a stable complex coordinating the replisome, these observations suggest a role of the helicase as the central organizing hub. We show here that the molecular origin of this newly found plasticity lies in the 500-fold increase in strength of the interaction between the polymerase holoenzyme and the replicative helicase upon association of the primase with the replisome. By combining in vitro ensemble-averaged and single-molecule assays, we demonstrate that this conformational switch operates during replication and promotes recruitment of multiple holoenzymes at the fork. Our observations provide a molecular mechanism for polymerase exchange and offer a revised model for the replication reaction that emphasizes its stochasticity.
Collapse
Affiliation(s)
- Enrico Monachino
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, and Illawarra Health and Medical Research Institute, Wollongong, NSW 2522, Australia; Zernike Institute for Advanced Materials, University of Groningen, Groningen 9747, the Netherlands
| | - Slobodan Jergic
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, and Illawarra Health and Medical Research Institute, Wollongong, NSW 2522, Australia
| | - Jacob S Lewis
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, and Illawarra Health and Medical Research Institute, Wollongong, NSW 2522, Australia
| | - Zhi-Qiang Xu
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, and Illawarra Health and Medical Research Institute, Wollongong, NSW 2522, Australia
| | - Allen T Y Lo
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, and Illawarra Health and Medical Research Institute, Wollongong, NSW 2522, Australia
| | - Valerie L O'Shea
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - James M Berger
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Nicholas E Dixon
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, and Illawarra Health and Medical Research Institute, Wollongong, NSW 2522, Australia.
| | - Antoine M van Oijen
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, and Illawarra Health and Medical Research Institute, Wollongong, NSW 2522, Australia.
| |
Collapse
|
10
|
Wiegand T. A solid-state NMR tool box for the investigation of ATP-fueled protein engines. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2020; 117:1-32. [PMID: 32471533 DOI: 10.1016/j.pnmrs.2020.02.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2019] [Revised: 02/18/2020] [Accepted: 02/20/2020] [Indexed: 06/11/2023]
Abstract
Motor proteins are involved in a variety of cellular processes. Their main purpose is to convert the chemical energy released during adenosine triphosphate (ATP) hydrolysis into mechanical work. In this review, solid-state Nuclear Magnetic Resonance (NMR) approaches are discussed allowing studies of structures, conformational events and dynamic features of motor proteins during a variety of enzymatic reactions. Solid-state NMR benefits from straightforward sample preparation based on sedimentation of the proteins directly into the Magic-Angle Spinning (MAS) rotor. Protein resonance assignment is the crucial and often time-limiting step in interpreting the wealth of information encoded in the NMR spectra. Herein, potentials, challenges and limitations in resonance assignment for large motor proteins are presented, focussing on both biochemical and spectroscopic approaches. This work highlights NMR tools available to study the action of the motor domain and its coupling to functional processes, as well as to identify protein-nucleotide interactions during events such as DNA replication. Arrested protein states of reaction coordinates such as ATP hydrolysis can be trapped for NMR studies by using stable, non-hydrolysable ATP analogues that mimic the physiological relevant states as accurately as possible. Recent advances in solid-state NMR techniques ranging from Dynamic Nuclear Polarization (DNP), 31P-based heteronuclear correlation experiments, 1H-detected spectra at fast MAS frequencies >100 kHz to paramagnetic NMR are summarized and their applications to the bacterial DnaB helicase from Helicobacter pylori are discussed.
Collapse
Affiliation(s)
- Thomas Wiegand
- Physical Chemistry, ETH Zurich, 8093 Zurich, Switzerland.
| |
Collapse
|
11
|
Bergsch J, Allain FHT, Lipps G. Recent advances in understanding bacterial and archaeoeukaryotic primases. Curr Opin Struct Biol 2019; 59:159-167. [PMID: 31585372 DOI: 10.1016/j.sbi.2019.08.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 08/05/2019] [Accepted: 08/26/2019] [Indexed: 11/16/2022]
Abstract
DNA replication in all forms of life relies upon the initiation of synthesis on a single strand template by formation of a short oligonucleotide primer, which is subsequently elongated by DNA polymerases. Two structurally distinct classes of enzymes have evolved to perform this function, namely the bacterial DnaG-type primases and the Archaeal and Eukaryotic primases (AEP). Structural and mechanistic insights have provided a clear understanding of the role of the different domains of these enzymes in the context of the replisome and recent work sheds light upon primase-substrate interactions. We herein review the emerging picture of the primase mechanism on the basis of the structural knowledge obtained to date and propose future directions of this essential aspect of DNA replication.
Collapse
Affiliation(s)
- Jan Bergsch
- Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, 8093 Zurich, Switzerland; Institute of Chemistry and Bioanalytics, University of Applied Sciences Northwestern Switzerland, Hofackerstrasses 30, 4132 Muttenz, Switzerland
| | - Frédéric H-T Allain
- Department of Biology, Institute of Molecular Biology and Biophysics, ETH Zurich, 8093 Zurich, Switzerland
| | - Georg Lipps
- Institute of Chemistry and Bioanalytics, University of Applied Sciences Northwestern Switzerland, Hofackerstrasses 30, 4132 Muttenz, Switzerland.
| |
Collapse
|
12
|
Oakley AJ. A structural view of bacterial DNA replication. Protein Sci 2019; 28:990-1004. [PMID: 30945375 DOI: 10.1002/pro.3615] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Accepted: 04/03/2019] [Indexed: 11/11/2022]
Abstract
DNA replication mechanisms are conserved across all organisms. The proteins required to initiate, coordinate, and complete the replication process are best characterized in model organisms such as Escherichia coli. These include nucleotide triphosphate-driven nanomachines such as the DNA-unwinding helicase DnaB and the clamp loader complex that loads DNA-clamps onto primer-template junctions. DNA-clamps are required for the processivity of the DNA polymerase III core, a heterotrimer of α, ε, and θ, required for leading- and lagging-strand synthesis. DnaB binds the DnaG primase that synthesizes RNA primers on both strands. Representative structures are available for most classes of DNA replication proteins, although there are gaps in our understanding of their interactions and the structural transitions that occur in nanomachines such as the helicase, clamp loader, and replicase core as they function. Reviewed here is the structural biology of these bacterial DNA replication proteins and prospects for future research.
Collapse
Affiliation(s)
- Aaron J Oakley
- Molecular Horizons and School of Chemistry and Molecular Bioscience, University of Wollongong, and Illawarra Health and Medical Research Institute, Wollongong, New South Wales, Australia
| |
Collapse
|
13
|
Structural insights into the interaction of helicase and primase in Mycobacterium tuberculosis. Biochem J 2018; 475:3493-3509. [DOI: 10.1042/bcj20180673] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2018] [Revised: 10/05/2018] [Accepted: 10/10/2018] [Indexed: 11/17/2022]
Abstract
The helicase–primase interaction is an essential event in DNA replication and is mediated by the highly variable C-terminal domain of primase (DnaG) and N-terminal domain of helicase (DnaB). To understand the functional conservation despite the low sequence homology of the DnaB-binding domains of DnaGs of eubacteria, we determined the crystal structure of the helicase-binding domain of DnaG from Mycobacterium tuberculosis (MtDnaG-CTD) and did so to a resolution of 1.58 Å. We observed the overall structure of MtDnaG-CTD to consist of two subdomains, the N-terminal globular region (GR) and the C-terminal helical hairpin region (HHR), connected by a small loop. Despite differences in some of its helices, the globular region was found to have broadly similar arrangements across the species, whereas the helical hairpins showed different orientations. To gain insights into the crucial helicase–primase interaction in M. tuberculosis, a complex was modeled using the MtDnaG-CTD and MtDnaB-NTD crystal structures. Two nonconserved hydrophobic residues (Ile605 and Phe615) of MtDnaG were identified as potential key residues interacting with MtDnaB. Biosensor-binding studies showed a significant decrease in the binding affinity of MtDnaB-NTD with the Ile605Ala mutant of MtDnaG-CTD compared with native MtDnaG-CTD. The loop, connecting the two helices of the HHR, was concluded to be largely responsible for the stability of the DnaB–DnaG complex. Also, MtDnaB-NTD showed micromolar affinity with DnaG-CTDs from Escherichia coli and Helicobacter pylori and unstable binding with DnaG-CTD from Vibrio cholerae. The interacting domains of both DnaG and DnaB demonstrate the species-specific evolution of the replication initiation system.
Collapse
|
14
|
Ilic S, Cohen S, Singh M, Tam B, Dayan A, Akabayov B. DnaG Primase-A Target for the Development of Novel Antibacterial Agents. Antibiotics (Basel) 2018; 7:E72. [PMID: 30104489 PMCID: PMC6163395 DOI: 10.3390/antibiotics7030072] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Revised: 08/06/2018] [Accepted: 08/09/2018] [Indexed: 12/21/2022] Open
Abstract
The bacterial primase-an essential component in the replisome-is a promising but underexploited target for novel antibiotic drugs. Bacterial primases have a markedly different structure than the human primase. Inhibition of primase activity is expected to selectively halt bacterial DNA replication. Evidence is growing that halting DNA replication has a bacteriocidal effect. Therefore, inhibitors of DNA primase could provide antibiotic agents. Compounds that inhibit bacterial DnaG primase have been developed using different approaches. In this paper, we provide an overview of the current literature on DNA primases as novel drug targets and the methods used to find their inhibitors. Although few inhibitors have been identified, there are still challenges to develop inhibitors that can efficiently halt DNA replication and may be applied in a clinical setting.
Collapse
Affiliation(s)
- Stefan Ilic
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel.
| | - Shira Cohen
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel.
| | - Meenakshi Singh
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel.
| | - Benjamin Tam
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel.
| | - Adi Dayan
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel.
| | - Barak Akabayov
- Department of Chemistry, Ben-Gurion University of the Negev, Beer-Sheva 8410501, Israel.
| |
Collapse
|
15
|
Kaguni JM. The Macromolecular Machines that Duplicate the Escherichia coli Chromosome as Targets for Drug Discovery. Antibiotics (Basel) 2018. [PMID: 29538288 PMCID: PMC5872134 DOI: 10.3390/antibiotics7010023] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
DNA replication is an essential process. Although the fundamental strategies to duplicate chromosomes are similar in all free-living organisms, the enzymes of the three domains of life that perform similar functions in DNA replication differ in amino acid sequence and their three-dimensional structures. Moreover, the respective proteins generally utilize different enzymatic mechanisms. Hence, the replication proteins that are highly conserved among bacterial species are attractive targets to develop novel antibiotics as the compounds are unlikely to demonstrate off-target effects. For those proteins that differ among bacteria, compounds that are species-specific may be found. Escherichia coli has been developed as a model system to study DNA replication, serving as a benchmark for comparison. This review summarizes the functions of individual E. coli proteins, and the compounds that inhibit them.
Collapse
Affiliation(s)
- Jon M Kaguni
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824-1319, USA.
| |
Collapse
|
16
|
Chilingaryan Z, Headey SJ, Lo ATY, Xu ZQ, Otting G, Dixon NE, Scanlon MJ, Oakley AJ. Fragment-Based Discovery of Inhibitors of the Bacterial DnaG-SSB Interaction. Antibiotics (Basel) 2018; 7:E14. [PMID: 29470422 PMCID: PMC5872125 DOI: 10.3390/antibiotics7010014] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2018] [Revised: 02/09/2018] [Accepted: 02/13/2018] [Indexed: 12/30/2022] Open
Abstract
In bacteria, the DnaG primase is responsible for synthesis of short RNA primers used to initiate chain extension by replicative DNA polymerase(s) during chromosomal replication. Among the proteins with which Escherichia coli DnaG interacts is the single-stranded DNA-binding protein, SSB. The C-terminal hexapeptide motif of SSB (DDDIPF; SSB-Ct) is highly conserved and is known to engage in essential interactions with many proteins in nucleic acid metabolism, including primase. Here, fragment-based screening by saturation-transfer difference nuclear magnetic resonance (STD-NMR) and surface plasmon resonance assays identified inhibitors of the primase/SSB-Ct interaction. Hits were shown to bind to the SSB-Ct-binding site using 15N-¹H HSQC spectra. STD-NMR was used to demonstrate binding of one hit to other SSB-Ct binding partners, confirming the possibility of simultaneous inhibition of multiple protein/SSB interactions. The fragment molecules represent promising scaffolds on which to build to discover new antibacterial compounds.
Collapse
Affiliation(s)
- Zorik Chilingaryan
- Molecular Horizons and School of Chemistry, University of Wollongong, and Illawarra Health and Medical Research Institute, Wollongong, NSW 2522, Australia.
| | - Stephen J Headey
- Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC 3052, Australia.
| | - Allen T Y Lo
- Molecular Horizons and School of Chemistry, University of Wollongong, and Illawarra Health and Medical Research Institute, Wollongong, NSW 2522, Australia.
| | - Zhi-Qiang Xu
- Molecular Horizons and School of Chemistry, University of Wollongong, and Illawarra Health and Medical Research Institute, Wollongong, NSW 2522, Australia.
| | - Gottfried Otting
- Research School of Chemistry, Australian National University, Canberra, ACT 2601, Australia.
| | - Nicholas E Dixon
- Molecular Horizons and School of Chemistry, University of Wollongong, and Illawarra Health and Medical Research Institute, Wollongong, NSW 2522, Australia.
| | - Martin J Scanlon
- Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, VIC 3052, Australia.
| | - Aaron J Oakley
- Molecular Horizons and School of Chemistry, University of Wollongong, and Illawarra Health and Medical Research Institute, Wollongong, NSW 2522, Australia.
| |
Collapse
|
17
|
Felczak MM, Chodavarapu S, Kaguni JM. DnaC, the indispensable companion of DnaB helicase, controls the accessibility of DnaB helicase by primase. J Biol Chem 2017; 292:20871-20882. [PMID: 29070678 DOI: 10.1074/jbc.m117.807644] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Revised: 10/11/2017] [Indexed: 11/06/2022] Open
Abstract
Former studies relying on hydrogen/deuterium exchange analysis suggest that DnaC bound to DnaB alters the conformation of the N-terminal domain (NTD) of DnaB to impair the ability of this DNA helicase to interact with primase. Supporting this idea, the work described herein based on biosensor experiments and enzyme-linked immunosorbent assays shows that the DnaB-DnaC complex binds poorly to primase in comparison with DnaB alone. Using a structural model of DnaB complexed with the C-terminal domain of primase, we found that Ile-85 is located at the interface in the NTD of DnaB that contacts primase. An alanine substitution for Ile-85 specifically interfered with this interaction and impeded DnaB function in DNA replication, but not its activity as a DNA helicase or its ability to bind to ssDNA. By comparison, substitutions of Asn for Ile-136 (I136N) and Thr for Ile-142 (I142T) in a subdomain previously named the helical hairpin in the NTD of DnaB altered the conformation of the helical hairpin and/or compromised its pairwise arrangement with the companion subdomain in each brace of protomers of the DnaB hexamer. In contrast with the I85A mutant, the latter were defective in DNA replication due to impaired binding to both ssDNA and primase. In view of these findings, we propose that DnaC controls the ability of DnaB to interact with primase by modifying the conformation of the NTD of DnaB.
Collapse
Affiliation(s)
- Magdalena M Felczak
- From the Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319
| | - Sundari Chodavarapu
- From the Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319
| | - Jon M Kaguni
- From the Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319
| |
Collapse
|
18
|
Zhao D, Chen X, Li K, Fu YV. The application of thermophilic DNA primase TtDnaG2 to DNA amplification. Sci Rep 2017; 7:12809. [PMID: 28993626 PMCID: PMC5634424 DOI: 10.1038/s41598-017-12241-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Accepted: 09/06/2017] [Indexed: 11/09/2022] Open
Abstract
For DNA replication in vivo, DNA primase uses a complementary single-stranded DNA template to synthesize RNA primers ranging from 4 to 20 nucleotides in length, which are then elongated by DNA polymerase. Here, we report that, in the presence of double-stranded DNA, the thermophilic DNA primase TtDnaG2 synthesizes RNA primers of around 100 nucleotides with low initiation specificity at 70 °C. Analysing the structure of TtDnaG2, we identified that it adopts a compact conformation. The conserved sites in its zinc binding domain are sequestered away from its RNA polymerase domain, which might give rise to the low initiation specificity and synthesis of long RNA segments by TtDnaG2. Based on these unique features of TtDnaG2, a DNA amplification method has been developed. We utilized TtDnaG2 to synthesize RNA primers at 70 °C after 95 °C denaturation, followed by isothermal amplification with the DNA polymerase Bst3.0 or phi29. Using this method, we successfully amplified genomic DNA of a virus with 100% coverage and low copy number variation. Our data also demonstrate that this method can efficiently amplify circular DNA from a mixture of circular DNA and linear DNA, thus providing a tool to amplify low-copy-number circular DNA such as plasmids.
Collapse
Affiliation(s)
- D Zhao
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences (CAS), Beijing, 100101, China.,Savaid Medical School, University of Chinese Academy of Sciences, Beijing, 100101, China
| | - Xiuqiang Chen
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences (CAS), Beijing, 100101, China.,Savaid Medical School, University of Chinese Academy of Sciences, Beijing, 100101, China
| | - Kuan Li
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences (CAS), Beijing, 100101, China
| | - Yu V Fu
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences (CAS), Beijing, 100101, China. .,Savaid Medical School, University of Chinese Academy of Sciences, Beijing, 100101, China.
| |
Collapse
|
19
|
Abstract
It has been assumed that DNA synthesis by the leading- and lagging-strand polymerases in the replisome must be coordinated to avoid the formation of significant gaps in the nascent strands. Using real-time single-molecule analysis, we establish that leading- and lagging-strand DNA polymerases function independently within a single replisome. Although average rates of DNA synthesis on leading and lagging strands are similar, individual trajectories of both DNA polymerases display stochastically switchable rates of synthesis interspersed with distinct pauses. DNA unwinding by the replicative helicase may continue during such pauses, but a self-governing mechanism, where helicase speed is reduced by ∼80%, permits recoupling of polymerase to helicase. These features imply a more dynamic, kinetically discontinuous replication process, wherein contacts within the replisome are continually broken and reformed. We conclude that the stochastic behavior of replisome components ensures complete DNA duplication without requiring coordination of leading- and lagging-strand synthesis. PAPERCLIP.
Collapse
|
20
|
Catazaro J, Periago J, Shortridge MD, Worley B, Kirchner A, Powers R, Griep MA. Identification of a Ligand-Binding Site on the Staphylococcus aureus DnaG Primase C-Terminal Domain. Biochemistry 2017; 56:932-943. [PMID: 28125218 PMCID: PMC6476306 DOI: 10.1021/acs.biochem.6b01273] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The interface between the DnaG primase C-terminal domain (CTD) and the N-terminal domain of DnaB helicase is essential for bacterial DNA replication because it allows coordinated priming of DNA synthesis at the replication fork while the DNA is being unwound. Because these two proteins are conserved in all bacteria and distinct from those in eukaryotes, their interface is an attractive antibiotic target. To learn more about this interface, we determined the solution structure and dynamics of the DnaG primase CTD from Staphylococcus aureus, a medically important bacterial species. Comparison with the known primase CTD structures shows there are two biologically relevant conformations, an open conformation that likely binds to DnaB helicase and a closed conformation that does not. The S. aureus primase CTD is in the closed conformation, but nuclear magnetic resonance (NMR) dynamic studies indicate there is considerable movement in the linker between the two subdomains and that N564 is the most dynamic residue within the linker. A high-throughput NMR ligand affinity screen identified potential binding compounds, among which were acycloguanosine and myricetin. Although the affinity for these compounds and adenosine was in the millimolar range, all three bind to a common pocket that is present only on the closed conformation of the CTD. This binding pocket is at the opposite end of helices 6 and 7 from N564, the key hinge residue. The identification of this binding pocket should allow the development of stronger-binding ligands that can prevent formation of the CTD open conformation that binds to DnaB helicase.
Collapse
Affiliation(s)
| | | | | | - Bradley Worley
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304
| | - Andrew Kirchner
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304
| | - Robert Powers
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304
| | - Mark A. Griep
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304
| |
Collapse
|
21
|
Abstract
DNA replication in Escherichia coli initiates at oriC, the origin of replication and proceeds bidirectionally, resulting in two replication forks that travel in opposite directions from the origin. Here, we focus on events at the replication fork. The replication machinery (or replisome), first assembled on both forks at oriC, contains the DnaB helicase for strand separation, and the DNA polymerase III holoenzyme (Pol III HE) for DNA synthesis. DnaB interacts transiently with the DnaG primase for RNA priming on both strands. The Pol III HE is made up of three subassemblies: (i) the αɛθ core polymerase complex that is present in two (or three) copies to simultaneously copy both DNA strands, (ii) the β2 sliding clamp that interacts with the core polymerase to ensure its processivity, and (iii) the seven-subunit clamp loader complex that loads β2 onto primer-template junctions and interacts with the α polymerase subunit of the core and the DnaB helicase to organize the two (or three) core polymerases. Here, we review the structures of the enzymatic components of replisomes, and the protein-protein and protein-DNA interactions that ensure they remain intact while undergoing substantial dynamic changes as they function to copy both the leading and lagging strands simultaneously during coordinated replication.
Collapse
Affiliation(s)
- J S Lewis
- Centre for Medical & Molecular Bioscience, University of Wollongong, Wollongong, NSW, Australia
| | - S Jergic
- Centre for Medical & Molecular Bioscience, University of Wollongong, Wollongong, NSW, Australia
| | - N E Dixon
- Centre for Medical & Molecular Bioscience, University of Wollongong, Wollongong, NSW, Australia.
| |
Collapse
|
22
|
Gardiennet C, Wiegand T, Bazin A, Cadalbert R, Kunert B, Lacabanne D, Gutsche I, Terradot L, Meier BH, Böckmann A. Solid-state NMR chemical-shift perturbations indicate domain reorientation of the DnaG primase in the primosome of Helicobacter pylori. JOURNAL OF BIOMOLECULAR NMR 2016; 64:189-95. [PMID: 26961129 DOI: 10.1007/s10858-016-0018-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Accepted: 01/24/2016] [Indexed: 05/09/2023]
Abstract
We here investigate the interactions between the DnaB helicase and the C-terminal domain of the corresponding DnaG primase of Helicobacter pylori using solid-state NMR. The difficult crystallization of this 387 kDa complex, where the two proteins interact in a six to three ratio, is circumvented by simple co-sedimentation of the two proteins directly into the MAS-NMR rotor. While the amount of information that can be extracted from such a large protein is still limited, we can assign a number of amino-acid residues experiencing significant chemical-shift perturbations upon helicase-primase complex formation. The location of these residues is used as a guide to model the interaction interface between the two proteins in the complex. Chemical-shift perturbations also reveal changes at the interaction interfaces of the hexameric HpDnaB assembly on HpDnaG binding. A structural model of the complex that explains the experimental findings is obtained.
Collapse
Affiliation(s)
- Carole Gardiennet
- Molecular Microbiology and Structural Biochemistry, Labex Ecofect, UMR 5086 CNRS, Université de Lyon 1, 7 passage du Vercors, 69007, Lyon, France
- CNRS, CRM2, UMR 7036, Université de Lorraine, 54506, Vandoeuvre-lès-Nancy, France
| | - Thomas Wiegand
- Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093, Zurich, Switzerland
| | - Alexandre Bazin
- Molecular Microbiology and Structural Biochemistry, Labex Ecofect, UMR 5086 CNRS, Université de Lyon 1, 7 passage du Vercors, 69007, Lyon, France
| | - Riccardo Cadalbert
- Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093, Zurich, Switzerland
| | - Britta Kunert
- Molecular Microbiology and Structural Biochemistry, Labex Ecofect, UMR 5086 CNRS, Université de Lyon 1, 7 passage du Vercors, 69007, Lyon, France
| | - Denis Lacabanne
- Molecular Microbiology and Structural Biochemistry, Labex Ecofect, UMR 5086 CNRS, Université de Lyon 1, 7 passage du Vercors, 69007, Lyon, France
| | - Irina Gutsche
- Institut de Biologie Structurale (IBS), CNRS, IBS; CEA, IBS, Université Grenoble Alpes, 38044, Grenoble, France
| | - Laurent Terradot
- Molecular Microbiology and Structural Biochemistry, Labex Ecofect, UMR 5086 CNRS, Université de Lyon 1, 7 passage du Vercors, 69007, Lyon, France.
| | - Beat H Meier
- Physical Chemistry, ETH Zurich, Vladimir-Prelog-Weg 2, 8093, Zurich, Switzerland.
| | - Anja Böckmann
- Molecular Microbiology and Structural Biochemistry, Labex Ecofect, UMR 5086 CNRS, Université de Lyon 1, 7 passage du Vercors, 69007, Lyon, France.
| |
Collapse
|
23
|
Strycharska MS, Arias-Palomo E, Lyubimov AY, Erzberger JP, O'Shea VL, Bustamante CJ, Berger JM. Nucleotide and partner-protein control of bacterial replicative helicase structure and function. Mol Cell 2014; 52:844-54. [PMID: 24373746 DOI: 10.1016/j.molcel.2013.11.016] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Revised: 11/17/2013] [Accepted: 11/26/2013] [Indexed: 10/25/2022]
Abstract
Cellular replication forks are powered by ring-shaped, hexameric helicases that encircle and unwind DNA. To better understand the molecular mechanisms and control of these enzymes, we used multiple methods to investigate the bacterial replicative helicase, DnaB. A 3.3 Å crystal structure of Aquifex aeolicus DnaB, complexed with nucleotide, reveals a newly discovered conformational state for this motor protein. Electron microscopy and small angle X-ray scattering studies confirm the state seen crystallographically, showing that the DnaB ATPase domains and an associated N-terminal collar transition between two physical states in a nucleotide-dependent manner. Mutant helicases locked in either collar state are active but display different capacities to support critical activities such as duplex translocation and primase-dependent RNA synthesis. Our findings establish the DnaB collar as an autoregulatory hub that controls the ability of the helicase to transition between different functional states in response to both nucleotide and replication initiation/elongation factors.
Collapse
Affiliation(s)
- Melania S Strycharska
- Biophysics Program, University of California, Berkeley, Berkeley, CA 94720-3220, USA
| | - Ernesto Arias-Palomo
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Artem Y Lyubimov
- The James H Clark Center, Stanford School of Medicine, Stanford, CA 94305, USA
| | - Jan P Erzberger
- Institute of Molecular Biology and Biophysics, ETH Zürich, 8093 Zürich, Switzerland
| | - Valerie L O'Shea
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Carlos J Bustamante
- Biophysics Program, University of California, Berkeley, Berkeley, CA 94720-3220, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815-6789, USA; Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720-3220, USA
| | - James M Berger
- Biophysics Program, University of California, Berkeley, Berkeley, CA 94720-3220, USA; Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720-3220, USA.
| |
Collapse
|
24
|
Beck JL, Urathamakul T, Watt SJ, Sheil MM, Schaeffer PM, Dixon NE. Proteomic dissection of DNA polymerization. Expert Rev Proteomics 2014; 3:197-211. [PMID: 16608433 DOI: 10.1586/14789450.3.2.197] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
DNA polymerases replicate the genome by associating with a range of other proteins that enable rapid, high-fidelity copying of DNA. This complex of proteins and nucleic acids is termed the replisome. Proteins of the replisome must interact with other networks of proteins, such as those involved in DNA repair. Many of the proteins involved in DNA polymerization and the accessory proteins are known, but the array of proteins they interact with, and the spatial and temporal arrangement of these interactions, are current research topics. Mass spectrometry is a technique that can be used to identify the sites of these interactions and to determine the precise stoichiometries of binding partners in a functional complex. A complete understanding of the macromolecular interactions involved in DNA replication and repair may lead to discovery of new targets for antibiotics against bacteria and biomarkers for diagnosis of diseases, such as cancer, in humans.
Collapse
Affiliation(s)
- Jennifer L Beck
- Department of Chemistry, University of Wollongong, Wollongong, NSW 2522, Australia.
| | | | | | | | | | | |
Collapse
|
25
|
Crystal structure and mode of helicase binding of the C-terminal domain of primase from Helicobacter pylori. J Bacteriol 2013; 195:2826-38. [PMID: 23585534 DOI: 10.1128/jb.00091-13] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
To better understand the poor conservation of the helicase binding domain of primases (DnaGs) among the eubacteria, we determined the crystal structure of the Helicobacter pylori DnaG C-terminal domain (HpDnaG-CTD) at 1.78 Å. The structure has a globular subdomain connected to a helical hairpin. Structural comparison has revealed that globular subdomains, despite the variation in number of helices, have broadly similar arrangements across the species, whereas helical hairpins show different orientations. Further, to study the helicase-primase interaction in H. pylori, a complex was modeled using the HpDnaG-CTD and HpDnaB-NTD (helicase) crystal structures using the Bacillus stearothermophilus BstDnaB-BstDnaG-CTD (helicase-primase) complex structure as a template. By using this model, a nonconserved critical residue Phe534 on helicase binding interface of DnaG-CTD was identified. Mutation guided by molecular dynamics, biophysical, and biochemical studies validated our model. We further concluded that species-specific helicase-primase interactions are influenced by electrostatic surface potentials apart from the critical hydrophobic surface residues.
Collapse
|
26
|
Naue N, Beerbaum M, Bogutzki A, Schmieder P, Curth U. The helicase-binding domain of Escherichia coli DnaG primase interacts with the highly conserved C-terminal region of single-stranded DNA-binding protein. Nucleic Acids Res 2013; 41:4507-17. [PMID: 23430154 PMCID: PMC3632105 DOI: 10.1093/nar/gkt107] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
During bacterial DNA replication, DnaG primase and the χ subunit of DNA polymerase III compete for binding to single-stranded DNA-binding protein (SSB), thus facilitating the switch between priming and elongation. SSB proteins play an essential role in DNA metabolism by protecting single-stranded DNA and by mediating several important protein-protein interactions. Although an interaction of SSB with primase has been previously reported, it was unclear which domains of the two proteins are involved. This study identifies the C-terminal helicase-binding domain of DnaG primase (DnaG-C) and the highly conserved C-terminal region of SSB as interaction sites. By ConSurf analysis, it can be shown that an array of conserved amino acids on DnaG-C forms a hydrophobic pocket surrounded by basic residues, reminiscent of known SSB-binding sites on other proteins. Using protein-protein cross-linking, site-directed mutagenesis, analytical ultracentrifugation and nuclear magnetic resonance spectroscopy, we demonstrate that these conserved amino acid residues are involved in the interaction with SSB. Even though the C-terminal domain of DnaG primase also participates in the interaction with DnaB helicase, the respective binding sites on the surface of DnaG-C do not overlap, as SSB binds to the N-terminal subdomain, whereas DnaB interacts with the ultimate C-terminus.
Collapse
Affiliation(s)
- Natalie Naue
- Institute for Biophysical Chemistry, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany
| | | | | | | | | |
Collapse
|
27
|
Abstract
Helicases are fundamental components of all replication complexes since unwinding of the double-stranded template to generate single-stranded DNA is essential to direct DNA synthesis by polymerases. However, helicases are also required in many other steps of DNA replication. Replicative helicases not only unwind the template DNA but also play key roles in regulating priming of DNA synthesis and coordination of leading and lagging strand DNA polymerases. Accessory helicases also aid replicative helicases in unwinding of the template strands in the presence of proteins bound to the DNA, minimising the risks posed by nucleoprotein complexes to continued fork movement. Helicases also play critical roles in Okazaki fragment processing in eukaryotes and may also be needed to minimise topological problems when replication forks converge. Thus fork movement, coordination of DNA synthesis, lagging strand maturation and termination of replication all depend on helicases. Moreover, if disaster strikes and a replication fork breaks down then reloading of the replication machinery is effected by helicases, at least in bacteria. This chapter describes how helicases function in these multiple steps at the fork and how DNA unwinding is coordinated with other catalytic processes to ensure efficient, high fidelity duplication of the genetic material in all organisms.
Collapse
Affiliation(s)
- Peter McGlynn
- Department of Biology, University of York, York, Yorkshire, UK,
| |
Collapse
|
28
|
Biswas T, Resto-Roldán E, Sawyer SK, Artsimovitch I, Tsodikov OV. A novel non-radioactive primase-pyrophosphatase activity assay and its application to the discovery of inhibitors of Mycobacterium tuberculosis primase DnaG. Nucleic Acids Res 2012; 41:e56. [PMID: 23267008 PMCID: PMC3575809 DOI: 10.1093/nar/gks1292] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Bacterial DNA primase DnaG synthesizes RNA primers required for chromosomal DNA replication. Biochemical assays measuring primase activity have been limited to monitoring formation of radioactively labelled primers because of the intrinsically low catalytic efficiency of DnaG. Furthermore, DnaG is prone to aggregation and proteolytic degradation. These factors have impeded discovery of DnaG inhibitors by high-throughput screening (HTS). In this study, we expressed and purified the previously uncharacterized primase DnaG from Mycobacterium tuberculosis (Mtb DnaG). By coupling the activity of Mtb DnaG to that of another essential enzyme, inorganic pyrophosphatase from M. tuberculosis (Mtb PPiase), we developed the first non-radioactive primase–pyrophosphatase assay. An extensive optimization of the assay enabled its efficient use in HTS (Z′ = 0.7 in the 384-well format). HTS of 2560 small molecules to search for inhibitory compounds yielded several hits, including suramin, doxorubicin and ellagic acid. We demonstrate that these three compounds inhibit Mtb DnaG. Both suramin and doxorubicin are potent (low-µM) DNA- and nucleotide triphosphate-competitive priming inhibitors that interact with more than one site on Mtb DnaG. This novel assay should be applicable to other primases and inefficient DNA/RNA polymerases, facilitating their characterization and inhibitor discovery.
Collapse
Affiliation(s)
- Tapan Biswas
- Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, 428 Church Street, Ann Arbor, MI 48109, USA
| | | | | | | | | |
Collapse
|
29
|
Robinson A, Causer RJ, Dixon NE. Architecture and conservation of the bacterial DNA replication machinery, an underexploited drug target. Curr Drug Targets 2012; 13:352-72. [PMID: 22206257 PMCID: PMC3290774 DOI: 10.2174/138945012799424598] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2011] [Revised: 11/03/2011] [Accepted: 11/05/2011] [Indexed: 11/22/2022]
Abstract
New antibiotics with novel modes of action are required to combat the growing threat posed by multi-drug resistant bacteria. Over the last decade, genome sequencing and other high-throughput techniques have provided tremendous insight into the molecular processes underlying cellular functions in a wide range of bacterial species. We can now use these data to assess the degree of conservation of certain aspects of bacterial physiology, to help choose the best cellular targets for development of new broad-spectrum antibacterials. DNA replication is a conserved and essential process, and the large number of proteins that interact to replicate DNA in bacteria are distinct from those in eukaryotes and archaea; yet none of the antibiotics in current clinical use acts directly on the replication machinery. Bacterial DNA synthesis thus appears to be an underexploited drug target. However, before this system can be targeted for drug design, it is important to understand which parts are conserved and which are not, as this will have implications for the spectrum of activity of any new inhibitors against bacterial species, as well as the potential for development of drug resistance. In this review we assess similarities and differences in replication components and mechanisms across the bacteria, highlight current progress towards the discovery of novel replication inhibitors, and suggest those aspects of the replication machinery that have the greatest potential as drug targets.
Collapse
Affiliation(s)
- Andrew Robinson
- School of Chemistry, University of Wollongong, NSW 2522, Australia
| | | | | |
Collapse
|
30
|
Lajoie MJ, Gregg CJ, Mosberg JA, Washington GC, Church GM. Manipulating replisome dynamics to enhance lambda Red-mediated multiplex genome engineering. Nucleic Acids Res 2012; 40:e170. [PMID: 22904085 PMCID: PMC3526312 DOI: 10.1093/nar/gks751] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Disrupting the interaction between primase and helicase in Escherichia coli increases Okazaki fragment (OF) length due to less frequent primer synthesis. We exploited this feature to increase the amount of ssDNA at the lagging strand of the replication fork that is available for λ Red-mediated Multiplex Automatable Genome Engineering (MAGE). Supporting this concept, we demonstrate that MAGE enhancements correlate with OF length. Compared with a standard recombineering strain (EcNR2), the strain with the longest OFs displays on average 62% more alleles converted per clone, 239% more clones with 5 or more allele conversions and 38% fewer clones with 0 allele conversions in 1 cycle of co-selection MAGE (CoS-MAGE) with 10 synthetic oligonucleotides. Additionally, we demonstrate that both synthetic oligonucleotides and accessible ssDNA targets on the lagging strand of the replication fork are limiting factors for MAGE. Given this new insight, we generated a strain with reduced oligonucleotide degradation and increased genomic ssDNA availability, which displayed 111% more alleles converted per clone, 527% more clones with 5 or more allele conversions and 71% fewer clones with 0 allele conversions in 1 cycle of 10-plex CoS-MAGE. These improvements will facilitate ambitious genome engineering projects by minimizing dependence on time-consuming clonal isolation and screening.
Collapse
Affiliation(s)
- M J Lajoie
- Department of Genetics, Harvard Medical School, Boston, MA 02115, USA
| | | | | | | | | |
Collapse
|
31
|
Shortridge MD, Griep MA, Powers R. ¹H, ¹³C, and ¹⁵N NMR assignments for the helicase interaction domain of Staphylococcus aureus DnaG primase. BIOMOLECULAR NMR ASSIGNMENTS 2012; 6:35-38. [PMID: 21644056 PMCID: PMC6690350 DOI: 10.1007/s12104-011-9320-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2011] [Accepted: 05/23/2011] [Indexed: 05/30/2023]
Abstract
The interaction between DnaG primase and DnaB helicase is essential for stimulating primer synthesis during bacterial DNA replication. The interaction occurs between the N-terminal domain of helicase and the C-terminal domain of primase. Here we present the (1)H, (13)C, and (15)N backbone and side-chain resonance assignments for the C-terminal helicase interaction domain of Staphylococcus aureus primase.
Collapse
Affiliation(s)
- Matthew D Shortridge
- Department of Chemistry, University of Nebraska-Lincoln, 721 Hamilton Hall, Lincoln, NE 68588-0304, USA.
| | | | | |
Collapse
|
32
|
Abstract
Threading of DNA through the central channel of a replicative ring helicase is known as helicase loading, and is a pivotal event during replication initiation at replication origins. Once loaded, the helicase recruits the primase through a direct protein-protein interaction to complete the initial 'priming step' of DNA replication. Subsequent assembly of the polymerases and processivity factors completes the structure of the replisome. Two replisomes are assembled, one on each strand, and move in opposite directions to replicate the parental DNA during the 'elongation step' of DNA replication. Replicative helicases are the motor engines of replisomes powered by the conversion of chemical energy to mechanical energy through ATP binding and hydrolysis. Bidirectional loading of two ring helicases at a replication origin is achieved by strictly regulated and intricately choreographed mechanisms, often through the action of replication initiation and helicase-loader proteins. Current structural and biochemical data reveal a wide range of different helicase-loading mechanisms. Here we review advances in this area and discuss their implications.
Collapse
Affiliation(s)
- Panos Soultanas
- School of Chemistry, Centre for Biomolecular Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
| |
Collapse
|
33
|
Stelter M, Gutsche I, Kapp U, Bazin A, Bajic G, Goret G, Jamin M, Timmins J, Terradot L. Architecture of a Dodecameric Bacterial Replicative Helicase. Structure 2012; 20:554-64. [DOI: 10.1016/j.str.2012.01.020] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2011] [Revised: 01/17/2012] [Accepted: 01/22/2012] [Indexed: 10/28/2022]
|
34
|
Shortridge MD, Triplet T, Revesz P, Griep MA, Powers R. Bacterial protein structures reveal phylum dependent divergence. Comput Biol Chem 2011; 35:24-33. [PMID: 21315656 DOI: 10.1016/j.compbiolchem.2010.12.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2010] [Revised: 12/28/2010] [Accepted: 12/29/2010] [Indexed: 01/26/2023]
Abstract
Protein sequence space is vast compared to protein fold space. This raises important questions about how structures adapt to evolutionary changes in protein sequences. A growing trend is to regard protein fold space as a continuum rather than a series of discrete structures. From this perspective, homologous protein structures within the same functional classification should reveal a constant rate of structural drift relative to sequence changes. The clusters of orthologous groups (COG) classification system was used to annotate homologous bacterial protein structures in the Protein Data Bank (PDB). The structures and sequences of proteins within each COG were compared against each other to establish their relatedness. As expected, the analysis demonstrates a sharp structural divergence between the bacterial phyla Firmicutes and Proteobacteria. Additionally, each COG had a distinct sequence/structure relationship, indicating that different evolutionary pressures affect the degree of structural divergence. However, our analysis also shows the relative drift rate between sequence identity and structure divergence remains constant.
Collapse
Affiliation(s)
- Matthew D Shortridge
- Department of Chemistry, University of Nebraska-Lincoln, 68588-0304, United States
| | | | | | | | | |
Collapse
|
35
|
Essential biological processes of an emerging pathogen: DNA replication, transcription, and cell division in Acinetobacter spp. Microbiol Mol Biol Rev 2010; 74:273-97. [PMID: 20508250 DOI: 10.1128/mmbr.00048-09] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Within the last 15 years, members of the bacterial genus Acinetobacter have risen from relative obscurity to be among the most important sources of hospital-acquired infections. The driving force for this has been the remarkable ability of these organisms to acquire antibiotic resistance determinants, with some strains now showing resistance to every antibiotic in clinical use. There is an urgent need for new antibacterial compounds to combat the threat imposed by Acinetobacter spp. and other intractable bacterial pathogens. The essential processes of chromosomal DNA replication, transcription, and cell division are attractive targets for the rational design of antimicrobial drugs. The goal of this review is to examine the wealth of genome sequence and gene knockout data now available for Acinetobacter spp., highlighting those aspects of essential systems that are most suitable as drug targets. Acinetobacter spp. show several key differences from other pathogenic gammaproteobacteria, particularly in global stress response pathways. The involvement of these pathways in short- and long-term antibiotic survival suggests that Acinetobacter spp. cope with antibiotic-induced stress differently from other microorganisms.
Collapse
|
36
|
Larson MA, Griep MA, Bressani R, Chintakayala K, Soultanas P, Hinrichs SH. Class-specific restrictions define primase interactions with DNA template and replicative helicase. Nucleic Acids Res 2010; 38:7167-78. [PMID: 20591822 PMCID: PMC2978363 DOI: 10.1093/nar/gkq588] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Bacterial primase is stimulated by replicative helicase to produce RNA primers that are essential for DNA replication. To identify mechanisms regulating primase activity, we characterized primase initiation specificity and interactions with the replicative helicase for gram-positive Firmicutes (Staphylococcus, Bacillus and Geobacillus) and gram-negative Proteobacteria (Escherichia, Yersinia and Pseudomonas). Contributions of the primase zinc-binding domain, RNA polymerase domain and helicase-binding domain on de novo primer synthesis were determined using mutated, truncated, chimeric and wild-type primases. Key residues in the β4 strand of the primase zinc-binding domain defined class-associated trinucleotide recognition and substitution of these amino acids transferred specificity across classes. A change in template recognition provided functional evidence for interaction in trans between the zinc-binding domain and RNA polymerase domain of two separate primases. Helicase binding to the primase C-terminal helicase-binding domain modulated RNA primer length in a species-specific manner and productive interactions paralleled genetic relatedness. Results demonstrated that primase template specificity is conserved within a bacterial class, whereas the primase-helicase interaction has co-evolved within each species.
Collapse
Affiliation(s)
- Marilynn A Larson
- Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE 68198-5900, USA.
| | | | | | | | | | | |
Collapse
|
37
|
Two distantly homologous DnaG primases from Thermoanaerobacter tengcongensis exhibit distinct initiation specificities and priming activities. J Bacteriol 2010; 192:2670-81. [PMID: 20348261 DOI: 10.1128/jb.01511-09] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Primase, encoded by dnaG in bacteria, is a specialized DNA-dependent RNA polymerase that synthesizes RNA primers de novo for elongation by DNA polymerase. Genome sequence analysis has revealed two distantly related dnaG genes, TtdnaG and TtdnaG(2), in the thermophilic bacterium Thermoanaerobacter tengcongensis. Both TtDnaG (600 amino acids) and TtDnaG2 (358 amino acids) exhibit primase activities in vitro at a wide range of temperatures. Interestingly, the template recognition specificities of these two primases are quite distinctive. When trinucleotide-specific templates were tested, TtDnaG initiated RNA primer synthesis efficiently only on templates containing the trinucleotide 5'-CCC-3', not on the other 63 possible trinucleotides. When the 5'-CCC-3' sequence was flanked by additional cytosines or guanines, the initiation efficiency of TtDnaG increased remarkably. Significantly, TtDnaG could specifically and efficiently initiate RNA primer synthesis on a limited set of tetranucleotides composed entirely of cytosines and guanines, indicating that TtDnaG initiated RNA primer synthesis more preferably on GC-containing tetranucleotides. In contrast, it seemed that TtDnaG2 had no specific initiation nucleotides, as it could efficiently initiate RNA primer synthesis on all templates tested. The DNA binding affinity of TtDnaG2 was usually 10-fold higher than that of TtDnaG, which might correlate with its high activity but low template specificity. These distinct priming activities and specificities of TtDnaG and TtDnaG2 might shed new light on the diversity in the structure and function of the primases.
Collapse
|
38
|
Makowska-Grzyska M, Kaguni JM. Primase directs the release of DnaC from DnaB. Mol Cell 2010; 37:90-101. [PMID: 20129058 DOI: 10.1016/j.molcel.2009.12.031] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2009] [Revised: 09/03/2009] [Accepted: 12/18/2009] [Indexed: 10/20/2022]
Abstract
An AAA+ ATPase, DnaC, delivers DnaB helicase at the E. coli chromosomal origin by a poorly understood process. This report shows that mutant proteins bearing alanine substitutions for two conserved arginines in a motif named box VII are defective in DNA replication, but this deficiency does not arise from impaired interactions with ATP, DnaB, or single-stranded DNA. Despite their ability to deliver DnaB to the chromosomal origin to form the prepriming complex, this intermediate is inactive. Quantitative analysis of the prepriming complex suggests that the DnaB-DnaC complex contains three DnaC monomers per DnaB hexamer and that the interaction of primase with DnaB and primer formation triggers the release of DnaC, but not the mutants, from DnaB. The interaction of primase with DnaB and the release of DnaC mark discrete events in the transition from initiation to the elongation stage of DNA replication.
Collapse
Affiliation(s)
- Magdalena Makowska-Grzyska
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824-1319, USA
| | | |
Collapse
|
39
|
Abstract
Replisomes are the protein assemblies that replicate DNA. They function as molecular motors to catalyze template-mediated polymerization of nucleotides, unwinding of DNA, the synthesis of RNA primers, and the assembly of proteins on DNA. The replisome of bacteriophage T7 contains a minimum of proteins, thus facilitating its study. This review describes the molecular motors and coordination of their activities, with emphasis on the T7 replisome. Nucleotide selection, movement of the polymerase, binding of the processivity factor, unwinding of DNA, and RNA primer synthesis all require conformational changes and protein contacts. Lagging-strand synthesis is mediated via a replication loop whose formation and resolution is dictated by switches to yield Okazaki fragments of discrete size. Both strands are synthesized at identical rates, controlled by a molecular brake that halts leading-strand synthesis during primer synthesis. The helicase serves as a reservoir for polymerases that can initiate DNA synthesis at the replication fork. We comment on the differences in other systems where applicable.
Collapse
Affiliation(s)
- Samir M Hamdan
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
| | | |
Collapse
|
40
|
Shereda RD, Kozlov AG, Lohman TM, Cox MM, Keck JL. SSB as an organizer/mobilizer of genome maintenance complexes. Crit Rev Biochem Mol Biol 2008; 43:289-318. [PMID: 18937104 PMCID: PMC2583361 DOI: 10.1080/10409230802341296] [Citation(s) in RCA: 412] [Impact Index Per Article: 25.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
When duplex DNA is altered in almost any way (replicated, recombined, or repaired), single strands of DNA are usually intermediates, and single-stranded DNA binding (SSB) proteins are present. These proteins have often been described as inert, protective DNA coatings. Continuing research is demonstrating a far more complex role of SSB that includes the organization and/or mobilization of all aspects of DNA metabolism. Escherichia coli SSB is now known to interact with at least 14 other proteins that include key components of the elaborate systems involved in every aspect of DNA metabolism. Most, if not all, of these interactions are mediated by the amphipathic C-terminus of SSB. In this review, we summarize the extent of the eubacterial SSB interaction network, describe the energetics of interactions with SSB, and highlight the roles of SSB in the process of recombination. Similar themes to those highlighted in this review are evident in all biological systems.
Collapse
Affiliation(s)
- Robert D Shereda
- Department of Biomolecular Chemistry, University of Wisconsin School of Medicine and Public Health, Madison, WI, USA
| | | | | | | | | |
Collapse
|
41
|
Chintakayala K, Larson MA, Griep MA, Hinrichs SH, Soultanas P. Conserved residues of the C-terminal p16 domain of primase are involved in modulating the activity of the bacterial primosome. Mol Microbiol 2008; 68:360-71. [PMID: 18366438 DOI: 10.1111/j.1365-2958.2008.06155.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The bacterial primosome comprises the replicative homo-hexameric ring helicase DnaB and the primase DnaG. It is an integral component of the replisome as it unwinds the parental DNA duplex to allow progression of the replication fork, synthesizes the initiation primers at the replication origin, oriC, and the primers required for Okazaki fragment synthesis during lagging strand replication. The interaction between the two component proteins is mediated by a distinct C-terminal domain (p16) of the primase. Both proteins mutually regulate each other's activities and a putative network of conserved residues has been proposed to mediate these effects. We have targeted 10 residues from this network. To investigate the functional contributions of these residues to the primase, ATPase and helicase activities of the primosome, we have used site-directed mutagenesis and in vitro functional assays. Five of these residues (E464, H494, R495, Y548 and R555) exhibited some functional significance while the remaining five (E483, R484, E506, D512 and E530) exhibited no effects. E464 participates in functional modulation of the primase activity, whereas H494, R495 and R555 participate in allosteric functional modulation of the ATPase and/or helicase activities. Y548 contributes directly to the structural interaction with DnaB.
Collapse
Affiliation(s)
- Kiran Chintakayala
- Centre for Biomolecular Sciences, School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK
| | | | | | | | | |
Collapse
|
42
|
Biswas T, Tsodikov OV. Hexameric ring structure of the N-terminal domain of Mycobacterium tuberculosis DnaB helicase. FEBS J 2008; 275:3064-71. [PMID: 18479467 DOI: 10.1111/j.1742-4658.2008.06460.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Hexameric DnaB helicase unwinds the DNA double helix during replication of genetic material in bacteria. DnaB is an essential bacterial protein; therefore, it is an important potential target for antibacterial drug discovery. We report a crystal structure of the N-terminal region of DnaB from the pathogen Mycobacterium tuberculosis (MtDnaBn), determined at 2.0 A resolution. This structure provides atomic resolution details of formation of the hexameric ring of DnaB by two distinct interfaces. An extensive hydrophobic interface stabilizes a dimer of MtDnaBn by forming a four-helix bundle. The other, less extensive, interface is formed between the dimers, connecting three of them into a hexameric ring. On the basis of crystal packing interactions between MtDnaBn rings, we suggest a model of a helicase-primase complex that explains previously observed effects of DnaB mutations on DNA priming.
Collapse
Affiliation(s)
- Tapan Biswas
- Department of Medicinal Chemistry, College of Pharmacy, University of Michigan, Ann Arbor, MI 48109, USA
| | | |
Collapse
|
43
|
Tanner NA, Hamdan SM, Jergic S, Loscha KV, Schaeffer PM, Dixon NE, van Oijen AM. Single-molecule studies of fork dynamics in Escherichia coli DNA replication. Nat Struct Mol Biol 2008; 15:170-6. [PMID: 18223657 DOI: 10.1038/nsmb.1381] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2007] [Accepted: 01/03/2008] [Indexed: 11/09/2022]
Abstract
We present single-molecule studies of the Escherichia coli replication machinery. We visualize individual E. coli DNA polymerase III (Pol III) holoenzymes engaging in primer extension and leading-strand synthesis. When coupled to the replicative helicase DnaB, Pol III mediates leading-strand synthesis with a processivity of 10.5 kilobases (kb), eight-fold higher than that by Pol III alone. Addition of the primase DnaG causes a three-fold reduction in the processivity of leading-strand synthesis, an effect dependent upon the DnaB-DnaG protein-protein interaction rather than primase activity. A single-molecule analysis of the replication kinetics with varying DnaG concentrations indicates that a cooperative binding of two or three DnaG monomers to DnaB halts synthesis. Modulation of DnaB helicase activity through the interaction with DnaG suggests a mechanism that prevents leading-strand synthesis from outpacing lagging-strand synthesis during slow primer synthesis on the lagging strand.
Collapse
Affiliation(s)
- Nathan A Tanner
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 250 Longwood Avenue, Boston, Massachusetts 02115, USA
| | | | | | | | | | | | | |
Collapse
|
44
|
The structure of a DnaB-family replicative helicase and its interactions with primase. Nat Struct Mol Biol 2007; 15:94-100. [PMID: 18157148 DOI: 10.1038/nsmb1356] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2007] [Accepted: 12/04/2007] [Indexed: 11/08/2022]
Abstract
Helicases are essential enzymes for DNA replication, a fundamental process in all living organisms. The DnaB family are hexameric replicative helicases that unwind duplex DNA and coordinate with RNA primase and other proteins at the replication fork in prokaryotes. Here, we report the full-length crystal structure of G40P, a DnaB family helicase. The hexamer complex reveals an unusual architectural feature and a new type of assembly mechanism. The hexamer has two tiers: a three-fold symmetric N-terminal tier and a six-fold symmetric C-terminal tier. Monomers with two different conformations, termed cis and trans, come together to provide a topological solution for the dual symmetry within a hexamer. Structure-guided mutational studies indicate an important role for the N-terminal tier in binding primase and regulating primase-mediated stimulation of helicase activity. This study provides insights into the structural and functional interplay between G40P helicase and DnaG primase.
Collapse
|
45
|
Bailey S, Eliason WK, Steitz TA. Structure of hexameric DnaB helicase and its complex with a domain of DnaG primase. Science 2007; 318:459-63. [PMID: 17947583 DOI: 10.1126/science.1147353] [Citation(s) in RCA: 163] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The complex between the DnaB helicase and the DnaG primase unwinds duplex DNA at the eubacterial replication fork and synthesizes the Okazaki RNA primers. The crystal structures of hexameric DnaB and its complex with the helicase binding domain (HBD) of DnaG reveal that within the hexamer the two domains of DnaB pack with strikingly different symmetries to form a distinct two-layered ring structure. Each of three bound HBDs stabilizes the DnaB hexamer in a conformation that may increase its processivity. Three positive, conserved electrostatic patches on the N-terminal domain of DnaB may also serve as a binding site for DNA and thereby guide the DNA to a DnaG active site.
Collapse
Affiliation(s)
- Scott Bailey
- Department of Molecular Biophysics and Biochemistry and Howard Hughes Medical Institute, Yale University, New Haven, CT 06520, USA
| | | | | |
Collapse
|
46
|
Bailey S, Eliason WK, Steitz TA. The crystal structure of the Thermus aquaticus DnaB helicase monomer. Nucleic Acids Res 2007; 35:4728-36. [PMID: 17606462 PMCID: PMC1950529 DOI: 10.1093/nar/gkm507] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The ring-shaped hexameric DnaB helicase unwinds duplex DNA at the replication fork of eubacteria. We have solved the crystal structure of the full-length Thermus aquaticus DnaB monomer, or possibly dimer, at 2.9 A resolution. DnaB is a highly flexible two domain protein. The C-terminal domain exhibits a RecA-like core fold and contains all the conserved sequence motifs that are characteristic of the DnaB helicase family. The N-terminal domain contains an additional helical hairpin that makes it larger than previously appreciated. Several DnaB mutations that modulate its interaction with primase are found in this hairpin. The similarity in the fold of the DnaB N-terminal domain with that of the C-terminal helicase-binding domain (HBD) of the DnaG primase also includes this hairpin. Comparison of hexameric homology models of DnaB with the structure of the papillomavirus E1 helicase suggests the two helicases may function through different mechanisms despite their sharing a common ancestor.
Collapse
Affiliation(s)
- Scott Bailey
- Department of Molecular Biophysics and Biochemistry, Department of Chemistry and Howard Hughes Medical Institute, Yale University, New Haven, Connecticut 06520, USA
| | - William K. Eliason
- Department of Molecular Biophysics and Biochemistry, Department of Chemistry and Howard Hughes Medical Institute, Yale University, New Haven, Connecticut 06520, USA
| | - Thomas A. Steitz
- Department of Molecular Biophysics and Biochemistry, Department of Chemistry and Howard Hughes Medical Institute, Yale University, New Haven, Connecticut 06520, USA
- *To whom correspondence should be addressed.+1 203 432 5619+1 203 432 3282
| |
Collapse
|
47
|
Chintakayala K, Larson MA, Grainger WH, Scott DJ, Griep MA, Hinrichs SH, Soultanas P. Domain swapping reveals that the C- and N-terminal domains of DnaG and DnaB, respectively, are functional homologues. Mol Microbiol 2007; 63:1629-39. [PMID: 17367384 PMCID: PMC3035176 DOI: 10.1111/j.1365-2958.2007.05617.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The bacterial primase (DnaG)-helicase (DnaB) interaction is mediated by the C-terminal domain of DnaG (p16) and a linker that joins the N- and C-terminal domains (p17 and p33 respectively) of DnaB. The crystal and nuclear magnetic resonance structures of p16 from Escherichia coli and Bacillus stearothermophilus DnaG proteins revealed a unique structural homology with p17, despite the lack of amino acid sequence similarity. The functional significance of this is not clear. Here, we have employed a 'domain swapping' approach to replace p17 with its structural homologue p16 to create chimeras. p33 alone hydrolyses ATP but exhibits no helicase activity. Fusing p16 (p16-p33) or DnaG (G-p33) to the N-terminus of p33 produced chimeras with partially restored helicase activities. Neither chimera interacted with DnaG. The p16-p33 chimera formed hexamers while G-p33 assembled into tetramers. Furthermore, G-p33 and DnaB formed mixed oligomers with ATPase activity better than that of the DnaB/DnaG complex and helicase activity better than the sum of the individual DnaB and G-p33 activities but worse than that of the DnaB/DnaG complex. Our combined data provide direct evidence that p16 and p17 are not only structural but also functional homologues, albeit their amino acid composition differences are likely to influence their precise roles.
Collapse
Affiliation(s)
- Kiran Chintakayala
- Centre for Biomolecular Sciences, School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK
| | - Marilynn A. Larson
- Department of Pathology/Microbiology, 984080 University of Nebraska Medical Center, Omaha, NE 68198-4080, USA
| | - William H. Grainger
- Centre for Biomolecular Sciences, School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK
| | - David J. Scott
- National Centre for Macromolecular Hydrodynamics, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Leicestershire LE12 5RD, UK
| | - Mark A. Griep
- Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE 68588-0304, USA
| | - Steven H. Hinrichs
- Department of Pathology/Microbiology, 984080 University of Nebraska Medical Center, Omaha, NE 68198-4080, USA
| | - Panos Soultanas
- Centre for Biomolecular Sciences, School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, UK
- For correspondence. ; Tel. (+44) 115 9513525; Fax (+44) 115 8468002
| |
Collapse
|
48
|
Roucourt B, Chibeu A, Lecoutere E, Lavigne R, Volckaert G, Hertveldt K. Homotypic interactions among bacteriophage phiKMV early proteins. Arch Virol 2007; 152:1467-75. [PMID: 17534690 DOI: 10.1007/s00705-007-0967-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2006] [Accepted: 03/07/2007] [Indexed: 11/26/2022]
Abstract
Little is known about the bacteriophage proteins expressed immediately after infection of the host cell. Most of these early proteins are probably involved in bacteriophage-host interactions redirecting the bacterial metabolism to phage production. Interaction analysis of the first 16 phiKMV gene products (gp) identified homotypic interactions of gp7, gp9 and gp15. Two related yeast two-hybrid procedures, a matrix and a minilibrary approach, were applied to detect protein-protein interactions. A two-step selection procedure enabled drastic reduction of the background. Interactions were confirmed by drop tests. Multimerization of gp15 is consistent with its putative function as a DNA helicase involved in DNA replication. Homotypic interaction of gp7 and gp9 suggests they function as dimers or multimers. The absence of heterotypic interactions among early phiKMV proteins hints at their functional independence from other early phage proteins and their involvement in phage-host interactions that are important for creating optimal conditions for phage propagation. Besides, these results demonstrate the compatibility of phiKMV early gene products with the yeast two-hybrid system. Therefore, they are promising candidates to screen for interactions with host proteins.
Collapse
Affiliation(s)
- B Roucourt
- Division of Gene Technology, Department of Biosystems, Katholieke Universiteit Leuven, Leuven, Belgium
| | | | | | | | | | | |
Collapse
|
49
|
Berrera M, Pantano S, Carloni P. Catabolite Activator Protein in Aqueous Solution: A Molecular Simulation Study. J Phys Chem B 2007; 111:1496-501. [PMID: 17243667 DOI: 10.1021/jp0667893] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The homodimeric catabolite activator protein (CAP) is a bacterial DNA binding transcription regulator whose activity is controlled by the binding of the intracellular mediator cyclic adenosine monophosphate (cAMP). Each CAP subunit consists of a cyclic nucleotide and a DNA binding domain. Here, we investigate the structural features of the ligand-bound CAP in aqueous solution by molecular dynamics simulations based on the available X-ray structures (Passner et al. J. Mol. Biol. 2000, 304, 847-859 and Chen et al. J. Mol. Biol. 2001, 314, 63-74). Our calculations suggest that the homodimer in solution assumes a symmetric arrangement in which both DNA binding domains are separated from the respective cyclic nucleotide binding domains by a cleft. This contrasts with the X-ray structure, which exhibits instead an asymmetric conformation. On the basis of electrostatics calculations, we propose that the symmetric structure in solution may be an important feature for DNA molecular recognition.
Collapse
Affiliation(s)
- Marco Berrera
- Scuola Internazionale Superiore di Studi Avanzati (SISSA) and INFM, Democritos Modeling Center for Research In Atomistic Simulation, via Beirut 4, 34014 Trieste, Italy
| | | | | |
Collapse
|
50
|
Su XC, Schaeffer PM, Loscha KV, Gan PHP, Dixon NE, Otting G. Monomeric solution structure of the helicase-binding domain of Escherichia coli DnaG primase. FEBS J 2006; 273:4997-5009. [PMID: 17010164 DOI: 10.1111/j.1742-4658.2006.05495.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
DnaG is the primase that lays down RNA primers on single-stranded DNA during bacterial DNA replication. The solution structure of the DnaB-helicase-binding C-terminal domain of Escherichia coli DnaG was determined by NMR spectroscopy at near-neutral pH. The structure is a rare fold that, besides occurring in DnaG C-terminal domains, has been described only for the N-terminal domain of DnaB. The C-terminal helix hairpin present in the DnaG C-terminal domain, however, is either less stable or absent in DnaB, as evidenced by high mobility of the C-terminal 35 residues in a construct comprising residues 1-171. The present structure identifies the previous crystal structure of the E. coli DnaG C-terminal domain as a domain-swapped dimer. It is also significantly different from the NMR structure reported for the corresponding domain of DnaG from the thermophile Bacillus stearothermophilus. NMR experiments showed that the DnaG C-terminal domain does not bind to residues 1-171 of the E. coli DnaB helicase with significant affinity.
Collapse
Affiliation(s)
- Xun-Cheng Su
- Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia
| | | | | | | | | | | |
Collapse
|