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Amundsen SK, Smith GR. RecBCD enzyme: mechanistic insights from mutants of a complex helicase-nuclease. Microbiol Mol Biol Rev 2023; 87:e0004123. [PMID: 38047637 PMCID: PMC10732027 DOI: 10.1128/mmbr.00041-23] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2023] Open
Abstract
SUMMARYRecBCD enzyme is a multi-functional protein that initiates the major pathway of homologous genetic recombination and DNA double-strand break repair in Escherichia coli. It is also required for high cell viability and aids proper DNA replication. This 330-kDa, three-subunit enzyme is one of the fastest, most processive helicases known and contains a potent nuclease controlled by Chi sites, hotspots of recombination, in DNA. RecBCD undergoes major changes in activity and conformation when, during DNA unwinding, it encounters Chi (5'-GCTGGTGG-3') and nicks DNA nearby. Here, we discuss the multitude of mutations in each subunit that affect one or another activity of RecBCD and its control by Chi. These mutants have given deep insights into how the multiple activities of this complex enzyme are coordinated and how it acts in living cells. Similar studies could help reveal how other complex enzymes are controlled by inter-subunit interactions and conformational changes.
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Affiliation(s)
| | - Gerald R. Smith
- Fred Hutchinson Cancer Center Seattle, Seattle, Washington, USA
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2
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Zhou K, Xue CX, Xu T, Shen P, Wei S, Wyres KL, Lam MMC, Liu J, Lin H, Chen Y, Holt KE, Xiao Y. A point mutation in recC associated with subclonal replacement of carbapenem-resistant Klebsiella pneumoniae ST11 in China. Nat Commun 2023; 14:2464. [PMID: 37117217 PMCID: PMC10147710 DOI: 10.1038/s41467-023-38061-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2022] [Accepted: 04/13/2023] [Indexed: 04/30/2023] Open
Abstract
Adaptation to selective pressures is crucial for clinically important pathogens to establish epidemics, but the underlying evolutionary drivers remain poorly understood. The current epidemic of carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a significant threat to public health. In this study we analyzed the genome sequences of 794 CRKP bloodstream isolates collected in 40 hospitals in China between 2014 and 2019. We uncovered a subclonal replacement in the predominant clone ST11, where the previously prevalent subclone OL101:KL47 was replaced by O2v1:KL64 over time in a stepwise manner. O2v1:KL64 carried a higher load of mobile genetic elements, and a point mutation exclusively detected in the recC of O2v1:KL64 significantly promotes recombination proficiency. The epidemic success of O2v1:KL64 was further associated with a hypervirulent sublineage with enhanced resistance to phagocytosis, sulfamethoxazole-trimethoprim, and tetracycline. The phenotypic alterations were linked to the overrepresentation of hypervirulence determinants and antibiotic genes conferred by the acquisition of an rmpA-positive pLVPK-like virulence plasmid and an IncFII-type multidrug-resistant plasmid, respectively. The dissemination of the sublineage was further promoted by more frequent inter-hospital transmission. The results collectively demonstrate that the expansion of O2v1:KL64 is correlated to a repertoire of genomic alterations convergent in a subpopulation with evolutionary advantages.
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Affiliation(s)
- Kai Zhou
- Shenzhen Institute of Respiratory Diseases, Shenzhen People's Hospital (Second Clinical Medical College, Jinan University; The First Affiliated Hospital, Southern University of Science and Technology), Shenzhen, 518020, China.
| | - Chun-Xu Xue
- Shenzhen Institute of Respiratory Diseases, Shenzhen People's Hospital (Second Clinical Medical College, Jinan University; The First Affiliated Hospital, Southern University of Science and Technology), Shenzhen, 518020, China
| | - Tingting Xu
- Shenzhen Institute of Respiratory Diseases, Shenzhen People's Hospital (Second Clinical Medical College, Jinan University; The First Affiliated Hospital, Southern University of Science and Technology), Shenzhen, 518020, China
| | - Ping Shen
- State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, National Clinical Research Center for Infectious Diseases, National Medical Center for Infectious Diseases, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, 310003, China
| | - Sha Wei
- Shenzhen Institute of Respiratory Diseases, Shenzhen People's Hospital (Second Clinical Medical College, Jinan University; The First Affiliated Hospital, Southern University of Science and Technology), Shenzhen, 518020, China
| | - Kelly L Wyres
- Department of Infectious Diseases, Central Clinical School, Monash University, Melbourne, VIC, 3004, Australia
| | - Margaret M C Lam
- Department of Infectious Diseases, Central Clinical School, Monash University, Melbourne, VIC, 3004, Australia
| | - Jinquan Liu
- Shenzhen Institute of Respiratory Diseases, Shenzhen People's Hospital (Second Clinical Medical College, Jinan University; The First Affiliated Hospital, Southern University of Science and Technology), Shenzhen, 518020, China
| | - Haoyun Lin
- Department of Clinical Laboratory, Shenzhen People's Hospital, Shenzhen, China
| | - Yunbo Chen
- State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, National Clinical Research Center for Infectious Diseases, National Medical Center for Infectious Diseases, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, 310003, China
| | - Kathryn E Holt
- Department of Infectious Diseases, Central Clinical School, Monash University, Melbourne, VIC, 3004, Australia
- Department of Infection Biology, Faculty of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London, WC1E 7HT, UK
| | - Yonghong Xiao
- State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, National Clinical Research Center for Infectious Diseases, National Medical Center for Infectious Diseases, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, 310003, China.
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3
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Badonyi M, Marsh JA. Large protein complex interfaces have evolved to promote cotranslational assembly. eLife 2022; 11:79602. [PMID: 35899946 PMCID: PMC9365393 DOI: 10.7554/elife.79602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Accepted: 07/27/2022] [Indexed: 11/13/2022] Open
Abstract
Assembly pathways of protein complexes should be precise and efficient to minimise misfolding and unwanted interactions with other proteins in the cell. One way to achieve this efficiency is by seeding assembly pathways during translation via the cotranslational assembly of subunits. While recent evidence suggests that such cotranslational assembly is widespread, little is known about the properties of protein complexes associated with the phenomenon. Here, using a combination of proteome-specific protein complex structures and publicly available ribosome profiling data, we show that cotranslational assembly is particularly common between subunits that form large intermolecular interfaces. To test whether large interfaces have evolved to promote cotranslational assembly, as opposed to cotranslational assembly being a non-adaptive consequence of large interfaces, we compared the sizes of first and last translated interfaces of heteromeric subunits in bacterial, yeast, and human complexes. When considering all together, we observe the N-terminal interface to be larger than the C-terminal interface 54% of the time, increasing to 64% when we exclude subunits with only small interfaces, which are unlikely to cotranslationally assemble. This strongly suggests that large interfaces have evolved as a means to maximise the chance of successful cotranslational subunit binding.
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Affiliation(s)
- Mihaly Badonyi
- MRC Human Genetics Unit, Institute of Genetics and Cancer, University of Edinburgh, Edinburgh, United Kingdom
| | - Joseph A Marsh
- MRC Human Genetics Unit, Institute of Genetics and Cancer, University of Edinburgh, Edinburgh, United Kingdom
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4
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Taylor AF, Amundsen SK, Guttman M, Lee KK, Luo J, Ranish J, Smith GR. Control of RecBCD enzyme activity by DNA binding- and Chi hotspot-dependent conformational changes. J Mol Biol 2014; 426:3479-99. [PMID: 25073102 DOI: 10.1016/j.jmb.2014.07.017] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Revised: 07/02/2014] [Accepted: 07/20/2014] [Indexed: 11/28/2022]
Abstract
Faithful repair of DNA double-strand breaks by homologous recombination is crucial to maintain functional genomes. The major Escherichia coli pathway of DNA break repair requires RecBCD enzyme, a complex protein machine with multiple activities. Upon encountering a Chi recombination hotspot (5' GCTGGTGG 3') during DNA unwinding, RecBCD's unwinding, nuclease, and RecA-loading activities change dramatically, but the physical basis for these changes is unknown. Here, we identify, during RecBCD's DNA unwinding, two Chi-stimulated conformational changes involving RecC. One produced a marked, long-lasting, Chi-dependent increase in protease sensitivity of a small patch, near the Chi recognition domain, on the solvent-exposed RecC surface. The other change was identified by crosslinking of an artificial amino acid inserted in this RecC patch to RecB. Small-angle X-ray scattering analysis confirmed a major conformational change upon binding of DNA to the enzyme and is consistent with these two changes. We propose that, upon DNA binding, the RecB nuclease domain swings from one side of RecC to the other; when RecBCD encounters Chi, the nuclease domain returns to its initial position determined by crystallography, where it nicks DNA exiting from RecC and loads RecA onto the newly generated 3'-ended single-stranded DNA during continued unwinding; a crevice between RecB and RecC increasingly narrows during these steps. This model provides a physical basis for the intramolecular "signal transduction" from Chi to RecC to RecD to RecB inferred previously from genetic and enzymatic analyses, and it accounts for the enzymatic changes that accompany Chi's stimulation of recombination.
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Affiliation(s)
- Andrew F Taylor
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
| | - Susan K Amundsen
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
| | - Miklos Guttman
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195, USA
| | - Kelly K Lee
- Department of Medicinal Chemistry, University of Washington, Seattle, WA 98195, USA
| | - Jie Luo
- Institute for Systems Biology, Seattle, WA 98109, USA
| | | | - Gerald R Smith
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA.
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5
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Abstract
Homologous recombination is an ubiquitous process that shapes genomes and repairs DNA damage. The reaction is classically divided into three phases: presynaptic, synaptic, and postsynaptic. In Escherichia coli, the presynaptic phase involves either RecBCD or RecFOR proteins, which act on DNA double-stranded ends and DNA single-stranded gaps, respectively; the central synaptic steps are catalyzed by the ubiquitous DNA-binding protein RecA; and the postsynaptic phase involves either RuvABC or RecG proteins, which catalyze branch-migration and, in the case of RuvABC, the cleavage of Holliday junctions. Here, we review the biochemical properties of these molecular machines and analyze how, in light of these properties, the phenotypes of null mutants allow us to define their biological function(s). The consequences of point mutations on the biochemical properties of recombination enzymes and on cell phenotypes help refine the molecular mechanisms of action and the biological roles of recombination proteins. Given the high level of conservation of key proteins like RecA and the conservation of the principles of action of all recombination proteins, the deep knowledge acquired during decades of studies of homologous recombination in bacteria is the foundation of our present understanding of the processes that govern genome stability and evolution in all living organisms.
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6
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How RecBCD enzyme and Chi promote DNA break repair and recombination: a molecular biologist's view. Microbiol Mol Biol Rev 2012; 76:217-28. [PMID: 22688812 DOI: 10.1128/mmbr.05026-11] [Citation(s) in RCA: 115] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The repair of DNA double-strand breaks (DSBs) is essential for cell viability and important for homologous genetic recombination. In enteric bacteria such as Escherichia coli, the major pathway of DSB repair requires the RecBCD enzyme, a complex helicase-nuclease regulated by a simple unique DNA sequence called Chi. How Chi regulates RecBCD has been extensively studied by both genetics and biochemistry, and two contrasting mechanisms to generate a recombinogenic single-stranded DNA tail have been proposed: the nicking of one DNA strand at Chi versus the switching of degradation from one strand to the other at Chi. Which of these reactions occurs in cells has remained unproven because of the inability to detect intracellular DNA intermediates in bacterial recombination and DNA break repair. Here, I discuss evidence from a combination of genetics and biochemistry indicating that nicking at Chi is the intracellular (in vivo) reaction. This example illustrates the need for both types of analysis (i.e., molecular biology) to uncover the mechanism and control of complex processes in living cells.
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7
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Vlašić I, Simatović A, Brčić-Kostić K. The hybrid recombinational repair pathway operates in a χ activity deficient recC1004 mutant of Escherichia coli. Biochimie 2012; 94:1918-25. [PMID: 22617484 DOI: 10.1016/j.biochi.2012.05.008] [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: 02/23/2012] [Accepted: 05/10/2012] [Indexed: 11/19/2022]
Abstract
Homologous recombination is a crucial process for the maintenance of genome integrity. The two main recombination pathways in Escherichia coli (RecBCD and RecF) differ in the initiation of recombination. The RecBCD enzyme is the only component of the RecBCD pathway which acts in the initiation of recombination, and possesses all biochemical activities (helicase, 5'-3' exonuclease, χ cutting and loading of the RecA protein onto single-stranded (ss) DNA) needed for the processing of double stranded (ds) DNA breaks (DSB). When the nuclease and RecA loading activities of the RecBCD enzyme are inactivated, the proteins of the RecF recombination machinery, i.e., RecJ and RecFOR substitute for the missing 5'-3' exonuclease and RecA loading activity respectively. The above mentioned activities of the RecBCD enzyme are regulated by an octameric sequence known as the χ site (5'-GCTGGTGG-3'). One class of recC mutations, designated recC*, leads to reduced χ cutting in vitro. The recC1004 strain (a member of the recC* mutant class) is recombination proficient and resistant to UV radiation. In this paper, we studied the effects of mutations in RecF pathway genes on DNA repair (after UV and γ radiation) and on conjugational recombination in recC1004 and recC1004 recD backgrounds. We found that DNA repair after UV and γ radiation in the recC1004 and recC1004 recD backgrounds depends on recFOR and recJ gene products. We also showed that the recC1004 mutant has reduced survival after γ radiation. This phenotype is suppressed by the recD mutation which abolishes the RecBCD dependent nuclease activity. Finally, the genetic requirements for conjugational recombination differ from those for DNA repair. Conjugational recombination in recC1004 recD mutants is dependent on the recJ gene product. Our results emphasize the importance of the canonical χ recognition activity in DSB repair and the significance of interchange between the components of two recombination machineries in achieving efficient DNA repair.
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Affiliation(s)
- Ignacija Vlašić
- Division of Molecular Biology, Ruđer Bošković Institute, Bijenička 54, 10000 Zagreb, Croatia
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8
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Amundsen SK, Fero J, Salama NR, Smith GR. Dual nuclease and helicase activities of Helicobacter pylori AddAB are required for DNA repair, recombination, and mouse infectivity. J Biol Chem 2009; 284:16759-16766. [PMID: 19395381 DOI: 10.1074/jbc.m109.005587] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Helicobacter pylori infection of the human stomach is associated with disease-causing inflammation that elicits DNA damage in both bacterial and host cells. Bacteria must repair their DNA to persist. The H. pylori AddAB helicase-exonuclease is required for DNA repair and efficient stomach colonization. To dissect the role of each activity in DNA repair and infectivity, we altered the AddA and AddB nuclease (NUC) domains and the AddA helicase (HEL) domain by site-directed mutagenesis. Extracts of Escherichia coli expressing H. pylori addA(NUC)B or addAB(NUC) mutants unwound DNA but had approximately half of the exonuclease activity of wild-type AddAB; the addA(NUC)B(NUC) double mutant lacked detectable nuclease activity but retained helicase activity. Extracts with AddA(HEL)B lacked detectable helicase and nuclease activity. H. pylori with the single nuclease domain mutations were somewhat less sensitive to the DNA-damaging agent ciprofloxacin than the corresponding deletion mutant, suggesting that residual nuclease activity promotes limited DNA repair. The addA(NUC) and addA(HEL) mutants colonized the stomach less efficiently than the wild type; addB(NUC) showed partial attenuation. E. coli DeltarecBCD expressing H. pylori addAB was recombination-deficient unless H. pylori recA was also expressed, suggesting a species-specific interaction between AddAB and RecA and also that H. pylori AddAB participates in both DNA repair and recombination. These results support a role for both the AddAB nuclease and helicase in DNA repair and promoting infectivity.
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Affiliation(s)
| | - Jutta Fero
- Human Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109
| | - Nina R Salama
- Human Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109
| | - Gerald R Smith
- From the Divisions of Basic Sciences, Seattle, Washington 98109.
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9
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RecBCD enzyme and the repair of double-stranded DNA breaks. Microbiol Mol Biol Rev 2009; 72:642-71, Table of Contents. [PMID: 19052323 DOI: 10.1128/mmbr.00020-08] [Citation(s) in RCA: 404] [Impact Index Per Article: 26.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The RecBCD enzyme of Escherichia coli is a helicase-nuclease that initiates the repair of double-stranded DNA breaks by homologous recombination. It also degrades linear double-stranded DNA, protecting the bacteria from phages and extraneous chromosomal DNA. The RecBCD enzyme is, however, regulated by a cis-acting DNA sequence known as Chi (crossover hotspot instigator) that activates its recombination-promoting functions. Interaction with Chi causes an attenuation of the RecBCD enzyme's vigorous nuclease activity, switches the polarity of the attenuated nuclease activity to the 5' strand, changes the operation of its motor subunits, and instructs the enzyme to begin loading the RecA protein onto the resultant Chi-containing single-stranded DNA. This enzyme is a prototypical example of a molecular machine: the protein architecture incorporates several autonomous functional domains that interact with each other to produce a complex, sequence-regulated, DNA-processing machine. In this review, we discuss the biochemical mechanism of the RecBCD enzyme with particular emphasis on new developments relating to the enzyme's structure and DNA translocation mechanism.
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10
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Portakal O, Doğan P. Construction of recB-recD genetic fusion and functional analysis of RecBDC fusion enzyme in Escherichia coli. BMC BIOCHEMISTRY 2008; 9:27. [PMID: 18847457 PMCID: PMC2586629 DOI: 10.1186/1471-2091-9-27] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/05/2007] [Accepted: 10/10/2008] [Indexed: 11/12/2022]
Abstract
Background recD, located between recB and argA, encodes the smallest polypeptide (60 kDa) of the heterotrimeric enzyme RecBCD in Escherichia coli. RecD is a 5'-3' helicase and is required for the nuclease activity of RecBCD and for tight binding to dsDNA ends. Here, we have tested the hypothesis that RecD regulates the structure and activities of RecBCD, including RecA loading. Results To characterize its regulatory functions, recD was genetically fused to recB through deletion and substitution mutations. The recB-recD fusion led to a decreased amount of the heterotrimer. Both fusion mutants proved to be recombination proficient, viable and resistant to DNA damaging agents, and to have DNA unwinding, ATP-dependent dsDNA exonuclease and Chi genetic activities. Conclusion Our findings suggest that the recB-recD fusion may form a RecBD fusion protein and therefore affect RecD assembly, but this does not change the three-dimensional structure of the heterotrimer.
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Affiliation(s)
- Oytun Portakal
- Biochemistry Department, Hacettepe University Medical School, 06100 Sihhiye, Ankara, Turkey.
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11
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Amundsen SK, Taylor AF, Reddy M, Smith GR. Intersubunit signaling in RecBCD enzyme, a complex protein machine regulated by Chi hot spots. Genes Dev 2007; 21:3296-307. [PMID: 18079176 PMCID: PMC2113030 DOI: 10.1101/gad.1605807] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2007] [Accepted: 10/16/2007] [Indexed: 11/24/2022]
Abstract
The Escherichia coli RecBCD helicase-nuclease, a paradigm of complex protein machines, initiates homologous genetic recombination and the repair of broken DNA. Starting at a duplex end, RecBCD unwinds DNA with its fast RecD helicase and slower RecB helicase on complementary strands. Upon encountering a Chi hot spot (5'-GCTGGTGG-3'), the enzyme produces a new 3' single-strand end and loads RecA protein onto it, but how Chi regulates RecBCD is unknown. We report a new class of mutant RecBCD enzymes that cut DNA at novel positions that depend on the DNA substrate length and that are strictly correlated with the RecB:RecD helicase rates. We conclude that in the mutant enzymes when RecD reaches the DNA end, it signals RecB's nuclease domain to cut the DNA. As predicted by this interpretation, the mutant enzymes cut closer to the entry point on DNA when unwinding is blocked by another RecBCD molecule traveling in the opposite direction. Furthermore, when RecD is slowed by a mutation altering its ATPase site such that RecB reaches the DNA end before RecD does, the length-dependent cuts are abolished. These observations lead us to hypothesize that, in wild-type RecBCD enzyme, Chi is recognized by RecC, which then signals RecD to stop, which in turn signals RecB to cut the DNA and load RecA. We discuss support for this "signal cascade" hypothesis and tests of it. Intersubunit signaling may regulate other complex protein machines.
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Affiliation(s)
- Susan K. Amundsen
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA
| | - Andrew F. Taylor
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA
| | - Manjula Reddy
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA
| | - Gerald R. Smith
- Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA
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Amundsen SK, Smith GR. Chi hotspot activity in Escherichia coli without RecBCD exonuclease activity: implications for the mechanism of recombination. Genetics 2007; 175:41-54. [PMID: 17110484 PMCID: PMC1774988 DOI: 10.1534/genetics.106.065524] [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] [Received: 08/31/2006] [Accepted: 10/23/2006] [Indexed: 11/18/2022] Open
Abstract
The major pathway of genetic recombination and DNA break repair in Escherichia coli requires RecBCD enzyme, a complex nuclease and DNA helicase regulated by Chi sites (5'-GCTGGTGG-3'). During its unwinding of DNA containing Chi, purified RecBCD enzyme has two alternative nucleolytic reactions, depending on the reaction conditions: simple nicking of the Chi-containing strand at Chi or switching of nucleolytic degradation from the Chi-containing strand to its complement at Chi. We describe a set of recC mutants with a novel intracellular phenotype: retention of Chi hotspot activity in genetic crosses but loss of detectable nucleolytic degradation as judged by the growth of mutant T4 and lambda phages and by assay of cell-free extracts. We conclude that RecBCD enzyme's nucleolytic degradation of DNA is not necessary for intracellular Chi hotspot activity and that nicking of DNA by RecBCD enzyme at Chi is sufficient. We discuss the bearing of these results on current models of RecBCD pathway recombination.
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Affiliation(s)
- Susan K Amundsen
- Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA
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13
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Wong CJ, Lucius AL, Lohman TM. Energetics of DNA end binding by E.coli RecBC and RecBCD helicases indicate loop formation in the 3'-single-stranded DNA tail. J Mol Biol 2005; 352:765-82. [PMID: 16126227 DOI: 10.1016/j.jmb.2005.07.056] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2005] [Revised: 07/20/2005] [Accepted: 07/20/2005] [Indexed: 10/25/2022]
Abstract
We examined the equilibrium binding of Escherichia coli RecBC and RecBCD helicases to duplex DNA ends possessing pre-existing single-stranded (ss) DNA ((dT)(n)) tails varying in length (n=0 to 20 nucleotides) in order to determine the contributions of both the 3' and 5' single strands to the energetics of complex formation. Protein binding was monitored by the fluorescence enhancement of a reference DNA labeled at its end with a Cy3 fluorophore. Binding to unlabeled DNA was examined by competition titrations with the Cy3-labeled reference DNA. The affinities of both RecBC and RecBCD increase as the 3'-(dT)(n) tail length increases from zero to six nucleotides, but then decrease dramatically as the 3'-(dT)(n) tail length increases from six to 20 nucleotides. Isothermal titration calorimetry experiments with RecBC show that the binding enthalpy is negative and increases in magnitude with increasing 3'-(dT)(n) tail length up to n=6 nucleotides, but remains constant for n > or =6. Hence, the decrease in binding affinity for 3'-(dT)(n) tail lengths with n > or =6 is due to an unfavorable entropic contribution. RecBC binds optimally to duplex DNA with (dT)6 tails on both the 3' and 5'-ends while RecBCD prefers duplex DNA with 3'-(dT)6 and 5'-(dT)10 tails. These data suggest that both RecBC and RecBCD helicases can destabilize or "melt out" six base-pairs upon binding to a blunt DNA duplex end in the absence of ATP. These results also provide the first evidence that a loop in the 3'-ssDNA tail can form upon binding of RecBC or RecBCD with DNA duplexes containing a pre-formed 3'-ssDNA tail with n > or =6 nucleotides. Such loops may be representative of those hypothesized to form upon interaction of a Chi site contained within the unwound 3' ss-DNA tail with the RecC subunit during DNA unwinding.
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Affiliation(s)
- C Jason Wong
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 S. Euclid Avenue, Box 8231, Saint Louis, MO 63110-1093, USA
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Regha K, Satapathy AK, Ray MK. RecD plays an essential function during growth at low temperature in the antarctic bacterium Pseudomonas syringae Lz4W. Genetics 2005; 170:1473-84. [PMID: 15956672 PMCID: PMC1449786 DOI: 10.1534/genetics.104.038943] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The Antarctic psychrotrophic bacterium Pseudomonas syringae Lz4W has been used as a model system to identify genes that are required for growth at low temperature. Transposon mutagenesis was carried out to isolate mutant(s) of the bacterium that are defective for growth at 4 degrees but normal at 22 degrees . In one such cold-sensitive mutant (CS1), the transposon-disrupted gene was identified to be a homolog of the recD gene of several bacteria. Trans-complementation and freshly targeted gene disruption studies reconfirmed that the inactivation of the recD gene leads to a cold-sensitive phenotype. We cloned, sequenced, and analyzed approximately 11.2 kbp of DNA from recD and its flanking region from the bacterium. recD was the last gene of a putative recCBD operon. The RecD ORF was 694 amino acids long and 40% identical (52% similar) to the Escherichia coli protein, and it could complement the E. coli recD mutation. The recD gene of E. coli, however, could not complement the cold-sensitive phenotype of the CS1 mutant. Interestingly, the CS1 strain showed greater sensitivity toward the DNA-damaging agents, mitomycin C and UV. The inactivation of recD in P. syringae also led to cell death and accumulation of DNA fragments of approximately 25-30 kbp in size at low temperature (4 degrees ). We propose that during growth at a very low temperature the Antarctic P. syringae is subjected to DNA damage, which requires direct participation of a unique RecD function. Additional results suggest that a truncated recD encoding the N-terminal segment of (1-576) amino acids is sufficient to support growth of P. syringae at low temperature.
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Affiliation(s)
- K Regha
- Centre for Cellular and Molecular Biology, Hyderabad 500007, India
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15
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Ivancic-Bace I, Salaj-Smic E, Brcic-Kostic K. Effects of recJ, recQ, and recFOR mutations on recombination in nuclease-deficient recB recD double mutants of Escherichia coli. J Bacteriol 2005; 187:1350-6. [PMID: 15687199 PMCID: PMC545629 DOI: 10.1128/jb.187.4.1350-1356.2005] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The two main recombination pathways in Escherichia coli (RecBCD and RecF) have different recombination machineries that act independently in the initiation of recombination. Three essential enzymatic activities are required for early recombinational processing of double-stranded DNA ends and breaks: a helicase, a 5'-->3' exonuclease, and loading of RecA protein onto single-stranded DNA tails. The RecBCD enzyme performs all of these activities, whereas the recombination machinery of the RecF pathway consists of RecQ (helicase), RecJ (5'-->3' exonuclease), and RecFOR (RecA-single-stranded DNA filament formation). The recombination pathway operating in recB (nuclease-deficient) mutants is a hybrid because it includes elements of both the RecBCD and RecF recombination machineries. In this study, genetic analysis of recombination in a recB (nuclease-deficient) recD double mutant was performed. We show that conjugational recombination and DNA repair after UV and gamma irradiation in this mutant are highly dependent on recJ, partially dependent on recFOR, and independent of recQ. These results suggest that the recombination pathway operating in a nuclease-deficient recB recD double mutant is also a hybrid. We propose that the helicase and RecA loading activities belong to the RecBCD recombination machinery, while the RecJ-mediated 5'-->3' exonuclease is an element of the RecF recombination machinery.
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Affiliation(s)
- Ivana Ivancic-Bace
- Department of Molecular Biology, Ruder Bosković Institute, Bijenicka 54, HR-10002 Zagreb, Croatia
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Singleton MR, Dillingham MS, Gaudier M, Kowalczykowski SC, Wigley DB. Crystal structure of RecBCD enzyme reveals a machine for processing DNA breaks. Nature 2004; 432:187-93. [PMID: 15538360 DOI: 10.1038/nature02988] [Citation(s) in RCA: 317] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2004] [Accepted: 09/02/2004] [Indexed: 11/09/2022]
Abstract
RecBCD is a multi-functional enzyme complex that processes DNA ends resulting from a double-strand break. RecBCD is a bipolar helicase that splits the duplex into its component strands and digests them until encountering a recombinational hotspot (Chi site). The nuclease activity is then attenuated and RecBCD loads RecA onto the 3' tail of the DNA. Here we present the crystal structure of RecBCD bound to a DNA substrate. In this initiation complex, the DNA duplex has been split across the RecC subunit to create a fork with the separated strands each heading towards different helicase motor subunits. The strands pass along tunnels within the complex, both emerging adjacent to the nuclease domain of RecB. Passage of the 3' tail through one of these tunnels provides a mechanism for the recognition of a Chi sequence by RecC within the context of double-stranded DNA. Gating of this tunnel suggests how nuclease activity might be regulated.
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Affiliation(s)
- Martin R Singleton
- Cancer Research UK Clare Hall Laboratories, The London Research Institute, Blanche Lane, South Mimms, Potters Bar, Herts. EN6 3LD, UK
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