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Roske Y, Cappel C, Cremer N, Hoffmann P, Koudelka T, Tholey A, Heinemann U, Daumke O, Damme M. Structural analysis of PLD3 reveals insights into the mechanism of lysosomal 5' exonuclease-mediated nucleic acid degradation. Nucleic Acids Res 2024; 52:370-384. [PMID: 37994783 PMCID: PMC10783504 DOI: 10.1093/nar/gkad1114] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2023] [Revised: 10/31/2023] [Accepted: 11/15/2023] [Indexed: 11/24/2023] Open
Abstract
The phospholipase D (PLD) family is comprised of enzymes bearing phospholipase activity towards lipids or endo- and exonuclease activity towards nucleic acids. PLD3 is synthesized as a type II transmembrane protein and proteolytically cleaved in lysosomes, yielding a soluble active form. The deficiency of PLD3 leads to the slowed degradation of nucleic acids in lysosomes and chronic activation of nucleic acid-specific intracellular toll-like receptors. While the mechanism of PLD phospholipase activity has been extensively characterized, not much is known about how PLDs bind and hydrolyze nucleic acids. Here, we determined the high-resolution crystal structure of the luminal N-glycosylated domain of human PLD3 in its apo- and single-stranded DNA-bound forms. PLD3 has a typical phospholipase fold and forms homodimers with two independent catalytic centers via a newly identified dimerization interface. The structure of PLD3 in complex with an ssDNA-derived thymidine product in the catalytic center provides insights into the substrate binding mode of nucleic acids in the PLD family. Our structural data suggest a mechanism for substrate binding and nuclease activity in the PLD family and provide the structural basis to design immunomodulatory drugs targeting PLD3.
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Affiliation(s)
- Yvette Roske
- Structural Biology, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), 13125 Berlin, Germany
| | - Cedric Cappel
- Biochemical Institute, Kiel University, Kiel, Germany
| | - Nils Cremer
- Leibniz-Institut für Molekulare Pharmakologie (FMP), Robert-Rössle-Straβe 10, 13125 Berlin, Germany
| | | | - Tomas Koudelka
- Institute of Experimental Medicine, Kiel University, 24188 Kiel, Germany
| | - Andreas Tholey
- Institute of Experimental Medicine, Kiel University, 24188 Kiel, Germany
| | - Udo Heinemann
- Structural Biology, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), 13125 Berlin, Germany
- Institute for Chemistry and Biochemistry, Freie Universität Berlin, 14195 Berlin, Germany
| | - Oliver Daumke
- Structural Biology, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), 13125 Berlin, Germany
- Institute for Chemistry and Biochemistry, Freie Universität Berlin, 14195 Berlin, Germany
| | - Markus Damme
- Biochemical Institute, Kiel University, Kiel, Germany
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2
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Shan Z, Ghadirian N, Lyumkis D, Horton NC. Pretransition state and apo structures of the filament-forming enzyme SgrAI elucidate mechanisms of activation and substrate specificity. J Biol Chem 2022; 298:101760. [PMID: 35202658 PMCID: PMC8960973 DOI: 10.1016/j.jbc.2022.101760] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2021] [Revised: 02/14/2022] [Accepted: 02/16/2022] [Indexed: 12/01/2022] Open
Abstract
Enzyme filamentation is a widespread phenomenon that mediates enzyme regulation and function. For the filament-forming sequence-specific DNA endonuclease SgrAI, the process of filamentation both accelerates its DNA cleavage activity and expands its DNA sequence specificity, thus allowing for many additional DNA sequences to be rapidly cleaved. Both outcomes-the acceleration of DNA cleavage and the expansion of sequence specificity-are proposed to regulate critical processes in bacterial innate immunity. However, the mechanistic bases underlying these events remain unclear. Herein, we describe two new structures of the SgrAI enzyme that shed light on its catalytic function. First, we present the cryo-EM structure of filamentous SgrAI bound to intact primary site DNA and Ca2+ resolved to ∼2.5 Å within the catalytic center, which represents the trapped enzyme-DNA complex prior to the DNA cleavage reaction. This structure reveals important conformational changes that contribute to the catalytic mechanism and the binding of a second divalent cation in the enzyme active site, which is expected to contribute to increased DNA cleavage activity of SgrAI in the filamentous state. Second, we present an X-ray crystal structure of DNA-free (apo) SgrAI resolved to 2.0 Å resolution, which reveals a disordered loop involved in DNA recognition. Collectively, these multiple new observations clarify the mechanism of expansion of DNA sequence specificity of SgrAI, including the indirect readout of sequence-dependent DNA structure, changes in protein-DNA interactions, and the disorder-to-order transition of a crucial DNA recognition element.
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Affiliation(s)
- Zelin Shan
- Laboratory of Genetics, The Salk Institute of Biological Sciences, La Jolla, California, USA
| | - Niloofar Ghadirian
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona, USA
| | - Dmitry Lyumkis
- Laboratory of Genetics, The Salk Institute of Biological Sciences, La Jolla, California, USA; Department of Integrative Structural and Computational Biology, The Scripps Research Institute, La Jolla, California, USA.
| | - Nancy C Horton
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, Arizona, USA.
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3
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Nagamalleswari E, Vasu K, Nagaraja V. Ca(2+) binding to the ExDxD motif regulates the DNA cleavage specificity of a promiscuous endonuclease. Biochemistry 2012; 51:8939-49. [PMID: 23072305 DOI: 10.1021/bi301151y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Most of the restriction endonucleases (REases) are dependent on Mg(2+) for DNA cleavage, and in general, Ca(2+) inhibits their activity. R.KpnI, an HNH active site containing ββα-Me finger nuclease, is an exception. In presence of Ca(2+), the enzyme exhibits high-fidelity DNA cleavage and complete suppression of Mg(2+)-induced promiscuous activity. To elucidate the mechanism of unusual Ca(2+)-mediated activity, we generated alanine variants in the putative Ca(2+) binding motif, E(132)xD(134)xD(136), of the enzyme. Mutants showed decreased levels of DNA cleavage in the presence of Ca(2+). We demonstrate that ExDxD residues are involved in Ca(2+) coordination; however, the invariant His of the catalytic HNH motif acts as a general base for nucleophile activation, and the other two active site residues, D148 and Q175, also participate in Ca(2+)-mediated cleavage. Insertion of a 10-amino acid linker to disrupt the spatial organization of the ExDxD and HNH motifs impairs Ca(2+) binding and affects DNA cleavage by the enzyme. Although ExDxD mutant enzymes retained efficient cleavage at the canonical sites in the presence of Mg(2+), the promiscuous activity was greatly reduced, indicating that the carboxyl residues of the acidic triad play an important role in sequence recognition by the enzyme. Thus, the distinct Ca(2+) binding motif that confers site specific cleavage upon Ca(2+) binding is also critical for the promiscuous activity of the Mg(2+)-bound enzyme, revealing its role in metal ion-mediated modulation of DNA cleavage.
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Affiliation(s)
- Easa Nagamalleswari
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560 012, India
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4
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Vasu K, Saravanan M, Rajendra BVRN, Nagaraja V. Generation of a Manganese Specific Restriction Endonuclease with Nicking Activity. Biochemistry 2010; 49:8425-33. [DOI: 10.1021/bi101035k] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Kommireddy Vasu
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | - Matheshwaran Saravanan
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
| | | | - Valakunja Nagaraja
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India
- Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560012, India
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5
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Solt I, Simon I, Császár AG, Fuxreiter M. Electrostatic versus nonelectrostatic effects in DNA sequence discrimination by divalent ions Mg2+ and Mn2+. J Phys Chem B 2007; 111:6272-9. [PMID: 17497910 DOI: 10.1021/jp0668192] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Mg2+ and Mn2+ ions are critical to the functioning of phosphoryl transfer enzymes, such as restriction endonucleases. Although these ions play similar roles in the chemical steps, they govern substrate specificity via modulating sequence discrimination by up to a factor of 10(5) with Mg2+ and only up to a factor of 10 with Mn2+. To explain whether such diversity originates in fundamental differences in the electronic structures of the nucleobase-hydrated-metal ion complexes, structures and interaction energies were determined at the density functional (DFT) and second-order Møller-Plesset (MP2) levels of theory. Although both metal ions favor identical binding sites, Mn2+ complexes exhibit greater distortions from the ideal octahedral geometry and larger variability than the corresponding Mg2+ systems. In inner-shell complexes, with direct contact between the metal and the nucleobase, Mg2+ is preferred over Mn2+ in the gas phase, due primarily to nonelectrostatic effects. The interaction energies of the two metal ions are more similar in the outer-shell complexes, likely due to reduced charge transfer between the hydrated metal ion and the base moieties. Inclusion of solvation effects can amplify the relative nucleobase preferences of Mg2+ and Mn2+, indicating that bulk hydration modulates the balance between electrostatic and nonelectrostatic terms. In most cases, the base substitutions in solution are facilitated more by Mn2+ than by Mg2+. Electrostatic properties of the environment were demonstrated to have a major influence on the nucleobase preferences of the two metal ions. Overall, quantum chemical calculations suggest that the contrasting selectivity of Mg2+ and Mn2+ cofactors toward nucleobases derives from the larger flexibility of the Mn2+ complexes accompanied by the excessive polarization and charge-transfer effects as well as less favorable solvation.
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Affiliation(s)
- Iván Solt
- Institute of Enzymology, Biological Research Center, Hungarian Academy of Sciences, H-1518 Budapest PO Box 7, Hungary
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6
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Saravanan M, Vasu K, Kanakaraj R, Rao DN, Nagaraja V. R.KpnI, an HNH superfamily REase, exhibits differential discrimination at non-canonical sequences in the presence of Ca2+ and Mg2+. Nucleic Acids Res 2007; 35:2777-86. [PMID: 17430971 PMCID: PMC1885652 DOI: 10.1093/nar/gkm114] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
KpnI REase recognizes palindromic sequence, GGTAC↓C, and forms complex in the absence of divalent metal ions, but requires the ions for DNA cleavage. Unlike most other REases, R.KpnI shows promiscuous DNA cleavage in the presence of Mg2+. Surprisingly, Ca2+ suppresses the Mg2+-mediated promiscuous activity and induces high fidelity cleavage. To further analyze these unique features of the enzyme, we have carried out DNA binding and kinetic analysis. The metal ions which exhibit disparate pattern of DNA cleavage have no role in DNA recognition. The enzyme binds to both canonical and non-canonical DNA with comparable affinity irrespective of the metal ions used. Further, Ca2+-imparted exquisite specificity of the enzyme is at the level of DNA cleavage and not at the binding step. With the canonical oligonucleotides, the cleavage rate of the enzyme was comparable for both Mg2+- and Mn2+-mediated reactions and was about three times slower with Ca2+. The enzyme discriminates non-canonical sequences poorly from the canonical sequence in Mg2+-mediated reactions unlike any other Type II REases, accounting for the promiscuous behavior. R.KpnI, thus displays properties akin to that of typical Type II REases and also endonucleases with degenerate specificity in its DNA recognition and cleavage properties.
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Affiliation(s)
- Matheshwaran Saravanan
- Department of Microbiology and Cell Biology, Department of Biochemistry, Indian Institute of Science, Bangalore 560 012 and Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560 064, India
| | - Kommireddy Vasu
- Department of Microbiology and Cell Biology, Department of Biochemistry, Indian Institute of Science, Bangalore 560 012 and Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560 064, India
| | - Radhakrishnan Kanakaraj
- Department of Microbiology and Cell Biology, Department of Biochemistry, Indian Institute of Science, Bangalore 560 012 and Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560 064, India
| | - Desirazu N. Rao
- Department of Microbiology and Cell Biology, Department of Biochemistry, Indian Institute of Science, Bangalore 560 012 and Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560 064, India
| | - Valakunja Nagaraja
- Department of Microbiology and Cell Biology, Department of Biochemistry, Indian Institute of Science, Bangalore 560 012 and Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560 064, India
- *To whom correspondence should be addressed +91-80-2360066891-80-23602697
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7
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de los Rios S, Perona JJ. Structure of the Escherichia coli leucine-responsive regulatory protein Lrp reveals a novel octameric assembly. J Mol Biol 2007; 366:1589-602. [PMID: 17223133 PMCID: PMC1933502 DOI: 10.1016/j.jmb.2006.12.032] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2006] [Revised: 12/08/2006] [Accepted: 12/13/2006] [Indexed: 11/28/2022]
Abstract
The structure of Escherichia coli leucine-responsive regulatory protein (Lrp) co-crystallized with a short duplex oligodeoxynucleotide reveals a novel quaternary assembly in which the protein octamer forms an open, linear array of four dimers. In contrast, structures of the Lrp homologs LrpA, LrpC and AsnC crystallized in the absence of DNA show that these proteins instead form highly symmetrical octamers in which the four dimers form a closed ring. Although the DNA is disordered within the Lrp crystal, comparative analyses suggest that the observed differences in quaternary state may arise from DNA interactions during crystallization. Interconversion of these conformations, possibly in response to DNA or leucine binding, provides an underlying mechanism to alter the relative spatial orientation of the DNA-binding domains. Breaking of the closed octamer symmetry may be a common essential step in the formation of active DNA complexes by all members of the Lrp/AsnC family of transcriptional regulatory proteins.
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MESH Headings
- Amino Acid Sequence
- Binding Sites
- Crystallography, X-Ray
- DNA/isolation & purification
- DNA/metabolism
- Dimerization
- Escherichia coli/genetics
- Escherichia coli/growth & development
- Escherichia coli/metabolism
- Gene Deletion
- Gene Expression Regulation, Bacterial
- Hydrogen Bonding
- Leucine/genetics
- Leucine/metabolism
- Leucine-Responsive Regulatory Protein/chemistry
- Leucine-Responsive Regulatory Protein/genetics
- Leucine-Responsive Regulatory Protein/isolation & purification
- Leucine-Responsive Regulatory Protein/metabolism
- Models, Molecular
- Molecular Sequence Data
- Mutagenesis
- Operon
- Protein Binding
- Protein Structure, Quaternary
- Protein Structure, Tertiary
- Sequence Homology, Amino Acid
- Spectrometry, Mass, Electrospray Ionization
- Spectrum Analysis, Raman
- Static Electricity
- Transcription, Genetic
- X-Ray Diffraction
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Affiliation(s)
- Stephanie de los Rios
- Interdepartmental Program in Biomolecular Science and Engineering, University of California at Santa Barbara, CA 93106-9510, USA
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8
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Hiller DA, Perona JJ. Positively charged C-terminal subdomains of EcoRV endonuclease: contributions to DNA binding, bending, and cleavage. Biochemistry 2006; 45:11453-63. [PMID: 16981705 PMCID: PMC2515858 DOI: 10.1021/bi0606400] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The carboxy-terminal subdomains of the homodimeric EcoRV restriction endonuclease each bear a net charge of +4 and are positioned on the inner concave surface of the 50 degree DNA bend that is induced by the enzyme. A complete kinetic and structural analysis of a truncated EcoRV mutant lacking these domains was performed to assess the importance of this diffuse charge in facilitating DNA binding, bending, and cleavage. At the level of formation of an enzyme-DNA complex, the association rate for the dimeric mutant enzyme was sharply decreased by 10(3)-fold, while the equilibrium dissociation constant was weakened by nearly 10(6)-fold compared with that of wild-type EcoRV. Thus, the C-terminal subdomains strongly stabilize the enzyme-DNA ground-state complex in which the DNA is known to be bent. Further, the extent of DNA bending as observed by fluorescence resonance energy transfer was also significantly decreased. The crystal structure of the truncated enzyme bound to DNA and calcium ions at 2.4 A resolution reveals that the global fold is preserved and suggests that a divalent metal ion crucial to catalysis is destabilized in the active site. This may explain the 100-fold decrease in the rate of metal-dependent phosphoryl transfer observed for the mutant. These results show that diffuse positive charge associated with the C-terminal subdomains of EcoRV plays a key role in DNA association, bending, and cleavage.
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Affiliation(s)
| | - John J. Perona
- Corresponding author Telephone: 805−893−7389 FAX: 805−893−4120
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9
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Hiller DA, Rodriguez AM, Perona JJ. Non-cognate Enzyme–DNA Complex: Structural and Kinetic Analysis of EcoRV Endonuclease Bound to the EcoRI Recognition Site GAATTC. J Mol Biol 2005; 354:121-36. [PMID: 16236314 DOI: 10.1016/j.jmb.2005.09.046] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2005] [Revised: 09/14/2005] [Accepted: 09/15/2005] [Indexed: 11/25/2022]
Abstract
The crystal structure of EcoRV endonuclease bound to non-cognate DNA at 2.0 angstroms resolution shows that very small structural adaptations are sufficient to ensure the extreme sequence specificity characteristic of restriction enzymes. EcoRV bends its specific GATATC site sharply by 50 degrees into the major groove at the center TA step, generating unusual base-base interactions along each individual DNA strand. In the symmetric non-cognate complex bound to GAATTC, the center step bend is relaxed to avoid steric hindrance caused by the different placement of the exocyclic thymine methyl groups. The decreased base-pair unstacking in turn leads to small conformational rearrangements in the sugar-phosphate backbone, sufficient to destabilize binding of crucial divalent metal ions in the active site. A second crystal structure of EcoRV bound to the base-analog GAAUTC site shows that the 50 degrees center-step bend of the DNA is restored. However, while divalent metals bind at high occupancy in this structure, one metal ion shifts away from binding at the scissile DNA phosphate to a position near the 3'-adjacent phosphate group. This may explain why the 10(4)-fold attenuated cleavage efficiency toward GAATTC is reconstituted by less than tenfold toward GAAUTC. Examination of DNA binding and bending by equilibrium and stopped-flow florescence quenching and fluorescence resonance energy transfer (FRET) methods demonstrates that the capacity of EcoRV to bend the GAATTC non-cognate site is severely limited, but that full bending of GAAUTC is achieved at only a threefold reduced rate compared with the cognate complex. Together, the structural and biochemical data demonstrate the existence of distinct mechanisms for ensuring specificity at the bending and catalytic steps, respectively. The limited conformational rearrangements observed in the EcoRV non-cognate complex provide a sharp contrast to the extensive structural changes found in a non-cognate BamHI-DNA crystal structure, thus demonstrating a diversity of mechanisms by which restriction enzymes are able to achieve specificity.
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Affiliation(s)
- David A Hiller
- Department of Chemistry and Biochemistry, and Interdepartmental Program in Biomolecular Science and Engineering, University of California at Santa Barbara, Santa Barbara, CA 93106-9510, USA
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10
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Rabiller-Baudry M, Chaufer B. Small molecular ion adsorption on proteins and DNAs revealed by separation techniques. J Chromatogr B Analyt Technol Biomed Life Sci 2004; 797:331-45. [PMID: 14630159 DOI: 10.1016/s1570-0232(03)00488-4] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Ion binding is a term that assumes that the ion is included in the solvation sphere characterising the biomolecule. The binding forces are not clearly stated except for electrostatic attraction; weak forces (hydrogen bonds and Van der Waals forces) are likely involved. Many publications have dealt with ion binding to proteins and the consequences over the past 10 years, but only a few studies were performed using high-performance liquid chromatography (HPLC: ion exchange, reversed phase without the well-identified immobilised metal affinity chromatography) and capillary zone electrophoresis (CZE). This review focuses on the binding of proteins and DNAs mainly to the oxyanions (phosphate, borate, citrate) and amines used as buffers for both the HPLC eluent and the background electrolyte of CZE. Such specific ion adsorption on biomolecules is evidenced by physico-chemical characteristics such as the mobility or retention volume, closely associated with the net charge, which differ from the expected or experimental data obtained under the conditions of an indifferent electrolyte. It is shown that ion binding to proteins is a key parameter in the electrostatic repulsion between the free protein and a fouled membrane in the ultrafiltration separation of a protein mixture.
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Affiliation(s)
- Murielle Rabiller-Baudry
- Laboratoire des Procédés de Séparation, Université Rennes 1, UC INRA, Campus de Beaulieu, Bat. 10A, 263 Avenue du Général Leclerc, CS 74205, 35042 Rennes Cedex, France.
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12
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Abstract
Type II restriction endonucleases have emerged as important paradigms for the study of protein-nucleic acid interactions. This is due to their ability to catalyse phosphodiester bond cleavage with very large rate enhancements while also maintaining exquisite sequence selectivities. The principles and methods developed to analyze site-specific binding and catalysis for restriction endonucleases can be applied to other enzymes which also operate on nucleic acids. This paper reviews biochemical and structural approaches to characterization of these enzymes, with particular attention to the multiple crucial roles of divalent metal ions, the possibilities for use of alternative substrates in binding and catalytic experiments, the strategies for exploring the detailed chemistry of phosphoryl transfer, and the use of X-ray crystallography to provide descriptions of conformational pathways at specific, nonspecific, and noncognate DNA sites.
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Affiliation(s)
- John J Perona
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106-9510, USA.
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13
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Abstract
Tn10/IS10 transposition involves assembly of a synaptic complex (or transpososome) in which two transposon ends are paired, followed by four distinct chemical steps at each transposon end. The chemical steps are dependent on the presence of a suitable divalent metal cation (Me(2+)). Transpososome assembly and structure are also affected by Me(2+). To gain further insight into the mechanisms of Me(2+) action in Tn10/IS10 transposition we have investigated the effects of substituting Mn(2+) for Mg(2+), the physiologic Me(2+), in transposition. We have also investigated the significance of an Me(2+)-assisted conformational change in transpososome structure. We show that Mn(2+) has two previously unrecognized effects on the Tn10 donor cleavage reaction. It accelerates the rates of hairpin formation and hairpin resolution without significantly affecting the rate of the first chemical step, first strand nicking. Mn(2+) also relaxes the specificity of first strand nicking. We also show that Me(2+)-assisted transpososome unfolding coincides with a structural transition in the transposon-donor junction that may be necessary for hairpin formation. Possible mechanisms for these observations are considered.
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Affiliation(s)
- John S Allingham
- Department of Biochemistry, University of Western Ontario, London, Ontario, Canada N6A 5B7
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14
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Bitinaite J, Schildkraut I. Self-generated DNA termini relax the specificity of SgrAI restriction endonuclease. Proc Natl Acad Sci U S A 2002; 99:1164-9. [PMID: 11818524 PMCID: PMC122161 DOI: 10.1073/pnas.022346799] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The primary target of SgrAI restriction endonuclease is a multiple sequence of the form 5'-CPu/CCGGPyG. Previous work had indicated that SgrAI must bind two recognition sites simultaneously for catalysis [Bilcock, D. T., Daniels, L. E., Bath, A. J. & Halford, S. E. (1999) J. Biol. Chem. 274, 36379-36386]. In the present study, SgrAI is shown to cleave not only its canonical sequences, but also the sequences 5'-CPuCCGGPy(A,T,C) and 5'-CPuCCGGGG, both referred to as secondary sequences. On plasmid pSK7, SgrAI cleaves secondary sites 26-fold slower than the canonical site. However, the same plasmid, but without the canonical site, is cleaved 200-fold slower. We show that DNA termini generated by cleaving the canonical site for SgrAI assist in the cleavage of secondary sites. The SgrAI-termini in cis with respect to secondary site are markedly preferred over those in trans. The SgrAI-termini provided in a form of oligonucleotide duplex are also shown to stimulate canonical site cleavage. At a 40-fold molar excess of the SgrAI-termini over substrate, the SgrAI specificity is shown to improve by two orders of magnitude, because of concurrent 10-fold increase in the cleavage of canonical site and 50-fold decrease in the cleavage of secondary sites. The unconventional reaction pathway by which SgrAI utilizes the self-generated DNA termini to cleave its DNA targets has not been observed hitherto among type II restriction endonucleases. Based on our work and previous reports, a pathway of DNA binding and cleavage by the SgrAI restriction endonuclease is proposed.
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Affiliation(s)
- Jurate Bitinaite
- New England Biolabs, Inc., 32 Tozer Road, Beverly, MA 01915, USA.
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15
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Pingoud A, Jeltsch A. Structure and function of type II restriction endonucleases. Nucleic Acids Res 2001; 29:3705-27. [PMID: 11557805 PMCID: PMC55916 DOI: 10.1093/nar/29.18.3705] [Citation(s) in RCA: 432] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2001] [Revised: 03/23/2001] [Accepted: 06/07/2001] [Indexed: 11/13/2022] Open
Abstract
More than 3000 type II restriction endonucleases have been discovered. They recognize short, usually palindromic, sequences of 4-8 bp and, in the presence of Mg(2+), cleave the DNA within or in close proximity to the recognition sequence. The orthodox type II enzymes are homodimers which recognize palindromic sites. Depending on particular features subtypes are classified. All structures of restriction enzymes show a common structural core comprising four beta-strands and one alpha-helix. Furthermore, two families of enzymes can be distinguished which are structurally very similar (EcoRI-like enzymes and EcoRV-like enzymes). Like other DNA binding proteins, restriction enzymes are capable of non-specific DNA binding, which is the prerequisite for efficient target site location by facilitated diffusion. Non-specific binding usually does not involve interactions with the bases but only with the DNA backbone. In contrast, specific binding is characterized by an intimate interplay between direct (interaction with the bases) and indirect (interaction with the backbone) readout. Typically approximately 15-20 hydrogen bonds are formed between a dimeric restriction enzyme and the bases of the recognition sequence, in addition to numerous van der Waals contacts to the bases and hydrogen bonds to the backbone, which may also be water mediated. The recognition process triggers large conformational changes of the enzyme and the DNA, which lead to the activation of the catalytic centers. In many restriction enzymes the catalytic centers, one in each subunit, are represented by the PD. D/EXK motif, in which the two carboxylates are responsible for Mg(2+) binding, the essential cofactor for the great majority of enzymes. The precise mechanism of cleavage has not yet been established for any enzyme, the main uncertainty concerns the number of Mg(2+) ions directly involved in cleavage. Cleavage in the two strands usually occurs in a concerted fashion and leads to inversion of configuration at the phosphorus. The products of the reaction are DNA fragments with a 3'-OH and a 5'-phosphate.
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Affiliation(s)
- A Pingoud
- Institut für Biochemie (FB 08), Justus-Liebig-Universität, Heinrich-Buff-Ring 58, D-35392 Giessen, Germany.
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