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Wojdyla Z, Srnec M. Radical ligand transfer: mechanism and reactivity governed by three-component thermodynamics. Chem Sci 2024; 15:8459-8471. [PMID: 38846394 PMCID: PMC11151871 DOI: 10.1039/d4sc01507j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2024] [Accepted: 04/19/2024] [Indexed: 06/09/2024] Open
Abstract
Here, we demonstrate that the relationship between reactivity and thermodynamics in radical ligand transfer chemistry can be understood if this chemistry is dissected as concerted ion-electron transfer (cIET). Namely, we investigate radical ligand transfer reactions from the perspective of thermodynamic contributions to the reaction barrier: the diagonal effect of the free energy of the reaction, and the off-diagonal effect resulting from asynchronicity and frustration, which we originally derived from the thermodynamic cycle for concerted proton-electron transfer (cPET). This study on the OH transfer reaction shows that the three-component thermodynamic model goes beyond cPET chemistry, successfully capturing the changes in radical ligand transfer reactivity in a series of model FeIII-OH⋯(diflouro)cyclohexadienyl systems. We also reveal the decisive role of the off-diagonal thermodynamics in determining the reaction mechanism. Two possible OH transfer mechanisms, in which electron transfer is coupled with either OH- and OH+ transfer, are associated with two competing thermodynamic cycles. Consequently, the operative mechanism is dictated by the cycle yielding a more favorable off-diagonal effect on the barrier. In line with this thermodynamic link to the mechanism, the transferred OH group in OH-/electron transfer retains its anionic character and slightly changes its volume in going from the reactant to the transition state. In contrast, OH+/electron transfer develops an electron deficiency on OH, which is evidenced by an increase in charge and a simultaneous decrease in volume. In addition, the observations in the study suggest that an OH+/electron transfer reaction can be classified as an adiabatic radical transfer, and the OH-/electron transfer reaction as a less adiabatic ion-coupled electron transfer.
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Affiliation(s)
- Zuzanna Wojdyla
- J. Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences Dolejškova 3 Prague 8 18223 Czech Republic
| | - Martin Srnec
- J. Heyrovský Institute of Physical Chemistry, The Czech Academy of Sciences Dolejškova 3 Prague 8 18223 Czech Republic
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2
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Woodman TJ, Lloyd MD. Analysis of enzyme reactions using NMR techniques: A case study with α-methylacyl-CoA racemase (AMACR). Methods Enzymol 2023; 690:159-209. [PMID: 37858529 DOI: 10.1016/bs.mie.2023.07.005] [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: 10/21/2023]
Abstract
α-Methylacyl-CoA racemase (AMACR; P504S) catalyzes the conversion of R-2-methylacyl-CoA esters into their corresponding S-2-methylacyl-CoA epimers enabling their degradation by β-oxidation. The enzyme also catalyzes the key epimerization reaction in the pharmacological activation pathway of ibuprofen and related drugs. AMACR protein levels and enzymatic activity are increased in prostate cancer, and the enzyme is a recognized drug target. Key to the development of novel treatments based on AMACR inhibition is the development of functional assays. Synthesis of substrates and purification of recombinant human AMACR are described. Incubation of R- or S-2-methylacyl-CoA esters with AMACR in vitro resulted in formation of epimers (at a near 1-1 ratio at equilibrium) via removal of their α-protons to form an enolate intermediate followed by reprotonation. Conversion can be conveniently followed by incubation in buffer containing 2H2O followed by 1H NMR analysis to monitor conversion of the α-methyl doublet to a single peak upon deuterium incorporation. Incubation of 2-methylacyl-CoA esters containing leaving groups results in an elimination reaction, which was also characterized by 1H NMR. The synthesis of substrates, including a double labeled substrate for mechanistic studies, and subsequent analysis is also described.
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Affiliation(s)
- Timothy J Woodman
- Department of Life Sciences, University of Bath, Claverton Down, Bath, United Kingdom.
| | - Matthew D Lloyd
- Department of Life Sciences, University of Bath, Claverton Down, Bath, United Kingdom.
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3
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Rabe P, Kamps JJAG, Schofield CJ, Lohans CT. Roles of 2-oxoglutarate oxygenases and isopenicillin N synthase in β-lactam biosynthesis. Nat Prod Rep 2018; 35:735-756. [PMID: 29808887 PMCID: PMC6097109 DOI: 10.1039/c8np00002f] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Indexed: 01/01/2023]
Abstract
Covering: up to 2017 2-Oxoglutarate (2OG) dependent oxygenases and the homologous oxidase isopenicillin N synthase (IPNS) play crucial roles in the biosynthesis of β-lactam ring containing natural products. IPNS catalyses formation of the bicyclic penicillin nucleus from a tripeptide. 2OG oxygenases catalyse reactions that diversify the chemistry of β-lactams formed by both IPNS and non-oxidative enzymes. Reactions catalysed by the 2OG oxygenases of β-lactam biosynthesis not only involve their typical hydroxylation reactions, but also desaturation, epimerisation, rearrangement, and ring-forming reactions. Some of the enzymes involved in β-lactam biosynthesis exhibit remarkable substrate and product selectivities. We review the roles of 2OG oxygenases and IPNS in β-lactam biosynthesis, highlighting opportunities for application of knowledge of their roles, structures, and mechanisms.
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Affiliation(s)
- Patrick Rabe
- Department of Chemistry, Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK.
| | - Jos J A G Kamps
- Department of Chemistry, Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK.
| | - Christopher J Schofield
- Department of Chemistry, Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK.
| | - Christopher T Lohans
- Department of Chemistry, Chemistry Research Laboratory, University of Oxford, 12 Mansfield Road, Oxford, OX1 3TA, UK.
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4
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Lemke A, Ducho C. Synthesis of Deuterium-Labelled 3-Hydroxy- L-arginine: Comparative Studies on Different Protecting-Group Strategies. European J Org Chem 2016. [DOI: 10.1002/ejoc.201501109] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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5
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Huang Z, Wang KKA, Lee J, van der Donk WA. Biosynthesis of fosfazinomycin is a convergent process. Chem Sci 2015; 6:1282-1287. [PMID: 25621145 PMCID: PMC4303578 DOI: 10.1039/c4sc03095h] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Fosfazinomycin A is a phosphonate natural product in which the C-terminal carboxylate of a Val-Arg dipeptide is connected to methyl 2-hydroxy-2-phosphono-acetate (Me-HPnA) via a unique hydrazide linkage. We report here that Me-HPnA is generated from phosphonoacetaldehyde (PnAA) in three biosynthetic steps through the combined action of an O-methyltransferase (FzmB) and an α-ketoglutarate (α-KG) dependent non-heme iron dioxygenase (FzmG). Unexpectedly, the latter enzyme is involved in two different steps, oxidation of the PnAA to phosphonoacetic acid as well as hydroxylation of methyl 2-phosphonoacetate. The N-methyltransferase (FzmH) was able to methylate Arg-NHNH2 (3) to give Arg-NHNHMe (4), constituting the second segment of the fosfazinomycin molecule. Methylation of other putative intermediates such as desmethyl fosfazinomycin B was not observed. Collectively, our current data support a convergent biosynthetic pathway to fosfazinomycin.
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Affiliation(s)
- Zedu Huang
- Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801. ; Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801. ; Howard Hughes Medical Institute, University of Illinois at Urbana-Champaign, Urbana, IL 61801
| | - Kwo-Kwang A Wang
- Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801. ; Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801. ; Howard Hughes Medical Institute, University of Illinois at Urbana-Champaign, Urbana, IL 61801
| | - Jaeheon Lee
- Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801
| | - Wilfred A van der Donk
- Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801. ; Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801. ; Howard Hughes Medical Institute, University of Illinois at Urbana-Champaign, Urbana, IL 61801
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6
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Hamed RB, Gomez-Castellanos JR, Henry L, Ducho C, McDonough MA, Schofield CJ. The enzymes of β-lactam biosynthesis. Nat Prod Rep 2013; 30:21-107. [DOI: 10.1039/c2np20065a] [Citation(s) in RCA: 146] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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7
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Knauer SH, Hartl-Spiegelhauer O, Schwarzinger S, Hänzelmann P, Dobbek H. The Fe(II)/α-ketoglutarate-dependent taurine dioxygenases from Pseudomonas putida and Escherichia coli are tetramers. FEBS J 2012; 279:816-31. [PMID: 22221834 DOI: 10.1111/j.1742-4658.2012.08473.x] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Fe(II)/α-ketoglutarate-dependent oxygenases are versatile catalysts associated with a number of different biological functions in which they use the oxidizing power of activated dioxygen to convert a variety of substrates. A mononuclear nonheme iron center is used to couple the decarboxylation of the cosubstrate α-ketoglutarate with a two-electron oxidation of the substrate, which is a hydroxylation in most cases. Although Fe(II)/α-ketoglutarate-dependent oxygenases have diverse amino acid sequences and substrate specifity, it is assumed that they share a common mechanism. One representative of this enzyme family is the Fe(II)/α-ketoglutarate-dependent taurine dioxygenase that catalyzes the hydroxylation of taurine yielding sulfite and aminoacetaldehyde. Its mechanism has been studied in detail becoming a model system for the whole enzyme family. However, its oligomeric state and architecture have been disputed. Here, we report the biochemical and kinetic characterization of the Fe(II)/α-ketoglutarate-dependent taurine dioxygenase from Pseudomonas putida KT2440 (TauD(Pp) ). We also present three crystal structures of the apo form of this enzyme. Comparisons with taurine dioxygenase from Escherichia coli (TauD(Ec) ) demonstrate that both enzymes are quite similar regarding their spectra, structure and kinetics, and only minor differences for the accumulation of intermediates during the reaction have been observed. Structural data and analytical gel filtration, as well as sedimentation velocity analytical ultracentrifugation, show that both TauD(Pp) and TauD(Ec) are tetramers in solution and in the crystals, which is in contrast to the earlier description of taurine dioxygenase from E. coli as a dimer. Database The atomic coordinates and structure factors have been deposited with the Brookhaven Protein Data Bank (entry 3PVJ, 3V15, 3V17) Structured digital abstract • tauDpp and tauDpp bind by molecular sieving (View interaction) • tauDpp and tauDpp bind by x-ray crystallography (View interaction) • tauDEc and tauDEc bind by molecular sieving (View interaction).
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Affiliation(s)
- Stefan H Knauer
- Institut für Biologie, Strukturbiologie/Biochemie, Humboldt-Universität zu Berlin, Germany
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8
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DeSieno MA, van der Donk WA, Zhao H. Characterization and application of the Fe(II) and α-ketoglutarate dependent hydroxylase FrbJ. Chem Commun (Camb) 2011; 47:10025-7. [PMID: 21829824 DOI: 10.1039/c1cc13597j] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The Fe(II) and α-ketoglutarate-dependent hydroxylase FrbJ was previously demonstrated to utilize FR-900098 synthesizing a second phosphonate FR-33289. Here we assessed its ability to hydroxylate other possible substrates, generating a library of potential antimalarial compounds. Through a series of bioassays and in vitro experiments, we identified two new antimalarials.
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Affiliation(s)
- Matthew A DeSieno
- Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, 600 S. Mathews Avenue, Urbana, IL 61801, USA
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9
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Improvement of clavulanic acid production in Streptomyces clavuligerus by genetic manipulation of structural biosynthesis genes. Biotechnol Lett 2011; 33:1221-6. [DOI: 10.1007/s10529-011-0561-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2010] [Accepted: 02/02/2011] [Indexed: 11/24/2022]
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10
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Raber ML, Castillo A, Greer A, Townsend CA. A conserved lysine in beta-lactam synthetase assists ring cyclization: Implications for clavam and carbapenem biosynthesis. Chembiochem 2010; 10:2904-12. [PMID: 19882698 DOI: 10.1002/cbic.200900389] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
beta-Lactam synthetase (beta-LS) is the paradigm of a growing class of enzymes that form the critical beta-lactam ring in the clavam and carbapenem antibiotics. beta-LS catalyzes a two-stage reaction in which N(2)-(2-carboxyethyl)-L-arginine is first adenylated, and then undergoes intramolecular ring closure. It was previously shown that the forward kinetic commitment to beta-lactam formation is high, and that the overall rate of reaction is partially limited to a protein conformational change rather than to the chemical step alone of closing the strained ring. beta-Lactam formation was evaluated on the basis of X-ray crystal structures, site-specific mutation, and kinetic and computational studies. The combined evidence clearly points to a reaction coordinate involving the formation of a tetrahedral transition state/intermediate stabilized by a conserved Lys. The combination of substrate preorganization, a well-stabilized transition state and an excellent leaving group facilitates this acyl substitution to account for the strong forward commitment to catalysis and to lower the barrier of four-membered ring formation to the magnitude of a protein conformational change.
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Affiliation(s)
- Mary L Raber
- Department of Chemistry, The Johns Hopkins University, Baltimore, MD 21218, USA
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11
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Lemke A, Büschleb M, Ducho C. Concise synthesis of both diastereomers of 3-hydroxy-l-arginine. Tetrahedron 2010. [DOI: 10.1016/j.tet.2009.10.102] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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12
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Raber ML, Arnett SO, Townsend CA. A conserved tyrosyl-glutamyl catalytic dyad in evolutionarily linked enzymes: carbapenam synthetase and beta-lactam synthetase. Biochemistry 2009; 48:4959-71. [PMID: 19371088 DOI: 10.1021/bi900432n] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Beta-lactam-synthesizing enzymes carbapenam synthetase (CPS) and beta-lactam synthetase (beta-LS) are evolutionarily linked to a common ancestor, asparagine synthetase B (AS-B). These three relatives catalyze substrate acyl-adenylation and nucleophilic acyl substitution by either an external (AS-B) or internal (CPS, beta-LS) nitrogen source. Unlike AS-B, crystal structures of CPS and beta-LS revealed a putative Tyr-Glu dyad (CPS, Y345/E380; beta-LS, Y348/E382) proposed to deprotonate the respective internal nucleophile. CPS and beta-LS site-directed mutagenesis (Y345/8A, Y345/8F, E380/2D, E380/2Q, E380A) resulted in the reduction of their catalytic efficiency, with Y345A, E380A, and E382Q producing undetectable amounts of beta-lactam product. However, [(32)P]PP(i)-ATP exchange assays demonstrated Y345A and E380A undergo the first half-reaction, with the remaining active mutants showing decreased forward commitment to beta-lactam cyclization. pH-rate profiles of CPS and beta-LS supported the importance of a Tyr-Glu dyad in beta-lactam formation and suggested its reverse protonation in beta-LS. The kinetics of CPS double-site mutants reinforced the synergism of Tyr-Glu in catalysis. Furthermore, significant solvent isotope effects on k(cat) ((D)k(cat)) for Y345F (1.9) and Y348F (1.7) maintained the assignment of Y345/8 in proton transfer. A proton inventory on Y348F determined its (D)(k(cat)/K(m)) = 0.2 to arise from multiple reactant-state fractionation factors, presumably from water molecule(s) replacing the missing Tyr hydroxyl. The role of a CPS and beta-LS Tyr-Glu catalytic dyad was solidified by a significant decrease in mutant k(cat) viscosity dependence with respect to the wild-type enzymes. The evolutionary relation and potential for engineered biosynthesis were demonstrated by beta-LS acting as a carbapenam synthetase.
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Affiliation(s)
- Mary L Raber
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218, USA
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13
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Directed evolution and rational approaches to improving Streptomyces clavuligerus deacetoxycephalosporin C synthase for cephalosporin production. J Ind Microbiol Biotechnol 2009; 36:619-33. [DOI: 10.1007/s10295-009-0549-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2008] [Accepted: 02/12/2009] [Indexed: 10/21/2022]
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14
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Raber ML, Freeman MF, Townsend CA. Dissection of the stepwise mechanism to beta-lactam formation and elucidation of a rate-determining conformational change in beta-lactam synthetase. J Biol Chem 2008; 284:207-217. [PMID: 18955494 DOI: 10.1074/jbc.m805390200] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Clavulanic acid is a widely used beta-lactamase inhibitor whose key beta-lactam core is formed by beta-lactam synthetase. beta-Lactam synthetase exhibits a Bi-Ter mechanism consisting of two chemical steps, acyl-adenylation followed by beta-lactam formation. 32PPi-ATP exchange assays showed the first irreversible step of catalysis is acyl-adenylation. From a small, normal solvent isotope effect (1.38 +/- 0.04), it was concluded that beta-lactam synthesis contributes at least partially to kcat. Site-specific mutation of Lys-443 identified this residue as the ionizable group at pKa approximately 8.1 apparent in the pH-kcat profile that stabilizes the beta-lactam-forming step. Viscosity studies demonstrated that a protein conformational change was also partially rate-limiting on kcat attenuating the observed solvent isotope effect on beta-lactam formation. Adherence to Kramers' theory gave a slope of 1.66 +/- 0.08 from a plot of log(o kcat/kcat) versus log(eta/eta(o)) consistent with opening of a structured loop visible in x-ray data preceding product release. Internal "friction" within the enzyme contributes to a slope of > 1 in this analysis. Correspondingly, earlier in the catalytic cycle ordering of a mobile active site loop upon substrate binding was manifested by an inverse solvent isotope effect (0.67 +/- 0.15) on kcat/Km. The increased second-order rate constant in heavy water was expected from ordering of this loop over the active site imposing torsional strain. Finally, an Eyring plot displayed a large enthalpic change accompanying loop movement (DeltaH approximately 20 kcal/mol) comparable to the chemical barrier of beta-lactam formation.
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Affiliation(s)
- Mary L Raber
- Department of Chemistry and Department of Biology, The Johns Hopkins University, Baltimore, Maryland 21218
| | - Michael F Freeman
- Department of Chemistry and Department of Biology, The Johns Hopkins University, Baltimore, Maryland 21218
| | - Craig A Townsend
- Department of Chemistry and Department of Biology, The Johns Hopkins University, Baltimore, Maryland 21218.
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15
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Abstract
High-valent non-heme iron-oxo intermediates have been proposed for decades as the key intermediates in numerous biological oxidation reactions. In the past three years, the first direct characterization of such intermediates has been provided by studies of several alphaKG-dependent oxygenases that catalyze either hydroxylation or halogenation of their substrates. In each case, the Fe(IV)-oxo intermediate is implicated in cleavage of the aliphatic C-H bond to initiate hydroxylation or halogenation. The observation of non-heme Fe(IV)-oxo intermediates and Fe(II)-containing product(s) complexes with almost identical spectroscopic parameters in the reactions of two distantly related alphaKG-dependent hydroxylases suggests that members of this subfamily follow a conserved mechanism for substrate hydroxylation. In contrast, for the alphaKG-dependent non-heme iron halogenase, CytC3, two distinct Fe(IV) complexes form and decay together, suggesting that they are in rapid equilibrium. The existence of two distinct conformers of the Fe site may be the key factor accounting for the divergence of the halogenase reaction from the more usual hydroxylation pathway after C-H bond cleavage. Distinct transformations catalyzed by other mononuclear non-heme enzymes are likely also to involve initial C-H bond cleavage by Fe(IV)-oxo complexes, followed by diverging reactivities of the resulting Fe(III)-hydroxo/substrate radical intermediates.
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Affiliation(s)
- Carsten Krebs
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802
| | | | - Christopher T. Walsh
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
| | - J. Martin Bollinger
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802
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16
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Purpero V, Moran GR. The diverse and pervasive chemistries of the alpha-keto acid dependent enzymes. J Biol Inorg Chem 2007; 12:587-601. [PMID: 17431691 DOI: 10.1007/s00775-007-0231-0] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2006] [Accepted: 03/15/2007] [Indexed: 12/01/2022]
Abstract
The number of identified and confirmed alpha-keto acid dependent oxygenases is increasing rapidly. All of these enzymes have a relatively simple liganding arrangement for a single ferrous ion but collectively conduct a highly diverse set of chemistries. While hydroxylations and a variety of oxidation reactions have been most commonly observed, new reactions involving dealkylations, epimerizations and halogenations have recently been discovered. In this minireview we present what is known of the alpha-keto acid dependent enzymes and offer an argument that the chemistry that is unique to each enzyme occurs only after the production of a pivotal ferryl-oxo intermediate.
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Affiliation(s)
- Vincent Purpero
- Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, 3210 N. Cramer Street, Milwaukee, WI 53211-3029, USA
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17
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Nakata M, Mori T, Miyagi M, Suzuki K, Shibasaki M, Saikawa Y. Synthetic Studies on Chlorofusin: Synthesis of the Cyclic Peptide Portion. HETEROCYCLES 2007. [DOI: 10.3987/com-06-s(k)11] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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18
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Clifton IJ, McDonough MA, Ehrismann D, Kershaw NJ, Granatino N, Schofield CJ. Structural studies on 2-oxoglutarate oxygenases and related double-stranded β-helix fold proteins. J Inorg Biochem 2006; 100:644-69. [PMID: 16513174 DOI: 10.1016/j.jinorgbio.2006.01.024] [Citation(s) in RCA: 335] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2005] [Revised: 01/12/2006] [Accepted: 01/12/2006] [Indexed: 01/09/2023]
Abstract
Mononuclear non-heme ferrous iron dependent oxygenases and oxidases constitute an extended enzyme family that catalyze a wide range of oxidation reactions. The largest known sub-group employs 2-oxoglutarate as a cosubstrate and catalysis by these and closely related enzymes is proposed to proceed via a ferryl intermediate coordinated to the active site via a conserved HXD/E...H motif. Crystallographic studies on the 2-oxoglutarate oxygenases and related enzymes have revealed a common double-stranded beta-helix core fold that supports the residues coordinating the iron. This fold is common to proteins of the cupin and the JmjC transcription factor families. The crystallographic studies on 2-oxoglutarate oxygenases and closely related enzymes are reviewed and compared with other metallo-enzymes/related proteins containing a double-stranded beta-helix fold. Proposals regarding the suitability of the active sites and folds of the 2-oxoglutarate oxygenases to catalyze reactions involving reactive oxidizing species are described.
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Affiliation(s)
- Ian J Clifton
- The Oxford Centre for Molecular Sciences and the Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, Oxon OX1 3TA, UK
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Arulanantham H, Kershaw NJ, Hewitson KS, Hughes CE, Thirkettle JE, Schofield CJ. ORF17 from the clavulanic acid biosynthesis gene cluster catalyzes the ATP-dependent formation of N-glycyl-clavaminic acid. J Biol Chem 2005; 281:279-87. [PMID: 16251194 DOI: 10.1074/jbc.m507711200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
(3R,5R)-Clavulanic acid, a clinically used inhibitor of serine beta-lactamases, is produced by fermentation of Streptomyces clavuligerus. The early steps in clavulanic acid biosynthesis leading to the bicyclic beta-lactam intermediate (3S,5S)-clavaminic acid have been defined. However, the mechanism by which (3S,5S)-clavaminic acid is converted to the penultimate intermediate (3R,5R)-clavaldehyde is unclear. Disruption of orf15 or orf16, of the clavulanic acid biosynthesis gene cluster, blocks clavulanic acid production and leads to the accumulation of N-acetyl-glycyl-clavaminic acid and N-glycyl-clavaminic acid, suggesting that these compounds are intermediates in the pathway. Two alternative start codons have been proposed for orf17 to encode for two possible polypeptides, one of which has 92 N-terminal residues less then the other. The shorter version of orf17 was successfully expressed in Escherichia coli and purified as a monomeric protein. Sequence analyses predicting the ORF17 protein to be a member of the ATP-grasp fold superfamily were supported by soft ionization mass spectrometric analyses that demonstrated binding of ATP to the ORF17 protein. Semisynthetic clavaminic acid, prepared by in vitro reconstitution of the biosynthetic pathway from the synthetically accessible intermediate proclavaminic acid, was shown by mass spectrometric analyses to be converted to N-glycyl-clavaminic acid in the presence of ORF17, ATP, and glycine. Under the same conditions N-acetyl-glycine and clavaminic acid were not converted to N-acetyl-glycyl-clavaminic acid. The specificity of ORF17 as an N-glycyl-clavaminic acid synthetase, together with the reported accumulation of N-glycyl-clavaminic acid in orf15 and orf16 disruption mutants, suggested that N-glycyl-clavaminic acid is an intermediate in clavulanic acid biosynthesis.
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Affiliation(s)
- Haren Arulanantham
- Department of Chemistry and The Oxford Centre for Molecular Sciences, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, United Kingdom
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20
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Bollinger JM, Price JC, Hoffart LM, Barr EW, Krebs C. Mechanism of Taurine: α‐Ketoglutarate Dioxygenase (TauD) from
Escherichia coli. Eur J Inorg Chem 2005. [DOI: 10.1002/ejic.200500476] [Citation(s) in RCA: 162] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- J. Martin Bollinger
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA, Fax: +1‐814‐863‐7024
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
| | - John C. Price
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA, Fax: +1‐814‐863‐7024
| | - Lee M. Hoffart
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA, Fax: +1‐814‐863‐7024
| | - Eric W. Barr
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA, Fax: +1‐814‐863‐7024
| | - Carsten Krebs
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802, USA, Fax: +1‐814‐863‐7024
- Department of Chemistry, The Pennsylvania State University, University Park, PA 16802, USA
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21
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Welford RWD, Kirkpatrick JM, McNeill LA, Puri M, Oldham NJ, Schofield CJ. Incorporation of oxygen into the succinate co-product of iron(II) and 2-oxoglutarate dependent oxygenases from bacteria, plants and humans. FEBS Lett 2005; 579:5170-4. [PMID: 16153644 DOI: 10.1016/j.febslet.2005.08.033] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2005] [Revised: 08/17/2005] [Accepted: 08/17/2005] [Indexed: 11/24/2022]
Abstract
The ferrous iron and 2-oxoglutarate (2OG) dependent oxygenases catalyse two electron oxidation reactions by coupling the oxidation of substrate to the oxidative decarboxylation of 2OG, giving succinate and carbon dioxide coproducts. The evidence available on the level of incorporation of one atom from dioxygen into succinate is inconclusive. Here, we demonstrate that five members of the 2OG oxygenase family, AlkB from Escherichia coli, anthocyanidin synthase and flavonol synthase from Arabidopsis thaliana, and prolyl hydroxylase domain enzyme 2 and factor inhibiting hypoxia-inducible factor-1 from Homo sapiens all incorporate a single oxygen atom, almost exclusively derived from dioxygen, into the succinate co-product.
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22
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Welford RWD, Clifton IJ, Turnbull JJ, Wilson SC, Schofield CJ. Structural and mechanistic studies on anthocyanidin synthase catalysed oxidation of flavanone substrates: the effect of C-2 stereochemistry on product selectivity and mechanism. Org Biomol Chem 2005; 3:3117-26. [PMID: 16106293 DOI: 10.1039/b507153d] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
During the biosynthesis of the tricyclic flavonoid natural products in plants, oxidative modifications to the central C-ring are catalysed by Fe(ii) and 2-oxoglutarate dependent oxygenases. The reactions catalysed by three of these enzymes; flavone synthase I, flavonol synthase and anthocyanidin synthase (ANS), are formally desaturations. In comparison, flavanone 3beta-hydroxylase catalyses hydroxylation at the C-3 pro-R position of 2S-naringenin. Incubation of ANS with the unnatural substrate (+/-)-naringenin results in predominantly C-3 hydroxylation to give cis-dihydrokaempferol as the major product; trans-dihydrokaempferol and the desaturation product, apigenin are also observed. Labelling studies have demonstrated that some of the formal desaturation reactions catalysed by ANS proceed via initial C-3 hydroxylation followed by dehydration at the active site. We describe analyses of the reaction of ANS with 2S- and 2R-naringenin substrates, including the anaerobic crystal structure of an ANS-Fe-2-oxoglutarate-naringenin complex. Together the results reveal that for the 'natural' C-2 stereochemistry of 2S-naringenin, C-3 hydroxylation predominates (>9 : 1) over desaturation, probably due to the inaccessibility of the C-2 hydrogen to the iron centre. For the 2R-naringenin substrate, desaturation is significantly increased relative to C-3 hydroxylation (ca. 1 : 1); this is probably a result of both the C-3 pro-S and C-2 hydrogen atoms being accessible to the reactive oxidising intermediate in this substrate. In contrast to the hydroxylation-elimination desaturation mechanism for some ANS substrates, the results imply that the ANS catalysed desaturation of 2R-naringenin to form apigenin proceeds with a syn-arrangement of eliminated hydrogen atoms and not via an oxygenated (gem-diol) flavonoid intermediate. Thus, by utilising flavonoid substrates with different C-2 stereochemistries, the balance between C-3 hydroxylation or C-2, C-3 desaturation mechanisms can be altered.
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Affiliation(s)
- Richard W D Welford
- Chemical Research Laboratory, Department of Chemistry and Oxford Centre for Molecular Sciences, Mansfield Road, Oxford OX1 3TA, UK
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23
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Hewitson KS, Granatino N, Welford RWD, McDonough MA, Schofield CJ. Oxidation by 2-oxoglutarate oxygenases: non-haem iron systems in catalysis and signalling. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2005; 363:807-28; discussion 1035-40. [PMID: 15901537 DOI: 10.1098/rsta.2004.1540] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
The 2-oxoglutarate (2OG) and ferrous iron dependent oxygenases are a superfamily of enzymes that catalyse a wide range of reactions including hydroxylations, desaturations and oxidative ring closures. Recently, it has been discovered that they act as sensors in the hypoxic response in humans and other animals. Substrate oxidation is coupled to conversion of 2OG to succinate and carbon dioxide. Kinetic, spectroscopic and structural studies are consistent with a consensus mechanism in which ordered binding of (co)substrates enables control of reactive intermediates. Binding of the substrate to the active site triggers the enzyme for ligation of dioxygen to the metal. Oxidative decarboxylation of 2OG then generates the ferryl species thought to mediate substrate oxidation. Structural studies reveal a conserved double-stranded beta-helix core responsible for binding the iron, via a 2His-1carboxylate motif and the 2OG side chain. The rigidity of this core contrasts with the conformational flexibility of surrounding regions that are involved in binding the substrate. Here we discuss the roles of 2OG oxygenases in terms of the generic structural and mechanistic features that render the 2OG oxygenases suited for their functions.
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Affiliation(s)
- K S Hewitson
- The Department of Chemistry and The Oxford Centre for Molecular Sciences, Chemistry Research Laboratory, Mansfield Road, Oxford OX1 3TA, UK
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24
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Kershaw NJ, Caines MEC, Sleeman MC, Schofield CJ. The enzymology of clavam and carbapenem biosynthesis. Chem Commun (Camb) 2005:4251-63. [PMID: 16113715 DOI: 10.1039/b505964j] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The enzyme-catalysed reactions involved in formation of the bicyclic clavam and carbapenem nuclei, including beta-amino acid and beta-lactam formation, are discussed and compared with those involved in penicillin and cephalosporin biosynthesis. The common role of unusual oxidation reactions in the biosynthetic pathways and the lack of synthetic reagents available to effect them are highlighted.
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Affiliation(s)
- Nadia J Kershaw
- Department of Chemistry and Oxford Centre for Molecular Sciences, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK
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25
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Bornscheuer UT, Kazlauskas RJ. Untreue Enzyme in der Biokatalyse: mit alten Enzymen zu neuen Bindungen und Synthesewegen. Angew Chem Int Ed Engl 2004. [DOI: 10.1002/ange.200460416] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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26
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Bornscheuer UT, Kazlauskas RJ. Catalytic Promiscuity in Biocatalysis: Using Old Enzymes to Form New Bonds and Follow New Pathways. Angew Chem Int Ed Engl 2004; 43:6032-40. [PMID: 15523680 DOI: 10.1002/anie.200460416] [Citation(s) in RCA: 428] [Impact Index Per Article: 21.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Biocatalysis has expanded rapidly in the last decades with the discoveries of highly stereoselective enzymes with broad substrate specificity. A new frontier for biocatalysis is broad reaction specificity, where enzymes catalyze alternate reactions. Although often under-appreciated, catalytic promiscuity has a natural role in evolution and occasionally in the biosynthesis of secondary metabolites. Examples of catalytic promiscuity with current or potential applications in synthesis are reviewed here. Combined with protein engineering, the catalytic promiscuity of enzymes may broadly extend their usefulness in organic synthesis.
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Affiliation(s)
- Uwe T Bornscheuer
- Institute of Chemistry and Biochemistry, Department of Technical Chemistry and Biotechnology, Greifswald University, Soldmannstrasse 16, 17487 Greifswald, Germany.
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27
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Sleeman MC, Smith P, Kellam B, Chhabra SR, Bycroft BW, Schofield CJ. Biosynthesis of Carbapenem Antibiotics: New Carbapenam Substrates for Carbapenem Synthase (CarC). Chembiochem 2004; 5:879-82. [PMID: 15174175 DOI: 10.1002/cbic.200300908] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Mark C Sleeman
- Dyson Perrins Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QY, UK
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28
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Lloyd MD, Lipscomb SJ, Hewitson KS, Hensgens CMH, Baldwin JE, Schofield CJ. Controlling the Substrate Selectivity of Deacetoxycephalosporin/deacetylcephalosporin C Synthase. J Biol Chem 2004; 279:15420-6. [PMID: 14734549 DOI: 10.1074/jbc.m313928200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Deacetoxycephalosporin/deacetylcephalosporin C synthase (DAOC/DACS) is an iron(II) and 2-oxoglutarate-dependent oxygenase involved in the biosynthesis of cephalosporin C in Cephalosporium acremonium. It catalyzes two oxidative reactions, oxidative ring-expansion of penicillin N to deacetoxycephalosporin C, and hydroxylation of the latter to give deacetylcephalosporin C. The enzyme is closely related to deacetoxycephalosporin C synthase (DAOCS) and DACS from Streptomyces clavuligerus, which selectively catalyze ring-expansion or hydroxylation reactions, respectively. In this study, structural models based on DAOCS coupled with site-directed mutagenesis were used to identify residues within DAOC/DACS that are responsible for controlling substrate and reaction selectivity. The M306I mutation abolished hydroxylation of deacetylcephalosporin C, whereas the W82A mutant reduced ring-expansion of penicillin G (an "unnatural" substrate). Truncation of the C terminus of DAOC/DACS to residue 310 (Delta310 mutant) enhanced ring-expansion of penicillin G by approximately 2-fold. A double mutant, Delta310/M306I, selectively catalyzed the ring-expansion reaction and had similar kinetic parameters to the wild-type DAOC/DACS. The Delta310/N305L/M306I triple mutant selectively catalyzed ring-expansion of penicillin G and had improved kinetic parameters (K(m) = 2.00 +/- 0.47 compared with 6.02 +/- 0.97 mm for the wild-type enzyme). This work demonstrates that a single amino acid residue side chain within the DAOC/DACS active site can control whether the enzyme catalyzes ring-expansion, hydroxylation, or both reactions. The catalytic efficiency of mutant enzymes can be improved by combining active site mutations with other modifications including C-terminal truncation and modification of Asn-305.
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Affiliation(s)
- Matthew D Lloyd
- Department of Pharmacy & Pharmacology, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.
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29
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Costas M, Mehn MP, Jensen MP, Que L. Dioxygen Activation at Mononuclear Nonheme Iron Active Sites: Enzymes, Models, and Intermediates. Chem Rev 2004; 104:939-86. [PMID: 14871146 DOI: 10.1021/cr020628n] [Citation(s) in RCA: 2014] [Impact Index Per Article: 100.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Miquel Costas
- Departament de Quimica, Universitat de Girona, 17071, Girona, Spain
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30
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Turnbull JJ, Nakajima JI, Welford RWD, Yamazaki M, Saito K, Schofield CJ. Mechanistic Studies on Three 2-Oxoglutarate-dependent Oxygenases of Flavonoid Biosynthesis. J Biol Chem 2004; 279:1206-16. [PMID: 14570878 DOI: 10.1074/jbc.m309228200] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Anthocyanidin synthase (ANS), flavonol synthase (FLS), and flavanone 3beta-hydroxylase (FHT) are involved in the biosynthesis of flavonoids in plants and are all members of the family of 2-oxoglutarate- and ferrous iron-dependent oxygenases. ANS, FLS, and FHT are closely related by sequence and catalyze oxidation of the flavonoid "C ring"; they have been shown to have overlapping substrate and product selectivities. In the initial steps of catalysis, 2-oxoglutarate and dioxygen are thought to react at the ferrous iron center producing succinate, carbon dioxide, and a reactive ferryl intermediate, the latter of which can then affect oxidation of the flavonoid substrate. Here we describe work on ANS, FLS, and FHT utilizing several different substrates carried out in 18O2/16OH2, 16O2/18OH2, and 18O2/18OH2 atmospheres. In the 18O2/16OH2 atmosphere close to complete incorporation of a single 18O label was observed in the dihydroflavonol products (e.g. (2R,3R)-trans-dihydrokaempferol) from incubations of flavanones (e.g. (2S)naringenin) with FHT, ANS, and FLS. This and other evidence supports the intermediacy of a reactive oxidizing species, the oxygen of which does not exchange with that of water. In the case of products formed by oxidation of flavonoid substrates with a C-3 hydroxyl group (e.g. (2R,3R)-trans-dihydroquercetin), the results imply that oxygen exchange can occur at a stage subsequent to initial oxidation of the C-ring, probably via an enzyme-bound C-3 ketone/3,3-gem-diol intermediate.
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Affiliation(s)
- Jonathan J Turnbull
- The Dyson Perrins Laboratory and The Oxford Centre for Molecular Sciences, South Parks Road, Oxford OX1 3QY, United Kingdom
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31
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Sleeman MC, Schofield CJ. Carboxymethylproline synthase (CarB), an unusual carbon-carbon bond-forming enzyme of the crotonase superfamily involved in carbapenem biosynthesis. J Biol Chem 2003; 279:6730-6. [PMID: 14625287 DOI: 10.1074/jbc.m311824200] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Carboxymethylproline synthase (CarB) catalyzes the committed step in the biosynthesis of (R)-1-carbapen-2-em-3-carboxylate, the simplest member of the carbapenem family of beta-lactam antibiotics, some of which are used clinically. CarB displays sequence homology with members of the crotonase family including enoyl-CoA hydratase (crotonase) and methylmalonyl-CoA decarboxylase. The CarB reaction has been proposed to comprise condensation of acetyl coenzyme A (AcCoA) and glutamate semi-aldehyde to give (2S,5S)-carboxymethylproline ((2S,5S)-CMP). (2S,5S)-CMP is then cyclized in an ATP-driven reaction catalyzed by CarA to give a carbapenam, which is subsequently epimerized and desaturated to give a carbapenem in a CarC-mediated reaction. Here we report the purification of recombinant CarB and that it exists predominantly in a trimeric form as do other members of the crotonase family. AcCoA was not found to be a substrate for CarB. Instead malonyl-CoA was found to be a substrate, efficiently producing (2S,5S)-CMP in the presence of glutamate semi-aldehyde. In the absence of glutamate semi-aldehyde, mass spectrometric analysis indicated that CarB catalyzed the decarboxylation of malonyl-CoA to AcCoA. The reactions of CarB, CarA, and CarC were coupled in vitro demonstrating the viability of malonyl-CoA as a carbapenem precursor. CarB was also shown to accept methylmalonyl CoA as a substrate to form 6-methyl-(2S,5S)CMP, which in turn is a substrate for CarA. The implications of the results for the biosynthesis of both carbapenem-3-carboxylate and C-2/C-6-substituted carbapenems, such as thienamycin, are discussed.
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Affiliation(s)
- Mark C Sleeman
- Department of Chemistry, University of Oxford, Chemistry Research Laboratory, Mansfield Road, Oxford OX1 3TA, UK
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32
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Mehn MP, Fujisawa K, Hegg EL, Que L. Oxygen activation by nonheme iron(II) complexes: alpha-keto carboxylate versus carboxylate. J Am Chem Soc 2003; 125:7828-42. [PMID: 12823001 DOI: 10.1021/ja028867f] [Citation(s) in RCA: 137] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Mononuclear iron(II) alpha-keto carboxylate and carboxylate compounds of the sterically hindered tridentate face-capping ligand Tp(Ph2) (Tp(Ph2) = hydrotris(3,5-diphenylpyrazol-1-yl)borate) were prepared as models for the active sites of nonheme iron oxygenases. The structures of an aliphatic alpha-keto carboxylate complex, [Fe(II)(Tp(Ph2))(O(2)CC(O)CH(3))], and the carboxylate complexes [Fe(II)(Tp(Ph2))(OBz)] and [Fe(II)(Tp(Ph2))(OAc)(3,5-Ph(2)pzH)] were determined by single-crystal X-ray diffraction, all of which have five-coordinate iron centers. Both the alpha-keto carboxylate and the carboxylate compounds react with dioxygen resulting in the hydroxylation of a single ortho phenyl position of the Tp(Ph2) ligand. The oxygenation products were characterized spectroscopically, and the structure of the octahedral iron(III) phenolate product [Fe(III)(Tp(Ph2))(OAc)(3,5-Ph(2)pzH)] was established by X-ray diffraction. The reaction of the alpha-keto carboxylate model compounds with oxygen to produce the phenolate product occurs with concomitant oxidative decarboxylation of the alpha-keto acid. Isotope labeling studies show that (18)O(2) ends up in the Tp(Ph2) phenolate oxygen and the carboxylate derived from the alpha-keto acid. The isotope incorporation mirrors the dioxygenase nature of the enzymatic systems. Parallel studies on the carboxylate complexes demonstrate that the oxygen in the hydroxylated ligand is also derived from molecular oxygen. The oxygenation of the benzoylformate complex is demonstrated to be first order in metal complex and dioxygen, with activation parameters DeltaH++ = 25 +/- 2 kJ mol(-1) and DeltaS++ = -179 +/- 6 J mol(-1) K(-1). The rate of appearance of the iron(III) phenolate product is sensitive to the nature of the substituent on the benzoylformate ligand, exhibiting a Hammett rho value of +1.3 indicative of a nucleophilic mechanism. The proposed reaction mechanism involves dioxygen binding to produce an iron(III) superoxide species, nucleophilic attack of the superoxide at the alpha-keto functionality, and oxidative decarboxylation of the adduct to afford the oxidizing species that attacks the Tp(Ph2) phenyl ring. Interestingly, the alpha-keto carboxylate complexes react 2 orders of magnitude faster than the carboxylate complexes, thus emphasizing the key role that the alpha-keto functionality plays in oxygen activation by alpha-keto acid-dependent iron enzymes.
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Affiliation(s)
- Mark P Mehn
- Department of Chemistry and Center for Metals in Biocatalysis, 207 Pleasant Street Southeast, University of Minnesota, Minneapolis, MN 55455, USA
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33
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Clifton IJ, Doan LX, Sleeman MC, Topf M, Suzuki H, Wilmouth RC, Schofield CJ. Crystal structure of carbapenem synthase (CarC). J Biol Chem 2003; 278:20843-50. [PMID: 12611886 DOI: 10.1074/jbc.m213054200] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The proposed biosynthetic pathway to the carbapenem antibiotics proceeds via epimerization/desaturation of a carbapenam in an unusual process catalyzed by an iron- and 2-oxoglutarate-dependent oxygenase, CarC. Crystal structures of CarC complexed with Fe(II) and 2-oxoglutarate reveal it to be hexameric (space group C2221), consistent with solution studies. CarC monomers contain a double-stranded beta-helix core that supports ligands binding a single Fe(II) to which 2-oxoglutarate complexes in a bi-dentate manner. A structure was obtained with l-N-acetylproline acting as a substrate analogue. Quantum mechanical/molecular mechanical modeling studies with stereoisomers of carbapenams and carbapenems were used to investigate substrate binding. The combined work will stimulate further mechanistic studies and aid in the engineering of carbapenem biosynthesis.
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Affiliation(s)
- Ian J Clifton
- Oxford Centre for Molecular Sciences and The Dyson Perrins Laboratory, South Parks Road, Oxford OX1 3QZ, United Kingdom
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34
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McNeill LA, Hewitson KS, Gleadle JM, Horsfall LE, Oldham NJ, Maxwell PH, Pugh CW, Ratcliffe PJ, Schofield CJ. The use of dioxygen by HIF prolyl hydroxylase (PHD1). Bioorg Med Chem Lett 2002; 12:1547-50. [PMID: 12039559 DOI: 10.1016/s0960-894x(02)00219-6] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The hypoxic response in animals is mediated by hydroxylation of proline residues in the alpha-subunit of hypoxia inducible factor (HIF). Hydroxylation is catalysed by prolyl-4-hydroxylases (PHD isozymes in humans) which are iron(II) and 2-oxoglutarate dependent oxygenases. Mutation of the arginine proposed to bind 2-oxoglutarate and of the 2His-1-carboxylate iron(II) binding motif in PHD1 dramatically reduces its activity. The source of the oxygen of the product alcohol is (>95%) dioxygen.
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Affiliation(s)
- Luke A McNeill
- Oxford Centre for Molecular Sciences, Dyson Perrins Laboratory, South Parks Road, Oxford OX1 3QY, UK
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35
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Mukherji M, Kershaw NJ, Schofield CJ, Wierzbicki AS, Lloyd MD. Utilization of sterol carrier protein-2 by phytanoyl-CoA 2-hydroxylase in the peroxisomal alpha oxidation of phytanic acid. CHEMISTRY & BIOLOGY 2002; 9:597-605. [PMID: 12031666 DOI: 10.1016/s1074-5521(02)00139-4] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Since it possesses a 3-methyl group, phytanic acid is degraded by a peroxisomal alpha-oxidation pathway, the first step of which is catalyzed by phytanoyl-CoA 2-hydroxylase (PAHX). Mutations in human PAHX cause phytanic acid accumulations leading to Adult Refsum's Disease (ARD), which is also observed in a sterol carrier protein 2 (SCP-2)-deficient mouse model. Phytanoyl-CoA is efficiently 2-hydroxylated by PAHX in vitro in the presence of mature SCP-2. Other straight-chain fatty acyl-CoA esters were also 2-hydroxylated and the products isolated and characterized. Use of SCP-2 increases discrimination between straight-chain (e.g., hexadecanoyl-CoA) and branched-chain (e.g., phytanoyl-CoA) substrates by PAHX. The results explain the phytanic acid accumulation in the SCP-2-deficient mouse model and suggest that some of the common symptoms of ARD and other peroxisomal diseases may arise in part due to defects in SCP-2 function caused by increased phytanic acid levels.
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Affiliation(s)
- Mridul Mukherji
- The Oxford Centre for Molecular Science, The Dyson Perrins Laboratory, South Parks Road, OX1 3QY, Oxford, United Kingdom
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36
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Zhang Z, Ren JS, Harlos K, McKinnon CH, Clifton IJ, Schofield CJ. Crystal structure of a clavaminate synthase-Fe(II)-2-oxoglutarate-substrate-NO complex: evidence for metal centered rearrangements. FEBS Lett 2002; 517:7-12. [PMID: 12062399 DOI: 10.1016/s0014-5793(02)02520-6] [Citation(s) in RCA: 126] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Clavaminate synthase (CAS), a 2-oxoglutarate (2OG) dependent dioxygenase, catalyses three steps in the biosynthesis of clavulanic acid. Crystals of CAS complexed with Fe(II), 2OG and deoxyguanidinoproclavaminate were exposed to nitric oxide (NO) acting as a dioxygen analogue. Prior to exposure with NO, the active site Fe(II) is octahedrally coordinated by a water molecule, the 2-oxo and 1-carboxylate groups of 2OG, and the side-chains of an aspartyl and two histidinyl residues. NO binds to the position previously occupied by the 2OG 1-carboxylate concomitant with rearrangement of the latter to the position previously occupied by the displaced water.
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Affiliation(s)
- Zhihong Zhang
- The Oxford Centre for Molecular Sciences and The Dyson Perrins Laboratory, The Department of Chemistry, South Parks Road, Oxford, UK
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37
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Kershaw NJ, McNaughton HJ, Hewitson KS, Hernández H, Griffin J, Hughes C, Greaves P, Barton B, Robinson CV, Schofield CJ. ORF6 from the clavulanic acid gene cluster of Streptomyces clavuligerus has ornithine acetyltransferase activity. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:2052-9. [PMID: 11985581 DOI: 10.1046/j.1432-1033.2002.02853.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The clinically used beta-lactamase inhibitor clavulanic acid is produced by fermentation of Streptomyces clavuligerus. The orf6 gene of the clavulanic acid biosynthetic gene cluster in S. clavuligerus encodes a protein that shows sequence homology to ornithine acetyltransferase (OAT), the fifth enzyme of the arginine biosynthetic pathway. Orf6 was overexpressed in Escherichia coli (at approximately 15% of total soluble protein by SDS/PAGE analysis) indicating it was not toxic to the host cells. The recombinant protein was purified (to > 95% purity) by a one-step technique. Like other OATs it was synthesized as a precursor protein which underwent autocatalytic internal cleavage in E. coli to generate alpha and beta subunits. Cleavage was shown to occur between the alanine and threonine residues in a KGXGMXXPX--(M/L)AT (M/L)L motif conserved within all identified OAT sequences. Gel filtration and native electrophoresis analyses implied that the ORF6 protein was an alpha2beta2 heterotetramer and direct evidence for this came from mass spectrometric analyses. Although anomalous migration of the beta subunit was observed by standard SDS/PAGE analysis, which indicated the presence of two bands (as previously observed for other OATs), mass spectrometric analyses did not reveal any evidence for post-translational modification of the beta subunit. Extended denaturation with SDS before PAGE resulted in observation of a single major beta subunit band. Purified ORF6 was able to catalyse the reversible transfer of an acetyl group from N-acetylornithine to glutamate, but not the formation of N-acetylglutamate from glutamate and acetyl-coenzyme A, nor (detectably) the hydrolysis of N-acetylornithine. Mass spectrometry also revealed the reaction proceeds via acetylation of the beta subunit.
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Affiliation(s)
- Nadia J Kershaw
- Oxford Centre for Molecular Sciences and The Dyson Perrins Laboratory, UK
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38
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Doan LX, Hassan A, Lipscomb SJ, Dhanda A, Zhang Z, Schofield CJ. Mutagenesis studies on the iron binding ligands of clavaminic acid synthase. Biochem Biophys Res Commun 2000; 279:240-4. [PMID: 11112446 DOI: 10.1006/bbrc.2000.3915] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Mutagenesis studies on conserved histidine residues identified as possible metal binding ligands in clavaminic acid synthase isozyme 2 were consistent with His-145 and His-280 acting as iron ligands, in support of crystallographic and previous mutagenesis studies. Mutagenesis of the four cysteines and a glutamine residue, conserved in both clavaminic acid synthase isozymes 1 and 2, demonstrated that none of these residues is essential for activity.
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Affiliation(s)
- L X Doan
- The Oxford Centre for Molecular Sciences, Oxford University, South Parks Road, Oxford, OX1 3QY, United Kingdom
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39
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Affiliation(s)
- D E Cane
- Department of Chemistry, Brown University, Providence, RI 02912-9108, USA.
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40
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Schofield CJ, Zhang Z. Structural and mechanistic studies on 2-oxoglutarate-dependent oxygenases and related enzymes. Curr Opin Struct Biol 1999; 9:722-31. [PMID: 10607676 DOI: 10.1016/s0959-440x(99)00036-6] [Citation(s) in RCA: 292] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Mononuclear nonheme-Fe(II)-dependent oxygenases comprise an extended family of oxidising enzymes, of which the 2-oxoglutarate-dependent oxygenases and related enzymes are the largest known subgroup. Recent crystallographic and mechanistic studies have helped to define the overall fold of the 2-oxoglutarate-dependent enzymes and have led to the identification of coordination chemistry closely related to that of other nonheme-Fe(II)-dependent oxygenases, suggesting related mechanisms for dioxygen activation that involve iron-mediated electron transfer.
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Affiliation(s)
- C J Schofield
- Department of Chemistry, The Oxford Centre for Molecular Sciences, The Dyson Perrins Laboratory, Oxford, OX1 3QY, UK
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Khaleeli N, Li R, Townsend CA. Origin of the β-Lactam Carbons in Clavulanic Acid from an Unusual Thiamine Pyrophosphate-Mediated Reaction. J Am Chem Soc 1999. [DOI: 10.1021/ja9923134] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Nusrat Khaleeli
- Department of Chemistry, The Johns Hopkins University Baltimore, Maryland 21218
| | - Rongfeng Li
- Department of Chemistry, The Johns Hopkins University Baltimore, Maryland 21218
| | - Craig A. Townsend
- Department of Chemistry, The Johns Hopkins University Baltimore, Maryland 21218
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