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Beaupre BA, Moran GR. N5 Is the New C4a: Biochemical Functionalization of Reduced Flavins at the N5 Position. Front Mol Biosci 2020; 7:598912. [PMID: 33195440 PMCID: PMC7662398 DOI: 10.3389/fmolb.2020.598912] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Accepted: 10/05/2020] [Indexed: 12/31/2022] Open
Abstract
For three decades the C4a-position of reduced flavins was the known site for covalency within flavoenzymes. The reactivity of this position of the reduced isoalloxazine ring with the dioxygen ground-state triplet established the C4a as a site capable of one-electron chemistry. Within the last two decades new types of reduced flavin reactivity have been documented. These studies reveal that the N5 position is also a protean site of reactivity, that is capable of nucleophilic attack to form covalent bonds with substrates. In addition, though the precise mechanism of dioxygen reactivity is yet to be definitively demonstrated, it is clear that the N5 position is directly involved in substrate oxygenation in some enzymes. In this review we document the lineage of discoveries that identified five unique modes of N5 reactivity that collectively illustrate the versatility of this position of the reduced isoalloxazine ring.
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Affiliation(s)
- Brett A Beaupre
- Department of Chemistry and Biochemistry, Loyola University Chicago, Chicago, IL, United States
| | - Graham R Moran
- Department of Chemistry and Biochemistry, Loyola University Chicago, Chicago, IL, United States
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Flavin-N5-oxide: A new, catalytic motif in flavoenzymology. Arch Biochem Biophys 2017; 632:4-10. [PMID: 28784589 DOI: 10.1016/j.abb.2017.08.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2017] [Revised: 08/01/2017] [Accepted: 08/03/2017] [Indexed: 11/22/2022]
Abstract
Flavin-N5-oxide is a recently discovered intermediate used by EncM (1,3-diketone oxidation), DszA (sulfone monooxygenase) and RutA (amide monooxygenase). This review describes the mechanism of these enzymes and proposes criteria for the identification of additional Flavin-N5-oxide dependent enzymes.
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Teufel R, Stull F, Meehan MJ, Michaudel Q, Dorrestein PC, Palfey B, Moore BS. Biochemical Establishment and Characterization of EncM's Flavin-N5-oxide Cofactor. J Am Chem Soc 2015; 137:8078-85. [PMID: 26067765 DOI: 10.1021/jacs.5b03983] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The ubiquitous flavin-dependent monooxygenases commonly catalyze oxygenation reactions by means of a transient C4a-peroxyflavin. A recent study, however, suggested an unprecedented flavin-oxygenating species, proposed as the flavin-N5-oxide (Fl(N5[O])), as key to an oxidative Favorskii-type rearrangement in the biosynthesis of the bacterial polyketide antibiotic enterocin. This stable superoxidized flavin is covalently tethered to the enzyme EncM and converted into FADH2 (Fl(red)) during substrate turnover. Subsequent reaction of Fl(red) with molecular oxygen restores the postulated Fl(N5[O]) via an unknown pathway. Here, we provide direct evidence for the Fl(N5[O]) species via isotope labeling, proteolytic digestion, and high-resolution tandem mass spectrometry of EncM. We propose that formation of this species occurs by hydrogen-transfer from Fl(red) to molecular oxygen, allowing radical coupling of the formed protonated superoxide and anionic flavin semiquinone at N5, before elimination of water affords the Fl(N5[O]) cofactor. Further biochemical and spectroscopic investigations reveal important features of the Fl(N5[O]) species and the EncM catalytic mechanism. We speculate that flavin-N5-oxides may be intermediates or catalytically active species in other flavoproteins that form the anionic semiquinone and promote access of oxygen to N5.
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Affiliation(s)
- Robin Teufel
- †Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, California 92093, United States
| | - Frederick Stull
- ‡Program in Chemical Biology, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Michael J Meehan
- §Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, San Diego, California 92093, United States
| | - Quentin Michaudel
- ⊥Department of Chemistry, The Scripps Research Institute, La Jolla, California 92037, United States
| | - Pieter C Dorrestein
- †Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, California 92093, United States.,§Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, San Diego, California 92093, United States
| | - Bruce Palfey
- ‡Program in Chemical Biology, University of Michigan, Ann Arbor, Michigan 48109, United States.,∥Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Bradley S Moore
- †Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, California 92093, United States.,§Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, San Diego, California 92093, United States
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Teufel R, Miyanaga A, Michaudel Q, Stull F, Louie G, Noel JP, Baran PS, Palfey B, Moore BS. Flavin-mediated dual oxidation controls an enzymatic Favorskii-type rearrangement. Nature 2013; 503:552-556. [PMID: 24162851 PMCID: PMC3844076 DOI: 10.1038/nature12643] [Citation(s) in RCA: 123] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Accepted: 09/09/2013] [Indexed: 12/25/2022]
Abstract
Flavoproteins catalyze a diversity of fundamental redox reactions and are one of the most studied enzyme families1,2. As monooxygenases, they are universally thought to control oxygenation by means of a peroxyflavin species that transfers a single atom of molecular oxygen to an organic substrate1,3,4. Here we report that the bacterial flavoenzyme EncM5,6 catalyzes the peroxyflavin-independent oxygenation-dehydrogenation dual oxidation of a highly reactive poly(β-carbonyl). The crystal structure of EncM with bound substrate mimics coupled with isotope labeling studies reveal previously unknown flavin redox biochemistry. We show that EncM maintains an unanticipated stable flavin oxygenating species, proposed to be a flavin-N5-oxide, to promote substrate oxidation and trigger a rare Favorskii-type rearrangement that is central to the biosynthesis of the antibiotic enterocin. This work provides new insight into the fine-tuning of the flavin cofactor in offsetting the innate reactivity of a polyketide substrate to direct its efficient electrocyclization.
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Affiliation(s)
- Robin Teufel
- Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, 92093, USA
| | - Akimasa Miyanaga
- Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, 92093, USA
| | - Quentin Michaudel
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Frederick Stull
- Program in Chemical Biology, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Gordon Louie
- Howard Hughes Medical Institute, The Salk Institute for Biological Studies, Jack H. Skirball Center for Chemical Biology and Proteomics, La Jolla, California 92037, USA
| | - Joseph P Noel
- Howard Hughes Medical Institute, The Salk Institute for Biological Studies, Jack H. Skirball Center for Chemical Biology and Proteomics, La Jolla, California 92037, USA
| | - Phil S Baran
- Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Bruce Palfey
- Program in Chemical Biology, University of Michigan, Ann Arbor, Michigan 48109, USA.,Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Bradley S Moore
- Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, 92093, USA.,Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California San Diego, La Jolla, California 92093, USA
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Kantz A, Gassner GT. Nature of the reaction intermediates in the flavin adenine dinucleotide-dependent epoxidation mechanism of styrene monooxygenase. Biochemistry 2010; 50:523-32. [PMID: 21166448 DOI: 10.1021/bi101328r] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Styrene monooxygenase (SMO) is a two-component flavoenzyme composed of an NADH-specific flavin reductase (SMOB) and FAD-specific styrene epoxidase (NSMOA). NSMOA binds tightly to reduced FAD and catalyzes the stereospecific addition of one atom of molecular oxygen to the vinyl side chain of styrene in the enantioselective synthesis of S-styrene oxide. In this mechanism, molecular oxygen first reacts with NSMOA(FAD(red)) to yield an FAD C(4a)-peroxide intermediate. This species is nonfluorescent and has an absorbance maximum of 382 nm. Styrene then reacts with the peroxide intermediate with a second-order rate constant of (2.6 ± 0.1) × 10(6) M(-1) s(-1) to yield a fluorescent intermediate with an absorbance maximum of 368 nm. We compute an activation free energy of 8.7 kcal/mol for the oxygenation step, in good agreement with that expected for a peroxide-catalyzed epoxidation, and acid-quenched samples recovered at defined time points in the single-turnover reaction indicate that styrene oxide synthesis is coincident with the formation phase of the fluorescent intermediate. These findings support FAD C(4a)-peroxide being the oxygen atom donor and the identity of the fluorescent intermediate as an FAD C(4a)-hydroxide product of the styrene epoxidation. Overall, four pH-dependent rate constants corresponding to peroxyflavin formation (pK(a) = 7.2), styrene epoxidation (pK(a) = 7.7), styrene oxide dissociation (pK(a) = 8.3), and hydroxyflavin dehydration (pK(a) = 7.6) are needed to fit the single-turnover kinetics.
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Affiliation(s)
- Auric Kantz
- Department of Chemistry and Biochemistry, San Francisco State University, San Francisco, CA 94132, USA
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Huang CC, Hohn KL. Tetrakis(dimethylamino)ethylene Chemiluminescence (TDE CL) Characterization of the CMC and the Viscosity of Reversed Microemulsions. J Phys Chem B 2010; 114:2685-94. [DOI: 10.1021/jp9077618] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Chien-Chang Huang
- Department of Chemical Engineering, Kansas State University, 1005 Durland Hall, Manhattan, Kansas 66506-5102
| | - Keith L. Hohn
- Department of Chemical Engineering, Kansas State University, 1005 Durland Hall, Manhattan, Kansas 66506-5102
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Hanquet G, Lusinchi X, Milliet P. Acid catalyzed oxygen transfer from an oxaziridine to a thioether. Tetrahedron Lett 1988. [DOI: 10.1016/0040-4039(88)85218-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Milliet P, Lusinchi X. Action des sulfonyloxaziridines sur une imine. Obtention d'une nitrone par transfert regioselectif de l'oxygene sur l'azote. Tetrahedron Lett 1985. [DOI: 10.1016/s0040-4039(00)89252-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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10
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Wessiak A, Schopfer LM, Massey V. pH dependence of the reoxidation of p-hydroxybenzoate hydroxylase 2,4-dihydroxybenzoate complex. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(18)90782-9] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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Bailey SW, Weintraub ST, Hamilton SM, Ayling JE. Incorporation of molecular oxygen into pyrimidine cofactors by phenylalanine hydroxylase. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)34325-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Dixon DA, Lindner DL, Branchaud B, Lipscomb WN. Conformations and electronic structures of oxidized and reduced isoalloxazine. Biochemistry 1979; 18:5770-5. [PMID: 518869 DOI: 10.1021/bi00593a004] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The conformations of oxidized and reduced isoalloxazine have been examined by a molecular orbital method, PRDDO (partial retention of diatomic differential overlap). The angle theta of fold about the N...N line of the central ring is zero for the planar oxidized form, but a bend of theta = 10 degrees requires only 2 kcal/mol. On the other hand, the reduced form is nonplanar (theta approximately 15 degrees), and the barrier for reversal of this bend is 4 kcal/mol, comparable with that in simple amines. Molecular properties and reactivity are interpreted in terms of charge and orbital distributions, and localized molecular orbitals have been derived by the method of Boys.
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Hart RC, Cormier MJ. RECENT ADVANCES IN THE MECHANISMS OF BIO- AND CHEMILUMINESCENT REACTIONS. Photochem Photobiol 1979. [DOI: 10.1111/j.1751-1097.1979.tb09284.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Oxaziridines and oxygen transfer. A revised mechanism for the kinetic resolution of 2--propyl-3-methyl-3--butyloxaziridine by brucine. Tetrahedron Lett 1979. [DOI: 10.1016/s0040-4039(01)95407-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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21
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Testa B, Jenner P. Novel drug metabolites produced by functionalization reactions: chemistry and toxicology. Drug Metab Rev 1978; 7:325-69. [PMID: 79468 DOI: 10.3109/03602537808993771] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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22
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Favaudon V. Oxidation kinetics of 1,5-dihydroflavin by oxygen in non-aqueous solvent. EUROPEAN JOURNAL OF BIOCHEMISTRY 1977; 78:293-307. [PMID: 21077 DOI: 10.1111/j.1432-1033.1977.tb11740.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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23
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Ghisla S, Entsch B, Massey V, Husein M. On the structure of flavin-oxygen intermediates involved in enzymatic reactions. EUROPEAN JOURNAL OF BIOCHEMISTRY 1977; 76:139-48. [PMID: 18348 DOI: 10.1111/j.1432-1033.1977.tb11579.x] [Citation(s) in RCA: 93] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
During the catalytic reactions of flavoprotein hydroxylases and bacterial luciferase, flavin peroxides are formed as intermediates [see Massey, V. and Hemmerich, P. (1976) in The Enzymes, 3rd edn (P. Boyer, ed.) pp. 421--505, Academic Press, New York]. These intermediates have been postulated to be C(4a) derivatives of the flavin coenzyme. To test this hypothesis, modified flavin coenzymes carrying an oxygen substituent at position C(4a) of the isoalloxazine ring were synthesized. They are tightly bound by the apoenzymes of D-amino acid oxidase, p-hydroxybenzoate hydroxylase and lactate oxidase; the resulting complexes show spectral properties closely similar to those of the transient oxygen adducts of the hydroxylases. The optical spectra of the lumiflavin model compounds were found to be highly dependent on the solvent environment and nature of the subsituents. Under appropriate conditions they simulate satisfactorily the spectra of the transient enzymatic oxygen adducts. The results support the proposal that the primary oxygen adducts formed with these flavoproteins on reaction of the reduced enzymes with oxygen are flavin C(4a) peroxides.
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24
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How Oxygen Meets the Electrons with Generation of ATP, and Other Stories. Biochemistry 1977. [DOI: 10.1016/b978-0-12-492550-2.50015-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Microbial Degradation of Organic Compounds in the Biosphere. ACTA ACUST UNITED AC 1977. [DOI: 10.1016/b978-0-12-610508-7.50009-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Coenzymes—Nature's Special Reagents. Biochemistry 1977. [DOI: 10.1016/b978-0-12-492550-2.50013-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Entsch B, Ballou DP, Massey V. Flavin-oxygen derivatives involved in hydroxylation by p-hydroxybenzoate hydroxylase. J Biol Chem 1976. [DOI: 10.1016/s0021-9258(17)33523-8] [Citation(s) in RCA: 274] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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The oxygenated bacterial luciferase-flavin intermediate. Reaction products via the light and dark pathways. J Biol Chem 1975. [DOI: 10.1016/s0021-9258(19)40942-3] [Citation(s) in RCA: 91] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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31
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Studies on the mechanism of Mycobacterium smegmatis L-lactate oxidase. 5-Deazaflavin mononucleotide as a coenzyme analogue. J Biol Chem 1975. [DOI: 10.1016/s0021-9258(19)41852-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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