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Malik R, Bu Y. Magnetic coupling modulation in meta-nitroxide-functionalized isoalloxazine magnets with redox-active units as efficient side-modulators. Phys Chem Chem Phys 2023. [PMID: 37335558 DOI: 10.1039/d3cp01611k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/21/2023]
Abstract
Magnetic conversion can be accomplished in a variety of ways, as organic molecules with switchable magnetic characteristics offer numerous technological applications. It is crucial to find magnetism-switchable systems because, in the field of organic magnetic materials, the redox-induced magnetic reversal is very simple to achieve and shows significant applications. Herein, we computationally design isoalloxazine-based diradicals through oxidizing N10 and adding a nitroxide to C8 as the spin source (i.e. 8-nitroxide-isoalloxazine 10-oxide, an m-phenylene-like nitroxide diradical expanded with a redox unit as a side-modulator) and its N1/N5-hydrogenated/protonated diradical derivatives and introducing substituents (-OH, -NH2, and -NO2) to C6. We demonstrate that the basically modified structure exhibits ferromagnetic (FM) characteristics with a magnetic coupling constant (J) of 561.3 cm-1 calculated at the B3LYP/6-311+G(d,p) level, obeying the meta-phenylene-mediated diradical character, and dihydrogenation can lead to an AFM diradical with considerably large J (-976.1 cm-1). Surprisingly, protonation at N1 or N5 can lead to distinctly different magnetic variations (561.3 → -1602.9 cm-1 at N1 versus 561.3 → 379.1 cm-1 at N5). Analyses indicate that small singlet-triplet energy gaps and small energy gaps between the highest occupied and lowest unoccupied molecular orbitals (HOMO, LUMO) of the closed shell singlet state are the key features of these isoalloxazine diradicals, and aromaticity variations, significant spin delocalization from the π-conjugated structure and spin polarization from the non-Kekule structure induced by modification are responsible for the magnetic conversion. Furthermore, the spin alternation rule, the singly occupied molecular orbital (SOMO) effect, and the SOMO-SOMO energy splitting of the triplet state are used to analyze these distinct variations. This work provides a novel understanding of the structures and characteristics of modified isoalloxazine diradicals, as well as essential details for the intricate design and characterization of new isoalloxazine-based potential organic magnetic switches.
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Affiliation(s)
- Rabia Malik
- School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, People's Republic of China.
| | - Yuxiang Bu
- School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, People's Republic of China.
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2
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Substrate-induced radical formation in 4-hydroxybutyryl coenzyme A dehydratase from Clostridium aminobutyricum. Appl Environ Microbiol 2014; 81:1071-84. [PMID: 25452282 DOI: 10.1128/aem.03099-14] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
4-Hydroxybutyryl-coenzyme A (CoA) dehydratase (4HBD) from Clostridium aminobutyricum catalyzes the reversible dehydration of 4-hydroxybutyryl-CoA to crotonyl-CoA and the irreversible isomerization of vinylacetyl-CoA to crotonyl-CoA. 4HBD is an oxygen-sensitive homotetrameric enzyme with one [4Fe-4S](2+) cluster and one flavin adenine dinucleotide (FAD) in each subunit. Upon the addition of crotonyl-CoA or the analogues butyryl-CoA, acetyl-CoA, and CoA, UV-visible light and electron paramagnetic resonance (EPR) spectroscopy revealed an internal one-electron transfer to FAD and the [4Fe-4S](2+) cluster prior to hydration. We describe an active recombinant 4HBD and variants produced in Escherichia coli. The variants of the cluster ligands (H292C [histidine at position 292 is replaced by cysteine], H292E, C99A, C103A, and C299A) had no measurable dehydratase activity and were composed of monomers, dimers, and tetramers. Variants of other potential catalytic residues were composed only of tetramers and exhibited either no measurable (E257Q, E455Q, and Y296W) hydratase activity or <1% (Y296F and T190V) dehydratase activity. The E455Q variant but not the Y296F or E257Q variant displayed the same spectral changes as the wild-type enzyme after the addition of crotonyl-CoA but at a much lower rate. The results suggest that upon the addition of a substrate, Y296 is deprotonated by E455 and reduces FAD to FADH·, aided by protonation from E257 via T190. In contrast to FADH·, the tyrosyl radical could not be detected by EPR spectroscopy. FADH· appears to initiate the radical dehydration via an allylic ketyl radical that was proposed 19 years ago. The mode of radical generation in 4HBD is without precedent in anaerobic radical chemistry. It differs largely from that in enzymes, which use coenzyme B12, S-adenosylmethionine, ATP-driven electron transfer, or flavin-based electron bifurcation for this purpose.
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3
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Paulus B, Illarionov B, Nohr D, Roellinger G, Kacprzak S, Fischer M, Weber S, Bacher A, Schleicher E. One Protein, Two Chromophores: Comparative Spectroscopic Characterization of 6,7-Dimethyl-8-ribityllumazine and Riboflavin Bound to Lumazine Protein. J Phys Chem B 2014; 118:13092-105. [DOI: 10.1021/jp507618f] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Bernd Paulus
- Institute
of Physical Chemistry, Albert-Ludwigs-University Freiburg, Albertstrasse
21, 79104 Freiburg, Germany
| | - Boris Illarionov
- Institute for Biochemistry & Food Chemistry, University of Hamburg, Bundesstrasse 45, 20146 Hamburg, Germany
| | - Daniel Nohr
- Institute
of Physical Chemistry, Albert-Ludwigs-University Freiburg, Albertstrasse
21, 79104 Freiburg, Germany
| | - Guillaume Roellinger
- Institute
of Physical Chemistry, Albert-Ludwigs-University Freiburg, Albertstrasse
21, 79104 Freiburg, Germany
| | - Sylwia Kacprzak
- Institute
of Physical Chemistry, Albert-Ludwigs-University Freiburg, Albertstrasse
21, 79104 Freiburg, Germany
| | - Markus Fischer
- Institute for Biochemistry & Food Chemistry, University of Hamburg, Bundesstrasse 45, 20146 Hamburg, Germany
| | - Stefan Weber
- Institute
of Physical Chemistry, Albert-Ludwigs-University Freiburg, Albertstrasse
21, 79104 Freiburg, Germany
| | - Adelbert Bacher
- Institute for Biochemistry & Food Chemistry, University of Hamburg, Bundesstrasse 45, 20146 Hamburg, Germany
- Chemistry
Department, Technical University Munich, Lichtenbergstrasse 4, 85748 Garching, Germany
| | - Erik Schleicher
- Institute
of Physical Chemistry, Albert-Ludwigs-University Freiburg, Albertstrasse
21, 79104 Freiburg, Germany
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4
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Abstract
Flavoproteins often employ radical mechanisms in their enzymatic reactions. This involves paramagnetic species, which can ideally be investigated with electron paramagnetic resonance (EPR) spectroscopy. In this chapter we focus on the example of flavin-based photoreceptors and discuss, how different EPR methods have been used to extract information about the flavin radical's electronic state, its binding pocket, electron-transfer pathways, and about the protein's tertiary and quaternary structure.
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Affiliation(s)
- Richard Brosi
- Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, Berlin, 14195, Germany,
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5
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Chowdhury NP, Mowafy AM, Demmer JK, Upadhyay V, Koelzer S, Jayamani E, Kahnt J, Hornung M, Demmer U, Ermler U, Buckel W. Studies on the mechanism of electron bifurcation catalyzed by electron transferring flavoprotein (Etf) and butyryl-CoA dehydrogenase (Bcd) of Acidaminococcus fermentans. J Biol Chem 2013; 289:5145-57. [PMID: 24379410 DOI: 10.1074/jbc.m113.521013] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Electron bifurcation is a fundamental strategy of energy coupling originally discovered in the Q-cycle of many organisms. Recently a flavin-based electron bifurcation has been detected in anaerobes, first in clostridia and later in acetogens and methanogens. It enables anaerobic bacteria and archaea to reduce the low-potential [4Fe-4S] clusters of ferredoxin, which increases the efficiency of the substrate level and electron transport phosphorylations. Here we characterize the bifurcating electron transferring flavoprotein (EtfAf) and butyryl-CoA dehydrogenase (BcdAf) of Acidaminococcus fermentans, which couple the exergonic reduction of crotonyl-CoA to butyryl-CoA to the endergonic reduction of ferredoxin both with NADH. EtfAf contains one FAD (α-FAD) in subunit α and a second FAD (β-FAD) in subunit β. The distance between the two isoalloxazine rings is 18 Å. The EtfAf-NAD(+) complex structure revealed β-FAD as acceptor of the hydride of NADH. The formed β-FADH(-) is considered as the bifurcating electron donor. As a result of a domain movement, α-FAD is able to approach β-FADH(-) by about 4 Å and to take up one electron yielding a stable anionic semiquinone, α-FAD, which donates this electron further to Dh-FAD of BcdAf after a second domain movement. The remaining non-stabilized neutral semiquinone, β-FADH(•), immediately reduces ferredoxin. Repetition of this process affords a second reduced ferredoxin and Dh-FADH(-) that converts crotonyl-CoA to butyryl-CoA.
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Affiliation(s)
- Nilanjan Pal Chowdhury
- From the Laboratorium für Mikrobiologie, Fachbereich Biologie and SYNMIKRO, Philipps-Universität, 35032 Marburg, Germany
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6
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Martínez JI, Alonso PJ, Medina M. The electronic structure of the neutral isoalloxazine semiquinone within Anabaena flavodoxin: new insights from HYSCORE experiments. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2012; 218:153-162. [PMID: 22446506 DOI: 10.1016/j.jmr.2012.02.011] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/2011] [Revised: 02/11/2012] [Accepted: 02/18/2012] [Indexed: 05/31/2023]
Abstract
A complete study of Anabaena flavodoxin in the neutral semiquinone state by means of the EPR pulse technique HYSCORE is here presented. The results provide new information about the hyperfine interactions of the unpaired electronic spin and the nuclei in the isoalloxazine ring. This allows a better knowledge of the electronic structure of the neutral flavin radical within the protein. Combination of these results with other previously obtained by using other EPR related techniques allowed producing a very precise mapping of the flavin spin distribution in the neutral semiquinone state. This information can be very useful for determining the relationship between the electronic structure and mechanisms in flavoproteins. An experimental protocol for measuring the electronic structure details available to date is suggested.
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Affiliation(s)
- Jesús I Martínez
- Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-Consejo Superior de Investigaciones Científicas, Facultad de Ciencias, C/Pedro Cerbuna 12, 50009 Zaragoza, Spain.
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7
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Enzyme catalyzed radical dehydrations of hydroxy acids. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2011; 1824:1278-90. [PMID: 22178228 DOI: 10.1016/j.bbapap.2011.11.009] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2011] [Accepted: 11/28/2011] [Indexed: 11/24/2022]
Abstract
BACKGROUND The steadily increasing field of radical biochemistry is dominated by the large family of S-adenosylmethionine dependent enzymes, the so-called radical SAM enzymes, of which several new members are discovered every year. Here we report on 2- and 4-hydroxyacyl-CoA dehydratases which apply a very different method of radical generation. In these enzymes ketyl radicals are formed by one-electron reduction or oxidation and are recycled after each turnover without further energy input. Earlier reviews on 2-hydroxyacyl-CoA dehydratases were published in 2004 [J. Kim, M. Hetzel, C.D. Boiangiu, W. Buckel, FEMS Microbiol. Rev. 28 (2004) 455-468. W. Buckel, M. Hetzel, J. Kim, Curr. Opin. Chem. Biol. 8 (2004) 462-467.] SCOPE OF REVIEW The review focuses on four types of 2-hydroxyacyl-CoA dehydratases that are involved in the fermentation of amino acids by anaerobic bacteria, especially clostridia. These enzymes require activation by one-electron transfer from an iron-sulfur protein driven by hydrolysis of ATP. The review further describes the proposed mechanism that is highlighted by the identification of the allylic ketyl radical intermediate and the elucidation of the crystal structure of 2-hydroxyisocapryloyl-CoA dehydratase. With 4-hydroxybutyryl-CoA dehydratase the crystal structure, the complete stereochemistry and the function of several conserved residues around the active site could be identified. Finally potential biotechnological applications of the radical dehydratases are presented. GENERAL SIGNIFICANCE The action of the activator as an 'Archerase' shooting electrons into difficultly reducible acceptors becomes an emerging principle in anaerobic metabolism. The dehydratases may provide useful tools in biotechnology. This article is part of a Special Issue entitled: Radical SAM enzymes and Radical Enzymology.
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9
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Brosi R, Illarionov B, Mathes T, Fischer M, Joshi M, Bacher A, Hegemann P, Bittl R, Weber S, Schleicher E. Hindered rotation of a cofactor methyl group as a probe for protein-cofactor interaction. J Am Chem Soc 2010; 132:8935-44. [PMID: 20536240 DOI: 10.1021/ja910681z] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Exploring protein-cofactor interactions on a molecular level is one of the major challenges in modern biophysics. Based on structural data alone it is rarely possible to identify how subtle interactions between a protein and its cofactor modulate the protein's reactivity. In the case of enzymatic processes in which paramagnetic molecules play a certain role, EPR and related methods such as ENDOR are suitable techniques to unravel such important details. In this contribution, we describe how cryogenic-temperature ENDOR spectroscopy can be applied to various LOV domains, the blue-light sensing domains of phototropin photoreceptors, to gain information on the direct vicinity of the flavin mononucleotide (FMN) cofactor by analyzing the temperature dependence of methyl-group rotation attached to C(8) of the FMN's isoalloxazine ring. More specifically, mutational studies of three amino acids surrounding the methyl group led to the identification of Asn425 as an important amino acid that critically influences the dark-state recovery of Avena sativa LOV2 domains. Consequently, it is possible to probe protein-cofactor interactions on a sub-angstrom level by following the temperature dependencies of hyperfine couplings.
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Affiliation(s)
- Richard Brosi
- Fachbereich Physik, Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
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10
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Schleicher E, Wenzel R, Ahmad M, Batschauer A, Essen LO, Hitomi K, Getzoff ED, Bittl R, Weber S, Okafuji A. The Electronic State of Flavoproteins: Investigations with Proton Electron-Nuclear Double Resonance. APPLIED MAGNETIC RESONANCE 2010; 37:339-352. [PMID: 26089595 PMCID: PMC4469238 DOI: 10.1007/s00723-009-0101-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
Electron-nuclear double resonance (ENDOR) spectroscopy provides useful information on hyperfine interactions between nuclear magnetic moments and the magnetic moment of an unpaired electron spin. Because the hyperfine coupling constant reacts quite sensitively to polarity changes in the direct vicinity of the nucleus under consideration, ENDOR spectroscopy can be favorably used for the detection of subtle protein-cofactor interactions. A number of pulsed ENDOR studies on flavoproteins have been published during the past few years; most of them were designed to characterize the flavin cofactor by means of its protonation state, or to detect individual protein-cofactor interactions. The aim of this study is to compare the pulsed ENDOR spectra from different flavoproteins in terms of variations of characteristic proton hyperfine values. The general concept is to observe limits of possible influences on the cofactor's electronic state by surrounding amino acids. Furthermore, we compare ENDOR data obtained from in vivo experiments with in vitro data to emphasize the potential of the method for gaining molecular information in complex media.
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Affiliation(s)
- Erik Schleicher
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr.21, 79104 Freiburg, Germany
| | - Ringo Wenzel
- Institut für Experimentalphysik, Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | | | - Alfred Batschauer
- Fachbereich Biologie, Philipps-Universität Marburg, Marburg, Germany
| | | | - Kenichi Hitomi
- Department of Molecular Biology, The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Elizabeth D Getzoff
- Department of Molecular Biology, The Skaggs Institute for Chemical Biology, The Scripps Research Institute, La Jolla, CA, USA
| | - Robert Bittl
- Institut für Experimentalphysik, Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
| | - Stefan Weber
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr.21, 79104 Freiburg, Germany
| | - Asako Okafuji
- Institut für Physikalische Chemie, Albert-Ludwigs-Universität Freiburg, Albertstr.21, 79104 Freiburg, Germany
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11
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Schleicher E, Bittl R, Weber S. New roles of flavoproteins in molecular cell biology: Blue-light active flavoproteins studied by electron paramagnetic resonance. FEBS J 2009; 276:4290-303. [DOI: 10.1111/j.1742-4658.2009.07141.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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12
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Abstract
This review describes enzymes that contain radicals and/or catalyze reactions with radical intermediates. Because radicals irreversibly react with dioxygen, most of these enzymes occur in anaerobic bacteria and archaea. Exceptions are the families of coenzyme B(12)- and S-adenosylmethionine (SAM)-dependent radical enzymes, of which some members also occur in aerobes. Especially oxygen-sensitive radical enzymes are the glycyl radical enzymes and 2-hydroxyacyl-CoA dehydratases. The latter are activated by an ATP-dependent one-electron transfer and act via a ketyl radical anion mechanism. Related enzymes are the ATP-dependent benzoyl-CoA reductase and the ATP-independent 4-hydroxybenzoyl-CoA reductase. Ketyl radical anions may also be generated by one-electron oxidation as shown by the flavin-adenine-dinucleotide (FAD)- and [4Fe-4S]-containing 4-hydroxybutyryl-CoA dehydratase. Finally, two radical enzymes are discussed, pyruvate:ferredoxin oxidoreductase and methane-forming methyl-CoM reductase, which catalyze their main reaction in two-electron steps, but subsequent electron transfers proceed via radicals.
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Affiliation(s)
- Wolfgang Buckel
- Fachbereich Biologie, Philipps-Universität, D-35032 Marburg, Germany.
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13
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Buckel W, Martins BM, Messerschmidt A, Golding BT. Radical-mediated dehydration reactions in anaerobic bacteria. Biol Chem 2005; 386:951-9. [PMID: 16218867 DOI: 10.1515/bc.2005.111] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
AbstractMost dehydratases catalyse the elimination of water from β-hydroxy ketones, β-hydroxy carboxylic acids or β-hydroxyacyl-CoA. The electron-withdrawing carbonyl functionalities acidify the α-hydrogens to enable their removal by basic amino acid side chains. Anaerobic bacteria, however, ferment amino acids via α- or γ-hydroxyacyl-CoA, dehydrations of which involve the abstraction of a β-hydrogen, which is ostensibly non-acidic (pKca. 40). Evidence is accumulating that β-hydrogens are acidified via transient conversion of the CoA derivatives to enoxy radicals by one-electron transfers, which decrease the pKto 14. The dehydrations of (R)-2-hydroxyacyl-CoA to (E)-2-enoyl-CoA are catalysed by heterodimeric [4Fe-4S]-containing dehydratases, which require reductive activation by an ATP-dependent one-electron transfer mediated by a homodimeric protein with a [4Fe-4S] cluster between the two subunits. The electron is further transferred to the substrate, yielding a ketyl radical anion, which expels the hydroxyl group and forms an enoxy radical. The dehydration of 4-hydroxybutyryl-CoA to crotonyl-CoA involves a similar mechanism, in which the ketyl radical anion is generated by one-electron oxidation. The structure of the FAD- and [4Fe-4S]-containing homotetrameric dehydratase is related to that of acyl-CoA dehydrogenases, suggesting a radical-based mechanism for both flavoproteins.
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Affiliation(s)
- Wolfgang Buckel
- Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, D-35032 Marburg, Germany.
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14
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Näser U, Pierik AJ, Scott R, Cinkaya I, Buckel W, Golding BT. Synthesis of (13)C-labeled gamma-hydroxybutyrates for EPR studies with 4-hydroxybutyryl-CoA dehydratase. Bioorg Chem 2005; 33:53-66. [PMID: 15668183 DOI: 10.1016/j.bioorg.2004.09.001] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2004] [Indexed: 10/26/2022]
Abstract
4-Hydroxybutyryl-CoA dehydratase from Clostridium aminobutyricum catalyses the reversible dehydration of its substrate 4-hydroxybutyryl-CoA (4-HB-CoA) to crotonyl CoA. The enzyme contains one [4Fe-4S](2+) cluster and one flavin adenine dinucleotide (FAD) molecule per homotetramer. Incubation of the enzyme with its substrate under equilibrium conditions followed by freezing at 77K induced the EPR-spectrum of a neutral flavin semiquinone (g=2.005, linewidth 2.1 mT), while at 10K additional signals were detected. In an attempt to characterize these signals, 4-HB-CoA molecules specifically labeled with (13)C have been synthesized. This was achieved via (13)C-labeled gamma-butyrolactones, which were obtained from (13)C-labeled bromoacetic acids by efficient synthetic routes. Incubation of the (13)C-labeled 4-hydroxybutyrate-CoA molecules with 4-hydroxybutyryl-CoA dehydratase did not lead to marked broadening of the signals.
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Affiliation(s)
- Ulrike Näser
- School of Natural Sciences--Chemistry, University of Newcastle upon Tyne, Bedson Building, Newcastle upon Tyne, NE1 7RU, United Kingdom
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15
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Martins BM, Dobbek H, Cinkaya I, Buckel W, Messerschmidt A. Crystal structure of 4-hydroxybutyryl-CoA dehydratase: radical catalysis involving a [4Fe-4S] cluster and flavin. Proc Natl Acad Sci U S A 2004; 101:15645-9. [PMID: 15496473 PMCID: PMC524839 DOI: 10.1073/pnas.0403952101] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2004] [Accepted: 09/10/2004] [Indexed: 11/18/2022] Open
Abstract
Dehydratases catalyze the breakage of a carbon-oxygen bond leading to unsaturated products via the elimination of water. The 1.6-A resolution crystal structure of 4-hydroxybutyryl-CoA dehydratase from the gamma-aminobutyrate-fermenting Clostridium aminobutyricum represents a new class of dehydratases with an unprecedented active site architecture. A [4Fe-4S](2+) cluster, coordinated by three cysteine and one histidine residues, is located 7 A from the Re-side of a flavin adenine dinucleotide (FAD) moiety. The structure provides insight into the function of these ubiquitous prosthetic groups in the chemically nonfacile, radical-mediated dehydration of 4-hydroxybutyryl-CoA. The substrate can be bound between the [4Fe-4S](2+) cluster and the FAD with both cofactors contributing to its radical activation and catalytic conversion. Our results raise interesting questions regarding the mechanism of acyl-CoA dehydrogenases, which are involved in fatty acid oxidation, and address the divergent evolution of the ancestral common gene.
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Affiliation(s)
- Berta M Martins
- Max-Planck-Institut Biochemie, Strukturforschung, 82152 Martinsried, Germany.
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16
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Fuchs MR, Schleicher E, Schnegg A, Kay CWM, Törring JT, Bittl R, Bacher A, Richter G, Möbius K, Weber S. g-Tensor of the Neutral Flavin Radical Cofactor of DNA Photolyase Revealed by 360-GHz Electron Paramagnetic Resonance Spectroscopy. J Phys Chem B 2002. [DOI: 10.1021/jp0259869] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Martin R. Fuchs
- Institute of Experimental Physics, Free University Berlin, 14195 Berlin, Germany, and Institute of Organic Chemistry and Biochemistry, Technical University Munich, 85747 Garching, Germany
| | - Erik Schleicher
- Institute of Experimental Physics, Free University Berlin, 14195 Berlin, Germany, and Institute of Organic Chemistry and Biochemistry, Technical University Munich, 85747 Garching, Germany
| | - Alexander Schnegg
- Institute of Experimental Physics, Free University Berlin, 14195 Berlin, Germany, and Institute of Organic Chemistry and Biochemistry, Technical University Munich, 85747 Garching, Germany
| | - Christopher W. M. Kay
- Institute of Experimental Physics, Free University Berlin, 14195 Berlin, Germany, and Institute of Organic Chemistry and Biochemistry, Technical University Munich, 85747 Garching, Germany
| | - Jens T. Törring
- Institute of Experimental Physics, Free University Berlin, 14195 Berlin, Germany, and Institute of Organic Chemistry and Biochemistry, Technical University Munich, 85747 Garching, Germany
| | - Robert Bittl
- Institute of Experimental Physics, Free University Berlin, 14195 Berlin, Germany, and Institute of Organic Chemistry and Biochemistry, Technical University Munich, 85747 Garching, Germany
| | - Adelbert Bacher
- Institute of Experimental Physics, Free University Berlin, 14195 Berlin, Germany, and Institute of Organic Chemistry and Biochemistry, Technical University Munich, 85747 Garching, Germany
| | - Gerald Richter
- Institute of Experimental Physics, Free University Berlin, 14195 Berlin, Germany, and Institute of Organic Chemistry and Biochemistry, Technical University Munich, 85747 Garching, Germany
| | - Klaus Möbius
- Institute of Experimental Physics, Free University Berlin, 14195 Berlin, Germany, and Institute of Organic Chemistry and Biochemistry, Technical University Munich, 85747 Garching, Germany
| | - Stefan Weber
- Institute of Experimental Physics, Free University Berlin, 14195 Berlin, Germany, and Institute of Organic Chemistry and Biochemistry, Technical University Munich, 85747 Garching, Germany
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17
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García JI, Medina M, Sancho J, Alonso PJ, Gómez-Moreno C, Mayoral JA, Martínez JI. Theoretical Analysis of the Electron Spin Density Distribution of the Flavin Semiquinone Isoalloxazine Ring within Model Protein Environments. J Phys Chem A 2002. [DOI: 10.1021/jp014696+] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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18
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Weber S, Richter G, Schleicher E, Bacher A, Möbius K, Kay CW. Substrate binding to DNA photolyase studied by electron paramagnetic resonance spectroscopy. Biophys J 2001; 81:1195-204. [PMID: 11463661 PMCID: PMC1301589 DOI: 10.1016/s0006-3495(01)75777-3] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
Structural changes in Escherichia coli DNA photolyase induced by binding of a (cis,syn)-cyclobutane pyrimidine dimer (CPD) are studied by continuous-wave electron paramagnetic resonance and electron-nuclear double resonance spectroscopies, using the flavin adenine dinucleotide (FAD) cofactor in its neutral radical form as a naturally occurring electron spin probe. The electron paramagnetic resonance/electron-nuclear double resonance spectral changes are consistent with a large distance (> or =0.6 nm) between the CPD lesion and the 7,8-dimethyl isoalloxazine ring of FAD, as was predicted by recent model calculations on photolyase enzyme-substrate complexes. Small shifts of the isotropic proton hyperfine coupling constants within the FAD's isoalloxazine moiety can be understood in terms of the cofactor binding site becoming more nonpolar because of the displacement of water molecules upon CPD docking to the enzyme. Molecular orbital calculations of hyperfine couplings using density functional theory, in conjunction with an isodensity polarized continuum model, are presented to rationalize these shifts in terms of the changed polarity of the medium surrounding the FAD cofactor.
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Affiliation(s)
- S Weber
- Institute of Experimental Physics, Free University Berlin, 14195 Berlin, Germany.
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Weber S, Möbius K, Richter G, Kay CW. The electronic structure of the flavin cofactor in DNA photolyase. J Am Chem Soc 2001; 123:3790-8. [PMID: 11457111 DOI: 10.1021/ja003426m] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Density functional theory is used to calculate the electronic structure of the neutral flavin radical, FADH(*), formed in the light-induced electron-transfer reaction of DNA repair in cis,syn-cyclobutane pyrimidine dimer photolyases. Using the hybrid B3LYP functional together with the double-zeta basis set EPR-II, (1)H, (13)C, (15)N, and (17)O isotropic and anisotropic hyperfine couplings are calculated and explained by reference to the electron densities of the highest occupied molecular orbital and of the unpaired spin distribution on the radical. Comparison of calculated and experimental hyperfine couplings obtained from EPR and ENDOR/TRIPLE resonance leads to a refined structure for the FAD cofactor in Escherichia coli DNA photolyase. Hydrogen bonding at N3H, O4, and N5H results in significant changes in the unpaired spin density distribution and hyperfine coupling constants. The calculated electronic structure of FADH(*) provides evidence for a superexchange-mediated electron transfer between the cyclobutane pyrimidine dimer lesion and the 7,8-dimethyl isoalloxazine moiety of the flavin cofactor via the adenine moiety.
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Affiliation(s)
- S Weber
- Institute of Experimental Physics, Free University Berlin, Arnimallee 14, 14195 Berlin, Germany.
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Hans M, Sievers J, Müller U, Bill E, Vorholt JA, Linder D, Buckel W. 2-hydroxyglutaryl-CoA dehydratase from Clostridium symbiosum. EUROPEAN JOURNAL OF BIOCHEMISTRY 1999; 265:404-14. [PMID: 10491198 DOI: 10.1046/j.1432-1327.1999.00748.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Component D (HgdAB) of 2-hydroxyglutaryl-CoA dehydratase from Clostridium symbiosum was purified to homogeneity. It is able to use component A from Acidaminococcus fermentans (HgdC) to initiate catalysis together with ATP, Mg2+ and a strong reducing agent such as Ti(III)citrate. Component D from C. symbiosum has a 6 x higher specific activity compared with that from A. fermentans and contains a second [4Fe-4S] cluster but the same amount of riboflavin 5'-phosphate (1.0 per heterodimeric enzyme, m = 100 kDa). Mössbauer spectroscopy revealed symmetric cube-type structures of the two [4Fe-4S]2+ clusters. EPR spectroscopy showed the resistance of the clusters to reducing agents, but detected a sharp signal at g = 2. 004 probably due to a stabilized flavin semiquinone. Three genes from C. symbiosum coding for components D (hgdA and hgdB) and A (hgdC) were cloned and sequenced. Primer extension experiments indicated that the genes are transcribed in the order hgdCAB from an operon only half the size of that from A. fermentans. Sequence comparisons detected a close relationship to the dehydratase system from A. fermentans and HgdA from Fusobacterium nucleatum, as well as to putative proteins of unknown function from Archaeoglobus fulgidus. Lower, but significant, identities were found with putative enzymes from several methanogenic Archaea and Escherichia coli, as well as with the mechanistically related benzoyl-CoA reductases from the Proteobacteria Rhodopseudomonas palustris and Thauera aromatica.
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Affiliation(s)
- M Hans
- Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, Marburg, Germany
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Medina M, Lostao A, Sancho J, Gómez-Moreno C, Cammack R, Alonso PJ, Martínez JI. Electron-nuclear double resonance and hyperfine sublevel correlation spectroscopic studies of flavodoxin mutants from Anabaena sp. PCC 7119. Biophys J 1999; 77:1712-20. [PMID: 10465780 PMCID: PMC1300457 DOI: 10.1016/s0006-3495(99)77017-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The influence of the amino acid residues surrounding the flavin ring in the flavodoxin of the cyanobacterium Anabaena PCC 7119 on the electron spin density distribution of the flavin semiquinone was examined in mutants of the key residues Trp(57) and Tyr(94) at the FMN binding site. Neutral semiquinone radicals of the proteins were obtained by photoreduction and examined by electron-nuclear double resonance (ENDOR) and hyperfine sublevel correlation (HYSCORE) spectroscopies. Significant differences in electron density distribution were observed in the flavodoxin mutants Trp(57) --> Ala and Tyr(94) --> Ala. The results indicate that the presence of a bulky residue (either aromatic or aliphatic) at position 57, as compared with an alanine, decreases the electron spin density in the nuclei of the benzene flavin ring, whereas an aromatic residue at position 94 increases the electron spin density at positions N(5) and C(6) of the flavin ring. The influence of the FMN ribityl and phosphate on the flavin semiquinone was determined by reconstituting apoflavodoxin samples with riboflavin and with lumiflavin. The coupling parameters of the different nuclei of the isoalloxazine group, as detected by ENDOR and HYSCORE, were very similar to those of the native flavodoxin. This indicates that the protein conformation around the flavin ring and the electron density distribution in the semiquinone form are not influenced by the phosphate and the ribityl of FMN.
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Affiliation(s)
- M Medina
- Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, Universidad de Zaragoza, 50009-Zaragoza, Spain
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Buckel W, Golding BT. Radical species in the catalytic pathways of enzymes from anaerobes. FEMS Microbiol Rev 1998. [DOI: 10.1111/j.1574-6976.1998.tb00385.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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