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Seo D. The Role of the si-Face Tyrosine of a Homodimeric Ferredoxin-NADP + Oxidoreductase from Bacillus subtilis during Complex Formation and Redox Equivalent Transfer with NADP +/H and Ferredoxin. Antioxidants (Basel) 2023; 12:1741. [PMID: 37760044 PMCID: PMC10526003 DOI: 10.3390/antiox12091741] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Revised: 08/18/2023] [Accepted: 08/28/2023] [Indexed: 09/29/2023] Open
Abstract
In the crystal structure of ferredoxin-NADP+ oxidoreductase from Bacillus subtilis (BsFNR), Tyr50 stacks on the si-face of the isoalloxazine ring portion of the FAD prosthetic group. This configuration is highly conserved among the homodimeric ferredoxin-NAD(P)+ oxidoreductases (FNR) from Gram-positive bacteria and photosynthetic bacteria. In this report, pre-steady state reactions of Tyr50 variants with NADP+/NADPH and ferredoxin from B. subtilis (BsFd) were examined with stopped-flow spectrophotometry to assess the effects of the mutation on the formation of FNR-substrate complexes and following redox equivalent transfer. Mixing oxidized BsFNRs with NADPH resulted in a rapid complex formation followed by a rate-limiting hydride transfer. The substitution substantially modulated the intensity of the charge transfer absorption band and decreased the observed hydride transfer rates compared to the wild type. Reduction of the Y50W mutant by NADPH proceeded in a monophasic manner, while the Y50G and Y50S mutants did in biphasic phases. The reduced Tyr50 mutants hardly promoted the reduction of NADP+. Mixing oxidized BsFNRs with reduced BsFd resulted in the reduction of the FNRs. The observed FNR reduction rates of the three variants were comparable, but in the Y50G and Y50S mutants, the amount of the reduced FNR at the rapid phase was decreased, and a slow FNR reduction phase was observed. The obtained results suggest that the replacements of Tyr50 with Gly and Ser permitted the conformational change in the reduced form, which induced an asymmetric kinetic behavior between the protomers of the homodimeric BsFNR.
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Affiliation(s)
- Daisuke Seo
- Division of Material Science, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan
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2
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Mulo P, Medina M. Interaction and electron transfer between ferredoxin-NADP + oxidoreductase and its partners: structural, functional, and physiological implications. PHOTOSYNTHESIS RESEARCH 2017; 134:265-280. [PMID: 28361449 DOI: 10.1007/s11120-017-0372-0] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Accepted: 03/20/2017] [Indexed: 05/25/2023]
Abstract
Ferredoxin-NADP+ reductase (FNR) catalyzes the last step of linear electron transfer in photosynthetic light reactions. The FAD cofactor of FNR accepts two electrons from two independent reduced ferredoxin molecules (Fd) in two sequential steps, first producing neutral semiquinone and then the fully anionic reduced, or hydroquinone, form of the enzyme (FNRhq). FNRhq transfers then both electrons in a single hydride transfer step to NADP+. We are presenting the recent progress in studies focusing on Fd:FNR interaction and subsequent electron transfer processes as well as on interaction of FNR with NADP+/H followed by hydride transfer, both from the structural and functional point of views. We also present the current knowledge about the physiological role(s) of various FNR isoforms present in the chloroplasts of higher plants and the functional impact of subchloroplastic location of FNR. Moreover, open questions and current challenges about the structure, function, and physiology of FNR are discussed.
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Affiliation(s)
- Paula Mulo
- Molecular Plant Biology, University of Turku, 20520, Turku, Finland
| | - Milagros Medina
- Department of Biochemistry and Molecular and Cellular Biology, Faculty of Sciences, and Institute of Biocomputation and Physics of Complex Systems (Joint Units: BIFI-IQFR and GBsC-CSIC), University of Zaragoza, 50009, Zaragoza, Spain.
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3
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Seo D, Naito H, Nishimura E, Sakurai T. Replacement of Tyr50 stacked on the si-face of the isoalloxazine ring of the flavin adenine dinucleotide prosthetic group modulates Bacillus subtilis ferredoxin-NADP(+) oxidoreductase activity toward NADPH. PHOTOSYNTHESIS RESEARCH 2015; 125:321-328. [PMID: 25698107 DOI: 10.1007/s11120-015-0099-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Accepted: 02/11/2015] [Indexed: 06/04/2023]
Abstract
Ferredoxin-NAD(P)(+) oxidoreductases ([EC 1.18.1.2], [EC 1.18.1.3], FNRs) from green sulfur bacteria, purple non-sulfur bacteria and most of Firmicutes, such as Bacillus subtilis (BsFNR) are homo-dimeric flavoproteins homologous to bacterial NADPH-thioredoxin reductase. These FNRs contain two unique aromatic residues stacked on the si- and re-face of the isoalloxazine ring moiety of the FAD prosthetic group whose configurations are often found among other types of flavoproteins including plant-type FNR and flavodoxin, but not in bacterial NADPH-thioredoxin reductase. To investigate the role of the si-face Tyr50 residue in BsFNR, we replaced Tyr50 with Gly, Ser, and Trp and examined its spectroscopic properties and enzymatic activities in the presence of NADPH and ferredoxin (Fd) from B. subtilis (BsFd). The replacement of Tyr50 to Gly (Y50G), Ser (Y50S), and Trp (Y50W) in BsFNR resulted in a blue shift of the FAD transition bands. The Y50G and Y50S mutations enhanced the FAD fluorescence emission, whereas those of the wild type and Y50W mutant were quenched. All three mutants decreased thermal stabilities compared to wild type. Using a diaphorase assay, the k cat values for the Y50G and Y50S mutants in the presence of NADPH and ferricyanide were decreased to less than 5 % of the wild type activity. The Y50W mutant retained approximately 20 % reactivity in the diaphorase assay and BsFd-dependent cytochrome c reduction assay relative to wild type. The present results suggest that Tyr50 modulates the electronic properties and positioning of the prosthetic group.
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Affiliation(s)
- Daisuke Seo
- Division of Material Science, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa, 920-1192, Japan,
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4
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Hamdane D, Bou-Nader C, Cornu D, Hui-Bon-Hoa G, Fontecave M. Flavin-Protein Complexes: Aromatic Stacking Assisted by a Hydrogen Bond. Biochemistry 2015; 54:4354-64. [PMID: 26120776 DOI: 10.1021/acs.biochem.5b00501] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Enzyme-catalyzed reactions often rely on a noncovalently bound cofactor whose reactivity is tuned by its immediate environment. Flavin cofactors, the most versatile catalyst encountered in biology, are often maintained within the protein throughout numbers of complex ionic and aromatic interactions. Here, we have investigated the role of π-π stacking and hydrogen bond interactions between a tyrosine and the isoalloxazine moiety of the flavin adenine dinucleotide (FAD) in an FAD-dependent RNA methyltransferase. Combining several static and time-resolved spectroscopies as well as biochemical approaches, we showed that aromatic stacking is assisted by a hydrogen bond between the phenol group and the amide of an adjacent active site loop. A mechanism of recognition and binding of the redox cofactor is proposed.
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Affiliation(s)
- Djemel Hamdane
- †Laboratoire de Chimie des Processus Biologiques, CNRS-UMR 8229, Collège De France, France 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France
| | - Charles Bou-Nader
- †Laboratoire de Chimie des Processus Biologiques, CNRS-UMR 8229, Collège De France, France 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France
| | - David Cornu
- ‡INSERM U779, 78 Rue du Général Leclerc, 94275 Le Kremlin-Bicêtre, France
| | - Gaston Hui-Bon-Hoa
- §Plateforme IMAGIF, Centre de Recherche de Gif, Centre National de la Recherche Scientifique, 1 avenue de le terrasse, 91191 Gif Sur Yvette, France
| | - Marc Fontecave
- †Laboratoire de Chimie des Processus Biologiques, CNRS-UMR 8229, Collège De France, France 11 place Marcelin Berthelot, 75231 Paris Cedex 05, France
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5
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Sánchez-Azqueta A, Herguedas B, Hurtado-Guerrero R, Hervás M, Navarro JA, Martínez-Júlvez M, Medina M. A hydrogen bond network in the active site of Anabaena ferredoxin-NADP+ reductase modulates its catalytic efficiency. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2014; 1837:251-63. [DOI: 10.1016/j.bbabio.2013.10.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2013] [Revised: 10/13/2013] [Accepted: 10/23/2013] [Indexed: 10/26/2022]
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Kumar SP, Jasrai YT, Pandya HA, George LB, Patel SK. Structural insights into the theoretical model of Plasmodium falciparum NADH dehydrogenase and its interaction with artemisinin and derivatives: towards global health therapeutics. OMICS-A JOURNAL OF INTEGRATIVE BIOLOGY 2013; 17:231-41. [PMID: 23638880 DOI: 10.1089/omi.2012.0129] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
It is a continuing quest to uncover the principal molecular targets of malarial parasites to understand the antimalarial activity and mechanism of action of artemisinin, a potent antimalarial. A series of parasite proteins are experimentally validated as potential targets, such as translationally controlled tumor protein (TCTP) and sarco/endoplasmic reticulum membrane calcium ATP-ase (SERCA). The present study addressed the development of a theoretical model of Plasmodium falciparum NADH dehydrogenase with inference from artemisinin in vivo inhibitory activity. We report here the predicted binding modes of artemisinin and its derivatives. The modeled protein resembled the structural architecture of flavoproteins and oxidoreductases, consisting of two Rossmann folds and dedicated binding sites for its cofactors. Docked poses of the ligand dataset revealed its interactions at or near the si face, indicating being activated. This may aid in generation of reactive oxygen species, thereby disrupting the membrane potential of parasite mitochondria and leading to the clearance from the blood. These observations open up new strategies for development of novel therapeutics, or improvement of existing pharmacotherapies against malaria, a major burden for global health.
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Affiliation(s)
- Sivakumar Prasanth Kumar
- Department of Bioinformatics, Applied Botany Centre, University School of Sciences, Gujarat University, Ahmedabad, India
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7
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Tyagi A, Penzkofer A, Mathes T, Hegemann P. Photophysical characterisation and photo-cycle dynamics of LOV1-His domain of phototropin from Chlamydomonas reinhardtii with roseoflavin monophosphate cofactor. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2010; 101:76-88. [PMID: 20655238 DOI: 10.1016/j.jphotobiol.2010.06.014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2010] [Revised: 06/29/2010] [Accepted: 06/29/2010] [Indexed: 11/19/2022]
Abstract
The wild-type phototropin protein phot from the green alga Chlamydomonas reinhardtii with the blue-light photoreceptor domains LOV1 and LOV2 has flavin mononucleotide (FMN) as cofactor. For the LOV1-His domain from phot of C. reinhardtii studied here, the FMN chromophore was replaced by roseoflavin monophosphate (8-dimethylamino-8-demethyl-FMN, RoFMN) during heterologous expression in a riboflavin auxotropic Escherichia coli strain. An absorption and emission spectroscopic characterisation of the cofactor exchanged-LOV1-His (RoLOV1) domain was carried out in aqueous pH 8 phosphate buffer. The fluorescence of RoLOV1 is quenched by photo-induced charge transfer at room temperature. The photo-cyclic dynamics of RoLOV1 was observed by blue-light induced hypochromic and bathochromic absorption changes which recover on a minute timescale in the dark. Photo-excited RoFMN is thought to cause reversible protein and cofactor structural changes. Prolonged intense blue-light exposure caused photo-degradation of RoFMN in RoLOV1 to fully reduced flavin and lumichrome derivatives. Photo-cycle schemes of RoLOV1 and LOV1 are presented, and the photo-degradation dynamics of RoLOV1 is discussed.
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Affiliation(s)
- A Tyagi
- Fakultät für Physik, Universität Regensburg, Universitätsstrasse 31, D-93053 Regensburg, Germany
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8
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Medina M. Structural and mechanistic aspects of flavoproteins: photosynthetic electron transfer from photosystem I to NADP+. FEBS J 2009; 276:3942-58. [PMID: 19583765 DOI: 10.1111/j.1742-4658.2009.07122.x] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This minireview covers the research carried out in recent years into different aspects of the function of the flavoproteins involved in cyanobacterial photosynthetic electron transfer from photosystem I to NADP(+), flavodoxin and ferredoxin-NADP(+) reductase. Interactions that stabilize protein-flavin complexes and tailor the midpoint potentials in these proteins, as well as many details of the binding and electron transfer to protein and ligand partners, have been revealed. In addition to their role in photosynthesis, flavodoxin and ferredoxin-NADP(+) reductase are ubiquitous flavoenzymes that deliver NAD(P)H or low midpoint potential one-electron donors to redox-based metabolisms in plastids, mitochondria and bacteria. They are also the basic prototypes for a large family of diflavin electron transferases with common functional and structural properties. Understanding their mechanisms should enable greater comprehension of the many physiological roles played by flavodoxin and ferredoxin-NADP(+) reductase, either free or as modules in multidomain proteins. Many aspects of their biochemistry have been extensively characterized using a combination of site-directed mutagenesis, steady-state and transient kinetics, spectroscopy and X-ray crystallography. Despite these considerable advances, various key features of the structural-function relationship are yet to be explained in molecular terms. Better knowledge of these systems and their particular properties may allow us to envisage several interesting applications of these proteins beyond their physiological functions.
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Affiliation(s)
- Milagros Medina
- Departamento de Bioquímica y Biología Molecular y Celular and BFIF, Universidad de Zaragoza, Spain.
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Velu S, Buniyamin I, Ching L, Feroz F, Noorbatcha I, Gee L, Awang K, Wahab I, Weber JF. Regio- and Stereoselective Biomimetic Synthesis of Oligostilbenoid Dimers from Resveratrol Analogues: Influence of the Solvent, Oxidant, and Substitution. Chemistry 2008; 14:11376-84. [DOI: 10.1002/chem.200801575] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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10
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Musumeci MA, Arakaki AK, Rial DV, Catalano-Dupuy DL, Ceccarelli EA. Modulation of the enzymatic efficiency of ferredoxin-NADP(H) reductase by the amino acid volume around the catalytic site. FEBS J 2008; 275:1350-66. [PMID: 18279389 DOI: 10.1111/j.1742-4658.2008.06298.x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ferredoxin (flavodoxin)-NADP(H) reductases (FNRs) are ubiquitous flavoenzymes that deliver NADPH or low-potential one-electron donors (ferredoxin, flavodoxin, adrenodoxin) to redox-based metabolic reactions in plastids, mitochondria and bacteria. Plastidic FNRs are quite efficient reductases. In contrast, FNRs from organisms possessing a heterotrophic metabolism or anoxygenic photosynthesis display turnover numbers 20- to 100-fold lower than those of their plastidic and cyanobacterial counterparts. Several structural features of these enzymes have yet to be explained. The residue Y308 in pea FNR is stacked nearly parallel to the re-face of the flavin and is highly conserved amongst members of the family. By computing the relative free energy for the lumiflavin-phenol pair at different angles with the relative position found for Y308 in pea FNR, it can be concluded that this amino acid is constrained against the isoalloxazine. This effect is probably caused by amino acids C266 and L268, which face the other side of this tyrosine. Simple and double FNR mutants of these amino acids were obtained and characterized. It was observed that a decrease or increase in the amino acid volume resulted in a decrease in the catalytic efficiency of the enzyme without altering the protein structure. Our results provide experimental evidence that the volume of these amino acids participates in the fine-tuning of the catalytic efficiency of the enzyme.
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Affiliation(s)
- Matías A Musumeci
- Molecular Biology Division, Instituto de Biología Molecular y Celular de Rosario (IBR), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Argentina
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11
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Hiromoto T, Fujiwara S, Hosokawa K, Yamaguchi H. Crystal structure of 3-hydroxybenzoate hydroxylase from Comamonas testosteroni has a large tunnel for substrate and oxygen access to the active site. J Mol Biol 2006; 364:878-96. [PMID: 17045293 DOI: 10.1016/j.jmb.2006.09.031] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2006] [Revised: 09/08/2006] [Accepted: 09/12/2006] [Indexed: 11/23/2022]
Abstract
The 3-hydroxybenzoate hydroxylase (MHBH) from Comamonas testosteroni KH122-3s is a single-component flavoprotein monooxygenase, a member of the glutathione reductase (GR) family. It catalyzes the conversion of 3-hydroxybenzoate to 3,4-dihydroxybenzoate with concomitant requirements for equimolar amounts of NADPH and molecular oxygen. The production of dihydroxy-benzenoid derivative by hydroxylation is the first step in the aerobic degradation of various phenolic compounds in soil microorganisms. To establish the structural basis for substrate recognition, the crystal structure of MHBH in complex with its substrate was determined at 1.8 A resolution. The enzyme is shown to form a physiologically active homodimer with crystallographic 2-fold symmetry, in which each subunit consists of the first two domains comprising an active site and the C-terminal domain involved in oligomerization. The protein fold of the catalytic domains and the active-site architecture, including the FAD and substrate-binding sites, are similar to those of 4-hydroxybenzoate hydroxylase (PHBH) and phenol hydroxylase (PHHY), which are members of the GR family, providing evidence that the flavoprotein aromatic hydroxylases share similar catalytic actions for hydroxylation of the respective substrates. Structural comparison of MHBH with the homologous enzymes suggested that a large tunnel connecting the substrate-binding pocket to the protein surface serves for substrate transport in this enzyme. The internal space of the large tunnel is distinctly divided into hydrophilic and hydrophobic regions. The characteristically stratified environment in the tunnel interior and the size of the entrance would allow the enzyme to select its substrate by amphiphilic nature and molecular size. In addition, the structure of the Xe-derivative at 2.5 A resolution led to the identification of a putative oxygen-binding site adjacent to the substrate-binding pocket. The hydrophobic nature of the xenon-binding site extends to the solvent through the tunnel, suggesting that the tunnel could be involved in oxygen transport.
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Affiliation(s)
- Takeshi Hiromoto
- Department of Chemistry, Nanobiotechnology Research Center, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337, Japan
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Marohnic CC, Crowley LJ, Davis CA, Smith ET, Barber MJ. Cytochrome b5 reductase: role of the si-face residues, proline 92 and tyrosine 93, in structure and catalysis. Biochemistry 2005; 44:2449-61. [PMID: 15709757 DOI: 10.1021/bi048045q] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The conserved sequence motif "RxY(T)(S)xx(S)(N)" coordinates flavin binding in NADH:cytochrome b(5) reductase (cb(5)r) and other members of the flavin transhydrogenase superfamily of oxidoreductases. To investigate the roles of Y93, the third and only aromatic residue of the "RxY(T)(S)xx(S)(N)" motif, that stacks against the si-face of the flavin isoalloxazine ring, and P92, the second residue in the motif that is also in close proximity to the FAD moiety, a series of rat cb(5)r variants were produced with substitutions at either P92 or Y93, respectively. The proline mutants P92A, G, and S together with the tyrosine mutants Y93A, D, F, H, S, and W were recombinantly expressed in E. coli and purified to homogeneity. Each mutant protein was found to bind FAD in a 1:1 cofactor:protein stoichiometry while UV CD spectra suggested similar secondary structure organization among all nine variants. The tyrosine variants Y93A, D, F, H, and S exhibited varying degrees of blue-shift in the flavin visible absorption maxima while visible CD spectra of the Y93A, D, H, S, and W mutants exhibited similar blue-shifted maxima together with changes in absorption intensity. Intrinsic flavin fluorescence was quenched in the wild type, P92S and A, and Y93H and W mutants while Y93A, D, F, and S mutants exhibited increased fluorescence when compared to free FAD. The tyrosine variants Y93A, D, F, and S also exhibited greater thermolability of FAD binding. The specificity constant (k(cat)/K(m)(NADH)) for NADH:FR activity decreased in the order wild type > P92S > P92A > P92G > Y93F > Y93S > Y93A > Y93D > Y93H > Y93W with the Y93W variant retaining only 0.5% of wild-type efficiency. Both K(s)(H4NAD) and K(s)(NAD+) values suggested that Y93A, F, and W mutants had compromised NADH and NAD(+) binding. Thermodynamic measurements of the midpoint potential (E degrees ', n = 2) of the FAD/FADH(2) redox couple revealed that the potentials of the Y93A and S variants were approximately 30 mV more positive than that of wild-type cb(5)r (E degrees ' = -268 mV) while that of Y93H was approximately 30 mV more negative. These results indicate that neither P92 nor Y93 are critical for flavin incorporation in cb(5)r and that an aromatic side chain is not essential at position 93, but they demonstrate that Y93 forms contacts with the FAD that effectively modulate the spectroscopic, catalytic, and thermodynamic properties of the bound cofactor.
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Affiliation(s)
- Christopher C Marohnic
- Department of Biochemistry and Molecular Biology, College of Medicine, University of South Florida, Tampa, Florida 33612, USA
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Chatwood LL, Müller J, Gross JD, Wagner G, Lippard SJ. NMR structure of the flavin domain from soluble methane monooxygenase reductase from Methylococcus capsulatus (Bath). Biochemistry 2004; 43:11983-91. [PMID: 15379538 DOI: 10.1021/bi049066n] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Soluble methane monooxygenase (sMMO) catalyzes the hydroxylation of methane by dioxygen to methanol, the first step in carbon assimilation by methanotrophs. This multicomponent system transfers electrons from NADH through a reductase component to the non-heme diiron center in the hydroxylase where O(2) is activated. The reductase component comprises three distinct domains, a [2Fe-2S] ferredoxin domain along with FAD- and NADH-binding domains. We report the solution structure of the reduced 27.6 kDa FAD- and NADH-binding domains (MMOR-FAD) of the reductase from Methylococcus capsulatus (Bath). The FAD-binding domain consists of a six-stranded antiparallel beta-barrel and one alpha-helix, with the first 10 N-terminal residues unstructured. In the interface between the two domains, the FAD cofactor is tightly bound in an unprecedented extended conformation. The NADH-binding domain consists of a five-stranded parallel beta-sheet with four alpha-helices packing closely around this sheet. MMOR-FAD is structurally homologous to other FAD-containing oxidoreductases, and we expect similar structures for the FAD/NADH-binding domains of reductases that occur in other multicomponent monooxygenases.
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Affiliation(s)
- Lisa L Chatwood
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139-4307, USA
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Carrillo N, Ceccarelli EA. Open questions in ferredoxin-NADP+ reductase catalytic mechanism. EUROPEAN JOURNAL OF BIOCHEMISTRY 2003; 270:1900-15. [PMID: 12709048 DOI: 10.1046/j.1432-1033.2003.03566.x] [Citation(s) in RCA: 208] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Ferredoxin (flavodoxin)-NADP(H) reductases (FNR) are ubiquitous flavoenzymes that deliver NADPH or low potential one-electron donors (ferredoxin, flavodoxin) to redox-based metabolisms in plastids, mitochondria and bacteria. The plant-type reductase is also the basic prototype for one of the major families of flavin-containing electron transferases that display common functional and structural properties. Many aspects of FNR biochemistry have been extensively characterized in recent years using a combination of site-directed mutagenesis, steady-state and transient kinetic experiments, spectroscopy and X-ray crystallography. Despite these considerable advances, various key features in the enzymology of these important reductases remain yet to be explained in molecular terms. This article reviews the current status of these open questions. Measurements of electron transfer rates and binding equilibria indicate that NADP(H) and ferredoxin interactions with FNR result in a reciprocal decrease of affinity, and that this induced-fit step is a mandatory requisite for catalytic turnover. However, the expected conformational movements are not apparent in the reported atomic structures of these flavoenzymes in the free state or in complex with their substrates. The overall reaction catalysed by FNR is freely reversible, but the pathways leading to NADP+ or ferredoxin reduction proceed through entirely different kinetic mechanisms. Also, the reductases isolated from various sources undergo inactivating denaturation on exposure to NADPH and other electron donors that reduce the FAD prosthetic group, a phenomenon that might have profound consequences for FNR function in vivo. The mechanisms underlying this reductive inhibition are so far unknown. Finally, we provide here a rationale to interpret FNR evolution in terms of catalytic efficiency. Using the formalism of the Albery-Knowles theory, we identified which parameter(s) have to be modified to make these reductases even more proficient under a variety of conditions, natural or artificial. Flavoenzymes with FNR activity catalyse a number of reactions with potential importance for biotechnological processes, so that modification of their catalytic competence is relevant on both scientific and technical grounds.
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Affiliation(s)
- Néstor Carrillo
- Molecular Biology Division, Instituto de Biología Molecular y Celular de Rosario (IBR), Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Argentina.
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