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Bell D, Lindemann F, Gerland L, Aucharova H, Klein A, Friedrich D, Hiller M, Grohe K, Meier T, van Rossum B, Diehl A, Hughes J, Mueller LJ, Linser R, Miller AF, Oschkinat H. Sedimentation of large, soluble proteins up to 140 kDa for 1H-detected MAS NMR and 13C DNP NMR - practical aspects. JOURNAL OF BIOMOLECULAR NMR 2024:10.1007/s10858-024-00444-9. [PMID: 38904893 DOI: 10.1007/s10858-024-00444-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2024] [Accepted: 05/08/2024] [Indexed: 06/22/2024]
Abstract
Solution NMR is typically applied to biological systems with molecular weights < 40 kDa whereas magic-angle-spinning (MAS) solid-state NMR traditionally targets very large, oligomeric proteins and complexes exceeding 500 kDa in mass, including fibrils and crystalline protein preparations. Here, we propose that the gap between these size regimes can be filled by the approach presented that enables investigation of large, soluble and fully protonated proteins in the range of 40-140 kDa. As a key step, ultracentrifugation produces a highly concentrated, gel-like state, resembling a dense phase in spontaneous liquid-liquid phase separation (LLPS). By means of three examples, a Sulfolobus acidocaldarius bifurcating electron transfer flavoprotein (SaETF), tryptophan synthases from Salmonella typhimurium (StTS) and their dimeric β-subunits from Pyrococcus furiosus (PfTrpB), we show that such samples yield well-resolved proton-detected 2D and 3D NMR spectra at 100 kHz MAS without heterogeneous broadening, similar to diluted liquids. Herein, we provide practical guidance on centrifugation conditions and tools, sample behavior, and line widths expected. We demonstrate that the observed chemical shifts correspond to those obtained from µM/low mM solutions or crystalline samples, indicating structural integrity. Nitrogen line widths as low as 20-30 Hz are observed. The presented approach is advantageous for proteins or nucleic acids that cannot be deuterated due to the expression system used, or where relevant protons cannot be re-incorporated after expression in deuterated medium, and it circumvents crystallization. Importantly, it allows the use of low-glycerol buffers in dynamic nuclear polarization (DNP) NMR of proteins as demonstrated with the cyanobacterial phytochrome Cph1.
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Affiliation(s)
- Dallas Bell
- Faculty II-Mathematics and Natural Sciences, Technische Universität Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany
| | - Florian Lindemann
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany
| | - Lisa Gerland
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany
| | - Hanna Aucharova
- Department of Chemistry and Chemical Biology, TU Dortmund University, Otto-Hahn-Str. 4a, 44227, Dortmund, Germany
| | - Alexander Klein
- Department of Chemistry and Chemical Biology, TU Dortmund University, Otto-Hahn-Str. 4a, 44227, Dortmund, Germany
| | - Daniel Friedrich
- Department of Chemistry and Biochemistry, University of Cologne, Greinstr. 4, 50939, Cologne, Germany
| | - Matthias Hiller
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany
| | - Kristof Grohe
- Bruker BioSpin GmbH & Co. KG, Rudolf-Plank-Str. 23, 76275, Ettlingen, Germany
| | - Tobias Meier
- Bruker BioSpin GmbH & Co. KG, Rudolf-Plank-Str. 23, 76275, Ettlingen, Germany
| | - Barth van Rossum
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany
| | - Anne Diehl
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany
| | - Jon Hughes
- Institute for Plant Physiology, Justus Liebig University, Senckenbergstr. 3, 35360, Gießen, Germany
- Department of Physics, Free University of Berlin, Arnimallee 14, 14195, Berlin, Germany
| | - Leonard J Mueller
- Department of Chemistry, University of California - Riverside, Riverside, CA, 92521, USA
| | - Rasmus Linser
- Department of Chemistry and Chemical Biology, TU Dortmund University, Otto-Hahn-Str. 4a, 44227, Dortmund, Germany
| | - Anne-Frances Miller
- Faculty II-Mathematics and Natural Sciences, Technische Universität Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany.
- Department of Chemistry, University of Kentucky, Lexington, KY, 40506, USA.
| | - Hartmut Oschkinat
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany.
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Madeira CA, Anselmo C, Costa JM, Bonito CA, Ferreira RJ, Santos DJVA, Wanders RJ, Vicente JB, Ventura FV, Leandro P. Functional and structural impact of 10 ACADM missense mutations on human medium chain acyl-Coa dehydrogenase. Biochim Biophys Acta Mol Basis Dis 2023; 1869:166766. [PMID: 37257730 DOI: 10.1016/j.bbadis.2023.166766] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2023] [Revised: 05/10/2023] [Accepted: 05/23/2023] [Indexed: 06/02/2023]
Abstract
Medium chain acyl-CoA dehydrogenase (MCAD) deficiency (MCADD) is associated with ACADM gene mutations, leading to an impaired function and/or structure of MCAD. Importantly, after import into the mitochondria, MCAD must incorporate a molecule of flavin adenine dinucleotide (FAD) per subunit and assemble into tetramers. However, the effect of MCAD amino acid substitutions on FAD incorporation has not been investigated. Herein, the commonest MCAD variant (p.K304E) and 11 additional rare variants (p.Y48C, p.R55G, p.A88P, p.Y133C, p.A140T, p.D143V, p.G224R, p.L238F, p.V264I, p.Y372N, and p.G377V) were functionally and structurally characterized. Half of the studied variants presented a FAD content <65 % compared to the wild-type. Most of them were recovered as tetramers, except the p.Y372N (mainly as dimers). No correlation was found between the levels of tetramers and FAD content. However, a correlation between FAD content and the cofactor's affinity, proteolytic stability, thermostability, and thermal inactivation was established. We showed that the studied amino acid changes in MCAD may alter the substrate chain-length dependence and the interaction with electron-transferring-flavoprotein (ETF) necessary for a proper functioning electron transfer thus adding additional layers of complexity to the pathological effect of ACADM missense mutations. Although the majority of the variant MCADs presented an impaired capacity to retain FAD during their synthesis, some of them were structurally rescued by cofactor supplementation, suggesting that in the mitochondrial environment the levels and activity of those variants may be dependent of FAD's availability thus contributing for the heterogeneity of the MCADD phenotype found in patients presenting the same genotype.
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Affiliation(s)
- Catarina A Madeira
- Research Institute for Medicines, Faculty of Pharmacy, Universidade de Lisboa, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal
| | - Carolina Anselmo
- Research Institute for Medicines, Faculty of Pharmacy, Universidade de Lisboa, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal
| | - João M Costa
- Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal
| | - Cátia A Bonito
- LAQV@REQUIMTE/Department of Chemistry and Biochemistry, Faculty of Sciences, University of Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
| | | | - Daniel J V A Santos
- LAQV@REQUIMTE/Department of Chemistry and Biochemistry, Faculty of Sciences, University of Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal; Center for Research in Biosciences & Health Technologies (CBIOS), Universidade Lusófona de Humanidades e Tecnologias, Lisboa, Portugal
| | - Ronald J Wanders
- Laboratory Genetic Metabolic Diseases, Department of Clinical Chemistry, Amsterdam University Medical Centers-University of Amsterdam, 1105 AZ Amsterdam, The Netherlands
| | - João B Vicente
- Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal.
| | - Fátima V Ventura
- Research Institute for Medicines, Faculty of Pharmacy, Universidade de Lisboa, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal.
| | - Paula Leandro
- Research Institute for Medicines, Faculty of Pharmacy, Universidade de Lisboa, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal.
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3
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González-Viegas M, Kar RK, Miller AF, Mroginski MA. Non-covalent interactions that tune the reactivities of the flavins in bifurcating electron transferring flavoprotein. J Biol Chem 2023:104762. [PMID: 37119850 DOI: 10.1016/j.jbc.2023.104762] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Revised: 04/20/2023] [Accepted: 04/25/2023] [Indexed: 05/01/2023] Open
Abstract
Bifurcating electron transferring flavoproteins (Bf-ETFs) tune chemically identical flavins to two contrasting roles. To understand how, we used hybrid quantum mechanical molecular mechanical calculations to characterize non-covalent interactions applied to each flavin by the protein. Our computations replicated the differences between the reactivities of the flavins: the electron transferring flavin (ETflavin) was calculated to stabilize anionic semiquinone (ASQ) as needed to execute its single-electron transfers, whereas the Bf flavin (Bfflavin) was found to disfavor the ASQ state more than does free flavin and to be less susceptible to reduction. The stability of ETflavin ASQ was attributed in part to H-bond donation to the flavin O2 from a nearby His side chain, via comparison of models employing different tautomers of His. This H-bond between O2 and the ET site was uniquely strong in the ASQ state, whereas reduction of ETflavin to the anionic hydroquinone (AHQ) was associated with side chain reorientation, backbone displacement and reorganization of its H-bond network including a Tyr from the other domain and subunit of the ETF. The Bf site was less responsive overall, but formation of the Bfflavin AHQ allowed a nearby Arg side chain to adopt an alternative rotamer that can H-bond to the Bfflavin O4. This would stabilize the anionic Bfflavin and rationalize effects of mutation at this position. Thus, our computations provide insights on states and conformations that have not been possible to characterize experimentally, offering explanations for observed residue conservation and raising possibilities that can now be tested.
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Affiliation(s)
- María González-Viegas
- Department of Chemistry, Technische Universität - Berlin, Berlin, Germany; Department of Physics, Freie Universität Berlin, Berlin, Germany
| | - Rajiv K Kar
- Department of Chemistry, Technische Universität - Berlin, Berlin, Germany
| | - Anne-Frances Miller
- Department of Chemistry, Technische Universität - Berlin, Berlin, Germany; Department of Chemistry, University of Kentucky, Lexington KY, U.S.A..
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Unusual reactivity of a flavin in a bifurcating electron-transferring flavoprotein leads to flavin modification and a charge-transfer complex. J Biol Chem 2022; 298:102606. [PMID: 36257407 PMCID: PMC9713284 DOI: 10.1016/j.jbc.2022.102606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2022] [Revised: 10/08/2022] [Accepted: 10/10/2022] [Indexed: 11/06/2022] Open
Abstract
From the outset, canonical electron transferring flavoproteins (ETFs) earned a reputation for containing modified flavin. We now show that modification occurs in the recently recognized bifurcating (Bf) ETFs as well. In Bf ETFs, the 'electron transfer' (ET) flavin mediates single electron transfer via a stable anionic semiquinone state, akin to the FAD of canonical ETFs, whereas a second flavin mediates bifurcation (the Bf FAD). We demonstrate that the ET FAD undergoes transformation to two different modified flavins by a sequence of protein-catalyzed reactions that occurs specifically in the ET site, when the enzyme is maintained at pH 9 in an amine-based buffer. Our optical and mass spectrometric characterizations identify 8-formyl flavin early in the process and 8-amino flavins (8AFs) at later times. The latter have not previously been documented in an ETF to our knowledge. Mass spectrometry of flavin products formed in Tris or bis-tris-aminopropane solutions demonstrates that the source of the amine adduct is the buffer. Stepwise reduction of the 8AF demonstrates that it can explain a charge transfer band observed near 726 nm in Bf ETF, as a complex involving the hydroquinone state of the 8AF in the ET site with the oxidized state of unmodified flavin in the Bf site. This supports the possibility that Bf ETF can populate a conformation enabling direct electron transfer between its two flavins, as has been proposed for cofactors brought together in complexes between ETF and its partner proteins.
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Mohamed-Raseek N, Miller AF. Contrasting roles for two conserved arginines: stabilizing flavin semiquinone or quaternary structure, in bifurcating electron transfer flavoproteins. J Biol Chem 2022; 298:101733. [PMID: 35176283 PMCID: PMC8958531 DOI: 10.1016/j.jbc.2022.101733] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2021] [Revised: 02/11/2022] [Accepted: 02/12/2022] [Indexed: 01/02/2023] Open
Abstract
Bifurcating electron transfer flavoproteins (Bf ETFs) are important redox enzymes that contain two flavin adenine dinucleotide (FAD) cofactors, with contrasting reactivities and complementary roles in electron bifurcation. However, for both the “electron transfer” (ET) and the “bifurcating” (Bf) FADs, the only charged amino acid within 5 Å of the flavin is a conserved arginine (Arg) residue. To understand how the two sites produce different reactivities utilizing the same residue, we investigated the consequences of replacing each of the Arg residues with lysine, glutamine, histidine, or alanine. We show that absence of a positive charge in the ET site diminishes accumulation of the anionic semiquinone (ASQ) that enables the ET flavin to act as a single electron carrier, due to depression of the oxidized versus. ASQ reduction midpoint potential, E°OX/ASQ. Perturbation of the ET site also affected the remote Bf site, whereas abrogation of Bf FAD binding accelerated chemical modification of the ET flavin. In the Bf site, removal of the positive charge impaired binding of FAD or AMP, resulting in unstable protein. Based on pH dependence, we propose that the Bf site Arg interacts with the phosphate(s) of Bf FAD or AMP, bridging the domain interface via a conserved peptide loop (“zipper”) and favoring nucleotide binding. We further propose a model that rationalizes conservation of the Bf site Arg even in non-Bf ETFs, as well as AMP's stabilizing role in the latter, and provides a mechanism for coupling Bf flavin redox changes to domain-scale motion.
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Xia C, Lou B, Fu Z, Mohsen AW, Shen AL, Vockley J, Kim JJP. Molecular mechanism of interactions between ACAD9 and binding partners in mitochondrial respiratory complex I assembly. iScience 2021; 24:103153. [PMID: 34646991 PMCID: PMC8497999 DOI: 10.1016/j.isci.2021.103153] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Revised: 08/09/2021] [Accepted: 09/16/2021] [Indexed: 01/05/2023] Open
Abstract
The dual function protein ACAD9 catalyzes α,β-dehydrogenation of fatty acyl-CoA thioesters in fatty acid β-oxidation and is an essential chaperone for mitochondrial respiratory complex I (CI) assembly. ACAD9, ECSIT, and NDUFAF1 interact to form the core mitochondrial CI assembly complex. Current studies examine the molecular mechanism of ACAD9/ECSIT/NDUFAF1interactions. ACAD9 binds to the carboxy-terminal half and NDUFAF1 to the amino-terminal half of ECSIT. Binary complexes are unstable and aggregate easily, while the ACAD9/ECSIT/NDUFAF1 ternary complex is soluble and highly stable. Molecular modeling and small-angle X-ray scattering studies identified intra-complex interaction sites and binding sites for other assembly factors. Binding of ECSIT at the ETF binding site in the amino-terminal domain of ACAD9 is consistent with observed loss of FAD and enzymatic activity and demonstrates that the two functions of ACAD9 are mutually exclusive. Mapping of 42 known pathogenic mutations onto the homology-modeled ACAD9 structure provides structural insights into pathomechanisms of CI deficiency.
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Affiliation(s)
- Chuanwu Xia
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Baoying Lou
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Zhuji Fu
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Al-Walid Mohsen
- Department of Pediatrics, School of Medicine, University of Pittsburgh, Children’s Hospital of Pittsburgh of UPMC, Pittsburgh, PA 15224, USA
- Department of Human Genetics, School of Public Health, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Anna L. Shen
- McArdle Laboratory for Cancer Research, Department of Oncology, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Jerry Vockley
- Department of Pediatrics, School of Medicine, University of Pittsburgh, Children’s Hospital of Pittsburgh of UPMC, Pittsburgh, PA 15224, USA
- Department of Human Genetics, School of Public Health, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Jung-Ja P. Kim
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA
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Cryoelectron microscopy structure and mechanism of the membrane-associated electron-bifurcating flavoprotein Fix/EtfABCX. Proc Natl Acad Sci U S A 2021; 118:2016978118. [PMID: 33372143 DOI: 10.1073/pnas.2016978118] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The electron-transferring flavoprotein-menaquinone oxidoreductase ABCX (EtfABCX), also known as FixABCX for its role in nitrogen-fixing organisms, is a member of a family of electron-transferring flavoproteins that catalyze electron bifurcation. EtfABCX enables endergonic reduction of ferredoxin (E°' ∼-450 mV) using NADH (E°' -320 mV) as the electron donor by coupling this reaction to the exergonic reduction of menaquinone (E°' -80 mV). Here we report the 2.9 Å structure of EtfABCX, a membrane-associated flavin-based electron bifurcation (FBEB) complex, from a thermophilic bacterium. EtfABCX forms a superdimer with two membrane-associated EtfCs at the dimer interface that contain two bound menaquinones. The structure reveals that, in contrast to previous predictions, the low-potential electrons bifurcated from EtfAB are most likely directly transferred to ferredoxin, while high-potential electrons reduce the quinone via two [4Fe-4S] clusters in EtfX. Surprisingly, EtfX shares remarkable structural similarity with mammalian [4Fe-4S] cluster-containing ETF ubiquinone oxidoreductase (ETF-QO), suggesting an unexpected evolutionary link between bifurcating and nonbifurcating systems. Based on this structure and spectroscopic studies of a closely related EtfABCX, we propose a detailed mechanism of the catalytic cycle and the accompanying structural changes in this membrane-associated FBEB system.
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8
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Henriques BJ, Katrine Jentoft Olsen R, Gomes CM, Bross P. Electron transfer flavoprotein and its role in mitochondrial energy metabolism in health and disease. Gene 2021; 776:145407. [PMID: 33450351 DOI: 10.1016/j.gene.2021.145407] [Citation(s) in RCA: 43] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 12/08/2020] [Accepted: 12/16/2020] [Indexed: 12/15/2022]
Abstract
Electron transfer flavoprotein (ETF) is an enzyme with orthologs from bacteria to humans. Human ETF is nuclear encoded by two separate genes, ETFA and ETFB, respectively. After translation, the two subunits are imported to the mitochondrial matrix space and assemble into a heterodimer containing one FAD and one AMP as cofactors. ETF functions as a hub taking up electrons from at least 14 flavoenzymes, feeding them into the respiratory chain. This represents a major source of reducing power for the electron transport chain from fatty acid oxidation and amino acid degradation. Transfer of electrons from the donor enzymes to ETF occurs by direct transfer between the enzyme bound flavins, a process that is tightly regulated by the polypeptide chain and by protein:protein interactions. ETF, in turn relays electrons to the iron sulfur cluster of the inner membrane protein ETF:QO, from where they travel via the FAD in ETF:QO to ubiquinone, entering the respiratory chain at the level of complex III. ETF recognizes its dehydrogenase partners via a recognition loop that anchors the protein on its partner followed by dynamic movements of the ETF flavin domain that bring redox cofactors in close proximity, thus promoting electron transfer. Genetic mutations in the ETFA or ETFB genes cause the Mendelian disorder multiple acyl-CoA dehydrogenase deficiency (MADD; OMIM #231680). We here review the knowledge on human ETF and investigations of the effects of disease-associated missense mutations in this protein that have promoted the understanding of the essential role that ETF plays in cellular metabolism and human disease.
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Affiliation(s)
- Bárbara J Henriques
- Biosystems and Integrative Sciences Institute, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal; Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal.
| | - Rikke Katrine Jentoft Olsen
- Research Unit for Molecular Medicine, Department of Clinical Medicine, Aarhus University and Aarhus University Hospital, 8200 Aarhus, Denmark.
| | - Cláudio M Gomes
- Biosystems and Integrative Sciences Institute, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal; Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal.
| | - Peter Bross
- Research Unit for Molecular Medicine, Department of Clinical Medicine, Aarhus University and Aarhus University Hospital, 8200 Aarhus, Denmark.
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Duan HD, Mohamed-Raseek N, Miller AF. Spectroscopic evidence for direct flavin-flavin contact in a bifurcating electron transfer flavoprotein. J Biol Chem 2020; 295:12618-12634. [PMID: 32661195 DOI: 10.1074/jbc.ra120.013174] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2020] [Revised: 07/10/2020] [Indexed: 12/15/2022] Open
Abstract
A remarkable charge transfer (CT) band is described in the bifurcating electron transfer flavoprotein (Bf-ETF) from Rhodopseudomonas palustris (RpaETF). RpaETF contains two FADs that play contrasting roles in electron bifurcation. The Bf-FAD accepts electrons pairwise from NADH, directs one to a lower-reduction midpoint potential (E°) carrier, and the other to the higher-E° electron transfer FAD (ET-FAD). Previous work noted that a CT band at 726 nm formed when ET-FAD was reduced and Bf-FAD was oxidized, suggesting that both flavins participate. However, existing crystal structures place them too far apart to interact directly. We present biochemical experiments addressing this conundrum and elucidating the nature of this CT species. We observed that RpaETF missing either FAD lacked the 726 nm band. Site-directed mutagenesis near either FAD produced altered yields of the CT species, supporting involvement of both flavins. The residue substitutions did not alter the absorption maximum of the signal, ruling out contributions from residue orbitals. Instead, we propose that the residue identities modulate the population of a protein conformation that brings the ET-flavin and Bf-flavin into direct contact, explaining the 726 nm band based on a CT complex of reduced ET-FAD and oxidized Bf-FAD. This is corroborated by persistence of the 726 nm species during gentle protein denaturation and simple density functional theory calculations of flavin dimers. Although such a CT complex has been demonstrated for free flavins, this is the first observation of such, to our knowledge, in an enzyme. Thus, Bf-ETFs may optimize electron transfer efficiency by enabling direct flavin-flavin contact.
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Affiliation(s)
- H Diessel Duan
- Department of Chemistry, University of Kentucky, Lexington, Kentucky, USA
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10
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Jing X, Zeng H, Wang S, Xu J. A Web-Based Protocol for Interprotein Contact Prediction by Deep Learning. Methods Mol Biol 2020; 2074:67-80. [PMID: 31583631 DOI: 10.1007/978-1-4939-9873-9_6] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Identifying residue-residue contacts in protein-protein interactions or complex is crucial for understanding protein and cell functions. DCA (direct-coupling analysis) methods shed some light on this, but they need many sequence homologs to yield accurate prediction. Inspired by the success of our deep-learning method for intraprotein contact prediction, we have developed RaptorX-ComplexContact, a web server for interprotein residue-residue contact prediction. Given a pair of interacting protein sequences, RaptorX-ComplexContact first searches for their sequence homologs and builds two paired multiple sequence alignments (MSA) based on genomic distance and phylogeny information, respectively. Then, RaptorX-ComplexContact uses two deep convolutional residual neural networks (ResNet) to predict interprotein contacts from sequential features and coevolution information of paired MSAs. RaptorX-ComplexContact shall be useful for protein docking, protein-protein interaction prediction, and protein interaction network construction.
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Affiliation(s)
- Xiaoyang Jing
- Toyota Technological Institute at Chicago, Chicago, IL, USA
- School of Computer Science, Fudan University, Shanghai, China
| | - Hong Zeng
- School of Computer Science and Technology, Hangzhou Dianzi University, Hangzhou, China
| | - Sheng Wang
- Toyota Technological Institute at Chicago, Chicago, IL, USA
| | - Jinbo Xu
- Toyota Technological Institute at Chicago, Chicago, IL, USA.
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11
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Vogt MS, Schühle K, Kölzer S, Peschke P, Chowdhury NP, Kleinsorge D, Buckel W, Essen LO, Heider J. Structural and Functional Characterization of an Electron Transfer Flavoprotein Involved in Toluene Degradation in Strictly Anaerobic Bacteria. J Bacteriol 2019; 201:e00326-19. [PMID: 31405915 PMCID: PMC6779460 DOI: 10.1128/jb.00326-19] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2019] [Accepted: 08/08/2019] [Indexed: 11/20/2022] Open
Abstract
(R)-Benzylsuccinate is the characteristic initial intermediate of anaerobic toluene metabolism, which is formed by a radical-type addition of toluene to fumarate. Its further degradation proceeds by activation to the coenzyme A (CoA)-thioester and β-oxidation involving a specific (R)-2-benzylsuccinyl-CoA dehydrogenase (BbsG) affiliated with the family of acyl-CoA dehydrogenases. In this report, we present the biochemical properties of electron transfer flavoproteins (ETFs) from the strictly anaerobic toluene-degrading species Geobacter metallireducens and Desulfobacula toluolica and the facultatively anaerobic bacterium Aromatoleum aromaticum We determined the X-ray structure of the ETF paralogue involved in toluene metabolism of G. metallireducens, revealing strong overall similarities to previously characterized ETF variants but significantly different structural properties in the hinge regions mediating conformational changes. We also show that all strictly anaerobic toluene degraders utilize one of multiple genome-encoded related ETF paralogues, which constitute a distinct clade of similar sequences in the ETF family, for β-oxidation of benzylsuccinate. In contrast, facultatively anaerobic toluene degraders contain only one ETF species, which is utilized in all β-oxidation pathways. Our phylogenetic analysis of the known sequences of the ETF family suggests that at least 36 different clades can be differentiated, which are defined either by the taxonomic group of the respective host species (e.g., clade P for Proteobacteria) or by functional specialization (e.g., clade T for anaerobic toluene degradation).IMPORTANCE This study documents the involvement of ETF in anaerobic toluene metabolism as the physiological electron acceptor for benzylsuccinyl-CoA dehydrogenase. While toluene-degrading denitrifying proteobacteria use a common ETF species, which is also used for other β-oxidation pathways, obligately anaerobic sulfate- or ferric-iron-reducing bacteria use specialized ETF paralogues for toluene degradation. Based on the structure and sequence conservation of these ETFs, they form a new clade that is only remotely related to the previously characterized members of the ETF family. An exhaustive analysis of the available sequences indicated that the protein family consists of several closely related clades of proven or potential electron-bifurcating ETF species and many deeply branching nonbifurcating clades, which either follow the host phylogeny or are affiliated according to functional criteria.
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Affiliation(s)
| | - Karola Schühle
- Faculty of Biology, Philipps-Universität Marburg, Marburg, Germany
| | - Sebastian Kölzer
- Faculty of Biology, Philipps-Universität Marburg, Marburg, Germany
| | - Patrick Peschke
- Faculty of Chemistry, Philipps-Universität Marburg, Marburg, Germany
- Faculty of Biology, Philipps-Universität Marburg, Marburg, Germany
| | | | - Daniel Kleinsorge
- Faculty of Biology, Philipps-Universität Marburg, Marburg, Germany
- LOEWE Center for Synthetic Microbiology, Philipps-Universität Marburg, Marburg, Germany
| | - Wolfgang Buckel
- Faculty of Biology, Philipps-Universität Marburg, Marburg, Germany
- LOEWE Center for Synthetic Microbiology, Philipps-Universität Marburg, Marburg, Germany
- Max-Planck-Institut für Terrestrische Mikrobiologie, Marburg, Germany
| | - Lars-Oliver Essen
- Faculty of Chemistry, Philipps-Universität Marburg, Marburg, Germany
- LOEWE Center for Synthetic Microbiology, Philipps-Universität Marburg, Marburg, Germany
| | - Johann Heider
- Faculty of Biology, Philipps-Universität Marburg, Marburg, Germany
- LOEWE Center for Synthetic Microbiology, Philipps-Universität Marburg, Marburg, Germany
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12
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Toplak M, Brunner J, Tabib CR, Macheroux P. Closing the gap: yeast electron-transferring flavoprotein links the oxidation of d-lactate and d-α-hydroxyglutarate to energy production via the respiratory chain. FEBS J 2019; 286:3611-3628. [PMID: 31081204 PMCID: PMC6771786 DOI: 10.1111/febs.14924] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Revised: 03/19/2019] [Accepted: 05/10/2019] [Indexed: 01/07/2023]
Abstract
Electron-transferring flavoproteins (ETFs) have been found in all kingdoms of life, mostly assisting in shuttling electrons to the respiratory chain for ATP production. While the human (h) ETF has been studied in great detail, very little is known about the biochemical properties of the homologous protein in the model organism Saccharomyces cerevisiae (yETF). In view of the absence of client dehydrogenases, for example, the acyl-CoA dehydrogenases involved in the β-oxidation of fatty acids, d-lactate dehydrogenase 2 (Dld2) appeared to be the only relevant enzyme that is serviced by yETF for electron transfer to the mitochondrial electron transport chain. However, this hypothesis was never tested experimentally. Here, we report the biochemical properties of yETF and Dld2 as well as the electron transfer reaction between the two proteins. Our study revealed that Dld2 oxidizes d-α-hydroxyglutarate more efficiently than d-lactate exhibiting kcatapp /KMapp values of 1200 ± 300 m-1 ·s-1 and 11 ± 2 m-1 ·s-1 , respectively. As expected, substrate-reduced Dld2 very slowly reacted with oxygen or the artificial electron acceptor 2,6-dichlorophenol indophenol. However, photoreduced Dld2 was rapidly reoxidized by oxygen, suggesting that the reaction products, that is, α-ketoglutarate and pyruvate, 'lock' the reduced enzyme in an unreactive state. Interestingly, however, we could demonstrate that substrate-reduced Dld2 rapidly transfers electrons to yETF. Therefore, we conclude that the formation of a product-reduced Dld2 complex suppresses electron transfer to dioxygen but favors the rapid reduction in yETF, thus preventing the loss of electrons and the generation of reactive oxygen species.
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Affiliation(s)
- Marina Toplak
- Institute of BiochemistryGraz University of TechnologyAustria
| | - Julia Brunner
- Institute of BiochemistryGraz University of TechnologyAustria
| | | | - Peter Macheroux
- Institute of BiochemistryGraz University of TechnologyAustria
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13
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Toplak M, Brunner J, Schmidt J, Macheroux P. Biochemical characterization of human D-2-hydroxyglutarate dehydrogenase and two disease related variants reveals the molecular cause of D-2-hydroxyglutaric aciduria. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2019; 1867:140255. [PMID: 31349060 DOI: 10.1016/j.bbapap.2019.07.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2019] [Revised: 07/12/2019] [Accepted: 07/19/2019] [Indexed: 02/06/2023]
Abstract
D-2-hydroxyglutaric aciduria is a neurometabolic disorder, characterized by the accumulation of D-2-hydroxyglutarate (D-2HG) in human mitochondria. Increased levels of D-2HG are detected in humans exhibiting point mutations in the genes encoding isocitrate dehydrogenase, citrate carrier, the electron transferring flavoprotein (ETF) and its downstream electron acceptor ETF-ubiquinone oxidoreductase or D-2-hydroxyglutarate dehydrogenase (hD2HGDH). However, while the pathogenicity of several amino acid replacements in the former four proteins has been studied extensively, not much is known about the effect of certain point mutations on the biochemical properties of hD2HGDH. Therefore, we recombinantly produced wild type hD2HGDH as well as two recently identified disease-related variants (hD2HGDH-I147S and -V444A) and performed their detailed biochemical characterization. We could show that hD2HGDH is a FAD dependent protein, which is able to catalyze the oxidation of D-2HG and D-lactate to α-ketoglutarate and pyruvate, respectively. The two variants were obtained as apo-proteins and were thus catalytically inactive. The addition of FAD failed to restore enzymatic activity of the variants, indicating that the cofactor binding site is compromised by the single amino acid replacements. Further analyses revealed that both variants form aggregates that are apparently unable to bind the FAD cofactor. Since, D-2-hydroxyglutaric aciduria may also result from a loss of function of either the ETF or its downstream electron acceptor ETF-ubiquinone oxidoreductase, ETF may serve as the cognate electron acceptor of reduced hD2HGDH. Here, we show that hD2HGDH directly reduces recombinant human ETF, thus establishing a metabolic link between the oxidation of D-2-hydroxyglutarate and the mitochondrial electron transport chain.
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Affiliation(s)
- Marina Toplak
- Institute of Biochemistry, Graz University of Technology, Petersgasse 12/2, A-8010 Graz, Austria
| | - Julia Brunner
- Institute of Biochemistry, Graz University of Technology, Petersgasse 12/2, A-8010 Graz, Austria
| | - Julia Schmidt
- Institute of Biochemistry, Graz University of Technology, Petersgasse 12/2, A-8010 Graz, Austria
| | - Peter Macheroux
- Institute of Biochemistry, Graz University of Technology, Petersgasse 12/2, A-8010 Graz, Austria.
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14
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Augustin P, Toplak M, Fuchs K, Gerstmann EC, Prassl R, Winkler A, Macheroux P. Oxidation of the FAD cofactor to the 8-formyl-derivative in human electron-transferring flavoprotein. J Biol Chem 2018; 293:2829-2840. [PMID: 29301933 PMCID: PMC5827430 DOI: 10.1074/jbc.ra117.000846] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Revised: 12/14/2017] [Indexed: 11/06/2022] Open
Abstract
The heterodimeric human (h) electron-transferring flavoprotein (ETF) transfers electrons from at least 13 different flavin dehydrogenases to the mitochondrial respiratory chain through a non-covalently bound FAD cofactor. Here, we describe the discovery of an irreversible and pH-dependent oxidation of the 8α-methyl group to 8-formyl-FAD (8f-FAD), which represents a unique chemical modification of a flavin cofactor in the human flavoproteome. Furthermore, a set of hETF variants revealed that several conserved amino acid residues in the FAD-binding pocket of electron-transferring flavoproteins are required for the conversion to the formyl group. Two of the variants generated in our study, namely αR249C and αT266M, cause glutaric aciduria type II, a severe inherited disease. Both of the variants showed impaired formation of 8f-FAD shedding new light on the potential molecular cause of disease development. Interestingly, the conversion of FAD to 8f-FAD yields a very stable flavin semiquinone that exhibited slightly lower rates of electron transfer in an artificial assay system than hETF containing FAD. In contrast, the formation of 8f-FAD enhanced the affinity to human dimethylglycine dehydrogenase 5-fold, indicating that formation of 8f-FAD modulates the interaction of hETF with client enzymes in the mitochondrial matrix. Thus, we hypothesize that the FAD cofactor bound to hETF is subject to oxidation in the alkaline (pH 8) environment of the mitochondrial matrix, which may modulate electron transport between client dehydrogenases and the respiratory chain. This discovery challenges the current concepts of electron transfer processes in mitochondria.
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Affiliation(s)
- Peter Augustin
- Institute of Biochemistry, Graz University of Technology, Petersgasse 12/II
| | - Marina Toplak
- Institute of Biochemistry, Graz University of Technology, Petersgasse 12/II
| | - Katharina Fuchs
- Institute of Biochemistry, Graz University of Technology, Petersgasse 12/II
| | | | - Ruth Prassl
- Institute of Biophysics, Medical University of Graz, Neue Stiftingtalstrasse 6/IV, 8010 Graz, Austria
| | - Andreas Winkler
- Institute of Biochemistry, Graz University of Technology, Petersgasse 12/II
| | - Peter Macheroux
- Institute of Biochemistry, Graz University of Technology, Petersgasse 12/II.
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15
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Molecular Basis for Converting (2S)-Methylsuccinyl-CoA Dehydrogenase into an Oxidase. Molecules 2017; 23:molecules23010068. [PMID: 29283425 PMCID: PMC6017585 DOI: 10.3390/molecules23010068] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Revised: 12/18/2017] [Accepted: 12/21/2017] [Indexed: 11/17/2022] Open
Abstract
Although flavoenzymes have been studied in detail, the molecular basis of their dioxygen reactivity is only partially understood. The members of the flavin adenosine dinucleotide (FAD)-dependent acyl-CoA dehydrogenase and acyl-CoA oxidase families catalyze similar reactions and share common structural features. However, both enzyme families feature opposing reaction specificities in respect to dioxygen. Dehydrogenases react with electron transfer flavoproteins as terminal electron acceptors and do not show a considerable reactivity with dioxygen, whereas dioxygen serves as a bona fide substrate for oxidases. We recently engineered (2S)-methylsuccinyl-CoA dehydrogenase towards oxidase activity by rational mutagenesis. Here we characterized the (2S)-methylsuccinyl-CoA dehydrogenase wild-type, as well as the engineered (2S)-methylsuccinyl-CoA oxidase, in detail. Using stopped-flow UV-spectroscopy and liquid chromatography-mass spectrometry (LC-MS) based assays, we explain the molecular base for dioxygen reactivity in the engineered oxidase and show that the increased oxidase function of the engineered enzyme comes at a decreased dehydrogenase activity. Our findings add to the common notion that an increased activity for a specific substrate is achieved at the expense of reaction promiscuity and provide guidelines for rational engineering efforts of acyl-CoA dehydrogenases and oxidases.
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16
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Liu Y, Wu X, Hou W, Li P, Sha W, Tian Y. Structure and function of seed storage proteins in faba bean (Vicia faba L.). 3 Biotech 2017; 7:74. [PMID: 28452019 DOI: 10.1007/s13205-017-0691-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 03/10/2017] [Indexed: 02/07/2023] Open
Abstract
The protein subunit is the most important basic unit of protein, and its study can unravel the structure and function of seed storage proteins in faba bean. In this study, we identified six specific protein subunits in Faba bean (cv. Qinghai 13) combining liquid chromatography (LC), liquid chromatography-electronic spray ionization mass (LC-ESI-MS/MS) and bio-information technology. The results suggested a diversity of seed storage proteins in faba bean, and a total of 16 proteins (four GroEL molecular chaperones and 12 plant-specific proteins) were identified from 97-, 96-, 64-, 47-, 42-, and 38-kD-specific protein subunits in faba bean based on the peptide sequence. We also analyzed the composition and abundance of the amino acids, the physicochemical characteristics, secondary structure, three-dimensional structure, transmembrane domain, and possible subcellular localization of these identified proteins in faba bean seed, and finally predicted function and structure. The three-dimensional structures were generated based on homologous modeling, and the protein function was analyzed based on the annotation from the non-redundant protein database (NR database, NCBI) and function analysis of optimal modeling. The objective of this study was to identify the seed storage proteins in faba bean and confirm the structure and function of these proteins. Our results can be useful for the study of protein nutrition and achieve breeding goals for optimal protein quality in faba bean.
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Affiliation(s)
- Yujiao Liu
- State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Qinghai Academy of Agricultural and Forestry Science, Xining, Qinghai, 810016, People's Republic of China.
| | - Xuexia Wu
- State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Qinghai Academy of Agricultural and Forestry Science, Xining, Qinghai, 810016, People's Republic of China
| | - Wanwei Hou
- State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Qinghai Academy of Agricultural and Forestry Science, Xining, Qinghai, 810016, People's Republic of China
| | - Ping Li
- State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Qinghai Academy of Agricultural and Forestry Science, Xining, Qinghai, 810016, People's Republic of China
| | - Weichao Sha
- State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Qinghai Academy of Agricultural and Forestry Science, Xining, Qinghai, 810016, People's Republic of China
| | - Yingying Tian
- State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Qinghai Academy of Agricultural and Forestry Science, Xining, Qinghai, 810016, People's Republic of China
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17
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Berstis L, Beckham GT, Crowley MF. Electronic coupling through natural amino acids. J Chem Phys 2015; 143:225102. [PMID: 26671404 DOI: 10.1063/1.4936588] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Affiliation(s)
- Laura Berstis
- National Renewable Energy Laboratory, National Bioenergy Center, 15013 Denver West Pkwy, Golden, Colorado 80401, USA
| | - Gregg T. Beckham
- National Renewable Energy Laboratory, National Bioenergy Center, 15013 Denver West Pkwy, Golden, Colorado 80401, USA
| | - Michael F. Crowley
- National Renewable Energy Laboratory, National Bioenergy Center, 15013 Denver West Pkwy, Golden, Colorado 80401, USA
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18
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Kinetic and spectral properties of isovaleryl-CoA dehydrogenase and interaction with ligands. Biochimie 2014; 108:108-19. [PMID: 25450250 DOI: 10.1016/j.biochi.2014.11.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Accepted: 11/10/2014] [Indexed: 11/21/2022]
Abstract
Isovaleryl-CoA dehydrogenase (IVD) catalyzes the conversion of isovaleryl-CoA to 3-methylcrotonyl-CoA and the transfer of electrons to the electron transfer flavoprotein (ETF). Recombinant human IVD purifies with bound CoA-persulfide. A modified purification protocol was developed to isolate IVD without bound CoA-persulfide and to protect the protein thiols from oxidation. The CoA-persulfide-free IVD specific activity was 112.5 μmol porcine ETF min(-)(1) mg(-)(1), which was ∼20-fold higher than that of its CoA-persulfide bound form. The Km and catalytic efficiency (kcat/Km) for isovaleryl-CoA were 1.0 μM and 4.3 × 10(6) M(-1) s(-1) per monomer, respectively, and its Km for ETF was 2.0 μM. Anaerobic titration of isovaleryl-CoA into an IVD solution resulted in a stable blue complex with increased absorbance at 310 nm, decreased absorbance at 373 and 447 nm, and the appearance of the charge transfer complex band at 584 nm. The apparent dissociation constant (KDapp) determined spectrally for isovaleryl-CoA was 0.54 μM. Isovaleryl-CoA, acetoacetyl-CoA, methylenecyclopropyl-acetyl-CoA, and ETF induced CD spectral changes at the 250-500 nm region while isobutyryl-CoA did not, suggesting conformational changes occur at the flavin ring that are ligand specific. Replacement of the IVD Trp166 with a Phe did not block IVD interaction with ETF, indicating that its indole ring is not essential for electron transfer to ETF. A twelve amino acid synthetic peptide that matches the sequence of the ETF docking peptide competitively inhibited the enzyme reaction when ETF was used as the electron acceptor with a Ki of 1.5 mM.
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19
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Menon BRK, Fisher K, Rigby SEJ, Scrutton NS, Leys D. A conformational sampling model for radical catalysis in pyridoxal phosphate- and cobalamin-dependent enzymes. J Biol Chem 2014; 289:34161-74. [PMID: 25213862 PMCID: PMC4256349 DOI: 10.1074/jbc.m114.590471] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Cobalamin-dependent enzymes enhance the rate of C–Co bond cleavage by up to ∼1012-fold to generate cob(II)alamin and a transient adenosyl radical. In the case of the pyridoxal 5′-phosphate (PLP) and cobalamin-dependent enzymes lysine 5,6-aminomutase and ornithine 4,5 aminomutase (OAM), it has been proposed that a large scale domain reorientation of the cobalamin-binding domain is linked to radical catalysis. Here, OAM variants were designed to perturb the interface between the cobalamin-binding domain and the PLP-binding TIM barrel domain. Steady-state and single turnover kinetic studies of these variants, combined with pulsed electron-electron double resonance measurements of spin-labeled OAM were used to provide direct evidence for a dynamic interface between the cobalamin and PLP-binding domains. Our data suggest that following ligand binding-induced cleavage of the Lys629-PLP covalent bond, dynamic motion of the cobalamin-binding domain leads to conformational sampling of the available space. This supports radical catalysis through transient formation of a catalytically competent active state. Crucially, it appears that the formation of the state containing both a substrate/product radical and Co(II) does not restrict cobalamin domain motion. A similar conformational sampling mechanism has been proposed to support rapid electron transfer in a number of dynamic redox systems.
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Affiliation(s)
- Binuraj R K Menon
- From the Manchester Institute of Biotechnology, Faculty of Life Sciences, The University of Manchester, Manchester M1 7DN, United Kingdom
| | - Karl Fisher
- From the Manchester Institute of Biotechnology, Faculty of Life Sciences, The University of Manchester, Manchester M1 7DN, United Kingdom
| | - Stephen E J Rigby
- From the Manchester Institute of Biotechnology, Faculty of Life Sciences, The University of Manchester, Manchester M1 7DN, United Kingdom
| | - Nigel S Scrutton
- From the Manchester Institute of Biotechnology, Faculty of Life Sciences, The University of Manchester, Manchester M1 7DN, United Kingdom
| | - David Leys
- From the Manchester Institute of Biotechnology, Faculty of Life Sciences, The University of Manchester, Manchester M1 7DN, United Kingdom
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20
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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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21
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Rodrigues JV, Gomes CM. Mechanism of superoxide and hydrogen peroxide generation by human electron-transfer flavoprotein and pathological variants. Free Radic Biol Med 2012; 53:12-9. [PMID: 22588007 DOI: 10.1016/j.freeradbiomed.2012.04.016] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/14/2012] [Revised: 04/10/2012] [Accepted: 04/12/2012] [Indexed: 11/26/2022]
Abstract
Reactive oxygen species production by mitochondrial enzymes plays a fundamental role both in cellular signaling and in the progression of dysfunctional states. However, sources of reactive oxygen species and the mechanisms by which enzymes produce these reactive species still remain elusive. We characterized the generation of reactive oxygen species by purified human electron-transfer flavoprotein (ETF), a mitochondrial enzyme that has a central role in the metabolism of lipids, amino acids, and choline. The results showed that ETF produces significant amounts of both superoxide and hydrogen peroxide in the presence of its partner enzyme medium-chain acyl-CoA dehydrogenase (MCAD). ETF-mediated production of reactive oxygen species is partially inhibited at high MCAD/ETF ratios, whereas it is enhanced at high ionic strength. Determination of the reduction potentials of ETF showed that thermodynamic properties of the FAD cofactor are changed upon formation of a complex between ETF and MCAD, supporting the notion that protein:protein interactions modulate the reactivity of the protein with dioxygen. Two pathogenic ETF variants were also studied to determine which factors modulate the reactivity toward molecular oxygen and promote reactive oxygen species production. The results obtained show that destabilized conformations and defective protein:protein interactions increase the ability of ETF to generate reactive oxygen species. A possible role for these processes in mitochondrial dysfunction in metabolic disorders of fatty acid β-oxidation is discussed.
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Affiliation(s)
- João V Rodrigues
- Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, 2780-157 Oeiras, Portugal
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22
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Swanson MA, Kathirvelu V, Majtan T, Frerman FE, Eaton GR, Eaton SS. Electron transfer flavoprotein domain II orientation monitored using double electron-electron resonance between an enzymatically reduced, native FAD cofactor, and spin labels. Protein Sci 2011; 20:610-20. [PMID: 21308847 DOI: 10.1002/pro.595] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Human electron transfer flavoprotein (ETF) is a soluble mitochondrial heterodimeric flavoprotein that links fatty acid β-oxidation to the main respiratory chain. The crystal structure of human ETF bound to medium chain acyl-CoA dehydrogenase indicates that the flavin adenine dinucleotide (FAD) domain (αII) is mobile, which permits more rapid electron transfer with donors and acceptors by providing closer access to the flavin and allows ETF to accept electrons from at least 10 different flavoprotein dehydrogenases. Sequence homology is high and low-angle X-ray scattering is identical for Paracoccus denitrificans (P. denitrificans) and human ETF. To characterize the orientations of the αII domain of P. denitrificans ETF, distances between enzymatically reduced FAD and spin labels in the three structural domains were measured by double electron-electron resonance (DEER) at X- and Q-bands. An FAD to spin label distance of 2.8 ± 0.15 nm for the label in the FAD-containing αII domain (A210C) agreed with estimates from the crystal structure (3.0 nm), molecular dynamics simulations (2.7 nm), and rotamer library analysis (2.8 nm). Distances between the reduced FAD and labels in αI (A43C) were between 4.0 and 4.5 ± 0.35 nm and for βIII (A111C) the distance was 4.3 ± 0.15 nm. These values were intermediate between estimates from the crystal structure of P. denitrificans ETF and a homology model based on substrate-bound human ETF. These distances suggest that the αII domain adopts orientations in solution that are intermediate between those which are observed in the crystal structures of free ETF (closed) and ETF bound to a dehydrogenase (open).
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Affiliation(s)
- Michael A Swanson
- Department of Chemistry and Biochemistry, University of Denver, Denver, Colorado 80208, USA
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23
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A polymorphic position in electron transfer flavoprotein modulates kinetic stability as evidenced by thermal stress. FEBS Lett 2011; 585:505-10. [PMID: 21219902 DOI: 10.1016/j.febslet.2011.01.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2010] [Revised: 12/31/2010] [Accepted: 01/03/2011] [Indexed: 10/18/2022]
Abstract
The electron transfer flavoprotein (ETF) is a hub interacting with at least 11 mitochondrial flavoenzymes and linking them to the respiratory chain. Here we report the effect of the ETFα-T/I171 polymorphism on protein conformation and kinetic stability under thermal stress. Although variants have comparable thermodynamic stabilities, kinetically their behavior is rather distinct as ETFα-T171 displays increased susceptibility to cofactor flavin adenine dinucleotide (FAD) loss and enhanced kinetics of inactivation during thermal stress. Mimicking a fever episode yields substantial activity loss. However, the presence of substoichiometric concentrations of GroEL is sufficient to act as an effective buffer against long-term thermal denaturation. Our investigations are compatible with the notion that the ETFα-T171 variant displays an altered conformational landscape that results in reduced protein function under thermal stress.
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Henriques BJ, Bross P, Gomes CM. Mutational hotspots in electron transfer flavoprotein underlie defective folding and function in multiple acyl-CoA dehydrogenase deficiency. Biochim Biophys Acta Mol Basis Dis 2010; 1802:1070-7. [PMID: 20674745 DOI: 10.1016/j.bbadis.2010.07.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2010] [Revised: 07/13/2010] [Accepted: 07/16/2010] [Indexed: 10/19/2022]
Abstract
We have carried out an extensive in silico analysis on 18 disease associated missense mutations found in electron transfer flavoprotein (ETF), and found that mutations fall essentially in two groups, one in which mutations affect protein folding and assembly, and another one in which mutations impair catalytic activity and disrupt interactions with partner dehydrogenases. We have further experimentally analyzed three of these mutations, ETFβ-p.Cys42Arg, ETFβ-p.Asp128Asn and ETFβ-p.Arg191Cys, which have been found in homozygous form in patients and which typify different scenarios in respect to the clinical phenotypes. The ETFβ-p.Cys42Arg mutation, related to a severe form of multiple acyl-CoA dehydrogenase deficiency (MADD), affects directly the AMP binding site and intersubunit contacts and impairs correct protein folding. The two other variations, ETFβ-p.Asp128Asn and ETFβ-p.Arg191Cys, are both associated with mild MADD, but these mutations have a different impact on ETF. Although none affects the overall α/β fold topology as shown by far-UV CD, analysis of the purified proteins shows that both have substantially decreased enzymatic activity and conformational stability. Altogether, this study combines in silico analysis of mutations with experimental data and has allowed establishing structural hotspots within the ETF fold that are useful to provide a rationale for the prediction of effects of mutations in ETF.
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Affiliation(s)
- Bárbara J Henriques
- Instituto Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal
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25
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Tejero J, Hannibal L, Mustovich A, Stuehr DJ. Surface charges and regulation of FMN to heme electron transfer in nitric-oxide synthase. J Biol Chem 2010; 285:27232-27240. [PMID: 20592038 DOI: 10.1074/jbc.m110.138842] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The nitric-oxide synthases (NOS, EC 1.14.13.39) are modular enzymes containing attached flavoprotein and heme (NOSoxy) domains. To generate nitric oxide (NO), the NOS FMN subdomain must interact with the NOSoxy domain to deliver electrons to the heme for O(2) activation during catalysis. The molecular basis and how the interaction is regulated is unclear. We explored the role of eight positively charged residues that create an electropositive patch on NOSoxy in enabling the electron transfer by incorporating mutations that neutralized or reversed their individual charges. Stopped-flow and steady-state experiments revealed that individual charges at Lys(423), Lys(620), and Lys(660) were the most important in enabling heme reduction in nNOS. Charge reversal was more disruptive than neutralization in all cases, and the effects on heme reduction were not due to a weakening in the thermodynamic driving force for heme reduction. Mutant NO synthesis activities displayed a complex pattern that could be simulated by a global model for NOS catalysis. This analysis revealed that the mutations impact the NO synthesis activity only through their effects on heme reduction rates. We conclude that heme reduction and NO synthesis in nNOS is enabled by electrostatic interactions involving Lys(423), Lys(620), and Lys(660), which form a triad of positive charges on the NOSoxy surface. A simulated docking study reveals how electrostatic interactions of this triad can enable an FMN-NOSoxy interaction that is productive for electron transfer.
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Affiliation(s)
- Jesús Tejero
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
| | - Luciana Hannibal
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
| | - Anthony Mustovich
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195
| | - Dennis J Stuehr
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195.
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26
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Gobin-Limballe S, McAndrew RP, Djouadi F, Kim JJ, Bastin J. Compared effects of missense mutations in Very-Long-Chain Acyl-CoA Dehydrogenase deficiency: Combined analysis by structural, functional and pharmacological approaches. Biochim Biophys Acta Mol Basis Dis 2010; 1802:478-84. [PMID: 20060901 DOI: 10.1016/j.bbadis.2010.01.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Revised: 12/21/2009] [Accepted: 01/04/2010] [Indexed: 12/30/2022]
Abstract
Very-Long-Chain Acyl-CoA Dehydrogenase deficiency (VLCADD) is an autosomal recessive disorder considered as one of the more common ss-oxidation defects, possibly associated with neonatal cardiomyopathy, infantile hepatic coma, or adult-onset myopathy. Numerous gene missense mutations have been described in these VLCADD phenotypes, but only few of them have been structurally and functionally analyzed, and the molecular basis of disease variability is still poorly understood. To address this question, we first analyzed fourteen disease-causing amino acid changes using the recently described crystal structure of VLCAD. The predicted effects varied from the replacement of amino acid residues lining the substrate binding cavity, involved in holoenzyme-FAD interactions or in enzyme dimerisation, predicted to have severe functional consequences, up to amino acid substitutions outside key enzyme domains or lying on near enzyme surface, with predicted milder consequences. These data were combined with functional analysis of residual fatty acid oxidation (FAO) and VLCAD protein levels in patient cells harboring these mutations, before and after pharmacological stimulation by bezafibrate. Mutations identified as detrimental to the protein structure in the 3-D model were generally associated to profound FAO and VLCAD protein deficiencies in the patient cells, however, some mutations affecting FAD binding or monomer-monomer interactions allowed a partial response to bezafibrate. On the other hand, bezafibrate restored near-normal FAO rates in some mutations predicted to have milder consequences on enzyme structure. Overall, combination of structural, biochemical, and pharmacological analysis allowed assessment of the relative severity of individual mutations, with possible applications for disease management and therapeutic approach.
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27
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Ilagan RP, Tejero J, Aulak KS, Ray SS, Hemann C, Wang ZQ, Gangoda M, Zweier JL, Stuehr DJ. Regulation of FMN subdomain interactions and function in neuronal nitric oxide synthase. Biochemistry 2009; 48:3864-76. [PMID: 19290671 DOI: 10.1021/bi8021087] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Nitric oxide synthases (NOS) are modular, calmodulin- (CaM-) dependent, flavoheme enzymes that catalyze oxidation of l-arginine to generate nitric oxide (NO) and citrulline. During catalysis, the FMN subdomain cycles between interaction with an NADPH-FAD subdomain to receive electrons and interaction with an oxygenase domain to deliver electrons to the NOS heme. This process can be described by a three-state, two-equilibrium model for the conformation of the FMN subdomain, in which it exists in two distinct bound states (FMN-shielded) and one common unbound state (FMN-deshielded). We studied how each partner subdomain, the FMN redox state, and CaM binding may regulate the conformational equilibria of the FMN module in rat neuronal NOS (nNOS). We utilized four nNOS protein constructs of different subdomain composition, including the isolated FMN subdomain, and determined changes in the conformational state by measuring the degree of FMN shielding by fluorescence, electron paramagnetic resonance, or stopped-flow spectroscopic techniques. Our results suggest the following: (i) The NADPH-FAD subdomain has a far greater capacity to interact with the FMN subdomain than does the oxygenase domain. (ii) CaM binding has no direct effects on the FMN subdomain. (iii) CaM destabilizes interaction of the FMN subdomain with the NADPH-FAD subdomain but does not measurably increase its interaction with the oxygenase domain. Our results imply that a different set point and CaM regulation exists for either conformational equilibrium of the FMN subdomain. This helps to explain the unique electron transfer and catalytic behaviors of nNOS, relative to other dual-flavin enzymes.
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Affiliation(s)
- Robielyn P Ilagan
- Department of Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio 44195, USA
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28
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Burgess SG, Messiha HL, Katona G, Rigby SEJ, Leys D, Scrutton NS. Probing the dynamic interface between trimethylamine dehydrogenase (TMADH) and electron transferring flavoprotein (ETF) in the TMADH-2ETF complex: role of the Arg-alpha237 (ETF) and Tyr-442 (TMADH) residue pair. Biochemistry 2008; 47:5168-81. [PMID: 18407658 DOI: 10.1021/bi800127d] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We have used multiple solution state techniques and crystallographic analysis to investigate the importance of a putative transient interaction formed between Arg-alpha237 in electron transferring flavoprotein (ETF) and Tyr-442 in trimethylamine dehydrogenase (TMADH) in complex assembly, electron transfer, and structural imprinting of ETF by TMADH. We have isolated four mutant forms of ETF altered in the identity of the residue at position 237 (alphaR237A, alphaR237K, alphaR237C, and alphaR237E) and with each form studied electron transfer from TMADH to ETF, investigated the reduction potentials of the bound ETF cofactor, and analyzed complex formation. We show that mutation of Arg-alpha237 substantially destabilizes the semiquinone couple of the bound FAD and impedes electron transfer from TMADH to ETF. Crystallographic structures of the mutant ETF proteins indicate that mutation does not perturb the overall structure of ETF, but leads to disruption of an electrostatic network at an ETF domain boundary that likely affects the dynamic properties of ETF in the crystal and in solution. We show that Arg-alpha237 is required for TMADH to structurally imprint the as-purified semiquinone form of wild-type ETF and that the ability of TMADH to facilitate this structural reorganization is lost following (i) redox cycling of ETF, or simple conversion to the oxidized form, and (ii) mutagenesis of Arg-alpha237. We discuss this result in light of recent apparent conflict in the literature relating to the structural imprinting of wild-type ETF. Our studies support a mechanism of electron transfer by conformational sampling as advanced from our previous analysis of the crystal structure of the TMADH-2ETF complex [Leys, D. , Basran, J. , Sutcliffe, M. J., and Scrutton, N. S. (2003) Nature Struct. Biol. 10, 219-225] and point to a key role for the Tyr-442 (TMADH) and Arg-alpha237 (ETF) residue pair in transiently stabilizing productive electron transfer configurations. Our work also points to the importance of Arg-alpha237 in controlling the thermodynamics of electron transfer, the dynamics of ETF, and the protection of reducing equivalents following disassembly of the TMADH-2ETF complex.
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Affiliation(s)
- Selena G Burgess
- Department of Biochemistry, University of Leicester, Leicester LE1 9HN, UK
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29
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Brizio C, Brandsch R, Douka M, Wait R, Barile M. The purified recombinant precursor of rat mitochondrial dimethylglycine dehydrogenase binds FAD via an autocatalytic reaction. Int J Biol Macromol 2008; 42:455-62. [PMID: 18423846 DOI: 10.1016/j.ijbiomac.2008.03.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2007] [Revised: 02/29/2008] [Accepted: 03/03/2008] [Indexed: 11/15/2022]
Abstract
The precursor of the rat mitochondrial flavoenzyme dimethylglycine dehydrogenase (Me(2)GlyDH) has been produced in Escherichia coli as a C-terminally 6-His-tagged fusion protein, purified by one-step affinity chromatography and identified by ESI-MS/MS. It was correctly processed into its mature form upon incubation with solubilized rat liver mitoplasts. The purified precursor was mainly in its apo-form as demonstrated by immunological and fluorimetric detection of covalently bound flavin adenine dinucleotide (FAD). Results described here definitively demonstrate that: (i) covalent attachment of FAD to Me(2)GlyDH apoenzyme can proceed in vitro autocatalytically, without third reactants; (ii) the removal of mitochondrial presequence by mitochondrial processing peptidase is not required for covalent autoflavinylation.
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Affiliation(s)
- Carmen Brizio
- Dipartimento di Biochimica e Biologia Molecolare E. Quagliariello, Università degli Studi di Bari, Via Orabona 4, 70126 Bari, Italy
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30
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Sato K, Nishina Y, Shiga K, Tanaka F. Isomers in the excited state of electron-transferring flavoprotein from Megasphaera elsdenii: spectral resolution from the time-resolved fluorescence spectra. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2008; 90:134-40. [PMID: 18234505 DOI: 10.1016/j.jphotobiol.2007.12.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2007] [Revised: 11/24/2007] [Accepted: 12/15/2007] [Indexed: 10/22/2022]
Abstract
Electron-transferring flavoprotein (Holo-ETF) from Megasphaera elsdenii contains two FAD's, one of which easily dissociates to form Iso-ETF (contains one FAD). Time-resolved fluorescence of FAD in Iso-ETF, and Holo-ETF were measured at 5 degrees C and 25 degrees C. Wavelength-dependent fluorescence decays of the both ETF at 5 degrees C and 25 degrees C were analyzed to resolve them into two independent spectra. It was found that Iso-ETF displayed two spectra with lifetime of 0.605 ns (emission peak, 508 nm) and with lifetime of 1.70 ns (emission peak, 540 nm) at 5 degrees C, and with lifetime of 0.693 ns (emission peak, 508 nm) and with lifetime of 2.75 ns (emission peak, 540 nm) at 25 degrees C. Holo-ETF displayed two spectra with lifetime of 0.739 ns (emission peak, 508 nm) and with lifetime of 2.06 ns (emission peak, 545 nm) at 5 degrees C, and with lifetime of 0.711 ns (emission peak, 527 nm) and with lifetime of 3.08 ns (emission peak, 540 nm) at 25 degrees C. Thus fluorescence lifetimes of every spectrum increased upon elevating temperature. Emission peaks Iso-ETF did not change much upon elevating temperature. Activation enthalpy changes, activation entropy changes and activation Gibbs energy changes of quenching rates all displayed negative. Two emission species in the both ETF may be hydrogen-bonding isomers, because isoalloxazine ring of FAD contains four hydrogen acceptors and one donor.
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Affiliation(s)
- Kyosuke Sato
- Department of Molecular Physiology, Graduate School of Medical Sciences, Kumamoto University, Honjo 1-1-1, Kumamoto 860-8556, Japan
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31
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Toogood HS, Leys D, Scrutton NS. Dynamics driving function − new insights from electron transferring flavoproteins and partner complexes. FEBS J 2007; 274:5481-504. [DOI: 10.1111/j.1742-4658.2007.06107.x] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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32
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Wolthers KR, Scrutton NS. Protein interactions in the human methionine synthase-methionine synthase reductase complex and implications for the mechanism of enzyme reactivation. Biochemistry 2007; 46:6696-709. [PMID: 17477549 DOI: 10.1021/bi700339v] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Methionine synthase (MS) is a cobalamin-dependent enzyme. It transfers a methyl group from methyltetrahydrofolate to homocysteine forming methionine and tetrahydrofolate. On the basis of sequence similarity with Escherichia coli cobalamin-dependent MS (MetH), human MS comprises four discrete functional modules that bind from the N- to C-terminus, respectively, homocysteine, methyltetrahydrofolate, cobalamin, and S-adenosylmethionine (AdoMet). The C-terminal activation domain also interacts with methionine synthase reductase (MSR), a NADPH-dependent diflavin oxidoreductase required for the reductive regeneration of catalytically inert cob(II)alamin (which is formed every 200-1000 catalytic cycles of MS) to cob(I)alamin. We have investigated complex formation between the (i) MS activation domain and MSR and (ii) MS activation domain and the isolated FMN-binding domain of MSR. We show that the MS activation domain interacts directly with the FMN-binding domain of MSR. Binding is weakened at high ionic strength, emphasizing the importance of electrostatic interactions at the protein-protein interface. Mutagenesis of conserved lysine residues (Lys1071 and Lys987) in the human activation domain weakens this protein interaction. Chemical cross-linking demonstrates complex formation mediated by acidic residues (FMN-binding domain) and basic residues (activation domain). The activation domain and isolated FMN-domain form a 1:1 complex, but a 1:2 complex is formed with activation domain and MSR. The midpoint reduction potentials of the FAD and FMN cofactors of MSR are not perturbed significantly on forming this complex, implying that electron transfer to cob(II)alamin is endergonic. The kinetics of electron transfer in MSR and the MSR-activation domain complex are similar. Our studies indicate (i) conserved binding determinants, but differences in protein stoichiometry, between human MS and bacterial MetH in complex formation with redox partners; (ii) a substantial endergonic barrier to electron transfer in the reactivation complex; and (iii) a lack of control on the thermodynamics and kinetics of electron transfer in MSR exerted by complex formation with activation domain. The structural and functional consequences of complex formation are discussed in light of the known crystal structure of human activation domain and the inferred conformational heterogeneity of the multidomain MSR-MS complex.
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Affiliation(s)
- Kirsten R Wolthers
- Faculty of Life Sciences, Manchester Interdisciplinary Biocentre, University of Manchester, 131 Princess Street, Manchester M1 7DN, United Kingdom
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