1
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Dolińska MM, Kirwan AJ, Megarity CF. Retuning the potential of the electrochemical leaf. Faraday Discuss 2024. [PMID: 38848142 DOI: 10.1039/d4fd00020j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2024]
Abstract
The electrochemical leaf enables the electrification and control of multi-enzyme cascades by exploiting two discoveries: (i) the ability to electrify the photosynthetic enzyme ferredoxin NADP+ reductase (FNR), driving it to catalyse the interconversion of NADP+/NADPH whilst it is entrapped in a highly porous, metal oxide electrode, and (ii) the evidence that additional enzymes can be co-entrapped in the electrode pores where, through one NADP(H)-dependent enzyme, extended cascades can be driven by electrical connection to FNR, via NADP(H) recycling. By changing a critical active-site tyrosine to serine, FNR's exclusivity for NADP(H) is swapped for unphosphorylated NAD(H). Here we present an electrochemical study of this variant FNR, and show that in addition to the intended inversion of cofactor preference, this change to the active site has altered FNR's tuning of the flavin reduction potential, making it less reductive. Exploiting the ability to monitor the variant's activity with NADP(H) as a function of potential has revealed a trapped intermediate state, relieved only by applying a negative overpotential, which allows catalysis to proceed. Inhibition by NADP+ (very tightly bound) with respect to NAD(H) turnover was also revealed and interestingly, this inhibition changes depending on the applied potential. These findings are of critical importance for future exploitation of the electrochemical leaf.
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Affiliation(s)
- Marta M Dolińska
- School of Chemistry, Manchester Institute of Biotechnology, University of Manchester, 131 Princess Street, Manchester M1 7DN, UK.
| | - Adam J Kirwan
- School of Chemistry, Manchester Institute of Biotechnology, University of Manchester, 131 Princess Street, Manchester M1 7DN, UK.
| | - Clare F Megarity
- School of Chemistry, Manchester Institute of Biotechnology, University of Manchester, 131 Princess Street, Manchester M1 7DN, UK.
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2
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Silvestri G, Arrigoni F, Persico F, Bertini L, Zampella G, De Gioia L, Vertemara J. Assessing the Performance of Non-Equilibrium Thermodynamic Integration in Flavodoxin Redox Potential Estimation. Molecules 2023; 28:6016. [PMID: 37630271 PMCID: PMC10459689 DOI: 10.3390/molecules28166016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2023] [Revised: 08/07/2023] [Accepted: 08/09/2023] [Indexed: 08/27/2023] Open
Abstract
Flavodoxins are enzymes that contain the redox-active flavin mononucleotide (FMN) cofactor and play a crucial role in numerous biological processes, including energy conversion and electron transfer. Since the redox characteristics of flavodoxins are significantly impacted by the molecular environment of the FMN cofactor, the evaluation of the interplay between the redox properties of the flavin cofactor and its molecular surroundings in flavoproteins is a critical area of investigation for both fundamental research and technological advancements, as the electrochemical tuning of flavoproteins is necessary for optimal interaction with redox acceptor or donor molecules. In order to facilitate the rational design of biomolecular devices, it is imperative to have access to computational tools that can accurately predict the redox potential of both natural and artificial flavoproteins. In this study, we have investigated the feasibility of using non-equilibrium thermodynamic integration protocols to reliably predict the redox potential of flavodoxins. Using as a test set the wild-type flavodoxin from Clostridium Beijerinckii and eight experimentally characterized single-point mutants, we have computed their redox potential. Our results show that 75% (6 out of 8) of the calculated reaction free energies are within 1 kcal/mol of the experimental values, and none exceed an error of 2 kcal/mol, confirming that non-equilibrium thermodynamic integration is a trustworthy tool for the quantitative estimation of the redox potential of this biologically and technologically significant class of enzymes.
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Affiliation(s)
| | | | | | | | | | - Luca De Gioia
- Department of Biotechnology and Biosciences BtBs, University of Milano-Bicocca, Piazza dell’Ateneo Nuovo 1, 20126 Milan, Italy
| | - Jacopo Vertemara
- Department of Biotechnology and Biosciences BtBs, University of Milano-Bicocca, Piazza dell’Ateneo Nuovo 1, 20126 Milan, Italy
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3
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Galuzzi BG, Mirarchi A, Viganò EL, De Gioia L, Damiani C, Arrigoni F. Machine Learning for Efficient Prediction of Protein Redox Potential: The Flavoproteins Case. J Chem Inf Model 2022; 62:4748-4759. [PMID: 36126254 PMCID: PMC9554915 DOI: 10.1021/acs.jcim.2c00858] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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Determining the redox
potentials of protein cofactors
and how they
are influenced by their molecular neighborhoods is essential for basic
research and many biotechnological applications, from biosensors and
biocatalysis to bioremediation and bioelectronics. The laborious determination
of redox potential with current experimental technologies pushes forward
the need for computational approaches that can reliably predict it.
Although current computational approaches based on quantum and molecular
mechanics are accurate, their large computational costs hinder their
usage. In this work, we explored the possibility of using more efficient
QSPR models based on machine learning (ML) for the prediction of protein
redox potential, as an alternative to classical approaches. As a proof
of concept, we focused on flavoproteins, one of the most important
families of enzymes directly involved in redox processes. To train
and test different ML models, we retrieved a dataset of flavoproteins
with a known midpoint redox potential (Em) and 3D structure. The features of interest, accounting for both
short- and long-range effects of the protein matrix on the flavin
cofactor, have been automatically extracted from each protein PDB
file. Our best ML model (XGB) has a performance error below 1 kcal/mol
(∼36 mV), comparing favorably to more sophisticated computational
approaches. We also provided indications on the features that mostly
affect the Em value, and when possible,
we rationalized them on the basis of previous studies.
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Affiliation(s)
- Bruno Giovanni Galuzzi
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy.,SYSBIO Centre of Systems Biology/ISBE.IT, Piazza della Scienza 2, 20126, Milan, Italy
| | - Antonio Mirarchi
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy
| | - Edoardo Luca Viganò
- Istituto di Ricerche Farmacologiche Mario Negri, Via Mario Negri 2, 20156 Milan, Italy
| | - Luca De Gioia
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy
| | - Chiara Damiani
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy.,SYSBIO Centre of Systems Biology/ISBE.IT, Piazza della Scienza 2, 20126, Milan, Italy
| | - Federica Arrigoni
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milan, Italy
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4
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Gudim I, Lofstad M, van Beek W, Hersleth HP. High-resolution crystal structures reveal a mixture of conformers of the Gly61-Asp62 peptide bond in an oxidized flavodoxin from Bacillus cereus. Protein Sci 2019; 27:1439-1449. [PMID: 29722453 PMCID: PMC6153408 DOI: 10.1002/pro.3436] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Revised: 04/27/2018] [Accepted: 04/27/2018] [Indexed: 02/03/2023]
Abstract
Flavodoxins (Flds) are small proteins that shuttle electrons in a range of reactions in microorganisms. Flds contain a redox‐active cofactor, a flavin mononucleotide (FMN), and it is well established that when Flds are reduced by one electron, a peptide bond close to the FMN isoalloxazine ring flips to form a new hydrogen bond with the FMN N5H, stabilizing the one‐electron reduced state. Here, we present high‐resolution crystal structures of Flavodoxin 1 from Bacillus cereus in both the oxidized (ox) and one‐electron reduced (semiquinone, sq) state. We observe a mixture of conformers in the oxidized state; a 50:50 distribution between the established oxidized conformation where the peptide bond is pointing away from the flavin, and a conformation where the peptide bond is pointing toward the flavin, approximating the conformation in the semiquinone state. We use single‐crystal spectroscopy to demonstrate that the mixture of conformers is not caused by radiation damage to the crystal. This is the first time that such a mixture of conformers is reported in a wild‐type Fld. We therefore carried out a survey of published Fld structures, which show that several proteins have a pronounced conformational flexibility of this peptide bond. The degree of flexibility seems to be modulated by the presence, or absence, of stabilizing interactions between the peptide bond carbonyl and its surrounding amino acids. We hypothesize that the degree of conformational flexibility will affect the Fld ox/sq redox potential.
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Affiliation(s)
- Ingvild Gudim
- Department of Biosciences, Section for Biochemistry and Molecular Biology, Department of Biosciences should be before Section for Biochemistry and Molecular Biology, University of Oslo, Oslo, Norway
| | - Marie Lofstad
- Department of Biosciences, Section for Biochemistry and Molecular Biology, Department of Biosciences should be before Section for Biochemistry and Molecular Biology, University of Oslo, Oslo, Norway
| | - Wouter van Beek
- Swiss-Norwegian Beam Lines, European Synchrotron Radiation Facility, Grenoble, France
| | - Hans-Petter Hersleth
- Department of Biosciences, Section for Biochemistry and Molecular Biology, Department of Biosciences should be before Section for Biochemistry and Molecular Biology, University of Oslo, Oslo, Norway.,Department of Chemistry, Section for Chemical Life Sciences, University of Oslo, Oslo, Norway
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5
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Ye Q, Hu Y, Jin C. Conformational dynamics of Escherichia coli flavodoxins in apo- and holo-states by solution NMR spectroscopy. PLoS One 2014; 9:e103936. [PMID: 25093851 PMCID: PMC4122359 DOI: 10.1371/journal.pone.0103936] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2014] [Accepted: 07/08/2014] [Indexed: 11/23/2022] Open
Abstract
Flavodoxins are a family of small FMN-binding proteins that commonly exist in prokaryotes. They utilize a non-covalently bound FMN molecule to act as the redox center during the electron transfer processes in various important biological pathways. Although extensive investigations were performed, detailed molecular mechanisms of cofactor binding and electron transfer remain elusive. Herein we report the solution NMR studies on Escherichia coli flavodoxins FldA and YqcA, belonging to the long-chain and short-chain flavodoxin subfamilies respectively. Our structural studies demonstrate that both proteins show the typical flavodoxin fold, with extensive conformational exchanges observed near the FMN binding pocket in their apo-forms. Cofactor binding significantly stabilizes both proteins as revealed by the extension of secondary structures in the holo-forms, and the overall rigidity shown by the backbone dynamics data. However, the 50 s loops of both proteins in the holo-form still show conformational exchanges on the µs-ms timescales, which appears to be a common feature in the flavodoxin family, and might play an important role in structural fine-tuning during the electron transfer reactions.
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Affiliation(s)
- Qian Ye
- Beijing Nuclear Magnetic Resonance Center, Peking University, Beijing, China
- College of Life Sciences, Peking University, Beijing, China
| | - Yunfei Hu
- Beijing Nuclear Magnetic Resonance Center, Peking University, Beijing, China
- College of Chemistry and Molecular Engineering, Peking University, Beijing, China
- * E-mail: (YF); (CJ)
| | - Changwen Jin
- Beijing Nuclear Magnetic Resonance Center, Peking University, Beijing, China
- College of Life Sciences, Peking University, Beijing, China
- College of Chemistry and Molecular Engineering, Peking University, Beijing, China
- Beijing National Laboratory for Molecular Sciences, Peking University, Beijing, China
- * E-mail: (YF); (CJ)
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6
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Flavodoxin cofactor binding induces structural changes that are required for protein-protein interactions with NADP(+) oxidoreductase and pyruvate formate-lyase activating enzyme. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2013; 1834:2512-9. [PMID: 24016774 DOI: 10.1016/j.bbapap.2013.08.014] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2013] [Revised: 08/27/2013] [Accepted: 08/30/2013] [Indexed: 11/23/2022]
Abstract
Flavodoxin (Fld) conformational changes, thermal stability, and cofactor binding were studied using circular dichroism (CD), isothermal titration calorimetry (ITC), and limited proteolysis. Thermodynamics of apo and holo-Fld folding were examined to discern the features of this important electron transfer protein and to provide data on apo-Fld. With the exception of fluorescence and UV-vis binding experiments with its cofactor flavin mononucleotide (FMN), apo-Fld is almost completely uncharacterized in Escherichia coli. Fld is more structured when the FMN cofactor is bound; the association is tight and driven by enthalpy of binding. Surface plasmon resonance binding experiments were carried out under anaerobic conditions for both apo- and holo-Fld and demonstrate the importance of structure and conformation for the interaction with binding partners. Holo-Fld is capable of associating with NADP(+)-dependent flavodoxin oxidoreductase (FNR) and pyruvate formate-lyase activating enzyme (PFL-AE) whereas there is no detectable interaction between apo-Fld and either protein. Limited proteolysis experiments were analyzed by LC-MS to identify the regions in Fld that are involved in conformation changes upon cofactor binding. Docking software was used to model the Fld/PFL-AE complex to understand the interactions between these two proteins and gain insight into electron transfer reactions from Fld to PFL-AE.
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7
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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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8
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Goñi G, Herguedas B, Hervás M, Peregrina JR, De la Rosa MA, Gómez-Moreno C, Navarro JA, Hermoso JA, Martínez-Júlvez M, Medina M. Flavodoxin: a compromise between efficiency and versatility in the electron transfer from Photosystem I to Ferredoxin-NADP(+) reductase. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2008; 1787:144-54. [PMID: 19150326 DOI: 10.1016/j.bbabio.2008.12.006] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2008] [Revised: 12/01/2008] [Accepted: 12/09/2008] [Indexed: 11/18/2022]
Abstract
Under iron-deficient conditions Flavodoxin (Fld) replaces Ferredoxin in Anabaena as electron carrier from Photosystem I (PSI) to Ferredoxin-NADP(+) reductase (FNR). Several residues modulate the Fld interaction with FNR and PSI, but no one appears as specifically critical for efficient electron transfer (ET). Fld shows a strong dipole moment, with its negative end directed towards the flavin ring. The role of this dipole moment in the processes of interaction and ET with positively charged surfaces exhibited by PSI and FNR has been analysed by introducing single and multiple charge reversal mutations on the Fld surface. Our data confirm that in this system interactions do not rely on a precise complementary surface of the reacting molecules. In fact, they indicate that the initial orientation driven by the alignment of dipole moment of the Fld molecule with that of the partner contributes to the formation of a bunch of alternative binding modes competent for the efficient ET reaction. Additionally, the fact that Fld uses different interaction surfaces to dock to PSI and to FNR is confirmed.
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Affiliation(s)
- Guillermina Goñi
- Departamento de Bioquímica y Biología Molecular y Celular, Universidad de Zaragoza, 50009-Zaragoza, Spain
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9
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Ishikita H. Redox potential difference between Desulfovibrio vulgaris and Clostridium beijerinckii flavodoxins. Biochemistry 2008; 47:4394-402. [PMID: 18355044 DOI: 10.1021/bi702151k] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The redox potential of the flavin mononucleotide (FMN) hydroquinones for one-electron reduction in the Desulfovibrio vulgaris ( D. vulgaris) flavodoxin ( E sq/hq for FMNH (*)/FMNH (-)) was calculated using the crystal structure of the relevant hydroquinone form and compared to the results of the Clostridium beijerinckii ( C. beijerinckii) flavodoxin. In D. vulgaris and C. beijerinckii flavodoxins, the protein side chain causes significant downshifts of 170 and 240 mV in E sq/hq, respectively. In the C. beijerinckii flavodoxin, the E sq/hq downshift because of the protein side chain is essentially compensated by the counter influence of the protein backbone ( E sq/hq upshift of 260 mV). However, in the D. vulgaris flavodoxin, the corresponding protein backbone influence on E sq/hq is significantly small, i.e., less than half of that in the C. beijerinckii flavodoxin. In particular, there is a significant difference in the influence of the protein backbone of the so-called 60s loop region between the two flavodoxins. The E sq/hq difference can be best explained by the lower compensation of the side chain influence by the backbone influence in the D. vulgaris flavodoxin than in the C. beijerinckii flavodoxin.
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Affiliation(s)
- Hiroshi Ishikita
- Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA.
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10
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Frago S, Goñi G, Herguedas B, Peregrina JR, Serrano A, Perez-Dorado I, Molina R, Gómez-Moreno C, Hermoso JA, Martínez-Júlvez M, Mayhew SG, Medina M. Tuning of the FMN binding and oxido-reduction properties by neighboring side chains in Anabaena flavodoxin. Arch Biochem Biophys 2007; 467:206-17. [PMID: 17904516 DOI: 10.1016/j.abb.2007.08.024] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2007] [Revised: 08/13/2007] [Accepted: 08/13/2007] [Indexed: 11/23/2022]
Abstract
Contribution of three regions (phosphate-binding, 50's and 90's loops) of Anabaena apoflavodoxin to FMN binding and reduction potential was studied. Thr12 and Glu16 did not influence FMN redox properties, but Thr12 played a role in FMN binding. Replacement of Trp57 with Glu, Lys or Arg moderately shifted E(ox/sq) and E(sq/hq) and altered the energetic of the FMN redox states binding profile. Our data indicate that the side chain of position 57 does not modulate E(ox/sq) by aromatic stacking or solvent exclusion, but rather by influencing the relative strength of the H-bond between the N(5) of the flavin and the Asn58-Ile59 bond. A correlation was observed between the isoalloxazine increase in solvent accessibility and less negative E(sq/hq). Moreover, E(sq/hq) became less negative as positively charged residues were added near to the isoalloxazine. Ile59 and Ile92 were simultaneously mutated to Ala or Glu. These mutations impaired FMN binding, while shifting E(sq/hq) to less negative values and E(ox/sq) to more negative. These effects are discussed on the bases of the X-ray structures of some of the Fld mutants, suggesting that in Anabaena Fld the structural control of both electron transfer steps is much more subtle than in other Flds.
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Affiliation(s)
- Susana Frago
- Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias, Universidad de Zaragoza, 50009-Zaragoza, Spain
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11
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Hu Y, Li Y, Zhang X, Guo X, Xia B, Jin C. Solution structures and backbone dynamics of a flavodoxin MioC from Escherichia coli in both Apo- and Holo-forms: implications for cofactor binding and electron transfer. J Biol Chem 2006; 281:35454-66. [PMID: 16963438 DOI: 10.1074/jbc.m607336200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Flavodoxins play central roles in the electron transfer involving various biological processes in microorganisms. The mioC gene of Escherichia coli encodes a 16-kDa flavodoxin and locates next to the chromosomal replication initiation origin (oriC). Extensive researches have been carried out to investigate the relationship between mioC transcription and replication initiation. Recently, the MioC protein was proposed to be essential for the biotin synthase activity in vitro. Nevertheless, the exact role of MioC in biotin synthesis and its physiological function in vivo remain elusive. In order to understand the molecular basis of the biological functions of MioC and the cofactor-binding mechanisms of flavodoxins, we have determined the solution structures of both the apo- and holo-forms of E. coli MioC protein at high resolution by nuclear magnetic resonance spectroscopy. The overall structures of both forms consist of an alpha/beta sandwich, which highly resembles the classical flavodoxin fold. However, significant diversities are observed between the two forms, especially the stabilization of the FMN-binding loops and the notable extension of secondary structures upon FMN binding. Structural comparison reveals fewer negative charged and aromatic residues near the FMN-binding site of MioC, as compared with that of flavodoxin 1 from E. coli, which may affect both the redox potentials and the redox partner interactions. Furthermore, the backbone dynamics studies reveal the conformational flexibility at different time scales for both apo- and holo-forms of MioC, which may play important roles for cofactor binding and electron transfer.
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Affiliation(s)
- Yunfei Hu
- Beijing Nuclear Magnetic Resonance Center, College of Life Sciences, Peking University, Beijing 100871, China
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12
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Campos LA, Sancho J. Native-specific stabilization of flavodoxin by the FMN cofactor: structural and thermodynamical explanation. Proteins 2006; 63:581-94. [PMID: 16444751 DOI: 10.1002/prot.20855] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Flavodoxins are useful models to investigate protein/cofactor interactions. The binding energy of the apoflavodoxin-FMN complex is high and therefore the holoflavodoxin is expected to be more stable than the apoprotein. This expectation has been challenged by reports on the stability of Desulfovibrio desulfuricans flavodoxin indicating that FMN binds to the unfolded polypeptide with similar affinity as to the native state, thus causing no net effect on protein stability. In previous work, we have analyzed in detail the stability of the apoflavodoxin from Anabaena PCC 7119 and the energetics of its functional complex with FMN. Here, we use the Anabaena holoprotein to directly investigate the contribution of the bound cofactor to protein stability through a detailed analysis of the chemical and thermal denaturation equilibria. Our data clearly shows that FMN binding largely stabilizes the protein towards both chemical and thermal denaturation, and that the stabilization observed at 25 degrees C in low ionic strength conditions is precisely the one expected if full release of the cofactor takes place upon flavodoxin unfolding. On the other hand, the binding of FMN to the native polypeptide is shown to simplify the thermal unfolding so that, while apoflavodoxin follows a three-state mechanism, the holoprotein unfolds in a two-state fashion. Comparison of the X-ray structure of native apoflavodoxin with the phi-structure of the thermal intermediate indicates that the increase in cooperativity driven by the cofactor originates in its preferential binding to the native state, which is a consequence of the disorganization in the intermediate of the FMN binding loops and of an adjacent longer loop.
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Affiliation(s)
- L A Campos
- Departamento de Bioquímica y Biología Molecular y Celular, Facultad de Ciencias & Biocomputation and Complex Systems Physics Institute, Universidad de Zaragoza, Zaragoza, Spain
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13
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Hanley SC, Ost TWB, Daff S. The unusual redox properties of flavocytochrome P450 BM3 flavodoxin domain. Biochem Biophys Res Commun 2004; 325:1418-23. [PMID: 15555585 DOI: 10.1016/j.bbrc.2004.10.189] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2004] [Indexed: 11/26/2022]
Abstract
Flavocytochrome P450 BM3 FMN domain is unique among the family of flavodoxins and homologues, in not forming a stable neutral blue FMN semiquinone radical. Anaerobic, one-electron reduction of the isolated domain over the pH 7-9.5 range showed that it forms an anionic red semiquinone that disproportionates slowly (0.014s(-1) at pH 7). The rate of disproportionation decreased at higher pH, indicating that protonation of the anionic semiquinone is an important feature of the mechanism. The reduction potential for the oxidised-semiquinone couple was determined to be -240mV and was largely independent of pH. The semiquinone appears, therefore, to be kinetically trapped by a slow protonation event, enabling it to act as a low-potential electron donor to the P450 heme.
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Affiliation(s)
- Sinead C Hanley
- School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, UK
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