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Javier Sancho - One of the best experts on this subject based on the ideXlab platform.
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Flavodoxins as Novel Therapeutic Targets Against Helicobacter pylori and Other Gastric Pathogens
International journal of molecular sciences, 2020Co-Authors: Sandra Salillas, Javier SanchoAbstract:Flavodoxins are small soluble electron transfer proteins widely present in bacteria and absent in vertebrates. Flavodoxins participate in different metabolic pathways and, in some bacteria, they have been shown to be essential proteins representing promising therapeutic targets to fight bacterial infections. Using purified Flavodoxin and chemical libraries, leads can be identified that block Flavodoxin function and act as bactericidal molecules, as it has been demonstrated for Helicobacter pylori (Hp), the most prevalent human gastric pathogen. Increasing antimicrobial resistance by this bacterium has led current therapies to lose effectiveness, so alternative treatments are urgently required. Here, we summarize, with a focus on Flavodoxin, opportunities for pharmacological intervention offered by the potential protein targets described for this bacterium and provide information on other gastrointestinal pathogens and also on bacteria from the gut microbiota that contain Flavodoxin. The process of discovery and development of novel antimicrobials specific for Hp Flavodoxin that is being carried out in our group is explained, as it can be extrapolated to the discovery of inhibitors specific for other gastric pathogens. The high specificity for Hp of the antimicrobials developed may be of help to reduce damage to the gut microbiota and to slow down the development of resistant Hp mutants.
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streptococcus pneumoniae tigr4 Flavodoxin structural and biophysical characterization of a novel drug target
PLOS ONE, 2016Co-Authors: Angela Rodriguezcardenas, Adriana L Rojas, Maria Condegimenez, Adrian Velazquezcampoy, Ramon Hurtadoguerrero, Javier SanchoAbstract:Streptococcus pneumoniae (Sp) strain TIGR4 is a virulent, encapsulated serotype that causes bacteremia, otitis media, meningitis and pneumonia. Increased bacterial resistance and limited efficacy of the available vaccine to some serotypes complicate the treatment of diseases associated to this microorganism. Flavodoxins are bacterial proteins involved in several important metabolic pathways. The Sp Flavodoxin (Spfld) gene was recently reported to be essential for the establishment of meningitis in a rat model, which makes SpFld a potential drug target. To facilitate future pharmacological studies, we have cloned and expressed SpFld in E. coli and we have performed an extensive structural and biochemical characterization of both the apo form and its active complex with the FMN cofactor. SpFld is a short-chain Flavodoxin containing 146 residues. Unlike the well-characterized long-chain apoFlavodoxins, the Sp apoprotein displays a simple two-state thermal unfolding equilibrium and binds FMN with moderate affinity. The X-ray structures of the apo and holo forms of SpFld differ at the FMN binding site, where substantial rearrangement of residues at the 91–100 loop occurs to permit cofactor binding. This work will set up the basis for future studies aiming at discovering new potential drugs to treat S. pneumoniae diseases through the inhibition of SpFld.
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native specific stabilization of Flavodoxin by the fmn cofactor structural and thermodynamical explanation
Proteins, 2006Co-Authors: Luis A Campos, Javier SanchoAbstract: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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Towards a new therapeutic target: Helicobacter pylori Flavodoxin.
Biophysical Chemistry, 2005Co-Authors: Nunilo Cremades, Marta Bueno, Miguel Toja, Javier SanchoAbstract:Helicobacter pylori Flavodoxin is the electronic acceptor of the pyruvate-oxidoreductase complex (POR) that catalyzes pyruvate oxidative decarboxilation. Inactivation of this metabolic route precludes bacterial survival. Because Flavodoxin is not present in the human host, substances interfering electronic transport from POR might be well suited for eradication therapies against the bacterium. H. pylori Flavodoxin presents a peculiar cofactor (FMN) binding site, compared to other known Flavodoxins, where a conserved aromatic residue is replaced by alanine. A cavity thus appears under the cofactor that can be filled with small organic molecules. We have cloned H. pylori fldA gene, expressed the protein in Escherichia coli and characterized the purified Flavodoxin. Thermal up-shift assays of Flavodoxin with different concentrations of benzylamine, as well as fluorescence titration experiments indicate benzylamine binds in the pocket near the FMN binding site. It seems thus that low affinity inhibitors of H. pylori Flavodoxin can be easily found that, after improvement, may give rise to leads.
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The Long and Short Flavodoxins I. THE ROLE OF THE DIFFERENTIATING LOOP IN APOFlavodoxin STRUCTURE AND FMN BINDING
The Journal of biological chemistry, 2004Co-Authors: Jon López-llano, Marta Bueno, Anabel Lostao, Susana Maldonado, Maria Ángeles-jiménez, Mariá P. Lillo, Javier SanchoAbstract:Flavodoxins are well known one-domain alpha/beta electron-transfer proteins that, according to the presence or absence of a approximately 20-residue loop splitting the fifth beta-strand of the central beta-sheet, have been classified in two groups: long and short-chain Flavodoxins, respectively. Although the Flavodoxins have been extensively used as models to study electron transfer, ligand binding, protein stability and folding issues, the role of the loop has not been investigated. We have constructed two shortened versions of the long-chain Anabaena Flavodoxin in which the split beta-strand has been spliced to remove the original loop. The two variants have been carefully analyzed using various spectroscopic and hydrodynamic criteria, and one of them is clearly well folded, indicating that the long loop is a peripheral element of the structure of long Flavodoxins. However, the removal of the loop (which is not in contact with the cofactor in the native structure) markedly decreases the affinity of the apoFlavodoxin-FMN complex. This seems related to the fact that, in long Flavodoxins, the adjacent tyrosine-bearing FMN binding loop (which is longer and thus more flexible than in short Flavodoxins) is stabilized in its competent conformation by interactions with the excised loop. The modest role played by the long loop of long Flavodoxins in the structure of these proteins (and in its conformational stability, see Lopez-Llano, J., Maldonado, S., Jain, S., Lostao, A., Godoy-Ruiz, R., Sanchez-Ruiz, Cortijo, M., Fernandez-Recio, J., and Sancho, J. (2004) J. Biol. Chem. 279, 47184-47191) opens the possibility that its conservation in so many species is related to a functional role yet to be discovered. In this respect, we discuss the possibility that the long loop is involved in the recognition of some Flavodoxin partners. In addition, we report on a structural feature of Flavodoxins that could indicate that the short Flavodoxins derive from the long ones.
Richard P Swenson - One of the best experts on this subject based on the ideXlab platform.
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mechanism of flavin mononucleotide cofactor binding to the desulfovibrio vulgaris Flavodoxin 1 kinetic evidence for cooperative effects associated with the binding of inorganic phosphate and the 5 phosphate moiety of the cofactor
Biochemistry, 2003Co-Authors: Tracey Arnold Murray, Richard P SwensonAbstract:The pathway(s) by which the flavin cofactor binds to the apoflavoprotein is the subject of some debate. The crystal and NMR structures of several different Flavodoxins have provided some insight, although there is disagreement about the location of the initial interaction between the flavin mononucleotide (FMN) and the apoFlavodoxin and the degree of protein conformational change associated with cofactor binding [Genzor, C. G., Perales-Alcon, A., Sancho, J., and Romero, A. (1996) Nat. Struct. Biol. 3, 329−332; Steensma, E., and van Mierlo, C. P. M. (1998) J. Mol. Biol. 282, 653−666]. Binding kinetics using stopped-flow spectrofluorimetry and phosphate competition studies were used to develop a model for flavin binding to the Flavodoxin from Desulfovibrio vulgaris. In the presence of phosphate, the time course of fluorescence quenching associated with FMN binding to apoFlavodoxin was biphasic, whereas riboflavin, which lacks the 5‘-phosphate group of FMN, displayed monophasic binding kinetics. When the con...
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role of glutamate 59 hydrogen bonded to n 3 h of the flavin mononucleotide cofactor in the modulation of the redox potentials of the clostridium beijerinckii Flavodoxin glutamate 59 is not responsible for the ph dependency but contributes to the stab
Biochemistry, 1999Co-Authors: Luke H Bradley, Richard P SwensonAbstract:: The midpoint potentials for both redox couples of the noncovalently bound flavin mononucleotide (FMN) cofactor in the Flavodoxin are known to be pH dependent. While the pH dependency for the oxidized-semiquinone (ox/sq) couple is consistent with the formation of the blue neutral form of the flavin semiquinone, that of the semiquinone-hydroquinone (sq/hq) couple is more enigmatic. The apparent pK(a) of 6.7 for this couple in the Flavodoxin from Clostridium beijerinckii has been attributed to the ionization of the FMN(HQ); however, nuclear magnetic resonance data strongly suggest the FMN(HQ) remains anionic over the entire pH range testable. As an alternative explanation, a specific glutamate residue (Glu59 in this Flavodoxin), which is hydrogen-bonded to N(3)H of the FMN, has been postulated to be the primary redox-linked proton acceptor responsible for the pH effect in some Flavodoxins. This model was directly tested in this study by permanently neutralizing Glu59 by its replacement with glutamine. This conservative substitution resulted in an increase of 86 mV (at pH 7) in midpoint potential of the sq/hq couple; however, the pH dependency of this couple was not altered. Thus, the redox-linked protonation of Glu59 clearly cannot be responsible for this effect as proposed. The pH dependency of the ox/sq couple was also similar to wild type, but the midpoint potential has decreased by 65 mV (pH 7). The K(d) values for the oxidized, semiquinone, and hydroquinone complexes increased by 43-, 590-, and 20-fold, respectively, relative to the wild type. Thus, the Glu59 to glutamine substitution substantially effects the stability of the semiquinone but, on a relative basis, slightly favors the formation of the hydroquinone. On the basis of (1)H-(15)N HSQC nuclear magnetic resonance spectroscopic studies, the increased temperature coefficients for the protons on N(3) and N(5) of the reduced FMN in E59Q suggest that the hydrogen-bonding interactions at these positions are significantly weakened in this mutant. The increase for N(5)H correlates with the reduced stability of the FMN(SQ) and the more negative midpoint potential for the ox/sq couple. On the basis of the X-ray structure, an "anchoring" role is proposed for the side chain carboxylate of Glu59 that stabilizes the structure of the 50's loop in such a way so as to promote the crucial hydrogen-bonding interaction that stabilizes the flavin semiquinone, contributing to the low potential of this Flavodoxin.
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the cumulative electrostatic effect of aromatic stacking interactions and the negative electrostatic environment of the flavin mononucleotide binding site is a major determinant of the reduction potential for the Flavodoxin from desulfovibrio vulgari
Biochemistry, 1996Co-Authors: Zhimin Zhou, Richard P SwensonAbstract:Flavodoxins are typified by the very low one-electron reduction potential for the semiquinone/hydroquinone couple (Esq/hq) of the flavin mononucleotide (FMN) cofactor. In the Desulfovibrio vulgaris Flavodoxin, the elimination of the side chain of Tyr98, which flanks the outer or si face of the flavin, through the Y98A mutation results in a substantial increase in Esq/hq of 139 mV, representing about one-half of the total shift in Esq/hq in this Flavodoxin [Swenson, R. P., & Krey, G. D. (1994) Biochemistry 33, 8505−8514]. The extent to which this large effect was the result of the elimination of unfavorable coplanar aromatic stacking interactions or to the greater solvent exposure of the flavin ring was not known. The significance of the latter effect was heightened by the characterization of the Fld+6 mutant which demonstrated that the unfavorable interaction between the negative electrostatic environment provided by the asymmetric clustering of acidic residues surrounding the cofactor and the FMN hydroqu...
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the cumulative electrostatic effect of aromatic stacking interactions and the negative electrostatic environment of the flavin mononucleotide binding site is a major determinant of the reduction potential for the Flavodoxin from desulfovibrio vulgari
Biochemistry, 1996Co-Authors: Zhimin Zhou, Richard P SwensonAbstract:Flavodoxins are typified by the very low one-electron reduction potential for the semiquinone/hydroquinone couple (Esq/hq) of the flavin mononucleotide (FMN) cofactor. In the Desulfovibrio vulgaris Flavodoxin, the elimination of the side chain of Tyr98, which flanks the outer or si face of the flavin, through the Y98A mutation results in a substantial increase in Esq/hq of 139 mV, representing about one-half of the total shift in Esq/hq in this Flavodoxin [Swenson, R. P., & Krey, G. D. (1994) Biochemistry 33, 8505-8514]. The extent to which this large effect was the result of the elimination of unfavorable coplanar aromatic stacking interactions or to the greater solvent exposure of the flavin ring was not known. The significance of the latter effect was heightened by the characterization of the Fld+6 mutant which demonstrated that the unfavorable interaction between the negative electrostatic environment provided by the asymmetric clustering of acidic residues surrounding the cofactor and the FMN hydroquinone anion is responsible for about one-third of the total decrease in Esq/hq in this Flavodoxin [Zhou, Z., & Swenson, R. P. (1995) Biochemistry 34, 3183-3192]. In this study, a Flavodoxin mutant was generated in which an alanine was substituted for Tyr98 while at the same time the negative electrostatic surface was partially neutralized by the substitution of the six acidic amino acid residues with their amide equivalents. The Esq/hq value of this mutant was found to have increased by 221 mV relative to wild type, which accounts for 70-80% of the total shift in Esq/hq in this Flavodoxin. This increase is very similar to the sum of the individual changes in Esq/hq introduced independently in the Y98A and Fld+6 mutants. The similarity in the magnitude of the effect of the neutralization of the six acidic residues in the context of an alanine residue at position 98 (Y98A) relative to an aromatic tyrosine residue (wild type) suggests that the increase in Esq/hq observed for the Y98A mutant is more likely due to the elimination of unfavorable pi-pi interactions between Tyr98 and the FMN hydroquinone rather than to the increased solvent exposure of the flavin. This study provides further support for the concept that the cumulative effect of the unfavorable electrostatic interactions introduced by coplanar aromatic or pi-pi stacking interactions and the negative electrostatic environment of the FMN binding site is a major determinant of the low one-electron reduction potential of the Flavodoxin.
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site directed mutagenesis of tyrosine 98 in the Flavodoxin from desulfovibrio vulgaris hildenborough regulation of oxidation reduction properties of the bound fmn cofactor by aromatic solvent and electrostatic interactions
Biochemistry, 1994Co-Authors: Richard P Swenson, Grigorios KreyAbstract:The contributions made by tyrosine-98 in establishing the redox properties of the Flavodoxin from Desulfovibrio vulgaris were investigated by substituting a number of amino acids at this position using site-directed mutagenesis. Tyr98, which makes extensive van der Waals contacts with the isoalloxazine ring of the flavin mononucleotide cofactor, is often found in the cofactor binding site of Flavodoxins and related flavoproteins. Solution studies suggest that tyrosine may assist in the stabilization of the neutral flavin semiquinone through preferential complex formation relative to the other oxidation states. In this study, the midpoint potentials of the oxidized/semiquinone couple of the Y98W and Y98F mutants were found to be very similar to the wild-type Flavodoxin. However, significantly more negative midpoint potentials (by 25-60 mV) were observed in the Y98A, Y98H, and Y98R mutants. These results imply that it is the general apolar environment provided by the aromatic amino acids rather than preferential affinities suggested by solution studies that is at least partially responsible for the thermodynamic stabilization of the neutral flavin semiquinone in this Flavodoxin. The midpoint potential of the semiquinone/hydroquinone couple is profoundly dependent on the properties of the amino acid at this position. Compared to phenylalanine, the more electron-rich aromatic side chains of tryptophan and tyrosine decrease the midpoint potential of this couple by 30-40 mV. Greater solvent exposure of the isoalloxazine ring in the Y98A mutant increases the midpoint potential by 140 mV relative to wild type. The positively charged amino acids increase the midpoint potential of this couple by > 180 mV, most probably through favorable electrostatic interactions with the flavin hydroquinone anion. These observations strongly support the proposition that the functional role of the electron-rich, apolar aromatic amino acid residues adjacent to the flavin isoalloxazine ring is to substantially destabilize the flavin hydroquinone anion, resulting in the very low oxidation-reduction potentials for the semiquinone/hydroquinone couple that typify the Flavodoxin family.
Alexander V. Bogachev - One of the best experts on this subject based on the ideXlab platform.
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Flavodoxin with an air-stable flavin semiquinone in a green sulfur bacterium
Photosynthesis Research, 2019Co-Authors: Yulia V. Bertsova, Leonid V. Kulik, Mahir D. Mamedov, Alexander A. Baykov, Alexander V. BogachevAbstract:Flavodoxins are small proteins with a non-covalently bound FMN that can accept two electrons and accordingly adopt three redox states: oxidized (quinone), one-electron reduced (semiquinone), and two-electron reduced (quinol). In iron-deficient cyanobacteria and algae, Flavodoxin can substitute for ferredoxin as the electron carrier in the photosynthetic electron transport chain. Here, we demonstrate a similar function for Flavodoxin from the green sulfur bacterium Chlorobium phaeovibrioides ( cp -Fld). The expression of the cp -Fld gene, found in a close proximity with the genes for other proteins associated with iron transport and storage, increased in a low-iron medium. cp -Fld produced in Escherichia coli exhibited the optical, ERP, and electron-nuclear double resonance spectra that were similar to those of known Flavodoxins. However, unlike all other Flavodoxins, cp -Fld exhibited unprecedented stability of FMN semiquinone to oxidation by air and difference in midpoint redox potentials for the quinone–semiquinone and semiquinone–quinol couples (− 110 and − 530 mV, respectively). cp -Fld could be reduced by pyruvate:ferredoxin oxidoreductase found in the membrane-free extract of Chl. phaeovibrioides cells and photo-reduced by the photosynthetic reaction center found in membrane vesicles from these cells. The green sulfur bacterium Chl. phaeovibrioides appears thus to be a new type of the photosynthetic organisms that can use Flavodoxin as an alternative electron carrier to cope with iron deficiency.
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Flavodoxin with an air-stable flavin semiquinone in a green sulfur bacterium
Photosynthesis Research, 2019Co-Authors: Yulia V. Bertsova, Leonid V. Kulik, Mahir D. Mamedov, Alexander A. Baykov, Alexander V. BogachevAbstract:Flavodoxins are small proteins with a non-covalently bound FMN that can accept two electrons and accordingly adopt three redox states: oxidized (quinone), one-electron reduced (semiquinone), and two-electron reduced (quinol). In iron-deficient cyanobacteria and algae, Flavodoxin can substitute for ferredoxin as the electron carrier in the photosynthetic electron transport chain. Here, we demonstrate a similar function for Flavodoxin from the green sulfur bacterium Chlorobium phaeovibrioides ( cp -Fld). The expression of the cp -Fld gene, found in a close proximity with the genes for other proteins associated with iron transport and storage, increased in a low-iron medium. cp -Fld produced in Escherichia coli exhibited the optical, ERP, and electron-nuclear double resonance spectra that were similar to those of known Flavodoxins. However, unlike all other Flavodoxins, cp -Fld exhibited unprecedented stability of FMN semiquinone to oxidation by air and difference in midpoint redox potentials for the quinone–semiquinone and semiquinone–quinol couples (− 110 and − 530 mV, respectively). cp -Fld could be reduced by pyruvate:ferredoxin oxidoreductase found in the membrane-free extract of Chl. phaeovibrioides cells and photo-reduced by the photosynthetic reaction center found in membrane vesicles from these cells. The green sulfur bacterium Chl. phaeovibrioides appears thus to be a new type of the photosynthetic organisms that can use Flavodoxin as an alternative electron carrier to cope with iron deficiency.
GW Canters - One of the best experts on this subject based on the ideXlab platform.
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A crystallographic study of Cys69Ala Flavodoxin II from Azotobacter vinelandii: Structural determinants of redox potential
PROTEIN SCI, 2005Co-Authors: GW CantersAbstract:Flavodoxin II from Azotobacter vinelandii is a "long-chain" Flavodoxin and has one of the lowest E-1 midpoint potentials found within the Flavodoxin family. To better understand the relationship between structural features and redox potentials, the oxidized form of the C69A mutant of this Flavodoxin was crystallized and its three-dimensional structure determined to a resolution of 2.25 A by molecular replacement. Its overall fold is similar to that of other Flavodoxins, with a central five-stranded parallel P-sheet flanked on either side by alpha-helices. An eight-residue insertion, compared with other long-chain Flavodoxins, forms a short 310 helix preceding the start of the alpha(3) helix. The flavin mononucleotide (FMN) cofactor is flanked by a leucine on its re face instead of the more conserved tryptophan, resulting in a more solvent-accessible FMN binding site and stabilization of the hydroquirione (hq) state. In particular the absence of a hydrogen bond to the N5 atom of the oxidized FMN was identified, which destabilizes the ox form, as well as an exceptionally large patch of acidic residues in the vicinity of the FMN N1 atom, which destabilizes the hq form. It is also argued that the presence of a Gly at position 58 in the sequence stabilizes the serniquinone (sq) form, as a result, raising the E-2 value in particular.
Yulia V. Bertsova - One of the best experts on this subject based on the ideXlab platform.
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Flavodoxin with an air-stable flavin semiquinone in a green sulfur bacterium
Photosynthesis Research, 2019Co-Authors: Yulia V. Bertsova, Leonid V. Kulik, Mahir D. Mamedov, Alexander A. Baykov, Alexander V. BogachevAbstract:Flavodoxins are small proteins with a non-covalently bound FMN that can accept two electrons and accordingly adopt three redox states: oxidized (quinone), one-electron reduced (semiquinone), and two-electron reduced (quinol). In iron-deficient cyanobacteria and algae, Flavodoxin can substitute for ferredoxin as the electron carrier in the photosynthetic electron transport chain. Here, we demonstrate a similar function for Flavodoxin from the green sulfur bacterium Chlorobium phaeovibrioides ( cp -Fld). The expression of the cp -Fld gene, found in a close proximity with the genes for other proteins associated with iron transport and storage, increased in a low-iron medium. cp -Fld produced in Escherichia coli exhibited the optical, ERP, and electron-nuclear double resonance spectra that were similar to those of known Flavodoxins. However, unlike all other Flavodoxins, cp -Fld exhibited unprecedented stability of FMN semiquinone to oxidation by air and difference in midpoint redox potentials for the quinone–semiquinone and semiquinone–quinol couples (− 110 and − 530 mV, respectively). cp -Fld could be reduced by pyruvate:ferredoxin oxidoreductase found in the membrane-free extract of Chl. phaeovibrioides cells and photo-reduced by the photosynthetic reaction center found in membrane vesicles from these cells. The green sulfur bacterium Chl. phaeovibrioides appears thus to be a new type of the photosynthetic organisms that can use Flavodoxin as an alternative electron carrier to cope with iron deficiency.
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Flavodoxin with an air-stable flavin semiquinone in a green sulfur bacterium
Photosynthesis Research, 2019Co-Authors: Yulia V. Bertsova, Leonid V. Kulik, Mahir D. Mamedov, Alexander A. Baykov, Alexander V. BogachevAbstract:Flavodoxins are small proteins with a non-covalently bound FMN that can accept two electrons and accordingly adopt three redox states: oxidized (quinone), one-electron reduced (semiquinone), and two-electron reduced (quinol). In iron-deficient cyanobacteria and algae, Flavodoxin can substitute for ferredoxin as the electron carrier in the photosynthetic electron transport chain. Here, we demonstrate a similar function for Flavodoxin from the green sulfur bacterium Chlorobium phaeovibrioides ( cp -Fld). The expression of the cp -Fld gene, found in a close proximity with the genes for other proteins associated with iron transport and storage, increased in a low-iron medium. cp -Fld produced in Escherichia coli exhibited the optical, ERP, and electron-nuclear double resonance spectra that were similar to those of known Flavodoxins. However, unlike all other Flavodoxins, cp -Fld exhibited unprecedented stability of FMN semiquinone to oxidation by air and difference in midpoint redox potentials for the quinone–semiquinone and semiquinone–quinol couples (− 110 and − 530 mV, respectively). cp -Fld could be reduced by pyruvate:ferredoxin oxidoreductase found in the membrane-free extract of Chl. phaeovibrioides cells and photo-reduced by the photosynthetic reaction center found in membrane vesicles from these cells. The green sulfur bacterium Chl. phaeovibrioides appears thus to be a new type of the photosynthetic organisms that can use Flavodoxin as an alternative electron carrier to cope with iron deficiency.