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Gene Review

isiB  -  flavodoxin FldA

Synechococcus elongatus PCC 6301

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Disease relevance of isiB

  • The gene for flavodoxin was cloned from the cyanobacterium Anacystis nidulans R2 by using three mixed oligonucleotide probes derived from the partial Synechococcus sp. strain PCC 6301 amino acid sequence [1].
  • Here we report that nucleotide sequence analyses of DNA located immediately upstream of the flavodoxin gene revealed an open reading frame of 1,026 bases (designated isiA; iron stress inducible) with a deduced amino acid sequence showing similarity to that of the psbC polypeptide of higher plants and cyanobacteria [2].
  • In addition, atoms N-3 and O-2 alpha of the isoalloxazine appear to form hydrogen bonds to the backbone at CO97 and NH99 in a conformation entirely different from that found in Clostridium MP flavodoxin but structurally analogous to Desulfovibrio vulgaris flavodoxin [3].
  • The sequences of peptides isolated after cyanogen bromide cleavage and after digestion with Staphylococcus aureus protease, reported here, fit into the electron density map of A. nidulans flavodoxin, starting near the middle of the third helix, and verify that the major insertion interrupts the fifth strand of parallel sheet [4].
  • The PsaE subunit is required for complex formation between photosystem I and flavodoxin from the cyanobacterium Synechocystis sp. PCC 6803 [5].

High impact information on isiB

  • In contrast, the light-induced reduction of oxidized flavodoxin can be observed only by first-flash experiments following excessive dark adaptation [6].
  • Laser flash-absorption spectroscopy indicates that the bound flavodoxin of this complex is stabilized in the semiquinone state and is photoreduced to the quinol form upon light excitation [6].
  • Crystal structure analyses and refinements of three orthorhombic forms of oxidized A. nidulans flavodoxin are reported, and salient features of the fold and the FMN binding site are compared with other flavodoxins [7].
  • The structure of oxidized flavodoxin from the cyanobacterium Anacystis nidulans has been determined at 2.5 A resolution with phases calculated from ethylmercury phosphate and dimercuriacetate derivatives [3].
  • The kinetics of the reduction of oxidized flavodoxin display a single-exponential component for both PSI preparations [5].

Biological context of isiB

  • However, under iron-deficient growth conditions the flavodoxin gene appeared to be transcribed as part of a larger operon [1].
  • The first was of approximately 1,100 bases (designated RNA 1) and terminated immediately upstream from the 5' end of the flavodoxin open reading frame [1].
  • Southern blot hybridization under conditions of reduced stringency detected only one copy of the flavodoxin sequence in the A. nidulans R2 genome [1].
  • Insertional mutagenesis of the cloned cyanobacterial fur gene led to the creation of heteroallelic mutants that showed iron-deficiency symptoms in iron-replete medium, including the constitutive production of flavodoxin and of hydroxamate siderophores [8].
  • The kinetics of reduction of oxidized flavodoxin displays a single-exponential component [9].

Anatomical context of isiB

  • 3. In mediating electron transfer from chloroplast membranes to Clostridium pasteurianum hydrogenase the flavodoxin from Anacystis nidulans proved the most active with Nostoc strain MAC flavodoxin and Porphyra umbilicalis ferredoxin also being appreciably more active than other cyanobacterial and higher plant ferredoxins [10].

Associations of isiB with chemical compounds

  • Assuming proteolytic cleavage of the initial methionine residue, the molecular weight of the A. nidulans R2 flavodoxin is 18,609 [1].
  • The semiquinone form of flavodoxin being protonated, this rate corresponds to a rate-limiting reaction which could be either an electron transfer reaction or a protonation reaction [9].
  • The finding that FA fails to donate electrons to flavodoxin in F(B)-less (HgCl2-treated) PS I complexes suggests that F(B) is the direct electron donor to flavodoxin [11].
  • The increase of the relative contribution of the slow components of the membrane potential decay kinetics in the presence of both native (ferredoxin, flavodoxin) and artificial (methyl viologen) electron acceptors indicate the effective interaction between the terminal 14Fe-4S] cluster and acceptors [11].
  • Pyruvate:ferredoxin (flavodoxin) oxidoreductase (PFO, EC catalyses the oxidative cleavage of pyruvate and coenzyme A to acetylcoenzyme A and CO2 with the simultaneous reduction of ferredoxin or flavodoxin [12].

Analytical, diagnostic and therapeutic context of isiB


  1. Isolation, sequence analysis, and transcriptional studies of the flavodoxin gene from Anacystis nidulans R2. Laudenbach, D.E., Reith, M.E., Straus, N.A. J. Bacteriol. (1988) [Pubmed]
  2. Characterization of a cyanobacterial iron stress-induced gene similar to psbC. Laudenbach, D.E., Straus, N.A. J. Bacteriol. (1988) [Pubmed]
  3. Structure of oxidized flavodoxin from Anacystis nidulans. Smith, W.W., Pattridge, K.A., Ludwig, M.L., Petsko, G.A., Tsernoglou, D., Tanaka, M., Yasunobu, K.T. J. Mol. Biol. (1983) [Pubmed]
  4. Determination of the sequence which spans the beginning of the insertion region in Anacystis nidulans flavodoxin. Tarr, G.E. J. Mol. Biol. (1983) [Pubmed]
  5. The PsaE subunit is required for complex formation between photosystem I and flavodoxin from the cyanobacterium Synechocystis sp. PCC 6803. Meimberg, K., Lagoutte, B., Bottin, H., Mühlenhoff, U. Biochemistry (1998) [Pubmed]
  6. Characterization of a redox-active cross-linked complex between cyanobacterial photosystem I and its physiological acceptor flavodoxin. Mühlenhoff, U., Kruip, J., Bryant, D.A., Rögner, M., Sétif, P., Boekema, E. EMBO J. (1996) [Pubmed]
  7. Refined structures of oxidized flavodoxin from Anacystis nidulans. Drennan, C.L., Pattridge, K.A., Weber, C.H., Metzger, A.L., Hoover, D.M., Ludwig, M.L. J. Mol. Biol. (1999) [Pubmed]
  8. Fur regulates the expression of iron-stress genes in the cyanobacterium Synechococcus sp. strain PCC 7942. Ghassemian, M., Straus, N.A. Microbiology (Reading, Engl.) (1996) [Pubmed]
  9. Laser flash absorption spectroscopy study of flavodoxin reduction by photosystem I in Synechococcus sp. PCC 7002. Mühlenhoff, U., Sétif, P. Biochemistry (1996) [Pubmed]
  10. Efficiency of ferredoxins and flavodoxins as mediators in systems for hydrogen evolution. Fitzgerald, M.P., Rogers, L.J., Rao, K.K., Hall, D.O. Biochem. J. (1980) [Pubmed]
  11. Electrometrical study of electron transfer from the terminal FA/FB iron-sulfur clusters to external acceptors in photosystem I. Mamedova, A.A., Mamedov, M.D., Gourovskaya, K.N., Vassiliev, I.R., Golbeck, J.H., Semenov, A.Y. FEBS Lett. (1999) [Pubmed]
  12. Molecular evidence for the aerobic expression of nifJ, encoding pyruvate:ferredoxin oxidoreductase, in cyanobacteria. Schmitz, O., Gurke, J., Bothe, H. FEMS Microbiol. Lett. (2001) [Pubmed]
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