Flavodoxin with an air-stable flavin semiquinone in a green sulfur bacterium

Yulia V. Bertsova, Leonid V. Kulik, Mahir D. Mamedov, Alexander A. Baykov, Alexander V. Bogachev

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)127-136
Number of pages10
JournalPhotosynthesis Research
Issue number2
Publication statusPublished - 1 Nov 2019


  • Electron transport
  • Flavodoxin
  • Green sulfur bacteria
  • Iron deficiency
  • Redox titration


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