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

• Published in: Photosynthesis research 2019-11, Vol.142 (2), p.127-136
• Main Authors: Bertsova, Yulia V., Kulik, Leonid V., Mamedov, Mahir D., Baykov, Alexander A., Bogachev, Alexander V.
• Format: Article
• Language: English
• Subjects: Air; Algae; Bacteria; Biochemistry; Biomedical and Life Sciences; Chlorobi - genetics; Chlorobi - metabolism; Electron Spin Resonance Spectroscopy; Electron transport; Electron transport chain; Electrons; Escherichia coli; Escherichia coli - metabolism; Ethylenediaminetetraacetic acid; Ferredoxin; Flavin mononucleotide; Flavin-Adenine Dinucleotide - analogs & derivatives; Flavin-Adenine Dinucleotide - metabolism; Flavodoxin; Flavodoxin - metabolism; Genetic aspects; Green sulfur bacteria; Hydroquinone; Iron; Iron deficiency; Life Sciences; Membrane vesicles; Nutrient deficiency; Original Article; Oxidation; Oxidation-Reduction; Oxidoreductase; Photosynthesis; Plant Genetics and Genomics; Plant Physiology; Plant Sciences; Protein binding; Proteins; Pyruvate Synthase - metabolism; Pyruvic acid; Quinone; Quinones; Sulfur; Sulfur compounds
• ISSN: 0166-8595; 1573-5079
• DOI: 10.1007/s11120-019-00658-1

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.