TY - JOUR

T1 - Flavodoxin with an air-stable flavin semiquinone in a green sulfur bacterium

AU - Bertsova, Yulia V.

AU - Kulik, Leonid V.

AU - Mamedov, Mahir D.

AU - Baykov, Alexander A.

AU - Bogachev, Alexander V.

PY - 2019/11/1

Y1 - 2019/11/1

N2 - 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.

AB - 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.

KW - Electron transport

KW - ENDOR

KW - Flavodoxin

KW - Green sulfur bacteria

KW - Iron deficiency

KW - Redox titration

UR - http://www.scopus.com/inward/record.url?scp=85068998844&partnerID=8YFLogxK

U2 - 10.1007/s11120-019-00658-1

DO - 10.1007/s11120-019-00658-1

M3 - Article

C2 - 31302833

AN - SCOPUS:85068998844

VL - 142

SP - 127

EP - 136

JO - Photosynthesis Research

JF - Photosynthesis Research

SN - 0166-8595

IS - 2

ER -