A novel enzyme of type VI sulfide:quinone oxidoreductases in purple sulfur photosynthetic bacteria

Ágnes Duzs, András Tóth, Brigitta Németh, Tímea Balogh, Péter B. Kós, Gábor Rákhely

Research output: Contribution to journalArticle

3 Citations (Scopus)


Sulfide detoxification can be catalyzed by ancient membrane-bound flavoproteins, sulfide:quinone oxidoreductases (Sqr), which have important roles in sulfide homeostasis and sulfide-dependent energy conservation processes by transferring electrons from sulfide to respiratory or photosynthetic membrane electron flow. Sqr enzymes have been categorized into six groups. Several members of the groups I, II, III, and V are well-known, but type IV and VI Sqrs are, as yet, uncharacterized or hardly characterized at all. Here, we report detailed characterization of a type VI sulfide:quinone oxidoreductase (TrSqrF) from a purple sulfur bacterium, Thiocapsa roseopersicina. Phylogenetic analysis classified this enzyme in a special group composed of SqrFs of endosymbionts, while a weaker relationship could be observed with SqrF of Chlorobaculum tepidum which is the only type VI enzyme characterized so far. Directed mutagenesis experiments showed that TrSqrF contributed substantially to the sulfide:quinone oxidoreductase activity of the membranes. Expression of the sqrF gene could be induced by sulfide. Homologous recombinant TrSqrF protein was expressed and purified from the membranes of a SqrF-deleted T. roseopersicina strain. The purified protein contains redox-active covalently bound FAD cofactor. The recombinant TrSqrF enzyme catalyzes sulfur-dependent quinone reduction and prefers ubiquinone-type quinone compounds. Kinetic parameters of TrSqrF show that the affinity of the enzyme is similar to duroquinone and decylubiquinone, but the reaction has substantially lower activation energy with decylubiquinone, indicating that the quinone structure has an effect on the catalytic process. TrSqrF enzyme affinity for sulfide is low, therefore, in agreement with the gene expressional analyis, SqrF could play a role in energy-conserving sulfide oxidation at high sulfide concentrations. TrSqrF is a good model enzyme for the subgroup of type VI Sqrs of endosymbionts and its characterization might provide deeper insight into the molecular details of the ancient, anoxic, energy-gaining processes using sulfide as an electron donor.

Original languageEnglish
Pages (from-to)5133-5147
Number of pages15
JournalApplied Microbiology and Biotechnology
Issue number12
Publication statusPublished - Jun 1 2018


  • Anoxic energy gaining
  • Enzyme kinetics
  • Purple sulfur photosynthetic bacteria
  • Quinone reduction
  • Sulfide:quinone oxidoreductase (Sqr)
  • Sulfur metabolism

ASJC Scopus subject areas

  • Biotechnology
  • Applied Microbiology and Biotechnology

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