Sulfide:quinone reductase

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Sulfide:quinone reductase
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EC no. 1.8.5.4
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Sulfide:quinone reductase (SQR , EC 1.8.5.4) is an enzyme with systematic name sulfide:quinone oxidoreductase. [1] [2] [3] [4] [5] [6] This enzyme catalyses the following chemical reaction

Contents

n HS− + n quinone polysulfide + n quinol

SQR contains FAD. Ubiquinone, plastoquinone or menaquinone can act as acceptor in different species.

The Enzyme Commission (EC) number for SQR is 1.8.5.’. The number indicates that the protein is an oxidoreductase (indicated by 1). The oxidoreductase reacts with a sulfur molecule (sulfide in this case) to donate electrons (indicated by 8). The donated electrons are accepted by a quinone (indicated by 5). [7] Multiple sulfide:quinone oxidoreductases are found in bacteria, archaea, and eukaryotes, but the function highlighted in the EC numbers 1.8.5.’. which are all constant except the final digit which is 4 in bacteria and 8 in eukaryotic mitochondria. [8] [7]

Crystalline structure

The SQR in Aquifex aeolicus is composed of three subunits with a negatively charged hydrophilic side exposed to the periplasmic space and a hydrophobic region that integrates into the cell’s plasma membrane. The protein's active site is composed of an FAD cofactor covalently linked by a thioether bond to the enzyme. On the si side of the FAD the sulfide reacts and donates its electrons to FAD, while the re side of FAD is connected to a disulfide bridge and donates electrons to the quinone. 2, 3 The quinone is surrounded by Phe-385 and Ile-346. Both amino acids are located in the hydrophobic region of the plasma membrane and are conserved among all sulfide: quinone oxidoreductases. [9]

Reaction Pathway

In A. aeolicus, SQR is an integral monotopic protein, so it penetrates into the hydrophobic region of the plasma membrane. The SQR reaction takes place in two half reactions, sulfide oxidation and quinone reduction. The active site of SQR is composed of a region that interacts with the periplasmic space and sulfide connected by a FAD cofactor and a trisulfide bridge to a quinone. FAD receives two electrons from sulfide and transfers the electrons one at time to the quinone. The amino acids surrounding the quinone are all hydrophobic. Also, there is a highly conserved region of uncharged amino acids, phenylalanine and isoleucine, that surround the benzene ring of the quinone. [10]

SQR is a member of the flavoprotein disulfide reductase (FDR) superfamily. FDRs are typically characterized as being dimeric or two subunit proteins, but sulfide quinone oxidoreductase is a trimeric protein. The main purpose of SQR is to detoxify sulfide. Sulfide is a toxic chemical that inhibits enzymatic reactions, especially those with metal cofactors. Most notably, sulfide inhibits cytochrome oxidase found in the electron transport chain. SQR oxidizes sulfide and produces non-toxic products. [11]

Role in metabolism

SQR is an integral protein that enters cells' plasma membrane (or inner mitochondrial membrane). [12] The plasma membrane is the site of the electron transport chain for respiration. [13] The electron transport chain depends on two factors: 1) ability of a membrane to store an ion gradient; 2) the ability of an organism to pump hydrogen ions against a gradient (from low to high concentration). [12] SQR enhances the formation of an ion gradient by donating two electrons to the quinone. [13] Once the electrons are in the quinone, they are transported to the quinone pool. [12] The quinone pool is located inside the hydrophobic region of the plasma membrane and plays a role in transporting hydrogen ions to the periplasm. From the quinone pool, electrons travel to cytochrome c oxidase where oxygen is waiting as the final electron acceptor. [12] [13]

Electrons from carbon sources react in a similar fashion to those in sulfide. Two main differences separate the carbon pathway and the sulfur pathway: 1) sulfur (sulfide in this case) skips glycolysis and the tricarboxylic acid cycle (TCA), while the carbon pathway requires both cycles to store electrons in NADH l [10] [14] 2) electrons from sulfide are donated to SQR, while the electrons from NADH are donated to the NADH:quinone oxidoreductase. [14] In both cases, the electrons are shuttled to the quinone pool, then to cytochrome c oxidase where the final electron acceptor is waiting. [14] SQR is such a conserved protein because SQR enhances energy conservation and synthesizes ATP when carbon sources are depleted, but the main incentive to conserve SQR is to detoxify sulfide. [10] [14]

A 2021 study found that increased SQR levels were protective against hypoxia in squirrels and mice. [15]

Related Research Articles

<span class="mw-page-title-main">Oxidative phosphorylation</span> Metabolic pathway

Oxidative phosphorylation or electron transport-linked phosphorylation or terminal oxidation is the metabolic pathway in which cells use enzymes to oxidize nutrients, thereby releasing chemical energy in order to produce adenosine triphosphate (ATP). In eukaryotes, this takes place inside mitochondria. Almost all aerobic organisms carry out oxidative phosphorylation. This pathway is so pervasive because it releases more energy than alternative fermentation processes such as anaerobic glycolysis.

<span class="mw-page-title-main">Coenzyme Q – cytochrome c reductase</span> Class of enzymes

The coenzyme Q : cytochrome c – oxidoreductase, sometimes called the cytochrome bc1 complex, and at other times complex III, is the third complex in the electron transport chain, playing a critical role in biochemical generation of ATP. Complex III is a multisubunit transmembrane protein encoded by both the mitochondrial and the nuclear genomes. Complex III is present in the mitochondria of all animals and all aerobic eukaryotes and the inner membranes of most bacteria. Mutations in Complex III cause exercise intolerance as well as multisystem disorders. The bc1 complex contains 11 subunits, 3 respiratory subunits, 2 core proteins and 6 low-molecular weight proteins.

<span class="mw-page-title-main">Green sulfur bacteria</span> Family of bacteria

The green sulfur bacteria are a phylum, Chlorobiota, of obligately anaerobic photoautotrophic bacteria that metabolize sulfur.

In biochemistry, an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule, the reductant, also called the electron donor, to another, the oxidant, also called the electron acceptor. This group of enzymes usually utilizes NADP+ or NAD+ as cofactors. Transmembrane oxidoreductases create electron transport chains in bacteria, chloroplasts and mitochondria, including respiratory complexes I, II and III. Some others can associate with biological membranes as peripheral membrane proteins or be anchored to the membranes through a single transmembrane helix.

<span class="mw-page-title-main">Succinate dehydrogenase</span> Enzyme

Succinate dehydrogenase (SDH) or succinate-coenzyme Q reductase (SQR) or respiratory complex II is an enzyme complex, found in many bacterial cells and in the inner mitochondrial membrane of eukaryotes. It is the only enzyme that participates in both the citric acid cycle and the electron transport chain. Histochemical analysis showing high succinate dehydrogenase in muscle demonstrates high mitochondrial content and high oxidative potential.

Ferredoxins are iron–sulfur proteins that mediate electron transfer in a range of metabolic reactions. The term "ferredoxin" was coined by D.C. Wharton of the DuPont Co. and applied to the "iron protein" first purified in 1962 by Mortenson, Valentine, and Carnahan from the anaerobic bacterium Clostridium pasteurianum.

<span class="mw-page-title-main">Flavin adenine dinucleotide</span> Redox-active coenzyme

In biochemistry, flavin adenine dinucleotide (FAD) is a redox-active coenzyme associated with various proteins, which is involved with several enzymatic reactions in metabolism. A flavoprotein is a protein that contains a flavin group, which may be in the form of FAD or flavin mononucleotide (FMN). Many flavoproteins are known: components of the succinate dehydrogenase complex, α-ketoglutarate dehydrogenase, and a component of the pyruvate dehydrogenase complex.

Aquifex is a bacterial genus, belonging to phylum Aquificota. There is one species of Aquifex with a validly published name – A. pyrophilus – but "A. aeolicus" is sometimes considered as species though it has no standing as a name given it has not been validly or effectively published. Aquifex spp. are extreme thermophiles, growing best at temperature of 85 °C to 95 °C. They are members of the Bacteria as opposed to the other inhabitants of extreme environments, the Archaea.

"Aquifex aeolicus" is a chemolithoautotrophic, Gram-negative, motile, hyperthermophilic bacterium. "A. aeolicus" is generally rod-shaped with an approximate length of 2.0-6.0μm and a diameter of 0.4-0.5μm. "A. aeolicus" is neither validly nor effectively published and, having no standing in nomenclature, should be styled in quotation marks. It is one of a handful of species in the Aquificota phylum, an unusual group of thermophilic bacteria that are thought to be some of the oldest species of bacteria, related to filamentous bacteria first observed at the turn of the century. "A. aeolicus" is also believed to be one of the earliest diverging species of thermophilic bacteria. "A. aeolicus" grows best in water between 85 °C and 95 °C, and can be found near underwater volcanoes or hot springs. It requires oxygen to survive but has been found to grow optimally under microaerophilic conditions. Due to its high stability against high temperature and lack of oxygen, "A. aeolicus" is a good candidate for biotechnological applications as it is believed to have potential to be used as hydrogenases in an attractive H2/O2 biofuel cell, replacing chemical catalysts. This can be useful for improving industrial processes.

Trimethylamine N-oxide reductase is a microbial enzyme that can reduce trimethylamine N-oxide (TMAO) into trimethylamine (TMA), as part of the electron transport chain. The enzyme has been purified from E. coli and the photosynthetic bacteria Roseobacter denitrificans.

In enzymology, a sulfhydrogenase, also known as sulfur reductase, is an enzyme that catalyzes the reduction of elemental sulfur or polysulfide to hydrogen sulfide using hydrogen as electron donor.

In enzymology, a malate dehydrogenase (quinone) (EC 1.1.5.4), formerly malate dehydrogenase (acceptor) (EC 1.1.99.16), is an enzyme that catalyzes the chemical reaction

In enzymology, a ferredoxin-NADP+ reductase (EC 1.18.1.2) abbreviated FNR, is an enzyme that catalyzes the chemical reaction

In enzymology, a rubredoxin-NAD+ reductase (EC 1.18.1.1) is an enzyme that catalyzes the chemical reaction.

In enzymology, a hydrogen:quinone oxidoreductase (EC 1.12.5.1) is an enzyme that catalyzes the chemical reaction

<span class="mw-page-title-main">Sulfite reductase</span> Enzyme family

Sulfite reductases (EC 1.8.99.1) are enzymes that participate in sulfur metabolism. They catalyze the reduction of sulfite to hydrogen sulfide and water. Electrons for the reaction are provided by a dissociable molecule of either NADPH, bound flavins, or ferredoxins.

<span class="mw-page-title-main">Flavocytochrome c sulfide dehydrogenase</span>

Flavocytochrome c sulfide dehydrogenase, also known as Sulfide-cytochrome-c reductase (flavocytochrome c) (EC 1.8.2.3), is an enzyme with systematic name hydrogen-sulfide:flavocytochrome c oxidoreductase. It is found in sulfur-oxidising bacteria such as the purple phototrophic bacteria Allochromatium vinosum. This enzyme catalyses the following chemical reaction:

<span class="mw-page-title-main">Fumarate reductase (quinol)</span>

Fumarate reductase (quinol) (EC 1.3.5.4, QFR,FRD, menaquinol-fumarate oxidoreductase, quinol:fumarate reductase) is an enzyme with systematic name succinate:quinone oxidoreductase. This enzyme catalyzes the following chemical reaction:

<span class="mw-page-title-main">NDH-2</span>

NDH-2, also known as type II NADH:quinone oxidoreductase or alternative NADH dehydrogenase, is an enzyme which catalyzes the electron transfer from NADH to a quinone, being part of the electron transport chain. NDH-2 are peripheral membrane protein, functioning as dimers in vivo, with approximately 45 KDa per subunit and a single FAD as their cofactor.

<i>Prosthecochloris aestuarii</i> Species of bacterium

Prosthecochloris aestuarii is a green sulfur bacterium in the genus Prosthecochloris. This organism was originally isolated from brackish lagoons located in Sasyk-Sivash and Sivash. They are characterized by the presence of "prosthecae" on their cell surface; the inner part of these appendages house the photosynthetic machinery within chlorosomes, which are characteristic structures of green sulfur bacteria. Additionally, like other green sulfur bacteria, they are Gram-negative, non-motile, and non-spore forming. Of the four major groups of green sulfur bacteria, P. aestuarii serves as the type species for Group 4.

References

  1. ↑ Arieli B, Shahak Y, Taglicht D, Hauska G, Padan E (February 1994). "Purification and characterization of sulfide-quinone reductase, a novel enzyme driving anoxygenic photosynthesis in Oscillatoria limnetica". The Journal of Biological Chemistry. 269 (8): 5705–11. doi: 10.1016/S0021-9258(17)37518-X . PMID   8119908.
  2. ↑ Reinartz M, Tschäpe J, Brüser T, Trüper HG, Dahl C (July 1998). "Sulfide oxidation in the phototrophic sulfur bacterium Chromatium vinosum". Archives of Microbiology. 170 (1): 59–68. doi:10.1007/s002030050615. PMID   9639604. S2CID   38868444.
  3. ↑ Nübel T, Klughammer C, Huber R, Hauska G, Schütz M (April 2000). "Sulfide:quinone oxidoreductase in membranes of the hyperthermophilic bacterium Aquifex aeolicus (VF5)". Archives of Microbiology. 173 (4): 233–44. doi:10.1007/s002030000135. PMID   10816041. S2CID   6412823.
  4. ↑ Brito JA, Sousa FL, Stelter M, Bandeiras TM, Vonrhein C, Teixeira M, Pereira MM, Archer M (June 2009). "Structural and functional insights into sulfide:quinone oxidoreductase". Biochemistry. 48 (24): 5613–22. doi:10.1021/bi9003827. PMID   19438211.
  5. ↑ Cherney MM, Zhang Y, Solomonson M, Weiner JH, James MN (April 2010). "Crystal structure of sulfide:quinone oxidoreductase from Acidithiobacillus ferrooxidans: insights into sulfidotrophic respiration and detoxification". Journal of Molecular Biology. 398 (2): 292–305. doi:10.1016/j.jmb.2010.03.018. PMID   20303979.
  6. ↑ Marcia M, Langer JD, Parcej D, Vogel V, Peng G, Michel H (November 2010). "Characterizing a monotopic membrane enzyme. Biochemical, enzymatic and crystallization studies on Aquifex aeolicus sulfide:quinone oxidoreductase". Biochimica et Biophysica Acta (BBA) - Biomembranes. 1798 (11): 2114–23. doi: 10.1016/j.bbamem.2010.07.033 . PMID   20691146.
  7. 1 2 "BRENDA - Information on EC 1.8.5.4 - bacterial sulfide:quinone reductase". www.brenda-enzymes.org. Retrieved 2020-10-17.
  8. ↑ "BRENDA - Information on EC 1.8.5.8 - eukaryotic sulfide quinone oxidoreductase". www.brenda-enzymes.org. Retrieved 2020-10-17.
  9. ↑ Brito, José A.; Sousa, Filipa L.; Stelter, Meike; Bandeiras, Tiago M.; Vonrhein, Clemens; Teixeira, Miguel; Pereira, Manuela M.; Archer, Margarida (2009-06-23). "Structural and Functional Insights into Sulfide:Quinone Oxidoreductase". Biochemistry. 48 (24): 5613–5622. doi:10.1021/bi9003827. ISSN   0006-2960. PMID   19438211.
  10. 1 2 3 Marcia, Marco; Ermler, Ulrich; Peng, Guohong; Michel, Hartmut (2009-06-16). "The structure of Aquifex aeolicus sulfide:quinone oxidoreductase, a basis to understand sulfide detoxification and respiration". Proceedings of the National Academy of Sciences. 106 (24): 9625–9630. Bibcode:2009PNAS..106.9625M. doi: 10.1073/pnas.0904165106 . ISSN   0027-8424. PMC   2689314 . PMID   19487671.
  11. ↑ Marcia, Marco; Langer, Julian D.; Parcej, David; Vogel, Vitali; Peng, Guohong; Michel, Hartmut (2010-11-01). "Characterizing a monotopic membrane enzyme. Biochemical, enzymatic and crystallization studies on Aquifex aeolicus sulfide:quinone oxidoreductase". Biochimica et Biophysica Acta (BBA) - Biomembranes. 1798 (11): 2114–2123. doi: 10.1016/j.bbamem.2010.07.033 . ISSN   0005-2736. PMID   20691146.
  12. 1 2 3 4 van der Stel, Anne-Xander; Wösten, Marc M. S. M. (2019-07-30). "Regulation of Respiratory Pathways in Campylobacterota: A Review". Frontiers in Microbiology. 10: 1719. doi: 10.3389/fmicb.2019.01719 . ISSN   1664-302X. PMC   6682613 . PMID   31417516.
  13. 1 2 3 Nübel, Tobias; Klughammer, Christof; Huber, Robert; Hauska, Günter; Schütz, Michael (2000-04-01). "Sulfide:quinone oxidoreductase in membranes of the hyperthermophilic bacterium Aquifex aeolicus (VF5)". Archives of Microbiology. 173 (4): 233–244. doi:10.1007/s002030000135. ISSN   1432-072X. PMID   10816041. S2CID   6412823.
  14. 1 2 3 4 Kracke, Frauke; Vassilev, Igor; Krömer, Jens O. (2015-06-11). "Microbial electron transport and energy conservation – the foundation for optimizing bioelectrochemical systems". Frontiers in Microbiology. 6: 575. doi: 10.3389/fmicb.2015.00575 . ISSN   1664-302X. PMC   4463002 . PMID   26124754.
  15. ↑ "Serendipitous discovery could lead to treatment for strokes, cardiac arrest". medicalxpress.com. Retrieved 2021-05-26.
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