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.’. are all constant except that the final digit with 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">Electron transport chain</span> Energy-producing metabolic pathway

An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples this electron transfer with the transfer of protons (H+ ions) across a membrane. The electrons that are transferred from NADH and FADH2 to the ETC involves four multi-subunit large enzymes complexes and two mobile electron carriers. Many of the enzymes in the electron transport chain are embedded within the membrane.

<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 eubacteria. 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.

<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.

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.

<span class="mw-page-title-main">Electron-transferring-flavoprotein dehydrogenase</span> Protein family

Electron-transferring-flavoprotein dehydrogenase is an enzyme that transfers electrons from electron-transferring flavoprotein in the mitochondrial matrix, to the ubiquinone pool in the inner mitochondrial membrane. It is part of the electron transport chain. The enzyme is found in both prokaryotes and eukaryotes and contains a flavin and FE-S cluster. In humans, it is encoded by the ETFDH gene. Deficiency in ETF dehydrogenase causes the human genetic disease multiple acyl-CoA dehydrogenase deficiency.

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 ferredoxin-NADP+ reductase (EC 1.18.1.2) abbreviated FNR, 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">Adenylyl-sulfate reductase</span> Class of enzymes

Adenylyl-sulfate reductase is an enzyme that catalyzes the chemical reaction of the reduction of adenylyl-sulfate/adenosine-5'-phosphosulfate (APS) to sulfite through the use of an electron donor cofactor. The products of the reaction are AMP and sulfite, as well as an oxidized electron donor cofactor.

<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:

NADH:ubiquinone reductase (Na+-transporting) (EC 1.6.5.8 is an enzyme with systematic name NADH:ubiquinone oxidoreductase (Na+-translocating). In bacteria, three different types of respiratory NADH:quinone oxidoreductases (NQr) have been described: the electrogenic complex I, also called NDH I in bacteria, the non-electrogenic NADH:quinone oxidoreductases (NDH II), and the Na+-translocating NADH:quinone oxidoreductases Na+-NQr. The common function of these transmembrane enzymes in respiration is to oxidize NADH using ubiquinone (Q) as electron acceptor. The net reaction thus yields ubiquinol (QH2), the reducing substrate of enzyme complexes further along the respiratory chain, and NAD+, which is used as oxidizing agent in numerous cellular processes.

YedZ of E. coli has been examined topologically and has 6 transmembrane segments (TMSs) with both the N- and C-termini localized to the cytoplasm. von Rozycki et al. 2004 identified homologues of YedZ in bacteria and animals. YedZ homologues exhibit conserved histidyl residues in their transmembrane domains that may function in heme binding. Some of the homologues encoded in the genomes of various bacteria have YedZ domains fused to transport, electron transfer and biogenesis proteins. One of the animal homologues is the 6 TMS epithelial plasma membrane antigen of the prostate (STAMP1) that is over-expressed in prostate cancer. Some animal homologues have YedZ domains fused C-terminal to homologues of NADP oxidoreductases.

<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.

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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