This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: Sox enzyme system, Paracoccus sulfur oxidation pathway, PSO pathway
|Superclasses:||Degradation/Utilization/Assimilation → Inorganic Nutrients Metabolism → Sulfur Compounds Metabolism → Thiosulfate Oxidation|
Some taxa known to possess this pathway include : Aquifex aeolicus, Methylobacterium extorquens AM1, Paracoccus denitrificans, Paracoccus pantotrophus, Paracoccus versutus, Rhodopseudomonas palustris, Rhodovulum sulfidophilum, Starkeya novella
Expected Taxonomic Range:
Thiosulfate is a relatively stable environmentally abundant sulfur compound of intermediate oxidation state. Several pathways of thiosulfate oxidation are known. The two best understood pathways are the direct oxidation of thiosulfate to sulfate, catalyzed by the Sox enzyme system, and the indirect oxidation of thiosulfate through polythionate intermediates, the main of which is tetrathionate (see thiosulfate oxidation I (to tetrathionate)).
Two versions of the direct oxidation pathway are known. A number of facultatively chemo- or photolithotrophic organisms such as Paracoccus pantotrophus or Rhodovulum sulfidophilum, which possess the SoxCD proteins, oxidize a single molecule of thiosulfate to two molecules of sulfate (this pathway). Organisms that lack the SoxCD proteins utilize a different route, in which one molecule of thiosulfate is converted into only one molecule of sulfate while the other sulfur atom is added to inorganic sulfur globules that are deposited either in the periplasmic space or outside the cells (see thiosulfate oxidation IV (multienzyme complex)).
About This Pathway
Paracoccus pantotrophus is a Gram-negative, neutrophilic, facultatively lithoautotrophic bacterium that is able to grow with thiosulfate as an energy source using the first type of pathway. The organism posseses a periplasmic enzyme complex known as the Sox enzyme system (for sulfur oxidation) that is able to oxidize thiosulfate to sulfate with no intermediates [Friedrich00].
The sox gene cluster of Paracoccus pantotrophus comprises at least two transcriptional units with 15 genes. Seven of these genes, soxXYZABCD, encode 4 proteins which can be combined in vitro to reconstitute an active Sox enzyme complex. The four proteins encoded by these seven genes are SoxXA, SoxYZ, SoxB, and SoxCD. SoxXA is a heterodimeric c-type cytochrome; SoxYZ is a heterodimeric protein that binds thiosulfate covalently. SoxB is a monomer that contains two manganese atoms [Wodara97]. SoxCD is an α2β2 heterotetramer composed of two units each of SoxC, a molybdenum cofactor-containing subunit, and SoxD, a diheme c-type cytochrome [Quentmeier00].
An in vitro reconstituted Sox system mediates not only thiosulfate, but also sulfite-, S0-, and hydrogen sulfide-dependent cytochrome c reduction [Wodara97, Rother01]. While thiosulfate oxidation yields eight electrons, sulfite oxidation follows the following equation, and yields only 2 electrons per mol substrate:
Sulfite oxidation does not require the presence of the SoxCD protein.
The overall reaction of thiosulfate oxidation is:
A model for the mechanism of the Sox system in Paracoccus pantotrophus has been proposed [Friedrich01]. According to this model, the first step is the SoxXA-mediated binding of thiosulfate or sulfite to a cysteine residue of SoxY. When thiosulfate binds, a a [SoxY protein]-thiocysteine-S-sulfate is formed, which is then hydrolyzed by SoxB, liberating a sulfate, and forming a a [SoxY protein]-S-thiocysteine. SoxCD would then successively oxidize the outer sulfur atom, using three water molecules and forming a [SoxY protein]-L-cysteine-S-sulfate. Finally, the second sulfate group is hydrolyzed by SoxB, bringing the cysteine residue of SoxY to its initial condition.
Bagchi05: Bagchi A, Ghosh TC (2005). "A structural study towards the understanding of the interactions of SoxY, SoxZ, and SoxB, leading to the oxidation of sulfur anions via the novel global sulfur oxidizing (sox) operon." Biochem Biophys Res Commun 335(2);609-15. PMID: 16084835
Dahl13: Dahl C, Franz B, Hensen D, Kesselheim A, Zigann R (2013). "Sulfite oxidation in the purple sulfur bacterium Allochromatium vinosum: identification of SoeABC as a major player and relevance of SoxYZ in the process." Microbiology 159(Pt 12);2626-38. PMID: 24030319
Friedrich00: Friedrich CG, Quentmeier A, Bardischewsky F, Rother D, Kraft R, Kostka S, Prinz H (2000). "Novel genes coding for lithotrophic sulfur oxidation of Paracoccus pantotrophus GB17." J Bacteriol 182(17);4677-87. PMID: 10940005
Friedrich01: Friedrich CG, Rother D, Bardischewsky F, Quentmeier A, Fischer J (2001). "Oxidation of reduced inorganic sulfur compounds by bacteria: emergence of a common mechanism?." Appl Environ Microbiol 67(7);2873-82. PMID: 11425697
Quentmeier00: Quentmeier A, Kraft R, Kostka S, Klockenkamper R, Friedrich CG (2000). "Characterization of a new type of sulfite dehydrogenase from Paracoccus pantotrophus GB17." Arch Microbiol 173(2);117-25. PMID: 10795683
Quentmeier01: Quentmeier A, Friedrich CG (2001). "The cysteine residue of the SoxY protein as the active site of protein-bound sulfur oxidation of Paracoccus pantotrophus GB17." FEBS Lett 503(2-3);168-72. PMID: 11513876
Quentmeier03: Quentmeier A, Hellwig P, Bardischewsky F, Grelle G, Kraft R, Friedrich CG (2003). "Sulfur oxidation in Paracoccus pantotrophus: interaction of the sulfur-binding protein SoxYZ with the dimanganese SoxB protein." Biochem Biophys Res Commun 312(4);1011-8. PMID: 14651972
Rother01: Rother D, Henrich HJ, Quentmeier A, Bardischewsky F, Friedrich CG (2001). "Novel genes of the sox gene cluster, mutagenesis of the flavoprotein SoxF, and evidence for a general sulfur-oxidizing system in Paracoccus pantotrophus GB17." J Bacteriol 183(15);4499-508. PMID: 11443084
Wodara97: Wodara C, Bardischewsky F, Friedrich CG (1997). "Cloning and characterization of sulfite dehydrogenase, two c-type cytochromes, and a flavoprotein of Paracoccus denitrificans GB17: essential role of sulfite dehydrogenase in lithotrophic sulfur oxidation." J Bacteriol 1997;179(16);5014-23. PMID: 9260941
AppiaAyme01: Appia-Ayme C, Little PJ, Matsumoto Y, Leech AP, Berks BC (2001). "Cytochrome complex essential for photosynthetic oxidation of both thiosulfate and sulfide in Rhodovulum sulfidophilum." J Bacteriol 183(20);6107-18. PMID: 11567011
Bamford02: Bamford VA, Bruno S, Rasmussen T, Appia-Ayme C, Cheesman MR, Berks BC, Hemmings AM (2002). "Structural basis for the oxidation of thiosulfate by a sulfur cycle enzyme." EMBO J 21(21);5599-610. PMID: 12411478
Bardischewsky05: Bardischewsky F, Quentmeier A, Rother D, Hellwig P, Kostka S, Friedrich CG (2005). "Sulfur dehydrogenase of Paracoccus pantotrophus: the heme-2 domain of the molybdoprotein cytochrome c complex is dispensable for catalytic activity." Biochemistry 44(18);7024-34. PMID: 15865447
Cheesman01: Cheesman MR, Little PJ, Berks BC (2001). "Novel heme ligation in a c-type cytochrome involved in thiosulfate oxidation: EPR and MCD of SoxAX from Rhodovulum sulfidophilum." Biochemistry 40(35);10562-9. PMID: 11523998
Dambe05: Dambe T, Quentmeier A, Rother D, Friedrich C, Scheidig AJ (2005). "Structure of the cytochrome complex SoxXA of Paracoccus pantotrophus, a heme enzyme initiating chemotrophic sulfur oxidation." J Struct Biol 152(3);229-34. PMID: 16297640
Epel05: Epel B, Schafer KO, Quentmeier A, Friedrich C, Lubitz W (2005). "Multifrequency EPR analysis of the dimanganese cluster of the putative sulfate thiohydrolase SoxB of Paracoccus pantotrophus." J Biol Inorg Chem 10(6);636-42. PMID: 16133204
Hard92: Hard K, Van Zadelhoff G, Moonen P, Kamerling JP, Vliegenthart FG (1992). "The Asn-linked carbohydrate chains of human Tamm-Horsfall glycoprotein of one male. Novel sulfated and novel N-acetylgalactosamine-containing N-linked carbohydrate chains." Eur J Biochem 209(3);895-915. PMID: 1425697
Kappler04: Kappler U, Aguey-Zinsou KF, Hanson GR, Bernhardt PV, McEwan AG (2004). "Cytochrome c551 from Starkeya novella: characterization, spectroscopic properties, and phylogeny of a diheme protein of the SoxAX family." J Biol Chem 279(8);6252-60. PMID: 14645228
Mukhopadhyaya00: Mukhopadhyaya PN, Deb C, Lahiri C, Roy P (2000). "A soxA gene, encoding a diheme cytochrome c, and a sox locus, essential for sulfur oxidation in a new sulfur lithotrophic bacterium." J Bacteriol 182(15);4278-87. PMID: 10894738
Rother02: Rother D, Friedrich CG (2002). "The cytochrome complex SoxXA of Paracoccus pantotrophus is produced in Escherichia coli and functional in the reconstituted sulfur-oxidizing enzyme system." Biochim Biophys Acta 1598(1-2);65-73. PMID: 12147345
Schneider94: Schneider A, Friedrich C (1994). "Sulfide dehydrogenase is identical with the SoxB protein of the thiosulfate-oxidizing enzyme system of Paracoccus denitrificans GB17." FEBS Lett 350(1);61-5. PMID: 8062925
Welte09: Welte C, Hafner S, Kratzer C, Quentmeier A, Friedrich CG, Dahl C (2009). "Interaction between Sox proteins of two physiologically distinct bacteria and a new protein involved in thiosulfate oxidation." FEBS Lett 583(8);1281-6. PMID: 19303410
Wodara94: Wodara C, Kostka S, Egert M, Kelly DP, Friedrich CG (1994). "Identification and sequence analysis of the soxB gene essential for sulfur oxidation of Paracoccus denitrificans GB17." J Bacteriol 1994;176(20);6188-91. PMID: 7928987
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