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: 3-sulfolactate degradation I
|Superclasses:||Degradation/Utilization/Assimilation → Inorganic Nutrients Metabolism → Sulfur Compounds Metabolism → Sulfolactate Degradation|
Some taxa known to possess this pathway include : Chromohalobacter salexigens DSM 3043
Expected Taxonomic Range: Bacteria
Organosulfonate compounds are found in the environment as both natural products and xenobiotics. They are catabolized by microorganisms that utilize the carbon and sulfur moieties. Aliphatic C3 sulfonates are widespread natural products found in the environment and are derived from microbial, plant and animal sources. The bacterial catabolism of C3 sulfonates such as (RS)-3-sulfolactate (racemic sulfolactate), 3-sulfopyruvate, and L-cysteate has been studied. The work has focused on the catabolism of the carbon moiety, the fate of the sulfonate group, and the transport systems necessary for organosulfonates to cross the cell membrane. Bioinformatics analyses have shown a diversity in pathways of sulfonate degradation in bacteria from both marine and terrestrial environments (in [Denger10] and reviewed in [Cook06]).
To date, three desulfonation pathways have been proposed for the degradation of (RS)-3-sulfolactate including:
(1) sulfolactate degradation I: direct desulfonation of (2R)-3-sulfolactate by the enzyme R-sulfolactate sulfo-lyase, encoded by the suyA and suyB genes. (2S)-3-sulfolactate is isomerized to (2R)-3-sulfolactate via 3-sulfopyruvate by two dehydrogenases of opposite stereochemistry, encoded by slcC and comC.
(2) sulfolactate degradation II: oxidation of (RS)-3-sulfolactate to 3-sulfopyruvate by sulfolactate dehydrogenase (slcD), followed by decarboxylation of sulfopyruvate to sulfoacetaldehyde by the sulfopyruvate decarboxylase encoded by the comD and comE genes, desulfonation to acetyl phosphate by xsc, and conversion of acetyl phosphate to acetyl-CoA.
(3) sulfolactate degradation III: oxidation of (RS)-3-sulfolactate to 3-sulfopyruvate by sulfolactate dehydrogenase (slcD), transamination of 3-sulfopyruvate to L-cysteate, and desulfonation of L-cysteate to pyruvate by the product of the cuyA gene.
In all of these pathways the bisulfite or sulfite produced by the desulfonation reaction is proposed to be transported through the cell membrane and oxidized to sulfate by a periplasmic enzyme, possibly the product of genes sorAB in some organisms [Denger09, Mayer10, Cook06].
In each of these pathways a different enzymatic desulfonation mechanism is used. In sulfolactate degradation I desulfonation occurs via (2R)-3-sulfolactate by EC 18.104.22.168, sulfolactate sulfo-lyase (see 3-sulfolactate sulfo-lyase from Paracoccus pantotrophus NKNCYSA and R-sulfolactate sulfo-lyase from Chromohalobacter salexigens DSM 3043 for examples [Rein05].
In sulfolactate degradation II desulfonation occurs via sulfoacetaldehyde by EC 22.214.171.124, sulfoacetaldehyde acetyltransferase. See sulfoacetaldehyde acetyltransferase, encoded by the xsc gene in Roseovarius nubinhibens ISM for example [Denger09, Mayer10].
In sulfolactate degradation III desulfonation occurs via L-cysteate by EC 126.96.36.199, (S)-cysteate sulfo-lyase. See L-cysteate sulfo-lyase from Ruegeria pomeroyi DSS-3 and L-cysteate sulfo-lyase from Roseovarius nubinhibens ISM for examples [Denger09, Denger06].
About This Pathway
The marine γ-proteobacterium Chromohalobacter salexigens DSM 3043 grows aerobically with (RS)-3-sulfolactate as the sole source of carbon and energy. This compound was used quantitatively with stoichiometric release of the sulfonate moiety as sulfate. Thus, both enantiomers ((2R)-3-sulfolactate and (2S)-3-sulfolactate) were oxidized. A postulated pathway was supported by enzymatic studies utilizing cell extracts and purified enzymes. Genes encoding the pathway enzymes, a putative regulator and a putative transporter were located in a cluster [Denger10].
The pathway is inducible although its regulation has not yet been elucidated. A putative transcriptional regulator gene suyR has been identified. In this pathway a transporter(s) is necessary for one or both enantiomers of the polar (RS)-3-sulfolactate to cross the cytoplasmic membrane. Genes slcHFG have been proposed to encode a putative 3-component uptake system, although this remains to be firmly established [Denger10].
S-sulfolactate dehydrogenase (slcC) is a novel enzyme with an unusual role as a partial racemase in a degradative pathway. Full racemization is achieved by the successive action of two dehydrogenases of different stereochemistry [Denger10]. The bisulfite (sulfite) produced by SuyAB was proposed to be exported from the cell although the nature of the putative cytoplasmic membrane export system and a putative periplasmic sulfite dehydrogenase remains unknown. The carbon skeleton enters central metabolism as pyruvate [Denger10].
Denger06: Denger K, Smits TH, Cook AM (2006). "L-cysteate sulpho-lyase, a widespread pyridoxal 5'-phosphate-coupled desulphonative enzyme purified from Silicibacter pomeroyi DSS-3(T)." Biochem J 394(Pt 3);657-64. PMID: 16302849
Denger09: Denger K, Mayer J, Buhmann M, Weinitschke S, Smits TH, Cook AM (2009). "Bifurcated degradative pathway of 3-sulfolactate in Roseovarius nubinhibens ISM via sulfoacetaldehyde acetyltransferase and (S)-cysteate sulfolyase." J Bacteriol 191(18);5648-56. PMID: 19581363
Denger10: Denger K, Cook AM (2010). "Racemase activity effected by two dehydrogenases in sulfolactate degradation by Chromohalobacter salexigens: purification of (S)-sulfolactate dehydrogenase." Microbiology 156(Pt 3);967-74. PMID: 20007648
Mayer10: Mayer J, Huhn T, Habeck M, Denger K, Hollemeyer K, Cook AM (2010). "2,3-Dihydroxypropane-1-sulfonate degraded by Cupriavidus pinatubonensis JMP134: purification of dihydroxypropanesulfonate 3-dehydrogenase." Microbiology 156(Pt 5);1556-64. PMID: 20150239
Rein05: Rein U, Gueta R, Denger K, Ruff J, Hollemeyer K, Cook AM (2005). "Dissimilation of cysteate via 3-sulfolactate sulfo-lyase and a sulfate exporter in Paracoccus pantotrophus NKNCYSA." Microbiology 151(Pt 3);737-47. PMID: 15758220
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