Dissimilatory sulfite reductase explained

dissimilatory sulfite reductase
Ec Number:	1.8.99.5
Go Code:	0016002
Pdb:	2V4J, 3MM5

Dissimilatory sulfite reductase is an enzyme that participates in sulfur metabolism in dissimilatory sulfate reduction.^[1]

The enzyme is essential in prokaryotic sulfur-based energy metabolism, including sulfate/sulfite reducing organisms, sulfur-oxidizing bacteria, and organosulfonate reducers. In sulfur reducers it catalyses the reduction of sulfite to sulfide (reaction 1), while in sulfur oxidizers it catalyses the opposite reaction (reaction 2).^[2] The reaction involves the small protein DsrC, which is present in all the organisms that contain dissimilatory sulfite reductase.^[3] During the process an intramolecular trisulfide is formed between two L-cysteine residues of DsrC and the sulfur atom from sulfite.^[4] This trisulfide can be reduced by a number of proteins including DsrK and TcmB.^[5]

Reaction in organisms performing dissimilatory sulfate reduction:

(1) sulfite + a [DsrC protein]-dithiol + 2 reduced acceptor + 2 H⁺ = hydrogen sulfide + a [DsrC protein]-disulfide + 2 acceptor + 3 H₂O (overall reaction)

(1a) sulfite + a [DsrC protein]-dithiol + 2 reduced acceptor + 2 H⁺ = a [DsrC protein]-S-sulfanyl-L-cysteine + 2 acceptor + 3 H₂O

(1b) a [DsrC protein]-S-sulfanyl-L-cysteine = hydrogen sulfide + a [DsrC protein]-disulfide

Reaction in organisms performing sulfur oxidation:

(2) a [DsrC protein]-S-sulfanyl-L-cysteine + 3 acceptor + 3 H₂O = sulfite + a [DsrC protein]-disulfide + 3 reduced acceptor + 2 H⁺ (overall reaction)

(2a) a [DsrC protein]-S-sulfanyl-L-cysteine + 3 acceptor + 3 H2O = a [DsrC]-S-sulfo-L-cysteine + 3 reduced acceptor + H⁺

(2b) a [DsrC]-S-sulfo-L-cysteine = sulfite + a [DsrC protein]-disulfide

The systematic name of this enzyme class is hydrogen-sulfide:[DsrC sulfur-carrier protein],acceptor oxidoreductase.

This enzyme is different from EC 1.8.1.2, assimilatory sulfite reductase (NADPH), and EC 1.8.7.1, assimilatory sulfite reductase (ferredoxin), which are involved in sulfate assimilation.

Notes and References

1. Parey K, Warkentin E, Kroneck PM, Ermler U . Reaction cycle of the dissimilatory sulfite reductase from Archaeoglobus fulgidus . Biochemistry . 49 . 41 . 8912–21 . October 2010 . 20822098 . 10.1021/bi100781f .
2. Schedel M, Vanselow M, Trüper HG . Siroheme sulfite reductase isolated from Chromatium vinosum. Purification and investigation of some of its molecular and catalytic properties . Archives of Microbiology . 1979 . 121 . 1 . 29–36 . 10.1007/BF00409202. 1979ArMic.121...29S . 22126920 .
3. Oliveira TF, Vonrhein C, Matias PM, Venceslau SS, Pereira IA, Archer M . The crystal structure of Desulfovibrio vulgaris dissimilatory sulfite reductase bound to DsrC provides novel insights into the mechanism of sulfate respiration . The Journal of Biological Chemistry . 283 . 49 . 34141–9 . December 2008 . 18829451 . 10.1074/jbc.M805643200 . 2662231 . free .
4. Santos AA, Venceslau SS, Grein F, Leavitt WD, Dahl C, Johnston DT, Pereira IA . A protein trisulfide couples dissimilatory sulfate reduction to energy conservation . Science . 350 . 6267 . 1541–5 . December 2015 . 26680199 . 10.1126/science.aad3558 . 2015Sci...350.1541S . 206643054 .
5. Venceslau SS, Stockdreher Y, Dahl C, Pereira IA . The "bacterial heterodisulfide" DsrC is a key protein in dissimilatory sulfur metabolism . Biochimica et Biophysica Acta (BBA) - Bioenergetics . 1837 . 7 . 1148–64 . July 2014 . 24662917 . 10.1016/j.bbabio.2014.03.007 . free .