ExplorEnz: EC 1.8.4.17

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1.8.4.17

Accepted name:

sulfur-oxidizing heterodisulfide reductase-like enzyme system (type I)

Reaction:

[TusA sulfur-carrier protein]-S-sulfanyl-L-cysteine + 2 [LbpA protein]-N⁶-lipoyl-L-lysine + 3 H₂O = [TusA sulfur-carrier protein]-L-cysteine + 2 [LbpA protein]-N⁶-dihydrolipoyl-L-lysine + sulfite

Other name(s):

sHdr system (type I)

Systematic name:

[TusA sulfur-carrier protein]-S-sulfanyl-L-cysteine:[LbpA protein]-N⁶-lipoyl-L-lysine oxidoreductase

Comments:

This enzyme complex, usually referred to as the sHdr system (type I), is a cytoplasmic sulfur oxidation system found in many bacterial and archaeal sulfur oxidizers. The system consists of a dimer of the iron-sulfur flavoprotein sHdrA and one subunit each of the proposed catalytic subunit sHdrB1, the disulfide reductase sHdrB2, and the ferredoxin-like electron carrier proteins sHdrC1 and sHdrC₂. The system oxidizes a sulfane sulfur, provided by the TusA sulfur-carrier protein, to sulfite, using a dedicated lipoylated protein (LbpA) as the electron acceptor.

Links to other databases:

BRENDA, EXPASY, KEGG, MetaCyc

References:

1.	Boughanemi, S., Lyonnet, J., Infossi, P., Bauzan, M., Kosta, A., Lignon, S., Giudici-Orticoni, M.T. and Guiral, M. Microbial oxidative sulfur metabolism: biochemical evidence of the membrane-bound heterodisulfide reductase-like complex of the bacterium Aquifex aeolicus. FEMS Microbiol. Lett. 363 (2016) . [DOI] [PMID: 27284018]
2.	Koch, T. and Dahl, C. A novel bacterial sulfur oxidation pathway provides a new link between the cycles of organic and inorganic sulfur compounds. ISME J. 12 (2018) 2479–2491. [DOI] [PMID: 29930335]
3.	Cao, X., Koch, T., Steffens, L., Finkensieper, J., Zigann, R., Cronan, J.E. and Dahl, C. Lipoate-binding proteins and specific lipoate-protein ligases in microbial sulfur oxidation reveal an atpyical role for an old cofactor. Elife 7 (2018) . [DOI] [PMID: 30004385]
4.	Ernst, C., Kayastha, K., Koch, T., Venceslau, S.S., Pereira, I.AC., Demmer, U., Ermler, U. and Dahl, C. Structural and spectroscopic characterization of a HdrA-like subunit from Hyphomicrobium denitrificans. FEBS J. 288 (2021) 1664–1678. [DOI] [PMID: 32750208]
5.	Appel, L., Willistein, M., Dahl, C., Ermler, U. and Boll, M. Functional diversity of prokaryotic HdrA(BC) modules: Role in flavin-based electron bifurcation processes and beyond. Biochim Biophys Acta Bioenerg 1862:148379 (2021). [DOI] [PMID: 33460586]
6.	Tanabe, T.S., Bach, E., D'Ermo, G., Mohr, M.G., Hager, N., Pfeiffer, N., Guiral, M. and Dahl, C. A cascade of sulfur transferases delivers sulfur to the sulfur-oxidizing heterodisulfide reductase-like complex. Protein Sci. 33:e5014 (2024). [DOI] [PMID: 38747384]

[EC 1.8.4.17 created 2025]