InterPro domain: IPR019020

This entry represents a haem-binding domain found in cytochromes b558/566 (subunit A), c-551 and c-552, as well as in members of the type-II members of the microbial dimethyl sulphoxide (DMSO) reductase family.

The DMSO reductase family is a large and rapidly expanding group of enzymes found in bacteria and archaea that share a common form of molybdenum cofactor known as bis(molybdopterin guanine dinucleotide)Mo [ 1 ]. In addition to the molybdopterin subunit, these enzymes also contain an iron-sulphur subunit. These include two distinct but very closely related periplasmic proteins of anaerobic respiration: selenate reductase and chlorate reductase [ 2 ]. Other proteins containing this subunit include dimethyl sulphide dehydrogenase and ethylbenzene dehydrogenase [ 3 , 4 , 5 ].

One member of the DMSO reductase family is eythylbenzene dehydrogenase, which is a heterotrimer of three subunits that catalyses the anaerobic degradation of hydrocarbons (alpha, beta and gamma subunits). This entry matches the gamma subunit, whose structure is known [ 6 ]. The alpha subunit contains the catalytic centre as a Molybdenum cofactor-complex. This removes an electron-pair from the hydrocarbon and passes it along an electron transport system involving iron-sulphur complexes held in the beta subunit and a Haem b molecule contained in the gamma subunit. The electron-pair is then subsequently passed to an as yet unknown receiver. The enzyme is found in a variety of different bacteria.

1. Mo and W bis-MGD enzymes: nitrate reductases and formate dehydrogenases. J. Biol. Inorg. Chem. 9, 791-9
2. The C subunit of Ideonella dechloratans chlorate reductase: expression, purification, refolding, and heme reconstitution. Protein Expr. Purif. 41, 306-12
3. Ethylbenzene dehydrogenase, a novel hydrocarbon-oxidizing molybdenum/iron-sulfur/heme enzyme. J. Biol. Chem. 276, 21381-6
4. Molecular analysis of dimethyl sulphide dehydrogenase from Rhodovulum sulfidophilum: its place in the dimethyl sulphoxide reductase family of microbial molybdopterin-containing enzymes. Mol. Microbiol. 44, 1575-87
5. Identification, characterization, and classification of genes encoding perchlorate reductase. J. Bacteriol. 187, 5090-6
6. Crystal structure of ethylbenzene dehydrogenase from Aromatoleum aromaticum. Structure 14, 1377-88