InterPro: IPR015881 Aromatic-ring-hydroxylating dioxygenase, 2Fe-2S-binding site

Aromatic ring hydroxylating dioxygenases are multicomponent 1,2-dioxygenase complexes that convert closed-ring structures to non-aromatic cis-diols [1]. The complex has both hydroxylase and electron transfer components. The hydroxylase component is itself composed of two subunits: an alpha-subunit of about 50 kDa, and a beta-subunit of about 20 kDa. The electron transfer component is either composed of two subunits: a ferredoxin and a ferredoxin reductase or by a single bifunctional ferredoxin/reductase subunit. Sequence analysis of hydroxylase subunits of ring hydroxylating systems (including toluene, benzene and napthalene 1,2-dioxygenases) suggests they are derived from a common ancestor [1]. The alpha-subunit binds both a Rieske-like 2Fe-2S cluster and an iron atom: conserved Cys and His residues in the N-terminal region may provide 2Fe-2S ligands, while conserved His and Tyr residues may coordinate the iron. The beta subunit may be responsible for the substrate specificity of the dioxygenase system [1].

The alpha-subunit of the hydroxylase components bind both a 2Fe-2S type iron-sulphur centre and an iron atom. There is, in the N-terminal section of these proteins, a conserved region of 24 residues which contains two cysteines and two histidines which have been shown to be involved in the binding of the iron-sulphur centre [2].