title: The electron-transport proteins of hydroxylating bacterial dioxygenases.
abstract: The degradation of aromatic compounds by aerobic bacteria frequently begins with the dihydroxylation of the substrate by nonheme iron-containing dioxygenases. These enzymes consist of two or three soluble proteins that interact to form an electron-transport chain that transfers electrons from reduced nucleotides (NADH) via flavin and [2Fe-2S] redox centers to a terminal dioxygenase. The dioxygenases may be classified in terms of the number of constituent components and the nature of the redox centers. Class I consists of two-component enzymes in which the first protein is a reductase containing both a flavin and a [2Fe-2S] redox center and the second component is the oxygenase; Class II consists of three-component enzymes in which the flavin and [2Fe-2S] redox centers of the reductase are on a separate flavoprotein and ferredoxin, respectively; and Class III consists of three-component enzymes in which the reductase contains both a flavin and [2Fe-2S] redox center but also requires a second [2Fe-2S] center on a ferredoxin for electron transfer to the terminal oxygenase. Further subdivision is based on the the type of flavin (FMN or FAD) in the reductase, the coordination of the [2Fe-2S] center in the ferredoxin, and the number of terminal oxygenase subunits. From the deduced amino acid sequence of several dioxygenases the ligands involved in the coordination of the nucleotides, iron-sulfur centers, and mononuclear nonheme iron active site are proposed. On the basis of their spectroscopic properties and unusually high redox potentials, the [2Fe-2S] clusters of the ferredoxins and terminal oxygenases have been assigned to the class of Rieske-type iron-sulfur proteins. The iron atoms in the Rieske iron-sulfur cluster are coordinated to the protein by two histidine nitrogens and two cysteine sulfurs.
authors.affiliation: Division of Biosphere Sciences, King's College London, United Kingdom.
authors.forename: J R
authors.initials: JR
authors.lastname: Mason
authors.forename: R
authors.initials: R
authors.lastname: Cammack
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry*; D004579:Electron Transport; D006900:Hydroxylation; D008969:Molecular Sequence Data; D010105:Oxygenases / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D010105:Oxygenases