Aromatic-ring-hydroxylating dioxygenases

Aromatic-ring-hydroxylating dioxygenases

Aromatic-ring-hydroxylating dioxygenases (ARHD) incorporate two atoms of dioxygen (O2) into their substrates in the dihydroxylation reaction. The product is (substituted) "cis"-1,2-dihydroxycyclohexadiene, which is subsequently converted to (substituted) benzene glycol by a "cis"-diol dehydrogenase.

A large family of multicomponent mononuclear (non-heme) iron oxygenases has been identified. Components of bacterial aromatic-ring dioxygenases constitute two different functional classes: hydroxylase components and electron transfer components. Hydroxylase components are either (αβ)"n" or (α)"n" oligomers. Two prosthetic groups, a Rieske-type [Fe2S2] center and a mononuclear iron, are associated with the α-subunit in the (αβ)"n"-type enzymes. Electron transfer components are composed of flavoprotein (NADH:ferredoxin oxidoreductase) and Rieske-type [Fe2S2] ferredoxin. In benzoate and toluate 1,2-dioxygenase systems, a single protein containing reductase and Rieske-type ferredoxin domains transfers the electrons from NADH to the hydroxylase component. In the phthalate 4,5-dioxygenase system, phthalate dioxygenase reductase (PDR) has the same function. PDR is a single protein comprising FMN-binding reductase and plant-type ferredoxin domains. Thus, the electron transfer in ARHD systems can be summarised as:

Biochemical classification

EC number| benzene 1,2-dioxygenase: benzene + NADH + H+ + O2 = "cis"-cyclohexa-3,5-diene-1,2-diol + NAD+

EC number| phthalate 4,5-dioxygenase: phthalate + NADH + H+ + O2 = "cis"-4,5-dihydroxycyclohexa-1(6),2-diene-1,2-dicarboxylate + NAD+

EC number| 4-sulfobenzoate 3,4-dioxygenase: 4-sulfobenzoate + NADH + H+ + O2 = 3,4-dihydroxybenzoate + sulfite + NAD+

EC number| 4-chlorophenylacetate 3,4-dioxygenase: 4-chlorophenylacetate + NADH + H+ + O2 = 3,4-dihydroxyphenylacetate + chloride + NAD+

EC number| benzoate 1,2-dioxygenase: benzoate + NADH + H+ + O2 = 1,2-dihydroxycyclohexa-3,5-diene-1-carboxylate + NAD+

EC number| toluene dioxygenase: toluene + NADH + H+ + O2 = (1"S",2"R")-3-methylcyclohexa-3,5-diene-1,2-diol + NAD+

EC number| naphthalene 1,2-dioxygenase: naphthalene + NADH + H+ + O2 = (1"R",2"S")-1,2-dihydronaphthalene-1,2-diol + NAD+

EC number| terephthalate 1,2-dioxygenase: terephthalate + NADH + H+ + O2 = (1"R",6"S")-dihydroxycyclohexa-2,4-diene-1,4-dicarboxylate + NAD+

EC number| biphenyl 2,3-dioxygenase: biphenyl + NADH + H+ + O2 = (1"S",2"R")-3-phenylcyclohexa-3,5-diene-1,2-diol + NAD+


The crystal structure of the hydroxylase component of naphthalene 1,2-dioxygenase from "Pseudomonas" has been determined. The protein is an (αβ)3 hexamer. The β-subunit belongs to theα+β class. It has no prosthetic groups and its role in catalysis is unknown. The α-subunit can be divided into two domains: a Rieske domain that contains the [Fe2S2] center and the catalytic domain that contains the active site mononuclear iron. The Rieske domain (residues 38-158) consists of four β-sheets. The overall fold is very similar to that of the soluble fragment of the Rieske protein from bovine heart mitochondrial cytochrome "bc"1 complex. In the [Fe2S2] center, Fe1 is coordinated by two cysteine residues (Cys-81 and Cys-101) while Fe2 is coordinated by Nδ atoms of two histidine residues (His-83 and His-104). The catalytic domain belongs to the α+β class and is dominated by a nine-stranded antiparallel β-sheet. The iron of the active site is located at the bottom of a narrow channel, approximately 15 Å from the protein surface. The mononuclear iron is coordinated by His-208, His-213, Asp-362 (bidentate) and a water molecule. The geometry can be described as a distorted octahedral with one ligand missing. The structure of the hexamer suggests cooperativity between adjacent α-subunits, where electrons from the [Fe2S2] center in one α-subunit (A) are transferred to the mononuclear iron in the adjacent α-subunit (B) through AspB-205, which is hydrogen-bonded to HisA-104 of the Rieske center and HisB-208 of the active site.



External links

* - structure of napthalene 1,2-dioxygenase from "Pseudomonas putida"
* - structure of biphenyl 2,3-dioxygenase from "Rhodococcus" sp. strain RHA1
* - InterPro entry for Bacterial ring hydroxylating dioxygenase, alpha subunit

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  • Rieske protein — Pfam box Symbol = Rieske Name = width =260 caption =Mitochondrial cytochrome bc1 complex. (PDB|1bcc) Pfam= PF00355 InterPro= IPR005806 SMART= PROSITE= PDOC00177 SCOP = 1rie TCDB = 3.E.2 OPM family= OPM protein= 1q90 PDB=PDB3|1ww9A:28 131… …   Wikipedia

  • Phenylalanine hydroxylase — predicted 3D structure of phenylalanine hydroxylase …   Wikipedia

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