title: Structural characterization of 2,6-dichloro-p-hydroquinone 1,2-dioxygenase (PcpA) from Sphingobium chlorophenolicum, a new type of aromatic ring-cleavage enzyme.
abstract: PcpA (2,6-dichloro-p-hydroquinone 1,2-dioxygenase) from Sphingobium chlorophenolicum, a non-haem Fe(II) dioxygenase capable of cleaving the aromatic ring of p-hydroquinone and its substituted variants, is a member of the recently discovered p-hydroquinone 1,2-dioxygenases. Here we report the 2.6 Å structure of PcpA, which consists of four βαβββ motifs, a hallmark of the vicinal oxygen chelate superfamily. The secondary co-ordination sphere of the Fe(II) centre forms an extensive hydrogen-bonding network with three solvent exposed residues, linking the catalytic Fe(II) to solvent. A tight hydrophobic pocket provides p-hydroquinones access to the Fe(II) centre. The p-hydroxyl group is essential for the substrate-binding, thus phenols and catechols, lacking a p-hydroxyl group, do not bind to PcpA. Site-directed mutagenesis and kinetic analysis confirm the critical catalytic role played by the highly conserved His10, Thr13, His226 and Arg259. Based on these results, we propose a general reaction mechanism for p-hydroquinone 1,2-dioxygenases.
authors.affiliation: Department of Chemistry, Washington State University, Pullman, WA 99164-4630, USA.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Hayes
authors.forename: Abigail R
authors.initials: AR
authors.lastname: Green
authors.forename: Mark S
authors.initials: MS
authors.lastname: Nissen
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Lewis
authors.forename: Luying
authors.initials: L
authors.lastname: Xun
authors.forename: Chulhee
authors.initials: C
authors.lastname: Kang
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002151:Calorimetry; D002384:Catalysis; D002396:Catechols / Q000494:pharmacology; D049308:Dioxygenases / Q000737:chemistry*; D005296:Ferrous Compounds; D006873:Hydroquinones / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D016415:Sequence Alignment; D042301:Sphingomonadaceae / Q000201:enzymology* / Q000235:genetics
chemical_list: D002396:Catechols; D005296:Ferrous Compounds; D006873:Hydroquinones; C119974:2,6-dichlorohydroquinone dioxygenase; D049308:Dioxygenases; C031927:hydroquinone