title: Exploration of the relationship between tetrachlorohydroquinone dehalogenase and the glutathione S-transferase superfamily.
abstract: Tetrachlorohydroquinone dehalogenase is found in Sphingomonas chlorophenolica, a soil bacterium that degrades pentachlorophenol, a widely used wood preservative. This enzyme converts tetrachlorohydroquinone (TCHQ) to trichlorohydroquinone (TriCHQ) and TriCHQ to dichlorohydroquinone (DCHQ) (Xun et al. (1992) J. Bacteriol. 174, 8003-8007). The reducing equivalents for each step are provided by two molecules of glutathione (Xun et al. (1992) Biochem. Biophys. Res. Commun. 182, 361-366). In addition to the expected TriCHQ and DCHQ products, the enzyme also produces substantial amounts of 2,3,5-trichloro-6-S-glutathionylhydroquinone (GS-TriCHQ) and an unidentified isomer of dichloro-S-glutathionylhydroquinone (GS-DCHQ). Treatment of the purified enzyme with dithiothreitol dramatically decreases the formation of GS-TriCHQ and GS-DCHQ. Furthermore, enzyme in freshly-prepared crude extracts forms only very small amounts of GS-TriCHQ and GS-DCHQ. We conclude that GS-TriCHQ and GS-DCHQ are produced by enzyme that has undergone some type of oxidative damage and are therefore not physiologically relevant products. The fact that the oxidative damage can be repaired by DTT suggests that a cysteine or methionine residue may be involved. We have created the C13S and C156S mutants of the enzyme. The C13S mutant converts TCHQ to GS-TriCHQ and GS-DCHQ, rather than to DCHQ. Thus, Cys13 is required for the reductive dehalogenation of TCHQ. A mechanism for the reaction which involves Cys13 is proposed.
authors.affiliation: Department of Chemistry and Biochemistry, University of Colorado at Boulder 80309, USA.
authors.forename: D L
authors.initials: DL
authors.lastname: McCarthy
authors.forename: S
authors.initials: S
authors.lastname: Navarrete
authors.forename: W S
authors.initials: WS
authors.lastname: Willett
authors.forename: P C
authors.initials: PC
authors.lastname: Babbitt
authors.forename: S D
authors.initials: SD
authors.lastname: Copley
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019117:Burkholderia; D002851:Chromatography, High Pressure Liquid; D004175:Diptera; D004330:Drosophila; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D006867:Hydrolases / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010944:Plants; D011511:Proteus; D011549:Pseudomonas; D051381:Rats; D016415:Sequence Alignment
chemical_list: D005982:Glutathione Transferase; D006867:Hydrolases; C078610:2,3,5,6-tetrachloro-4-hydroquinone reductive dehalogenase; D005978:Glutathione