title: A glutathione S-transferase catalyzes the dehalogenation of inhibitory metabolites of polychlorinated biphenyls.
abstract: BphK is a glutathione S-transferase of unclear physiological function that occurs in some bacterial biphenyl catabolic (bph) pathways. We demonstrated that BphK of Burkholderia xenovorans strain LB400 catalyzes the dehalogenation of 3-chloro 2-hydroxy-6-oxo-6-phenyl-2,4-dienoates (HOPDAs), compounds that are produced by the cometabolism of polychlorinated biphenyls (PCBs) by the bph pathway and that inhibit the pathway's hydrolase. A one-column protocol was developed to purify heterologously produced BphK. The purified enzyme had the greatest specificity for 3-Cl HOPDA (kcat/Km, approximately 10(4) M(-1) s(-1)), which it dechlorinated approximately 3 orders of magnitude more efficiently than 4-chlorobenzoate, a previously proposed substrate of BphK. The enzyme also catalyzed the dechlorination of 5-Cl HOPDA and 3,9,11-triCl HOPDA. By contrast, BphK did not detectably transform HOPDA, 4-Cl HOPDA, or chlorinated 2,3-dihydroxybiphenyls. The BphK-catalyzed dehalogenation proceeded via a ternary-complex mechanism and consumed 2 equivalents of glutathione (GSH) (Km for GSH in the presence of 3-Cl HOPDA, approximately 0.1 mM). A reaction mechanism consistent with the enzyme's specificity is proposed. The ability of BphK to dehalogenate inhibitory PCB metabolites supports the hypothesis that this enzyme was recruited to facilitate PCB degradation by the bph pathway.
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, 1365-2350 Health Sciences Mall, Vancouver, BC V6T 1Z3, Canada.
authors.forename: Pascal D
authors.initials: PD
authors.lastname: Fortin
authors.forename: Geoff P
authors.initials: GP
authors.lastname: Horsman
authors.forename: Hao M
authors.initials: HM
authors.lastname: Yang
authors.forename: Lindsay D
authors.initials: LD
authors.lastname: Eltis
mesh_terms: D019117:Burkholderia / Q000201:enzymology*; D004110:Diltiazem / Q000031:analogs & derivatives; D005231:Fatty Acids, Unsaturated / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism* / Q000493:pharmacokinetics; D011078:Polychlorinated Biphenyls / Q000378:metabolism*
chemical_list: D005231:Fatty Acids, Unsaturated; C446199:metabolite MB3; C018971:2-hydroxy-6-oxo-6-phenyl-2,4-hexadienoic acid; D011078:Polychlorinated Biphenyls; D005982:Glutathione Transferase; D004110:Diltiazem