Chlorinated Biphenyl Quinones and Phenyl-2,5-benzoquinone Differentially Modify the Catalytic Activity of Human Hydroxysteroid Sulfotransferase hSULT2A1

Abstract

Human hydroxysteroid sulfotransferase (hSULT2A1) catalyzes the sulfation of a broad range of environmental chemicals, drugs, and other xenobiotics in addition to endogenous compounds that include hydroxysteroids and bile acids. Polychlorinated biphenyls (PCBs) are persistent environmental contaminants, and oxidized metabolites of PCBs may play significant roles in the etiology of their adverse health effects. Quinones derived from oxidative metabolism of PCBs (PCB-quinones) react with nucleophilic sites in proteins and also undergo redox cycling to generate reactive oxygen species. This, along with the sensitivity of hSULT2A1 to oxidative modification at cysteine residues led us to hypothesize that electrophilic PCB-quinones react with hSULT2A1 to alter its catalytic function. Thus, we examined the effects of four phenylbenzoquinones on the ability of hSULT2A1 to catalyze the sulfation of the endogenous substrate, dehydroepiandrosterone (DHEA). The quinones studied were 2′-chlorophenyl-2,5-benzoquinone (2′-Cl-BQ), 4′-chlorophenyl-2,5-benzoquinone (4′-Cl-BQ), 4′-chlorophenyl-3,6-dichloro-2,5-benzoquinone (3,6,4′-triCl-BQ), and phenyl-2,5-benzoquinone (PBQ). At all concentrations examined, pretreatment of hSULT2A1 with the PCB-quinones decreased catalytic activity of hSULT2A1. Pretreatment with low concentrations of PBQ, however, increased the catalytic activity of the enzyme, while higher concentrations inhibited catalysis. A decrease in substrate inhibition with DHEA was seen following preincubation of hSULT2A1 with all of the quinones. Proteolytic digestion of the enzyme followed by LC/MS analysis indicated PCB-quinone- and PBQ-adducts at Cys55 and Cys199, as well as oxidation products at methionines in the protein. Equilibrium binding experiments and molecular modeling suggested that changes due to these modifications may affect the nucleotide binding site and the entrance to the sulfuryl acceptor binding site of hSULT2A1.

Metabolism and metabolites of polychlorinated biphenyls

“…superoxide anion radical, hydrogen peroxide, and hydroxyl radical) and the PCB quinone (Song et al, 2008a, Song et al, 2008b). In addition to the potential for generation of toxic oxygen species, the metabolic pathways of PCBs may include the formation of electrophilic PCB arene oxides and quinones that may bind to nucleophilic sites on cellular macromolecules (Robertson and Gupta, 2000, Lin et al, 2000, Qin et al, 2013, Wangpradit et al, 2009, James, 2001). In fact, a large number of in vitro studies have demonstrated adduct formation of PCBs and their metabolites, in particular PCB quinones, to proteins, RNA, DNA or lipids (Robertson and Gupta, 2000, Morck et al, 2002, Ludewig, 2001, Klasson Wehler et al, 1989, Klasson Wehler et al, 1993, Zhao et al, 2004).…”

Cytochrome c adducts with PCB quinoid metabolites

“…Thiol binding of PCB quinone metabolites has been found in glutathione and topoisomerase II, which caused a decrease of topoisomerase II activity (Srinivasan et al 2002). The covalent binding of different PCB quinones decreased the catalytic activity of human hydroxysteroid sulfotransferase hSULT2A1 (Qin et al 2013a). Using radioactive compounds, PCB3 and PCB77 were found covalently bound to nuclear proteins in liver in vivo (Pereg et al 2001) and lipids in vivo (Morck et al 2002).…”

Quinoid systems in chemistry and pharmacology

“…37) are capable of reacting with nucleophilic sites of either DNA or proteins and can participate in some redox processes, generating ROS. However, in a study with human hydroxysteroid transferase, an enzyme responsible for the detoxification of an organism through catalytic sulfonation of both endogenous and exogenous agents, the compounds increased, rather than inhibited, enzymatic activity (Qin et al, 2013).…”