title: Sulfated metabolites of polychlorinated biphenyls are high-affinity ligands for the thyroid hormone transport protein transthyretin.
abstract: BACKGROUND
  The displacement of l-thyroxine (T4) from binding sites on transthyretin (TTR) is considered a significant contributing mechanism in polychlorinated biphenyl (PCB)-induced thyroid disruption. Previous research has discovered hydroxylated PCB metabolites (OH-PCBs) as high-affinity ligands for TTR, but the binding potential of conjugated PCB metabolites such as PCB sulfates has not been explored.
  
  
  OBJECTIVE
  We evaluated the binding of five lower-chlorinated PCB sulfates to human TTR and compared their binding characteristics to those determined for their OH-PCB precursors and for T4.
  
  
  METHODS
  We used fluorescence probe displacement studies and molecular docking simulations to characterize the binding of PCB sulfates to TTR. The stability of PCB sulfates and the reversibility of these interactions were characterized by HPLC analysis of PCB sulfates after their binding to TTR. The ability of OH-PCBs to serve as substrates for human cytosolic sulfotransferase 1A1 (hSULT1A1) was assessed by OH-PCB-dependent formation of adenosine-3',5'-diphosphate, an end product of the sulfation reaction.
  
  
  RESULTS
  All five PCB sulfates were able to bind to the high-affinity binding site of TTR with equilibrium dissociation constants (Kd values) in the low nanomolar range (4.8-16.8 nM), similar to that observed for T4 (4.7 nM). Docking simulations provided corroborating evidence for these binding interactions and indicated multiple high-affinity modes of binding. All OH-PCB precursors for these sulfates were found to be substrates for hSULT1A1.
  
  
  CONCLUSIONS
  Our findings show that PCB sulfates are high-affinity ligands for human TTR and therefore indicate, for the first time, a potential relevance for these metabolites in PCB-induced thyroid disruption.
authors.affiliation: Interdisciplinary Graduate Program in Human Toxicology, Department of Pharmaceutical Sciences and Experimental Therapeutics, College of Pharmacy, College of Public Health, The University of Iowa, Iowa City, Iowa 52246, USA.
authors.forename: Fabian A
authors.initials: FA
authors.lastname: Grimm
authors.forename: Hans-Joachim
authors.initials: HJ
authors.lastname: Lehmler
authors.forename: Xianran
authors.initials: X
authors.lastname: He
authors.forename: Larry W
authors.initials: LW
authors.lastname: Robertson
authors.forename: Michael W
authors.initials: MW
authors.lastname: Duffel
mesh_terms: D015239:Arylsulfotransferase / Q000378:metabolism; D006801:Humans; D008024:Ligands; D062105:Molecular Docking Simulation; D011078:Polychlorinated Biphenyls / Q000378:metabolism*; D011228:Prealbumin / Q000378:metabolism*; D013431:Sulfates / Q000378:metabolism; D013974:Thyroxine / Q000378:metabolism
chemical_list: D008024:Ligands; D011228:Prealbumin; D013431:Sulfates; D011078:Polychlorinated Biphenyls; D015239:Arylsulfotransferase; C117544:SULT1A1 protein, human; D013974:Thyroxine