Recombinant Albumin and Transthyretin Transport Proteins from Two Gull Species and Human: Chlorinated and Brominated Contaminant Binding and Thyroid Hormones

摘要

Environmentally relevant concentrations of selected potychlo-rinated biphenyl (PCB) and polybrominated diphenyl ether (PBDE) flame retardant congeners and their hydroxylated (OH) and methoxylated(MeO) analogues that can perturb thyroid hormone-dependent processes were comparatively examined with respect to competitive binding with thyroxine (T_4) and 3,5,3'-triiodothyronine (T_3) thyroid hormones (THs) on recombinant human and gull albumin and transthyretin transport proteins. The liver tissue was from glaucous gulls (Laws hyperboreus) from Norway and herring gulls (Laws argentatus) from the Great Lakes of North America. We isolated, cloned, sequenced, purified, and expressed the cDNA (cDNA) of albumin from liver of herring and glaucous gull. Albumin amino acid sequences were identical for both gull species. Concentration-dependent competitive binding curves were generated for T_4 and T_3 binding alone and for selected substrates using gull and human recombinant albumin (recALB). Human recALB had high preference for T_4 relative to T_3, whereas it was reversed for gull recALB. Binding assays with recALB and recTTR gull proteins showed that relative to 2,2',4,4'-tetrabromoDE (BDE-47) and 2,2',3,4',5,5',6-heptaCB (CB-187) and the MeO-substituted (4-MeO-CB187 and 6-MeO-BDE47) analogues, 4-OH-CB187,6-OH-BDE47, and 4'-OH-BDE49 had the greatest binding affinity and potency, and that competitive binding was greater for T_3 relative to T_4. These results indicate that xenobiotic ligand binding to human ALB or TTR cannot be used as a surrogaternfor gull binding interactions. The combination of TH-like brominated diphenyl ether backbone (relative to the chlorinated biphenyl backbone), and the presence of OH-group produced a more effective competitive ligand on human and gull recALB and recTTR relative to both T_3 and T_4. This suggests the possibility that OH-substituted organohalogen contaminants may be an exposure concern to the thyroid system in free-ranging gulls as well as for humans.