Sammendrag
Top avian predator and aquatic food web species from contrasting ecosystems such as glaucous gulls (Larus hyperboreus) from Svalbard, Norway (marine) herring gulls (Larus argentatus) from the Great Lakes (freshwater) are differentially exposed to and bioaccumulate chlorine- and bromine-containing organic contaminants and degradation products that have potential activity with respect to thyroid hormone (TH)-dependent processes such as interaction with proteins. However, there is a dearth of information on TH transport proteins and such contaminant interactions in wild avian species. In the present study, sequenced a major TH transport protein in liver and brain of glaucous and herring gulls, transthyretin (TTR). The amino acid sequence showed 99% homology among TTR proteins regardless of gull species and tissue. We subsequently cloned, expressed and purified a general 'gull' TTR. The 'gull' pTTR2 plasmid cloned was subsequently transformed and the intact protein expressed using a BL21-RIPL E. Coli cell culture system. In comparison to commercially human TTR, the gullTTR was purified using Hi-Trap FF crude Kit , and used to assess the potency and efficacy of competitive binding of environmentally polychlorinated biphenyl (CB-187) and polybrominated diphenyl ether (BDE-47) flame retardant congeners and hydroxy- (4-OH-CB187, 6-OH-BDE47, OHBDE49) and methoxy- (4-MeO-CB187, 6-MeO-BDE47) analogue structures, relative to the natural ligands thyroxine (T4) and thyronine (T3). Relative the potency and efficacy of human and gull TTR competitive binding was in the order of OH-containing > MeO-containing > unsubstituted PCB or BDE addition, the potency and efficacy of binding was different between the human and gull TTR proteins. In conclusion this study increases our understanding these top predator avian species, and the interaction of contaminant ligands that can potentially perturb or disrupt the transport of thyroid hormones.
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