title: Post-translational modifications of transthyretin affect the triiodonine-binding potential.
abstract: Transthyretin (TTR) is a visceral protein, which facilitates the transport of thyroid hormones in blood and cerebrospinal fluid. The homotetrameric structure of TTR enables the simultaneous binding of two thyroid hormones per molecule. Each TTR subunit provides a single cysteine residue (Cys10 ), which is frequently affected by oxidative post-translational modifications. As Cys10 is part of the thyroid hormone-binding channel within the TTR molecule, PTM of Cys10 may influence the binding of thyroid hormones. Therefore, we analysed the effects of Cys10 modification with sulphonic acid, cysteine, cysteinylglycine and glutathione on binding of triiodothyronine (T3) by molecular modelling. Furthermore, we determined the PTM pattern of TTR in serum of patients with thyroid disease by immunoprecipitation and mass spectrometry to evaluate this association in vivo. The in silico assays demonstrated that oxidative PTM of TTR resulted in substantial reorganization of the intramolecular interactions and also affected the binding of T3 in a chemotype- and site-specific manner with S-glutathionylation as the most potent modulator of T3 binding. These findings were supported by the in vivo results, which indicated thyroid function-specific patterns of TTR with a substantial decrease in S-sulphonated, S-cysteinylglycinated and S-glutathionylated TTR in hypothyroid patients. In conclusion, this study provides evidence that oxidative modifications of Cys10 seem to affect binding of T3 to TTR probably because of the introduction of a sterical hindrance and induction of conformational changes. As oxidative modifications can be dynamically regulated, this may represent a sensitive mechanism to adjust thyroid hormone availability.
authors.affiliation: Institute of Nutrition, University of Potsdam, Nuthetal, Germany.
authors.forename: Andrea
authors.initials: A
authors.lastname: Henze
authors.forename: Thomas
authors.initials: T
authors.lastname: Homann
authors.forename: Mustafa
authors.initials: M
authors.lastname: Serteser
authors.forename: Ozge
authors.initials: O
authors.lastname: Can
authors.forename: Ozlem
authors.initials: O
authors.lastname: Sezgin
authors.forename: Abdurrahman
authors.initials: A
authors.lastname: Coskun
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Unsal
authors.forename: Florian J
authors.initials: FJ
authors.lastname: Schweigert
authors.forename: Aysel
authors.initials: A
authors.lastname: Ozpinar
mesh_terms: D001692:Biological Transport / Q000502:physiology; D003545:Cysteine / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011228:Prealbumin / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology*; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D014284:Triiodothyronine / Q000378:metabolism*
chemical_list: D011228:Prealbumin; D014284:Triiodothyronine; D003545:Cysteine
keywords: cysteine oxidation; mass spectrometry; molecular modelling; post-translational modifications; thyroid hormones; transthyretin; triiodthyronine