title: The oligomeric state of thyroid receptor regulates hormone binding kinetics.
abstract: We previously reported that mutations in the thyroid hormone receptor (TR) surface that mediates dimer and heterodimer formation do not alter affinity for cognate hormone (triiodothyronine (T(3))) yet dramatically enhance T(3) association and dissociation rates. This study aimed to show that TR oligomeric state influences binding and dissociation kinetics. We performed binding assays using marked hormone ((125)I-T(3)) and TRs expressed and purified by different methods. We find that T(3) associates with TRs with biphasic kinetics in solution; a rapid step (half-life ±0.1 h) followed by a slower second step (half-life ±5 h) and that purification of monomers suggests that biphasic kinetics are due to the presence of monomers and dimers in our preparations. In support of this idea, incubation of TR ligand binding domain monomers with corepressor peptide induces dimer formation and decreases association rates and T(3) binds to, and dissociates from, a TRβ mutant that only forms dimers (TRβD355R) with slow single-phase kinetics. In addition, heterodimer formation with retinoid X receptors also influences ligand binding kinetics. Together, these results suggest that the dimer/heterodimer surface is allosterically coupled to the hormone binding pocket and that different interactions at this surface exert different effects on ligand binding that may be relevant for TR actions in the cell.
authors.affiliation: Diabetes Center, University of California, 513 Parnassus Avenue, 94143 San Francisco, California, USA. stcunhalima@ufba.br
authors.forename: Suzana T
authors.initials: ST
authors.lastname: Cunha Lima
authors.forename: Edson D
authors.initials: ED
authors.lastname: Rodrigues
mesh_terms: D019943:Amino Acid Substitution; D056970:Co-Repressor Proteins; D019281:Dimerization; D024202:Electrophoretic Mobility Shift Assay; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D008024:Ligands; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D054730:Protein Interaction Domains and Motifs; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D047490:Retinoid X Receptor alpha / Q000235:genetics / Q000378:metabolism; D013499:Surface Properties; D037021:Thyroid Hormone Receptors alpha / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D037042:Thyroid Hormone Receptors beta / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism*; D014461:Ultracentrifugation
chemical_list: D056970:Co-Repressor Proteins; D007457:Iodine Radioisotopes; D008024:Ligands; D050505:Mutant Proteins; D010446:Peptide Fragments; D011994:Recombinant Proteins; D047490:Retinoid X Receptor alpha; D037021:Thyroid Hormone Receptors alpha; D037042:Thyroid Hormone Receptors beta; D014284:Triiodothyronine