Ligand induced interaction of thyroid hormone receptor beta with its coregulators

Thyroid hormones exert most of their physiological effects through two thyroid hormone receptor (TR) subtypes, TRα and TRβ, which associate with many transcriptional coregulators to mediate activation or repression of target genes. The search for selective TRβ ligands has been stimulated by the finding that several pharmacological actions mediated by TRβ might be beneficial in medical conditions such as obesity, hypercholesterolemia and diabetes. Here, we present a new methodology which employs surface plasmon resonance to investigate the interactions between TRβ ligand binding domain (LBD) complexes and peptides derived from the nuclear receptor interaction motifs of two of its coregulators, SRC2 and DAX1. The effect of several TRβ ligands, including the TRβ selective agonist GC-1 and the TRβ selective antagonist NH-3, were investigated. We also determined the kinetic rate constants for the interaction of TRβ-T3 with both coregulators, and accessed the thermodynamic parameters for the interaction with DAX1. Our findings suggest that flexibility plays an important role in the interaction between the receptor and its coregulators, and point out important aspects of experimental design that should be addressed when using TRβ LBD and its agonists. Furthermore, the methodology described here may be useful for the identification of new TRβ ligands.