A STRUCTURAL ROLE FOR HORMONE IN THE THYROID-HORMONE RECEPTOR

The crystal structure of the rat a, thyroid hormone receptor ligand-bi nding domain bound with a thyroid hormone agonist reveals that ligand is completely buried within the domain as part of the hydrophobic core . In addition, the carboxy-terminal activation domain forms an amphipa thic helix, with its hydrophobic face constituting part of the hormone binding cavity. These observations suggest a structural role for liga nd, in establishing the active conformation of the receptor, that is l ikely to underlie hormonal regulation of gene expression for the nucle ar receptors.