Steroid nuclear hormone receptors: The allosteric conversation

Nuclear hormone receptors (NHRs) regulate gene expression by forming complexes with small molecule ligands, other proteins, and DNA. Specific ligands, which include steroids, thyroids, and retinoids, are responsible for the regulation of complex processes in cellular differentiation, homeostasis, reproduction, and development. NHRs responding to steroid ligands (e.g., androgens, estrogens, glucocorticoids, mineralocorticoids, and progesterones) are the focus of this review, in particular, highlighting the subtle relationships between ligand structure and receptor function. In the light of x‐ray crystallographic information obtained in recent years, the structural organization of the ligand‐ and DNA‐binding domains of steroid nuclear hormone receptors is well understood. Less clear is the means by which a steroid ligand affects the three‐dimensional structure of a receptor, and how subtle differences in ligand structure can lead to major differences in functional activity (agonism, partial agonism, antagonism). Potential mechanisms by which ligands elicit such effects, statistical and mutational techniques used to identify key protein residues likely involved in the transmission of structural information, and novel sites of ligand–protein interaction are discussed in this review. Drug Dev Res 68:95–106, 2007. © 2007 Wiley‐Liss, Inc.