Description
Retinoid X Receptor (RXR) serves as a promiscuous heterodimerization partner for many nuclear receptors through the identity box, a 40-amino acid subregion within the ligand binding domain (LBD). RXR partners include Thyroid Hormone Receptors (TRs), Retinoic Acid Receptors (RARs), Peroxisome Proliferatoractivated Receptor, several constitutive active orphan nuclear receptors (e.g. Nuclear Growth Factor I-B), oxysterol receptors, and constitutive androstane receptors. RXRs also form homodimers to mediate the effects of 9-cis-retinoic acid (9-cRA). Depending on these protein-protein interactions, RXR-containing complexes have distinct ligand-dependent and constitutive functions. The LBD is functionally complex and mediates ligand binding, receptor homo- and heterodimerization, repression of transcription in the absence of ligand, and ligand-dependent activation of transcription. Hormone binding to the structurally conserved LBD of the RXR triggers a conformational change that principally affects the conserved C-terminal transactivation helix H12 involved in transcriptional activation. Coactivators directly recruited by liganded receptors include members of the steroid receptor coactivator/p160 family such as SRC-1, transcriptional intermediary factor 2/glucocorticoid receptor interacting protein 1, and RAC3/activator of thyroid and retinoic acid receptors/amplified in breast cancer 1. Recombinant GST-RXR-LBD is isolated from an E.coli strain that carries the coding sequence of the human RXR-LBD under the control of a T7 promoter