Considerations on the structural evidence of a ligand-binding function of ultraspiracle, an insect homolog of vertebrate RXR

This analysis considers the structural evidence of a ligand-binding function of the nuclear receptor ultraspiracle (USP). The positions and nature of residues in the ligand-binding domain of USP from six higher insects is evaluated in comparison to the function of conserved residues vertebrate receptors that have been co-crystallized with ligand. USP appears to conserve residues that in vertebrate receptors (1) form the hydrophobic ligand-binding pocket, (2) contact oxygen-containing moieties on ligands, such as hydroxyl, keto and carboxyl groups, and (3) in response to ligand-binding conformationally change to form a multi-helix hydrophobic groove for recruitment of transcriptional co-activators. These structural features are consistent with the recent report that USP can bind the epoxymethylfarnesoates (juvenile hormones) and thereupon is induced to change conformation. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.