title: Crystal structure of the ligand-binding domain of the ultraspiracle protein USP, the ortholog of retinoid X receptors in insects.
abstract: The major postembryonic developmental events happening in insect life, including molting and metamorphosis, are regulated and coordinated temporally by pulses of ecdysone. The biological activity of this steroid hormone is mediated by two nuclear receptors: the ecdysone receptor (EcR) and the Ultraspiracle protein (USP). The crystal structure of the ligand-binding domain from the lepidopteran Heliothis virescens USP reported here shows that the loop connecting helices H1 and H3 precludes the canonical agonist conformation. The key residues that stabilize this unique loop conformation are strictly conserved within the lepidopteran USP family. The presence of an unexpected bound ligand that drives an unusual antagonist conformation confirms the induced-fit mechanism accompanying the ligand binding. The ligand-binding pocket exhibits a retinoid X receptor-like anchoring part near a conserved arginine, which could interact with a USP ligand functional group. The structure of this receptor provides the template for designing inhibitors, which could be utilized as a novel type of environmentally safe insecticides.
authors.affiliation: Genomics and Structural Biology Laboratory, UPR 9004, Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/Université Louis Pasteur, 1 rue Laurent Fries, 67404 Illkirch Cedex, Cité Universitaire de Strasbourg, France.
authors.forename: I M
authors.initials: IM
authors.lastname: Billas
authors.forename: L
authors.initials: L
authors.lastname: Moulinier
authors.forename: N
authors.initials: N
authors.lastname: Rochel
authors.forename: D
authors.initials: D
authors.lastname: Moras
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018360:Crystallography, X-Ray; D019476:Insect Proteins / Q000737:chemistry*; D007313:Insecta; D007915:Lepidoptera; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D047488:Retinoid X Receptors; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D019476:Insect Proteins; D008024:Ligands; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D014157:Transcription Factors