title: Interaction of the N-terminus of ecdysone receptor isoforms with the ligand-binding domain.
abstract: Ecdysone receptor (EcR) isoforms exert different biological functions, although they vary only in their N-terminal domain. Despite identical C-termini, which mediate hormone-induced activity, the influence of ligand is isoform specific, which indicates an N/C-interaction. The position of helix 12 with and without hormone varies among isoforms and modifies N/C-interaction determined by fluorescence resonance-energy transfer (FRET), which depends on the salt bridge between helices 4 and 12 of the ligand-binding domain (LBD). Disruption of the salt bridge by mutation of K497 (helix 4) had no effect on basal N/C-interaction, but prevented the hormone-induced increase, which was partially restored by a salt bridge with reversed polarity. The heterodimerization partner Ultraspiracle (Usp) can compensate for the disruption of the salt bridge. Without ligand the AB-domains of EcR-A and EcR-B1, but not EcR-B2, interact with the LBD via K497 and repress transcriptional activity. This intramolecular cross talk between N- and C-terminus along with the position of helix 12 stabilized by K497 regulates transcriptional activity of EcR isoforms.
authors.affiliation: Institute of General Zoology and Endocrinology, Ulm University, 89069 Ulm, Germany.
authors.forename: Ch
authors.initials: Ch
authors.lastname: Tremmel
authors.forename: M
authors.initials: M
authors.lastname: Schaefer
authors.forename: A
authors.initials: A
authors.lastname: Azoitei
authors.forename: H
authors.initials: H
authors.lastname: Ruff
authors.forename: M
authors.initials: M
authors.lastname: Spindler-Barth
mesh_terms: D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D029721:Drosophila Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster / Q000235:genetics / Q000378:metabolism; D031541:Fluorescence Resonance Energy Transfer; D008024:Ligands; D009154:Mutation; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011987:Receptors, Steroid / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D029721:Drosophila Proteins; D008024:Ligands; D020033:Protein Isoforms; D011987:Receptors, Steroid; D011993:Recombinant Fusion Proteins; C055469:ecdysone receptor