TAILIEUCHUNG - Báo cáo Y học: Ligand-induced heterodimerization between the ligand binding domains of the Drosophila ecdysteroid receptor and ultraspiracle

The insect ecdysteroid receptor consists of a heterodimer between EcR and the RXR-orthologue, USP. We addressed the question of whether this heterodimer, like all other RXR heterodimers, may be formed in the absence of ligand and whether ligand promotes dimerization. We found that C-terminal protein fragments that comprised the ligand binding, but not the DNA binding domain of EcR and USP and which were equipped with the activation or DNA binding region of GAL4, respectively, exhibit a weak ability to interact spontaneously with each other. Moreover, the heterodimer formation is greatly enhanced upon administration of active ecdysteroids in a dose-dependent. | Eur. J. Biochem. 269 3237-3245 2002 FEBS 2002 doi Ligand-induced heterodimerization between the ligand binding domains of the Drosophila ecdysteroid receptor and ultraspiracle Markus Lezzi1 Thomas Bergman1 Vincent C. Henrich2 Martin Vogtli1 t Christina Fromel1 Marco Grebe3 Sabina Przibilla3 and Margarethe Spindler-Barth3 Institute for Cell Biology ETH-Honggerberg Zurich Switzerland department of Biology University of North Carolina Greensboro NC USA 3Abteilung fur allgemeine Zoologie und Endokrinologie Universitãt D-89069 Ulm Germany The insect ecdysteroid receptor consists of a heterodimer between EcR and the RXR-orthologue USP. We addressed the question of whether this heterodimer like all other RXR heterodimers may be formed in the absence of ligand and whether ligand promotes dimerization. We found that C-terminal protein fragments that comprised the ligand binding but not the DNA binding domain of EcR and USP and which were equipped with the activation or DNA binding region of GAL4 respectively exhibit a weak ability to interact spontaneously with each other. Moreover the heterodimer formation is greatly enhanced upon administration of active ecdysteroids in a dose-dependent manner. This was shown in vivo by a yeast two-hybrid system and in vitro by a modified electromobility shift assay. Furthermore the EcR fragment expressed in yeast was functional and bound radioactively labelled ecdysteroid specifically. Ligand binding was greatly enhanced by the presence of a USPligand binding domain. Therefore ecdysteroids are capable of inducing heterodimer formation between EcR and USP even when the binding of these receptor proteins to cognate DNA response elements does not occur. This capability may be a regulated aspect of ecdysteroid action during insect development. Keywords Drosophila melanogaster yeast two-hybrid ecdysone receptor dimerization ultraspiracle. Ecdysteroids are widespread steroid hormones found in invertebrates 1 .

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