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Biological Chemistry

Editor-in-Chief: Brüne, Bernhard

Editorial Board Member: Buchner, Johannes / Ludwig, Stephan / Sies, Helmut / Turk, Boris / Wittinghofer, Alfred

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Characterization of Calmodulin Binding to the Orphan Nuclear Receptor ERRγ

M. Hentschke / C. Schulze / U. Süsens / U. Borgmeyer

Citation Information: Biological Chemistry. Volume 384, Issue 3, Pages 473–482, ISSN (Print) 1431-6730, DOI: 10.1515/BC.2003.053, June 2005

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The estrogen receptorrelated receptor γ (ERγ/ERR3/NR3B3), a member of the nuclear receptor superfamily, activates transcription in the absence of ligands. In order to identify ligand-independent mechanisms of activation, we tested whether calmodulin (CaM), a key regulator of numerous cellular processes and a predominant intracellular receptor for Ca2+-signals, interacts with ERRγ. In vitro pulldown experiments with calmodulin-Sepharose demonstrated a Ca2+-dependent interaction with cellularly expressed ERRγ. As shown by truncation analysis, the CaM binding site is highly unusual in that it is composed of two discontinuous elements. Moreover, by surface plasmon resonance (SPR) biosensor technology, we detected a direct interaction of immobilized bacterially expressed ERRγ fusion protein with Ca2+-calmodulin. This is best described by a model which assumes a conformational change of the initially formed complex to a more stable form. Whereas in vitro DNA binding was calmodulinindependent, transient transfection analysis revealed a Ca2+-influxdependent ERRγmediated transcriptional activation of a luciferase reporter gene. Thus, we propose that CaM acts as a mediator in the Ca2+-dependent modulation of ERRγ.

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