Modulation of estradiol and DNA binding to estrogen receptor upon association with calmodulin.

The ability of calmodulin (CaM) to modify the conformation of the hormone binding domain (HBD) rat uterine estrogen receptor (ER) was investigated. Dissociation constant of estradiol (E2) binding to HBD increased almost 2-3-fold when CaM bound to ER; two other Ca(++)-binding proteins failed to show this property, demonstrating the specificity of the phenomenon. Elution on CaM-Sepharose of truncated ER molecules located the CaM binding domain of ER at the left edge of HBD. Association of CaM with activated [3H]E2-ER complexes increased the ability of the latter to interact with an estrogen response element (ERE) as demonstrated by DNA-cellulose competition assay; CaM also reinforces the potency of ERE to dissociate the [3H]E2-ER complex. We hypothesize that these CaM-induced conformational changes of ER may play a role in transcriptional activity of the latter.