The TR-FRET Progesterone Receptor Coactivator Assay Kit provides a sensitive and robust method for high-throughput screening of potential progesterone receptor (PR) ligands as agonists or antagonists of ligand-dependent coactivator recruitment. The kit uses a PR ligand--binding domain (PR-LBD) tagged with glutathione-S-transferase (GST) (also available separately), a terbium (Tb)-labeled anti-GST antibody, and a fluorescein-labeled coactivator peptide in a homogenous mix-and-read assay format.
Agonist Mode
When using the LanthaScreen TR-FRET Progesterone Receptor Coactivator Assay in agonist mode (to identify agonist compounds), PR-LBD is added to ligand test compounds, followed by the addition of a mixture of fluorescein-labeled coactivator peptide and Tb-labeled anti-GST antibody. After an incubation period at room temperature, the TR-FRET ratio of 520/495 nm is calculated and can be used to determine the EC50 from a dose response curve of the compound. Based on the biology of the PR-coactivator peptide interaction, this ligand EC50 is a composite value representing the amount of ligand required to bind to receptor, effect a conformational change, and recruit coactivator peptide.
Antagonist Mode
When using the TR-FRET Progesterone Receptor Coactivator Assay in antagonist mode (to identify antagonist compounds), PR-LBD is added to ligand test compounds followed by addition of a mixture of agonist, fluorescein-labeled coactivator peptide, and terbium-labeled anti-GST antibody. The concentration of agonist used in this mode is the EC80 concentration as determined by first running the assay in agonist mode.