Use of fluorescence polarization detection for the measurement of fluopeptidetm binding to G protein-coupled receptors

G protein-coupled receptors (GPCRs) represent the single largest molecular target of therapeutic drugs currently on the market, and are also the most common target in high throughput screening assays designed to identify potential new drug candidates. A large percentage of these assays are now formatted as radioligand binding assays. Fluorescence polarization ligand binding assays can offer a non-rad alternative to radioligand binding assays. In addition, fluorescence polarization assays are a homogenous format that is easy to automate for high throughput screening. We have developed a series of peptide ligands labeled with the fluorescent dye BODIPY TMR whose binding to GPCRs can be detected using fluorescence polarization methodology. BODIPY TMR has advantages over the more commonly used fluorescein dye in high throughput screening (HTS) assays due to the fact that its excitation and emission spectra are red-shifted approximately 50 nm relative to fluorescein. Assays based on BODIPY TMR ligands are therefore less susceptible to interference from tissue auto-fluorescence in the assay matrix, or the effects of colored or fluorescent compounds in the screening libraries. A series of BODIPY TMR labeled peptides have been prepared that bind to a range of GPCRs including melanin concentrating hormone, bradykinin, and melanocortin receptors. Conditions have been optimized in order to utilize a comparable amount of receptor membrane preparation as is used in a radioligand binding assay. The assays are formatted in 384-well microplates with a standard volume of 40 microL. We have compared the assays across the different fluorescence polarization (FP) readers available to determine the parameters for each instrument necessary to achieve the required precision.