GTP binding is a method used to study distribution and functional activation of seven transmembrane, heterotrimeric G protein coupled family (GPCRs) receptors. This assay works best with Gi-coupled receptors. Upon activation of the GPCR by an agonist, the receptor changes conformation exposing a binding site for a G-protein complex. Once this G-protein complex is bound, the Gα protein can release GDP and bind GTP. These types of assays are sometimes referred to as a GTP exchange assay. Because the GTP used in this assay is a radiolabeled non-hydrolyzable analog ([35S]-GTPγS, which is GTP labeled on the gamma phosphate with 35S), you will be able to measure the activation of the GPCR being studied by measuring the amount of [35S]-GTPγS bound to the receptor.
Functional Assays can be used to:
- Determine the pharmacological values of potency (EC50) & efficacy (EMAX) of the ligand to activate the GPCR of interest.
- Visualize regional differences of activated GPCRs by a ligand using Functional Autoradiography.
- Determine if the ligand is a full agonist, partial agonist, inverse agonist or antagonist.
Specializing in both standard and custom in vitro functional assays, we are focused on providing the right assays for assessing a GPCR therapeutic's potential efficacy and liabilities to help identify candidate compounds for preclinical and clinical development. Combined with our radioligand binding assays, these functional assays can provide an integrated assessment of a drug candidate's in vitro pharmacology profile.