The present invention relates to novel biosensors that are based on
bioluminescence resonance energy transfer (BRET). These biosensors may be used to monitor rapid interaction and conformational changes within
G protein-coupled
receptor /
G protein complexes and, in this way, reflect the activation status of the
receptor. Advantageously, the biosensors may be used as a
highly sensitive and
quantitative assay for the identification of ligands (agonists, antagonists, inverse agonists, partial agonists, etc.) targeting
G protein-coupled receptors (GPCRs) as well as for the analysis of the activation status of these receptors. Moreover,
multiplexing different biosensors within receptors / G
protein complexes allows for mapping ligand textures. Additionally, the biosensors permit the direct, real-time examination of interactions between receptors and G
protein in their
natural environment, the
living cell.