The collaboration, assisted by a grant from France's National Research Agency (ANR), developed new ways of analysing the structure, mechanisms and functionality of one of the most important drug target classes - G protein-coupled receptors (GPCRs). GPCRs comprise a large family of transmembrane receptors that detect the presence of molecules outside of the cell and activate signal pathways that lead to cell responses. These pathways play a critical role in a diverse range of medical conditions ranging from heart failure, high blood pressure, breast cancer and schizophrenia. Even though GPCR-based drugs make up 12 of the 20 top selling drugs and account for nearly $200bn (€159bn) in annual sales, little is known of how they are organised at the cell surface. One of the historical problems with analysing the organisation of GPCRs has been that traditional analysis methods such as FRET (fluorescence resonance energy transfer) and BRET (bioluminescence resonance energy transfer) have been unable to discriminate GPCRs at the cell surface from intracellular receptors. This problem can be solved by using the TR-FRET (time-resolved FRET) technique in combination with Cisbio's HTRF (homogeneous time resolved fluorescence) and SNAP tag technology. In papers recently published in Nature Methods and in The European Molecular Biology Organisation Journal the researchers described the development of TR-FRET assays using SNAP-tag technology to demonstrate for the first time that GPCRs adopt specific structures on the cell surface. According to Eric Trinquet, head of technology and chemistry at Cisbio, the papers show that different GPCRs assemble into either strict dimers or larger oligomers and these structures can play a key role in regulating cell signalling. "The existence of GPCR oligomers has long been a matter of intense debate," said Dr Jean-Philippe Pin, head of IGF's Department of Molecular Pharmacology. "Thanks to the TR-FRET/SNAP-Tag approach, we have been able to provide new and convincing evidence for the existence of such complexes that offer a number of possibilities to design more selective and more effective drugs." The researchers obtained evidence for the oligomeric state of class A and class C GPCRs as well as observing different quaternary structures of GPCRs for the neurotransmitters glutamate and bold gamma-aminobutyric acid (GABA). While metabotropic glutamate receptors (mGluR) assemble into strict dimers, the gamma aminobutyric acid type B (GABAB) receptors spontaneously form dimers of heterodimers. Trinquet told LabTechnologist.com that these results open up a new field of investigation that could lead to the discovery of more effective therapeutic medicines that exploit the complicated organisation of GPCRs at the cell surface. The new GPCR assay technology is currently available as part of Cisbio's custom assay development services and the team is investigating ways to expand its use to the study of other interactions. "This technology is so easy to use that we are now working on new assays allowing the analysis of receptor complexes in native tissues, and new efficient ways to quantify ligand-receptor interaction," said Dr Pin.