Multi-Coloured Sequential Resonance Energy Transfer for Simultaneous Ligand Binding at G Protein-Coupled Receptors

Abstract

G protein coupled receptors (GPCRs) are the largest family of signalling proteins and highly successful drug targets. Most GPCR drugs interact with a binding pocket for the natural ligand, typically near the extracellular region of the transmembrane domains. Advancements in structural biology have identified additional allosteric binding sites in other parts of these receptors. Allosteric sites provide theoretical advantages, including the ability to modulate natural ligand function, and there is a need for better ways to study how ligands interact with these binding sites. We have developed an approach to study multiple ligands binding to the same receptor at the same time based on sequential resonance energy transfer between two fluorescent ligands bound to a GPCR. We use this approach to identify novel ligand pharmacology and understand binding kinetics to the FFA1 free fatty acid receptor, a clinically relevant receptor. This novel method will aid development of new GPCR drugs.