G protein coupled receptor G protein-coupled receptors (GPCRs), comprise the largest integral membrane protein family with nearly 1000 members. They integrate extracellular signals from hormones, growth factors, neurotransmitters, etc to downstream cellular responses. They are important pharmacological targets, being associated with a number of diseases. Upon ligand binding extracellularly, the GPCR signals through a downstream heterotrimeric G protein complex, consisting of the α, β and γ subunits. transmembrane receptor