The human G protein-coupled receptor GPCR) superfamily is composed of over 800 seven transmembrane (7TM) receptors that can be divided into four classes based on their sequence homology: class A, B, and Frizzled (F). Class C GPCRs play important roles in many physiological processes such as synaptic transmission, taste sensation and calcium homeostasis. and include metabotropic glutamate receptors (mGlu), y-aminobutyric acid B receptors (GABAB), calcium sensing receptor (CaS), taste 1 receptors