PTH (parathyroid hormone) regulates Ca2+ and phosphate homeostasis through its action on specific receptors in kidney and bone. There are two known PTH receptors in humans, PTH receptor type 1 (PTH1 receptor) and PTH receptor type 2 (PTH2 receptor).The PTH2 receptor is a member of a class B subfamily of G-protein-coupled receptors that includes the receptors for the glucagon-GHRH-VIP family of peptides (glucagon, GLP-I, GIP, GHRH, VIP, secretin, PACAP) and for calcitonin and CRF2. PTH2 receptor shares the same basic structure of the GPCR superfamily of proteins. A defining feature of the family B receptors is the relatively long extracellular N-terminal domain, which comprises about 150 amino acids and is important for ligand binding. The seven transmembrane domains are believed to be arranged in a circular or oval configuration, as seen in rhodopsin. The transmembrane domains are connected by three extracellular and three intracellular loops, and a C-terminal tail of about 130 amino acids extends intracellularly