G-protein-coupled receptor that senses changes in the extracellular concentration of calcium ions and plays a key role in maintaining calcium homeostasis (PubMed:8255296). Senses fluctuations in the circulating calcium concentration and modulates the production of parathyroid hormone (PTH) in parathyroid glands (By similarity). The activity of this receptor is mediated by a G-protein that activates a phosphatidylinositol-calcium second messenger system (PubMed:8255296). The G-protein-coupled receptor activity is activated by a co-agonist mechanism: aromatic amino acids, such as Trp or Phe, act concertedly with divalent cations, such as calcium or magnesium, to achieve full receptor activation (By similarity). In resting state, adopts an open conformation, anion-binding promoting the inactive configuration. Upon aromatic amino acid-binding, the groove in the extracellular venus flytrap module is closed, thereby inducing the formation of a novel homodimer interface between subunits. Calcium ions stabilize the active state by enhancing homodimer interactions between membrane-proximal domains to fully activate the receptor. Homodimer; disulfide-linked. Interacts with VCP and RNF19A (By similarity). Interacts with ARRB1 (By similarity). The extracellular regions of the homodimer interact in a side-by-side fashion while facing opposite directions. Each extracellular region consists of three domains, LB1 (ligand-binding 1), LB2 and CR (cysteine-rich). The two lobe-shaped domains LB1 and LB2 form a venus flytrap module. In the inactive configuration, the venus flytrap modules of both protomers are in the open conformation associated with the resting state (open-open) and the interdomain cleft is empty. In addition, each protomer contains three anions, which reinforce the inactive conformation, and one calcium ion. In the active configuration, both protomers of extracellular regions have the closed conformation associated with agonist-binding (closed-closed). The ligand-binding cleft of each protomer is solely occupied by an aromatic amino-acid. Calcium is bound at four novel sites, including one at the homodimer interface. Agonist-binding induces large conformational changes within the extracellular region homodimer: first, the venus flytrap module of each protomer undergoes domain closure. Second, the LB2 regions of the two protomers approach each other, resulting in an expansion of the homodimer interactions involving LB2 domains. Third, the CR regions of the two subunits interact to form a large homodimer interface that is unique to the active state. The CR regions are brought into close contact by the motion involving LB2 since the two domains are rigidly associated within each subunit. N-glycosylated. Ubiquitinated by RNF19A; which induces proteasomal degradation. Belongs to the G-protein coupled receptor 3 family.