invertebrate parathyroid hormone-related receptors, member of the class B family of seven-transmembrane G protein-coupled receptors
This group includes parathyroid hormone (PTH)-related receptors found in invertebrates such as mollusks and annelid worms. The PTH family receptors are members of the B1 subfamily of class B GPCRs, which includes receptors for polypeptide hormones of 27-141 amino-acid residues such as secretin, glucagon, glucagon-like peptide (GLP), and calcitonin gene-related peptide. These receptors contain the large N-terminal extracellular domain (ECD), which plays a critical role in hormone recognition by binding to the C-terminal portion of the peptide. On the other hand, the N-terminal segment of the hormone induces receptor activation by interacting with the receptor transmembrane domains and connecting extracellular loops, triggering intracellular signaling pathways. The parathyroid hormone type 1 receptor (PTH1R) is found in all vertebrate species and is activated by two polypeptide ligands: parathyroid hormone (PTH), an endocrine hormone that regulates calcium homoeostasis and bone maintenance, and PTH-related peptide (PTHrP), a paracrine factor that regulates endochondral bone development. PTH1R couples predominantly to G(s)- protein that in turn activates adenylyl cyclase thereby producing cAMP, but it can also couple to several G protein subtypes, including G(q/11), G(i/o), and G(12/13), resulting in activation of multiple signaling pathways.
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