insect neuropeptide receptor subgroup B3 and related proteins belong to subfamily B1 of hormone receptors; member of the class B secretin-like seven-transmembrane G protein-coupled receptors
This subgroup includes a neuropeptide receptor found in Bombyx mori (silk worm) and its closely related proteins from arthropods. They belong to the B1 subfamily of class B GPCRs, also referred to as secretin-like receptor family, which includes receptors for polypeptide hormones of 27-141 amino-acid residues such as secretin, glucagon, glucagon-like peptide (GLP), calcitonin gene-related peptide, parathyroid hormone (PTH), and corticotropin-releasing factor. 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. All members of the B1 subfamily preferentially couple to G proteins of G(s) family, which positively stimulate adenylate cyclase, leading to increased intracellular cAMP formation and calcium influx. The class B GPCRs have been identified in all the vertebrates, from fishes to mammals, as well as invertebrates including Caenorhabditis elegans and Drosophila melanogaster, but are not present in plants, fungi, or prokaryotes.
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