PDB 1bl1 ; 17-30; PDB 1et2 S 184-46 PDB 1et3 S 184-46
Secretin family of 7 transmembrane receptors is a family of evolutionarily related proteins.
This family is known as Family B, the secretin-receptor family or family 2 of the G-protein-coupled receptors.They have been described in many animal species, but not in plants, fungi or prokaryotes. Three distinct sub-families (B1-B3) are recognized. Many secretin receptors are regulated by peptide hormoness from the glucagon hormone family.
The secretin-like GPCRs include secretin, calcitonin, parathyroid hormone/parathyroid hormone-related peptides and vasoactive intestinal peptide receptors, all of which activate adenylyl cyclase and the phosphatidyl-inositol-calcium pathway. These receptors have 7 transmembrane helices, like rhodopsin-like GPCRs. However,there is no significant sequence identity between these families: the secretin-like receptors thus bear their own unique '7TM' signature.
Subfamily B2 contains receptors with long extracellular N-termini, such as the leukocyte cell-surface antigen CD97; calcium-independent receptors for latrotoxin (such as UniProt O94910, and brain-specific angiogenesis inhibitor receptors (such as UniProt O14514) amongst others.
Subfamily B3 includes Methuselah and other Drosophila proteins. Other than the typical seven-transmembrane region, characteristic structural features include an amino-terminal extracellular domain involved in ligand binding, and an intracellular loop (IC3) required for specific G-protein coupling.