Secretin receptor family
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 B1
Subfamily B1 contains classical hormone receptors, such as receptors for secretin and glucagon, that are all involved in cAMP-mediated signalling pathways.
- Adenylate cyclase-activating type 1 receptor, pituitary InterPro: IPR002285
ADCYAP1R1
- ADCYAP1R1
- Calcitonin receptor InterPro: IPR003287
CALCR; CALCRL
- CALCR; CALCRL
- Corticotropin-releasing hormone receptor InterPro: IPR003051
CRHR1; CRHR2
- CRHR1; CRHR2
- Glucagon receptor-related InterPro: IPR003290
GLP1R; GLP2R; GPCR
- GLP1R; GLP2R; GPCR
- Growth hormone releasing hormone receptor InterPro: IPR003288
GHRHR
- GHRHR
- Parathyroid hormone receptor InterPro: IPR002170
PTHR1; PTHR2
- PTHR1; PTHR2
- Secretin receptor InterPro: IPR002144
SCTR
- SCTR
- Vasoactive intestinal peptide receptor InterPro: IPR001571
VIPR1;     VIPR2
- VIPR1;     VIPR2

# Subfamily B2
Subfamily B2 contains receptors with long extracellular N-termini, such as the leukocyte cell-surface antigen CD97; calcium-independent receptors for latrotoxin (such as O94910, and brain-specific angiogenesis inhibitor receptors (such as O14514) amongst others.
- Brain-specific angiogenesis inhibitor InterPro: IPR008077
BAI1; BAI2; BAI3
- BAI1; BAI2; BAI3
- CD97 antigen InterPro: IPR003056
CD97
- CD97
- EMR hormone receptor InterPro: IPR001740
CELSR1; CELSR2; CELSR3; EMR1; EMR2; EMR3; EMR4
- CELSR1; CELSR2; CELSR3; EMR1; EMR2; EMR3; EMR4
- Gastric inhibitory polypeptide receptor InterPro: IPR001749
GCGR; GIPR
- GCGR; GIPR
- GPR56 orphan receptor InterPro: IPR003910
GPR56; GPR64; GPR97; GPR110; GPR111; GPR112; GPR113; GPR114; GPR115; GPR123; GPR125; GPR126; GPR128; GPR133; GPR144; GPR157
- GPR56; GPR64; GPR97; GPR110; GPR111; GPR112; GPR113; GPR114; GPR115; GPR123; GPR125; GPR126; GPR128; GPR133; GPR144; GPR157
- Latrophilin receptor InterPro: IPR003924
ELTD1; LPHN1; LPHN2; LPHN3
- ELTD1; LPHN1; LPHN2; LPHN3

# Subfamily B3
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.
- Diuretic hormone receptor InterPro: IPR002001

# Unclassified subfamilies
- Ig-hepta receptor InterPro: IPR008078
GPR116
- GPR116

# Unclassified members
DREG; HCTR-5; HCTR-6; KPG_003; KPG_006; KPG_008; KPG_009; RESDA1