seven-transmembrane G protein-coupled receptor superfamily; This hierarchical evolutionary model represents the seven-transmembrane (7TM) receptors, often referred to as G protein-coupled receptors (GPCRs), which transmit physiological signals from the outside of the cell to the inside via G proteins. GPCRs constitute the largest known superfamily of transmembrane receptors across the three kingdoms of life that respond to a wide variety of extracellular stimuli including peptides, lipids, neurotransmitters, amino acids, hormones, and sensory stimuli such as light, smell and taste. All GPCRs share a common structural architecture comprising of seven-transmembrane (TM) alpha-helices interconnected by three extracellular and three intracellular loops. A general feature of GPCR signaling is agonist-induced conformational changes in the receptors, leading to activation of the heterotrimeric G proteins, which consist of the guanine nucleotide-binding G-alpha subunit and the dimeric G-beta-gamma subunits. The activated G proteins then bind to and activate numerous downstream effector proteins, which generate second messengers that mediate a broad range of cellular and physiological processes. However, some 7TM receptors, such as the type 1 microbial rhodopsins, do not activate G proteins. Based on sequence similarity, GPCRs can be divided into six major classes: class A (the rhodopsin-like family), class B (the Methuselah-like, adhesion and secretin-like receptor family), class C (the metabotropic glutamate receptor family), class D (the fungal mating pheromone receptors), class E (the cAMP receptor family), and class F (the frizzled/smoothened receptor family). Nearly 800 human GPCR genes have been identified and are involved essentially in all major physiological processes. Approximately 40% of clinically marketed drugs mediate their effects through modulation of GPCR function for the treatment of a variety of human diseases including bacterial infections.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 148682934  62 ASYFYGVLQDFAGTSWDCVLQGALSTFANTSSFFWTVAIALYLYLSIVRTTrgPSTDHLIWAFHLISWGVPLAITVAAVS 141
Cdd:cd14940   51 IYTMLTLTQSARPDGFLCYLYAIVITYGSLSCWLWTLCLAISIYLLIVKRE--PEPEKFEKYYHFVCWGLPLISTIIMLI 128

                         90
                 ....*....|....*...
gi 148682934 142 LKKIGYdasdvSVGWCWI 159
Cdd:cd14940  129 KHHYGP-----VGNWCWI 141

slime mold cyclic AMP receptor, member of the class E family of seven-transmembrane G protein-coupled receptors; This family represents the class E of seven-transmembrane G-protein coupled receptors found in soil-living amoebas, commonly referred to as slime molds. The class E family includes cAMP receptors (cAR1-4) and cAMP receptors-like proteins (CrlA-C) from Dictyostelium discoideum, and their highly homologous cAMP receptors (TasA and TasB) from Polysphondylium pallidum. So far, four subtypes of cAMP receptors (cAR1-4) have been identified that play an essential role in the detection and transmit of the periodic extracellular cAMP waves that regulate chemotactic cell movement during Dictyostelium development, from the unicellular amoeba aggregate into many multicellular slugs and then differentiate into a sporocarp, a fruiting body with cells specialized for different functions. These four subtypes differ in their expression levels and patterns during development. cAR1 is high-affinity receptor that is the first one to be expressed highly during early aggregation and continues to be expressed at low levels during later developmental stages. cAR1 detects extracellular cAMP and is coupled to G-alpha2 protein. Cells lacking cAR1 fail to aggregate, demonstrating that cAR1 is responsible for aggregation. During later aggregation the high-affinity cAR3 receptor is expressed at low levels. Nonetheless, cells lacking cAR3 do not show an obviously altered pattern of development and are still able to aggregate into fruiting bodies. In contrast, cAR2 and cAR4 are low affinity receptors expressed predominantly after aggregation in pre-stalk cells. cAR2 is essential for normal tip formation and deletion of the receptor arrests development at the mound stage. On the other hand, CAR4 regulates axial patterning and cellular differentiation, and deletion of the receptor results in defects during culmination. Furthermore, three cAMP receptor-like proteins (CrlA-C) were identified in Dictyostelium that show limited sequence similarity to the cAMP receptors. Of these CrlA is thought to be required for normal cell growth and tip formation in developing aggregates.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 148682934  62 ASYFYGVLQDFAGTSWDCVLQGALSTFANTSSFFWTVAIALYLYLSIVRTTrgPSTDHLIWAFHLISWGVPLAITVAAVS 141
Cdd:cd14940   51 IYTMLTLTQSARPDGFLCYLYAIVITYGSLSCWLWTLCLAISIYLLIVKRE--PEPEKFEKYYHFVCWGLPLISTIIMLI 128

                         90
                 ....*....|....*...
gi 148682934 142 LKKIGYdasdvSVGWCWI 159
Cdd:cd14940  129 KHHYGP-----VGNWCWI 141

slime mold cyclic AMP receptor, member of the class E family of seven-transmembrane G protein-coupled receptors; This family represents the class E of seven-transmembrane G-protein coupled receptors found in soil-living amoebas, commonly referred to as slime molds. The class E family includes cAMP receptors (cAR1-4) and cAMP receptors-like proteins (CrlA-C) from Dictyostelium discoideum, and their highly homologous cAMP receptors (TasA and TasB) from Polysphondylium pallidum. So far, four subtypes of cAMP receptors (cAR1-4) have been identified that play an essential role in the detection and transmit of the periodic extracellular cAMP waves that regulate chemotactic cell movement during Dictyostelium development, from the unicellular amoeba aggregate into many multicellular slugs and then differentiate into a sporocarp, a fruiting body with cells specialized for different functions. These four subtypes differ in their expression levels and patterns during development. cAR1 is high-affinity receptor that is the first one to be expressed highly during early aggregation and continues to be expressed at low levels during later developmental stages. cAR1 detects extracellular cAMP and is coupled to G-alpha2 protein. Cells lacking cAR1 fail to aggregate, demonstrating that cAR1 is responsible for aggregation. During later aggregation the high-affinity cAR3 receptor is expressed at low levels. Nonetheless, cells lacking cAR3 do not show an obviously altered pattern of development and are still able to aggregate into fruiting bodies. In contrast, cAR2 and cAR4 are low affinity receptors expressed predominantly after aggregation in pre-stalk cells. cAR2 is essential for normal tip formation and deletion of the receptor arrests development at the mound stage. On the other hand, CAR4 regulates axial patterning and cellular differentiation, and deletion of the receptor results in defects during culmination. Furthermore, three cAMP receptor-like proteins (CrlA-C) were identified in Dictyostelium that show limited sequence similarity to the cAMP receptors. Of these CrlA is thought to be required for normal cell growth and tip formation in developing aggregates.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 148682934  62 ASYFYGVLQDFAGTSWDCVLQGALSTFANTSSFFWTVAIALYLYLSIVRTTrgPSTDHLIWAFHLISWGVPLAITVAAVS 141
Cdd:cd14940   51 IYTMLTLTQSARPDGFLCYLYAIVITYGSLSCWLWTLCLAISIYLLIVKRE--PEPEKFEKYYHFVCWGLPLISTIIMLI 128

                         90
                 ....*....|....*...
gi 148682934 142 LKKIGYdasdvSVGWCWI 159
Cdd:cd14940  129 KHHYGP-----VGNWCWI 141

adhesion receptors, subfamily B2 of the class B family of seven-transmembrane G protein-coupled receptors; The B2 subfamily of class B GPCRs consists of cell-adhesion receptors with 33 members in humans and vertebrates. The adhesion receptors are characterized by the presence of large N-terminal extracellular domains containing a variety of structural motifs, which play critical roles in cell-cell adhesion and cell-matrix interactions, linked to a class B seven-transmembrane domain. These include, for example, EGF (epidermal growth factor)-like domains in CD97, Celsr1 (cadherin family member), Celsr2, Celsr3, EMR1 (EGF-module-containing mucin-like hormone receptor-like 1), EMR2, EMR3, and Flamingo; two laminin A G-type repeats and nine cadherin domains in Flamingo and its human orthologs Celsr1, Celsr2 and Celsr3; olfactomedin-like domains in the latrotoxin receptors; and five or four thrombospondin type 1 repeats in BAI1 (brain-specific angiogenesis inhibitor 1), BAI2 and BAI3. Furthermore, almost all adhesion receptors, except GPR123, contain an evolutionarily conserved GPCR- autoproteolysis inducing (GAIN) domain that undergoes autoproteolytic processing at the GPCR proteolysis site (GPS) motif located immediately N-terminal to the first transmembrane region, to generate N- and C-terminal fragments (NTF and CTF), which may serve important biological functions.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 148682934  79 CVLQGALSTFANTSSFFWTVAIALYLYLSIVRTTrGPSTDHLIWAFHLISWGVPLAITVAAVSLKKIGYDASDvsvGWCW 158
Cdd:cd15040   68 CTAVAALLHYFLLASFMWMLVEALLLYLRLVKVF-GTYPRHFILKYALIGWGLPLIIVIITLAVDPDSYGNSS---GYCW 143

                 ..
gi 148682934 159 IN 160
Cdd:cd15040  144 LS 145

7 transmembrane receptor (Secretin family); This family is known as Family B, the secretin-receptor family or family 2 of the G-protein-coupled receptors (GCPRs). They have been described in many animal species, but not in plants, fungi or prokaryotes. Three distinct sub-families are recognized. Subfamily B1 contains classical hormone receptors, such as receptors for secretin and glucagon, that are all involved in cAMP-mediated signalling pathways. Subfamily B2 contains receptors with long extracellular N-termini, such as the leukocyte cell-surface antigen CD97; calcium-independent receptors for latrotoxin, and brain-specific angiogenesis inhibitors amongst others. Subfamily B3 includes Methuselah and other Drosophila proteins. Other than the typical seven-transmembrane region, characteriztic structural features include an amino-terminal extracellular domain involved in ligand binding, and an intracellular loop (IC3) required for specific G-protein coupling.

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                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 148682934   79 CVLQGALSTFANTSSFFWTVAIALYLYLSIVRTTrgPSTDHLIWAFHLISWGVPLAITVAAVSLKKIGYDASDVsvgwCW 158
Cdd:pfam00002  75 CKVVAVFLHYFFLANFFWMLVEGLYLYTLLVEVF--FSERKYFWWYLLIGWGVPALVVGIWAGVDPKGYGEDDG----CW 148

                  ....
gi 148682934  159 INLE 162
Cdd:pfam00002 149 LSNE 152

corticotropin-releasing factor receptors, member of the class B family of seven-transmembrane G protein-coupled receptors; The vertebrate corticotropin-releasing factor (CRF) receptors are predominantly expressed in central nervous system with high levels in cortex tissue, brain stem, and pituitary. They have two isoforms as a result of alternative splicing of the same receptor gene: CRF-R1 and CRF-R2, which differ in tissue distribution and ligand binding affinities. Recently, a third CRF receptor (CRF-R3) has been identified in catfish pituitary. The catfish CRF-R1 is highly homologous to CRF-R3. CRF is a 41-amino acid neuropeptide that plays a central role in coordinating neuroendocrine, behavioral, and autonomic responses to stress by acting as the primary neuroregulator of the hypothalamic-pituitary-adrenal axis, which controls the levels of cortisol and other stress related hormones. In addition, the CRF family of neuropeptides also includes structurally related peptides such as mammalian urocortin, fish urotensin I, and frog sauvagine. The actions of CRF and CRF-related peptides are mediated through specific binding to CRF-R1 and CRF-R2. CRF and urocortin 1 bind and activate mammalian CRF-R1 with similar high affinities. By contrast, urocortin 2 and urocortin 3 do not bind to CRF-R1 or stimulate CRF-R1-mediated cAMP formation. Urocortin 1 also shows high affinity for mammalian CRF-R2, whereas CRF has significantly lower affinity for this receptor. These evidence suggest that urocortin 1 is an endogenous ligand for CRF-R1 and CRF-R2. The CRF receptors are members of 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, and parathyroid hormone (PTH). 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. However, depending on its cellular location and function, CRF receptors can activate multiple G proteins, which can in turn stimulate different second messenger pathways.

                         10        20        30        40        50        60
                 ....*....|....*....|....*....|....*....|....*....|....*....|...
gi 148682934  77 WDCVLQGALSTFANTSSFFWTVAIALYLYLSIVRTTrgpSTDHL-IWAFHLISWGVPLAITVA 138
Cdd:cd15264   71 WVCRLIVTVYNYFQVTNFFWMFVEGLYLHTMIVWAY---SADKIrFWYYIVIGWCIPCPFVLA 130

The subfamily B1 of hormone receptors (secretin-like), member of the class B family seven-transmembrane G protein-coupled receptors; The B1 subfamily of class B GPCRs, also referred to as secretin-like receptor family, 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 this subfamily preferentially couple to G proteins of G(s) family, which positively stimulate adenylate cyclase, leading to increased intracellular cAMP formation and calcium influx. Moreover, the B1 subfamily receptors play key roles in hormone homeostasis and are promising drug targets in various human diseases including diabetes, osteoporosis, obesity, neurodegenerative conditions (Alzheimer###s and Parkinson's), cardiovascular disease, migraine, and psychiatric disorders (anxiety, depression). Furthermore, the subfamilies B2 and B3 consist of receptors that are capable of interacting with epidermal growth factors (EGF) and the Drosophila melanogaster Methuselah gene product (Mth), respectively. 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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                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 148682934  77 WDCVLQGALSTFANTSSFFWTVAIALYLYLSIVRTTRGPstDHLIWAFHLISWGVPLAITVAAVSLKKIGYDASdvsvgw 156
Cdd:cd15041   80 VGCKLLSVLKRYFKSANYFWMLCEGLYLHRLIVVAFFSE--PSSLKLYYAIGWGLPLVIVVIWAIVRALLSNES------ 151

                         90
                 ....*....|....*
gi 148682934 157 CWINlEAEDRVLWML 171
Cdd:cd15041  152 CWIS-YNNGHYEWIL 165

Cadherin EGF LAG seven-pass G-type receptor 1, member of the class B2 family of seven-transmembrane G protein-coupled receptors; The group IV adhesion GPCRs include the cadherin EGF LAG seven-pass G-type receptors (CELSRs) and their Drosophila homolog Flamingo (also known as Starry night). These receptors are also classified as that belongs to the EGF-TM7 group of subfamily B2 adhesion GPCRs, because they contain EGF-like domains. Functionally, the group IV receptors act as key regulators of many physiological processes such as endocrine cell differentiation, neuronal migration, dendrite growth, axon, guidance, lymphatic vessel and valve formation, and planar cell polarity (PCP) during embryonic development. Three mammalian orthologs of Flamingo, Celsr1-3, are widely expressed in the nervous system from embryonic development until the adult stage. Each Celsr exhibits different expression patterns in the developing brain, suggesting that they serve distinct functions. Mutations of CELSR1 cause neural tube defects in the nervous system, while mutations of CELSR2 are associated with coronary heart disease. Moreover, CELSR1 and several other PCP signaling molecules, such as dishevelled, prickle, frizzled, have been shown to be upregulated in B lymphocytes of chronic lymphocytic leukemia patients. The adhesion receptors are characterized by the presence of large N-terminal extracellular domains containing multiple adhesion motifs, which play critical roles in cell-cell adhesion and cell-matrix interactions, that are coupled to a class B seven-transmembrane domain. In the case of CELSR/Flamingo/Starry night, their extracellular domains comprise nine cadherin repeats linked to a series of epidermal growth factor (EGF)-like and laminin globular (G)-like domains. The cadherin repeats contain sequence motifs that mediate calcium-dependent cell-cell adhesion by homophilic interactions. Moreover, almost all adhesion receptors, except GPR123, contain an evolutionarily conserved GPCR- autoproteolysis inducing (GAIN) domain that undergoes autoproteolytic processing at the GPCR proteolysis site (GPS) motif located immediately N-terminal to the first transmembrane region, to generate N- and C-terminal fragments (NTF and CTF), which may serve important biological functions.

                         10        20        30        40        50        60        70        80
                 ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 148682934  79 CVLQGALSTFANTSSFFWTVAIALYLYlSIVRTTRGPSTDHLIWaFHLISWGVPLAITVAAVSLKKIGYDASDvsvgWCW 158
Cdd:cd15991   67 CTVVAILLHYFYMSTFAWMFVEGLHIY-RMLTEVRNINTGHMRF-YYVVGWGIPAIITGLAVGLDPQGYGNPD----FCW 140

                         90
                 ....*....|.
gi 148682934 159 INLeaEDRVLW 169
Cdd:cd15991  141 LSV--QDTLIW 149