Orphan and other 7TM receptors

Unless otherwise stated all data on this page refer to the human proteins. Gene information is provided for human (Hs), mouse (Mm) and rat (Rn).

Class A Orphans

Overview

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Table 1 lists a number of putative GPCRs identified by IUPHAR [28], for which preliminary evidence for an endogenous ligand has been published, or for which there exists a potential link to a disease, or disorder. The GPCRs in Table 1 are all Class A, rhodopsin-like GPCRs. Class A orphan GPCRs not listed in Table 1 are putative GPCRs with as-yet unidentified endogenous ligands.

Table 1: Class A orphan GPCRs with putative endogenous ligands

GPR1GPR3GPR4GPR6GPR12GPR15GPR17GRP20
GPR22GPR26GPR31GPR34GPR35GPR37GPR39GPR50
GPR63GRP65GPR68GPR75GPR84GPR87GPR88GPR132
GPR149GPR161GPR183LGR4LGR5LGR6MAS1MRGPRD
MRGPRX1MRGPRX2P2RY10TAAR2

In addition the orphan receptors GPR18, GPR55 and GPR119 which are reported to respond to endogenous agents analogous to the endogenous cannabinoid ligands have been grouped together (GPR18, GPR55 and GPR119).

Receptors

BB3 receptor Show summary » More detailed page

GPR1 Show summary » More detailed page

GPR3 Show summary » More detailed page

GPR4 Show summary » More detailed page

GPR6 Show summary » More detailed page

GPR12 Show summary » More detailed page

GPR15 Show summary » More detailed page

GPR17 Show summary » More detailed page

GPR18 Show summary » More detailed page

GPR19 Show summary » More detailed page

GPR20 Show summary » More detailed page

GPR21 Show summary » More detailed page

GPR22 Show summary » More detailed page

GPR25 Show summary » More detailed page

GPR26 Show summary » More detailed page

GPR27 Show summary » More detailed page

GPR31 Show summary » More detailed page

GPR32 Show summary » More detailed page

GPR33 Show summary » More detailed page

GPR34 Show summary » More detailed page

GPR35 Show summary » More detailed page

GPR37 Show summary » More detailed page

GPR37L1 Show summary » More detailed page

GPR39 Show summary » More detailed page

GPR42 Show summary » More detailed page

GPR45 Show summary » More detailed page

GPR50 Show summary » More detailed page

GPR52 Show summary » More detailed page

GPR55 Show summary » More detailed page

GPR61 Show summary » More detailed page

GPR62 Show summary » More detailed page

GPR63 Show summary » More detailed page

GPR65 Show summary » More detailed page

GPR68 Show summary » More detailed page

GPR75 Show summary » More detailed page

GPR78 Show summary » More detailed page

GPR79 Show summary » More detailed page

GPR82 Show summary » More detailed page

GPR83 Show summary » More detailed page

GPR84 Show summary » More detailed page

GPR85 Show summary » More detailed page

GPR87 Show summary » More detailed page

GPR88 Show summary » More detailed page

GPR101 Show summary » More detailed page

GPR119 Show summary » More detailed page

GPR132 Show summary » More detailed page

GPR135 Show summary » More detailed page

GPR139 Show summary » More detailed page

GPR141 Show summary » More detailed page

GPR142 Show summary » More detailed page

GPR146 Show summary » More detailed page

GPR148 Show summary » More detailed page

GPR149 Show summary » More detailed page

GPR150 Show summary » More detailed page

GPR151 Show summary » More detailed page

GPR152 Show summary » More detailed page

GPR153 Show summary » More detailed page

GPR160 Show summary » More detailed page

GPR161 Show summary » More detailed page

GPR162 Show summary » More detailed page

GPR171 Show summary » More detailed page

GPR173 Show summary » More detailed page

GPR174 Show summary » More detailed page

GPR176 Show summary » More detailed page

GPR182 Show summary » More detailed page

GPR183 Show summary » More detailed page

LGR4 Show summary » More detailed page

LGR5 Show summary » More detailed page

LGR6 Show summary » More detailed page

MAS1 Show summary » More detailed page

MAS1L Show summary » More detailed page

MRGPRD Show summary » More detailed page

MRGPRE Show summary » More detailed page

MRGPRF Show summary » More detailed page

MRGPRG Show summary » More detailed page

MRGPRX1 Show summary » More detailed page

MRGPRX2 Show summary » More detailed page

MRGPRX3 Show summary » More detailed page

MRGPRX4 Show summary » More detailed page

OPN3 Show summary » More detailed page

OPN4 Show summary » More detailed page

OPN5 Show summary » More detailed page

P2RY8 Show summary » More detailed page

P2RY10 Show summary » More detailed page

TAAR2 Show summary » More detailed page

TAAR3 Show summary » More detailed page

TAAR4P Show summary » More detailed page

TAAR5 Show summary » More detailed page

TAAR6 Show summary » More detailed page

TAAR8 Show summary » More detailed page

TAAR9 Show summary » More detailed page

NC-IUPHAR subcommittee and family contributors

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Class B Orphans

Overview

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The receptors in this family have been reclassified as Adhesion Class GPCRs

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Class C Orphans

Receptors

GPR156 Show summary » More detailed page

GPR158 Show summary » More detailed page

GPR179 Show summary » More detailed page

GPRC5A Show summary » More detailed page

GPRC5B Show summary » More detailed page

GPRC5C Show summary » More detailed page

GPRC5D Show summary » More detailed page

NC-IUPHAR subcommittee and family contributors

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Taste 1 receptors

Overview

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Whilst the taste of acid and salty foods appear to be sensed by regulation of ion channel activity, bitter, sweet and umami tastes are sensed by specialised GPCR. Two classes of taste GPCR have been identified, T1R and T2R, which are similar in sequence and structure to Class C and Class A GPCR, respectively. Activation of taste receptors appears to involve gustducin- (Gαt3) and Gα14-mediated signalling, although the precise mechanisms remain obscure. Gene disruption studies suggest the involvement of PLCβ2 [132], TRPM5 [132] and IP3 [38] receptors in post-receptor signalling of taste receptors. Although predominantly associated with the oral cavity, taste receptors are also located elsewhere, including further down the gastrointestinal system, in the lungs and in the brain.

Sweet/Umami
T1R3 acts as an obligate partner in T1R1/T1R3 and T1R2/T1R3 heterodimers, which sense umami or sweet, respectively. T1R1/T1R3 heterodimers respond to L-glutamic acid and may be positively allosterically modulated by 5’-nucleoside monophosphates, such as 5'-GMP [68]. T1R2/T1R3 heterodimers respond to sugars, such as sucrose, and artificial sweeteners, such as saccharin [85].

Receptors

TAS1R1 Show summary » More detailed page

TAS1R2 Show summary » More detailed page

TAS1R3 Show summary » More detailed page

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Taste 2 receptors

Overview

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Whilst the taste of acid and salty foods appear to be sensed by regulation of ion channel activity, bitter, sweet and umami tastes are sensed by specialised GPCR. Two classes of taste GPCR have been identified, T1R and T2R, which are similar in sequence and structure to Class C and Class A GPCR, respectively. Activation of taste receptors appears to involve gustducin- (Gαt3) and Gα14-mediated signalling, although the precise mechanisms remain obscure. Gene disruption studies suggest the involvement of PLCβ2 [132], TRPM5 [132] and IP3 [38] receptors in post-receptor signalling of taste receptors. Although predominantly associated with the oral cavity, taste receptors are also located elsewhere, including further down the gastrointestinal system, in the lungs and in the brain.

Bitter
The composition and stoichiometry of bitter taste receptors is not yet established. Bitter receptors appear to separate into two groups, with very restricted ligand specificity or much broader responsiveness. For example, T2R5 responded to cycloheximide, but not 10 other bitter compounds [14], while T2R14 responded to at least eight different bitter tastants, including (-)-α-thujone and picrotoxinin [