Metabotropic receptor

Type of membrane receptor that acts through a second messenger

A metabotropic receptor, also referred to by the broader term G-protein-coupled receptor,[1] is a type of membrane receptor that initiates a number of metabolic steps to modulate cell activity. The nervous system utilizes two types of receptors: metabotropic and ionotropic receptors. While ionotropic receptors form an ion channel pore, metabotropic receptors are indirectly linked with ion channels through signal transduction mechanisms, such as G proteins.

Both receptor types are activated by specific chemical ligands. When an ionotropic receptor is activated, it opens a channel that allows ions such as Na+, K+, or Cl− to flow. In contrast, when a metabotropic receptor is activated, a series of intracellular events are triggered that can also result in ion channels opening or other intracellular events, but involve a range of second messenger chemicals.[2]

## Mechanism

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Chemical messengers bind to metabotropic receptors to initiate a diversity of effects caused by biochemical signaling cascades. G protein-coupled receptors are all metabotropic receptors. When a ligand binds to a G protein-coupled receptor, a guanine nucleotide-binding protein, or G protein, activates a second messenger cascade which can alter gene transcription, regulate other proteins in the cell, release intracellular Ca2+, or directly affect ion channels on the membrane.[3][4] These receptors can remain open from seconds to minutes and are associated with long-lasting effects, such as modifying synaptic strength and modulating short- and long-term synaptic plasticity.[5]

Metabotropic receptors have a diversity of ligands, including but not limited to: small molecule transmitters, monoamines, peptides, hormones, and even gases.[5][6][7] In comparison to fast-acting neurotransmitters, these ligands are not taken up again or degraded quickly. They can also enter the circulatory system to globalize a signal.[3] Most metabotropic ligands have unique receptors. Some examples include: metabotropic glutamate receptors, muscarinic acetylcholine receptors, GABAB receptors.[2][8]

## Structure

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The G protein-coupled receptors have seven hydrophobic transmembrane domains. Most of them are monomeric proteins, although GABAB receptors require heterodimerization to function properly. The protein's N terminus is located on the extracellular side of the membrane and its C terminus is on the intracellular side.[2]

The 7 transmembrane spanning domains, with an external amino terminus, are often claimed as being alpha helix shaped, and the polypeptide chain is said to be composed of around 450-550 amino acids.

## References

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1. ^ Purves, Dale, ed. (2018). Neuroscience, 6th ed. Sunderland, Mass: Sinauer Associates. p. 103.
2. ^ a b c Williams, S. J.; Purves, Dale (2001). Neuroscience. Sunderland, Mass: Sinauer Associates. ISBN 0-87893-742-0.
3. ^ a b "Principles of Neural Design", The MIT Press, 2015, doi:10.7551/mitpress/9395.003.0019, ISBN 978-0-262-32731-2, retrieved October 18, 2020 `{{citation}}`: Missing or empty `|title=` (help)
4. ^ Ferguson, Duncan C. (January 1, 2018), Wallig, Matthew A.; Haschek, Wanda M.; Rousseaux, Colin G.; Bolon, Brad (eds.), "Chapter 4 - Principles of Pharmacodynamics and Toxicodynamics", Fundamentals of Toxicologic Pathology (Third Edition), Academic Press, pp. 47–58, doi:10.1016/b978-0-12-809841-7.00004-6, ISBN 978-0-12-809841-7, retrieved October 30, 2020
5. ^ a b Nadim, Farzan; Bucher, Dirk (December 2014). "Neuromodulation of Neurons and Synapses". Current Opinion in Neurobiology. 29: 48–56. doi:10.1016/j.conb.2014.05.003. ISSN 0959-4388. PMC 4252488. PMID 24907657.
6. ^ Burrows, Malcolm (1996). "Neurotransmitters, neuromodulators and neurohormones". The Neurobiology of an Insect Brain. Oxford Scholarship. doi:10.1093/acprof:oso/9780198523444.003.0005. ISBN 9780198523444.
7. ^ Marder, Eve (October 4, 2012). "Neuromodulation of Neuronal Circuits: Back to the Future". Neuron. 76 (1): 1–11. doi:10.1016/j.neuron.2012.09.010. ISSN 0896-6273. PMC 3482119. PMID 23040802.
8. ^ Hoehn K, Marieb EN (2007). "Fundamentals of the nervous system and nervous tissue". Human Anatomy & Physiology. San Francisco: Pearson Benjamin Cummings. ISBN 978-0-8053-5910-7.

## Further reading

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* Zimmerberg, B. 2002. Dopamine receptors: A representative family of metabotropic receptors. Multimedia Neuroscience Education Project [1]

* v
* t
* e

Cell surface receptor: G protein-coupled receptors

Class A: Rhodopsin-like

| Neurotransmitter|

| Adrenergic|

* α1 (A
* B
* D)
* α2 (A
* B
* C)
* β1
* β2
* β3

|

Purinergic|

* Adenosine (A1
* A2A
* A2B
* A3)
* P2Y (1
* 2
* 4
* 5
* 6
* 8
* 9
* 10
* 11
* 12
* 13
* 14)

Serotonin|

* (all but 5-HT3) 5-HT1 (A
* B
* D
* E
* F)
* 5-HT2 (A
* B
* C)
* 5-HT (4
* 5A
* 6
* 7)

Other|

* Acetylcholine (M1
* M2
* M3
* M4
* M5)
* Dopamine
* D1
* D2
* D3
* D4
* D5
* GHB receptor
* Histamine
* H1
* H2
* H3
* H4
* Melatonin (1A
* 1B
* 1C)
* TAAR (1
* 2
* 5
* 6
* 8
* 9)

Metabolites and
signaling molecules|

| Eicosanoid|

* CysLT (1
* 2)
* LTB4
* 1
* 2
* FPRL1
* OXE
* Prostaglandin
* DP (1
* 2), EP (1
* 2
* 3
* 4), FP
* Prostacyclin
* Thromboxane

|

Other|

* Bile acid
* Cannabinoid (CB1
* CB2, GPR (18
* 55
* 119))
* EBI2
* Estrogen
* Free fatty acid (1
* 2
* 3
* 4)
* Hydroxycarboxylic acids
* 1
* 2
* 3
* Lysophosphatidic acid (1
* 2
* 3
* 4
* 5
* 6)
* Lysophospholipid (1
* 2
* 3
* 4
* 5
* 6
* 7
* 8)
* Oxoglutarate
* PAF
* Sphingosine-1-phosphate (1
* 2
* 3
* 4
* 5)
* Succinate

Peptide|

| Neuropeptide|

* B/W (1
* 2)
* FF (1
* 2)
* S
* Y (1
* 2
* 4
* 5)
* Neuromedin (B
* U (1
* 2))
* Neurotensin (1
* 2)

|

Other|

* Anaphylatoxin (C3a
* C5a (1
* 2))
* Angiotensin (1
* 2)
* Apelin
* Bombesin
* BRS3
* GRPR
* NMBR)
* Bradykinin (B1
* B2)
* Chemokine
* Cholecystokinin (A
* B)
* Endothelin
* A
* B
* Formyl peptide (1
* 2
* 3)
* FSH
* Galanin (1
* 2
* 3)
* Gonadotropin-releasing hormone (1
* 2)
* Ghrelin
* Kisspeptin
* Luteinizing hormone/choriogonadotropin
* MAS (1
* 1L
* D
* E
* F
* G
* X1
* X2
* X3
* X4)
* Melanocortin (1
* 2
* 3
* 4
* 5)
* MCHR (1
* 2)
* Motilin
* Opioid (Delta
* Kappa
* Mu
* Nociceptin & Zeta, but not Sigma)
* Orexin (1
* 2)
* Oxytocin
* Prokineticin (1
* 2)
* Prolactin-releasing peptide
* Relaxin (1
* 2
* 3
* 4)
* Somatostatin (1
* 2
* 3
* 4
* 5)
* Tachykinin (1
* 2
* 3)
* Thyrotropin
* Thyrotropin-releasing hormone
* Urotensin-II
* Vasopressin (1A
* 1B
* 2)

Miscellaneous|

| Taste, bitter|

* TAS2R
* 1
* 3
* 4
* 5
* 7
* 8
* 9
* 10
* 13
* 14
* 16
* 19
* 20
* 30
* 31
* 38
* 39
* 40
* 41
* 42
* 43
* 45
* 46
* 50
* 60
* Vomeronasal receptor type 1

|

Orphan|

* GPR (1
* 3
* 4
* 6
* 12
* 15
* 17
* 18
* 19
* 20
* 21
* 22
* 23
* 25
* 26
* 27
* 31
* 32
* 33
* 34
* 35
* 37
* 39
* 42
* 44
* 45
* 50
* 52
* 55
* 61
* 62
* 63
* 65
* 68
* 75
* 78
* 81
* 82
* 83
* 84
* 85
* 87
* 88
* 92
* 101
* 103
* 109A
* 109B
* 119
* 120
* 132
* 135
* 137B
* 139
* 141
* 142
* 146
* 148
* 149
* 150
* 151
* 152
* 153
* 160
* 161
* 162
* 171
* 173
* 174
* 176
* 177
* 182
* 183)

Other|

* Adrenomedullin
* Olfactory
* Opsin (3
* 4
* 5
* 1LW
* 1MW
* 1SW
* RGR
* RRH)
* Protease-activated (1
* 2
* 3
* 4)
* SREB (1
* 2
* 3)

Class B: Secretin-like

| Adhesion|

* ADGRB
* Brain-specific angiogenesis inhibitor
* 1
* 2
* 3
* ADGRC
* Cadherin
* 1
* 2
* 3
* ADGRE
* EMR
* 1
* 2
* 3
* CD97
* ADGRG
* 1
* 2
* 3
* 4
* 5
* 6
* 7
* ADGRL
* Latrophilin
* 1
* 2
* 3
* ELTD1

|

Orphan|

* GPR (56
* 64
* 97
* 98
* 110
* 111
* 112
* 113
* 114
* 115
* 116
* 123
* 124
* 125
* 126
* 128
* 133
* 143
* 144
* 155
* 157)

Other|

* Calcitonin
* CALCRL
* Corticotropin-releasing hormone (1
* 2)
* Glucagon (GR
* GIPR
* GLP1R
* GLP2R)
* Growth-hormone-releasing hormone
* PACAPR1
* GPR
* Methuselah-like proteins
* Parathyroid hormone (1
* 2)
* Secretin
* Vasoactive intestinal peptide (1
* 2)

Class C: Metabotropic glutamate / pheromone

| Taste, sweet|

* TAS1R
* 1
* 2
* 3
* Vomeronasal receptor, type 2

|

Other|

* Calcium-sensing receptor
* GABAB (1
* 2)
* Glutamate receptor (Metabotropic glutamate (1
* 2
* 3
* 4
* 5
* 6
* 7
* 8))
* GPRC6A
* GPR (156
* 158
* 179)
* RAIG (1
* 2
* 3
* 4)

Class F: Frizzled & Smoothened

| Frizzled|

* Frizzled (1
* 2
* 3
* 4
* 5
* 6
* 7
* 8
* 9
* 10)

|

Smoothened|

* Smoothened

* v
* t
* e

Protein kinases: tyrosine kinases (EC 2.7.10)

Receptor tyrosine kinases (EC 2.7.10.1)

| Growth factor receptors|

| EGF receptor family|

* EGFR
* ERBB2
* ERBB3
* ERBB4

|

Insulin receptor family|

* IGF1R
* INSR
* INSRR

PDGF receptor family|

* CSF1R
* FLT3
* KIT
* PDGFR (PDGFRA
* PDGFRB)

FGF receptor family|

* FGFR1
* FGFR2
* FGFR3
* FGFR4

VEGF receptors family|

* VEGFR1
* VEGFR2
* VEGFR3

HGF receptor family|

* MET
* RON

Trk receptor family|

* NTRK1
* NTRK2
* NTRK3

EPH receptor family|

* EPHA1
* EPHA2
* EPHA3
* EPHA4
* EPHA5
* EPHA6
* EPHA7
* EPHA8
* EPHB1
* EPHB2
* EPHB3
* EPHB4
* EPHB5
* EPHB6
* EPHX

LTK receptor family|

* LTK
* ALK

TIE receptor family|

* TIE
* TEK

ROR receptor family|

* ROR1
* ROR2

DDR receptor family|

* DDR1
* DDR2

PTK7 receptor family|

* PTK7

RYK receptor family|

* RYK

MuSK receptor family|

* MUSK

ROS receptor family|

* ROS1

AATYK receptor family|

* AATYK
* AATYK2

AXL receptor family|

* AXL
* MER
* TYRO3

RET receptor family|

* RET

uncategorised|

* STYK1

Non-receptor tyrosine kinases (EC 2.7.10.2)

| ABL family|

* ABL1
* ARG

|

ACK family|

* ACK1
* TNK1

CSK family|

* CSK
* MATK

FAK family|

* FAK
* PYK2

FES family|

* FES
* FER

FRK family|

* FRK
* BRK
* SRMS

JAK family|

* JAK1
* JAK2
* JAK3
* TYK2

SRC-A family|

* SRC
* FGR
* FYN
* YES1

SRC-B family|

* BLK
* HCK
* LCK
* LYN

TEC family|

* TEC
* BMX
* BTK
* ITK
* TXK

SYK family|

* SYK
* ZAP70

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