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G protein-coupled receptors, often abbreviated GPCRs, are an abundant superfamily of proteins also known as seven-transmembrane domain receptors, 7TM receptors, 7 pass transmembrane receptors, heptahelical receptors, serpentine receptor, and G protein-linked receptors (GPLRs). G protein-coupled receptors are cell surface signalling proteins involved in many physiological functions and in multiple diseases. They are also the target of the majority of all modern medicinal drugs^[1][2]. The extracellular side is generally where the ligand enters for binding. On the intracellular side they interact with G proteins involved in signaling induced by the binding of the ligand.

Illustrating their importance and the largesse of the superfamily, there are roughly 800 known members of the superfamily in the human genome alone — estimated to be 4% of human protein-coding genes. Members are further subclassified into one of five families of GPCRs^[3].

Rhodopsin shares similar membrane topology with the members of the superfamily, specifically family A of the G protein-coupled receptors which include the seven transmembrane helices, an extracellular N-terminus and cytoplasmic C-terminus^[4].

Contents 1 List of the G protein-coupled receptors 1.1 Family A of GPCRs 1.1.1 Subfamily A2 1.1.1.1 CXC Chemokine receptors 1.1.2 Subfamily A4 1.1.2.1 Opioid receptors 1.1.3 Subfamily A6 1.1.3.1 Orexin receptor 1.1.3.2 Oxytocin receptor 1.1.4 Subfamily A10 1.1.5 Subfamily A11 1.1.5.1 Human GPR40 (hGPR40), also known as Free Fatty Acid Receptor 1 (FFAR1) 1.1.5.2 Sphingosine 1-phosphate Receptor 1.1.6 Subfamily A16 1.1.6.1 Rhodopsins 1.1.7 Subfamily A17 1.1.7.1 5-Hydroxytryptamine (5-HT) receptors (Serotonin receptors) 1.1.7.2 Adrenergic receptors 1.1.7.2.1 β1 adrenergic receptor 1.1.7.2.2 β2 adrenergic receptor 1.1.7.3 Dopamine Receptor 1.1.8 Subfamily A18 1.1.8.1 Histamine receptors 1.1.8.2 Adenosine A2A receptor 1.1.8.3 Muscarinic acetylcholine receptors 1.2 Family B of GPCRs 1.2.1 Subfamily B1 1.2.1.1 Glucose-dependent Insulinotropic Polypeptide Receptor 1.2.1.2 Glucagon receptor 1.2.1.3 Glucagon-like peptide 1 receptor 1.3 Family C of GPCRs, Metabotropic glutamate receptors 1.4 Metabotropic GABA receptors (GABAB) 2 Nobel Prize Related to the Structures 3 References and Notes 4 See Also 5 Additional Literature 5.1 External Resources

List of the G protein-coupled receptors

Family A of GPCRs

Neurotensin receptor

• Neurotensin receptor

Subfamily A2

CXC Chemokine receptors

• CXC chemokine receptor type 4

Subfamily A4

Opioid receptors

Opioid receptor (OpR) is a G protein-coupled receptor with opioids as ligands^[5]. OpR types are classified according to the ligands which bind to them.

• The μ-opioid receptor binds morphine. For more details on μ-opioid receptor see
  
  • Mu Opioid Receptor Bound to a Morphinan Antagonist
  • μ Opioid Receptors
  • Mu Opioid Receptor.
  • 6dde μ-opioid receptor: G protein complex
    
• The κ-opioid receptor binds opium-type ligands. For details see Student Project 3 for UMass Chemistry 423 Spring 2015.
  
• The δ-opioid receptor binds enkephalins. For details see Delta opioid receptor.
• The Nociceptin/orphanin FQ opioid receptor binds the heptadecapeptide orphanin^[6].

See also

• Opioids
• Treatments:Opioid drugs
• Tutorial: The opioid receptor, a molecular switch

Subfamily A6

Orexin receptor

• Orexin and Orexin receptor
• Belsomra and Orexin receptors
• Hypocretin and receptors

Oxytocin receptor

Subfamily A10

• Human Follicle-Stimulating Hormone Complexed with its Receptor

Subfamily A11

Human GPR40 (hGPR40), also known as Free Fatty Acid Receptor 1 (FFAR1)

• GPR40

Sphingosine 1-phosphate Receptor

The sphingosine-1-phosphate receptors are a class of G protein-coupled receptors that are targets of the lipid signalling molecule Sphingosine-1-phosphate (S1P).

• 3v2w,3v2y - human sphingosine 1-phosphate receptor 1 with a bound sphingolipid mimic

See User:Harish Srinivas/Sandbox 1

Subfamily A16

Rhodopsins

The product of light activation, Metarhodopsin II, initiates the visual phototransduction pathway by stimulating the G protein Transducin (G_t), resulting in the liberation of its α subunit. This GTP-bound subunit in turn activates cGMP phosphodiesterase. cGMP phosphodiesterase hydrolyzes (breaks down) cGMP, lowering its local concentration so it can no longer activate cGMP-dependent cation channels. Phosphodiesterase 6 is the primary effector of retinal phototransduction. See details in User:Rick H. Cote/PDE6.

• Rhodopsin
• Rhodopsin Structure and Function
• Transducin

Subfamily A17

5-Hydroxytryptamine (5-HT) receptors (Serotonin receptors)

• Serotonin receptors, main page
• 3D structures of Serotonin receptors

Adrenergic receptors

• Adrenergic receptors in general

β1 adrenergic receptor

• 3D structures in Adrenergic receptor.
• Beta-1 Adrenergic receptor
• G_s: adenylate cyclase activated, cAMP up.

• β1-adrenergic agonists:
  • Dobutamine, see Beta-1 Adrenergic receptor, 2y00, 2y01, 6h7l.
  • Isoprenaline, see Beta-1 Adrenergic receptor, 2y03.
  • Noradrenaline
  • Carmoterol, see 2y02.
  • Salbutamol (Albuterol in USA), 2y04.
• Beta blockers:
  • Metoprolol
  • Atenolol
  • Bisoprolol
  • Propranolol
  • Timolol
  • Nebivolol
  • Vortioxetine

β2 adrenergic receptor

	Show:Asymmetric Unit Biological Assembly   Export Animated Image An activated G protein-coupled receptor (human β-2 adrenergic receptor in blue ) in a complex with a heterotrimeric G protein (3 subunits:reddish to orange-brown) and hormone (gold) (3sn6), resolution 3.2Å. The boundaries of the membrane in which the GPCR sits are represented in light green.

• The human β2 adrenergic receptor bound to a G-protein (3sn6) is featured in a scene above, and additional structures are on the Adrenergic receptor page.
• Article Beta-2 Adrenergic Receptor by Wayne Decatur, David Canner, Dotan Shaniv, Joel L. Sussman, Michal Harel
• Article Beta-2 adrenergic receptor by Joel L. Sussman, Tala Curry, Michal Harel, Jaime Prilusky
• Group:SMART:A Physical Model of the beta-Adrenergic Receptor
• G_s: adenylate cyclase activated, cAMP up. For G_s see Beta2 adrenergic receptor-Gs protein complex updated.

β2-adrenergic agonists:

• • Salbutamol (Albuterol in USA)
  • Bitolterol mesylate
  • Formoterol
  • Isoprenaline
  • Levalbuterol
  • Metaproterenol
  • Salmeterol
  • Terbutaline
  • Ritodrine
• Beta blockers:
  • Butoxamine
  • Timolol
  • Propranolol
  • ICI-118,551
  • Paroxetine

Dopamine Receptor

There are five subtype dopamine receptors, D1, D2, D3, D4, and D5. The D3 receptor is a part of the D2-like family.^[7] The D2-like family receptors are coupled to the G protein Giα, which directly inhibits the formation of cAMP by inhibiting the enzyme adenylyl cyclase.

• Dopamine receptors 1 page
• Dopamine receptors 2 page

Subfamily A18

Histamine receptors

The H1 receptor is a histamine receptor belonging to the family of rhodopsin-like G-protein-coupled receptors. The H1 receptor is linked to an intracellular G-protein (G_q) that activates phospholipase C (see Unique bidirectional interactions of Phospholipase C beta 3 with G alpha Q and the inositol triphosphate (IP3) signalling pathway. When a ligand binds to a G protein-coupled receptorthat is coupled to a G_q heterotrimeric G protein, the α-subunit of G_q can bind to and induce activity in the PLC isozyme PLC-β, which results in the cleavage of PIP2 into IP3 and DAG.

• Histamine H1 receptor
• 3rze - human histamine H1 receptor with an antagonist doxepin.

Adenosine A2A receptor

G_s → cAMP up

• Adenosine A2A receptor
• Effect of Caffeine (Trimethylxanthine) on Human A2A Receptor
• Adenosine A2A receptor 3D structures

Agonists:

• N6-3-methoxyl-4-hydroxybenzyl adenine riboside (B2)
• ATL-146e
• CGS-21680
• Regadenoson
• Adenosine

Antagonists:

• Caffeine
• aminophylline
• theophylline
• istradefylline
• SCH-58261
• SCH-442,416
• ZM-241,385

Muscarinic acetylcholine receptors

M1, M3, M5 receptors are coupled with G_q proteins, while M2 and M4 receptors are coupled with G_i/o proteins.

• Muscarinic acetylcholine receptor

Family B of GPCRs

These receptors activate adenylyl cyclase and the phosphatidyl-inositol-calcium pathway. The glucagon receptor is a 62 kDa protein that is activated by glucagon and is a member of the class B G-protein coupled family of receptors, coupled to G alpha i, Gs and to a lesser extent G alpha q. Stimulation of the receptor results in the activation of adenylate cyclase and phospholipase C and in increased levels of the secondary messengers intracellular cAMP and calcium.

Subfamily B1

Glucose-dependent Insulinotropic Polypeptide Receptor

• Glucose-dependent Insulinotropic Polypeptide Receptor

Glucagon receptor

• Glucagon receptor

Glucagon-like peptide 1 receptor

• Glucagon-like peptide 1 receptor

Family C of GPCRs, Metabotropic glutamate receptors

Metabotropic glutamate receptors are glutamate receptors that activate ion channels indirectly through a signaling cascade involving G proteins^[8]. Glutamate receptors are classified into 3 groups based on their homology, mechanism and pharmacological properties.

• Metabotropic Glutamate Receptors
• Ligand Binding N-Terminal of Metabotropic Glutamate Receptors
• Metabotropic glutamate receptor 5

Metabotropic GABA receptors (GABAB)

GABAB receptors (GABABR) are G-protein coupled receptors for gamma-aminobutyric acid (GABA), therefore making them metabotropic receptors, that are linked via G-proteins to potassium channels. GABAB receptors also reduces the activity of adenylyl cyclase and Ca2+ channels by using G-proteins with Gi/G0 α subunits.

• GABA receptor
• User:Rana Saad/The human GABAb receptor

Nobel Prize Related to the Structures

Robert J. Lefkowitz and Brian K. Kobilka share the 2012 Nobel Prize in Chemistry for work on GPCRs that includes solving the first structures of a ligand-activated GPCR (2r4r, 2r4s, & 2rh1 in 2007)^[9][10][11] and the first activated GPCR in complex with its G protein (3sn6 in 2011)^{[12][13][14][15]}. A detailed description of the laureates' body of work on this class of receptors with images is here.

References and Notes

1. ↑ Overington JP, Al-Lazikani B, Hopkins AL. How many drug targets are there? Nat Rev Drug Discov. 2006 Dec;5(12):993-6. PMID:17139284 doi:10.1038/nrd2199
2. ↑ Peeters MC, van Westen GJ, Li Q, IJzerman AP. Importance of the extracellular loops in G protein-coupled receptors for ligand recognition and receptor activation. Trends Pharmacol Sci. 2011 Jan;32(1):35-42. PMID:21075459 doi:10.1016/j.tips.2010.10.001
3. ↑ Millar RP, Newton CL. The year in G protein-coupled receptor research. Mol Endocrinol. 2010 Jan;24(1):261-74. Epub 2009 Dec 17. PMID:20019124 doi:10.1210/me.2009-0473
4. ↑ Kristiansen K. Molecular mechanisms of ligand binding, signaling, and regulation within the superfamily of G-protein-coupled receptors: molecular modeling and mutagenesis approaches to receptor structure and function. Pharmacol Ther. 2004 Jul;103(1):21-80. PMID:15251227 doi:10.1016/j.pharmthera.2004.05.002
5. ↑ Feng Y, He X, Yang Y, Chao D, Lazarus LH, Xia Y. Current research on opioid receptor function. Curr Drug Targets. 2012 Feb;13(2):230-46. PMID:22204322
6. ↑ Donica CL, Awwad HO, Thakker DR, Standifer KM. Cellular mechanisms of nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor regulation and heterologous regulation by N/OFQ. Mol Pharmacol. 2013 May;83(5):907-18. doi: 10.1124/mol.112.084632. Epub 2013 Feb , 8. PMID:23395957 doi:http://dx.doi.org/10.1124/mol.112.084632
7. ↑ Girault JA, Greengard P. The neurobiology of dopamine signaling. Arch Neurol. 2004 May;61(5):641-4. PMID:15148138 doi:10.1001/archneur.61.5.641
8. ↑ Traynelis SF, Wollmuth LP, McBain CJ, Menniti FS, Vance KM, Ogden KK, Hansen KB, Yuan H, Myers SJ, Dingledine R. Glutamate receptor ion channels: structure, regulation, and function. Pharmacol Rev. 2010 Sep;62(3):405-96. doi: 10.1124/pr.109.002451. PMID:20716669 doi:http://dx.doi.org/10.1124/pr.109.002451
9. ↑ Cherezov V, Rosenbaum DM, Hanson MA, Rasmussen SG, Thian FS, Kobilka TS, Choi HJ, Kuhn P, Weis WI, Kobilka BK, Stevens RC. High-resolution crystal structure of an engineered human beta2-adrenergic G protein-coupled receptor. Science. 2007 Nov 23;318(5854):1258-65. Epub 2007 Oct 25. PMID:17962520
10. ↑ Rosenbaum DM, Cherezov V, Hanson MA, Rasmussen SG, Thian FS, Kobilka TS, Choi HJ, Yao XJ, Weis WI, Stevens RC, Kobilka BK. GPCR engineering yields high-resolution structural insights into beta2-adrenergic receptor function. Science. 2007 Nov 23;318(5854):1266-73. Epub 2007 Oct 25. PMID:17962519
11. ↑ Ranganathan R. Biochemistry. Signaling across the cell membrane. Science. 2007 Nov 23;318(5854):1253-4. PMID:18033872 doi:10.1126/science.1151656
12. ↑ Schwartz TW, Sakmar TP. Structural biology: snapshot of a signalling complex. Nature. 2011 Sep 28;477(7366):540-1. doi: 10.1038/477540a. PMID:21956322 doi:10.1038/477540a
13. ↑ Rasmussen SG, DeVree BT, Zou Y, Kruse AC, Chung KY, Kobilka TS, Thian FS, Chae PS, Pardon E, Calinski D, Mathiesen JM, Shah ST, Lyons JA, Caffrey M, Gellman SH, Steyaert J, Skiniotis G, Weis WI, Sunahara RK, Kobilka BK. Crystal structure of the beta2 adrenergic receptor-Gs protein complex. Nature. 2011 Jul 19;477(7366):549-55. doi: 10.1038/nature10361. PMID:21772288 doi:10.1038/nature10361
14. ↑ Chung KY, Rasmussen SG, Liu T, Li S, DeVree BT, Chae PS, Calinski D, Kobilka BK, Woods VL Jr, Sunahara RK. Conformational changes in the G protein Gs induced by the beta2 adrenergic receptor. Nature. 2011 Sep 28;477(7366):611-5. doi: 10.1038/nature10488. PMID:21956331 doi:10.1038/nature10488
15. ↑ Schwartz TW, Sakmar TP. Structural biology: snapshot of a signalling complex. Nature. 2011 Sep 28;477(7366):540-1. doi: 10.1038/477540a. PMID:21956322 doi:10.1038/477540a

See Also

• Nobel Prizes for 3D Molecular Structure
• Highest impact structures of all time
• G proteins
• Rhodopsin
• GTP-binding protein
• Pharmaceutical Drugs
• Membrane proteins
• Hormone
• Ligand Binding N-Terminal of Metabotropic Glutamate Receptors
• Receptor.

Additional Literature

• Carpenter B, Tate CG. Active state structures of G protein-coupled receptors highlight the similarities and differences in the G protein and arrestin coupling interfaces. Curr Opin Struct Biol. 2017 May 5;45:124-132. doi: 10.1016/j.sbi.2017.04.010. PMID:28482214 doi:http://dx.doi.org/10.1016/j.sbi.2017.04.010

External Resources

• Robert J. Lefkowitz and Brian K. Kobilka share the 2012 Nobel Prize in Chemistry for work on GPCRs that includes solving the first structures of a ligand-activated GPCR (2007) and the first activated GPCR in complex with its G protein (2011). A detailed description of the laureates' body of work on this class of receptors with images is here.
• The April 2008 RCSB PDB Molecule of the Month feature on Adrenergic Receptors by David S. Goodsell is 10.2210/rcsb_pdb/mom_2008_4.
• GPCRDB: database contains sequences, ligand binding constants and mutations, in addition GPCR multiple sequence alignments and homology models. Moreover, the site contains useful files where lysozyme and other inserts which are commonly used in the difficult process of crystallizing these transmembrane structures have been removed from the structures.
• GPCR Network site with tracking chart of ongoing structural programs
• The GPCR-SSFE Database: A Homology Model Resource for G-Protein Coupled Receptors
• The blog of the Computational Chemical Biology group at the EMBL-EBI does an excellent job tracking the new GPCR structures as they are emerging.
• Emerald Biosystems Blog that features solved structures and on another page features techniques and amounts needed for crystallization of a number of them.
• A 2012 article from Scripps Research Institute that covers a lot of history of solving the structures of GPCRs and their importance.
• A 2012 article from the Protein Structure Initiative on the screening technique to identify stabilizing fusion partners for solving GPCR structure.
• A 2011 article in Nature entitiled 'Cell Signalling Caught in the Act' describing the first determination of an activated GPCR — the β2 adrenergic receptor (β2AR) — in a complex with its G protein.
• tinyGRAP GPCR mutant database
• GPCR-OKB: GPCR Oligomerization Knowledge Base
• GPCR Natural Variants Database (NaVa)
• The PRED-GPCR server for GPCR recognition and family classification.
• GLASS database: a comprehensive database for experimentally validated GPCR-ligand associations
• GPCR-ModSim is a webserver for computational modeling and simulation of G-Protein Coupled Receptors (GPCRs). Models from sequence and also lets you place the models in a phospholipid bilayer and model them using Molecular Dynamics.