G protein-coupled receptor

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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

List of the G protein-coupled receptors

Family A of GPCRs

Neurotensin receptor

Subfamily A2

CXC Chemokine receptors

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.

See also

Subfamily A6

Orexin receptor

Subfamily A10

Subfamily A11

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

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 (Gt), 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.

Subfamily A17

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

Adrenergic receptors

β1 adrenergic receptor
β2 adrenergic receptor
 

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.


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.

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 (Gq) 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 Gq heterotrimeric G protein, the α-subunit of Gq can bind to and induce activity in the PLC isozyme PLC-β, which results in the cleavage of PIP2 into IP3 and DAG.

Adenosine A2A receptor

Gs → cAMP up

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 Gq proteins, while M2 and M4 receptors are coupled with Gi/o proteins.

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

Glucagon 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 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.

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

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

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