GPCRs
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| Blumer et al 2005 | Review of AGs proteins. These affect nucleotide exchange and interaction between g-protein subunits. Some bind inactive Ga, competing with Gby; this buffers Ga and allows greater effects of Gby.
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| Cismowski et al 1999 | Discovery of AGS proteins in a yeast model. Pheromone GPCR pathway made necessary for growth, added mammalian cDNA looking for a receptor independent effect.
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| Fang et al 2000 | Dexras (mouse homologue of human AGS-1) is activated by NO donors and nNOS through s-nitrosylation. Interacts with nNOS scaffold protein CAPON (co-IP). nNOS is linked to NMDA by scaffold, dexras may help NO signals to regulate NMDA.
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| Takahashi et al 2003 | Shows that Dexras fluctuates with a circadian rhythm in the supra-chiasmatic nucleus. Used real time PCR in mouse SCN RNA. cry knockout prevented rhythmic expression.
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| Graham et al 2002 | Pertussis toxin inhibited AGS1 activation of erk (which then activates elk). AGS1 normally binds and activates Gi, decreasing cAMP. Has partial agonist type effects in that it can prevent maximal activation by the receptor.
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| Bockaert & Pin 1999 | Review: GPCRs can form dimers with structurally different GPCRs. GPCRs can act through G proteins and also via C terminal connections. Phosphorylation can alter GPCR coupling to g protein. RNA splicing and editing alters coupling to G protein.
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| Bouvier 2001 (only author) | Review: GPCR oligomerisation. Early CoIP experiments required upregulation, since then better studies have been done. Claims they might be clumping due to hydrophobicity. Agonists have been shown to incr and decr dimerisation.
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| Maggio et al 1993 | Chimaeras of a2AR and M3 receptors couldnt work or bind radioligand alone, indicating they interact. a2AR expression allowed a faulty M3R to stimulate PI hydrolysis in response to carbachol. Not explained by improved ER trafficking as mutant binds ligand.
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| Monnot et al 1996 | Co-expression of two mutant AT1A receptors allowed binding which neither could achieve solo. Still no downstream activation however. Used radiolabelled ligands and IP for binding and downstream signalling respectively.
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| Angers et al 2000 | BRET found to occur between betaARs, BRET was increased by agonist but present at basal conditions. Fused some BARs to YFP, some to luciferase (luciferase quenched by YFP). Proximity <50Angstroms.
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| Benkirane et al 1997 | CCR5 heterozyg mutations are protective against HIV and retain wtCCR5 in the ER (dom negative). Confocal microscopy used to show wt at membrane and mutant in ER, both in ER when coexpressed. May be a mechanism for many dominant negative mutations
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| Samson et al 1996 | Shows that CCR5 mutation (homo & heterozyg) is protective against HIV using a case-control study to show reduced polymorphism prevalence in HIV infected community. Shows GPCR dimerisation can be clinically important (along with benkirane 1997).
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| Hebert et al 1996 | Used a construct mimicking dimer interface (tm6 of B2ARs) to block dimerisation, showed reduced activity. Cant be sure decr activity is due to reduced dimerisation, could use more constructs that prevent dimerisation to show multiple routes to same result
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| Mijares et al 2000 | Bivalent but not monovalent B2AR antibodies shown to act as agonists, crosslinking monovalent antibodies caused agonist-like effects. Dimerisation seems able to activate the receptor albeit less than binding of the agonist (scaffolds as partial agonists?)
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| Carrithers & Lerner 1996 | Dimerisation of an agonist using poly-lysine tract and single cysteine pair improved agonist properties. Looked for dispersal of pigment after MSH receptor activation. Dimerisation of an antagonist gave it agonist properties at high concentrations.
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| Vila-Coro et al 2000 | Anti CCR5 antibody causes dimerisation of the receptor and in doing so protects against HIV. Shown by immunoprecipitation to induce dimerisation. Plasma RNA of HIV was reduced in mice models relative to untreated controls.
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| Jordan et al 1999 | Used co-IP to show dimerisation of k and d opioid receptors. Shows synergistic binding of two selective agonists as well as synergistic effectiveness. Radiolabelled cAMP was used to measure activation.
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| McVey et al 2001 | BRET and coIP show interaction between d opioid receptors and B2ARs, difficulties of using coIPs with hydrophobic receptors. Couldnt show the same with FRET. Small incr in BRET with ligand binding. Conflicting results.
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| Jordan et al 2001 | Showed coIP of Kopioid and B2AR, also showed internalisation due to ligand of the other. Membrane binding assessed by labelled ligand. No altered cAMP response but B2ARs were shown to signal via MAPK when expressed with d opioid receptors (not with k)
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| Lagerstrom & Schioth 2008 | Review of GPCRs in therapeutics. Rhodopsin family is largest family, others are secretins, adhesion, glutamate & frizzled/taste 2.
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| Adler et al 2000 | Discovered bitter taste receptors, used genomic linkage to inability to detect certain tastes. Found a bitter receptor then used the sequence to find others (thought to be around 50 total). Showed selective expression in gustducin expressing cells.
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| Lohse et al 2012 | Review of FRET/BRET in GPCR studies. Discusses whether dimers are preformed or not. I'd presume dimers were preformed, because if dimerisation is needed for activity then it makes no sense to delay the signal.
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| Albizu et al 2010 | FRET between 2 bound ligands used to show oligomerisation, appears to show constant dimerisation as antagonists caused FRET consistent with dimers. Less FRET with agonists at oxytocin R's, only seem to bind one site on the dimer at conc used
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| Castro et al 2005 | Showed slow FRET between ligand and receptor representing ligand binding followed by slow FRET change indicating activation.
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| Elling et al 1995 | Tm helices 5&6 are important, antagonists that bind there stabilise an unfavourable conformation for agonists. Mutated competitive antag binding site without altering agonist affinity, made zinc the antag instead. Stabilises exclusive conformations
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| Zurn et al 2009 | Partial agonist conformational changes are less dramatic and slower than full agonist, shown by multiple site FRET in HEK cells. FRET changes detectable at all sites for full agonist, only at already approximated sites for partial agonist. Used a2AR.
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| Spengler et al 1993 | Early (1st?) example of biased agonism, differential response of PACAP to various splice variants of the endogenous ligand. Activation measured by cAMP and IP. PACAP 38&27 equally active in cAMP incr but 38 has a 100x lower EC50 for IP signalling.
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| Wilden et al 1986 | First sign of arrestin desensitisation, showed reduced rhodopsin activity after phosphorylation by rhodopsin kinase, increased by addition of arrestin. Receptor activation assayed using the pH change associated with cGMP hydrolysis
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| Lutrell et al 1999 | First example of b-arrestin signalling. b2AR activates src to activate MAPK. Blocking b-arrestin bindign to receptor or src blocked response, src binding mutation did nothing to sequestration but disrupted MAPK signalling (Less labelled phosphate on MAPK)
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| Ahn et al 2004 | MAPK activation by beta arrestin is slower and longer lasting than activation by g protein. siRNA KO of b-arrestin sped up kinetics, PKCinh thought to isolate b-arrestin left only slow activation. 3 components found in endosomes using immunohistochemisry.
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| Rajagopal et al 2010 | Review: Biased agonism can be plotted as G-prot vs b-arrestin signalling. FRET difficult as tagging beta arrestin gives small signals, tagging receptor may alter response. We are unsure if b-arrestin signalling and desensitisation always go together
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| Zidar et al 2009 | 2 agonists create 2 different receptor phosphorylation patterns. One pattern leads to receptor internalisation, the other allows more b-arrestin signalling. Biased agonists create a second biased agonist in the form of the receptor as b-arrestin substrate
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| Wisler et al 2007 | Looks at 16 beta blockers. Carvedilol unique as it antagonises cAMP rise due to agonists (genetically encoded cAMP sensor), potentiates MAPK signalling through b-arrestin while potentiating MAPK signalling via b-arrestin (western blotting of lysate).
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| Bohn et al 1999 | Knockout of b-arrestin2 increases the response to morphine, may be reduced desensitisation. Global KO, heavy handed approach. Incr response in hetero & homozyg. Morphine thought to be more selective for g-protein signalling (over b-arr) than enkephalins
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| Yao et al 2006 | Fluorescent bimane attached to cysteine, quenched by nearby tryptophans. Placed near ionic lock in tm3 of B2AR. Ionic lock breaking is necessary, not sufficient for full agonism. Couldnt show G-protein response so receptor function may be compromised.
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| Gane et al 2013 | Humans can detect deuterated compounds, presence of the extra neutron may be enough to cause a detectable biased agonism without being different enough to allow binding to a separate receptor.
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| Kubokawa et al 1996 | Shows a salmon homologue of mGluR activated by both glutamate and calcium, first description of a metabotropic receptor activated by two completely different physiological ligands. Found through chloride channel ability of the mGluR
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| Kubo et al 1998 | Several rat homologues of mGluR (seems to be a fairly common property of the family). Saturating concentrations of either agonist did not prevent response to the other, indicates distinct binding sites.
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| Fotiadis et al 2003 | Shows rhodopsin dimers using atomic force microscopy. GPCRs are naturally concentrated in native disc membranes.
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| Wechsler et al 2006 | Shows polymorphisms affect response of asthmatics to beta agonists. Not thought that polymorphisms contribute to asthma risk
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| (Quote) William Osler 1892 | If it were not for the great variability among individuals, Medicine might as well be a science and not an art.
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| Hall et al 1998 | Shows B2AR is capable of binding NHERF directly and is capable of signalling independently of beta arrestin and g prots. Colocalisation shown by fluorescence mutations (not FRET). Soluble B2AR c terminus blocked NHERF regulatory effects by sequestration
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| Bunemann et al 2003 | Shows incr FRET between Ga and Gby after receptor activation. G protein may be too mutated (added fluor proteins and made insensitive to pertussis toxin) still functional but may be working unusually. Also paired human and rat subunits (weird)
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| Li and Zhang 2013 | Although Gaq and Ga11 generally considered to have same effects (couple to same receptors, same activation of PLC pathway) they have differential effects on TRPM8 inhibition. Gaq more effective, diff due to one residue which incr Ga11 inhib when mutated
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