The Third Intracellular Loop Stabilizes the Inactive State of the Neuropeptide Y1 Receptor

Constitutively active G-protein-coupled receptors (GPCRs) can signal even in the absence of ligand binding. Most Class I GPCRs are stabilized in the resting conformation by intramolecular interactions involving transmembrane domain (TM) 3 and TM6, particularly at loci 6.30 and 6.34 of TM6. Signaling by Gi/Go-coupled receptors such as the Neuropeptide Y1 receptor decreases already low basal metabolite levels. Thus, we examined constitutive activity using a biochemical assay mediated by a Gi/Gq chimeric protein and a more direct electrophysiological assay. Wild-type (WT-Y1) receptors express no measurable, agonist-independent activation, while μ-opioid receptors (MOR) and P2Y12 purinoceptors showed clear evidence of constitutive activation, especially in the electrophysiological assay. Neither point mutations at TM6 (T6.30A or N6.34A) nor substitution of the entire TM3 and TM6 regions from the MOR into the Y1 receptor increased basal WT-Y1 activation. By contrast, chimeric substitution of the third intracellular loop (ICL3) generated a constitutively active, Y1-ICL3-MOR chimera. Furthermore, the loss of stabilizing interactions from the native ICL3 enhanced the role of surrounding residues to permit basal receptor activation; because constitutive activity of the Y1-ICL3-MOR chimera was further increased by point mutation at locus 6.34, which did not alter WT-Y1 receptor activity. Our results indicate that the ICL3 stabilizes the Y1 receptor in the inactive state and confers structural properties critical for regulating Y receptor activation and signal transduction. These studies reveal the active participation of the ICL3 in the stabilization and activation of Class I GPCRs. Constitutively active G-protein-coupled receptors (GPCRs) can signal even in the absence of ligand binding. Most Class I GPCRs are stabilized in the resting conformation by intramolecular interactions involving transmembrane domain (TM) 3 and TM6, particularly at loci 6.30 and 6.34 of TM6. Signaling by Gi/Go-coupled receptors such as the Neuropeptide Y1 receptor decreases already low basal metabolite levels. Thus, we examined constitutive activity using a biochemical assay mediated by a Gi/Gq chimeric protein and a more direct electrophysiological assay. Wild-type (WT-Y1) receptors express no measurable, agonist-independent activation, while μ-opioid receptors (MOR) and P2Y12 purinoceptors showed clear evidence of constitutive activation, especially in the electrophysiological assay. Neither point mutations at TM6 (T6.30A or N6.34A) nor substitution of the entire TM3 and TM6 regions from the MOR into the Y1 receptor increased basal WT-Y1 activation. By contrast, chimeric substitution of the third intracellular loop (ICL3) generated a constitutively active, Y1-ICL3-MOR chimera. Furthermore, the loss of stabilizing interactions from the native ICL3 enhanced the role of surrounding residues to permit basal receptor activation; because constitutive activity of the Y1-ICL3-MOR chimera was further increased by point mutation at locus 6.34, which did not alter WT-Y1 receptor activity. Our results indicate that the ICL3 stabilizes the Y1 receptor in the inactive state and confers structural properties critical for regulating Y receptor activation and signal transduction. These studies reveal the active participation of the ICL3 in the stabilization and activation of Class I GPCRs. Neuropeptide Y (NPY) 2The abbreviations used are: NPYneuropeptide YY,NPYreceptorGPCRG-protein-coupled receptorTMtransmembraneIPinositol phosphatePFprepulse facilitationBPFbasal PFICLintracellular loopMORμ-opioid receptorEGFPenhanced green fluorescent proteinEYFPenhanced yellow fluorescent proteinhhumanP2Ypurinergic receptorDMEMDulbecco's modified Eagle mediumpporcineFmoc/tBu9-fluorenylmethoxycarbonyl-ter-butylELISAenzyme-linked immunosorbent assayHAhemagglutininWTwild-typeTRITCtetramethylrhodamine isothiocyanateVDCCvoltage-dependent calcium channelECFPenhanced cyan fluorescent proteinIBabarium currentPtest pulseVhholding potentialPPprepulseIPbarium current produced by test pulseDAMGO[d-Ala2,N-MePhe4,Gly-ol5]enkephalinGDP-β-Sguanosine 5′-[β-thio]diphosphateIP2/P1ratio of current produced by P2 versus P1. is one of the most abundant peptides in the nervous system. NPY and its receptors have been implicated in various biological functions and neuronal disorders, such as epilepsy, obesity, and anxiety. There are 5 confirmed subtypes of NPY receptors (Y1, Y2, Y4, Y5, and y6), which are class I G-protein-coupled receptors (GPCRs) coupling to Gi/Go proteins (1Larhammar D. Regul. Pept. 1996; 65: 165-174Crossref PubMed Scopus (217) Google Scholar). Recent evidence indicates that an unexpectedly large number of the GPCRs demonstrate constitutive activity, so they can signal even in the absence of ligand binding (2Kenakin T. FASEB J. 2001; 15: 598-611Crossref PubMed Scopus (359) Google Scholar, 3Chalmers D.T. Behan D.P. Nat. Rev. Drug Discov. 2002; 1: 599-608Crossref PubMed Scopus (107) Google Scholar, 4Menzaghi F. Behan D.P. Chalmers D.T. Curr. Drug Targets CNS Neurol. Disord. 2002; 1: 105-121Crossref PubMed Scopus (26) Google Scholar). However, little is known about the activation properties of Y receptors or their propensity for constitutive activation. neuropeptide Y receptor G-protein-coupled receptor transmembrane inositol phosphate prepulse facilitation basal PF intracellular loop μ-opioid receptor enhanced green fluorescent protein enhanced yellow fluorescent protein human purinergic receptor Dulbecco's modified Eagle medium porcine 9-fluorenylmethoxycarbonyl-ter-butyl enzyme-linked immunosorbent assay hemagglutinin wild-type tetramethylrhodamine isothiocyanate voltage-dependent calcium channel enhanced cyan fluorescent protein barium current test pulse holding potential prepulse barium current produced by test pulse [d-Ala2,N-MePhe4,Gly-ol5]enkephalin guanosine 5′-[β-thio]diphosphate ratio of current produced by P2 versus P1. GPCR activation is determined by the flexibility of its transmembrane (TM) segments to move relative to each other (5Farrens D.L. Altenback C. Yang K. Hubbell W.L. Khorana H.G. Science. 1996; 274: 768-770Crossref PubMed Scopus (1117) Google Scholar). GPCRs are stabilized in the inactive state by a network of non-covalent, intramolecular interactions that restricts TM mobility (6Kjelsberg M.A. Cotecchia S. Ostrowski J. Caron M.G. Lefkowitz R.J. J. Biol. Chem. 1992; 267: 1430-1433Abstract Full Text PDF PubMed Google Scholar, 7Rasmussen S.G. Jensen A.D. Liapakis G. Ghanouni P. Javitch J.A. Gether U. Mol. Pharmacol. 1999; 56: 175-184Crossref PubMed Scopus (197) Google Scholar). The interactions between the (D/E)RY and X1BBX2X3B motif on TM3 and TM6, respectively, are considered to be critical for GPCR activation (8Kobilka B.K. Deupi X. Trends Pharmacol. Sci. 2007; 28: 397-406Abstract Full Text Full Text PDF PubMed Scopus (585) Google Scholar). Single point mutation at X 6.301 and/or X 6.343 is sufficient in some GPCRs to destabilize this covalent network, thus allowing the GPCR to adopt a conformation favorable for intracellular G-protein binding. In effect, point mutation(s) at loci 6.30 and/or 6.34 frequently induce constitutive activity in class I GPCRs (6Kjelsberg M.A. Cotecchia S. Ostrowski J. Caron M.G. Lefkowitz R.J. J. Biol. Chem. 1992; 267: 1430-1433Abstract Full Text PDF PubMed Google Scholar, 9Greasley P.J. Fanelli F. Rossier O. Abuin L. Cotecchia S. Mol. Pharmacol. 2002; 61: 1025-1032Crossref PubMed Scopus (108) Google Scholar, 10Ballesteros J.A. Jensen A.D. Liapakis G. Rasmussen S.G. Shi L. Gether U. Javitch J.A. J. Biol. Chem. 2001; 276: 29171-29177Abstract Full Text Full Text PDF PubMed Scopus (538) Google Scholar, 11Jensen A.D. Guarnieri F. Rasmussen S.G. Asmar F. Ballesteros J.A. Gether U. J. Biol. Chem. 2001; 276: 9279-9290Abstract Full Text Full Text PDF PubMed Scopus (147) Google Scholar). However, some GPCRs are resistant to constitutive activation in this way, suggesting the participation of alternative regions that regulate GPCR activation. Y receptors are coupled to the activation of Gi/Go proteins, hence detection of their receptor activation is complicated by the nature of Gi/Go-protein signaling that primarily inhibits adenylyl cyclase, thereby suppressing the production of readily detectable metabolites. We circumvented this by employing a biochemical assay in which a chimeric GαΔ6qi4myr protein positively coupled Y1 receptor activation to the Gq-signaling pathway, increasing inositol phosphate (IP) production (12Kostenis E. Trends Pharmacol. Sci. 2001; 22: 560-564Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar, 13Kostenis E. Degtyarev M.Y. Conklin B.R. Wess J. J. Biol. Chem. 1997; 242: 19107-19110Abstract Full Text Full Text PDF Scopus (75) Google Scholar). Secondly, we developed an electrophysiological assay whereby GPCR activation was measured as an increase in basal prepulse facilitation (BPF) of a co-expressed N-type voltage-dependent calcium channel (14Herlitze S. Garcia D.E. Mackie K. Hille B. Scheuer T. Catterall W.A. Nature. 1996; 280: 258-262Crossref Scopus (706) Google Scholar, 15Ikeda S.R. Nature. 1996; 380: 255-258Crossref PubMed Scopus (710) Google Scholar, X. S.R. D.L. Mol. Pharmacol. PubMed Scopus Google Scholar). The of the detection and of constitutive activity in this class of Gi/Go-coupled However, the WT-Y1 receptor did not express constitutive activity, nor was to constitutive activation by point mutations at 6.30 or 6.34 By chimeric substitution of such as a TM or intracellular loop into the Y1 receptor from regions in the constitutively active μ-opioid receptor we the structural that stabilizes the Y1 The loss of the that the most stabilizing interactions in the of a constitutively active chimeric Y1 Our indicate that the Y1 receptor is stabilized in the inactive state by the ICL3 and the relative of this for regulating the activation of other Y receptors and class I GPCRs. The of the human Y1 receptor into the been A.D. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The to the enhanced green fluorescent protein or yellow fluorescent protein for detection of the receptor and not alter the of Y receptors A.D. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The human Y1 receptor was into the a and an the The entire was to the of In the Y1-ICL3-MOR the for of the receptor by for of the The Y1-ICL3-MOR was at from the by point mutation from to to the chimera. In the for and of the receptor by for and of the this an to point mutation at The in was by The purinergic receptor in was by T. of of GPCRs at the X1BBX2X3B motif for a 22: PubMed Scopus Google Scholar). The was the for a at and the for a was at green in Dulbecco's modified medium and as at in a of and from The was used to the activation of by of the chimeric G-protein GαΔ6qi4myr by E. can to the this chimeric which a an of residues from and an (12Kostenis E. Trends Pharmacol. Sci. 2001; 22: 560-564Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar, 13Kostenis E. Degtyarev M.Y. Conklin B.R. Wess J. J. Biol. Chem. 1997; 242: 19107-19110Abstract Full Text Full Text PDF Scopus (75) Google Scholar). into and to be the GαΔ6qi4myr using of a the P2Y12 receptor and GαΔ6qi4myr a the and GαΔ6qi4myr of was measured of to The and in for or in to of an by the K. G. J. PubMed Scopus Google or as The by the of and of of intracellular determined by as J. PubMed Scopus Google Scholar, J. PubMed Scopus Google Scholar). of generated chimeric GPCRs was determined binding and signal for the WT-Y1 receptor and Y1 chimera are as the for binding studies and signal relative to for binding was receptor not be for binding was receptor not be for binding was receptor not be in a binding studies in the absence and of NPY as D. J. K. a enzyme-linked immunosorbent assay T. J. Wess J. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google was the WT-Y1 receptor and its an hemagglutinin The was from the protein and of the The entire was to the of into and of and of the the and a of was by a of and each in to as and the was by of was measured at and using an studies to the of not not and receptors into that and the an and a tetramethylrhodamine isothiocyanate The a in and and as at in a of and from the they and at to a calcium phosphate E. D. J. Nature. 1997; PubMed Scopus Google the for the N-type voltage-dependent calcium channel and ratio a of of In most proteins of a fluorescent protein that not their a was N-type co-expressed the or receptor the chimeric by was co-expressed in the as of The to a to the a at in the calcium the and to at for The to a to further the was in a to a that was of to The was and considered for using a in some a to of of to electrophysiological at to the of an or used in and a to a The at and the and at and was of and to the test The barium current by each test pulse or of a from a holding potential of In the prepulse a from to was the test pulse the test pulse was by a at the holding potential E. D. J. Nature. 1997; PubMed Scopus Google Scholar). In the absence of the the test from each other by The of the used and of and and of the to the of prepulse between and in to in the Drug and [d-Ala2,N-MePhe4,Gly-ol5]enkephalin into the from to their to of and was in and at or was into the for the for at In involving guanosine 5′-[β-thio]diphosphate was to the to a of to using using and produced using for involving and 3 or more was determined using the test and respectively, for was a for between of was determined using a of The considered to be at as WT-Y1 Constitutively activation of the WT-Y1 receptor was determined in the absence of a biochemical assay and an electrophysiological assay basal prepulse facilitation of the Gi/Go-coupled Y1 receptor the production of so that a direct of Y1 receptor activation is In the of the chimeric GαΔ6qi4myr (12Kostenis E. Trends Pharmacol. Sci. 2001; 22: 560-564Abstract Full Text Full Text PDF PubMed Scopus (158) Google coupled the activation of receptors to the of the and of In this biochemical basal activity of the constitutively active P2Y12 receptor T. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, S. Mol. Pharmacol. PubMed Google was readily not that of the native MOR D. J. PubMed Google Scholar). There was a increase in intracellular the of the constitutively active P2Y12 receptor not of the constitutively active MOR relative to the The assay is not to of GPCR constitutive activity. Furthermore, this assay did not reveal basal receptor activation by the WT-Y1 receptor The electrophysiological assay basal prepulse facilitation (BPF) can constitutive activity of Gi/Go-coupled receptors in (14Herlitze S. Garcia D.E. Mackie K. Hille B. Scheuer T. Catterall W.A. Nature. 1996; 280: 258-262Crossref Scopus (706) Google Scholar, 15Ikeda S.R. Nature. 1996; 380: 255-258Crossref PubMed Scopus (710) Google Scholar, X. S.R. D.L. Mol. Pharmacol. PubMed Scopus Google Scholar). was using a or an prepulse and results as the ratio of the current by the test pulse relative to that of the to the increase in by the in the absence of an activity of the P2Y12 receptor and MOR by the electrophysiological assay. of the P2Y12 receptor or the MOR in a increase in relative to in which no GPCRs co-expressed the N-type In contrast, of the WT-Y1 receptor did not a increase in that is in the absence of an WT-Y1 receptor activation and intracellular signaling in this as NPY produced a of and increased prepulse facilitation of barium at the test pulse and increase in PF receptor activation are as the and determined from not not in a in the absence of co-expressed a of was We the that the produced in the absence of co-expressed GPCRs was to the of in of the the of the chimeric that is by a GPCR the J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google was to the of the in the absence of co-expressed as as that in the of the WT-Y1 or even the known constitutively active MOR test the that the of the detection of constitutive WT-Y1 receptor activation, we examined the of an of G-protein activation, on We that or not the produced by the WT-Y1 receptor was by of In we a of that was of GPCR was the to basal activation of did not the of in the WT-Y1 or in that not GPCRs However, the of in The produced by was a The of to by was in the constitutively active P2Y12 receptor as is the that the basal activity of the MOR and P2Y12 receptors in an of binding to thus the for binding to the N-type In contrast, intracellular did not produced by the WT-Y1 receptor that the in WT-Y1 was not to basal WT-Y1 receptor activation. WT-Y1 to by Single at 6.30 and GPCR activation is by a loss of intramolecular interactions that the receptor in an state (6Kjelsberg M.A. Cotecchia S. Ostrowski J. Caron M.G. Lefkowitz R.J. J. Biol. Chem. 1992; 267: 1430-1433Abstract Full Text PDF PubMed Google Scholar, 7Rasmussen S.G. Jensen A.D. Liapakis G. Ghanouni P. Javitch J.A. Gether U. Mol. Pharmacol. 1999; 56: 175-184Crossref PubMed Scopus (197) Google Scholar, U. Ballesteros J.A. E. B.K. J. Biol. Chem. 1997; Full Text Full Text PDF PubMed Scopus Google Scholar). The of the of TM at locus 6.30 and 6.34, been implicated in such intramolecular interactions K. T. T. T. Science. PubMed Scopus Google Scholar). point mutation at locus 6.30 or 6.34 was to the WT-Y1 receptor to test the that the of the WT-Y1 receptor is at The and receptors and at the as by the assay not and receptors binding to that of the WT-Y1 receptor activation of Y1 receptors in the of and produced a increase in prepulse facilitation between the the WT-Y1 receptor and the and receptors showed that the nor the produced of relative to the WT-Y1 receptor that the and point mutations receptor nor constitutive activity the WT-Y1 the potential of stabilizing interactions between residues TM3 and TM6, transmembrane segments of the WT-Y1 receptor from the constitutively active to the WT-Y1 the chimera did not demonstrate a increase in the WT-Y1 receptor Furthermore, the chimera did not was to NPY that the chimeric receptor not express constitutive activity and that of the TM3 and TM6 regions from the WT-Y1 receptor receptor activation and signal the for binding. ICL3 WT-Y1 the WT-Y1 receptor was not to constitutive activation by point mutation at loci on TM6. The loci 6.30 and 6.34 on the WT-Y1 receptor on the between TM6 and the ICL3 regions of the test the that the ICL3 residues that the inactive state of the WT-Y1 receptor S. S. Caron M.G. Lefkowitz R.J. Sci. U. S. PubMed Scopus Google Scholar, P. Cotecchia S. T. R.J. J. Biol. Chem. Full Text PDF PubMed Google the ICL3 of the WT-Y1 receptor was that from the The Y1-ICL3-MOR chimera is a receptor that to NPY In the absence of the the Y1-ICL3-MOR chimera a The of the Y1-ICL3-MOR chimera was that of the WT-Y1 receptor Furthermore, a intracellular of the produced in the Y1-ICL3-MOR chimera was by that the in the chimeric Y1-ICL3-MOR receptor was in to basal activation of the Thus, of the ICL3 of the WT-Y1 receptor that of the MOR in the of a Y1 receptor that is constitutively We the that the ICL3 the constitutive activity of the WT-Y1 receptor is to further In the basal activity was increased a to point mutation at locus 6.34 of the to in the receptor P. J. C. 2001; PubMed Scopus Google Scholar). We examined the constitutive activity of the Y1-ICL3-MOR chimera an point mutation at the between the TM6 and ICL3 the is a of the increase in constitutive activity between the Y1-ICL3-MOR and be to that between the and the and to The chimeric produced a of as the the was to the the The point mutation produced a increase in the produced by the and the Y1-ICL3-MOR the in constitutive activity in the assay for and chimeric receptor the point the assay evidence of constitutive activity for the Our results showed that the of the native Y1 ICL3 that from the the Y1 receptor a to structural that increased basal receptor activation in the of constitutive activity in GPCRs is more GPCRs coupling to such as or that the production of readily examined In the biochemical assay the of a chimeric the into a signal that was by the of (12Kostenis E. Trends Pharmacol. Sci. 2001; 22: 560-564Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar, T. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, B.R. D. Nature. PubMed Scopus Google Scholar, S.R. J. Pharmacol. 2002; Scopus Google Scholar). The assay was to low of GPCR activation a thus be particularly to GPCRs that express constitutive activity. a biochemical of activity in by Gi/Go-coupled GPCRs been C. P.J. Mol. Pharmacol. PubMed Scopus Google its and to constitutive activity is In contrast, the electrophysiological detection of can even in constitutive activity a of the loss of in the of in an The of the assay can be to the of an because the of produced by the and GPCR state was one current The WT-Y1 receptor from class I GPCRs in that detectable constitutive activity nor to structural that constitutive activity in other By a TM or ICL3 from the MOR into the Y1 we which is most for the activation of the Y1 the activation of most class I GPCRs the TM3 and TM6 regions and T. Sci. they not to be critical for stabilizing the inactive state of the Y1 of the ICL3 not the TM3 and TM6 of the WT-Y1 receptor generated a constitutively active, chimeric Y1 that the ICL3 of the Y1 receptor intramolecular interactions that the Y1 receptor in the inactive the loss of interactions from the the residues at the of TM6 to more for stabilizing the inactive conformation of the Y1 of TM6 to WT-Y1 have that the Y receptor little or no basal activation G. J. S. C. K. T. Mol. Pharmacol. PubMed Scopus Google Scholar). The class I which the Y is stabilized in the inactive state by an (5Farrens D.L. Altenback C. Yang K. Hubbell W.L. Khorana H.G. Science. 1996; 274: 768-770Crossref PubMed Scopus (1117) Google Scholar, B.K. Deupi X. Trends Pharmacol. Sci. 2007; 28: 397-406Abstract Full Text Full Text PDF PubMed Scopus (585) Google Scholar, C. S. S. P. E. Trends 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, U. B.K. J. Biol. Chem. Full Text Full Text PDF Scopus Google Scholar). The a network of and interactions between the motif on TM3 and residues at locus 6.30 and 6.34 TM6 (5Farrens D.L. Altenback C. Yang K. Hubbell W.L. Khorana H.G. Science. 1996; 274: 768-770Crossref PubMed Scopus (1117) Google Scholar). Constitutively active can be generated in receptors by point mutation(s) at locus 6.30 and/or However, the of this on the of a is and GPCRs J.A. Jensen A.D. Liapakis G. Rasmussen S.G. Shi L. Gether U. Javitch J.A. J. Biol. Chem. 2001; 276: 29171-29177Abstract Full Text Full Text PDF PubMed Scopus (538) Google is not class I GPCRs receptor I receptor and is not in the Y1 receptor J.A. Scopus Google Scholar, D. 2001; 22: PubMed Scopus Google Scholar). of GPCR activation can be on the or absence of in the native is in the wild-type a constitutively active receptor be generated by point mutation at 6.30 or 6.34 receptor K. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, K. J. Pharmacol. Google receptor J. S. K. C. J. PubMed Google Scholar, S. T. Mol. Pharmacol. Google receptor D. P. J. 1997; Google Scholar, P. T. G. T. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, S. T. PubMed Scopus Google Scholar). the which that residues at loci 6.30 and 6.34 are to regulate GPCR activation J.A. Jensen A.D. Liapakis G. Rasmussen S.G. Shi L. Gether U. Javitch J.A. J. Biol. Chem. 2001; 276: 29171-29177Abstract Full Text Full Text PDF PubMed Scopus (538) Google Scholar, K. J. Biol. Chem. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). The in the absence of in the wild-type activity was at locus 6.34 P. J. C. 2001; PubMed Scopus Google not 6.30 P. 2002; PubMed Scopus Google Scholar). that one intramolecular at TM6 for GPCRs a P. 2002; PubMed Scopus Google Scholar). Our studies on the Y1 receptor evidence of a third for GPCR activation point mutation at locus 6.30 nor 6.34 can agonist-independent GPCR activation in the absence of a native to constitutive activity was in J.A. E. J. J. Pharmacol. PubMed Scopus Google and S. J. PubMed Scopus Google Scholar, X. L. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). In to the role of TM3 and TM6 for receptor stabilization in Class I studies that of TM regions residues that a role in constitutive activation of the WT-Y1 of ICL3 in the WT-Y1 the receptor the ICL3 of the Y1 receptor confers properties for activation and signal transduction. GPCR activation a an intracellular residues the ICL3 Caron M.G. Lefkowitz R.J. J. Biol. Chem. Full Text PDF PubMed Google Scholar, 2001; PubMed Scopus Google Scholar, X. Mol. 1997; PubMed Scopus Google Scholar, C. P. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, S. S. X. 1996; PubMed Scopus Google and at the D. J. Biol. Chem. 1996; Full Text Full Text PDF PubMed Scopus Google Scholar, C. C. J.A. Mol. PubMed Scopus Google are for the of a J. FASEB J. 1997; PubMed Scopus Google Scholar, J. D.L. PubMed Scopus Google Scholar, U. Rev. PubMed Scopus Google Scholar). the ICL3 G-protein and activation J. FASEB J. 1997; PubMed Scopus Google structural involving the ICL3 can of GPCR activation even in the is to the in basal activity the Y1 receptor a chimeric the to that the of the are at of the of basal activity. of ICL3 residues that have the most on Y1 receptor activation can be by point mutations the is the of the The ICL3 substitution structural to regions of the Y1 mutation at locus 6.34 of the WT-Y1 receptor no on its basal activity. By contrast, the basal activity of the Y1-ICL3-MOR chimera was increased by the point mutation at this indicates that the structural in the Y1-ICL3-MOR chimera the participation of residues TM6 in stabilizing the inactive conformation of the Y1 The NPY to be basal in Thus, is little or no of of NPY or its receptors on basal S. D. PubMed Scopus Google Scholar). are in the of NPY J. PubMed Scopus Google Scholar, B. S. T. G. J. 22: PubMed Scopus (107) Google the NPY is B. O. J. PubMed Scopus Google Scholar). of Gi/Go-coupled GPCRs to neuronal activity a number of J. 2002; 22: PubMed Google and signaling Gi/Go-coupled GPCRs to that of or receptors P. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, L. D.P. P. S. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar, S. Mol. Biol. PubMed Scopus Google Scholar). be to is no signaling in the absence of GPCRs that demonstrate the activation of their even in the absence of have the of the in GPCR activation. Constitutively active GPCRs are for regions or residues that the structural GPCR activation. Our the relative of the WT-Y1 which is resistant to constitutive activation by intramolecular interactions TM6. we that the ICL3 an role for its constitutive activation, which is relative to most class I GPCRs.

Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.