Agonist binding and Gq-stimulating activities of the purified human P2Y1 receptor.
The human P2Y1 receptor (P2Y1-R) was purified after high-level expression from a recombinant baculovirus in Sf9 insect cells. Quantification by protein staining and with a radioligand binding assay using the high-affinity P2Y1-R antagonist [3H]MRS2279 ([3H]2-chloro-N6-methyl-(N)-methanocarba-2'-deoxyadenosine 3',5'-bis-phosphate) indicated a nearly homogenous preparation of receptor protein. Ki values determined in [3H]MRS2279 binding assays for antagonists with the purified P2Y1-R were in good agreement with the Ki and KB values determined for these molecules in membrane binding and activity assays, respectively. Availability of P2Y1-R in purified form allowed direct determination of nucleotide agonist affinities under conditions not compromised by nucleotide metabolism/interconversion, and an order of affinities of 2-methylthio-ADP (2MeSADP) > ADP = 2-methylthioATP = adenosine-5'-O-(3-thio)triphosphate = adenosine-5'-O(2-thiodiphosphate) >> ATP was obtained. The signaling activity of the purified P2Y1-R was quantified after reconstitution in proteoliposomes with heterotrimeric G proteins. Steady-state GTP hydrolysis in vesicles reconstituted with P2Y1-R and Galpha(q)beta(1)gamma(2) was stimulated by the addition of either 2MeADP or RGS4 alone and was increased by up to 50-fold in their combined presence. EC50 values of agonists for activation of the purified P2Y1-R were similar to their respective Ki values determined in radioligand binding experiments with the purified receptor. Moreover, ATP exhibited 20-fold higher EC50 and Ki values than did ADP and was a partial agonist relative to ADP and 2MeSADP under conditions in which no metabolism of the nucleotide occurred. Both RGS4 and PLC-beta1 were potent and efficacious GTPase-activating proteins for Galphaq and Galpha11 in P2Y1-R-containing vesicles. These results illustrate that the binding and signaling properties of the human P2Y1-R can be studied with purified proteins under conditions that circumvent the complications that occur in vivo.
Waldo
Gary L
GL
Department of Pharmacology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599-7365, USA.
Harden
T Kendall
TK
D000244:Adenosine Diphosphate / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D004305:Dose-Response Relationship, Drug; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism*; D006801:Humans; D007313:Insecta; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D058472:Receptors, Purinergic P2Y1
C465253:2-chloro-N6-methyl-(N)-methanocarba-2'-deoxyadenosine-3',5'-bisphosphate; C546382:P2RY1 protein, human; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2; D058472:Receptors, Purinergic P2Y1; D000244:Adenosine Diphosphate; D043802:GTP-Binding Protein alpha Subunits, Gq-G11