Receptor-G protein gamma specificity: gamma11 shows unique potency for A(1) adenosine and 5-HT(1A) receptors.
G protein coupled receptors activate signal transducing guanine nucleotide-binding proteins (G proteins), which consist of an alpha subunit and a betagamma dimer. Whole cell studies have reported that receptors signal through specific betagamma subtypes. Membrane reconstitution studies with the adenosine A(1) and alpha(2A) adrenergic receptors have reached a similar conclusion. We aimed to test the generality of this finding by comparing the gamma subtype specificity for four G(i)-coupled receptors: alpha(2A) adrenergic; A1 adenosine (A(1)-R); 5-hydroxytryptamine(1A) (5-HT(1A)-R); mu opioid. Membranes were reconstituted with Galpha(i)(1) and five gamma subtypes (dimerized to beta1). Using a sensitive alpha-betagamma binding assay, we show that all recombinant betagamma (except beta1gamma1) had comparable affinity for alpha(i)(1). Using high affinity agonist binding as a measure of receptor-G protein coupling, betagamma-containing gamma11 was the most potent for A(1)-R and 5-HT(1A)-R (p < 0.05, one way ANOVA) while gamma7 was most potent for the other two receptors. gamma11 was 3-8-fold more potent for the A(1)-R than were the other gamma subtypes. Also, gamma11 was 2-8-fold more potent for A(1)-R than at the other receptors, suggesting a unique coupling specificity of the A(1)-R for gamma11. In contrast, the discrimination by receptors for the other betagamma subtypes (beta1 and gamma1, gamma2, gamma7, and gamma10) was limited (2-3-fold). Thus the exquisite betagamma specificity of individual receptors reported in whole cell studies may depend on in vivo mechanisms beyond direct receptor recognition of betagamma subtypes.
Lim
W K
WK
Department of Pharmacology, The University of Michigan, Ann Arbor, Michigan 48109-0632, USA.
Myung
C S
CS
Garrison
J C
JC
Neubig
R R
RR
D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D020962:Heterotrimeric GTP-Binding Proteins / Q000819:agonists / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000378:metabolism; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D011985:Receptors, Serotonin / Q000378:metabolism*; D044263:Receptors, Serotonin, 5-HT1; D013552:Swine; D014407:Tumor Cells, Cultured
D018341:Receptors, Adrenergic, alpha-2; D017450:Receptors, Opioid, mu; D018047:Receptors, Purinergic P1; D011985:Receptors, Serotonin; D044263:Receptors, Serotonin, 5-HT1; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D020962:Heterotrimeric GTP-Binding Proteins