The selectivity of D2 dopamine receptor-guanine nucleotide-binding protein (G protein) coupling was studied by reconstitution techniques utilizing purified D2 dopamine receptors from bovine anterior pituitary and resolved G proteins from bovine brain, bovine pituitary, and human erythrocyte. Titration of a fixed receptor concentration with varying G protein concentrations revealed two aspects of receptor-G protein coupling. First, G(i2) appeared to couple selectively with the D2 receptor with ~ 10-fold higher affinity than any other tested G(i) subtype. Second, the G proteins differed in the maximal receptor-mediated agonist stimulation of the intrinsic GTPase activity. G(i2) appeared to be maximally stimulated by agonist-receptor complex with turnover numbers of ~ 2 min-1. The other G(i) subtypes, G(i1) and G(i3), could be only partially activated, resulting in maximal rates of GTPase of ~ 1 min-1. Agonist-stimulated GTPase activity was not detected in preparations containing G(o) from bovine brain. The differences in maximal agonist-stimulated GTPase rates observed among the G(i) subtypes could be explained by differences in agonist-promoted guanyl nucleotide exchange. Both guanosine 5'-3-O-(thio)triphosphate (GTPγS) binding and GDP release parameters were enhanced 2-fold for the G(i2) subtype over the other G(i) subtypes. These results suggest that even though several types of pertussis toxin substrate may exist in most tissues, a receptor may interact discretely with G proteins, thereby dictating signal transduction mechanisms.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Biological Chemistry|
|State||Published - 1990|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology