The thrombin receptor second cytoplasmic loop confers coupling to G(q)-like G proteins in chimeric receptors - Additional evidence for a common transmembrane signaling and G protein coupling mechanism in G protein-coupled receptors

作者：Verrall S; Ishii M; Chen M; Wang L; Tram T; Coughlin SR

来源：Journal of Biological Chemistry, 1997, 272(11): 6898-6902.

Thrombin activates human platelets and other cells in part by cleaving an unusual G protein-coupled receptor, Thrombin cleavage of this receptor's amino-terminal exodomain unmasks a new amino terminus, This then binds intramolecularly to the body of the receptor to trigger transmembrane signaling and activation of G(i)-and G(q)-like G proteins, Toward identifying the domains responsible for thrombin receptor-G protein interactions, we examined the signaling properties of chimeric receptors in which thrombin receptor cytoplasmic sequences replaced the cognate sequences in the G(s)-coupled beta(2)-adrenergic receptor (beta(2)AR) or the G(i)-coupled dopamine D-2 receptor (D(2)R). In Xenopus oocytes, a chimeric beta(2)AR bearing the thrombin receptor second cytoplasmic (C2) loop gained the ability to trigger intracellular Ca2+ release in response to adrenergic agonist, whereas a beta(2)AR bearing the cognate C2 loop from the D(2)R did not. Similarly, in COS-7 cells, a chimeric D(2)R bearing the thrombin receptor C2 loop gained the ability to trigger phosphoinositide hydrolysis in response to dopaminergic agonist, apparently by coupling to a G(q)-like G protein. No detectable G(s) coupling was seen. Thus, the thrombin receptor C2 loop was able to confer G(q)-like coupling in several different receptor contexts. These observations suggest that the thrombin receptor C2 loop specifies G(q) coupling by directly contacting G(q) or by contributing to a structure required for G(q) coupling. The ability of the thrombin receptor C2 loop to function in the context of the D(2)R and beta(2)AR strongly suggests that the transmembrane switching and G protein activation strategies used by the thrombin receptor must be very similar to those used by the D(2)R and beta(2)AR despite the thrombin receptor's strikingly different liganding mechanism.

• 出版日期1997-3-14