Truncation of the receptor carboxyl terminus impairs membrane signaling but not ligand binding of human ETB endothelin receptor.

Human ETB endothelin receptor (hETBR) is a heptahelical G-protein-coupled receptor consisting of 442 amino acids whose carboxyl (C)-intracellular region has four and twelve sites for potential palmitoylation and phosphorylation, respectively. In order to elucidate the functional roles of these modification sites, we constructed a series of C-terminal truncated hETBRs and expressed them in Ltk- cells. All the truncated hETBRs showed ligand-binding profiles similar to those of the wild-type hETBR. The truncated receptors holding Cys-402 retained both normal intracellular calcium ([Ca2+]i) response and its rapid desensitization; however, the deleted receptors lacking Cys-402 failed to induce the [Ca2+]i response. These results showed that Cys-402 of hETBR is necessary for its intracellular calcium signaling and that at least ten of twelve putative phosphorylation sites are irresponsible for the agonist-induced desensitization.