TRUNCATION OF THE RECEPTOR CARBOXYL-TERMINUS IMPAIRS MEMBRANE SIGNALING BUT NOT LIGAND-BINDING OF HUMAN ET(B) ENDOTHELIN RECEPTOR

Human ET(B) endothelin receptor (hET(B)R) is a heptahelical G-protein- coupled receptor consisting of 442 amino acids whose carboxyl (C)-intr acellular region has four and twelve sites for potential palmitoylatio n and phosphorylation, respectively. In order to elucidate the functio nal roles of these modification sites, we constructed a series of C-te rminal truncated hET(B)Rs and expressed them in Ltk(-) cells. All the truncated hET(B)Rs showed ligand-binding profiles similar to those of the wild-type hET(B)R. The truncated receptors holding Cys-402 retaine d both normal intracellular calcium ([Ca2+](i)) response and its rapid desensitization; however, the deleted receptors lacking Cys-402 faile d to induce the [Ca2+](i) response. These results showed that Cys-402 of hET(B)R is necessary for its intracellular calcium signaling and th at at least ten of twelve putative phosphorylation sites are irrespons ible for the agonist-induced desensitization. (C) Academic Press, Inc.