A NOVEL SYSTEM THAT REPORTS THE G-PROTEINS LINKED TO A GIVEN RECEPTOR- A STUDY OF TYPE-3 SOMATOSTATIN RECEPTOR

SSTR3, a somatostatin (SST) receptor, is an adenylyl cyclase (AC)-inhi biting receptor, To assign the G-protein alpha-subunit (G alpha) linke d to this receptor, we created a novel reporter system which utilizes the well-established facts that the C-terminal 5 residues of G alpha a re the receptor contact site and G alpha(s) stimulates all subtypes of AC, We constructed chimeric G alpha(s), the C-terminal 5 residues of which were replaced with the corresponding C-terminus of each known G alpha, and examined which chimera confers SSTR3-induced activation of AC, Cellular transfection of SSTR3 and measurement of SST-dependent AC activity through co-transfected chimeric G alpha(s) revealed that SST R3 recognizes the C-termini of G alpha(i1/2) hut not of G alpha(o) or G alpha(z), and those of G alpha(14) and G alpha(16), but not of G alp ha(q) or G alpha(11). As predicted by the chimeric G alpha(s), SST-bou nd SSTR3 stimulated polyphosphoinositide turnover only when G alpha(16 ) or G alpha(14) was co-transfected, We conclude that the chimeric G a lpha(s), system provides a new approach towards the assignment of G-pr oteins linked to a given receptor. (C) 1997 Federation of European Bio chemical Societies.