A novel system that reports the G-proteins linked to a given receptor: a study of type3 somatostatin receptor

AbstractSSTR3, a somatostatin (SST) receptor, is an adenylyl cyclase (AC)-inhibiting receptor. To assign the G-protein α-subunit (Gα) linked to this receptor, we created a novel reporter system which utilizes the well-established facts that the C-terminal 5 residues of Gα are the receptor contact site and Gαs stimulates all subtypes of AC. We constructed chimeric Gαs the C-terminal 5 residues of which were replaced with the corresponding C-terminus of each known Gα, 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 Gαs revealed that SSTR3 recognizes the C-termini of Gαi1/2 but not of Gαo or Gαz, and those of Gα14 and Gα16, but not of Gαq or Gα11. As predicted by the chimeric Gαs, SST-bound SSTR3 stimulated polyphosphoinositide turnover only when Gα16 or Gα14 was co-transfected. We conclude that the chimeric Gαs system provides a new approach towards the assignment of G-proteins linked to a given receptor