A DOMAIN FOR G-PROTEIN COUPLING IN CARBOXYL-TERMINAL TAIL OF RAT ANGIOTENSIN-II RECEPTOR-TYPE 1A

To delineate domains essential for G(q) protein coupling in the C-term inal region (C-tail) of rat angiotensin II (Ang II) receptor type 1A ( AT(1A)), we modified the putative cytosolic regions of the receptor by truncation or alanine substitution and determined resultant changes i n the guanosine 5'-3-O-(thio)triphosphate (GTP gamma S) effect on Ang II binding and inositol trisphosphate production by the agonist, Indep endently, we studied the effect of synthetic C-tail peptides (P-5) and its alanine substitution analogs on [S-35]GTP gamma S binding to G(q) , Effects of GTP gamma S on Ang II binding (shift to a low affinity fo rm) and inositol trisphosphate production in the deletional mutant rec eptor 1-317 AT(1A) was similar to wild type AT(1A), whereas in shorter C-terminal deletion mutants 1-309, 1-311, 1-312, 1-313 AT(1A), and su bstitutional mutants Y312A, F313A, and L314A these activities were mar kedly reduced. The binding of [S-35]GTP gamma S to G(q) was promoted b y the synthetic C-terminal peptide P-5 but not when mutated at Tyr(312 ), Phe(313), or Leu(314). Results indicate that Tyr(312), Phe(313), an d Leu(314) in cytosolic carboxyl-terminal region of rat AT(1A) are ess ential for coupling and activation of G(q).