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-terminal 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 in the guanosine 5'-3-O-(thio)triphosphate (GTP gamma S) effect on Ang II binding and inositol trisphosphate production by the agonist, Independently, 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 form) and inositol trisphosphate production in the deletional mutant receptor 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 substitutional mutants Y312A, F313A, and L314A these activities were markedly reduced. The binding of [S-35]GTP gamma S to G(q) was promoted by 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), and Leu(314) in cytosolic carboxyl-terminal region of rat AT(1A) are essential for coupling and activation of G(q).