Identification of regions in the human Angiotensin II receptor Type 1 responsible for Gi and Gq coupling by mutagenesis study

Previous mutagenesis studies of angiotensin II (Ang II) receptor type 1 (AT(1)) have focused on determining the regions responsible for Gq coupling using the rat AT(1) receptor. We created human AT(1) receptor mutants, expressed them in COS-7 cells, and identified the domains crucial for Gi coupling as well as for Gq coupling. Substitution of Asp(125), Arg(126), Tyr(127), and Met(134) by Gly, Gly, Ala, and Ala in the highly conserved sequence of the second intracellular loop in most G protein-coupled receptors provided a mutant AT(1) receptor which lost the ability to couple to both Gq and Gi with no impairment in its binding to Ang II. A truncated mutant lacking the carboxyl terminal 50 residues was completely deficient in coupling to Gi, whereas it retained full ability to bind to Gq, in contrast to the rat AT(1) receptor. These findings demonstrate that the cytoplasmic tail in the human AT(1) receptor is the determinant of specific Gi coupling. (C) 1996 Academic Press, Inc.