MAPPING OF G-PROTEIN COUPLING SITES OF THE ANGIOTENSIN-II TYPE-1 RECEPTOR

Angiotensin II type 1 (AT(1)) receptors have been identified in a wide variety of tissues, including the kidney, liver, adrenal gland, cardiovascular system, and brain. AT(1) receptors also mediate complex signaling mechanisms that elicit a diversity of specific physiological effects. The rat AT(1A) receptor has seven transmembrane domains and couples with three distinct G proteins: G(q), G(i), and G(o). But it is unknown which domains of AT(1A) couple with and activate each type of G protein. To identify the domains responsible for the activation of various types of G protein, we studied the effect of five different synthetic peptides representing different domains of cytosolic segments of the rat AT(1A) receptor on the binding of the S-35-labeled stable analogue of GTP, GTP gamma S. Peptides P-3, which is located in the N-terminal region of the putative third intracellular loop of AT(1A) (residues 216 through 230), and P-5 (residues 306 through 320), corresponding to the N-terminal region of the C-terminal tail, were found to activate purified G(i1), G(i2), and G(o), proteins. These results indicate that not only the third cytosolic loop but also the C-terminal cytosolic domain of AT(1A) is important for G(i1), G(i2), and G(o) protein coupling and activation.