Mapping of G Protein Coupling Sites of the Angiotensin II Type 1 Receptor

Abstract

Abstract 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 ³⁵ S-labeled stable analogue of GTP, GTPγS. 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.