Antagonists of the receptor-G protein interface block G(1)-coupled signal transduction

The carboxyl terminus of heterotrimeric G protein alpha subunits plays an important Pole in receptor interaction. We demonstrate that peptides corresponding to the last 11 residues of G alpha(i1/2) or G alpha(o1) impair agonist binding to A(1) adenosine receptors, whereas G alpha(s) or G alpha(t) peptides have mo effect. Previously, by using a combinatorial library we identified a series of G alpha(t) peptide analogs that bind rhodopsin with high affinity (Martin, E. L., Rens-Domiano, S., Schatz, P. J., and Hamm, H. E. (1996) J. Biol. Chem. 271, 361-366). Native G alpha(i1/2) peptide as well as several analogs were tested for their ability to modulate agonist binding or antagonist-agonist competition using cells overexpressing human A(1) adenosine receptors. Three peptide analogs decreased the K-i, suggesting that they disrupt the high affinity receptor-G protein interaction and stabilize am intermediate affinity state. To study the ability of the peptides to compete with endogenous G alpha(i) proteins and block signal transduction in a native setting we measured activation of G protein-coupled K+ channels through A(1) adenosine or gamma-aminobutyric acid, type B, receptors in hippocampal CA1 pyramidal neurons. Native G alpha(i1/2), peptide, and certain analog peptides inhibited receptor-mediated K+ channel gating, dependent can which receptor was activated. This differential perturbation of receptor-G protein interaction suggests that receptors that act on the same G protein can be selectively disrupted.