A surface on the G protein β-subunit involved in interactions with adenylyl cyclases

Receptor activation of heterotrimeric G proteins dissociates Gα from the Gβγ complex, allowing both to regulate effectors. Little is known about the effector-interaction regions of Gβγ. We had used molecular modeling to dock a peptide encoding the region of residues 956-982 of adenylyl cyclase (AC) 2 onto Gβ to identify residues on Gβ that may interact with effectors. Based on predictions from the model, we synthesized peptides encoding sequences of residues 86-105 (Gβ86-105) and 115-135 (Gβ115-135) from Gβ. The Gβ86-105 peptide inhibited Gβγ stimulation of AC2 and blocked Gβγ inhibition of AC1 and by itself inhibited calmodulin-stimulated AC1, thus displaying partial agonist activity. Substitution of Met-101 with Asn in this peptide resulted in the loss of both the inhibitory and partial agonist activities. Most activities of the Gβ115-135 peptide were similar to those of Gβ86-105 but Gβ115-135 was less efficacious in blocking Gβγ inhibition of AC1. Substitution of Tyr-124 with Val in the Gβ115-135 peptide diminished all of its activities. These results identify the region encoded by amino acids 84-143 of Gβ as a surface that is involved in transmitting signals to effectors.