Evidence that a protein-protein interaction 'hot spot' on heterotrimeric G protein βγ subunits is used for recognition of a subclass of effectors

To understand the requirements for binding to G protein βγ subunits, phage-displayed random peptide libraries were screened using immobilized biotinylated βγ as the target. Selected peptides were grouped into four different families based on their sequence characteristics. One group (group I) had a clear conserved motif that has significant homology to peptides derived from phospholipase C β (PLC β) and to a short motif in phosducin that binds to G protein β subunits. The other groups had weaker sequence homologies or no homology to the group I sequences. A synthetic peptide from the strongest consensus group blocked activation of PLC by G protein βγ subunits. The peptide did not block βγ-mediated inhibition of voltage-gated calcium channels and had little effect on βγ-mediated inhibition of Gs-stimulated type I adenylate cyclase. Competition experiments indicated that peptides from all four families bound to a single site on βγ. These peptides may bind to a protein-protein interaction 'hot spot' on the surface of βγ subunits that is used by a subclass of effectors.