Role of the prenyl group on the G protein gamma subunit in coupling trimeric G proteins to A1 adenosine receptors

The coupling of receptors to heterotrimeric G proteins is determined by interactions between the receptor and the G protein alpha subunits and by the composition of the beta gamma dimers, To determine the role of the gamma subunit prenyl modification in this interaction, the CaaX motifs in the gamma(1), and gamma(2) subunits were altered to direct modification with different prenyl groups, recombinant beta gamma dimers expressed in the baculovirus/Sf9 insect cell system, and the dimers purified, The activity of the beta gamma dimers was compared in two assays: formation of the high affinity agonist binding conformation of the Al adenosine receptor and receptor-catalyzed exchange of GDP for GTP on the a subunit, The beta(1) gamma(1) dimer (modified with farnesyl) was significantly less effective than beta(1) gamma(2) (modified with geranylgeranyl) in either assay, The beta(1) gamma(1)-S74L dimer (modified with geranylgeranyl) was nearly as effective as beta(1) gamma(2) in either assay, The beta(1) gamma(2)-L71S dimer (modified with farnesyl) was significantly less active than beta(1) gamma(2). Using I-125-labeled beta gamma subunits, it was determined that native and altered beta gamma dimers reconstituted equally well into Sf9 membranes containing Al adenosine receptors. These data suggest that the prenyl group on the gamma subunit is an important determinant of the interaction between receptors and G protein gamma subunits.