Specific interaction with rhodopsin is dependent on the γ subunit type in a G protein

Interaction with a receptor is the first step in the proc-ess of signal transduction by heterotrimeric (αβγ) G proteins. We have examined the role of the G protein γ subunit in interaction between a receptor (rhodopsin) and a G protein, transducin (G_t). We have obtained recombinant βγ complexes containing the same β subunit but three different γ subunit types by expressing them in the baculovirus/insect cell system. We show that the different recombinant βγ complexes interact equally well with the α subunit of transducin (α_t) but only the γ subunit specific to rod photoreceptors (γ1) is able to support interaction of α_t with rhodopsin. This indicates a direct role for the G protein γ subunits, which are a family of proteins with diverse structures, in conferring specificity to receptor-G protein interaction.