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

Interaction with a receptor is the first step in the process of signal transduction by heterotrimeric (alpha beta gamma) G proteins. We have examined the role of the G protein gamma subunit in interaction between a receptor (rhodopsin) and a G protein, transducin (Gt). We have obtained recombinant beta gamma complexes containing the same beta subunit but three different gamma subunit types by expressing them in the baculovirus/insect cell system. We show that the different recombinant beta gamma complexes interact equally well with the alpha subunit of transducin (alpha t) but only the gamma subunit specific to rod photoreceptors (gamma 1) is able to support interaction of alpha t with rhodopsin. This indicates a direct role for the G protein gamma subunits, which are a family of proteins with diverse structures, in conferring specificity to receptor-G protein interaction.