A novel kind of G protein heterodimer: the G beta5-RGS complex

The fifth member of the G protein beta the subunit family, G beta5, has been shown to bind exclusively to a subfamily of regulators of G protein signaling (RGS) including RGS6, RGS7, RGS9, and RGS11. This interaction occurs through a G protein gamma-like (GGL) domain present in members of this RGS subfamily and is the only reported instance in which a G beta subunit is not bound to a G gamma subunit. The G beta5-RGS interaction has been demonstrated both in vitro and in vivo and has been shown to stabilize the dimer against proteolytic degradation. GTPase activating protein (GAP) assays suggest that G beta5-RGS7 acts specifically on G alphao, however in cell-based assays it also inhibited G alphai- and G alphaq-mediated signaling. The role of the dimer in signaling and the function of G beta5 moiety within the complex are poorly understood. This review summarizes the information about the assembly and function of G beta5-RGS dimers, as well as their posttranslational modifications and localization.