New dimensions in G protein signalling: Gβ5 and the RGS proteins

The βγ complex of G-proteins regulates effectors independently of the Gα subunits, such that upon activation G proteins give may signal downstream along one or both pathways. The Gβ₅ isoform exhibits much less homology with other Gβ isoforms (∼50%) and is preferentially expressed in brain. The Gβ₅ isoform exhibits novel properties in its activation of effector pathways such as MAPK, phospholipase C-β, and adenylyl cyclase type II when compared to Gβ₁. Recently specific native complexes between Gβ5 and the regulator of G protein signaling (RGS) protein-7 (RGS7) and between Gβ₅L (a splice variant with a 42 amino acid N-terminal extension) and RGS9 have been isolated from different retinal fractions. Such findings are not accounted for by current models as only the Gα subunits and not Gβ had been previously implicated in RGS protein function. These recent novel observations further reinforce the view of Gβ₅ as a unique and highly specialized G protein subunit.