The small G-protein ARF1 GDP binds to the G tβγ subunit of transducin, but not to G tαGDP-G tβγ

Abstract

AlF 4 − activates heterotrimeric G-proteins Gα subunits but not small GDP/GTP-binding proteins like ARF1. On retinal membranes containing holotransducin (G t α GDP-G t βγ and incubated with ARF GDP, AlF 4 − induced G t α GDP-AlF4 release and ARF GDP binding, probably to the remaining membrane-attached G t βγ. On phospholipid vesicles reconstitued with G t βγ, ARF GDP bound in proportion to G t βγ, and was released upon subsequent G tα GDP addition. Thus ARF GDP competes with G tα GDP for binding to G tβγ, probably through a conserved motif in the ‘α2 helix’ of G tα and ARF. This motif is found in the C-terminal helix of PH domains that bind to Gβγ.