GTP‐dependent binding of Gi, Go and Gs to the γ‐subunit of the effector of Gt

Abstract
The γ‐subunit of the cGMP‐phosphodiesterase (PDEγ) of retinal rods forms a tight complex with the activated α‐subunit of transducin (GtαGTPγS). We observe that while PDEγ is not the physiological effector of other Gα subtypes, it can still detectably interact with them. This interaction is strong with Gilα and Gi3α (K d ≈ 10 nM) and weaker with Goα and Ggα (K d ≈ 1 μM). For all these Gα subtypes, similar intrinsic fluorescence changes are observed upon PDEγ binding. Moreover, similar relative decreases in affinity are obtained when the GDP forms of Gilα, Gi3α or Gtα are used in lieu of the GTP forms. This points to a conserved GTP‐dependent effector‐interaction domain.