Heterotrimeric G protein

Generally, the alpha subunit binds membrane-bound effector proteins for the downstream signaling cascade, but the beta-gamma complex can carry out this function also.

[2] Reconstitution experiments carried out in the early 1980s showed that purified Gα subunits can directly activate effector enzymes.

For example, in adipose tissues, two different G-proteins with interchangeable beta-gamma complexes are used to activate or inhibit adenylyl cyclase.

This nomenclature is based on their sequence homologies:[6] The β and γ subunits are closely bound to one another and are referred to as the G beta-gamma complex.

The free Gβγ complex can act as a signaling molecule itself, by activating other second messengers or by gating ion channels directly.

Gβγ complexes bound to muscarinic acetylcholine receptors, on the other hand, directly open G protein-coupled inward rectifying potassium channels (GIRKs).

This heterotrimeric G protein is illustrated with its theoretical lipid anchors. GDP is black. Alpha chain is yellow. Beta and gamma chains are blue.
3D structure of a heterotrimeric G protein
G-protein's role in a G-protein coupled receptor activated pathway