heterotrimeric G-protein complex Any of a family of heterotrimeric GTP-binding and hydrolyzing proteins; they belong to a superfamily of GTPases that includes monomeric proteins such as EF-Tu and RAS. Heterotrimeric G-proteins consist of three subunits; the alpha subunit contains the guanine nucleotide binding site and possesses GTPase activity; the beta and gamma subunits are tightly associated and function as a beta-gamma heterodimer; extrinsic plasma membrane proteins (cytoplasmic face) that function as a complex to transduce signals from G-protein coupled receptors to an effector protein. GO:0005834 See also the molecular function term 'G-protein coupled receptor activity ; GO:0004930'. cellular_component go.owl heterotrimeric G-protein GTPase activity heterotrimeric G-protein GTPase, alpha-subunit heterotrimeric G-protein GTPase, beta-subunit heterotrimeric G-protein GTPase, gamma-subunit pro.owl intracellular part plasma membrane protein complex GTPase complex