G-Protein αq (GNAQ)
Hormone receptors elicit cellular responses most often not directly, but through diffusible second messengers. In the early 1970s it was found that second messenger synthesis requires guanosine triphosphate (GTP). Yet, GTP binds neither to hormone receptors nor to enzyme effectors. Instead, GTP binds to GTP-sensitive transducers (see Gilman 1987). These G-proteins are heterotrimers of α, β, and γ subunits. The first Gα subunits to be identified were Gαs, and transducin. Gαs triggers the formation of cAMP. Transducin mediates the effects of rhodopsin. Signaling by Gαs was found sensitive to pertussis toxin. Signaling by Gαi, which inhibits cAMP formation, was found sensitive to cholera toxin. Formation of the second messengers inositol trisphosphate (IP3) and diacylglycerol (DAG) by...