A Gq protein is a heterotrimeric G protein whose alpha subunit couples activated G protein-coupled receptors to effectors including phospholipase C. GTP binding changes the alpha subunit's interactions; subsequent GTP hydrolysis helps terminate the signal. The beta and gamma subunits are components of the same signalling system, not parts of the receptor. [ref]
Molecular Biology of the Cell, 4th edition by Bruce Alberts and others. Chapter 15, Signaling through G-Protein-Linked Cell-Surface Receptors: phospholipase C and inositol phospholipids
The inhibitor YM-254890 supplies a molecular probe: structural work showed stabilization of a GDP-bound arrangement that impedes nucleotide exchange. Suppressing exchange is distinct from blocking the downstream enzyme directly, so an inhibitor response can help identify which stage of a signalling pathway is being controlled. [ref]
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