The general function of Gq is to activate
intracellular signaling pathways in response to activation of cell surface
G protein-coupled receptors (GPCRs). GPCRs function as part of a three-component system of receptor-transducer-effector. The transducer in this system is a
heterotrimeric G protein, composed of three subunits: a Gα protein such as Gαq, and a complex of two tightly linked proteins called Gβ and Gγ in a
Gβγ complex. GTP-bound Gα and Gβγ are then freed to activate their respective downstream signaling enzymes. Gq/11/14/15 proteins all activate beta-type
phospholipase C (PLC-β) to signal through calcium and PKC signaling pathways. PLC-β then cleaves a specific
plasma membrane phospholipid,
phosphatidylinositol 4,5-bisphosphate (PIP2) into
diacyl glycerol (DAG) and
inositol 1,4,5-trisphosphate (IP3). DAG remains bound to the membrane, and IP3 is released as a soluble molecule into the
cytoplasm. IP3 diffuses to bind to
IP3 receptors, a specialized
calcium channel in the
endoplasmic reticulum (ER). These channels are specific to
calcium and only allow the passage of calcium from the ER into the cytoplasm. Since cells actively sequester calcium in the ER to keep cytoplasmic levels low, this release causes the cytosolic concentration of calcium to increase, causing a cascade of intracellular changes and activity through calcium binding proteins and calcium-sensitive processes. == Receptors ==