Molecular model of GABA-B receptor (centre, darker blue and purple), an example of a G-coupled protein receptor (GPCR), binding to the agonist baclofen (red). The binding of the drug baclofen to the GABA-B receptor causes the alpha subunit of the G-protein (bottom, light blue) to exchange its bound molecule of GDP (not seen, guanosine diphosphate) for a molecule of GTP (guanosine triphosphate). This releases the alpha subunit from the GABA-B receptor, allowing it to bind to the enzyme adenylyl cyclase and activate it. Adenylyl cyclase catalyses the conversion of ATP (adenosine triphosphate) to cyclic adenosine monophosphate (cAMP). cAMP regulates numerous cell functions.
