Setmelanotide anti-obesity drug, molecular mode

Molecular model of a molecule of the anti-obesity drug setmelanotide binding to a melanocortin 4 (MC4) receptor, an example of a G-protein-coupled receptor (GPCR, blue, left), and triggering a signalling cascade. MC4 receptors are found in the hypothalamus of the brain. They are crucial for appetite regulation, energy homeostasis and body-weight control. Binding of setmelanotide to MC4 causes the alpha subunit of the G-protein to exchange its bound molecule of GDP (guanosine triphosphate, yellow, centre left) for a molecule of GTP (guanosine triphosphate, orange, centre) and to be released from the GPCR. The G-alpha subunit binds to the enzyme adenylyl cyclase (blue, right), activating it. Adenylyl cyclase catalyses the conversion of ATP (adenosine triphosphate, leftmost red molecule at right) to cyclic adenosine monophosphate (cAMP, red, lower right of ATP) and pyrophosphate (red, above cAMP). cAMP regulates numerous cell functions. For a version of this image with labels see F033/3381., Photo by JUAN GAERTNER/SCIENCE PHOTO LIBRARY