G protein-coupled receptor



G protein-coupled receptor ( 2 receptors, which bind inflammatory substances called prostaglandins; and rhodopsin, which contains a photoreactive chemical called retinal that responds to light signals received by rod cells in the eye. The existence of GPCRs was demonstrated in the G protein-coupled receptor ( GPCR ), also called seven-transmembrane receptor or heptahelical receptor, protein located in the cell membrane that binds extracellular substances and transmits signals from these substances to an intracellular molecule called a G protein ( guanine nucleotide-binding protein ). GPCRs are found in the cell membranes of a wide range of organisms, including mammals, plants, microorganisms, and invertebrates. There are numerous different types of GPCRs —some 1,000 types are encoded by the human genome alone—and as a group they respond to a diverse range of substances, including light, hormones, amines, neurotransmitters , and lipids. Some examples of GPCRs include beta-adrenergic receptors, which bind epinephrine; prostaglandin Ereceptors, which bind inflammatory substances called prostaglandins; and rhodopsin, which contains a photoreactive chemical called retinal that responds to light signals received by rod cells in the eye. The existence of GPCRs was demonstrated in the 1970 s by American physician and molecular biologist Robert J. Lefkowitz. Lefkowitz shared the 2012 Nobel Prize for Chemistry with his colleague Brian K. Kobilka, who helped to elucidate GPCR structure and function.

A GPCR is made up of a long protein that has three basic regions: an extracellular portion (the N-terminus), an intracellular portion (the C-terminus), and a middle segment containing seven transmembrane domains. Beginning at the N-terminus, this long protein winds up and down through the cell membrane, with the long middle segment traversing the membrane seven times in a serpentine pattern. The last of the seven domains is connected to the C-terminus. When a GPCR binds a ligand (a molecule that possesses an affinity for the receptor), the ligand triggers a conformational change in the seven-transmembrane region of the receptor. This activates the C-terminus, which then recruits a substance that in turn activates the G protein associated with the GPCR. Activation of the G protein initiates a series of intracellular reactions that end ultimately in the generation of some effect, such as increased heart rate in response to epinephrine or changes in vision in response to dim light ( see second messenger ).