G Protein Coupled Receptors (GPCRs) - Structure, Mechanism of Action скачать в хорошем качестве

G Protein Coupled Receptors (GPCRs) - Structure, Mechanism of Action

A G protein coupled receptor is a cell surface transmembrane receptor. G protein coupled receptors are also called seven transmembrane receptors because they pass through the cell membrane seven times. Some parts of the receptor that protrude into the cell cytoplasm are coupled to G proteins that include three parts the alpha, beta , and gamma subunits. When there is no ligand attached to G protein coupled receptors, G protein coupled receptor waits at the plasma membrane in an inactive state. In the inactive state, the alpha subunit of the G protein is bound to GDP. The G protein coupled receptor is activated by an external signal in the form of a ligand or other signal mediator. This creates a conformational change in the receptor, causing activation of a G protein. Ligand binding changes the picture: the G protein coupled receptor is activated and causes the alpha subunit of G protein to exchange GDP for GTP. Now active G protein separates into two pieces one called the alpha subunit, the other consisting of the beta and gamma subunits.And they are also freed from the G protein coupled receptor. The subunits can interact with other proteins, triggering a signaling pathway that leads to a response. When the ligand is removed , the alpha subunit will hydrolyze GTP back to GDP, at which point the G protein becomes inactive. The inactive G protein reassembles as a three piece unit associated with a G protein coupled receptor. Cell signaling using G protein coupled receptors is a cycle, one that can repeat over and over in response to ligand binding.