G-protein linked receptor

G-protein linked receptors, also known as G-protein Coupled receptors (GPCR), are a family of receptor signal transducers which are involved in signalling pathways within cells .They can be further divided into to monomeric and trimeric regarding how many components make up the G-protein in question. Subtypes, each with an endogenous agonist, are involved in maintaining physiological systems such as rhodopsin in rod cells required for vision . 

Structure

The structure of these proteins comprises of seven transmembrane helices with an extracellular ligand binding domain and an intracellular G-protein binding domain .

Trimeric G-proteins

Ligand will bind to extracellular ligand-binding domain of G-protein coupled receptor. After binding of ligand, receptor undergoes conformational change and activate G-protein. α-subunit undergoes conformation change and causes GDP to dissociate from α-subunit. α-subunit binds GTP and causes further conformational change of G-protein. α subunit and βγ subunits are activated and dissociate. G-protein transduces signals by binding to target protein (eg. adenylyl cyclase, phospholipase C). Activated target proteins relay signal to the other components in signalling cascade. α subunit hydrolyses GTP to GDP and inactivate α subunit. Inactivated α subunit reassembles with βγ subunits to reform an inactivate G protein.