Insulin receptor

The insulin receptor is a heterotetrameric transmembrane protein, composed of two alpha and two beta subunits. The alpha subunits are extracellular, while the beta subunits are intracelluar. The  cytosolic face belongs to the large family of receptor tyrosine kinases. Insulin receptors are particularly abundant in adipocytes and muscle cells. Challenge by insulin causes the cytosolic receptor tyrosine kinase to autophosphorylate. The insulin receptor substrate (IRS) molecule can then dock to it, and this in turn acts as a docking station for other proteins with SH2 domains involved in a variety of enzymatic cascades, including the PKB pathway, and the MAP kinase cascade. One of the most important cellular processes that occurs when insulin binds to its receptor is the translocation of GLUT4 vesicles to the plasma membrane, thus allowing greater glucose uptake from the blood. Both the PKB and TC10 pathways are essential for GLUT4 translocation.