Phosphatidylinositol -4 ,5- bisphosphate [ PI ( 4,5) P2 ] is a lipid contained primarily in the inner layer of the cell membrane . Lipid controls the activity of the selected channels and membrane pumps , and modulates the activity of multiple proteins podbłonowych , including actin cytoskeletal proteins . The hydrolysis and phosphorylation of PI ( 4,5) P2 generated second-order three relays : IP3 , DAG , and PI ( 3,4,5) P3. Both PI (4,5) P2 and its derivatives are involved in signal transduction and control processes such as cell migration , exo- , endo- and phagocytosis and transport of ions. Multifunction PI ( 4,5) P2 indicates the existence of a pool of the plurality of discrete lipid in the cell membrane that result from local synthesis of PI ( 4,5) P2 and limits the lateral diffusion of PI (4,5) P2 resulting from the lipid binding podbłonowe proteins , such as MARCKS and GAP - 43 . The main source of PI ( 4,5) P2 is the reaction of phosphorylation of PI ( 4 ) P PIP5 catalyzed by type I kinase kinase Ia PIP5 - associates with the cell membrane by binding to its substrate , PI ( 4 ) P and to the product - PI ( 4,5) P2 . Several reports indicate that both the PI ( 4,5) P2 and PIP5 - kinase Ia gather in the cell membrane within the microdomains enriched in sphingolipids and cholesterol. The interaction of PI ( 4,5) P2 with effector proteins takes place by means of the interaction of lipid -rich protein sequences or basic amino acids with highly structured domains , among which a particularly high specificity for PI ( 4,5) P2 has a pleckstrin domain (PH) phospholipase Cr1 . Recombinant fusion proteins comprising this domain are used as tools in the study of the dynamics of PI ( 4,5) P2 in the cell.