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Phosphatidylinositol (3,4)-bisphosphate (PtdIns(3,4)P2) is a minor phospholipid component of cell membranes, yet an important second messenger. The generation of PtdIns(3,4)P2 at the plasma membrane activates a number of important cell signaling pathways.
PtdIns(3,4)P2 is dephophosphorylated by the phosphatase INPP4B on the 4 position of the inositol ring and by the TPTE (transmembrane phosphatases with tensin homology) family of phosphatases on the 3 position of the inositol ring.
The PH domain in a number of proteins binds to PtdIns(3,4)P2 including the PH domain in PKB. The generation of PtdIns(3,4)P2 at the plasma membrane upon the activation of class I PI 3-kinases and SHIP phosphatases causes these proteins to translocate to the plasma membrane, thereby affecting their activity.