Figure 1.

Seven distinct phosphoinositide molecules in the cell. The parent phosphoinositide (PI) contains a myo-inositol head group, and a glycerol backbone, and two fatty acids (FA1 and FA2) are attached to the C1 and C2 position of the glycerol (A). The free hydroxyl group, 3, 4, 5 on the inositol ring undergoes phosphorylation by PI kinases (green). Dephosphorylation by PI phosphatases (red) generates seven distinct phosphoinositide second messenger molecules (black) in the cell (B). PI, phosphatidylinositol; PI(3)P, phosphatidylinositol 3-phosphate; PI(4)P, phosphatidylinositol 4-phosphate; PI(5)P, phosphatidylinositol 5-phosphate; PI(3,4)P₂, phosphatidylinositol 3,4-bisphosphate; PI(4,5)P₂, phosphatidylinositol 4,5-bisphosphate; PI(3,5)P₂, phosphatidylinositol 3,5-bisphosphate; PI(3,4,5)P₃, phosphatidylinositol 3,4,5-trisphosphate; PI3K, phosphoinositide 3-kinase; PI4K, phosphoinositide 4-kinase; PI4P5K, phosphatidylinositol 4-phosphate 5-kinase; PI5P4K, phosphatidylinositol 5-phosphate 4-kinase; PTEN, phosphatase and tensin homolog; SHIP, Src homology 2 (SH2) domain-containing inositol polyphosphate 5-phosphatase; PIKfyve, phosphatidylinositol-3-phosphate 5-kinase type III or PIPKIII or FYVE phosphoinositide kinase.