PI(3)P ELISA Kit

As a phosphoinositide, phosphatidylinositol-3-phosphate (PI(3)P) has be found to be involved in endocytic and phagocytic traffic, and needed for the autophagic system. Most PI(3)P is bound to endosomes and to the autophagosome preassembly apparatus (presumably on the endoplasmic reticulum).

PI(3)P first gets generated by phosphoinositide 3-kinases (PI3K) phosphorylating the 3' OH side of PI. There are three different classes of PI3Ks with different substrate requirements and cell functions. Class I PI3 Kinases typically phosphorylate PI(4,5)P_₂ at its 3' OH group to generate PI(3,4,5)P_₃ (commonly referred to as PIP₃), rather than directly producing PI(3)P. Class II PI3 Kinases can phosphorylate multiple substrates, including PI, PI(4)P, and PI(4,5)P_₂, but they show a strong preference for PI. Class II kinases are in more narrow, signal-dependent contexts, where they make PI(3)P under certain conditions. Class III PI3 Kinases: This is the yeast counterpart to Vps34, which uses only PI as substrate for PI(3)P, and Class III enzymes are believed to do most PI(3)P synthesis in cells. By phosphorylating or dephosphorylating PI(3)P into another molecular form (PI(4)-kinase phosphorylating PI(3)P 4' to generate PI(3,4)P₂) for use in signal transduction). PIKfyve phosphorylates the 5' end of PI(3)P into PI(3,5)P₂, which is an endosomal and other cellular product. A number of phosphatases can interact with PI(3)P and strip away the phosphate at the 3' end. These include PTEN, myotubularin proteins, the yeast phosphatase Sac1p. These enzymes help regulate the levels of PI(3)P within cells by converting it back to unphosphorylated phosphatidylinositol or other forms of phosphoinositides

Figure 1. Methods of PI(3)P synthesis and oxidation to PI, PI(3,4)P₂ and PI(3,5)P₂
(Source: Burman C, et al. 2010)

PI3P mediates membrane movement and trafficking. PI3P orchestrates processes such as endosomal fusion, sorting and endosomal trafficking to lysosomes. It is essential for autophagosome formation. The class III PI3K complex makes PI3P on autophagosome pre-membrane membranes, and these recruit proteins involved in autophagy. Proteins with FYVE or PX domains, for instance, only bind to membranes rich in PI3P. They are sorting nexins (e.g., SNX1) and other effector proteins (e.g., EEA1) involved in endosomal sorting and membrane trafficking. PI3P can also act as part of signalling cascades following receptor stimulation at the plasma membrane.

Phosphatidylinositol-3-phosphate ELISA Kit