Phosphatidylinositol 5-phosphate

Phosphatidylinositol 5-phosphate (PtdIns5P or PI5P) is one of the seven phosphoinositides, and is the last to have been discovered to be naturally occurring.

In 1997 Lucia Rameh, while working as a postdoctoral fellow with Lewis C. Cantley observed that the enzymes referred to as type II PIP-kinases did not utilize PtdIns4P as a substrate (as had been proposed). In fact, they required PtdIns5P as a substrate to produce PtdIns(4,5)P2. The observation immediately suggested that cells must contain a natural pool of PtdIns(5)P, a prediction that was verified by Rameh, Cantley, and colleagues.

The function of PtdIns5P remains uncertain, especially since no specific PtdIns5P-binding proteins have been unambiguously identified. There is some thought that it may function in membrane trafficking from late endosomes to the plasma membrane.