Structural Biochemistry/Cell Signaling Pathways/Phosphoinositol Signaling
Inositol Phosphates are a type of mono-to-polyphosphated inisitols which act as secondary messengers in signal transduction. They play roles in cell growth, apoptosis, endocytosis, etc. There are several types of Phosphoinositol with the most prominent being inositol triphosphate (IP3).
This molecule is used in conjunction with diacylglycerol (DAG) in cell signaling as a secondary messenger. However, whereas DAG stays on the lipid bilayer, inositol triphosphate is soluble in the cytoplasm with the cleaving of phosphatidylinositol 4,5-bisphosphate (PIP2) which attaches it to the lipid bilayer. Once free, inositol triphosphate activates the IP3 receptor on the endoplasmic reticulum triggering the release of calcium ions. The increase in calcium ions raises the level of calcium in the cytoplasm, activating the next protein in the signaling chain until a cellular response is achieved.