Phosphatidylinositol - Phosphoinositides

Phosphoinositides

Phosphorylated forms of phosphatidylinositol (PI)are called phosphoinositides and play important roles in lipid signaling, cell signaling and membrane trafficking. The inositol ring can be phosphorylated by a variety of kinases on the three, four and five hydroxyl groups in seven different combinations. However, the two and six hydroxyl group is typically not phosphorylated due to steric hindrance.

All seven variations of the following phosphoinositides have been found in animals:

Phosphatidylinositol monophosphates:

• Phosphatidylinositol 3-phosphate, also known as PtdIns3P or PI(3)P
• Phosphatidylinositol 4-phosphate, also known as PtdIns4P or PI(4)P
• Phosphatidylinositol 5-phosphate, also known as PtdIns5P or PI(5)P

Phosphatidylinositol bisphophosphates:

• Phosphatidylinositol 3,4-bisphosphate, also known as PtdIns(3,4)P or PI(3,4)P₂
• Phosphatidylinositol 3,5-bisphosphate, also known as PtdIns(3,5)P or PI(3,5)P₂
• Phosphatidylinositol 4,5-bisphosphate, also known as PtdIns(4,5)P, PI(4,5)P₂ or often simply referred to as PIP₂

Phosphatidylinositol trisphophosphate:

• Phosphatidylinositol 3,4,5-trisphosphate, also known as PtdIns(3,4,5)P or PI(3,4,5)P₃

These phosphoinositides are also found in plant cells, with the exception of PIP₃.