How does the phosphatidylinositol second-messenger system work?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

A composite diagram shows the structural formulas, space-filling models, and simplified depictions of lipid molecules including stearic acid and phosphatidylcholine, and how these assemble into a micelle and lipid bilayer, with labels identifying hydrophilic heads and hydrophobic tails. — Lipid Structure and properties of two representative lipids. Both stearic acid (a fatty acid) and phosphatidylcholine (a phospholipid) are composed of chemical groups that form polar “heads” and nonpolar “tails.” The polar heads are hydrophilic, or soluble in water, whereas the nonpolar tails are hydrophobic, or insoluble in water. Lipid molecules of this composition spontaneously form aggregate structures such as micelles and lipid bilayers, with their hydrophilic ends oriented toward the watery medium and their hydrophobic ends shielded from the water.

The phosphatidylinositol system is a critical intracellular signaling pathway that utilizes two lipid-derived second messengers to transmit signals from the cell surface to internal biochemical systems.1

The process functions as follows:

Activation: An extracellular signal interacts with a cell membrane receptor, which activates the enzyme phospholipase C.1
Hydrolysis: Phospholipase C hydrolyzes a minor membrane phospholipid called phosphatidylinositol bisphosphate.1
Messenger Production: This reaction produces two distinct messengers:
- Diacylglycerol (diglyceride): Remaining within the membrane, it activates protein kinase C, which phosphorylates soluble proteins to trigger a physiological response.1
- Triphosphoinositol: This molecule is released and triggers the release of calcium from intracellular stores.1
Synergy: Calcium is required alongside diacylglycerol to fully activate protein kinase C, ensuring the signal is properly propagated.1

This system regulates diverse physiological processes, including muscle contraction, hormone release, and DNA synthesis.1