Fosfatidilinositol

Phosphatidylinositol (PI), known in Portuguese as fosfatidilinositol, is a glycerophospholipid that resides in the inner leaflet of eukaryotic cell membranes. It comprises a glycerol backbone with two fatty acids and a phosphatidylinositol headgroup derived from inositol. The inositol ring can be phosphorylated at various positions to yield phosphoinositides, including PI4P, PI(4,5)P2, and PI(3,4,5)P3, which act as key signaling lipids.

Biosynthesis and metabolism occur primarily in the endoplasmic reticulum and Golgi. PI is formed when CDP-diacylglycerol condenses with myo-inositol via phosphatidylinositol synthase. PI can then be phosphorylated by specific kinases to produce phosphoinositides such as PI4P and PI(4,5)P2, which can be further modified to PI(3,4,5)P3. Phosphatases and phospholipases regulate turnover, generating inositol phosphates and diacylglycerol as needed.

Functions include contributions to membrane structure and the formation of membrane identity, as well as serving as reservoirs for signaling lipids. PI(4,5)P2 is a substrate for phospholipase C, which cleaves it to generate IP3 and DAG, thereby coupling membrane signals to calcium signaling and PKC activation. Phosphoinositides recruit effector proteins with specific lipid-binding domains, coordinating processes such as actin dynamics, vesicular trafficking, and membrane trafficking.

Clinical and research relevance: dysregulation of phosphoinositide signaling is implicated in cancer, metabolic disorders, and neurodegenerative diseases. Phosphoinositides are widely used as markers of membrane identity in cell biology studies.