Cholesterol interactions with phospholipids in membranes

Mammalian cell membranes are composed of a complex array of glycerophosphol ipids and sphingolipids that vary in head-group and acyl-chain composition. In a given cell type, membrane phospholipids may amount to more than a tho usand molecular species. The complexity of phospholipid and sphingolipid st ructures is most likely a consequence of their diverse roles in membrane dy namics, protein regulation, signal transduction and secretion. This review is mainly focused on two of the major classes of membrane phospholipids in eukaryotic organisms, sphingomyelins and phosphatidylcholines. These phosph olipid classes constitute more than 50% of membra-ne phospholipids. Cholest erol is most likely to associate with these lipids in the membranes of the cells. We discuss the synthesis and distribution in the cell of these lipid s, how they are believed to interact with each other, and what cellular con sequences such interactions may have. We also include a discussion about fi ndings in the recent literature regarding cholesterol/phospholipid interact ions in model membrane systems. Finally, we look at the recent trends in co mputer and molecular dynamics simulations regarding phospholipid and choles terol/phospholipid behavior in bilayer membranes. (C) 2001 Elsevier Science Ltd. All rights reserved.