Cholesterol: An Essential Lipid in Organization and Function of Eukaryotic Membranes

Cholesterol is a major and essential constituent in higher eukaryotic cellular membranes and is crucial in membrane organization, dynamics, function, and sorting (Liscum and Underwood 1995 ; Simons and Ikonen 2000 ; Mouritsen and Zuckermann 2004 ) . Cholesterol is a predominantly hydrophobic molecule comprising a near planar tetracyclic fused steroid ring and a fl exible isooctyl hydrocarbon tail (see Fig. 14.1 ). The tetracyclic nucleus and isooctyl side chain create the bulky wedge-type shape of the molecule. The polar 3 b -hydroxyl group provides cholesterol its amphiphilic character and helps it to orient and anchor in the membrane (Villalaín 1996 ) . A unique characteristic of organization of membrane cholesterol is its nonrandom distribution in domains (Mouritsen and Zuckermann 2004 ; Mukherjee and Max fi eld 2004 ; Chaudhuri and Chattopadhyay 2011 ) . Many of these domains [sometimes termed as “lipid rafts” (Lingwood and Simons 2010 ) ] are thought to be important for the maintenance of membrane structure and function, although characterizing the