30 Apr 2004 18:28 AR AR214-BB33-13.tex AR214-BB33-13.sgm LaTeX2e(2002/01/18) P1: FHD 10.1146/annurev.biophys.32.110601.141803 Annu. Rev. Biophys. Biomol. Struct. 2004. 33:269–95 doi: 10.1146/annurev.biophys.32.110601.141803 Copyright c 2004 by Annual Reviews. All rights reserved First published online as a Review in Advance on February 2, 2004 MODEL SYSTEMS,LIPID RAFTS, AND CELL MEMBRANES1 Kai Simons Max-Planck-Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany; email:
[email protected] Winchil L.C. Vaz Departamento de Qu´ımica, Universidade de Coimbra, 3004-535 Coimbra, Portugal; email:
[email protected] Key Words sphingolipids, cholesterol, phase immiscibility, detergent resistance, membrane proteins ■ Abstract Views of how cell membranes are organized are presently changing. The lipid bilayer that constitutes these membranes is no longer understood to be a homogeneous fluid. Instead, lipid assemblies, termed rafts, have been introduced to provide fluid platforms that segregate membrane components and dynamically com- partmentalize membranes. These assemblies are thought to be composed mainly of sphingolipids and cholesterol in the outer leaflet, somehow connected to domains of unknown composition in the inner leaflet. Specific classes of proteins are associated with the rafts. This review critically analyzes what is known of phase behavior and liquid-liquid immiscibility in model systems and compares these data with what is known of domain formation in cell membranes. CONTENTS INTRODUCTION .....................................................270