On the lateral structure of model membranes containing cholesterol.

This article summarizes the current view of the sterol superlattice model, which provides a microscopic and molecular description of lateral structure of membranes containing cholesterol, ergosterol, or dehydroergosterol. Special attention is focused on the important, but not yet widely recognized, lessons learned from the studies of sterol superlattices. The major points are: (1) Fine details of cholesterol lateral organization depend on the materials and methods for membrane preparation and on the membrane type. (2) Cholesterol content is extremely important in determining cholesterol lateral organization, and the effect of cholesterol content on membranes should be examined using small cholesterol mole fraction increments. (3) Samples with high vesicle concentrations may need a long time to form sterol superlattices; however, long vesicle incubation in model membrane studies and the existence of sterol superlattice in cells are not mutually exclusive. (4) An increase in cholesterol content does not always condense membranes or make membranes more ordered. (5) The interfaces between regular and irregular regions could play an important role in membrane activities. The last part of this article discusses the use of the knowledge gained from model membrane studies of cholesterol superlattice to investigate membrane lateral organization in cells and to develop new liposome applications.