Aspects on Structure and Function of Sphingolipids in Cell Surface Membranes

Abstract

Sphingolipids are components of cell surface membranes and are probably exclusively located in the outer half of the lipid bilayer. It is shown by calculation that sphingolipid is a major part of the surface monolayer, in addition to protein, cholesterol and phosphatidylcholine. The lipophilic part, ceramide, has, beside a hydro-carbon chain variation as found for other membrane lipids, characteristic structural features (amide, hydroxyls) with a natural variation (number of hydroxyls), which are suggestive of lateral polar interactions with other surface layer components. This inter-mediate zone of the bilayer (between the hydrophobic part and the polar head groups) is proposed to be of importance for some of the matrix properties of surface membranes. It has, however, attracted almost no attention so far in model studies. Three surface membrane functions have been found associated with sphingolipid polar head groups composed of carbohydrate: Na+ transport (sulphatide), cholera toxin binding (a ganglioside), and recognition (surface antigens). A molecular model of Na+-K+ translocation is formulated, where sulphatide is postulated to be essential for K+ influx (cofactor site model).