Glycolipids are also a constituent of membranes. In this figure, they are shown as blue sugar groups projecting into the extracellular space. They may microaggregate in the membrane. These components of the membrane may be protective, insulators, and sites of receptor binding. Among the molecules bound by glycososphingolipids include cell poisons such as cholera and tetanus toxins. The lower figure shows the chemical structure of two examples of glycososphingolipids.
Top Figure modified from Alberts et al. Molecular Biology of the Cell, Garland Publishing, N.Y., 1994, Third Edition, Figure 10-11.
Formation of "Microdomains"
Sphingolipids and cholesterol work together to help cluster proteins in a region called a "microdomain". They function as "rafts" or platforms for the attachment of proteins as membranes are moved around the cell and also during signal transduction.
For more information about the rafts and "microdomains" see: Simons and Ikonen, Nature 387: 569, 1997. Also, R.E. Brown, J. Cell Science 111: 1-9, 1998