Sphingolipid

Structure

The sphingosine backbone is O-linked to a (usually) charged head group such as choline.

The backbone is also amide-linked to an fatty acid.

Types

There are three main types of sphingolipids:

• amide linkage to sphingosine.
• sphingomyelins. Sphingomyelins have a phosphorylcholine or phosphoroethanolamine molecule esterified to the 1-hydroxy group of a ceramide.
• glycosphingolipids, which differ in the substituents on their head group (see image). Glycosphingolipids are ceramides with one or more sugar residues joined in a β-glycosidic linkage at the 1-hydroxyl position. Glycosphingolipids may be further subdivided into cerebrosides and gangliosides.
  • Cerebrosides have a single galactose at the 1-hydroxy position.
  • Gangliosides have at least three sugars, one of which must be sialic acid.

Function and transport

Sphingolipids are commonly believed to protect the cell surface against harmful environmental factors by forming a mechanically stable and chemically resistant outer leaflet of the plasma membrane proteins.

Recently, relatively simple sphingolipid lipid rafts" were originally proposed to sort membrane proteins along the cellular pathways of membrane transport. At present, most research focuses on the organizing function during signal transduction.^[3]

Sphingolipids are synthesized in the ER and Golgi apparatus, but are enriched in the plasma membrane and in endosomes, where they perform many of their functions, thus travelling and evolving between organelles. Transport occurs via vesicles and monomeric transport in the cytosol. Sphingolipids are virtually absent from mitochondria and the ER, but constitute a 20-35 molar fraction of plasma membrane lipids.^[4]

Disorders

There are several disorders of sphingolipid metabolism, known as sphingolipidoses. The most common is Gaucher's disease.

Additional images

References

1. ^ Hannun, Y. A., and Obeid, L. M. (2002) J. Biol. Chem. 277, 25847-25850 (full text online)
2. ^ Spiegel, S., and Milstien, S. (2002) J. Biol. Chem. 277, 25851-25854 (full text online)
3. ^ Brown, D. A., and London, E. (2000) J. Biol. Chem. 275, 17221-17224 (full text online)
4. ^ van Meer, G., and Lisman, Q. (2002) J. Biol. Chem. 277, 25855-25858 (full text online)

Sources

• Grisham & Garret (2005). Biochemistry (3rd ed.). Thomson Brooks/Cole.