glycolipid

glycolipid [¦glī·kō¦lip·əd]

(biochemistry)

Any of a class of complex lipids which contain carbohydrate residues.

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Glycolipid

One of a class of compounds having solubility properties of a lipid and containing one or more molecules of a covalently attached sugar.

Glycosphingolipids, the most abundant and structurally diverse type of glycolipids in animals, are glycosides of ceramide, a fatty acid amide of the amino alcohol sphingosine. Galactosyl ceramide is enriched in brain tissue and is a major component of the myelin sheaths around nerves. Glucosyl ceramide is present in the cell membranes of many cell types and is abundant in serum.

Larger, neutral glycosphingolipids containing more than one sugar include lactosyl ceramide, abundant in leukocyte membranes; globosides; and other oligosaccharyl ceramides, some of which are important antigens defining blood groups. Gangliosides are oligosaccharyl ceramides, abundant in brain, spleen, erythrocytes, liver, and kidney, that contain glucose, galactose, N-acetylglucosamine, and sialic acids.

Glycosphingolipids carry blood group antigens and define tumor-specific or developmental antigens. In addition, they serve as receptors for many microorganisms and toxins, as modulators of cell surface receptors that mediate cell growth, and as mediators of cell adhesion. See Antigen, Cellular adhesion

Glycosyl phosphatidylinositols are a class of glycolipids that serve as membrane anchors for a multitude of proteins in organisms ranging from yeast to protozoa to humans. Glycosyl phosphatidylinositol–core structures can have many different modifications, depending upon the protein and cell type. Lipophosphoglycans are glycosyl phosphatidylinositols attached to large polysaccharide structures that coat the surfaces of many parasitic protozoa, such as Leishmania donovani, the causative agent of visceral leishmaniasis (kala azar). Lipophosphoglycans appear to protect these organisms from host defenses.

Mannosylphosphoryl dolichol, glucosylphophoryl dolichol, and oligosaccharyl phosphoryl dolichols are glycolipids with sugars attached to large polyisoprenoids by phosphate esters. Dolichols are structurally related to cholesterol. Saccharylphosphoryl dolichols serve as important biosynthetic intermediates in the assembly of both asparagine-linked glycoproteins and glycosyl phosphatidylinositols. See Glycoprotein

Glycosyl glycerides are glycolipids that have a structure analogous to phospholipids. They are the major glycolipids of plants and microorganisms but are rare in animals.

Bacteria produce a wide variety of glycolipids not easily categorized. Examples include fatty acid esters of carbohydrates, such as cord factor. Cord factor is a toxic component of the waxy capsular material of virulent strains of Mycobacterium tuberculosis, the causative agent of tuberculosis. Mycosides, glycolipids that are also found in tubercle bacilli, comprise long-chain, highly branched, hydroxylated hydrocarbon terminated by a phenol group, with the sugar glycosidically attached to the phenolic hydroxyl. See Lipid, Sphingolipid, Tuberculosis