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 also 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 also 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 also Lipid; Sphingolipid; Tuberculosis.

Fats found in the brain and nervous system which contain a carbohydrate constituent.

A lipid containing carbohydrate groups, often galactose but also glucose, inositol or others; the glycolipids include the cerebrosides.

Chemical structure of glycolipids

Glycolipids are carbohydrate-attached lipids. Their role is to provide energy and also serve as markers for cellular recognition.

They occur where a carbohydrate chain is associated with phospholipids on the exoplasmic surface of the cell membrane. The carbohydrates are found on the outer surface of all eukaryotic cell membranes. The carbohydrate structure of the glycolipid is controlled by the glycosyltransferases that add the lipids and glycosylhydrolases that modify the glycan after addition.

They extend from the phospholipid bilayer into the aqueous environment outside the cell where it acts as a recognition site for specific chemicals as well as helping to maintain the stability of the membrane and attaching cells to one another to form tissues.

Contents 1 Types of glycolipids 2 See also 3 References 4 External links

Types of glycolipids

The following is an incomplete listing of glycolipid types.

This list is incomplete; you can help by expanding it.

• Glyceroglycolipids
  • Galactolipids
  • Sulfolipids (SQDG)
• Glycosphingolipids
  • Cerebrosides
    • Galactocerebrosides
    • Glucocerebrosides
      • Glucobicaranateoets
  • Gangliosides (the most complex animal glycolipids; contain negatively charged oligosacchrides with one or more sialic acid residues; more than 200 ^[1] different gangliosides have been identified; they are most abundant in nerve cells)
  • Globosides
  • Sulfatides
  • Glycophosphosphingolipids (complex glycophospholipids from fungi, including yeasts, and in plants, where they were originally called "phytoglycolipids" by Herbert Carter, et al., may comprise as complicated a set of compounds as the negatively charged gangliosides in animals. The head group of a glycolipid is composed of sugars.

See also

• Glycocalyx
• Glycoproteins
• Niemann Pick disease Type C

References

1. ^ Role of ganglioside metabolism in the pathogenesis of Alzheimer's disease - a review-JOURNAL OF LIPID RESEARCH Volume: 49 Issue: 6 Pages: 1157-1175 Published: JUN 2008

External links

• MeSH Glycolipids

v • d • e Glycoconjugates, lipids and glycolipids: sphingolipids and glycosphingolipids, and metabolic intermediates Ceramide Cerebroside (Galactocerebroside, Glucocerebroside) · Lactosylceramide Ganglioside pathway From ganglioside GM1 · GM2 · GD2 From globoside Globotriaosylceramide From sphingomyelin Glucocerebroside From sulfatide Galactocerebroside To sphingosine Ceramide see also enzymes, disorders

v • d • e Metabolism: lipid metabolism · glycolipid enzymes Sphingolipid To glycosphingolipid Glycosyltransferase · Sulfotransferase To ceramide From ganglioside: Beta-galactosidase · Hexosaminidase A · Neuraminidase · Beta-galactosidase · Glucocerebrosidase From globoside: Hexosaminidase B · Alpha-galactosidase · Beta-galactosidase · Glucocerebrosidase From sphingomyelin: Sphingomyelin phosphodiesterase 1 From sulfatide: Arylsulfatase A · Galactosylceramidase To sphingosine Ceramidase (ACER1, ACER2, ACER3, ASAH1, ASAH2, ASAH2B, ASAH2C) NCL Palmitoyl thioesterase · Tripeptidyl peptidase I · CLN3 · CLN5 · CLN6 · CLN8 Ceramide synthesis Serine C-palmitoyltransferase (SPTLC1) · Ceramide glucosyltransferase (UGCG) see also lipid storage disorders, intermediates

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