Globosides (also known as globo-series glycosphingolipids) are a sub-class of the lipid class

glycosphingolipid Glycosphingolipids are a subtype of glycolipids containing the amino alcohol sphingosine. They may be considered as sphingolipids with an attached carbohydrate. Glycosphingolipids are a group of lipids (more specifically, sphingolipids) and are ...

with three to nine

sugar Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecul ...

molecules as the side chain (or R group) of

ceramide Ceramides are a family of waxy lipid molecules. A ceramide is composed of sphingosine and a fatty acid joined by an amide bond. Ceramides are found in high concentrations within the cell membrane of Eukaryote, eukaryotic cells, since they are co ...

. The sugars are usually a combination of ''N''-acetylgalactosamine, D-glucose or D-galactose. One characteristic of globosides is that the "core" sugars consists of Glucose-Galactose-Galactose (Ceramide-βGlc4-1βGal4-1αGal), like in the case of the most basic globoside, globotriaosylceramide (Gb3), also known as pk-antigen. Another important characteristic of globosides is that they are neutral at pH 7, because they usually do not contain

neuraminic acid Neuraminic acid (5-amino-3,5-dideoxy-D-''glycero''-D-''galacto''-non-2-ulosonic acid) is an Sugar acid, acidic (in particular Sugar acid#ulosonic acid, ulosonic) amino sugar, amino sugar with a backbone formed by nine carbon atoms. Although 9 ...

, a sugar with an acidic carboxy-group. However, some globosides with the core structure Cer-Glc-Gal-Gal do contain neuraminic acid, e.g. the globo-series glycosphingolipid "SSEA-4-antigen". The side chain can be cleaved by galactosidases and

glucosidases Glucosidases are the glycoside hydrolase enzymes categorized under the EC number 3.2.1. Function Alpha-glucosidases are enzymes involved in breaking down complex carbohydrates such as starch and glycogen into their monomers. They catalyze the ...

. The deficiency of α-galactosidase A causes

Fabry's disease Fabry disease, also known as Anderson–Fabry disease, is a rare genetic disease that can affect many parts of the body, including the kidneys, heart, brain, and skin. Fabry disease is one of a group of conditions known as lysosomal storage dis ...

, an inherited metabolic disease characterized by the accumulation of the globoside globotriaosylceramide.

Globoside-4 (Gb4)

Globoside 4 (Gb4) has been known as the receptor for

parvovirus B19 Parvovirus B19, also called B19 virus (B19V), Human parvovirus B19, or sometimes erythrovirus B19, is a human virus in the family ''Parvoviridae'', genus ''Erythroparvovirus''. It measures only 23–26 nm in diameter. The virus is assigned ...

, due to observations that B19V binds to the thin-layered

chromatogram In chemical analysis, chromatography is a laboratory technique for the Separation process, separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it ...

of the

structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...

. However, the binding on its surface does not match well with the

virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...

, which raised debates on whether or not GB4 is the cause for productive infection. Additional research using the technique Knockout Cell Line has shown that although GB4 does not have the direct entry

receptor Receptor may refer to: * Sensory receptor, in physiology, any neurite structure that, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and respond ...

for B19V, it plays a post-entry role in productive infection. Globoside 4 (Gb4) are a type of SSEA, stage-specific embryonic antigen, that is present in cellular development and tumorous tissues without the mechanism of Gb4 being completely known. However a study has shown Gb4 directly activates the epidermal growth factor receptor through a ERK signaling. When the globo-series glycosphingolipid (GSL) was reduced in the experiment the ERK signaling from the receptor tyrosine kinase was also inhibited. The ERK was reactivated with the addition of the Gb4 and henceforth heightened proliferation of tumorous cells and opened up the possibility of testing Gb4 for further studies on potential drugs that can target cancerous cells.

Globoside-5 (Gb5)

Globoside-5 is also known as

stage-specific embryonic antigen 3 Stage-specific embryonic antigen 3 (SSEA-3) is a glycosphingolipid, specifically, an oligosaccharide composed of five carbohydrate units connected to a sphingolipid, also known as globoside-5 (Gb5). Sphingolipids were originally discovered in 1884 ...

References

External links

* * {{transfusion medicine Glycolipids Blood antigen systems Transfusion medicine