Glycomics

See Also

• Aglycone
• Carbohydrates as Biological Markers
• Glycans
• Glycoconjugates
• Glycone
• Glycoside

Description

A glycocalyx is a network of polysaccharides that project from cellular surfaces, e.g. those of bacteria. It allows the bacterium to attach itself to inert surfaces (like teeth or rocks), prokaryotes (e.g. streptococcus pneumoniae attaches itself to lung cells), or other bacteria (their glycocalyxes can fuse to envelop the colony).

Its presence on inert materials (such as metal hardware implanted for fracture fixation or total joint replacement) make it difficult to eradicate deep infections as the bacteria will 'cling' on to the material via the glycocalyx. It is therefore often necessary to completely remove the hardware device in order to fully eradicate a wound infection.

The glycocalyx can be found just outside the cell wall of a bacterium. When its components are organized, it is called a capsule and when it is not organized, it can be called a slime layer. The bacteria can use this glycocalyx to its advantage by using it to aid in the protection from phagocytosis. It also helps in the formation of biofilms such as a coating on inert surfaces such as your teeth or rocks.

Discussion

The glycocalyx is chemically unique in everyone but identical twins, and acts like an identification tag that enables the body to distinguish its own healthy cells from transplanted tissues, invading organisms and diseased cells. Human blood types and transfusion compatibility are determined by glycoproteins.

The glycocalyx, the "sugar-rich" covering that coats plasma membranes, may be an extraneous coat and/or an integral part of the plasma membrane.(1) It is considered to form a hydrophilic polyanionic gel coat on the enterocyte surface and is thought to maintain cell surface charge, protect against physical trauma, regulate ionic and macromolecular access, and form a cationic store. (2)

Thus absence of the glycocalyx would have profound consequences on normal cell function and may result in an inability to maintain cellular homeostasis. This could explain why the vast majority of cases of microvillus atrophy do not exhibit hydramnios,1 as the amniotic fluid, which is swallowed by the fetus and bathes the luminal surface of the gut, is comparable in osmolality to serum,(3,4) resulting in no osmotic pressure across the gut in utero. This changes dramatically following birth and could explain the rapid onset of symptoms.

In the intestine, there are many glycosylated proteins associated with the apical epithelial membrane and it is uncertain which ones provide the physical characteristics of the glycocalyx listed above, or whether a particular component is responsible. Components include brush border enzymes, mucins, and a filamentous matrix (termed the filamentous brush border glycocalyx (FBBG)), the major component of which is an approximately 400 kDa molecular weight transmembrane mucin-type glycoprotein (5) containing O-acetylated sialic acid. (6) The 400 kDa FBBG in the rabbit has the same morphological appearance as the fine filamentous material on the microvilli of humans and various other species, including bats, rodents, and amphibians. (7)

As stated above, brush border enzymes are normally inserted into the apical membrane in microvillous atrophy,(8) and we could not detect differences in alcian blue staining of goblet cells and mucus between controls and microvillous atrophy cases. Thus the FBBG could be responsible for the abnormal histochemical staining pattern.

Functions of the glycocalyx

Links

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References