Proteoglycan

Source: Wikipedia, the free encyclopedia.
Not to be confused with peptidoglycan, glycoprotein, or glycopeptide.
Aggrecan, the major proteoglycan in cartilage, has 2316 amino acids

Proteoglycans are

Gly-X-Gly- (where X can be any amino acid residue but proline), although not every protein with this sequence has an attached glycosaminoglycan. The chains are long, linear carbohydrate polymers that are negatively charged under physiological conditions due to the occurrence of sulfate and uronic acid groups. Proteoglycans occur in connective tissue
.

Types

Proteoglycans are categorized by their relative size (large and small) and the nature of their glycosaminoglycan chains.[3] Types include:

Type Glycosaminoglycans (GAGs) Small proteoglycans Large proteoglycans
chondroitin sulfate/dermatan sulfate decorin, 36 kDa
biglycan, 38 kDa 		aggrecan, 220 kDa, the major proteoglycan in cartilage
Heparan sulfate proteoglycan

(HSPGs) 		heparan sulfate/chondroitin sulfate testican, 44 kDa
betaglycan, >300 kDa
agrin
, >500 kDa
Chondroitin sulfate proteoglycan
(CSPGs) 		chondroitin sulfate
bikunin
, 25 kDa

neurocan, 136 kDa
versican, 260–370 kDa, present in many adult tissues including blood vessels and skin
brevican, 145kDa

Keratan sulfate proteoglycan keratan sulfate fibromodulin, 42 kDa
lumican, 38 kDa

Certain members are considered members of the "small leucine-rich proteoglycan family" (SLRP).[4] These include decorin, biglycan, fibromodulin and lumican.

Function

Proteoglycans are a major component of the animal

cations (such as sodium, potassium and calcium) and water, and also regulating the movement of molecules through the matrix. Evidence also shows they can affect the activity and stability of proteins and signalling molecules within the matrix.[6][7]
Individual functions of proteoglycans can be attributed to either the protein core or the attached GAG chain. They can also serve as lubricants, by creating a hydrating gel that helps withstand high pressure.

Synthesis

The protein component of proteoglycans is synthesized by

vesicles
to the extracellular matrix of the tissue.

Clinical significance

An inability to break down the proteoglycans is characteristic of a group of

Ehlers–Danlos syndrome.[8]

Distinction between proteoglycans and glycoproteins

Quoting from recommendations for IUPAC:[9]

A glycoprotein is a compound containing carbohydrate (or glycan) covalently linked to protein. The carbohydrate may be in the form of a monosaccharide, disaccharide(s), oligosaccharide(s), polysaccharide(s), or their derivatives (e.g. sulfo- or phospho-substituted). One, a few, or many carbohydrate units may be present. Proteoglycans are a subclass of glycoproteins in which the carbohydrate units are polysaccharides that contain amino sugars. Such polysaccharides are also known as glycosaminoglycans.

References

  1. ^ Proteoglycans at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
  2. ISBN 978-0-323-02942-1
    . Retrieved 6 February 2011.
  3. PMID 25701227
    .
  4. ISBN 978-3-527-30888-0
    . Retrieved 6 February 2011.
  5. ISBN 978-1-118-91840-1
    .
  6. PMID 28270211
    .
  7. PMID 24392029
    .
  8. S2CID 10165577
    .
  9. ^ "Nomenclature of glycoproteins, glycopeptides and peptidoglycans, Recommendations 1985". www.qmul.ac.uk. Retrieved 16 March 2021.

External links

Retrieved from "https://en.wikipedia.org/w/index.php?title=Proteoglycan&oldid=1188140824"