Proteoglycans occur in connective tissue.
Proteoglycans are categorized by their relative size (large and small) and the nature of their glycosaminoglycan chains.
|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
|heparan sulfate/chondroitin sulfate||testican, 44 kDa||perlecan, 400–470 kDa
betaglycan, >300 kDa
|Chondroitin sulfate proteoglycan
|chondroitin sulfate||bikunin, 25 kDa||neurocan, 136 kDa
versican, 260–370 kDa, present in many adult tissues including blood vessels and skin
|Keratan sulfate proteoglycan||keratan sulfate||fibromodulin, 42 kDa
lumican, 38 kDa
Certain members are considered members of the "small leucine-rich proteoglycan family" (SLRP).
The combination of proteoglycans and collagen form cartilage, a sturdy tissue that is usually heavily hydrated (mostly due to the negatively charged sulfates in the glycosaminoglycan chains of the proteoglycans).
Evidence also shows they can affect the activity and stability of proteins and signalling molecules within the matrix.
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.
First, a special link tetrasaccharide is attached to a serine side chain on the core protein to serve as a primer for polysaccharide growth.
Then sugars are added one at a time by glycosyl transferase.
The completed proteoglycan is then exported in secretory vesicles to the extracellular matrix of the tissue.
The inactivity of specific lysosomal enzymes that normally degrade glycosaminoglycans leads to the accumulation of proteoglycans within cells.
This leads to a variety of disease symptoms, depending upon the type of proteoglycan that is not degraded.
Mutations in the gene encoding the galactosyltransferase B4GALT7 result in a reduced substitution of the proteoglycans decorin and biglycan with glycosaminoglycan chains, and cause a spondylodysplastic form of Ehlers-Danlos syndrome.
Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Proteoglycan.