Extracellular proteoglycans

The ability of dissociated cells of sponges to aggregate with cells only of a like type (p. 29) depends upon large extracellular proteoglycans. That of Microciona prolifera appears to be an aggregate of about three hundred 35-kDa core protein molecules with equal masses of attached carbohydrate. This aggregation factor has a total mass of 2 x 104 kDa.226 227 It apparently interacts specifically, in the presence of Ca2+ ions, with a 210-kDa cell matrix protein to hold cells of the same species together.227... 

P. Capek, M. Matulova, and B. Combourieu, The extracellular proteoglycan produced by Rhodella grisea, Int. J. Biol. Macromol., 43 (2008) 390-393. 

Part-time extracellular proteoglycans include variants of well-characterized extracellular glycoproteins such as type IX collagen [141], Clq [142], colony stimulating factor [143], amyloid precursor protein [144], fibronectin [145], and brain-specific receptor-type tyrosine phosphatase (3 [146]. 

Proteoglycans may be soluble and located in the extracellular matrix, as is the case for serglycin, versican, and the cartilage matrix proteoglycan, or they may be integral transmembrane proteins, such as syndecan. Both types of proteoglycan... 

Secreted or extracellular matrix proteoglyeans Large aggregating cartilage proteoglycans CS/KS 220,952 2124... 

FIGURE 9.32 Proteoglycans serve a variety of functions on the cytoplasmic and extracellular surfaces of the plasma membrane. Many of these functions appear to involve the binding of specific proteins to the glycosaminoglycan groups. 

Heparin sulfate proteoglycans (HSPGs) are heavily glycosylated proteins that are part of the extracellular matrix. Interaction with HSPGs help to stabilize and localize extracellular Wnts. 

Several natural polysaccharides are esterified with sulfuric or phosphoric acid. Sulfated bacterial polysaccharides are not, however, very common. One example is a polysaccharide from an Arthrobacter species, which is most probably linked to the proteoglycan and contains sulfated D-galactopy-ranosyl residues. An extracellular polysaccharide from a Phormidium spe-... 

This molecule is present on many cell sur ces as a proteoglycan and is extracellular. It contains GlcN with fewer N-sulfates than heparin, and, unhke heparin, its predominant uronic acid is GlcUA. 

Proteoglycans Glycosaminoglycans (mucopolysaccharides) bound to protein chains in covalent complexes. Proteoglycans are present in the extracellular matrix of connective tissue. 

Adhesion molecules such as LI, neural cell adhesion molecule (N-CAM) and N-cadherin promote axonal regeneration by homophilic interactions between axons and Schwann cell surfaces (see Ch. 7). The expression of p75 (low affinity NGF receptor, Ch. 27) is also increased at the Schwann cell surface after injury. Extracellular matrix molecules, such as tenascin and proteoglycans, increase the regenerative potential of damaged peripheral nerves by binding to integrins on the axonal surface. 

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