Proteoglycans of the extracellular matrix

Some cell-surface proteins and heavily glycosylated proteoglycans of the extracellular matrix are bound to the exo-... 

Kresse H, Schonherr E. Proteoglycans of the extracellular matrix and growth control. J Cell Physiol 2001 189 266-274. 

Figure 6.4 The role of chemokines in the recruitment of immune cells in atheroscelortic plaques. Low-density lipoprotein (LDL) diffuses from the blood into the innermost layer of the artery, where LDL particles can associate with proteoglycans of the extracellular matrix. The LDL of the extracellular pool is modified by enzymes and oxygen radicals to form molecules such as oxidized LDL (oxLDL). Biologically...

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. 

As constituents of proteoglycans (see p.346), the glycosaminoglycans—a group of acidic heteropolysaccharides—are important structural elements of the extracellular matrix. 

Yanagishita, M. (1993) Function of proteoglycans in the extracellular matrix, em Acta Path Jap 4 283-293... 

The main constituents of the extracellular matrix are (1.) collagen, particularly the fibrillary types I (36%), III (36%) and V (16%) as well as the non-fibrillary types FV (9%), VI (0.2%) and to a minor degree also type VII, (2.) glycoproteins (fibronectin, tenascin, laminin, undulin, elastin, entactin), and (2.) proteoglycans of both the core protein and the glycosaminoglycan type (e.g. chondroitin, heparan sulphate, hyaluronic add, dermatan sulphate). 

The PI anchor maintains adhesion of acetylcholinesterase (of the red blood cell) and of some proteoglycans (sulfated proteins of the extracellular matrix) to the ceU membrane. Palmitic acid is bound via thiol-ester bonds to Cys 322 and Cys 323 of rhodopsin (see the section on vitamin A), a 327-amino-acid protein. The polypeptide chain of rhodopsin loops in and out of the membrane several times, leaving the possible function of the lipid as an anchor in question. M5nistic acid is boimd to the catalytic subunit of the cAMP-dependent protein kinase, though this protein is cytosolic and soluble. 

Proteoglycans are major components of the extracellular matrix in animal cells. They are composed of core proteins and glycosaminoglycan polysaccharides. Heparin and heparan sulfate are the most complex glycosaminoglycans, a family of molecules that also includes chon-... 

For CKs to act in vivo, they require a solid phase in which normal conditions of blood flow would be unable to wash away the chemoattractant gradient. In this manner, CKs secreted by each cell trafficking through a vessel are sequestered and maintained by stable components of the extracellular matrix, such as proteoglycans. This model of CK action in leukocyte migration is summarized in Figure 22-33. 

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