Chemistry Reference
In-Depth Information
11
Proteoglycans
Eckhart Buddecke
Proteoglycans (PGs) make up a family of macromolecules consisting of a protein
core to which different high-molecular-weight polyanionic glycosaminoglycan
(GAG) chains are linked covalently. GAG chains are made of repeating disaccha-
ride units with sulfate groups linked by ester bonds to certain monosaccharides.
The macromolecular structure, the highly charged polyanionic nature of GAG and
the variable structure of the protein core make the PGs a widespread and numer-
ous family with essential functions for normal developmental processes in multi-
cellular organisms and in response to injury and disease. PGs play a key role in
cellular signaling, as storage depots for growth factors and cytokines, and interact
with a broad variety of counterpart molecules. They are involved in maintaining
the tensile strength of skin and tendons, the viscoelasticity of blood vessels, and
the compressive properties of cartilage by adsorbing large volumes of water.
11.1
Glycosaminoglycans: Components of Proteoglycans (PG s )
11.1.1
Structure
Figure 11.1 gives the major repeating disaccharide units of GAG chains [1] (for
structures of monosaccharides, see Figure 1.6). Although four major classes of
GAGs are recognized, certain features are common to all. All GAGs form long
unbranched chains containing 50-150 disaccharide units. They are attached to the
protein core via a carbohydrate-protein linkage region which is either a tetrasac-
charide (GlcA-Gal-Gal-Xyl) glycosidically linked to a serine residue (Figure 11.1)
or has a glycoprotein-like structure. The xylose residue of the linkage region may
be phosphorylated on the 2- position. Chondroitin sulfate s (CSs) are the most
abundant GAGs in the body. The GlcNAc residues may be sulfated in either the
4- or 6-position. Each CS chain contains between 30 and 50 disaccharide units
corresponding to a molecular weight of 15 000 - 25 000 Da. Dermatan sulfate ( DS )
