Proteoglycan aggregates, structure

Fig. 5-24 Portion of a proteoglycan aggregate showing the bottlebrush-like structure.

Mucopolysaccharides absorb significant quantities of water and tend to have a mucoid, or viscous consistency. This enables them to provide a structural or lubricatory role in connective tissue. They also help to maintain fluid and electrolyte balance throughout the body. Hyaluronic acid differs from the other five types in that it has not been shown to attach along the core protein, but does provide a backbone for proteoglycan aggregates (fig. 6.5). Also, it is not sulfeted. 

Buckwalter JA, Pita JC, Muller FJ, Nessler J. Structural differences between two populations of articular cartilage proteoglycan aggregates. J Orthop Res... 

Figure 32 Brush-like hierarchy of proteoglycan aggregate in cartilage (a) TEM micrograph of the aggregate (b) protein backbone with glucosami-noglycan side chains and (c) chemical structure of the disaccharide repeating unit of the side chains. Reprinted from Seog, J. Dean, D. Plaas, A. H. K. etal. Macromolecules 2002, 35 (14), 5601-5615, with permission from ACS. °...

Know the structures of typical methylpentoses, hexosamine, uronic acids, and sialic acids. Be familiar with the substances in which they occur, and know the differences among the various blood group substances. Be familiar with proteoglycans of connective tissue and how they are assembled into large aggregates. Be familiar with the various mucopolysaccharidoses. 

HA plays an extremely important structural role in cartilage and other connective tissues. For instance, the most important cartilage proteoglycan (PG), termed aggrecan, is bound specifically to HA chains with the help of special link proteins. The formed aggregates have masses of about 100 MDa and are deposited within the collagen framework in a highly ordered manner [64]. 

Rauch, U, Karthikeyan, L, Maurel, P, Margolis, R,U, and Margolis, R,K, (1992) Cloning and primary structure of neurocan, a developmentally regulated, aggregating chon-droitin sulfate proteoglycan of brain, J. Biol. Chem. 267 19536-19547,... 

---