Glycosaminoglycan Chains in the Biological State

Abstract

The molecular components of the extracellular matrix, which are the main topics of discussion in this volume, are hyaluronate (a linear all-carbohydrate polymer of very high molecular weight) and the family of proteoglycans, which are similar to each other in general structure, but differ in their carbohydrate side chains, their molecular weights, their capacities for interaction through polypeptide moities, and probably in other respects as well. There is now good evidence that proteoglycans may have a domain structure: for example, in chondroitin 4-sulfate proteoglycans from cartilage we distinguish (pp. 4–8) a globular headgroup (which binds hyaluronate), N-linked keratin sulfate chains in association with a distinct region of the polypeptide, and O-linked chondroitin sulfate chains attached to a region of the polypeptide that is further from the headgroup. The overall size and osmomechanical properties (Wells, 1973a), which relate to some of the biological functions (see below), are determined chiefly by the carbohydrate chains, whereas the proximity of these chains to each other in space is constrained by the polypeptide backbone, and both carbohydrate and protein moities can engage in specific noncovalent interactions (pp. 11ff, 53ff, 95ff).