Structure and function in extracellular matrices depend on interactions between anionic glycosaminoglycans.

Connective tissue extracellular matrices define and maintain shape. Collagen fibrils transmit and resist pulling forces and soluble interfibrillar carbohydrate-rich polymers (anionic glycosaminoglycans AGAGs) resist compressive forces. This article shows that AGAGs (chondroitin, dermochondan and keratan sulphates) form supramolecular organisations which take tensile stresses as well, helping to maintain shape as part of 'shape modules'. Specific interactions with collagen fibrils tie down the AGAGs but conversely they orientate and maintain the organisation of collagen fibrils by forming interfibrillar bridges. The shapes of the AGAG chains in solution, shown by NMR to be two-fold helices, are completely complementary, allowing duplexes and higher aggregates to form spontaneously, providing participating AGAGs are oriented head-to-head i.e. antiparallel to each other. These tertiary structures are exact analogues of the beta-sheets are the basic structure of the interfibrillar bridges in the shape modules. In the absence of key shape module components, in a genetic disorder, extracellular matrices do not form an ordered tissue.