Proteoglycan-fibrillar collagen interactions.

The future of biochemistry lies in understanding how single gene products associate and function together. Interactions in connective tissues, including those between the proteoglycans and collagens are especially piquant, evolutionarily conserved and physiologically significant. Connective tissues (e.g. skin, tendon, blood vessels, etc.) are systems of insoluble fibrils and soluble polymers which evolved to take the stresses of movement and the maintenance of shape [1]. The fibrils resist pulling forces, and the interfibrillar soluble polymers resist compressive forces, like the stuffing in a cushion. Cells communicate biochemically through the soluble polymer compartment. Within this simple framework, multicelled organisms developed [1]. It was often speculated that there were specific associations between fibrils and soluble polymers. These ideas were extremely general, lacking chemical knowledge of the participants, and methods for diagnosing interactions. The situation now tends to the other extreme. Sensitive methods discover many 'specific' liaisons in vitro. Even when these are observed at physiological pH, temperature and ionic strength, caution is needed. The very large polymers characteristic of connective tissues (collagens, proteoglycans etc.) have