Order and disorder in the extracellular matrix

This article examines order and disorder in the extracellular matrix (ECM). The mechanical and structural properties of the tissues in the human body are largely determined by the ECM, the fibrillar network of proteins surrounding the cells. The main component of the ECM is collagen, which self-assembles in vivo into fibrils and fibers that supply rigidity and tensile strength to the ECM. The protein is often found together with elastin, another self-assembling ECM scleroprotein, whose properties of elasticity, extensibility, and elastic recoil supplement the mechanical properties of collagen. This article first provides an overview of protein synthesis and structure, with particular emphasis on tropocollagen, tropoelastin, and recombinantly-made polypeptides. It then considers the hierarchical supramolecular organization of the ECM, collagen and elastin before concluding with an assessment of structure-function relations at the matrix level.