What is the composition of an extracellular matrix?

The extracellular matrix is composed of two classes of macromolecules: fibrous proteins and proteoglycans. The primary fibrous ECM proteins are elastins, collagens, laminins, tenascins and fibronectins. Collagens are the primary form of structural proteins found in the ECM, as they provide durability and also play a role in migration and adhesion. They are also the most abundant protein in the body. More specifically, collagen types I, II, III, V, and XI are found in the ECM. Collagen type IV is found in the basement membrane of the ECM. Elastin is closely linked with collagen, and provides the ability for the skin to recover from stretching in soft tissue. Fibronectin is found within the basement membrane of the ECM and has a key role in cell adhesion, wound healing, and embryonic development. Laminins are also located in the basement membrane and play key roles in differentiation and migration. In embryos, laminins are among the first proteins of the ECM to appear. Tenascins are a group of proteins that occurs in five different forms, TN-C, TN-R, TN-W, TN-X, and TN-Y. They are typically found in the connective tissue, and also in the brain.  

The ECM is also made out of sugars, and other components. Other components include growth factors, a group of MMPs, and non-structural proteins. Growth factors are bound to the ECM through either heparan sulfate or herparan. Some examples include vascular endothelial growth factor (VEGF), fibroblast growth factor (FGF) and transforming growth factor Beta. MMPS are involved in disintegration of the ECM for the purpose of reshaping it. For example, MMPs are used during bone remodeling and neovascularization.