ABSTRACT
Collagen is the most abundant protein in the extracellular matrix (ECM), and plays a central role in the formation of brillar and microbrillar networks, basement membranes, as well as other structures of the connective tissue (Hulmes 2002). Many genetically distinct collagen types have been described so far, and show dierent structures, functions, and distribution in tissues (Ricard-Blum and Ruggiero 2005). e characteristic feature of a collagen molecule is its long triple helical structure. ree polypeptide chains, called α chains and characterized by a (Gly-X-Y) repeated structure, are wrapped around one another in a ropelike right-handed superhelix (Beck and Brodsky 1998). e most abundant family of collagens with more than 90% of the total collagen consists of the bril-forming collagens: mainly collagen I, II, III, V, and XI, whose helical domains are continuous over typically 1000 amino acids. ey are found in a wide variety of tissues such as bone, tendon, skin, ligament, cornea, and internal organs. Once the procollagen molecules are secreted from the cells into the ECM, they are cleaved to collagen
15.6 Conclusion .........................................................................................366 Acknowledgments ........................................................................................366 References ......................................................................................................366
molecules which self-assemble into brils (diameter: 10-300 nm, length: up to several hundred μm). In tissues such as tendons, collagen I brils form bundles or bers with diameters between 0.5 and 3 μm. Other collagens, such as collagen IV, do not form brils, because of numerous interruptions in the helical sequence by non-collagenous domains. Individual collagen IV molecules assemble to form a twodimensional network in the matrix which is found mainly in basement membranes.
