Collagens comprise a large family of insoluble extracellular glycoproteins that are essential components of connective tissues such as tendons, ligaments, cartilage, bone and skin. The mature polypeptides are secreted as coiled, left-handed helices that subsequently assemble into rope-like collagen fibers. Collagen I is a fibril-forming collagen that requires N- and C- terminal processing. Collagen IV is a network forming collagen whose C-terminus forms dimers and N-terminus forms tetramers.