Collagen is the most abundant protein in the mammalian body. Collagen types I, II, and III are the major structural components of skin, bone, cartilage, and connective tissues. They exist as fibrils of crosslinked helical molecules composed of three α chains of approx 1000 amino acids each, with nonhelical extensions called telopeptides at both ends of each chain. During turnover in health and disease, after these fibrils are depolymerized, they are degraded, at neutral pH, by the proteolytic attack of enzymes, appropriately called mammalian collagenases, at a specific locus within the native triple-helical structure of each collagen molecule. These collagenases belong to the matrix metalloproteinase (MMP) enzyme family and include MMP-1 (collage-nase-1 or fibroblast/interstitial collagenase), MMP-8 (collagenase-2 or neutrophil collagenase), and MMP-13 (collagenase-3). All three, in addition to a membrane-type MMP (MT-MMP) designated MT1-MMP (MMP-14), cleave the collagen molecules to yield characteristic 3/4 (TCA ) and 1/4 (TCB ) fragments.
