MMP-1 has an archetypal structure consisting of a pre-domain, a pro-domain, a catalytic domain, a linker region and a hemopexin-like domain. Two main nomenclatures for the primary structure are currently in use, the original one from which the first amino-acid starts with the signalling peptide and a second one where the first amino-acid starts counting from the prodomain (proenzyme nomenclature). MMPs are involved in the breakdown of extracellular matrix in normal physiological processes, such as embryonic development, reproduction, and tissue remodeling, as well as in disease processes, such as arthritis and metastasis. Specifically, MMP-1 breaks down the interstitial collagens, types I, II, and III. Mechanical force may increase the expression of MMP1 in human periodontal ligament cells.