Matrix metalloproteinases (MMPs) are calcium-dependent zinc-containing proteases, of which 26 members (MMP-1 to MMP-26) have been identified. MMPs are involved in the degradation of extracellular matrix in normal physiological processes (such as embryonic development, reproduction, tissue remodeling) and pathological processes (such as arthritis and metastasis). MMP-13, also known as collagenase 3, is encoded by the MMP13 gene in humans. Like most MMPs, it is secreted as an inactive precursor. MMP-13 is activated once the propeptide domain is cleaved, and the activated enzyme consists of the catalytic domain and the heme-like domain PDB: 1PEX. During embryonic development, MMP-13 is expressed in bone and is essential for the reorganization of collagen matrix during bone mineralization. In pathological conditions, such as tumors, rheumatoid arthritis, and osteoarthritis, MMP-13 is highly overexpressed.