MMPs are typically made of a propeptide of approximately 80 amino acids, a linker peptide of varying lengths (the hinge region), a catalytic metalloproteinase domain containing a zinc ion- binding motif of approximately 170 amino acids, and a C-terminal hemopexin domain of approximately 200 amino acids linked to the catalytic domain via hinge region. Some exceptions to this basic structure include MMP-7, MMP-26, MMP-23, as they do not have the linker peptide and hemopexin domain. MMP-23 in specific has a cysteine-rich domain and an immunoglobulin-like domain preceding the metalloproteinase domain.