Metalloproteinases (or metalloproteases) constitute a family of enzymes from the group of proteinases, classified by the nature of the most prominent functional group in their active site. These are proteolytic enzymes whose catalytic mechanism involves a metal. Most metalloproteases are zinc-dependent, some use cobalt. The metal ion is coordinated to the protein via three Histadine imidazole ligands. The fourth coordination position is taken up by a labile water molecule.