Figure 3.

Basic structure of the MMP. MMPs consist of four main domains: a signal peptide that directs the secretion of the protein to the outside of the cell, a propeptide region that keeps the enzyme inactive until it is proteolytically cleaved, a catalytic domain that contains zinc and calcium and to which the cysteine of the propeptide region binds to keep it inactive (cysteine switch), and a hemopexin-like domain that mediates substrate specificity and interactions with endogenous inhibitors. MMP-2 and MMP-9 possess a fibronectin-type domain for matrix binding.