Structure of MMPs. MMP consists of a prodomain, catalytic domain, hinge region, and hemopexin domain. In the catalytic domain, MMP has a Zn2+ binding site, and a binding site for the specific substrate. MMP has cysteine switch motif PRCGXPD in the prodomain. Matrilysins lack a hemopexin domain. MT-MMP has an additional transmembrane binding domain.