IDENTIFICATION AND STRUCTURAL AND FUNCTIONAL-CHARACTERIZATION OF HUMAN ENAMELYSIN (MMP-20)

A cDNA encoding a new human matrix metalloproteinase (MMP) has been cl oned from RNA prepared from odontoblastic cells. The open reading fram e of the cloned cDNA codes for a polypeptide of 483 amino acids and is extensively similar to the sequence of recently described porcine ena melysin, suggesting that the isolated cDNA codes for the human homolog ue of this enzyme. Human enamelysin (MMP-20) has a domain organization similar to other MMPs, including a signal peptide, a prodomain with t he conserved motif PRCGVPD involved in maintaining enzyme latency, a c atalytic domain with a Zn-binding site, and a COOH-terminal fragment s imilar to the sequence of hemopexin. The calculated molecular mass of human enamelysin is about 54 kDa, which is similar to that of collagen ases or stromelysins. However, this human MMP lacks a series of struct ural features distinctive of these subfamilies of MMPs. The full-lengt h human enamelysin cDNA has been expressed in Escherichia coli, and th e purified and refolded recombinant protein is able to degrade synthet ic peptides used as substrates of MMPs, confirming that human enamelys in belongs to this family of proteases. Furthermore, the recombinant h uman enamelysin is able to degrade amelogenin, the major protein compo nent of the enamel matrix. On the basis of its degrading activity on a melogenin, and its highly restricted expression to dental tissues, we suggest that human enamelysin plays a central role in the process of t ooth enamel formation. Finally, we have found that the human enamelysi n gene (MMP-20) maps to chromosome 11q22, clustered to at least seven other members of the MMP gene family.