IDENTIFICATION AND CHARACTERIZATION OF A NOVEL HUMAN MATRIX METALLOPROTEINASE WITH UNIQUE STRUCTURAL CHARACTERISTICS, CHROMOSOMAL LOCATION,AND TISSUE DISTRIBUTION

We have cloned a novel member of the matrix metalloproteinase (MMP) fa mily of proteins from a human liver cDNA library, The isolated cDNA co ntains an open reading frame coding for a polypeptide of 508 amino aci ds, which has been tentatively called MMP-19. This protein exhibits th e domain structure characteristic of previously described MMPs, includ ing a signal sequence, a prodomain with the cysteine residue essential for maintaining the latency of these enzymes, an activation locus wit h the zinc-binding site, and a COOH-terminal fragment with sequence si milarity to hemopexin. However, it lacks a series of structural featur es distinctive of the diverse MMP subclasses, including the Asp, Tyr, and Gly residues located close to the zinc-binding site in collagenase s, the fibronectin-like domain of gelatinases, the transmembrane domai n of membrane-type (MT) MMPs, and the furin-activation sequence common to stromelysin-3 and MT-MMPs, In addition, the 9-residue insertion ri ch in hydrophobic amino acids present at the hinge region in stromelys ins is replaced in MMP-19 by a longer insertion very rich in acidic re sidues. On the basis of these structural characteristics, we propose t hat MMP-19 does not belong to any of the previously defined MMP-subcla sses and may represent the first member of a new MMP subfamily. Chromo somal location of the MMP-19 gene revealed that it maps to chromosome 12q14, which is also a unique location for any MMPs mapped to date. Th e cDNA encoding a full-length MMP-19 was expressed in Escherichia coli , and after purification and refolding, the recombinant protein was ab le to degrade synthetic substrates for MMPs. MMP-19 proteolytic activi ty was abolished by TIMP-2 and EDTA, thus providing additional evidenc e that the isolated cDNA codes for an authentic MMP. Northern blot ana lysis of polyadenylated RNAs isolated from a variety of human tissues revealed that MMP-19 is mainly expressed in placenta, lung, pancreas, ovary, spleen, and intestine, suggesting that it may play a specialize d role in these tissues.