Cloning and characterization of human MMP-23, a new matrix metalloproteinase predominantly expressed in reproductive tissues and lacking conserved domains in other family members

A cDNA encoding a new human matrix metalloproteinase (MMP), tentatively cal led MMP-23, has been cloned from an ovary cDNA Library. This protein exhibi ts sequence similarity with MMPs, but displays a different domain structure . Thus, MMP-23 lacks a recognizable signal sequence and has a short prodoma in, although it contains a single cysteine residue that can be part of the cysteine-switch mechanism operating for maintaining enzyme latency. The C-t erminal domain is considerably shortened and shows no sequence similarity t o hemopexin, whereas all human MMPs, with the exception of matrilysin, cont ain four hemopexin-like repeats. Furthermore, MMP-23 is devoid of structura l features distinctive of the diverse MMP subclasses, including the specifi c residues located close to the zinc-binding site in collagenases, the tran smembrane domain of membrane-type MMPs, or the fibronectin-like domain of g elatinases. Fluorescent in situ hybridization experiments showed that the h uman MMP-23 gene maps to 1p36, a location which differs from all MMP genes mapped to date. Recombinant MMP-23 produced in Escherichia coil exhibits lo w, but significant proteolytic activity against a synthetic substrate commo nly used for assaying MMPs. Northern blot analysis demonstrated that MMP-23 is predominantly expressed in ovary, testis, and prostate, suggesting that this new MMP may play a specialized role in reproductive processes.