The MMP15 cDNA encodes a 669-amino acid protein that has the typical structural features of an MMP. In addition, it contains a predicted transmembrane segment at the C terminus. MMP15 shares 73.9% sequence similarity with MMP14, a membrane-localized MMP that also contains a C-terminal transmembrane segment. the membrane-type MMPs are a subclass in the MMP family since the other members lack a C-terminal transmembrane domain and are secreted as soluble forms. Will and Hinzmann showed by immunoblotting that MMP15-specific antibodies detect a 72-kD protein in lung cell surface membranes, suggesting that MMP15 is membrane-bound. They demonstrated by Northern blotting that MMP15 is widely expressed as a 3.6-kb transcript, with highest levels in liver, placenta, testis, colon, and intestine.