Matrix metalloproteinases (MMPs) represent a family of proteolytic enzymes that contain a zinc ion at the active site of catalysis (Nagase and Woessner 1999). The MMPs constitute a family of secreted or cell surface enzymes that process or degrade numerous peri- and extracellular proteins, most notably those involved in the normal turnover and maintenance of extracellular matrix (ECM) proteins in connective tissue and basement membrane. MMPs have thus been proven essential in a variety of physiological processes. It is therefore not surprising that their expression is highly regulated and any excess of MMP activity will have a significant effect on the progression of various disorders, including inflammatory diseases. At present, at least 25 MMPs have been identified and can be grouped into five subclasses: four collagenases (including xenopus collagenase-4, MMP-18), two gelatinases, three stromelysins, four membrane-type MMPs (MT-MMPs) and others, including metalloelastase (MMP-12) and Matrilysin (MMP-7). The progress made so far in identifying the various MMP substrates that modulate the inflammatory response has significantly advanced our understanding of the molecular basis of the role MMPs play in airway inflammation.
