Researchers identify enzyme essential for battle against bacteria in the...( epithelium to find outits normal func...)

epithelium, to find out its normal function. In the laboratory of Lynn M. Matrisian, Ph.D., professor of cell biology at Vanderbilt University, Wilson had developed a strain of knockout mice lacking this enzyme. The researchers focused on the small intestine, which in normal mice produces high levels of matrilysin. The cells at the base of the small intestinal crypts -- called Paneth cells -- are believed to be defense cells in the intestines.

"That's what made us think that matrilysin could be associated with host defense against bacteria," Wilson said. Wilson started collaborating with Andre J. Ouellette, Ph.D., professor of pathology and of microbiology and molecular genetics at the University of California, Irvine, who studies a class of antimicrobial peptides made by Paneth cells. These peptides are called cryptdins, a term derived from crypt defensins.

Cutting off a short segment activates cryptdins. Parks and Wilson wanted to determine whether matrilysin could be responsible for the cleavage reaction.

Using purified proteins, they found that matrilysin can cleave cryptdin exactly at the site that is used to make an active defensin. And when they analyzed tissue from the small intestine of the mice tissue that lacked matrilysin, they found no evidence of activated cryptdins.

The researchers also discovered that this tissue couldn't kill bacteria. "We found a decrease in antimicrobial activity in the absence of matrilysin," Wilson said. "Therefore, we concluded that the enzyme is needed to activate these defensins." Depending on the assay the researchers used, there was between a 10-fold and 100-fold difference in the tissue's ability to kill bacteria.

The researchers were surprised by their findings. "This was an enzyme considered to be one of the most vigorous of those that can degrade connective tissue in the body," Parks said. "We determined it's going in a completely opposite direction, being re
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Contact: Diane Duke Williams
duke@medicine.wustl.edu
314-286-0111
Washington University School of Medicine
1-Oct-1999

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