Abstract
Mast cells of the rat intestinal mucosa express three chymotryptic enzymes named rMCP-2, -3 and 4. rMCP-2, the most abundant of these enzymes, has been shown to increase the permeability of the intestinal epithelium, most likely by cleavage of cell adhesion and junction proteins and thereby play a role in intestinal parasite clearance. However, no target for this effect has yet been identified. To address this question we here present its extended cleavage specificity. Phage display analysis showed that it is a chymase with a specificity similar to the corresponding enzyme in mice, mMCP-1, with a preference for Phe or Tyr in the P1 position, and a general preference for aliphatic amino acids both upstream and downstream of the cleavage site. The consensus sequence obtained from the phage display analysis was used to screen the rat proteome for potential targets. A few of the most interesting candidate substrates were cell adhesion and cell junction molecules. To see if these proteins were also susceptible to cleavage in their native conformation we cleaved 5 different recombinant cell adhesion and cell junction proteins. Three potential targets were identified: the loop 1 of occludin, protocadherin alpha 4 and cadherin 17, which indicated that these proteins were at least partly responsible for the previously observed prominent role of rMCP-2 in mucosal permeability and in parasite clearance.