Submitted to: Experimental Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 30, 1999
Publication Date: N/A
Interpretive Summary: Worms that infect livestock cause disease and economic losses estimated at over 200 million dollars annually. The effectiveness of drugs that are currently available for control of these diseases is limited because of cost and because drug resistance can occur. Because of their intimate contact with host components and their accessibility to host protective effector mechanisms, nematode secretory products have potential as targets vulnerable to either immune- or drug-mediated therapies. In this study we purified and characterized a unique enzyme inhibitor component of secretory products of Trichuris suis, the pig whipworm, that may function as a parasite defense mechanism for evasion of host attack. These results provide the frame work for development of novel control methods.
A trypsin/chymotrypsin inhibitor was identified in extracts of adult Trichuris suis as well as in culture fluids following 24-hr in vitro cultivation of adult parasites. The inhibitor, termed TsTCI, was isolated by acid precipitation, affinity chromatography (trypsin-agarose) and reverse phase HPLC as a single polypeptide. The molecular weight was estimated at 6.6 kDa by both SDS-PAGE and laser desorption mass spectrometry. TsTCI associated strongly with both trypsin (equilibrium dissociation inhibitory constant (Ki) of 0.0521 nM) and chymotrypsin (Ki = 0.883 nM); elastase, thrombin, factor Xa, plasmin and kallikrein were not inhibited. The NH2-terminal sequence and sequences of 4 peptides obtained following Lys C protease digestion of TsTCI showed no homology to any previously identified serine protease inhibitors. However, sequence similarity with the active site regions of Ascaris suum trypsin inhibitor (AsTI) and Ancylostoma caninum factor Xa inhibitor (AcAP) was apparent. This unique peptide inhibitor may be involved in protecting the parasite by interfering with protease-mediated host immune cell responses.