Isolation and partial structural characterization of new Kunitz-type trypsin inhibitors from the pike cestode Triaenophorus nodulosus.

The inhibitors produced by the parasitic worms successfully protect them from the host's proteases and are supposed to underlie the host-parasite specificity. Our previous study has shown that the extracts from the pike tapeworm Triaenophorus nodulosus inhibit host proteinases and commercial trypsin. We aimed to isolate and identify the components responsible for trypsin inactivation. After a two-step separation the molecular masses were measured by SE-HPLC. The sample proved to contain four fractions represented by polypeptides (1-45 kDa) and low-molecular hydrophobic compounds. According to SDS-PAGE analysis, the major polypeptides in the fractions displaying the highest inhibition had masses of 14.4 kDa. The study culminated in partial N-terminal amino acid sequence analysis with a further search for homology. The research revealed two novel Kunitz-type proteins potentially responsible for the inhibitory capacity of the tapeworms against trypsin. Our findings extend the list of cestodes relying on Kunitz-type proteins in the host-parasite molecular cross-talk.