CHARACTERIZATION OF A NOVEL KUNITZ-TYPE MOLECULE FROM THE TREMATODE FASCIOLA-HEPATICA

A low molecular mass monomeric protein termed Fh-KTM (Fasciola hepatic a Kunitz-type molecule) was isolated from the trematode Fasciola hepat ica. Fh-KTM is a single polypeptide of 58 amino acids and a Mr of 6751 . The complete amino acid sequence of Fh-KTM was determined and reveal ed significant similarity to the Kunitz-type (BPTI) family of proteina se inhibitors. Several polymorphisms were observed suggesting that mor e than one Fh-KTM molecule may be expressed by this parasite. Modified proline residues were shown to occur at all four positions in this pr otein as 3-hydroxy derivatives. This is the first report of 3-hydroxyp roline residues in a Kunitz-type molecule. Indirect immunofluorescence and immunogold labelling revealed that Fh-KTM is an abundant molecule within the parasite localised to the gut, the parenchymal tissue and the tegument of adult F. hepatica. Serine protease inhibition assays r evealed that Fh-KTM exhibited little or no inhibition against chymotry psin, kallikrein, urokinase or key serine proteases of the blood coagu lation pathways. However, Fh-KTM was able to inhibit trypsin even thou gh the P1 reactive amino acid of Fh-KTM was a leucine residue.