Se. Bozas et al., CHARACTERIZATION OF A NOVEL KUNITZ-TYPE MOLECULE FROM THE TREMATODE FASCIOLA-HEPATICA, Molecular and biochemical parasitology, 74(1), 1995, pp. 19-29
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.