Partial characterization of a novel cathepsin L-like protease from Fasciola hepatica

Proteases in egg, miracidium and adult of Fasciola gigantica. Characterization of serine and cysteine proteases from adult

Proteolytic activity of 0-12 day old eggs, miracidium and adult worm of Fasciola gigantica was assessed and proteases were partially purified by DEAE-Sepharose and CM-cellulose columns. Four forms of protease were separated, PIa, PIb, PIc and PII. Purifications were completed for PIc and PII using Sephacryl S-200 chromatography. A number of natural and synthetic proteins were tested as substrates for F. gigantica PIc and PII. The two proteases had moderate activity levels toward azoalbumin and casein compared to azocasein, while gelatin, hemoglobin, albumin and fibrin had very low affinity toward the two enzymes. Amidolytic substrates are more specific to protease activity. PIc had higher affinity toward BAPNA-HCl (N-benzoyl-arginine-p-nitroanilide-HCl) and BTPNA-HCl (N-benzoyl-tyrosine-p-nitroanilide-HCl) at pH 8.0 indicating that the enzyme was a serine protease. However, PII had higher affinity toward BAPNA at pH 6.5 in the presence of sulfhydryl groups (beta-mercaptoethanol) indicating that the enzyme was a cysteine protease. The effect of specific protease inhibitors on these enzymes was studied. The results confirmed that proteases PIc and PII could be serine and cysteine proteases, respectively. The molecular weights of F. gigantica PIc and PII were 60,000 and 25,000, respectively. F. gigantica PIc and PII had pH optima at 7.5 and 5.5 and K(M) of 2 and 5 mg azocasein/mL, respectively. For amidolytic substrates, PIc had K(M) of 0.3 mM BAPNA/mL and 0.5 mM BTPNA/mL at pH 8.0 and PII had K(M) of 0.6 mM BAPNA/mL at pH 6.5 with reducing agent. F. gigantica PIc and PII had the same optimum temperature at 50 degrees C and were stable up to 40 degrees C. All examined metal cations tested had inhibitory effects toward the two enzymes. From substrate specificity and protease inhibitor studies, PIc and PII could be designated as serine PIc and cysteine PII, respectively.

Fasciola hepatica proteolytic activity in liver revealed by in situ zymography

Fasciola hepatica secretes cysteine proteases that play a role in facilitating parasite migration. The aim of this study was to detect the inhibition of the proteolytic activity of F. hepatica cysteine proteases in the liver of C57BL/6 cathepsin B knockout mice (cat B-/-) and wild-type controls (cat B+/+) by intraperitoneal administration of N-[N-(L-3-trans-carboxyoxirane-2-carbonyl)-L-leucyl]-agmatine, (E-64) using the film in situ zymography (FIZ) technique and image analysis. The FIZ technique revealed that intraperitoneal administration of E-64 dramatically reduced (85%) F. hepatica proteolytic activity in the liver of experimentally infected mice with no discernable side effects. These results suggest the usefulness of the FIZ for determining in vivo activity of F. hepatica proteases, as well as their inhibition by intraperitoneal administration of E-64 in hepatic tissue of infected mice.

The evolution of enzyme specificity in Fasciola spp

Fasciola spp., commonly known as liver fluke, are significant trematode parasites of livestock and humans. They secrete several cathepsin L-like cysteine proteases, some of which differ in enzymatic properties and timing of expression in the parasite's life cycle. A detailed sequence and evolutionary analysis is presented, based on 18 cathepsin L-like enzymes isolated from Fasciola spp. (including a novel clone identified in this study). The enzymes form a monophyletic group which has experienced several gene duplication events over the last approximately 135 million years, giving rise to the present-day enzymatic repertoire of the parasite. This timing of these duplications appears to correlate with important points in the evolution of the mammalian hosts. Furthermore, the dates suggest that Fasciola hepatica and Fasciola gigantica diverged around 19 million years ago. A novel analysis, based on the pattern of amino acid diversity, was used to identify sites in the enzyme that are predicted to be subject to positive adaptive evolution. Many of these sites occur within the active site cleft of the enzymes, and hence would be expected to lead to differences in substrate specificity. Using homology modeling, with reference to previously obtained biochemical data, we are able to predict S2 subsite specificity for these enzymes: specifically those that can accommodate bulky hydrophobic residues in the P2 position and those that cannot. A number of other positions subject to evolutionary pressure and potentially significant for enzyme function are also identified, including sites anticipated to diminish cystatin binding affinity.

Characterisation and expression of the Fasciola gigantica cathepsin L gene

The gene structure of a cathepsin L from Fasciola gigantica was characterised. The gene spans approximately 2.0 kb and comprises four exons and three introns and is a compact gene as in the cases of crustaceous and platyhelminth cathepsins L. Southern blot analysis suggested that a few copies of the genes are sparsely organised in the genome. Of the three intron insertion positions, two of which are in the same position as in the mammalian cathepsin L gene. Phylogenetic analysis revealed that F. gigantica cathepsin L forms a clade with those from Fasciola hepatica, but not with those from Spirometra erinacei and schistosomes. Putative TATA-boxes were found upstream of a transcription initiation site. The sequence analysis of the 5'-upstream of the transcript revealed that the cathepsin L gene is transcribed by cis-splicing fashion. Furthermore, the experiments using recombinant F. gigantica procathepsin L showed that it was processed to an enzymatically active cathepsin L by pH-dependent autocatalysis. However, the pro-peptide deleted cathepsin L showed no enzyme activity, indicating that the pro-region of F. gigantica procathepsin L is essential for the folding and/or refolding of functional cathepsin L. These results are consistent with the observations in mammalian cathepsin L and papain.