Cathepsin L1, the major protease involved in liver fluke (Fasciola hepatica) virulence.

The secretion and activation of the major cathepsin L1 cysteine protease involved in the virulence of the helminth pathogen Fasciola hepatica was investigated. Only the fully processed and active mature enzyme can be detected in medium in which adult F. hepatica are cultured. However, immunocytochemical studies revealed that the inactive procathepsin L1 is packaged in secretory vesicles of epithelial cells that line the parasite gut. These observations suggest that processing and activation of procathepsin L1 occurs following secretion from these cells into the acidic gut lumen. Expression of the 37-kDa procathepsin L1 in Pichia pastoris showed that an intermolecular processing event within a conserved GXNXFXD motif in the propeptide generates an active 30-kDa intermediate form. Further activation of the enzyme was initiated by decreasing the pH to 5.0 and involved the progressive processing of the 37 and 30-kDa forms to other intermediates and finally to a fully mature 24.5 kDa cathepsin L with an additional 1 or 2 amino acids. An active site mutant procathepsin L, constructed by replacing the Cys26 with Gly26, failed to autoprocess. However, [Gly26]procathepsin L was processed by exogenous wild-type cathepsin L to a mature enzyme plus 10 amino acids attached to the N terminus. This exogenous processing occurred without the formation of a 30-kDa intermediate form. The results indicate that activation of procathepsin L1 by removal of the propeptide can occur by different pathways, and that this takes place within the parasite gut where the protease functions in food digestion and from where it is liberated as an active enzyme for additional extracorporeal roles.

Fasciola hepatica cathepsin L-like proteases: biology, function and potential in the development of first generation liver fluke vaccines.

Fasciola hepatica secretes cathepsin L proteases that facilitate the penetration of the parasite through the tissues of its host, and also participate in functions such as feeding and immune evasion. The major proteases, cathepsin L1 (FheCL1) and cathepsin L2 (FheCL2) are members of a lineage that gave rise to the human cathepsin Ls, Ks and Ss, but while they exhibit similarities in their substrate specificities to these enzymes they differ in having a wider pH range for activity and an enhanced stability at neutral pH. There are presently 13 Fasciola cathepsin L cDNAs deposited in the public databases representing a gene family of at least seven distinct members, although the temporal and spatial expression of each of these members in the developmental stage of F. hepatica remains unclear. Immunolocalisation and in situ hybridisation studies, using antibody and DNA probes, respectively, show that the vast majority of cathepsin L gene expression is carried out in the epithelial cells lining the parasite gut. Within these cells the enzyme is packaged into secretory vesicles that release their contents into the gut lumen for the purpose of degrading ingested host tissue and blood. Liver flukes also express a novel multi-domain cystatin that may be involved in the regulation of cathepsin L activity. Vaccine trials in both sheep and cattle with purified native FheCL1 and FheCL2 have shown that these enzymes can induce protection, ranging from 33 to 79%, to experimental challenge with metacercariae of F. hepatica, and very potent anti-embryonation/hatch rate effects that would block parasite transmission. In this article we review the vaccine trials carried out over the past 8 years, the role of antibody and T cell responses in mediating protection and discuss the prospects of the cathepsin Ls in the development of first generation recombinant liver fluke vaccines. Author Keywords: Helminths; Trematodes; Parasites; Cathepsins; Proteases; Vaccines; Immunology; Biochemistry

Characterisation of two calmodulin-like proteins from the liver fluke, Fasciola hepatica.

Calmodulin is a calcium ion-sensing signalling protein found in eukaryotics. Two calmodulin-like gene sequences were identified in an EST library from adult liver flukes. One codes for a protein (FhCaM1) homologous to mammalian calmodulins (98% identity), whereas the other protein (FhCaM2) has only 41% identity. These genes were cloned into expression vectors and the recombinant proteins were expressed in Escherichia coli. Gel shift assays showed that both proteins bind to calcium, magnesium and zinc ions. Homology models have been built for both proteins. As expected, FhCaM1 has a highly similar structure to other calmodulins. Although FhCaM2 has a similar fold, its surface charge is higher than FhCaM1. One of the potential metal ion-binding sites has lower metal-ion co-ordination capability, while another has an adjacent lysine residue, both of which may decrease the metal-binding affinity. These differences may reflect a specialised role for FhCaM2 in the liver fluke.

Alpha-1 antitrypsin deficiency: A conformational disease associated with lung and liver manifestations

Alpha-1 antitrypsin (A1AT) is a serine anti-protease produced chiefly by the liver. A1AT deficiency is a genetic disorder characterized by serum levels of less than 11 μmol/L and is associated with liver and lung manifestations. The liver disease, which occurs in up to 15% of A1AT-deficient individuals, is a result of toxic gain-of-function mutations in the A1AT gene, which cause the A1AT protein to fold aberrantly and accumulate in the endoplasmic reticulum of hepatocytes. The lung disease is associated with loss-of-function, specifically decreased anti-protease protection on the airway epithelial surface. The so-called 'Z' mutation in A1AT deficiency encodes a glutamic acid-to-lysine substitution at position 342 in A1AT and is the most common A1AT allele associated with disease. Here we review the current understanding of the molecular pathogenesis of A1AT deficiency and the best clinical management protocols. © Springer Science+Business Media B.V. 2008.

Liver fluke (Fasciola hepatica)-derived peptides activate rat peritoneal mast cells

Short peptides with sequences derived from those found in the tegumental antigen of Fasciola hepatica have been synthesised. Incubation of some of these peptides with rat peritoneal mast cells resulted in the degranulation of the cells as measured by a histamine release assay. This activity was shown to be associated with the proline-lysine-proline motif, which is responsible for the induction of mast cell degranulation by the mammalian bioactive peptide substance P. Studies on the mode of action of the fluke-derived peptide indicated that it was operating through the same biochemical pathways as substance P. The implications of these findings for the development of immune responses during parasite infections are discussed. (C) 2003 Elsevier Science B.V. All rights reserved.

Understanding genetic diversity of the liver fluke Fasciola hepatica

Economical breeding is important to obtain maximum gain from the breeding in the animal sector. The economic loss has to be eliminated or should be minimized. The liver fluke, Fasciola hepatica, present mostly in sheep and dairy cattle affect the yield of animals and even cause their death. To eliminate or minimize the impact of these parasites on the animals, it is important to understand the genetic diversity of the liver fluke populations and the relationship between parasite and host at regional bases. This research was carried out to determine diversity by sequence analysis of the mitochondrial ND1 gene and ribosomal ITS1 region.