Cathepsin B-like cysteine proteases of Leishmania mexicana

A "Golden Age" for the discovery of new antileishmanial agents: Current status of leishmanicidal gold complexes and prospective targets beyond the trypanothione system

Leishmaniasis is one of the most neglected diseases worldwide and is considered a serious public health issue. The current therapeutic options have several disadvantages that make the search for new therapeutics urgent. Gold compounds are emerging as promising candidates based on encouraging in vitro and limited in vivo results for several Au^I and Au^III complexes. The antiparasitic mechanisms of these molecules remain only partially understood. However, a few studies have proposed the trypanothione redox system as a target, similar to the mammalian thioredoxin system, pointed out as the main target for several gold compounds with significant antitumor activity. In this review, we present the current status of the investigation and design of gold compounds directed at treating leishmaniasis. In addition, we explore potential targets in Leishmania parasites beyond the trypanothione system, taking into account previous studies and structure modulation performed for gold-based compounds.

Cathepsin B gene disruption induced Leishmania donovani proteome remodeling implies cathepsin B role in secretome regulation

Leishmania cysteine proteases are potential vaccine candidates and drug targets. To study the role of cathepsin B cysteine protease, we have generated and characterized cathepsin B null mutant L. donovani parasites. L. donovani cathepsin B null mutants grow normally in culture, but they show significantly attenuated virulence inside macrophages. Quantitative proteome profiling of wild type and null mutant parasites indicates cathepsin B disruption induced remodeling of L. donovani proteome. We identified 83 modulated proteins, of which 65 are decreased and 18 are increased in the null mutant parasites, and 66% (55/83) of the modulated proteins are L. donovani secreted proteins. Proteins involved in oxidation-reduction (trypanothione reductase, peroxidoxins, tryparedoxin, cytochromes) and translation (ribosomal proteins) are among those decreased in the null mutant parasites, and most of these proteins belong to the same complex network of proteins. Our results imply virulence role of cathepsin B via regulation of Leishmania secreted proteins.

Proteinases as virulence factors in Leishmania spp. infection in mammals

Leishmania parasites cause human tegumentary and visceral infections that are commonly referred to as leishmaniasis. Despite the high incidence and prevalence of cases, leishmaniasis has been a neglected disease because it mainly affects developing countries. The data obtained from the analysis of patients' biological samples and from assays with animal models confirm the involvement of an array of the parasite's components in its survival inside the mammalian host. These components are classified as virulence factors. In this review, we focus on studies that have explored the role of proteinases as virulence factors that promote parasite survival and immune modulation in the mammalian host. Additionally, the direct involvement of proteinases from the host in lesion evolution is analyzed. The gathered data shows that both parasite and host proteinases are involved in the clinical manifestation of leishmaniasis. It is interesting to note that although the majority of the classes of proteinases are present in Leishmania spp., only cysteine-proteinases, metalloproteinases and, to a lesser scale, serine-proteinases have been adequately studied. Members from these classes have been implicated in tissue invasion, survival in macrophages and immune modulation by parasites. This review reinforces the importance of the parasite proteinases, which are interesting candidates for new chemo or immunotherapies, in the clinical manifestations of leishmaniasis.

Cysteine peptidases of kinetoplastid parasites

We review Clan CA Family C1 peptidases of kinetoplastid parasites (Trypanosoma and Leishmania) with respect to biochemical and genetic diversity, genomic organization and stage-specificity and control of expression. We discuss their contributions to parasite metabolism, virulence and pathogenesis and modulation of the host's immune response. Their applications as vaccine candidates and diagnostic markers as well as their chemical and genetic validation as drug targets are also summarized.

Cloning and characterization of angiotensin converting enzyme related dipeptidylcarboxypeptidase from Leishmania donovani

We report the first identification, gene cloning, recombinant expression and biochemical characterization of an angiotensin converting enzyme (ACE) related dipeptidylcarboxypeptidase (DCP) in a protozoan parasite. The mammalian counterpart of this enzyme, peptidyl dipeptidase A (a carboxyl dipeptidase) also known as ACE leads to the cleavage of angiotensin I to produce a potent vasopressor. The catalytic enzyme activity of its Escherichia coli DCP counter part can be inhibited by the antihypertensive drug captopril, suggesting that this class of enzymes constitutes a novel target for drugs and vaccines. By utilizing a DNA microarray expression profiling approach, we identified a gene encoding a DCP enzyme for the kinetoplast protozoan Leishmania donovani (LdDCP) that was differentially expressed in promastigote and amastigote stages of the parasite life cycle. Both RNA and protein levels of LdDCP are higher in axenic amastigotes compared to promastigotes. Immuno-fluorescence analysis revealed the cytosolic expression of the protein. Primary structure analysis of LdDCP revealed the presence of an active Zn binding site. When expressed in E. coli, the recombinant enzyme showed carboxy-dipeptidase activity with synthetic substrates. Replacement of two histidine and one glutamic acid at positions 466, 470 and 467, respectively, with alanine residues in its active site resulted in loss of enzyme activity. Captopril, an ACE specific inhibitor was able both to reduce significantly LdDCP enzyme activity and to inhibit promastigote growth. Both its cytosolic location and close homology to DCPs from bacterial species suggests a role in parasite nutrition. Further, identification of LdDCP now provides an opportunity to investigate Leishmania peptidases for their potential as drug and vaccine targets.

Carboxydipeptidase activities of recombinant cysteine peptidases

The recombinant cysteine peptidases, cruzain from Trypanosoma cruzi and CPB2.8DeltaCTE from Leishmania mexicana, are cathepsin L-like and characteristically endopeptidases. In this study, we characterized the carboxydipeptidase activities of these enzymes and compared them with those of human recombinant cathepsin B and cathepsin L. The analysis used the internally quenched fluorescent peptide Abz-FRFK*-OH and some of its analogues, where Abz is ortho-aminobenzoic acid and K* is (2,4-dinitrophenyl)-epsilon-NH2-lysine. These peptides were demonstrated to be very sensitive substrates, due to the strong quenching effect of K* on the fluorescence of the Abz group. The carboxydipeptidase activity of cruzain was shown to be very similar to that of cathepsin B, while that of CPB2.8DeltaCTE is closer to the carboxydipeptidase activity of cathepsin L. The S2 subsite architecture of cruzain and the nature of the amino acid at the P2 position of the substrates determine its carboxydipeptidase activity and gives further and direct support to the notion that the carboxydipeptidase activity of the papain family cysteine peptidases rely on the S2-P2 interaction [Nägler D. K., Tam, W., Storer, A.C., Krupa, J.C., Mort, J.S. & Menard, R. (1999) Biochemistry38, 4868-4874]. Cruzain and CPB2.8DeltaCTE presented a broad pH-range for both the endo- and exo-peptidase activities, although the later is approximately one order of magnitude lower. This feature, that is not common in related mammalian cysteine peptidases, is consistent with the enzymes being exposed to different environmental conditions and having different locations during parasite development.

Trypanosoma cruzi: partial characterization of minor cruzipain isoforms non-adsorbed to Concanavalin A–Sepharose

The present paper reports the partial characterization of a subset of atypical cruzipain molecules which do not bind to Concanavalin A-Sepharose column. They are present in different strains of epimastigote forms of Trypanosoma cruzi and represent a 2-4% of total cruzipain. They were purified by affinity chromatography on Cystatin-Sepharose, recognized by the polyclonal anti-cruzipain serum, and their activity in gelatin-containing gels was completely abolished by E-64, TLCK, leupeptin, and aprotinin but not by PMSF, pepstatin A, EDTA or 1,10-phenantroline. These cysteine proteinases, as well as cruzipain showed to be endoproteinases able to hydrolize azocasein, hemoglobin, and bovine serum albumin at acidic pHs. However, evidences are presented indicating that this subset of cruzipain isoforms were also able to use the same blocked chromogenic peptidyl substrates than cruzipain at similar optimal alkaline pH values although with a different order of preference. Moreover, they showed a different oligosaccharide pattern after enzymatic treatment by high pH anion exchange chromatography, suggesting that this structural difference may account for the atypical behaviour in the lectin column.

Molecular cloning and characterization of cathepsin B from the hepatopancreas of northern shrimp Pandalus borealis

We cloned a cDNA encoding cathepsin B from the hepatopancreas of northern shrimp Pandalus borealis (NsCtB). Nucleotide sequence of the isolated clone encoded a preproenzyme of 328 amino acids, comprising a 15-residue putative signal peptide, a 60-residue propeptide and the 253-residue mature enzyme. The mature NsCtB was 53% identical to human cathepsin B and conserved all the structural features characteristic of cysteine protease. The presence of an occluding loop in the mature region, a unique feature of cathepsin B, suggested the shrimp protein to be cathepsin B. Northern blot analysis revealed expression of NsCtB transcripts exclusively in the hepatopancreas tissues, suggesting a possible digestive role of this enzyme. An interesting feature of NsCtB was its remarkably high negative charge in comparison with other cysteine proteases, which was predicted to effectively locate and guide the positively charged residues of a substrate into the binding cleft. We also observed a repertoire of cysteine protease activities in the acidic milieu of shrimp hepatopancreas using synthetic substrates specific to various cathepsins. The activity profile revealed cathepsin B as the single most dominant enzyme with a specific activity comparable to that attributable to combined activities of other cathepsins. This activity could be blocked by E-64, a cysteine protease inhibitor, but not by Z-Phe-Tyr (t-Bu)-CHN(2), a specific inhibitor of cathepsin L.

Activation of TGF-beta by Leishmania chagasi: importance for parasite survival in macrophages

TGF-beta is a potent regulatory cytokine that suppresses expression of inducible NO synthase and IFN-gamma, and suppresses Th1 and Th2 cell development. We examined whether functionally active TGF-beta is present in the local environment surrounding the invading protozoan Leishmania chagasi. Our prior data showed that TGF-beta levels are significantly increased in L. chagasi-infected mice. In the current study, we found TGF-beta was also abundant in bone marrows of humans with acute visceral leishmaniasis but not in those of uninfected controls. Furthermore, L. chagasi infection caused an increase in biologically active TGF-beta in human macrophage cultures without changing the total TGF-beta. Therefore, we investigated the means through which leishmania could augment activated but not total TGF-beta. Incubation of latent TGF-beta with Leishmania sp. promastigotes caused active TGF-beta to be released from the latent complex. In contrast, the nonpathogenic protozoan Crithidia fasciculata could not activate TGF-beta. TGF-beta activation by leishmania was prevented by inhibitors of cysteine proteases and by the specific cathepsin B inhibitor CA074. Physiologic concentrations of TGF-beta inhibited killing of intracellular L. chagasi in macrophages, although the phagocytosis-induced respiratory burst remained intact. In contrast, supraphysiologic concentrations of TGF-beta had no effect on parasite survival. We hypothesize that the combined effect of abundant TGF-beta stores at extracellular sites during infection, and the ability of the parasite to activate TGF-beta in its local environment, leads to high levels of active TGF-beta in the vicinity of the infected macrophage. Locally activated TGF-beta could, in turn, enhance parasite survival through its effects on innate and adaptive immune responses.

Biochemical and biological characterization of the protective Leishmania pifanoi amastigote antigen P-8

The Leishmania pifanoi amastigote antigen P-8 has been previously shown to induce protective immunity in a murine model of cutaneous leishmaniasis (L. Soong, S. M. Duboise, P. Kima, and D. McMahon-Pratt, Infect. Immun. 63:3559-3566, 1995). As this antigen is of interest for further vaccine studies, the biochemical characterization of P-8 was undertaken. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western-blot analysis, and gel filtration chromatography revealed that P-8 antigen consisted of two proteoglycolipid complexes. The P-8 epitope is associated with the L. pifanoi amastigote-specific glycolipid components found in the two complexes. The P-8 complex 1 (P-8c1) consists of a 56-kDa serine metalloproteinase, apolipoprotein E (derived from fetal bovine serum), and amastigote-specific glycolipids. The P-8 complex 2 (P-8c2) consists of a 31-kDa cysteine proteinase associated with amastigote glycolipids. Biochemical analyses suggest that the P-8 antigenic glycolipids may be distinct from previously described Leishmania glycolipids (glycosylinositol-phospholipids and sphingoglycolipids). Protective immunity studies revealed that P-8c1 (serine metalloproteinase-glycolipid complex) confers comparable protection against infection as immunopurified P-8. The isolated P-8c2 (cysteine proteinase-glycolipid complex) does not provide significant protection, nor does stimulation with P-8c2 result in significant T-cell activation in P-8- or P-8c2-vaccinated mice. Consequently, the P-8c1 complex appears to be the immunodominant component of P-8.

Detection of cysteine-proteinases in Leishmania amazonensis promastigotes using a cross-reactive antiserum

Rabbit serum against the cysteine-proteinases papain has been employed for the cellular localization of cysteine-proteinases of in Leishmania amazonensis promastigotes. By immunocytochemistry, immune complexes were found in the plasma membrane and in the flagella pocket of the parasite. The antiserum immunoprecipitated major iodinated proteins with molecular masses of 66, 45, 28 and 24 kDa and a wide partitioning of the Triton X-114 detergent phase. The presence of cysteine-proteinase at the cell surface membrane was also suggested by the detection of proteolytic activity in living cells (19.0 microg azocasein min(-1) 10(-7) promastigotes (1.0 S.D. )).

Cloning and expression of a cysteine proteinase gene from Paragonimus westermani adult worms

A gene encoding a cysteine proteinase from Paragonimus westermani has been cloned and expressed in Escherichia coli. The cysteine proteinase cDNA fragment was amplified by reverse transcription-polymerase chain reaction (RT-PCR) using degenerate oligonucleotide primers derived from the conserved active site of the cysteine proteinase. The 5' and 3' regions of the gene were amplified using a PCR technique for the rapid amplification of cDNA ends. The cloned gene has an open reading frame of 687 bp and deduced amino acid sequence of 229. Sequence analysis and alignment showed significant homologies with the eukaryotic cysteine proteinases and conservation of the Cys, His, and Asp residues that form a catalytic triad. Analysis of the expressed protein on sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that the molecular weight of the protein was approximately 28.5 kDa. The expressed protein reacted with the sera of patients with paragonimiasis but not with the sera of fascioliasis and clonorchiasis. These results suggest that the expressed protein may be valuable as a specific diagnostic material for the immunodiagnosis of paragonimiasis.

Mosquito cathepsin B-like protease involved in embryonic degradation of vitellin is produced as a latent extraovarian precursor

Here we report identification of a novel member of the thiol protease superfamily in the yellow fever mosquito, Aedes aegypti. It is synthesized and secreted as a latent proenzyme in a sex-, stage-, and tissue-specific manner by the fat body, an insect metabolic tissue, of female mosquitoes during vitellogenesis in response to blood feeding. The secreted, hemolymph form of the enzyme is a large molecule, likely a hexamer, consisting of 44-kDa subunits. The deduced amino acid sequence of this 44-kDa precursor shares high similarity with cathepsin B but not with other mammalian cathepsins. We have named this mosquito enzyme vitellogenic cathepsin B (VCB). VCB decreases to 42 kDa after internalization by oocytes. In mature yolk bodies, VCB is located in the matrix surrounding the crystalline yolk protein, vitellin. At the onset of embryogenesis, VCB is further processed to 33 kDa. The embryo extract containing the 33-kDa VCB is active toward benzoyloxycarbonyl-Arg-Arg-para-nitroanilide, a cathepsin B-specific substrate, and degrades vitellogenin, the vitellin precursor. Both of these enzymatic activities are prevented by trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane (E-64), a thiol protease inhibitor. Furthermore, addition of the anti-VCB antibody to the embryonic extract prevented cleavage of vitellogenin, strongly indicating that the activated VCB is involved in embryonic degradation of vitellin.

Proteases of protozoan parasites

Proteolytic enzymes seem to play important roles in the life cycles of all medically important protozoan parasites, including the organisms that cause malaria, trypanosomiasis, leishmaniasis, amebiasis, toxoplasmosis, giardiasis, cryptosporidiosis and trichomoniasis. Proteases from all four major proteolytic classes are utilized by protozoans for diverse functions, including the invasion of host cells and tissues, the degradation of mediators of the immune response and the hydrolysis of host proteins for nutritional purposes. The biochemical and molecular characterization of protozoan proteases is providing tools to improve our understanding of the functions of these enzymes. In addition, studies in multiple systems suggest that inhibitors of protozoan proteases have potent antiparasitic effects. This review will discuss recent advances in the identification and characterization of protozoan proteases, in the determination of the function of these enzymes, and in the evaluation of protease inhibitors as potential antiprotozoan drugs.

Fasciola hepatica: characterization and cloning of the major cathepsin B protease secreted by newly excysted juvenile liver fluke

Proteolytic activity present in the excreted/secreted (ES) material of newly excysted juvenile (NEJ) Fasciola hepatica was biochemically analyzed. By gelatin substrate SDS-PAGE, only one region of activity was observed in the NEJ ES material at a molecular mass of 29 kDa. Both the secreted cathepsin L from adult fluke and the 29-kDa proteolytic activity of NEJ ES show a common pH optimum of 7.5, a cysteine protease inhibition profile, and preference for the N-benzyloxycarbonyl (Z)-Phe-Arg-NHMec fluorogenic substrate over Z-Arg-Arg-NHMec and Z-Arg-NHMec. In vitro analysis revealed that the NEJ protease activity digested sheep immunoglobulin heavy chain and bovine serum albumin but not bovine hemoglobin. Amino-terminal protein sequence analysis of the 29-kDa NEJ protease band revealed two sequences with homology to the cathepsin B family of proteases. Using degenerate oligonucleotides designed from the N-terminal sequence, reverse transcriptase polymerase chain reaction with NEJ RNA amplified a cDNA sequence encoding the first 236 amino acids of mature cathepsin B. Using this cDNA fragment an overlapping cDNA was isolated from a LambadaZAP cDNA library constructed with poly(A)+ RNA from immature 5-week-old liver fluke. Together with the N-terminal sequence, these cDNAs predict a mature cathepsin B sequence of 254 amino acids which shows 48-51% sequence identity to mammalian and Schistosoma mansoni cathepsin B. We conclude that, in contrast to the major proteases released by adult fluke, the major secreted protease of NEJ of F. hepatica is of the cathepsin B class.

Specific in vitro cleavage of a Leishmania virus capsid-RNA-dependent RNA polymerase polyprotein by a host cysteine-like protease

Antibodies raised against baculovirus-expressed RNA-dependent RNA polymerase (RDRP) recognized a 95-kDa antigen and two smaller proteins in sucrose-purified Leishmania virus particles isolated from infected parasites. The 95-kDa antigen is similar in size to one predicted by translation of the RDRP open reading frame (ORF) alone. In an effort to reconcile in vitro observations of translational frameshifting on Leishmania RNA virus 1-4 transcripts, we have developed an in vitro cleavage assay system to explore the possibility that the fusion polyprotein is proteolytically processed. We show that coincubation a synthetic Cap-Pol fusion protein with lysates from Leishmania parasites yields major cleavage products similar in size to those encoded by the individual capsid and RDRP genes as well as the antigens detected in vivo. The major 82- and 95-kDa major cleavage products are specifically immunoprecipitated by capsid- or polymerase-specific antibodies, respectively, showing that cleavage occurs at or near the junction of the two functional domains. Protease inhibitor studies suggest that a cysteine-like protease is responsible for cleavage in the in vitro assay system developed here. From these results, we suggest that failure to detect a capsid-polymerase fusion protein produced by translational frameshifting in vivo may be due to specific proteolytic processing.

Leishmania major: molecular modeling of cysteine proteases and prediction of new nonpeptide inhibitors

The crystal structures of papain, cruzain, and human liver cathepsin B were used to build homology-based enzyme models of a cathepsin L-like cysteine protease (cpL) and a cathepsin B-like cysteine protease (cpB) from the protozoan parasite Leishmania major. Although structurally a member of the cathepsin B subfamily, the L. major cpB is not able to cleave synthetic substrates having an arginine in position P2. This biochemical property correlates with the prediction of a glycine instead of a glutamic acid at position 205 (papain numbering). The modeled active sites of the L. major cpB and cpL were used to screen the Available Chemicals Directory (a database of about 150,000 commercially available compounds) for potential cysteine protease inhibitors, using DOCK3.5. Based on both steric and force field considerations, 69 compounds were selected. Of these, 18 showed IC50's between 50 and 100 microM and 3 had IC50's below 50 microM. A secondary library of compounds, originally derived from a structural screen against the homologous protease of Plasmodium falciparum (falcipain), and subsequently expanded by combinatorial chemistry, was also screened. Three inhibitors were identified which were not only effective against the L. major protease but also inhibited parasite growth at 5-50 microM.

Cathepsin B-like cysteine proteinase-deficient mutants of Leishmania mexicana

Mutants null for the cathepsin B-like cysteine proteinase gene (cpc) of Leishmania mexicana have been generated by targeted gene disruption. The gene deletion was confirmed using a polymerase chain reaction (PCR) method with cpc-specific primers and genomic DNA isolated from the mutants. cpc was re-expressed in the null mutants from an episomal vector. Re-expression of the enzyme (CPC) was detected by Western blotting with a specific anti-peptide antiserum. The cpc null mutants grew apparently normally as promastigotes and amastigotes in axenic cultures, but they showed greatly reduced infectivity to macrophages in vitro with only a low percentage of the cells being infected. Re-expression of cpc in the null mutant increased the parasite's infectivity in vitro. The null mutant parasites formed lesions in mice at a similar rate as wild type parasites, although somewhat smaller lesions were produced. The results suggest that although the cysteine proteinase encoded by cpc plays a role in the parasite's interaction with macrophages it alone is not crucial for infectivity or virulence.

Leishmania major: comparison of the cathepsin L- and B-like cysteine protease genes with those of other trypanosomatids

Cysteine proteases play important roles in the pathogenesis of several parasitic infections and have been proposed as targets for the structure-based strategy of drug design. As a first step toward applying this strategy to design inhibitors as antiparasitic agents for leishmaniasis, we have isolated and sequenced the full-length clones of two cysteine protease genes from Leishmania major. One of the genes is structurally similar to the cathepsin L-like family and the other is similar to the cathepsin B-like family of cysteine proteases. The L. major cathepsin L-like sequence has a proregion that shares high sequence similarity with other cathepsin L sequences but not cathepsin B sequences and has a proline/threonine-rich C-terminal extension. The cathepsin L-like gene occurs in multiple copies, whereas there may be only one copy of the cathepsin B-like gene. Northern blot analyses show that both genes are expressed in the promastigote and amastigote stages, and pulse field gel electrophoresis revealed that the cathepsin L- and B-like genes are each found on two nonhomologous chromosomes. The L. major L-like amino acid sequence is 75% identical to the L. mexicana sequence, 74% identical to the L. pifanoi sequence, 47% identical with the Trypanosoma cruzi sequence, 47% identical with the T. congolense sequence, and 45% identical with the T. brucei sequence. L. major is one of two trypanosomatid species for which a cathepsin B-like gene has been identified and sequenced; its amino acid sequence is 82% identical to the one from L. mexicana. Tree inference based on distance and parsimony methods of kinetoplastid cathepsin L proteins yielded independent support for phylogenetic hypotheses inferred from analyses of ribosomal RNA genes. Because the cathepsin L locus has a high level of phylogenetic signal with respect to trypanosomatid taxa, this locus has great potential utility for investigating the evolutionary history of trypanosomatids and related organisms.

Evidence from disruption of the lmcpb gene array of Leishmania mexicana that cysteine proteinases are virulence factors

The mammalian form of the protozoan parasite Leishmania mexicana contains high activity of a cysteine proteinase (LmCPb) encoded on a tandem array of 19 genes (lmcpb). Homozygous null mutants for lmcpb have been produced by targeted gene disruption. All life-cycle stages of the mutant can be cultured in vitro, demonstrating that the gene is not essential for growth or differentiation of the parasite. However, the mutant exhibits a marked phenotype affecting virulence-- its infectivity to macrophages is reduced by 80%. The mutants are as efficient as wild-type parasites in invading macrophages but they only survive in a small proportion of the cells. However, those parasites that successfully infect these macrophages grow normally. Despite their reduced virulence, the mutants are still able to produce subcutaneous lesions in mice, albeit at a slower rate than wild-type parasites. The product of a single copy of lmcpb re-expressed in the null mutant was enzymatically active and restored infectivity toward macrophages to wild-type levels. Double null mutants created for lmcpb and lmcpa (another cathepsin L-like cysteine proteinase) have a similar phenotype to the lmcpb null mutant, showing that LmCPa does not compensate for the loss of LmCPb.

Sequence, characterization and localization of a cysteine proteinase cathepsin L in Schistosoma mansoni

A cDNA encoding Schistosoma mansoni cathepsin L was isolated from a cDNA library and sequenced. Alignment of the proposed amino-acid sequence with known members of cathepsin L shows highest homologies with sequences from mouse and rat. An expression plasmid was constructed in Escherichia coli to produce recombinant schistosome cathepsin L with an extension of six histidines at its N terminus. Using antibodies raised against the purified fusion protein, two polypeptide bands with approx. molecular masses of 38 and 31 kDa were identified in a schistosome extract. By use of specific radioiodinated inhibitors, a radioactively labeled protein could be detected at 31 kDa, suggesting that this is the active mature enzyme. The larger protein of 38 kDa did not react with the inhibitor, indicating that it represents the inactive precursor molecule. Immunohistological experiments revealed that the proteinase is localized in structures associated with the reproductive system of females and with the subtegumental region of the gynecophoric canal of males. However, Northern blot hybridization demonstrates that more transcripts are present in female parasites than in males. Genomic Southern blotting suggests that schistosome cathepsin L is expressed from a single-copy gene.

An initial characterization of the proteolytic enzymes secreted by the adult stage of the human hookworm Necator americanus

The proteolytic activities present in adult Necator americanus excretory-secretory products have been assessed using biologically relevant, naturally occurring substrates (haemoglobin and fibrinogen) and a number of synthetic fluorogenic and chromogenic substrates. One broad peak of activity was observed against haemoglobin in the pH range 5 to 7, with maximum activity at pH 6.6, while fibrinogenolytic activity was shown to be greater at pH 3.5. Inhibition studies against haemoglobin, fibrinogen and synthetic substrates using a battery of appropriate protease inhibitors indicated the presence of a mixture of aspartyl, cysteinyl and serine proteases. Metal ion (Ca2+, Zn2+ and Fe2+) stimulation was demonstrated, with stimulation by Zn2+ being the most marked. These results are discussed in the context of recent developments in the field of parasite proteolytic enzymes, where they have been suggested as targets for immuno- and chemotherapy.

Distribution of parasite cysteine proteinases in lesions of mice infected with Leishmania mexicana amastigotes

It is well established that Leishmania mexicana amastigotes contain large amounts of cysteine proteinases in their extended lysosomes. In this study it is shown that the cell-free supernatant of homogenized lesion tissue from infected mice contains large amounts of acid proteinases. The majority of this enzymatic activity also corresponds to cysteine proteinases from L. mexicana amastigotes. Immunoelectron microscopy of mouse lesion sections suggests, that frequently amastigotes lyse and release lysosomal cysteine proteinases into the parasitophorous vacuole of infected macrophages. The cysteine proteinases are also found extracellularly in the tissue presumably as a result of macrophage rupture and appear to persist in the lesion tissue, where they may damage host cells and the extracellular matrix.