Entamoeba histolytica and E. invadens: sulfhydryl-dependent proteolytic activity

Diagnostic parameters of serological ELISA for invasive amoebiasis, using antigens preserved without enzymatic inhibitors

Amoebiasis is the third cause of death due to parasites in the world. Although, numerous serodiagnostic and salivary tests have been developed, the majority of these assays lack sensitivity in endemic zones to detect acute amoebic liver abscess. The two main limiting factors to develop reliable assays are the high levels of anti-amoeba antibodies in populations living in endemic zones, and the proteolysis of amoebic extracts even treated with inhibitors. Our group reported a method to preserve amoebic antigens without using enzymatic inhibitors (IC:MC fraction) that shows stability for years. Here we describe the development of a serologic ELISA to diagnose amoebiasis made with IC: MC antigens, and its validation for clinical use in endemic areas. In our study, we included sera from 66 patients diagnosed with acute amoebic liver abscess and 33 volunteers living in an endemic area for amoebiasis. Our assay was compared with an indirect haemagglutination assay (IHA) an ELISA elaborated with antigens derived from untreated trophozoites. The ELISA made with IC: MC antigens presented more reproducibility compared to other assays. Sera from 95% ALA patients showed a positive value. The ELISA (IC: MC) detected 97% of patients with ALA compared to an 81% using IHA. The parameters of ELISA (vs. IHA) were Sensitivity 98% (81%), Specificity 96% (97%), Positive predictive value 98% (96%), Negative predictive value 96% (73%) and Accuracy 98% (87%). A negative serologic test does not rule out the diagnosis of invasive amoebiasis. The ELISA made with antigens preserved without using enzymatic inhibitors has valuable serodiagnostic value to diagnose acute amoebic liver abscess, even in populations living in endemic zones of amoebiasis carrying antibodies against amoebas. In conclusion, ELISA-IC:MC presented better diagnostic parameters than IHA although a negative serologic test does not rule out acute invasive amoebiasis.

Proteases from Entamoeba spp. and Pathogenic Free-Living Amoebae as Virulence Factors

The standard reference for pathogenic and nonpathogenic amoebae is the human parasite Entamoeba histolytica; a direct correlation between virulence and protease expression has been demonstrated for this amoeba. Traditionally, proteases are considered virulence factors, including those that produce cytopathic effects in the host or that have been implicated in manipulating the immune response. Here, we expand the scope to other amoebae, including less-pathogenic Entamoeba species and highly pathogenic free-living amoebae. In this paper, proteases that affect mucin, extracellular matrix, immune system components, and diverse tissues and cells are included, based on studies in amoebic cultures and animal models. We also include proteases used by amoebae to degrade iron-containing proteins because iron scavenger capacity is currently considered a virulence factor for pathogens. In addition, proteases that have a role in adhesion and encystation, which are essential for establishing and transmitting infection, are discussed. The study of proteases and their specific inhibitors is relevant to the search for new therapeutic targets and to increase the power of drugs used to treat the diseases caused by these complex microorganisms.

Proteinases of females of the phytoparasiteGlobodera pallida(potato cyst nematode)

Sensitive assays capable of detecting proteinases in single females of the phytoparasiteGlobodera pallidahave been developed and used to define the proteinase activity of young adult females. Digestion of the large subunit of the plant protein Rubisco established a pH optimum for the proteinase activity at pH 5·7. The activity was inhibited by the cysteine proteinase inhibitorsp-chloromercuribenzoic acid (PMBA) andp-chloromercurisulphonic acid (PMSA) and stimulated by both cysteine and dithiothreitol (DTT). It was moderately reduced by L-trans-epoxysuccinyl-leucylamido-(4- guanidino) butane (E64) but not by specific inhibitors of serine, aspartate or metallo-proteinases. The activity separated into 3 bands on a non-denaturing gel but only I proteinase of 62 kDa was recovered following a combination of anion-exchange chromatography and affinity chromatography using PMBA. The effect of inhibitors was similar to that reported previously for some of the cysteine proteinase activity recovered fromCaenorhabditis elegansbut is apparently not that for which the corresponding gene has been cloned in this nematode andHaemonchus contortus.The proteinase may have a major role in digestion of dietary protein and so offers an exciting target for future control of this important plant-parasitic nematode.

Preparation ofEntamoeba histolyticaantigens without enzymatic inhibitors

The goal of this work is to report a novel assay that preserves antigenicity of extracts with high protease content without using enzymatic inhibitors. A great reduction of proteolytic activity in the insoluble chloroform/methanol and heated amoebic fraction (IC[ratio ]MC) was obtained by this method, even in the presence of sodium dodecyl sulphate and 2-mercaptoethanol. The substrates azo-casein and the hide powder azure were used to determine the reduction of proteolytic activity of IC[ratio ]MC compared with the activity of crude extract and crude extract with iodoacetamide. The IC[ratio ]MC SDS-PAGE pattern shows a higher quantity of bands than extract with the inhibitor iodoacetamide or than crude extract. In addition, anti-Entamoeba histolyticaantibodies from amoebic liver abscess patients recognized a richer antigenic Western blot pattern in the IC[ratio ]MC fraction than in crude extract alone or with inhibitor. The described method has proved to be suitable to preserve amoebic antigens for its use in diagnostic tests and it can be used for immunological response studies againstE. histolyticaantigens. Furthermore we propose that this method to obtain the IC[ratio ]MC fraction can be applied for the study of other microorganisms or cells with high enzymatic content.

Proteinase inhibitors TPCK and TLCK prevent Entamoeba histolytica induced disturbance of tight junctions and microvilli in enteric cell layers in vitro

Tight junctions and microvilli constitute an anti-invasive barrier at the luminal side of enteric cell layers. Both subcellular structures are disrupted following adhesion of Entamoeba histolytica trophozoites to enteric cell layers in vitro. It was our aim to analyse the molecular mechanism underlying this disruption. Therefore, we cocultured enteric T84 cell layers established on filter inserts with E. histolytica trophozoites and tested various modulators of enteric molecules, involved in the functional regulation of tight junctions, as well as inhibitors of trophozoite virulence factors on their capacity to maintain the transepithelial electrical resistance. Pretreatment of trophozoites with the proteinase inhibitor N-Tosyl-Phenylalanine chloromethyl ketone or N-Tosyl-l-Lysine chloromethyl ketone prevented the decrease in transepithelial electrical resistance whereas none of the modulators used to pretreat enterocytes were successful. Moreover, zymography and Western blot analysis revealed that both N-Tosyl-Phenylalanine chloromethyl ketone and N-Tosyl-l-Lysine chloromethyl ketone inhibited E. histolytica cysteine proteinases and prevented proteolysis of tight junction molecules ZO-1 and ZO-2 and of villin, the major actin bundling molecule in microvilli. Immunocytochemistry with an antibody against ezrin, an actin-binding molecule in microvilli, and phase contrast microscopy demonstrated that pretreatment of trophozoites with N-Tosyl-Phenylalanine chloromethyl ketone or N-Tosyl-l-Lysine chloromethyl ketone also prevented disturbance of microvilli and destruction of Caco-2 enteric cell layers in cocultures. Taken together, our results indicate that trophozoites use their proteinases to overcome microvilli and tight junction barriers during the invasion of enteric cell layers, that these phenomena could be prevented by pretreatment of trophozoites with N-Tosyl-Phenylalanine chloromethyl ketone or N-Tosyl-l-Lysine chloromethyl ketone, and that such pretreatment disabled trophozoites to destroy enteric cell layers in vitro.

Pathogenesis of intestinal amebiasis: from molecules to disease

In spite of a wealth of knowledge on the biochemistry and cellular and molecular biology of Entamoeba histolytica, little has been done to apply these advances to our understanding of the lesions observed in patients with intestinal amebiasis. In this review, the pathological and histological findings in acute amebic colitis are related to the molecular mechanisms of E. histolytica pathogenicity described to date. Infection of the human colon by E. histolytica produces focal ulceration of the intestinal mucosa, resulting in dysentery (diarrhea with blood and mucus). Although a complete picture has not yet been achieved, the basic mechanisms involved in the production of focal lytic lesions include complex multifactorial processes in which lectins facilitate adhesion, proteases degrade extracellular matrix components, porins help nourish the parasite and may also kill incoming polymorphonuclear leukocytes and macrophages, and motility is used by the parasite to invade deeper layers of the colon. In addition, E. histolytica has developed mechanisms to modulate the immune response during acute infection. Nevertheless, much still needs to be unraveled to understand how this microscopic parasite has earned its well-deserved histolytic name.

Pathogenesis of intestinal amebiasis: from molecules to disease

In spite of a wealth of knowledge on the biochemistry and cellular and molecular biology of Entamoeba histolytica, little has been done to apply these advances to our understanding of the lesions observed in patients with intestinal amebiasis. In this review, the pathological and histological findings in acute amebic colitis are related to the molecular mechanisms of E. histolytica pathogenicity described to date. Infection of the human colon by E. histolytica produces focal ulceration of the intestinal mucosa, resulting in dysentery (diarrhea with blood and mucus). Although a complete picture has not yet been achieved, the basic mechanisms involved in the production of focal lytic lesions include complex multifactorial processes in which lectins facilitate adhesion, proteases degrade extracellular matrix components, porins help nourish the parasite and may also kill incoming polymorphonuclear leukocytes and macrophages, and motility is used by the parasite to invade deeper layers of the colon. In addition, E. histolytica has developed mechanisms to modulate the immune response during acute infection. Nevertheless, much still needs to be unraveled to understand how this microscopic parasite has earned its well-deserved histolytic name.

Purification and biochemical characterization of a novel cysteine protease of Entamoeba histolytica

Cysteine proteases are important virulence factors of Entamoeba histolytica, the causative agent of amoebiasis. A novel cysteine protease from parasite extracts was purified 15-fold by a procedure including concanavalin A-Sepharose, hydroxylapatite and DEAE-Sepharose chromatography. The purification resulted in the obtainment of an homogeneous protein with a molecular mass of 66 kDa on native PAGE. In 10% SDS/PAGE, three bands of 60, 54 and 50 kDa were evident. Each of the three specific mouse antisera raised against these proteins showed cross-reactivity with the three bands obtained from the purified eluate. The N-terminal sequencing of the first 10 amino acids from the three proteins showed 100% identity. These results support the hypothesis of a common precursor for the 60, 54 and 50-kDa proteins. Protease activity of the purified enzyme was demonstrated by electrophoresis in a gelatine-acrylamide copolymerized gel. Its activity was quantified by cleaving a synthetic fluorogenic peptide substrate such as N-carbobenzyloxy-arginyl-arginyl-7-amido-4-methylcoumarin. The optimum pH for the protease activity was 6.5; however, enzymatic activity was observed between pH 5 and pH 7.5. Typical of cysteine proteases, the enzyme was inhibited by 4-[(2S, 3S)-carboxyoxiran-2-ylcarbonyl-L-leucylamido]butylg uanidine and iodoacetamide, and activated by free sulfhydryl groups. The cellular location of the enzyme was examined on trophozoites before and after contact with red blood cells using indirect immunofluorescence and cellular fractionation. The 60-kDa cysteine protease translocated to the amoebic surface upon the interaction of trophozoites with red blood cells. This result provided evidence for participation of the 60-kDa protease in erythrophagocytosis.

Specific and reversible inhibition of Entamoeba histolytica cysteine-proteinase activities by Zn2+: implications for adhesion and cell damage

BACKGROUND

Cysteine-proteinases are thought to play an important role in E. histolytica pathogenicity. Although effective blockage of proteolytic activities can be obtained with several known inhibitors, the high cellular toxicity of most of the inhibitors precludes experimentation with live cells or animal models. Specific cysteine-proteinase inhibitors that could be utilized in studies of virulence are of great need in the field of amebiasis.

METHODS

Cysteine-proteinase activities were determined in trophozoite lysates by azocasein degradation and after PAGE and gelatin zymograms. Inhibition of the activities was assessed in the presence of 0.01-2.5 mM concentrations of divalent cations of the IIB and VIII series such as Zn, Cd, Hg, Ni, and Co. Reversibility was induced with 25 mM L-cysteine or 50 mM L-histidine and by metal chelation with 5 mM phenantroline. The inhibitory effect of ZnCl2 was tested with live cells in fibronectin-binding and cytotoxicity assays.

RESULTS

ZnCl2 specifically inhibited cysteine-proteinase activities in trophozoite lysates in a concentration-dependent manner. Additionally, 1.0-2.5 mM ZnCl2 blocked proteolysis in more than 70%. This inhibition was completely reverted by L-cysteine, L-histidine, or phenantroline. Similar results were obtained by analyzing individual cysteine-proteinase activities separated in gelatin zymograms. At these concentrations, ZnCl2 significantly interfered with trophozoite adhesion, thus making amebas deficient in substrate degradation and cell damage.

CONCLUSIONS

ZnCl2 is an effective inhibitor of amebic cysteine-proteinases. Its low toxicity at relatively high concentrations, high solubility, and low cost make it adequate for live cell experimentation and animal models of amebic virulence.

Pathogenic action of Entamoeba invadens: intestinal epithelium invasion by trophozoites in vitro

Interactions between live Entamoeba invadens trophozoites and guinea-pig caecal explants were studied. A high percentage of amoebae adhering to the apical surface of epithelial cells was observed 10-20 min after infection, but no histopathological changes were observed. After 30 min, mild oedema at the base of the interglandular epithelium and death of some epithelial cells were evident. The epithelial barrier was invaded by amoebae at desquamating zones and phagocytosis of epithelial cells or cellular debris was occasionally observed. Invasion of the mucosa and tissue necrosis became more severe with increased time of incubation. The continuity of epithelial lining was severely compromised after 2 h of infection and erosive lesions were prominent in the mucosa. These results demonstrate that E. invadens is able to invade the intestinal epithelium although it reportedly lacks the powerful cytotoxic and cytolytic elements described for E. histolytica.

Proteolytic activity in extracts of invasive cervical carcinoma and precursor lesions

In this preliminary report, we showed that proteolytic activity of extracts from 85 cervical samples of patients with normal cervix, low and high-grade squamous intra-epithelial lesions and invasive carcinoma, increased according to the natural history of the cervical cancer when measured with three different substrates. Inhibitor assays for four different catalytic classes of endopeptidases indicated that the predominant catalytic class in extracts of all groups was that of metalloproteinases. Substrate gel electrophoresis revealed that invasive carcinoma extracts had two bands with proteolytic activity (with M(r) of 72 and 52 kDa) which were not present in normal tissue or biopsies with precursor lesions. Immunological and molecular characterization of these bands may provide information relevant to cervical cancer biology and clinical applications.

Coding of hemolysins within the ribosomal RNA repeat on a plasmid in Entamoeba histolytica

The pathogenesis of amoebic dysentery is a result of cytolysis of the colonic mucosa by the parasitic protozoan Entamoeba histolytica. The cytolysis results in extensive local ulceration and allows the amoeba to penetrate and metastasize to distant sites. Factors involved in this process were defined with three clones that express hemolytic activities in Escherichia coli. These potential amoebic virulence determinants were also toxic to human colonic epithelial cells, the primary cellular targets in amoebal invasion of the large intestine. The coding sequences for the hemolysins were close to each other on a 2.6-kilobase segment of a 25-kilobase extrachromosomal DNA element. The structural genes for the hemolysins were within inverted repeats that encode ribosomal RNAs.

Purification and immunologic characterization of a 30-kDa cysteine proteinase of Entamoeba histolytica

A 30-kDa cysteine proteinase was purified from extracts of axenically grown trophozoites of Entamoeba histolytica strain HM1:IMSS. The purification procedure involved two consecutive chromatographic steps. Sequence analysis revealed high similarity with histolysin and with other 27-kDa cysteine proteinase. Western-blot analysis using F(ab')2 fragments of a polyclonal antibody raised against the purified enzyme revealed that when the amebic extract was prepared in the absence of proteinase inhibitors there were many positive bands ranging in relative molecular weight from 115 to 12.5 kDa, but when the extract was prepared in the presence of proteinase inhibitors there was only a single 30-kDa positive band. Similar results were obtained with immunoprecipitates. This phenomenon would suggest the formation of multimer aggregates of the 30-kDa cysteine proteinase after partial proteolysis.

Structural analysis and demonstration of the 29 kDa antigen of pathogenic Entamoeba histolytica as the major accessible free thiol-containing surface protein

The 29 kDa protein of pathogenic Entamoeba histolytica is a cysteine-rich surface antigen which we recently characterized by cDNA sequencing and by using monoclonal antibodies which differentiated between pathogenic and non-pathogenic clinical isolates. To determine the structure and biochemical attributes of this protein, a repertoire of immunological techniques using monoclonal antibodies, and radiolabelling were employed. We demonstrated that the 29 kDa protein forms a 60 kDa dimer and a high-molecular-mass oligomer(s) on the surface of the organism through disulphide bonds, and is the major accessible free thiol-containing surface protein of E. histolytica. The deduced amino acid sequence encoding the 29 kDa protein was found to share a common amino acid domain with sequences reported for Helicobacter pylori, Salmonella typhimurium, MER5 gene expressed in murine erythroleukemia cells, Clostridium pasteurianum, and a Bacillus spp.

Expression of sequences related to c-myc in Entamoeba

The evolutionarily conserved proto-oncogene c-myc is involved in both proliferation and differentiation processes of higher eukaryotic cells. We report here the identification and characterization of sequences homologous to c-myc in different Entamoeba species using a fragment of the mammalian c-myc gene as a probe. This probe hybridized with fragments of 3.5 and 3.4 kilobases (kb) in E. histolytica HindIII of EcoRI digested DNA. In E. invadens it recognized fragments of 3.1 and 2.8 kb, and in Laredo strain (reported as E. moshkovskii by Clark and Diamond in 1991) the probe hybridized with fragments of 17 kb. The c-myc probe identified transcripts of 3.3 and 1.5 kb in E. histolytica, transcripts of 1.8 and 1.3 kb in Laredo strain, and transcripts of 3.7, 1.8, 1.5 and 1.1 kb in E. invadens. Antibodies against a highly conserved region of the c-myc protein recognized in E. histolytica polypeptides of 35, 40, and 60 kDa. The expression of the 60 kDa polypeptide was temperature-inducible in Laredo strain. In E. invadens a 110 kDa strong band was detected by the antibodies. Surprisingly, E. invadens myc-like sequences and proteins showed greater homology to mammalian c-myc gene and proteins. Expression of proteins antigenically related to c-myc varied according to the cell cycle phase of E. histolytica. These proteins peaked during D, G1, and S phases and declined during G2.

Cytotoxic and hemolytic effects of Tritrichomonas foetus on mammalian cells

Geographically distinct lines of Tritrichomonas foetus were assayed for their ability to cause cytotoxicity in nucleated mammalian cells and lysis of bovine erythrocytes. T. foetus was highly cytotoxic toward a human cervical cell line (HeLa) and early bovine lymphosarcoma (BL-3) but displayed low levels of cytotoxicity against African green monkey kidney (Vero) cells. In addition to variation in the extent of cytotoxicity toward different targets, differences in the levels of cytotoxicity in the same nucleated target occurred with different parasite lines. Whole T. foetus, unfractionated whole-cell extracts, and parasite-conditioned medium (RPMI 1640 without serum) all caused lysis of bovine erythrocytes. Lytic activity in the conditioned medium was substantially reduced by repeated freezing and thawing or heating to 90 degrees C for 30 min. Damage of mammalian target cells by live T. foetus could be reduced by the presence of protease inhibitors; however, such inhibitors did not diminish the lytic effects of conditioned medium. These results suggested that proteolytic enzymes were necessary for the lytic mechanism of the live parasites but were not required once lytic factors were released into the parasite-conditioned medium. They further suggested that the lytic molecules were either proteins or had proteinaceous components.

Characterization of proteases of Toxoplasma gondii

The proteases of Toxoplasma gondii were purified partially and characterized for some biochemical properties including various chromatographic patterns, major catalytic classes, and conditions to promote the activity of these enzymes. When Toxoplasma extract was incubated with 3H-casein at various pH, peak hydrolysis of casein was observed at pH 6.0 and at pH 8.5. Proteases working at pH 6.0 and at pH 8.5 were purified partially by conventional methods of chromatographies of DE52 anion exchange, Sephadex G-200 gel permeation, and hydroxylapatite chromatography. Partially purified enzymes were tested by site-specific inhibitors and promotors. The protease working at pH 6.0 was inactivated by iodoacetamide with LD50 of 10(-3) M and promoted by dithiothreitol, while the protease working at pH 8.5 was inhibited by phenylmethylsulfonyl fluoride with LD50 of 10(-5) M and was promoted by ATP (excess ATP beyond 2 mM inhibited the activity reversely). The protease of pH 8.5 had the activity of ATPase which might exert the energy to its action. Therefore the former was referred to as a cysteinyl acid protease and the latter, ATP-dependent neutral serine protease.

Specificity of a cysteine proteinase of Entamoeba histolytica against various unblocked synthetic peptides

The activity of highly purified cysteine proteinase of Entamoeba histolytica against different peptides of the sequence X-Gly-Phe-Phe was compared. The synthetic peptide Arg-Gly-Phe-Phe of the insulin B-chain was readily hydrolyzed yielding Arg-Gly and Phe-Phe as split products. Lys-Gly-Phe-Phe and Tyr-Gly-Phe-Phe were cleaved at rates of 20 and 4%, respectively. Val-Gly-Phe-Phe, Gly-Gly-Phe-Phe, Glu-Gly-Phe-Phe, and Ser-Gly-Phe-Phe were hydrolyzed at rates far below 1%. Gly-Arg-Phe-Phe, Gly-Phe-Phe, and Gly-Phe were completely resistant to the enzyme. Another good substrate was found in Arg-Gly-Leu-Hyp, which represents a model compound of a scissile site in collagen type I. Furthermore, peptide Arg-Arg-Phe-Phe was attacked by the enzyme releasing Arg-Arg and Phe-Phe. Compared with Arg-Gly-Phe-Phe at substrate concentrations of 2 mM the rates of hydrolysis of Arg-Arg-Phe-Phe and Arg-Gly-Leu-Hyp were 37 and 127%. The enzyme exhibited dipeptidyl peptidase activity against the nonapeptide Arg-Gly-Phe-Phe-Tyr-Thr-Pro-Lys-Ala releasing Arg-Gly.

Proteinases of Entamoeba histolytica associated with different subcellular fractions

Crude lysates of Entamoeba histolytica (strain HM 1:IMSS) analyzed by substrate gel electrophoresis in 12.5% acrylamide separating gels with reducing agents showed six hydrolysis zones with apparent molecular weights of 73,000 (high), 45,000, 36,000 (intermediate), 30,000, 26,000 and 23,000 (low molecular weight proteinases). Amebic lysates fractionated using the procedure of Aley et al. or the procedure of Rosenberg and Gitler and analyzed by the same method show all enzymes in the fractions with the soluble components and only the intermediate and low molecular weight proteinases in the fraction containing internal vesicles or membranes and plasma membrane. Some of these proteinases seem to be integral membrane proteins since they resist treatment with high salt, high urea buffer. All fractions are capable of digesting azocasein. Fractionation of amebic lysates by hydrophobic chromatography using phenyl-Sepharose or phase separation of amebic extracts with Triton X-114 show that proteinases with high, intermediate and low molecular weight behave as hydrophilic proteins while only proteinases of intermediate and low molecular weight behave as hydrophobic proteins. These results suggest that some proteinases are segregated in different compartments of the cell.

Entamoeba histolytica: role of amebic proteinases and polymorphonuclear leukocytes in acute experimental amebiasis in the rat

The injection of 1 x 10(6) trophozoites of axenically grown Entamoeba histolytica strain HM-1 in the subcutaneous tissue of the rat results in an acute and self-limited inflammatory process, characterized by the early onset of conspicuous tissue necrosis and focal hemorrhage in the vicinity of the parasites, followed by infiltration with polymorphonuclear leukocytes. The process develops for 5-10 hr but during that period amebic trophozoites progressively disappear, leukocytes undergo degenerative changes, and the lesion tends to heal in 72-96 hr. In leukopenic animals (less than 1000 white blood cells/ml) tissue necrosis and hemorrhage are equally conspicuous in the neighborhood of amebas. Inhibition of amebic proteinase activity prior to injection by heat denaturation, p-hydroxy-mercuri-benzoate (PHMB), soybean trypsin inhibitor (STI), and human alpha-2-macroglobulin (alpha 2M), alone or in various combinations, results in absence or notorious decrease in tissue necrosis as well as in clearly diminished inflammatory reaction. This effect is particularly evident when cysteine proteinases are either specifically or generally inhibited. On the other hand, amebic proteinase inhibition with alpha 2M and STI does not interfere with the cell-killing capacity of trophozoites co-incubated in vitro for 2 hr with rat peritoneal cells enriched for macrophages. We conclude that in acute experimental amebiasis produced in the subcutaneous tissue of the rat, amebic cysteine (and perhaps other) proteinases are primarily responsible for necrosis and are also important, but not essential, for inflammation. We also suggest that in this model polymorphonuclear leukocytes are not required for tissue necrosis. Finally, in an in vitro model, the cell-killing capacity of amebas is not influenced by the proteinase activity of the parasite.

Affinity purification and biochemical characterization of histolysin, the major cysteine proteinase of Entamoeba histolytica

We report a one-step method for the purification to homogeneity of a cysteine proteinase of Entamoeba histolytica (histolysin) by affinity chromatography of the soluble extract of the parasite on immobilized phenylalanyl(2-phenyl)aminoacetaldehyde semicarbazone. The enzyme has an apparent Mr of 26,000 by SDS/polyacrylamide-gel electrophoresis and 29,000 by gel chromatography. Its pH optimum varies widely, from 5.5 with azocasein to approx. 7 with other protein substrates and benzyloxycarbonylphenylalanyl-L-citrullylaminomethylcourmarin++ + (Z-Phe-Cit-NHMec), and to 9.5 with benzyloxycarbonylphenylalanylarginylaminomethylcoumarin (Z-Phe-Arg-NHMec) and benzyloxycarbonylarginylarginylaminomethylcourmarin (Z-Arg-Arg-NHMec). Values of Km, kcat. and kcat/Km are 1.5 microM, 130 s-1 and 87 X 10(6) M-1.s-1 for Z-Arg-Arg-NHMec, and 32 microM, 0.4 s-1 and 0.012 x 10(6) M-1.s-1 for Z-Phe-Arg-NHMec, respectively, at pH 7.5 and 37 degrees C. The enzyme is inhibited by leupeptin and such inhibitors of cysteine proteinases as L-transepoxysuccinyl-L-leucylamido-4-(guanidino)butane, peptidyldiazomethanes, iodoacetic acid and chicken cystatin. The tentative N-terminal amino acid sequence of the enzyme closely resembles that of papain. Histolysin does not degrade type I collagen or elastin, but it is active against cartilage proteoglycan and kidney glomerular basement-membrane collagen. It also detaches cells from their substratum in vitro, and could well play a role in tissue invasion.

Catalytic classes of proteinases of Entamoeba histolytica

Endopeptidase inhibitors were used to determine the catalytic classes of proteinases present in extracts of Entamoeba histolytica (strain HM 1:IMSS) axenically grown in vitro. Cysteine proteinases account for most of the proteolytic activity; one or more proteinases with different catalytic mechanisms are also present but could not be unambiguously assigned to a particular catalytic class. Proteinases in amebic lysates were resolved by polyacrylamide gel electrophoresis with sodium dodecyl sulfate. The detergent was exchanged with Triton X-100 and the proteolytic activity in the gels was demonstrated by overlaying it on another gel containing the substrate. Four lysis zones were observed corresponding to molecular weights of 66,000, 56,000, 40,000 and 27,000. The first cannot be classified yet, but the last three showed properties consistent with those of cysteine proteinases. Finally, a novel technique is described which uses purified human alpha-2-macroglobulin to trap, purify and characterize proteases from amebic lysates. The results obtained with this technique confirm those of the overlay technique, since both methods reveal four distinct proteinases in the two different amebic preparations examined.

The major neutral proteinase of Entamoeba histolytica

FPLC anion-exchange and chromatofocusing chromatography were used to purify the major neutral proteinase from secretions of axenically cultured Entamoeba histolytica trophozoites. HM-1 strain trophozoites, which were more proteolytically active than the less virulent HK-9 strain, were used for purification of the enzyme. It is a thiol proteinase with a subunit Mr of approximately 56,000, a neutral pH optimum, and a pI of 6. The importance of this enzyme in extraintestinal amoebiasis is suggested by its ability to degrade a model of connective tissue extracellular matrix as well as purified fibronectin, laminin, and type I collagen. The enzyme caused a loss of adhesion of mammalian cells in culture, probably because of its ability to degrade anchoring proteins. Experiments with a peptide substrate and inhibitors indicated that the proteinase preferentially binds peptides with arginine at P-1. It is also a plasminogen activator, and could thus potentiate host proteinase systems.