Catalytic classes of proteinases of Entamoeba histolytica

Extracellular Cysteine Proteases of Key Intestinal Protozoan Pathogens-Factors Linked to Virulence and Pathogenicity

Intestinal diseases caused by protistan parasites of the genera Giardia (giardiasis), Entamoeba (amoebiasis), Cryptosporidium (cryptosporidiosis) and Blastocystis (blastocystosis) represent a major burden in human and animal populations worldwide due to the severity of diarrhea and/or inflammation in susceptible hosts. These pathogens interact with epithelial cells, promoting increased paracellular permeability and enterocyte cell death (mainly apoptosis), which precede physiological and immunological disorders. Some cell-surface-anchored and molecules secreted from these parasites function as virulence markers, of which peptide hydrolases, particularly cysteine proteases (CPs), are abundant and have versatile lytic activities. Upon secretion, CPs can affect host tissues and immune responses beyond the site of parasite colonization, thereby increasing the pathogens' virulence. The four intestinal protists considered here are known to secrete predominantly clan A (C1- and C2-type) CPs, some of which have been characterized. CPs of Giardia duodenalis (e.g., Giardipain-1) and Entamoeba histolytica (EhCPs 1-6 and EhCP112) degrade mucin and villin, cause damage to intercellular junction proteins, induce apoptosis in epithelial cells and degrade immunoglobulins, cytokines and defensins. In Cryptosporidium, five Cryptopains are encoded in its genome, but only Cryptopains 4 and 5 are likely secreted. In Blastocystis sp., a legumain-activated CP, called Blastopain-1, and legumain itself have been detected in the extracellular medium, and the former has similar adverse effects on epithelial integrity and enterocyte survival. Due to their different functions, these enzymes could represent novel drug targets. Indeed, some promising results with CP inhibitors, such as vinyl sulfones (K11777 and WRR605), the garlic derivative, allicin, and purified amoebic CPs have been obtained in experimental models, suggesting that these enzymes might be useful drug targets.

Hemoglobin uptake and utilization by human protozoan parasites: a review

The protozoan disease is a major global health concern. Amoebiasis, leishmaniasis, Chagas disease, and African sleeping sickness affect several million people worldwide, leading to millions of deaths annually and immense social and economic problems. Iron is an essential nutrient for nearly all microbes, including invading pathogens. The majority of iron in mammalian hosts is stored intracellularly in proteins, such as ferritin and hemoglobin (Hb). Hb, present in blood erythrocytes, is a very important source of iron and amino acids for pathogenic microorganisms ranging from bacteria to eukaryotic pathogens, such as worms, protozoa, yeast, and fungi. These organisms have developed adequate mechanisms to obtain Hb or its byproducts (heme and globin) from the host. One of the major virulence factors identified in parasites is parasite-derived proteases, essential for host tissue degradation, immune evasion, and nutrient acquisition. The production of Hb-degrading proteases is a Hb uptake mechanism that degrades globin in amino acids and facilitates heme release. This review aims to provide an overview of the Hb and heme-uptake mechanisms utilized by human pathogenic protozoa to survive inside the host.

Rabeprazole inhibits several functions of Entamoeba histolytica related with its virulence

Amoebiasis is a human parasitic disease caused by Entamoeba histolytica. The parasite can invade the large intestine and other organs such as liver; resistance to the host tissue oxygen is a condition for parasite invasion and survival. Thioredoxin reductase of E. histolytica (EhTrxR) is a critical enzyme mainly involved in maintaining reduced the redox system and detoxifying the intracellular oxygen; therefore, it is necessary for E. histolytica survival under both aerobic in vitro and in vivo conditions. In the present work, it is reported that rabeprazole (Rb), a drug widely used to treat heartburn, was able to inhibit the EhTrxR recombinant enzyme. Moreover, Rb affected amoebic proliferation and several functions required for parasite virulence such as cytotoxicity, oxygen reduction to hydrogen peroxide, erythrophagocytosis, proteolysis, and oxygen and complement resistances. In addition, amoebic pre-incubation with sublethal Rb concentration (600 μM) promoted amoebic death during early liver infection in hamsters. Despite the high Rb concentration used to inhibit amoebic virulence, the wide E. histolytica pathogenic-related functions affected by Rb strongly suggest that its molecular structure can be used as scaffold to design new antiamoebic compounds with lower IC₅₀ values.

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.

Use and endocytosis of iron-containing proteins by Entamoeba histolytica trophozoites

Iron is essential for nearly all organisms; in mammals, it is part of proteins such as haemoglobin, and it is captured by transferrin and lactoferrin. Transferrin is present in serum, and lactoferrin is secreted by the mucosa and by neutrophils at infection sites, as a host iron-withholding response, sequestering iron away from invading microorganisms. Additionally, all cells contain ferritin, which sequesters iron when its intracellular levels are increased, detoxifying and preventing damage. Liver ferritin contains 50% of iron corporal reserves. During evolution, pathogens have evolved diverse strategies to obtain iron from their hosts in order to survive. The protozoan Entamoeba histolytica invades the intestinal mucosa, causing dysentery, and the trophozoites often travel to the liver producing hepatic abscesses; thus, intestine and liver proteins could be important iron supplies for E. histolytica. We found that E. histolytica trophozoites can grow in both ferrous and ferric iron, and that they can use haemoglobin, holo-transferrin, holo-lactoferrin, and ferritin as in vitro iron sources. These proteins supported the amoeba growth throughout consecutive passages, similarly to ferric citrate. By confocal microscopy and immunoblotting, iron-binding proteins were observed specifically bound to the amoeba surface, and they were endocytosed, trafficked through the endosomal/lysosomal route, and degraded by neutral and acidic cysteine-proteases. Transferrin and ferritin were mainly internalized through clathrin-coated vesicles, and holo-lactoferrin was mainly internalized by caveola-like structures. In contrast, apo-lactoferrin bound to membrane lipids and cholesterol, inducing cell death. The results suggest that in vivo trophozoites secrete products that can destroy enterocytes, erythrocytes, and hepatocytes, releasing transferrin, haemoglobin, ferritin, and other iron-containing proteins, which, together with lactoferrin derived from neutrophils and acinar cells, could be used as abundant iron supplies by amoebas.

Entamoeba histolytica: oxygen resistance and virulence

Entamoeba histolytica virulence has been attributed to several amoebic molecules such as adhesins, amoebapores and cysteine proteinases, but supporting evidence is either partial or indirect. In this work we compared several in vitro and in vivo features of both virulent E. histolytica (vEh) and non-virulent E. histolytica (nvEh) axenic HM-1 IMSS strains, such as complement resistance, proteinase activity, haemolytic, phagocytic and cytotoxic capacities, survival in mice caecum, and susceptibility to O(2). The only difference observed was a higher in vitro susceptibility of nvEh to O(2). The molecular mechanism of that difference was analyzed in both groups of amoebae after high O(2) exposure. vEh O(2) resistance correlated with: (i) higher O(2) reduction (O(2)(-) and H(2)O(2) production); (ii) increased H(2)O(2) resistance and thiol peroxidase activity, and (iii) reversible pyruvate: ferredoxin oxidoreductase (PFOR) inhibition. Despite the high level of carbonylated proteins in nvEh after O(2) exposure, membrane oxidation by reactive oxygen species was not observed. These results suggest that the virulent phenotype of E. histolytica is related to the greater ability to reduce O(2) and H(2)O(2) as well as PFOR reactivation, whereas nvEh undergoes irreversible PFOR inhibition resulting in metabolic failure and amoebic death.

Entamoeba histolytica: apoptosis induced in vitro by nitric oxide species

Apoptosis has been described in some parasites like Leishmania, Trypanosoma, and Trichomonas. This phenomenon has not been observed yet in Entamoeba histolytica. This work analyzed the in vitro effect of sodium nitroprusside, sodium nitrite and sodium nitrate (NOs) on E. histolytica apoptosis. Parasites incubated for 1h with NOs revealed apoptosis 6h later (95% viability), demonstrated by YOPRO-1, TUNEL, DNA fragmentation and low ATP levels. The caspase inhibitor Z-VAD-FMK inhibited total intracellular cysteine protease activity (CPA) but had no effect on apoptosis. When treated with NOs some amebic functions like complement resistance and hemolytic activity decreased but CPA and erythrophagocytosis remained unchanged. After treatment in vitro with NOs, parasite death was almost complete at 24h; but when injected into hamster livers they disappeared in less than 6h. These results show that apoptosis is induced in vitro by NOs in E. histolytica and renders them incapable of surviving in hamster's livers.

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.

Cysteine proteinases of parasitic protozoa

Proteinases are involved with many processes in living organisms. In recent years, there has been increasing interest in elucidating the functions the enzymes perform in parasites. These studies have revealed that one class of proteinases, the cysteine proteinases, predominates in many parasitic protozoa. In this article Mick North, Jeremy Mottram and Graham Coombs review what is known about the cysteine proteinases of parasitic protozoa and discuss the approaches being pursued in attempts to design antiparasite drugs based on inhibitors or substrates of these enzymes.

Entamoeba histolytica: correlation of assessment methods to measure erythrocyte digestion, and effect of cysteine proteinases inhibitors in HM-1:IMSS and HK-9:NIH strains

Entamoeba histolytica trophozoites are able to degrade human erythrocytes; the loss of erythrocyte cellular matrix and degradation of plasma membrane were observed, along with the decrease in the average size of digestive vacuoles. Ninety-six percent of hemoglobin ingested was hydrolyzed by trophozoites within 3h, as evidenced by electrophoresis. Accordingly, X-ray spectroscopy revealed the presence of iron inside vacuoles after erythrophagocytosis, the concentration of which decreased to control levels in a similar period. Quantification of erythrocyte digestion at the early and late periods was determined by a spectrophotometric procedure, with t(1/2)=1.67 h and 35-min for HM-1:IMSS and HK-9:NIH trophozoites, respectively. In the latter, activity was due to the combined action of intracellular enzymatic activity and exocytosis. E-64c and leupeptin totally inhibited erythrocyte digestion within a 3-h period, thereafter hydrolysis took place at lower rate. Our results suggest that erythrocyte digestion in E. histolytica proceeds in different ways in these two amebic strains, and can be blocked by proteinase inhibitors.

Cysteine proteinase activity is required for survival of the parasite in experimental acute amoebic liver abscesses in hamsters

Axenic trophozoites of Entamoeba histolytica strain HM1-IMSS grown in vitro in the presence of E-64, a potent irreversible inhibitor of cysteine proteinases, preserved their viability, their rate of replication, their resistance to complement, their haemolytic capacity and their ability to destroy target cells, despite complete inhibition of total cysteine proteinase activity. On the other hand, their erythrophagocytic capacity and their ability to decrease TER of MDCK cells was partially decreased. The same trophozoites injected into the portal vein of hamsters receiving a maintaining dose of E-64 failed to cause tissue damage and were rapidly eliminated. Our results suggest that amoebic cysteine proteinase activity is not required for amoebic functions in in vitro conditions, but that it becomes necessary for survival of trophozoites in in vivo conditions, whatever other role (if any) it may play in the parasite's virulence.

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.

Amebic cysteine proteinase 2 (EhCP2) plays either a minor or no role in tissue damage in acute experimental amebic liver abscess in hamsters

Amebic cysteine protease 2 (EhCP2) was purified from ethyl ether extracts of axenically grown trophozoites of Entamoeba histolytica strain HM1-IMSS. The purification procedure involved molecular filtration and electroelution. Sequence analysis of the purified product revealed EhCP2 and ubiquitin(s). Electrophoretic migration patterns, isoelectric point determination and Western blot studies failed to reveal other EhCP molecules. Polyclonal antibodies against the purified EhCP2 prepared in rabbits either stabilized or enhanced the enzyme activity in a dose-response manner. Purified EhCP2 was enclosed within inert resin microspheres (22-44 microm in diameter) and injected into the portal vein of normal hamsters. In the liver, the microspheres caused mild acute inflammation and occasional minimal necrosis of short duration. Sections of the liver were immunohistochemically stained with the anti-EhCP2 antibody and the microspheres were positive for only a very short period (1 h) after injection. Sections of experimental acute (1 day, 5 days) amebic liver abscess produced in hamsters were also stained with the anti-EhCP2 antibody; and amebas were intensely positive but no staining was observed at any time in the surrounding necrotic structures. It is suggested that EhCP2 plays either a minor or no role in the causation of tissue damage in experimental acute liver amebiasis.

Entamoeba histolytica cysteine proteinases disrupt the polymeric structure of colonic mucin and alter its protective function

The adherent mucous gel layer lining the colonic epithelium is the first line of host defense against invasive pathogens, such as Entamoeba histolytica. The mucous layer prevents the attachment of amoeba to the colonic epithelium by trapping and aiding in the expulsion of the parasite. Disruption of the mucous layer is thought to occur in invasive amebiasis, and the mechanism by which the parasite overcomes this barrier is not known. The aim of this study was to characterize the specific interactions occurring between E. histolytica secreted cysteine proteinases and colonic mucin as a model to examine the initial events of invasive amebiasis. E. histolytica secreted products were examined for mucinase activity utilizing mucin metabolically labeled with [(35)S]cysteine as a substrate. Cysteine proteinases degraded mucin in a time- and dose-dependent manner. A significant reduction (>50%) in high-molecular-weight mucin with altered buoyant density was observed when degraded mucin was analyzed by Sepharose 4B column chromatography, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography, and CsCl density gradient centrifugation. Mucinase activity was eliminated by the specific cysteine protease inhibitor trans-epoxysuccinyl-L-leucylamido-(4-guanidino)butane and was independent of glycosidase activity. Moreover, the degraded mucin was 38% less effective than native mucin at inhibiting amebic adherence to target epithelial cells. These results are the first to show that E. histolytica cysteine proteinases alter the protective function of the mucous barrier by disrupting the structure of the MUC2 polymer. Mechanistically, the parasite achieves this via proteolytic degradation of the terminal cysteine-rich domains.

Cholestasis-induced fibrosis is reduced by interferon alpha-2a and is associated with elevated liver metalloprotease activity

BACKGROUND/AIM

Several drugs have been tested for the treatment of hepatic cirrhosis induced by various etiologic agents. Although interferon (IFN)alpha-2a has mostly been used to treat viral hepatitis, its anti-fibrogenic properties remain to be established.

METHODS

An experimental model of cholestasis-induced cirrhosis was used to test the effect of IFNalpha-2a. Cirrhosis was induced in rats via ligation of the common bile duct. IFNalpha-2a (100,000 IU/rat, s.c.) was administered daily throughout the experiment. Collagens and TIMP-1 mRNA transcripts were determined by semi-quantitative reverse transcriptase-polymerase chain reaction in liver tissue samples. Activity of metalloproteases (MMPs) was measured using gelatin (denatured collagen) as substrate and the specific size of the enzymes was estimated by zymograms. Histology was performed using Sirius red as a specific stain for collagenous material, and computer-assisted morphometric analyses were carried out. A polyclonal mouse anti-plasminogen activator inhibitor (PAI-1) antibody was used to evaluate the distribution during treatment with IFNalpha-2a.

RESULTS/CONCLUSIONS

MMP-activity was up-regulated in bile duct ligated rats treated with IFNalpha-2a. MMP-activity in homogenates of total liver was minimal as compared with activity in non-parenchymal cells isolated from the same parental perfused liver, indicating a cryptic MMP activity which was completely abolished by EDTA and 1,10 phenanthroline. Three bands of gelatin degradation were detected by zymography, corresponding to 95, 75 and 65 kDa. IFNalpha-2a decreased PAI-1 immunoreactivity in liver tissue slices as well as biochemical activity in non-parenchymal cell extracts (3.3+/-0.08 vs 7.4+/-1.1 U/mg protein). Procollagen alpha1 (III) and alpha1 (IV) genes expression were also down-regulated 1.5 and 4-fold, respectively. Interestingly, TIMP-1 gene expression did not change. Functional hepatic tests: alanine aminotransferase, aspartate aminotransferase, bilirubins and alkaline phosphatase were significantly lower in IFNalpha-2a treated animals. Analysis of histology demonstrated that IFNalpha-2a promoted resolution of fibrosis and decreased bile duct proliferation.

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.

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.

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.

Influence of bacteria on electrophoretic proteinase patterns of Entamoeba histolytica isolates

Gelatin SDS- polyacrylamide gel electrophoresis was used to compare proteinase banding patterns under reducing conditions from whole cell lysates of four axenic and four xenic pathogenic strains of Entamoeba histolytica. All strains shared major bands in the 34 and 66-68 kDa regions, whereas only the axenic strains produced major bands at 26, 28, 30 and 45 kDa. One axenic strain, NIH 200, when reassociated with mixed bacterial flora, reverted to an electrophoretic banding pattern characteristic of other xenic strains. These results suggest that the 26-30 kDa and 45 kDa proteinases of E. histolytica are induced by bacterial starvation while others are constitutively expressed. It is also proposed that the axenic bands of 45 and 34 kDa represent respectively, the reduced forms of the 56 and 40 kDa bands reported elsewhere under non-reducing conditions.

Circulating antibodies to histolysain, the major cysteine proteinase of Entamoeba histolytica, in amoebic liver abscess patients

A solid-phase enzyme immunoassay (EIA) was used to detect circulating antibodies to histolysain, the major cysteine proteinase of Entamoeba histolytica. Serum samples from 40 healthy controls, 33 asymptomatic E. histolytica cyst passers and 22 patients with amoebic liver abscess were tested. Antibodies to histolysain were found in 72.7% of cases of amoebic liver abscess, 18.1% of the cyst passers and 2.5% of healthy controls, which suggests that a humoral immune response is induced by histolysain during amoebic liver abscess.

Role of leukocytes and amebic proteinases in experimental rat testicular necrosis produced by Entamoeba histolytica

To investigate the role of amebic proteinases and host leukocytes, we studied amebiasis experimentally in the rat testis. The degree of inflammation and necrosis produced by different strains was correlated with proteinase activity and with zymograms. Intratesticular injection of axenically grown trophozoites of a pathogenic strain (HM-1 of Entamoeba histolytica) produced indistinguishable lesions in normal animals and leukopenic rats (less than 1000 leukocytes/mm3), suggesting that granulocytes do not contribute to the formation of lesions in this model. Testicular lesions produced by five different strains of E. histolytica ranging from highly virulent to almost nonpathogenic were proportional to the proteinase activity of each amebic strain. Inhibition of amebic proteinases in vitro and subsequent injection into the rat testis markedly reduced the inflammatory lesions resulting from highly virulent E. histolytica. The pathogenicity of three other amebae (E. laredo, E. moshkovskii, and E. invadens) was generally proportional to their proteinase activity; however, E. laredo showed high proteinase activity and caused minimal tissue damage. These results suggest that the pathogenic potential of Entamoeba spp. in the rat testis may be related to the type as well as the level of their proteinase activity.

Non-pathogenic Entamoeba histolytica: functional and biochemical characterization of a monoxenic strain

We have cultured under monoxenic conditions and characterized an Entamoeba histolytica clone, MAV-I CINVESTAV (MAV-I), obtained from feces from an asymptomatic carrier. The clone shows the non-pathogenic E. histolytica zymodeme type I, which did not change through the process of monoxenization. Clone MAV-I was non-pathogenic in both in vivo and in vitro tests, and it did not have a functional 112-kDa adhesin. As far as we know, this is the first non-pathogenic monoxenic strain reported. Clone A (strain HM1:IMSS), a highly virulent clone with pathogenic zymodeme type II, and which has the 112-kDa adhesin, was used as a control. Protein patterns from both clones were almost identical in one-dimensional gels. In two-dimensional gels, differences in high-molecular-weight proteins were detected. Clone MAV-I adhered and phagocytosed only 12% of the red blood cells adhered and phagocytosed by clone A. MAV-I trophozoites did not destroy cell culture monolayers and did not produce hepatic abscesses in hamsters. They also showed deficiency in protease activity. The absence of virulence in clone MAV-I correlated directly with the absence of a functional 112-kDa adhesion, supporting the role that this protein plays in virulence.

Specific labeling of cysteine proteinases in pathogenic and nonpathogenic Entamoeba histolytica

Growth of Entamoeba histolytica trophozoites was inhibited by 50% at low concentrations (2.0 micrograms/ml) of the diazopeptidyl inhibitor benzyloxycarbonyl-leucyl-L-tyrosyldiazomethane (Z-L-Leu-L-Tyr-CHN2). Iodination of the tyrosine residue lowered the growth inhibitory efficacy of the diazopeptidyl inhibitor (50% inhibition, approximately 10 micrograms/ml). However, even at this concentration, practically all of the cysteine proteinase activity of the cells was irreversibly inactivated as shown by fluorescence microscopy with the dipeptide substrate L-Arg-L-Arg-4-methoxy-beta-napthylamide or colorimetrically with azocasein as the substrate. Growth of trophozoites of E. histolytica from various strains, including both pathogenic and nonpathogenic zymodemes, was similarly inhibited. The concentration of inhibitor required to inactivate the proteinase activity of nonpathogenic cells was lower. Lysates from trophozoites grown in the presence of sublethal concentrations of 125I-labeled protease inhibitor (10 micrograms/ml) showed as many as eight radioactive bands by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (molecular sizes, 73, 68, 56, 40, 39, 35, 29, and 27 kilodaltons). Two of these bands (molecular sizes, 29 and 27 kilodaltons) could be seen in gels of the cytoplasmic fraction, whereas the high-molecular-size bands were mostly associated with the membrane fraction. The radioactive bands in pathogenic and nonpathogenic strains were very similar with only minor differences. The results obtained show that E. histolytica cells, irrespective of their pathogenicity, possess a number of cysteine proteinases of similar molecular sizes which are vital for cell growth.

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.

Giardia lamblia: characterization of proteinase activity in trophozoites

The proteinase activity of Giardia lamblia trophozoites, Portland 1 strain, was characterized with respect to substrate specificities and inhibitor sensitivities. Proteinase activity with urea-denatured hemoglobin (UDH), alpha-N-benzoyl-DL-arginine-2-naphthylamide (BANA), and alpha-N-benzoyl-argininamide (BAA) as substrates exhibited pH optima of 5.8, 3.8, and 5.0, respectively. For BANA, the apparent Km was 0.20 mM and the Vmax was 2.56 microM. For BAA, the apparent Km was 4.0 mM and the Vmax was 8.69 microM. Dithiothreitol (DTT, 5 mM) enhanced proteinase activity threefold for UDH, fourfold for BAA, and fivefold for BANA. Iodoacetamide, L-tosylamide-2-phenylethyl chloromethyl ketone (TPCK), and N-alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK), each at 1 mM, inhibited proteinase activity by greater than 90% with BANA and BAA. Iodoacetamide inhibited proteinase activity by 35% with UDH; TPCK and TLCK inhibited activity greater than 70% with UDH. Activity on BAA was inhibited by 91% with Zn2+ and activity on UDH was inhibited by 30% with Cu2+. Virtually complete inhibition of proteinase activity on BANA and BAA was obtained with leupeptin and chymostatin at 1 microgram/ml. Pepstatin A, chelators, and other heavy metals had no apparent effect on proteinase activity. Two polypeptide bands (ca. 105 and 40 kDa) indicative of proteinase activity were visualized by sodium dodecyl sulfate-gelatin polyacrylamide gel electrophoresis. The 105 kDa band was visible over the pH range of 4 to 7, but with greater intensity from pH 5 to 7. The 40 kDa band, while present at pH 5, was most intense at pH 6 and 7.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of casein digestion by a fluorometric method

A qualitative and quantitative method to assay proteolytic degradation of casein with a spectrofluorometer was developed. Proteolysis produced by different pure or mixed proteinases in a pH range 2 to 7.4 quenches the fluorescence emitted at a wavelength of 350 nm by casein excited at 300 nm in less than 5 min. This method is very sensitive, fast, and requires minimal sample preparation. Proteinases that do not generate peptides appropriate for fluorescence quenching cannot be detected with this assay and proteinases with intrinsic fluorescence may require special adjustments of the spectrofluorometer. This method monitors the disappearance of intact substrate proteins continuously, omitting the separation step necessary in other methods to measure product peptides.

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.