The collagenase of Entamoeba histolytica

Purification and biochemical properties of calmodulin in Entamoeba histolytica and its distribution during secretion of electron-dense granules

1. Calmodulin (CaM) was detected during secretion of electron-dense granules by Entamoeba histolytica trophozoites with immunofluorescence. 2. It was purified to apparent homogeneity by chromatography with a yield of 2.26 micrograms of calmodulin/mg of protozoan protein. Purity was established by gel electrophoresis. 3. The parasite calmodulin has properties characteristic of calmodulin isolated from other eukaryotes: an apparent molecular weight of 19 or 17 kDa in presence of EGTA or CaCl2, respectively, activation in a calcium dependent manner of bovine heart cyclic nucleotide phosphodiesterase, and its UV spectrum.

Possible role of calmodulin in the secretion of Entamoeba histolytica electron-dense granules containing collagenase

Entamoeba histolytica cells secrete electron-dense granules (EDGs) that have collagenase activity. To study the possible involvement of calmodulin (CaM) on EDG secretion, the effect of several CaM antagonists (TFP, R24571, W-7, W-5, dibucaine and DL-propranolol) was tested on this cellular function. Except for W-5 and dibucaine, the rest of these compounds inhibited EDG secretion. Transmission electron microscopy of collagen-activated trophozoites showed numerous EDGs located in or near the surface membrane. In contrast, trophozoites incubated with TFP showed no EDGs. Protein kinase C inhibitors (H-7, ML-9) had no effect on EDG secretion, suggesting that CaM antagonists acted by selectively inhibiting CaM. These results suggest that a CaM-dependent process is involved in EDG secretion.

Antigens in electron-dense granules from Entamoeba histolytica as possible markers for pathogenicity

In vitro interaction of Entamoeba histolytica with collagen induces intracellular formation and release of electron-dense granules (EDG) and stimulation of collagenolytic activity. Purified EDG contain 1.66 U of collagenase per mg of protein. Thus, EDG may participate in tissue destruction during invasive amebiasis. Monoclonal antibodies (MAbs) L1.1 and L7.1 reacted specifically with EDG in enzyme-linked immunosorbent assay (ELISA) and immunofluorescence and immunoelectron microscopy. MAb L7.1 immunoprecipitated three polypeptides with molecular weights of 95,000, 68,000, and 28,000 from lysates of biosynthetically labeled E. histolytica. Both MAbs recognized the pathogenic E. histolytica axenic strains HM1:IMSS, HM38:IMSS, and HK-9 but failed to react in ELISA with Entamoeba moshkovskii, Entamoeba invadens, and E. histolytica-like Laredo. In addition, MAb L7.1 reacted with one E. histolytica isolate from a symptomatic patient but did not react with four of five isolates from asymptomatic patients. EDG antigens were detected by a MAb L7.1-based ELISA in E. histolytica-containing fecal samples from symptomatic, but not asymptomatic, individuals. These results suggest that the EDG antigen detected with MAb L7.1 may be differentially expressed in pathogenic and nonpathogenic E. histolytica.

Thiol proteinase expression and pathogenicity of Entamoeba histolytica

Expression of the 56-kilodalton (kDa) neutral thiol proteinase has been shown to correlate with the potential of clinical isolates of Entamoeba histolytica to produce invasive disease. A 56-kDa band was identified by gelatin substrate gel electrophoresis in 10 of 10 isolates from patients with colitis or amebic liver abscesses, but in only 1 of 10 isolates from asymptomatic patients. Pathogenic isolates appear capable of releasing significantly larger quantities of the proteinase, as measured by cleavage of a synthetic peptide substrate, ZRR-AMC (benzyloxy-carbonyl-arginine-arginine-4-amino-7-methylcoumarin). We have also shown that the proteinase is released during the course of clinical invasive amebic disease, as demonstrated by the presence of circulating antibodies detectable by enzyme-linked immunosorbent assay. These studies support the importance of the 56-kDa thiol proteinase in the pathogenesis of invasive amebiasis.

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)

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.

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.

Ameba-bacterium relationship in amebiasis

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A membrane-associated neuraminidase in Entamoeba histolytica trophozoites

Trophozoites of the parasitic amoeba Entamoeba histolytica HM-1:IMSS possess a surface neuraminidase capable of liberating N-acetylneuraminic acid (NANA) from N-acetylneuramin-lactose (alpha 2----3 or alpha 2----6) or mucin in their medium. The neuraminidase was found to be membrane associated, with more than 50% of the yield being recovered in the plasma membrane fraction. The neuraminidase specific activity of the plasma membrane fraction was six times that of internal membrane fraction enzyme. The optimum pH and temperature for this enzyme were 6.7 and 37 degrees C, respectively. Neuraminidase activity was inhibited by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, and the optimum Ca2+ concentration was 2 mM. The microfilament disruptor cytochalasin D (30 micrograms/ml) inhibited motility and neuraminidase activity of intact Entamoeba trophozoites. The cytochalasin D-induced loss of surface neuraminidase activity was explained in part by a redistribution of enzyme with a loss of plasma membrane enzyme and an increase in intracellular membrane enzyme. A qualitatively similar cytochalasin D effect was observed with two other membrane-associated enzymes, calcium-regulated ATPase and acid phosphatase. Membrane-associated enzyme was minimally affected by Triton X-100 and saponin. An N-acetylneuraminic acid aldolase, optimum pH, 7.4, was found in trophozoite homogenate supernatant fractions. NANA and NANA-containing compounds stimulated trophozoite-directed motility. This motility stimulation by NANA-containing compounds did not apparently require prior release of free NANA by the trophozoite surface neuraminidase. Entamoeba neuraminidase is one of a series of enzymes that may modify the mucus blanket and target cell surface and thereby play a role in the pathogenesis of amebiasis.

Studies on a filarial antigen with collagenase activity

We examined the ability of two filarial species, Onchocerca volvulus and Brugia malayi, to solubilize collagen molecules from native collagen fibrils. Collagenolytic activity was detected in extracts of adult worms, in living microfilariae of O. volvulus and in live infective larvae and adult female worms of B. malayi. Excretion-secretion factors produced in vitro by infective larvae of B. malayi also contained large amounts of collagenase. Studies with enzyme inhibitors suggest that the latter may be a metallo-protease. Antibodies to filarial collagenase were present in sera from patients with onchocerciasis and brugian filariasis and from mice immunized with B. malayi. These antibodies and a monoclonal antibody raised against O. volvulus antigens immunoprecipitate filarial collagenase but appear not to be directed against the active site of the enzyme.

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.

Adherence of Entamoeba histolytica trophozoites to rat and human colonic mucosa

We studied the adherence of [3H]thymidine-labeled axenic Entamoeba histolytica (strain HM1-IMSS) to in vitro preparations of rat and human colonic mucosa. Studies were performed with fixed or unfixed rat colonic mucosa, unfixed rat mucosa exposed to trypsin, unfixed rat submucosa, and fixed human colonic mucosa. Twenty percent of the amebae adhered to fixed rat colonic mucosa; adherence was specifically inhibited by N-acetyl-D-galactosamine (GalNAc), galactose, and asialofetuin. The adherence of amebae to fixed human colonic mucosa was also GalNAc inhibitable. Greater adherence was found with unfixed rat colonic mucosa (40.9%) and was not GalNAc inhibitable unless the tissue was first exposed to trypsin. However, GalNAc did inhibit the adherence of amebae to unfixed rat submucosa. Glutaraldehyde fixation of amebae inactivates known amebic adhesion proteins; there was a markedly decreased adherence of fixed amebae to trypsin-exposed mucosa or fixed rat colonic mucosa. However, fixed or viable amebae had equal levels of adherence to unfixed rat colonic mucosa, suggesting the presence of a host adhesion protein that binds to receptors on amebae. Human (10%) and rabbit (5%) immune sera reduced the adherence of viable amebae to fixed rat colonic mucosa. We concluded that the GalNAc-inhibitable adhesion protein on the surface of E. histolytica trophozoites mediated adherence to fixed rat mucosa, fixed human colonic mucosa, trypsin-exposed unfixed rat mucosa, and unfixed rat submucosa. The surface of unfixed rat colonic mucosa contained a glutaraldehyde- and trypsin-sensitive host adhesion protein, perhaps in the overlying mucus blanket, which bound viable or fixed E. histolytica trophozoites.

Structural bases of the cytolytic mechanisms of Entamoeba histolytica

The cellular bases of the powerful cytolytic activity of the human protozoan parasite Entamoeba histolytica were explored by studying the effect of the virulent strain HM1:IMSS on epithelial monolayers of MDCK cells using a combination of time-lapse microcinematography and transmission and scanning electron microscopy. Early alterations of the epithelial cell membranes were detected by measuring changes in the transepithelial electrical resistance of MDCK monolayers mounted in Ussing chambers. The aggressive mechanism of E. histolytica trophozoites was found to be a complex, multifactorial phenomenon that included hit-and-run damage to the plasma membrane of effector cells mediated through contact, phagocytosis of lysed or apparently intact, but detached, MDCK cells, and intracellular degradation of ingested cells. Following contact with amebas, the epithelial monolayers showed a pronounced lowering of transepithelial resistance, opening of tight junctions, distortion of microvilli, surface blebbing, and the presence of minute focal discontinuities in the plasma membrane. There was no evidence of amebic exocytosis, membrane fusion, or junction formation between the parasite and host plasma membranes. Although modifications in the epithelial cell membranes usually preceded lysis, the cytolytic activity of the parasite did not exclusively involve damage to the plasma membrane of the cultured host cells but also was mediated by avid phagocytosis, the displacement and separation of neighboring cells by means of pseudopodial activity, and the "pinching-off" of the peripheral cytoplasm of epithelial cells.

Cellular bases of experimental amebic liver abscess formation

The complete sequence of morphologic events during amebic liver abscess formation in the hamster has been studied, from the lodgement of amebas in the hepatic sinusoids to the development of extensive liver necrosis. Following intraportal inoculation of live amebas, the early stages of the lesion (from 1 to 12 hours) were characterized by acute cellular infiltration composed of an increasingly large number of polymorphonuclear leukocytes, which surrounded centrally located trophozoites. Histiocytes and lysed leukocytes were situated on the periphery of the lesions. Hepatocytes close to the early lesions showed degenerative changes which led to necrosis; however, direct contact of liver cells with amebas was very rarely observed. At later stages, the extent of necrosis increased, macrophages and epithelioid cells replaced most leukocytes, and well-organized granulomas developed. Extensive necrosis associated with fused granulomas was present by Day 7. The results suggest that Entamoeba histolytica trophozoites do not produce amebic liver abscesses in hamsters through direct lysis of hepatocytes. Rather, tissue destruction is the result of the accumulation and subsequent lysis of leukocytes and macrophages surrounding the amebas.

Entamoeba histolytica: collagenolytic activity and virulence

Several axenic strains of pathogenic and nonpathogenic Entamoeba histolytica were tested for their capacity to digest native radioactive type I collagen gels and to produce liver abscesses when injected into the liver of newborn hamsters. The results demonstrate that the pathogenic strains of amebas (HM1:IMSS, HM3:IMSS, HM38:IMSS and HK9) have a collagenolytic activity that closely correlates with their in vivo capacity to produce liver lesions. The nonpathogenic isolate (Laredo) did not show collagenolytic activity and failed to produce lesions in the liver of newborn hamsters. The results also demonstrate that type I collagen obtained from rodents and cats is degraded less by amebic collagenase than is bovine collagen, which is similar to human collagen. These findings suggest that species susceptibility to invasive infection may depend, among other factors, on the characteristics of the extracellular components of host tissues.

Virulence of Entamoeba histolytica trophozoites. Effects of bacteria, microaerobic conditions, and metronidazole

The association of axenically grown trophozoites of Entamoeba histolytica strains HK-9 or HM-1:IMSS with various types of gram-negative bacteria for relatively short periods markedly increased their virulence, as evidenced by their ability to destroy monolayers of tissue-cultured cells. Interaction of trophozoites with bacteria that were heat inactivated, glutaraldehyde fixed, or disrupted by sonication, or bacteria treated with inhibitors of protein synthesis, did not augment amebic virulence. Lethally irradiated bacteria, however, retained their stimulative properties and trophozoites that ingested bacteria were protected from the toxic effects of added hydrogen peroxide. An increase in virulent properties of amebae was also found in experiments carried out under microaerobic conditions (5% O2, 10% CO2). The augmentation of amebic virulence due to association with bacteria was specifically blocked by metronidazole, but not by tetracycline or aminoglycosides, and the rate of metronidazole uptake in stimulated trophozoites was two to three times higher. The results obtained suggest that virulence of axenically grown E. histolytica trophozoites may depend to a considerable extent on the cell's reducing power. Both microaerobic conditions and the association with bacteria apparently stimulate the electron transport system of the ameba. Bacteria may function as broad range scavengers for oxidized molecules and metabolites through the contribution of enzymatic systems, components, or products.

A weakly acidic protease has a powerful proteolytic activity in Entamoeba histolytica

A thiol dependent protease from homogenates of the parasite Entamoeba histolytica has been identified and partially purified by means of ammonium sulphate fractionation, gel filtration and isoelectric focusing. The protease, having a molecular mass of 21 +/- 2 kDa as judged by gel chromatography, represents a highly potent proteolytic capacity. The protease shows maximal activity against azocasein around the slightly acidic pH of 4.4 at 37 degrees C, but is also active at pH 3.4 and 8.5. At optimal pH, the turnover increases with increasing temperature up to 85 degrees C. The enzyme possesses a thiol group essential for activity, which is inhibited by the thiol blocking reagent p-chloromercuribenzoate. Solutions containing low concentrations of free Hg2+ cause conservation of protease activity. The native protein exhibits an isoelectric point of 4.9. This protease resembles the thiol endopeptidases of mammalian lysosomes, and appears to be a major proteolytic enzyme in Entamoeba histolytica.

Degradation of extracellular matrix by mouse trophoblast outgrowths: a model for implantation

During implantation the embryo attaches to the endometrial surface and trophoblast traverses the uterine epithelium, anchoring in the uterine connective tissue. To determine whether trophoblast can facilitate invasion of the uterus by degrading components of normal uterine extracellular matrix, mouse blastocysts were cultured on a radio-labeled extracellular matrix that contained glycoproteins, elastin, and collagen. The embryos attached to the matrix, and trophoblast spread over the surface. Starting on day 5 of culture there was a release of labeled peptides into the medium. The radioactive peptides released from the matrix by the embryos had molecular weights ranging from more than 25,000 to more than 200. By day 7 there were areas where individual trophoblast cells had separated from one another, revealing the underlying substratum that was cleared of matrix. When trophoblast cells were lysed with NH(4)OH on day 8, it was apparent that the area underneath the trophoblast outgrowth had been cleared of matrix. Scanning electron microscopy and time-lapse cinemicrography confirmed that the digestion of matrix was highly localized, taking place only underneath the trophoblast, with no evidence of digestion of the matrix beyond the periphery of the trophoblast outgrowth. The sharp boundaries of degredation observed may be due to localized proteinase secretion by trophoblast, to membrane proteinases on the surface of trophoblast, or to endocytosis. Digestion of the matrix was not dependent on plasminogen, thus ruling out a role for plasminogen activator. Digestion was not inhibited by a variety of hormones and inhibitors, including progesterone, 17beta-estradiol, leupeptin, EDTA, colchicine, NH(4)Cl, or epsilon-aminocaproic acid. This system of culturing embryos on extracellular matrix may be useful in determining the processes that regulate trophoblast migration and invasion into the maternal tissues during implantation.0

Degradation of biogenic oligosaccharides by beta-N-acetyl-glucosaminidase secreted by Entamoeba histolytica

beta-N-Acetylglucosaminidase secreted by Entamoeba histolytica was extracted from the growth medium by affinity chromatography on CH-Sepharose 4 B coupled to p-aminophenyl-1-thio-beta-2-acetamido-2-deoxyglucopyranoside. The enzyme was further purified by isoelectric focusing, by sequential chromatography on DEAE-cellulose and Sephadex G-150, and by preparative disc gel electrophoresis. Chitobiose (betaGlcNAc1-4GlcNAc) derived from chitin as well as the oligosaccharides betaGlcNAc1-4 betaGlcUA1-3GlcNAc, betaGlcNAc1-4 betaGlcUA1-3 betaGlcAc1-4GlcUA, and betaGlcNAc1-4 betaGlc-UA1-3 betaGlcNAc1-4 betaGlcUA1-3 betaGlcNAc1-4GlcUA derived from hyaluronic acid were tested as potential physiological substrates. All these oligosaccharides are susceptible to action of beta-N-acetylglucosaminidase from E. histolytica. Under identical conditions chitobiose is cleaved 38-48 times faster than hyhyauronate oligosaccharides. No release of N-acetylglucosamine was observed when glycopeptides from ovalbumin were used as substrate. The pH optimum of hydrolase activity was 4.5 when chitobiose was used as substrate. Optimal hydrolysis of aluronate oligosaccharides was observed at pH 3.0 for trisaccharide and pH 2.0 for tetra- and hexasaccharide, respectively. Estimation of molecular weight by means of gel filtration gave values of 75 000. The isoelectric point was 5.02 beta-N-Acetylglucosaminidase from E. histolytica does not act on macromolecular chitin and hyaluronic acid.