Specificity of a cysteine proteinase of Entamoeba histolytica towards the alpha 1-CB2 peptide of bovine collagen type I

Cysteinyl proteinases and their selective inactivation

The affinity-labeling of cysteinyl proteinases may now be carried out with a number of peptide-derived reagents with selectivity, particularly for reactions carried out in vitro. These reagents have been described with emphasis on their selectivity for cysteine proteinases and lack of action on serine proteinases, the most likely source of side reactions among proteinases. Perhaps a crucial feature of this selectivity is an enzyme-promoted activation due to initial formation of a hemiketal, which may destabilize the reagent. Prominent among the reagent types that have this class selectivity are the peptidyl diazomethyl ketones, the acyloxymethyl ketones, the peptidylmethyl sulfonium salts, and peptidyl oxides analogous to E-64. The need for specific inhibitors capable of inactivating the target enzyme in intact cells and animals is inevitably pushing the biochemical application of these inhibitors into more complex molecular environments where the possibilities of competing reactions are greatly increased. In dealing with the current state and potential developments for the in vivo use of affinity-labeling reagents of cysteine proteinases, the presently known variety of cysteinyl proteinases had to be considered. Therefore this chapter has, at the same time, attempted to survey these proteinases with respect to specificity and gene family. The continual discovery of new proteinases will increase the complexity of this picture. At present the lysosomal cysteine proteinases cathepsins B and L and the cytoplasmic calcium-dependent proteinases are reasonable goals for a fairly complete metabolic clarification. The ability of investigators to inactivate individual members of this family in vivo, possibly without complications due to concurrent inactivation of serine proteinases by improvements in reagent specificity, is increasing. Among the cysteine proteinases, at least those of the papain super family, hydrophobic interactions in the S2 and S3 subsites are important and some specificity has been achieved by taking advantage of topographical differences among members of this group. Some of this has probably involved surface differences removed from the regions involved in proteolytic action. The emerging cysteine proteinases include some which, in contrast to the papain family, have a pronounced specificity in S1 for the binding of basic side chains, familiar in the trypsin family of serine proteinases. At least a potential conflict with serine proteinases can be avoided by choice of a covalent bonding mechanism. The departing group region, has not been exploited. As a sole contributor to binding, this region may be rather limited as a source of specificity.(ABSTRACT TRUNCATED AT 400 WORDS)

Micellar electrokinetic chromatography: a convenient alternative to colorimetric and high performance liquid chromatographic detection to monitor protease activity

High performance capillary electrophoresis (HPCE) has been exploited as an analytical method alternative to current procedures for the determination of proteolytic activity of elastases from different sources. Due to some drawbacks with capillary zone electrophoresis (CZE), the mode of operation employed for the assay of elastolytic activity was micellar electrokinetic chromatography (MEKC). Using a background electrolyte consisting of 35 mM sodium tetraborate, pH 9.3, containing 65 mM SDS and 15% v/v methanol, separation of intact peptide substrate from products of proteolytic reaction was easily achieved in a fused-silica capillary of 50 cm effective length x 75 microm ID. This allowed us to determine the rate of hydrolysis of substrates and to calculate the kinetic parameters Km and k(cat) of the proteases investigated. A comparison of these data with those obtained from high performance liquid chromatography (HPLC)-based experiments showed that MEKC is a convenient technique for studying protease kinetics.

Cathepsin B-like cysteine proteases of Leishmania mexicana

A group of Leishmania mexicana cysteine proteases that differ from those previously found in this protozoon are described. The enzymes characteristically have a preference for peptidyl substrates with a phenylalanyl-valyl-arginyl moiety, do not hydrolyse gelatin in substrate-sodium dodecyl sulphate polyacrylamide gels, are stimulated by thiol-reducing agents and are sensitive to inhibitors specific for cysteine proteases. They have unusual solubility properties that indicate that the enzymes are amphiphilic proteins. Two of the cysteine proteases have been purified from L. mexicana amastigotes and shown to have molecular masses of 31 and 33 kDa. Their N-terminal amino acid sequences are very similar and show high homology to the mammalian cysteine protease, cathepsin B.

The partial characterization of proteases present in the excretory/secretory products and exsheathing fluid of the infective (L3) larva of Necator americanus

Following the observation that live third-stage larvae (L3) could digest gelatin in vitro, gelatinolytic protease activity has been demonstrated at pH 8.5, in both exsheathing fluid (EF) and excretory/secretory (ES) products of infective L3 of Necator americanus. EF resolved as a single band of proteolytic activity, with a mol. wt of 116 kDa, while L3 ES products exhibited multiple bands of proteolysis, at 219, 200, 195, 166, 137, 92, 72 and 62 kDa; weak bands were detectable at 92 and 72 kDa. The EF protease was characterized as cysteine, whereas ES apparently possessed one serine (195 kDa) and seven (219, 200, 166, 137, 92, 72 and 62 kDa) cysteine protease bands and a combination of metallo- and cysteine proteases of approximately the same mol. wts (62, 137 and 219 kDa). Though EF was not able to cleave immunoglobulins, ES was shown to cleave IgG, IgA and IgM, but not IgD or IgE. The activity appeared to be directed toward the Fc portion of the molecule, and was inhibited by PMSF, which is indicative of serine protease activity. The significance of the presence of such apparently diverse proteases in larval products is discussed.

Purification and substrate specificity of two cysteine proteinases of Giardia lamblia

The proteinase activity present in homogenates of trophozoites of Giardia lamblia, active on azocasein and urea-denaturated hemoglobin, was separated into two different enzymes by a series of purification procedures. These procedures included gel filtration on Fractogel TSK HW-55 (F), organomercurial agarose affinity chromatography, and ion exchange chromatography on DEAE-cellulose. By chromatography on Sephadex G-100, two purified enzymes exhibited relative molecular weights of Mr = 95,000 and 35,000 +/- 10%, respectively. On the basis of inhibition by thiol reagents and abrogation of this effect by dithiothreitol and cysteine, they were identified as cysteine proteinases. Proteinase I (Mr = 95,000) and proteinase II (Mr = 35,000) were active against the beta-chain of insulin releasing characteristic fragments. However, differences in substrate specificities of the two enzymes could be observed by using synthetic peptides that represent sequences 1-6, 8-18, and 20-30 of the insulin beta-chain. Furthermore, the synthetic tetrapeptides Arg-Gly-Phe-Phe, Arg-Gly-Leu-Hyp, and Arg-Arg-Phe-Phe were hydrolyzed by the two proteinases releasing Phe-Phe and Leu-Hyp, respectively. Compared with Arg-Gly-Phe-Phe, the rates of hydrolysis of Arg-Gly-Leu-Hyp and Arg-Arg-Phe-Phe at substrate concentrations of 1 mM were 91% and 63% (proteinase I) and 80% and 57% (proteinase II), respectively.

Entamoeba histolytica: correlation of the cytopathic effect of virulent trophozoites with secretion of a cysteine proteinase

Work from several laboratories suggests a correlation between expression of cysteine proteinase activity and the cytopathic effect of virulent HM1 strain Entamoeba histolytica trophozoites on cultured cell monolayers. Consistent with this relationship, we find that L-6 trophozoites, mutants cloned from the HM1 parent strain, are deficient in both proteinase expression and cytopathic effect. Three other clones, with proteinase expression equal to or greater than that of the HM1 strain, express the cytopathic effect. Furthermore, a nontoxic specific proteinase inhibitor, Z-phenylalanyl-alanyl-CH2F, inhibits the cytopathic effect of live trophozoites in a dose-dependent manner. These results support the hypothesis that expression and release of the cysteine proteinase is an important factor in producing the cytopathic effect, presumably by its degradation of cell anchoring proteins.

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.

Action of the major protease from Entamoeba histolytica on proteins of the extracellular matrix

The action of the major protease from the parasitic protozoon Entamoeba histolytica, a cysteine protease of Mr 27,000-29,000, on some important proteins of the extracellular matrix has been studied. The isolated protease degraded the extracellular matrix proteins from human tissue collagen type IV and V as well as laminin and fibronectin with different velocities and specificities under native conditions. Whereas the degradation of fibronectin and laminin proceeded rapidly, yielding distinct fragment patterns, the breakdown of the collagen types happened more slowly and incompletely. The digestion of the denatured isolated alpha 2-chain of bovine collagen type I was very fast and unspecific requiring only 1/10 of the enzyme activities as compared with the other substrates mentioned above. Nearly 85% of the overall proteolytic activity of a soluble fraction of E. histolytica was strongly inhibited by antibodies against the purified histolytic protease as well as by cystatin from chicken egg white, a specific protein inhibitor of cysteine proteases. We conclude that the histolytic protease represents by far the highest portion of soluble proteolytic activity in E. histolytica which is sufficient to destroy the extracellular matrix of the host.

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.