Intraperitoneal fluid accumulation induced by Clostridium perfringens alpha-toxin (phospholipase C)

We report that the intraperitoneal injection of Clostridium perfringens alpha-toxin into mice induces ascites. This phenomenon was monitored by measuring fluid volume and analyzing hematologic data. The mouse toxicity test provides a simple and useful model for examining C. perfringens alpha-toxin-induced vascular permeability.     

Purification and some properties of phospholipase C (alpha-toxin) of Clostridium perfringens.

1. Phospholipase C[EC 3.1.4.3] was purified from the culture filtrate of Clostridium perfringens by successive chromatographies on CM-Sephadex, DEAE-Sephadex, and Sephadex G-100. During the purification it was noted that, beside the monomer form of the enzyme which was purified, a part of the enzyme existed in active polymerized forms. 2. The purified preparation gave a single band on polyacrylamide gel electrophoresis and gave a single precipitin line in immunodiffusion with the National Standard gas gangrene (C. perfringens) antitoxin, indicating the homogeneity of the preparation. 3. The specific lecithin-hydrolyzing activity of the purified preparation was comparable to that of a preparation obtained by affinity chromatography, which had the highest specific activity previously reported. 4. The molecular weight of the purified enzyme was estimated to be 43,000 by SDS-polyacryl-amide gel electrophoresis, although the same preparation gave a molecular weight of 31,000 as determined by gel filtration on Sephadex G-150. From this and the above finding that a part of the enzyme exists in active polymerized forms, the discrepancy among reported values for the molecular weight of C. perfringens phospholipase C can be accounted for. 5. For maximum hydrolytic activity toward lecithin, the enzyme required sodium deoxycholate (SDC) and Ca2+ ions. In the presence of 6 mM Ca2+, the optimal molar ratio of SDC to lecithin for maximal hydrolytic activity was about 0.5 for dipalmitoyl lecithin and about 1.0 for egg lecithin. The effects of various divalent cations on the enzymatic hydrolysis were also investigated. 6. The effects of sodium deoxycholate and Ca2+ ions on the enzymatic hydrolysis are discussed, based on their possible roles in mixed micelle formation.     

In vitro aggregation of platelets induced by alpha-toxin (phospholipase C) of Clostridium perfringens.

Highly purified alpha-toxin (phospholipase C) of Clostridium perfringens prepared by affinity chromatography on agarose-linked egg-yolk lipoprotein induced the in vitro aggregation of platelets of an irreversible type. The aggregation started after a time lag, the length of which depended on the concentration of the toxin; the reciprocal of the time lag was found to be directly proportional to the toxin concentration. Using this assay method, we demonstrated that the platelet-aggregating activity of alpha-toxin reached minimum at around 70 C but heating at higher temperatures inactivated it to a lesser extent; the same anomaly in heat inactivation was observed with phospholipase C activity possessed by the toxin. By subjecting purified alpha-toxin to isoelectric focusing, four molecular forms were isolated, all of which were associated with both the platelet-aggregating and phospholipase C activities. From all these results we concluded that the entity responsible for the platelet-aggregating activity is identical with alpha-toxin (phospholipase C).     

Detection by in vitro amplification of the alpha-toxin (phospholipase C) gene from Clostridium perfringens

A polymerase chain reaction (PCR) with thermostable DNA polymerase from Thermus aquaticus is described for the specific amplification of the phospholipase C (alpha-toxin) gene of Clostridium perfringens. A set of primers selected for their high specificity could detect Cl. perfringens in stools with a detection limit of approximately 5 x 10² bacteria, after bi-amplification. A modified PCR without thermal steps was performed to rapidly amplify, with a yield of 60%, the DNA template. With this PCR method Cl. perfringens alpha-toxin gene could be detected within 2 h. The PCR method detected alpha-toxin positive Cl. perfringens but did not react with phospholipase C-producing Bacillus cereus, Pseudomonas aeruginosa, Cl. sordellii and Cl. bifermentans.
The amplified PCR products were screened through ethidium bromide agarose gel electrophoresis or, in only 1 h, with the PhastSystem (Pharmacia). This PCR satisfies the criteria of specificity, sensitivity and rapidity required for a useful tool in epidemiology and for the diagnosis of the pathogen Cl. perfringens as it may be used directly on stool samples.     

Role of tryptophan-1 in hemolytic and phospholipase C activities of Clostridium perfringens alpha-toxin

Replacement of the Trp-1 in Clostridium perfringens alpha-toxin with tyrosine caused no effect on hemolytic and phospholipase C (PLC) activities or on binding to the zinc ion, but that of the residue with alanine, glycine and histidine led to drastic decreases in these activities and a significant reduction in binding to the zinc ion. The hemolytic and PLC activities of W1H and W1A were significantly increased by the preincubation of these variant toxins with zinc ions, but the preincubation of W1G with the metal ion caused little effect on these activities. Gly-Ile-alpha-toxin, which contained an additional Gly-Ile linked to the N-terminal amino acid of alpha-toxin, did not show hemolytic activity, but showed about 6% PLC activity of the wild-type toxin. A mutant toxin, which contained an additional Gly-Ile linked to the N-terminus of a protein lacking 4 N-terminal residues of alpha-toxin, showed about 1 and 6% hemolytic and PLC activities of the wild-type toxin, respectively. Incubation of the mutant toxin with zinc ions caused a significant increase in PLC activity. These observations suggested that Trp-1 is not essential for toxin activity, but plays a role in binding to zinc ions.     

Inhibition of Clostridium perfringens phospholipase C by ammonium and sulfonium dications.

Polyamines, alkyldiammonium and alkyldisulfonium salts, inhibit the Clostridium perfringens phospholipase C-catalyzed hydrolysis of 1-S-phosphocholine-2-O-hexadecanoyl-1-mercapto-2-ethanol (1) at pH 7.5, 37 degrees C, mu = 1.0 with KCl. Simple saturation kinetics are observed as both 1 and [Ca2+] are varied and simple linear inhibition is observed. The data are consistent with a non-competitive mechanism that involves binding of the inhibitors to free enzyme, E.[Ca2+] and E.[Ca2+].[S]; the inhibition constants for decamethylenebis(trimethylammonium) and decamethylenebis(dimethylsulfonium) bromides are 90 and 0.28 mM, respectively. It is suggested that the enhanced inhibition by the alkyldisulfonium salts results from more favorable equilibrium constants for contact ion-pair formation or from the formation of tetracoordinate sulfuranes.     

A continuous fluorometric assay for phospholipase C from Clostridium perfringens.

A fluorescent assay for Clostridium perfringens phospholipase C is described using 1-palmitoyl-2-[6(pyren-1-yl)hexanoyl]-sn-glycero-3- phospho-N-(trinitrophenyl)aminoethanol (PPHTE) as the substrate. This method is based on the decrease of the quenching of pyrene monomer fluorescence when phospholipase C hydrolyzes PPHTE into pyrenediglyceride and phospho(trinitrophenyl)-aminoethanol. The hydrolysis of egg lecithin/PPHTE (25:1 molar ratio) substrate by C. perfringens phospholipase C was linear with time for at least 2 min. Optimal conditions for the hydrolysis by phospholipase C were 50 mM Tris-HCl pH 7.0-30 mM CaCl2/63 microM egg lecithin and 2.5 microM PPHTE. The Km and Vmax values for the hydrolysis of egg lecithin/PPHTE vesicles were 28 microM and 280 pmol min-1, respectively. The detection limit of the assay was 40 microU of C. perfringens phospholipase C. When diglyceride was included into egg lecithin/PPHTE vesicles up to 30 mol% the reaction velocity increased 13-fold. Higher molar proportions of diglyceride were inhibitory. When the hydrolysis of mixtures of different naturally occurring phospholipids and PPHTE was studied egg lecithin was found to be the best substrate. When dipalmitoylphospholipids with different polar head groups were used the reaction velocity decreased in the order egg lecithin greater than or equal to dipalmitoylphosphatidylserine greater than dipalmitoylphosphatidic acid greater than dipalmitoylphosphatidylcholine greater than dipalmitoylphosphatidylglycerol.     

A cellular deficiency of gangliosides causes hypersensitivity to Clostridium perfringens phospholipase C

Clostridium perfringens phospholipase C (Cp-PLC), also called alpha-toxin, is the major virulence factor in the pathogenesis of gas gangrene. Previously, a cellular UDP-Glc deficiency was related with a hypersensitivity to the cytotoxic effect of Cp-PLC. Because UDP-Glc is required in the synthesis of proteoglycans, N-linked glycoproteins, and glycosphingolipids, the role of these gly-coconjugates in the cellular sensitivity to Cp-PLC was studied. The cellular sensitivity to Cp-PLC was significantly enhanced by glycosphingolipid synthesis inhibitors, and a mutant cell line deficient in gangliosides was found to be hypersensitive to Cp-PLC. Gangliosides protected hypersensitive cells from the cytotoxic effect of Cp-PLC and prevented its membrane-disrupting effect on artificial membranes. Removal of sialic acids by C. perfringens sialidase increases the sensitivity of cultured cells to Cp-PLC and intramuscular co-injection of C. perfringens sialidase, and Cp-PLC in mice potentiates the myotoxic effect of the latter. This work demonstrated that a reduction in gangliosides renders cells more susceptible to the membrane damage caused by Cp-PLC and revealed a previously unrecognized synergism between Cp-PLC and C. perfringens sialidase, providing new insights toward understanding the pathogenesis of clostridial myonecrosis.     

Effect ofClostridium perfringens phospholipase C (alpha-toxin) on the human diploid fibroblast membrane

Summary Human diploid embryonic lung fibroblasts were cultivated in Eagle's Minimum Essential Medium and labeled with³H-uridine. The release of soluble radioactive substances into the medium was used as an indicator of damage to the cell membrane. The assay method described is simple, sensitive and rapid and allows quantitative estimation of changes in membrane permeability before any morphological damage is observed microscopically. Crude commercial preparations of phospholipase C (E.C. 3.1.4.3.) (40 g/ml) were highly active on the cell membrane but most of the membrane damaging activity was found to be due to contaminating theta-toxin. However, also highly purified phospholipase C caused a membrane damage as measured by release of isotope through the plasma membrane. The release could be increased by including an optimal concentration of calcium ions in the incubation buffer, by treating the cells in a hypotonic medium and by simultaneous treatment with sublytic concentrations of Triton X-100. To our knowledge this is the first report of membrane damage on a live, intact, metabolizing human diploid cell caused by a highly purified phospholipase C. The results are in agreement with a dynamic membrane structure with the polar groups of a part of the phospholipids accessible at the membrane surface.     

Production and properties of theta-toxin of Clostridium perfringens with special reference to lethal activity.

theta-Toxin of Clostridium perfringens produced in a synthetic medium showed high toxicity. The mouse was killed with 5-10 hemolytic units of the toxin. Neutralization experiments showed that lethal and hemolytic activities were due to the same toxic entity. The amount of theta-toxin expressed in lethal activity reached more than 30% that of alpha-toxin in the synthetic medium SM67. Although the activities of alpha-and theta-toxins were not additive in terms of LD50, increase in the ratio of theta-toxin to alpha-toxin resulted in reduction of the survival time of the mouse injected with a lethal dosis of the mixture of the two toxins when compared with alpha-toxin alone. Unlike those produced in other media, the hemolytic and lethal activities of theta-toxin produced in the synthetic medium was not activated by reduction with thioglycollate, even after partial purification. In other respects, the toxin was not different significantly from those reported in the past. The toxic form was detected also in complex medium. It was suggested that theta-toxin may be produced as a nascent entity.     

Effects of Clostridium perfringens phospholipase C in mammalian cells

Clostridium perfringens phospholipase C (Cp-PLC), the major virulence factor in the pathogenesis of gas gangrene, is a Zn(2+) metalloenzyme with lecithinase and sphingomyelinase activities. Its structure shows an N-terminal domain containing the active site, and a C-terminal Ca(2+) binding domain required for membrane interaction. Although the knowledge of the structure of Cp-PLC and its interaction with aggregated phospholipids has advanced significantly, an understanding of the effects of Cp-PLC in mammalian cells is still incomplete. Cp-PLC binds to artificial bilayers containing cholesterol and sphingomyelin or phosphatidylcholine (PC) and degrades them, but glycoconjugates present in biological membranes influence its binding or positioning toward its substrates. Studies with Cp-PLC variants harboring single amino-acid substitutions have revealed that the active site, the Ca(2+) binding region, and the membrane interacting surface are required for cytotoxic and haemolytic activity. Cp-PLC causes plasma membrane disruption at high concentrations, whereas at low concentrations it perturbs phospholipid metabolism, induces DAG generation, PKC activation, Ca(2+) mobilization, and activates arachidonic acid metabolism. The cellular susceptibility to Cp-PLC depends on the composition of the plasma membrane and the capacity to up-regulate PC synthesis. The composition of the plasma membrane determines whether Cp-PLC can bind and acquire its active conformation, and thus the extent of phospholipid degradation. The capacity of PC synthesis and the availability of precursors determine whether the cell can replace the degraded phospholipids. Whether the perturbations of signal transduction processes caused by Cp-PLC play a role in cytotoxicity is not clear. However, these perturbations in endothelial cells, platelets and neutrophils lead to the uncontrolled production of intercellular mediators and adhesion molecules, which inhibits bacterial clearance and induces thrombotic events, thus favouring bacterial growth and spread in the host tissues.     

Site-directed mutagenesis of histidine residues in Clostridium perfringens alpha-toxin.

Mutagenesis of H-68 or -148 in Clostridium perfringens alpha-toxin resulted in complete loss of hemolytic, phospholipase C, sphingomyelinase, and lethal activities of the toxin. These activities of the variant toxin at H-126 or -136 decreased by approximately 100-fold of the activities of the wild-type toxin. Mutation at H-46, -207, -212, or -241 showed no effect on the biological activities, indicating that these residues are not essential for these activities. The variant toxin at H-11 was not detected in culture supernatant and in cells of the transformant carrying the variant toxin gene. Wild-type toxin and the variant toxin at H-148 bound to erythrocytes in the presence of Ca2+; however, the variant toxins at H-68, -126, and -136 did not. Co2+ and Mn2+ ions stimulated binding of the variant toxin at H-68, -126, and -136 to membranes in the presence of Ca2+ and caused an increase in hemolytic activity. Wild-type toxin and the variant toxins at H-68, -126, and -136 contained two zinc atoms in the molecule. Wild-type toxin inactivated by EDTA contained two zinc atoms. These results suggest that wild-type toxin contains two tightly bound zinc atoms which are not coordinated to H-68, -126, and -136. The variant toxin at H-148 possessed only one zinc atom. Wild-type toxin and the variant toxin at H-148 showed [65Zn]2+ binding, but the variant toxins at H-68, -126, and -136 did not. Furthermore, [65Zn]2+ binding to wild-type toxin was competitively inhibited by unlabeled Zn2+, Co2+, and Mn2+. These results suggest that H-68, -126, and -136 residues bind an exchangeable and labile metal which is important for binding to membranes and that H-148 tightly binds one zinc atom which is essential for the active site of alpha-toxin.