Surface properties of membrane systems. Transport of staphylococcal delta-toxin from aqueous to membrane phase

Purification and characterization of a novel delta-lysin variant that inhibits Staphylococcus aureus and has limited hemolytic activity

Delta-lysins (DL) that are produced by various species of staphylococci are not widely known for their antimicrobial activity. We have purified and characterized a novel DL variant, E229DL and examined its spectrum of inhibitory activity. The biological activity of E229DL, produced by Staphylococcus epidermidis strain E229, shows relatively broad-spectrum activity against Gram-positive pathogens, including representatives of MRSA and epidemic MRSA type 15. E229DL was purified to homogeneity from 95% acidified-methanol extracts of cell cultures by using a series of reversed-phase chromatographic separations. The fully processed form of E229DL is a 25-amino-acid peptide with a predicted mass of 2841.4 Da, but the purified biologically active molecule appears to be N-formylated (mass 2867.33 Da). The DL gene (hld) resembles that of other types of DL, but differs in five codons with hld in Staphylococcus aureus (26 residues) and one codon with the closest homolog, the hld-II in S. warneri (25 residues). The characterization of E229DL showed that its activity is stable in agar exposed to high temperatures (80 degrees C/45 min). In addition, biological testing of the native and synthetic peptides against a range of human and animal erythrocytes and Vero cells indicated that E229DL is an antibacterial agent with no detectable cytopathic effects at concentrations equivalent to the minimum inhibitory concentration for EMRSA15-A208. Initial investigation of the mode of action of E229DL indicated that it is rapidly lytic for target cells. This is the first description of a native form of DL having only limited cytotoxic activity for eukaryotic cells at concentrations that are inhibitory to staphylococci.

delta-hemolysin, an update on a membrane-interacting peptide

delta-hemolysin is a hemolytic peptide produced by Staphylococcus, and it has been studied for nearly 50 years. Therefore, it has become a model in the study of peptides interacting with membranes. In this review, we report some recent findings and compare them with previous works. delta-hemolysin is a 26 amino acid peptide, somewhat hydrophobic and presenting a zero net charge. Study of its structure has shown that delta-hemolysin is alpha-helical and amphipathic, such as many antimicrobial peptides (e.g. magainin and melittin). However, delta-hemolysin had not displayed any reported antimicrobial activity until a recent publication showed its high potency against Legionella. Its mode of action is based on direct interaction with target membranes. In accordance with its concentration, delta-hemolysin may slightly perturb a membrane or lead to cell lysis. Peptide charge plays an important role in its interaction with membranes, as is shown in the study of peptide variants. Some positively charged variants become highly hemolytic and even active against Escherichia coli and Staphylococcus aureus. Finally, it has recently been demonstrated that peptide preferentially binds to lipid-disordered domains. It has been postulated that as a result, enrichment in lipid-ordered domains might increase peptide concentration in lipid-disordered domains and thereby improve its activity.

Staphylococcus aureus delta toxin as an enterotoxin

The classical enterotoxins are known primarily for their ability to cause emesis and diarrhoea in cases of staphylococcal food poisoning but they also exhibit other biological activities. The seven antigenic types of toxin have molecular weights in the range 25 000-35 000. All types induce emesis in man and monkey and are of comparable potency. The enterotoxins seem to induce emesis by stimulating neural receptors in the intestine rather than acting on the medulla directly. The mechanism whereby diarrhoea is produced is unclear. Another product of Staphylococcus aureus which meets the more recent definition of an enterotoxin is the delta toxin. This toxin is an amphipathic peptide having an Mr of 2977 and possessing the ability to interact with a variety of hydrophobic substances. It is cytotoxic, can increase vascular permeability in guinea-pig skin, and can increase cellular cyclic AMP levels in guinea-pig ileum. In the ileum delta toxin also inhibits water absorption, apparently by increasing the bidirectional movement of Na+ and Cl- across the mucosa. This response does not appear to be mediated by cyclic AMP since the changes in ion fluxes precede the increases in cellular cyclic AMP levels. In high doses delta toxin also elicits a positive response in the neonatal mouse after intragastric inoculation.

Molecular dynamics simulations of the insertion of two ideally amphipathic lytic peptides LK(15) and LK(9) in a 1,2-dimyristoylphosphatidylcholine monolayer

We present here the results of 1-ns molecular dynamics (MD) simulations of two ideally amphipathic lytic peptides, namely LK(15) and LK(9), in a 1,2-dimyristoylphosphatidylcholine monolayer with two different cross-sectional areas per lipid of 80 A(2) (loose film) and 63 A(2) (tight standard film). These peptides are lytic, ideally amphipathic with a minimalist composition L(i)K(j) and the following sequences: H(2)N-KLLKLLLKLLLKLLK-CO-Ph for LK(15) and H(2)N-KLKLKLKLK-CO-Ph for LK(9). From experimental data, LK(15) exhibits an alpha-helical secondary structure, whereas LK(9) was found to form antiparallel beta-sheets at the interface of a DMPC monolayer. Whatever the specific lipid surface is, the two peptides exhibit very different behavior: the alpha-helix inserts deeply into the monolayer whereas the beta-sheeted peptide stays at the surface within the upper polar part of the monolayer. In all cases, a loose monolayer (80 A(2)) results in noticeable artifacts whereas a monolayer with standard specific surface leads to very reliable behavior well in accordance with experimental data. Despite their different insertion depth, the two peptides exhibit identical lytic efficiency. This is very likely a direct consequence of the very strong Van der Waals interactions between the fatty alkyl chains of the lipids and the highly lipophilic lower part of the peptide, resulting in an identical thinning of the two monolayers.

The monolayer technique: a potent tool for studying the interfacial properties of antimicrobial and membrane-lytic peptides and their interactions with lipid membranes

Erudites of the antiquity already knew the calming effect of oil films on the sea waves. But one had to wait until 1774 to read the first scientific report on oil films from B. Franklin and again 1878 to learn the thermodynamic analysis on adsorption developed by J. Gibbs. Then, in 1891, Agnes Pockels described a technique to manipulate oil films by using barriers. Finally, in 1917, I. Langmuir introduced the experimental and theoretical modern concepts on insoluble monolayers. Since that time, and because it has been found to provide invaluable information at the molecular scale, the monolayer technique has been more and more extensively used, and, during the past decade, an explosive increase in the number of publications has occurred. Over the same period, considerable and ever-increasing interest in the antimicrobial peptides of various plants, bacteria, insects, amphibians and mammals has grown. Because many of these antimicrobial peptides act at the cell membrane level, the monolayer technique is entirely suitable for studying their physicochemical and biological properties. This review describes monolayer experiments performed with some of these antimicrobial peptides, especially gramicidin A, melittin, cardiotoxins and defensin A. After giving a few basic notions of surface chemistry, the surface-active properties of these peptides and their behavior when they are arranged in monomolecular films are reported and discussed in relation to their tridimensional structure and their amphipathic character. The penetration of these antimicrobial peptides into phospholipid monolayer model membranes, as well as their interactions with lipids in mixed films, are also emphasized.

Possible virulence factors of Staphylococcus aureus in a mouse septic model

Twenty clinical isolates of Staphylococcus aureus were examined to elucidate the virulence factors which are directly related to lethality in a mouse septic model. Heat or formalin treatment of the organism abolished the lethal activity of the live organism during challenge intravenously administered via the tail vein. Nevertheless, injection of ten times concentrated culture supernatant fluid (SUP) showed lethal activity in the mouse. However, there was no lethality when SUP was heated at 60 degrees C for 15 min. To examine variations of SUP lethality among strains, we collected 20 strains of S. aureus from four different hospitals. Then, we compared several factors for SUP lethality, which were the extracellular toxins and enzymes, such as toxic shock syndrome toxin 1, enterotoxin A, B, D, and hemolysins (alpha,beta,gamma), and also cytotoxic activity to human polymorphonuclear leukocytes and Vero cells. No difference was found among these factors except cytotoxic activity to Vero cells. Furthermore, we compared two strains in a mouse septic model according to the grade of bacteremia and lethal events. We found that mortality was higher with challenge by the strain whose SUP was lethal in comparison to the strain whose SUP was not lethal, even though the viable bacteria counts in the septic blood in both strains were not significantly different. This strongly supports the possibility that extracellular products, not the cell wall components, of S. aureus play the key role in the lethal event in this mouse septic model. In addition, among the extracellular products, those which have cytotoxic activity to Vero cells may contribute to the lethality in sepsis caused by S. aureus in this murine model.

Structure, orientation and affinity for interfaces and lipids of ideally amphipathic lytic LiKj(i=2j) peptides

The behavior of lytic ideally amphipathic peptides of generic composition LiKj(i=2j) and named LKn, n=i+j, is investigated in situ by the monolayer technique combined with the recently developed polarization modulation IR spectroscopy (PMIRRAS). A change in the secondary structure occurs versus peptide length. Peptides longer than 12 residues fold into alpha-helices at interfaces as expected from their design, while enough shorter peptides, from 9 down to 5 residues, form intermolecular antiparallel beta-sheets. Analysis of experimental and calculated PMIRRAS spectra in the amide I and II regions show that peptides are flat oriented at the interfaces. Structures and orientation are preserved whatever the nature of the interface, air/water or DMPC monolayer, and the lateral pressure. Peptide partition constants, KaffPi, are estimated from isobar surface increases of DMPC monolayers. They strongly increase when Pi decreases from 30 mN/m to 8 mN/m and they vary with peptide length with an optimum for 12 residues. This non-monotonous dependence fits with data obtained in bilayers and follows the hemolytic activity of the peptides. Lipid perturbations due to peptide insertion essentially detected on the PO4- and CO bands indicate disorder of the lipid head groups. Lysis induced on membranes by such peptides is proposed to first result from their flat asymmetric insertion.

In situ study by polarization modulated Fourier transform infrared spectroscopy of the structure and orientation of lipids and amphipathic peptides at the air-water interface

Free amphipathic peptides and peptides bound to dimyristoylphosphatidylcholine (DMPC) were studied directly at the air/water interface using polarization modulation infrared reflection absorption spectroscopy (PMIRRAS). Such differential reflectivity measurements proved to be a sensitive and efficient technique to investigate in situ the respective conformations and orientations of lipid and peptide molecules in pure and mixed films. Data obtained for melittin, a natural hemolytic peptide, are compared to those of L15K7, an ideally amphipathic synthetic peptide constituted by only apolar Leu and polar Lys residues. For pure peptidic films, the intensity, shape, and position of the amide I and II bands indicate that the L15K7 peptide adopts a totally alpha-helical structure, whereas the structure of melittin is mainly alpha-helical and presents some unordered domains. The L15K7 alpha-helix axis is oriented essentially parallel to the air-water interface plane; it differs for melittin. When injected into the subphase, L15K7 and melittin insert into preformed expanded DMPC monolayers and can be detected by PMIRRAS, even at low peptide content (> 50 DMPC molecules per peptide). In such conditions, peptides have the same secondary structure and orientation as in pure peptidic films.

Ion channel formation by synthetic analogues of staphylococcal delta-toxin

Ion channel formation by three analogues of staphylococcal delta-toxin, an amphipathic and alpha-helical channel-forming peptide, has been evaluated by measurement of ionic currents across planar lipid bilayers. Replacement of beta-branched, hydrophobic residues by leucine and movement of a tryptophan residue from the hydrophilic to the hydrophobic face of the helix does not significantly alter ion channel activity. Removal of the N-terminal blocking group combined with the substitution of glycine-10 by leucine changes the single channel properties of delta-toxin, without altering macroscopic conductance/voltage behaviour. Truncation of the N-terminus by three residues results in complete loss of channel-forming activity. These changes in channel-forming properties upon altering the peptide sequence do not mirror changes in haemolytic activity. The results lend support to the proposal that channel formation and haemolysis are distinct events. Channel properties are discussed in the context of a model in which the pore is formed by a bundle of approximately parallel transbilayer helices.

The amphiphilic alpha-helix concept. Consequences on the structure of staphylococcal delta-toxin in solution and bound to lipids

Staphylococcal delta-toxin, a synthetic analogue and a fragment were studied in order to determine their structure in solution and bound in lipids. In solution, a self-association process is observed. Analytical ultracentrifuge and quasi-elastic light-scattering experiments suggest an isodesmic aggregation in the high concentration domain above 2 microM up to very large asymmetrical species. Decreasing concentrations below 2 microM of delta-toxin and the analogue allows dissociation, probably into monomers. The self-associated species are essentially alpha-helical (70%) with buried and highly immobilized Trp either at position 15 for natural delta-toxin or 16 for the analogue. At the lowest concentration studied, the alpha-helix content severely decreases down to 35% while Trp fluorescence shows that these residues are exposed to buffer. The fragment 11-26 is always monomeric and structureless. From all the data, a structural model of aggregated species is proposed with stacked antiparallel amphipathic rods. When bound to lipids, whatever their initial structure in solution, 26-residue long peptides mainly adopt an alpha-helix conformation (80%) while fragment 11-26 exhibits about 50% alpha-helix. The lipid-peptide interactions were quantitatively analysed. For fragment 11-26, a single-step mechanism fits the spectroscopic changes and defines a single monomeric bound structure. On the other hand, for the 26-residue-long analogue, multiple-step processes must occur. The data were analysed with a partition of tetramers into lipids followed by a partial dissociation. Finally, the affinity of fragment 11-26 severely decreases from micelles to fluid and gel-state bilayers. The partition coefficient of the delta-toxin analogue is higher than those of other more apolar peptides, such as melittin and alamethicin, correlating with Eisenberg's hydrophobic moments. It is therefore proposed that delta-toxin probably lies parallel to the surface, only penetrating weakly in lipids, depending on their packing.

Effect of staphylococcal delta-toxin and bee venom peptide melittin on leukotriene induction and metabolism of human polymorphonuclear granulocytes

The abilities of delta-toxin from Staphylococcus aureus and melittin to induce and modulate the generation of leukotriene from human polymorphonuclear granulocytes (PMNs) were studied. Stimulation of PMNs with melittin (10 micrograms) induced leukotriene formation, whereas stimulation with delta-toxin did not. Preincubation of the PMNs with delta-toxin modulated the subsequent generation of leukotriene from PMNs induced by Ca ionophore A23187 or opsonized zymosan. The generation of leukotriene B4 (LTB4), induced by the Ca ionophore A23187, was increased when the PMNs were preincubated with delta-toxin for 5 min. When opsonized zymosan was used as a secondary stimulus to activate the delta-toxin-pretreated PMNs, LTB4 generation decreased. In contrast, melittin showed no significant modulatory effect on the generation of leukotriene from PMNs. In addition, preincubation of PMNs with delta-toxin inhibited the conversion of LTB4 to omega-oxidation products. Our data suggest that peptides with similar structures, e.g., delta-toxin and melittin, induce and modify leukotriene generation in different manners.

Interaction of staphylococcal delta-toxin and synthetic analogues with erythrocytes and phospholipid vesicles. Biological and physical properties of the amphipathic peptides

Staphylococcal delta-toxin, a 26-residue amphiphilic peptide is lytic for cells and phospholipid vesicles and is assumed to insert as an amphipathic helix and oligomerize in membranes. For the first time, the relationship between these properties and toxin structure is investigated by means of eight synthetic peptides, one identical in sequence to the natural toxin, five 26-residue analogues and two shorter peptides corresponding to residues 1-11 and 11-26. These peptides were designed by the Edmundson wheel axial projection in order to maintain: (a) the hydrophilic/hydrophobic balance while rationalizing the sequence, (b) the alpha-helical configuration and (c) the common epitopic structure. The fluorescence of the single Trp residue was used to monitor the behaviour of the natural toxin and analogues. All 26-residue analogues were hemolytically active although to a lesser extent than natural toxin. The peptide of residues 11-26 bound lipids weakly and was hemolytic at high concentration. The peptide of residues 1-11 did not bind lipids and was hemolytically inactive. All peptides except the latter cross-reacted in immunoprecipitation tests with the natural toxin. The study of a 26-residue analogue by circular dichroism revealed an alpha-helical configuration in both the free and lipid-bound state. Changes in the fluorescence of the peptides in the presence of lipid micelles and bilayers varied according to the position of the reporter group. When bound to lipids, Trp5, Trp16 and the Fmoc-1 positions of the analogues became buried while Trp15 of the natural toxin and its synthetic replicate remained more exposed. All changes are rationalized by the proposal of an amphipathic helix whose hydrophobic face is embedded within the apolar core of bilayers while the hydrophilic and charged face remains more exposed to solvent.

The interaction of delta-hemolysin with calmodulin

Delta-Hemolysin forms a 1:1 complex with Ca2+ -liganded calmodulin. Probably because of the pronounced tendency of delta-hemolysin to self-associate, the apparent binding affinity is much less than that for melittin. Complex formation is reflected by an increase in quantum yield of Trp-15 of delta-hemolysin and by increased shielding from acrylamide quenching. There is, however, no indication of a change in peptide molecular ellipticity. The binding of 2-toluidinyl-naphthalene-6-sulfonate is reduced by complex formation, suggesting the involvement of a hydrophobic region. Complex formation also blocks the proteolysis by trypsin of the bond between residues 77 and 78. The time decays of fluorescence intensity and anisotropy for tryptophan are multiexponential for both free and complexed delta-hemolysin; the average decay time for intensity is substantially increased for the complex. The localized mobility of tryptophan is greatly reduced in the complex. Complex formation appears to involve both the C-terminal lobe and the connecting strand of calmodulin.

The design, synthesis, and crystallization of an alpha-helical peptide

Twelve- and sixteen-residue peptides have been designed to form tetrameric alpha-helical bundles. Both peptides are capable of folding into amphiphilic alpha-helices, with leucyl residues along one face and glutamyl and lysyl residues along the opposite face. Four such amphiphilic alpha-helices are capable of forming a noncovalently bonded tetramer. Neighboring helices run in antiparallel directions in the design, so that the complex has 222 symmetry. In the designed tetramer, the leucyl side chains interdigitate in the center in a hydrophobic interaction, and charged side chains are exposed to the solvent. The designed 12-mer (ALPHA-1) has been synthesized, and it forms helical aggregates in aqueous solution as judged by circular dichroic spectroscopy. It has also been crystallized and characterized by x-ray diffraction. The crystal symmetry is compatible with (but does not prove) the design. The design can be extended to a four-alpha-helical bundle formed from a single polypeptide by adding three peptide linkers.

Conformational alteration in alpha-toxin from Staphylococcus aureus concomitant with the transformation of the water-soluble monomer to the membrane oligomer

The membrane-damaging alpha-toxin aggregate of Staphylococcus aureus was characterized physicochemically. The aggregate weight of the toxin formed by various methods appeared to be 6 times higher than the molecular weight of the monomer as determined by the laser light scattering technique, suggesting the presence of a hexamer in the membrane. The aggregates fluoresced 20 to 50% more than the monomer at 336 nm. Circular dichroism measurements revealed that both the monomer and the oligomer showed essentially beta-sheet structure with the maximum ellipticity about -8,400 deg.cm2.dmol-1 at 215 nm. Circular dichroism spectrum of the oligomers showed ellipticity difference of -6,600, -44 and +84 deg.cm2.dmol-1, at 200, 250 and 280 nm, respectively, compared with the monomer. All these results suggest that the conformational change in the toxin molecule occurs concomitant with the transformation of the water-soluble monomer to the membrane-embedded hexamer.

Surface properties of bacterial sulfhydryl-activated cytolytic toxins. Interaction with monomolecular films of phosphatidylcholine and various sterols

Sulfhydryl-activated cytolysins are a group of bacterial protein toxins which, in the reduced state, lyse eukaryotic cells by disruption of the cytoplasmic membrane. Cell surface cholesterol is thought to be the target of the toxins. In the present work, the monolayer technique was used to investigate the interaction of four SH-activated toxins (streptolysin 0, alveolysin , perfringolysin 0, pneumolysin ) with various lipid films as a model for studying toxin-induced membrane disruption. A surface pressure increase up to very high values was elicited by reduced toxins (approximately equal to 10 nM) on films of cholesterol, other toxin-binding 3 beta-hydroxy-sterols, thiocholesterol and cholesterol-phosphatidylcholine mixtures suggesting deformation or penetration of the films. The surface-active potency of the toxins was of the same order as that of melittin and snake cardiotoxins at similar concentrations. No pressure increase was observed on films made of pure phosphatidylcholine, lanosterol and other sterols lacking the 3 beta-OH group. Optimal efficiency was at cholesterol/phosphatidylcholine molar ratio of 1 to 1. The critical pressures for toxin interaction with phosphatidylcholine and cholesterol monolayers were 25 mN X m-1 and 45 mN X m-1 respectively. Toxin interaction with phosphatidylcholine [14C]-cholesterol films did not modify monolayer radioactivity, indicating no cholesterol desorption. No pressure increase was elicited by toxins inactivated by SH-group reagents, heating or neutralization with antibody. Toxin effect was dependent temperature and pH. The overall potency of the four toxins tested was streptolysin 0 greater than alveolysin approximately equal to perfringolysin 0 greater than pneumolysin . The monolayer system mimicked in several respects toxin interaction with eukaryotic cells.

In vitro synthesis of the delta-lysin of Staphylococcus aureus

The stability of mRNA for the delta-lysin of Staphylococcus aureus was determined by measuring the residual lysin synthesis after inhibition of DNA-dependent RNA polymerase activity with rifampin. At the late logarithmic-early stationary phase of growth the delta-lysin mRNA was very stable, with a half-life of ca. 20 min. Total cellular RNA was extracted from S. aureus and translated with a modified Escherichia coli S-30 system; delta-lysin was identified amongst the translation products by immunoprecipitation and immunoabsorption. The delta-lysin synthesized in vitro was of a size similar to mature delta-lysin and did not require a signal sequence for secretion from the cell.

Photolabeling of staphylococcal alpha-toxin from within rabbit erythrocyte membranes

Intrinsic membrane proteins of rabbit red blood cells were labeled with the photoreactive amphipatic reagent 12-(4-azido-2-nitrophenoxy) stearoyl (1-14C) glucosamine, which inserts into the hydrophobic membrane region and generates a reactive nitrene upon ultraviolet irradiation. Photolabeling of membrane-bound staphylococcal alpha-toxin after lysis of probe-treated rabbit red blood cells by this toxin implies its penetration into the hydrophobic region of the outer leaflet of the membrane. In contrast clostridial theta-toxin and staphylococcal delta-toxin were not labeled, but extraction of intrinsic membrane proteins by delta-toxin was evidenced.

Cytolytic toxins and surface activity

Surface-active properties of alpha-toxin and delta-lysin, two cytolytic protein exotoxins of the bacterium Staphylococcus aureus are summarised. The relevance of differences in surface charge density on membranes is discussed in relation to possible mechanisms of binding and membrane penetration by alpha-toxin. An hypothesis for the mechanism of membrane disruption by delta-lysin involving the formation of hydrophilic transmembrane pores is proposed.

Hydrophobic interaction chromatography of Staphylococcus aureus delta-toxin

Staphylococcus aureus delta-toxin bound avidly to agarose gels containing phenyl, octyl, or decyl ligands, but less so to agarose with hexyl groups. Agarose with ethyl or butyl moieties did not bind any more toxin than did agarose without attached ligands. About 10% of the applied toxin preparation did not bind to gels and eluted with the starting buffer. The nonadsorbed material was not hemolytic, did not react with anti-delta-toxin immunoglobulin G, and did not appear to be a peptide. Toxin bound to phenyl-Sepharose was not eluted with water, solutions containing chaotropic ions or ethylene glycol, or by increasing the pH, but was eluted with 50% ethanol. The ethanol-eluted delta-toxin (EEDT) was soluble in water, ethanol, 10% sucrose, or 6 M urea, but was poorly soluble in aqueous salt solutions at neutral pH. Regardless of whether the soluble or insoluble form of delta-toxin was applied to the gel, the resultant EEDT fraction was water soluble. The hemolytic activity of EEDT was markedly reduced when assayed in saline, but was the same as that of the original toxin preparation when assayed in isotonic sucrose. A significant portion of EEDT, when rechromatographed on phenyl-Sepharose, did not bind to the gel. This unbound fraction may represent toxin aggregates in which the hydrophobic regions of the toxin monomers are interiorized within the aggregates.

Activation of human lymphocytes in vitro by membrane-damaging toxins from Staphylococcus aureus

Purified staphylococcal alpha-, gamma-, and delta-toxin were shown to cause activation of lymphoid cells from adult human donors and of cord cells in vitro as measured by [14C]thymidine incorporation after 7 days of incubation. T cell-enriched and T cell-depleted lymphocyte suspensions were activated in a similar fashion. Beta-toxin, on the other hand, exerted no valid stimulation of the various lymphocyte preparations. The lymphocyte-activating properties of alpha- and gamma-toxin were shown to be independent of their hemolytic capacity. The results probably reflect unspecific mitogen effects, but a component of specific reactivity cannot be excluded. We suggest that the unspecific triggering of lymphocytes in vitro is caused by surface-active properties of the toxins.

Staphylococcal delta toxin stimulates endogenous phospholipase A2 activity and prostaglandin synthesis in fibroblasts

Delta toxin, one of at least four toxins produced by pathogenic strains of the skin bacterium Staphylococcus aureus, is an amphipathic polypeptide possessing hemolytic and cytolytic activity. Delta toxin stimulates high levels of phospholipase A2 activity in 3T3 mouse fibroblasts with concomitant synthesis and release of prostaglandins. Alpha toxin, another hemolytic toxin produced by strains of S. aureus, did not stimulate phospholipase A2 or prostaglandin release in these cells. Analysis of the release of lactate dehydrogenase and beta-galactosidase (cytoplasmic and lysosomal marker enzymes, respectively) from delta-toxin-treated cells indicated that cytolytic concentrations of the toxin damage the cell-surface membrane more extensively than lysosomal membranes. During a 30 min exposure, delta toxin stimulated 3T3 cells to hydrolyze up to 32% of the lipids biosynthetically labeled by incorporation of [3H]arachidonic acid. A relatively high percentage of the free arachidonic acid formed in delta-toxin-treated 3T3 cells was converted to prostaglandins (up to 41.3% and 8.3% converted to chromatographically identifiable prostaglandins E2 and F2 alpha, respectively, in 30 min), with optimal conversion occurring at sublytic toxin concentrations. The degree of activation of phospholipase A2 in 3T3 cells by a range of concentrations of delta toxin correlates with cytotoxicity assessed by failure to exclude trypan blue dye. Analysis of the calcium dependency of the toxin-activated phospholipase A2 was consistent with a cell-surface, Ca2+-dependent enzyme. The phospholipase A2 exhibits a degree of specificity for substrate lipids containing polyunsaturated fatty acid residues which can serve as precursors for prostaglandin formation. Enzymatic activity was not inhibited by diisopropylfluorophosphate (5 mM), N-ethylmaleimide (5 mM) or p-bromophenacylbromide (0.1 mM). Delta toxin did not activate detectable phospholipase A2 in subcellular preparations containing plasma membrane.