EFFECT OF STREPTOLYSIN O ON ERYTHROCYTE MEMBRANES, LIPOSOMES, AND LIPID DISPERSIONS A Protein-Cholesterol Interaction JAMES L. DUNCAN and RICHARD SCHLEGEL From the Departments of Microbiology and Pathology, Northwestern University Medical and Dental Schools, Chicago, Illinois 60611. Dr. Schlegel's present address is the Department of Pathology, Peter Bent Brigham Hospital, Harvard University Medical School, Boston, Massachusetts 02115. Downloaded from http://rupress.org/jcb/article-pdf/67/1/160/1266643/160.pdf by guest on 01 October 2021 ABSTRACT The effect of the bacterial cytolytic toxin, streptolysin O (SLO), on rabbit erythrocyte membranes, liposomes, and lipid dispersions was examined. SLO produced no gross alterations in the major erythrocyte membrane proteins or lipids. However, when erythrocytes were treated with SLO and examined by electron microscopy, rings and "C"-shaped structures were observed in the cell membrane. The rings had an electron-dense center, 24 nm in diameter, and the overall diameter of the structure was 38 nm. Ring formation also occurred when erythrocyte membranes were fixed with glutaraldehyde and OsO4 before the addition of toxin. In contrast, rings were not seen when erythrocytes were treated with toxin at 0~ indicating that adsorption of SLO to the membrane is not sufficient for ring formation since toxin is known to bind to erythrocytes at that temperature. The ring structures were present on lecithin-cholesterol-dicetylphos- phate liposomes after SLO treatment, but there was no release of the trapped, internal markers, K2CrO4 or glucose. The crucial role of cholesterol in the formation of rings and C's was demonstrated by the fact that these structures were present in toxin-treated cholesterol dispersions, but not in lecithin-dicetylphosphate dispersions nor in the SLO preparations alone. The importance of cholesterol was also shown by the finding that no rings were present in membranes or cholesterol dispersions which had been treated with digitonin before SLO was added. Al- though the rings do not appear to be "holes" in the membrane, a model is pro- posed which suggests that cholesterol molecules are sequestered during ring and C-structure formation, and that this process plays a role in SLO-induced hemoly- sis. Streptolysin O (SLO) is a bacterial toxin produced bacteria, and possess a number of common proper- by virtually all strains of Streptococcus pyogenes. ties: they are activated by SH compounds: they The toxin is a protein with a molecular weight of appear to be antigenically related; and their bio- approximately 60,000 daltons, and is characteristic logical activity is completely inhibited by low of a group of cytolytic toxins known as the concentrations of cholesterol and certain related oxygen-labile toxins (3). The toxins in this group sterols. are produced by several different gram-positive Hemolysis occurs within minutes after the addi- 160 THE JOURNALOF CELL BIOLOGY VOLUME67, 1975 pages 160-173 tion of SLO to erythrocytes, and toxic effects of collected and resuspcnded in 0.05 M Tris buffer, pH 8.4. SLO on several types of mammalian cells in The crude toxin preparation was applied to a 2.5 • culture have been demonstrated (13). The speed 100-cm G-100 Sephadex column with a bed volume of with which sensitive cells are affected by the toxin 400 ml, which had been equilibrated with Tris buffer at 4oC. The toxin was eluted and the active fractions were suggests that the cell membrane is the primary site pooled and applied to a 1.5 • 30-cm DEAE-Sephadex of action. Several lines of indirect evidence suggest column equilibrated in the same Tris buffer. The column that membrane cholesterol is the binding site was washed with 400-500 ml of buffer, and SLO was and/or target of SLO action. Only those cells eluted by the addition of a 0.3 M NaCI gradient. The which contain cholesterol in their membranes are toxin had a specific activity of approximately 200,000 susceptible to the toxin, SLO is "inactivated" only hemolytic units (HU) per mg protein, and gave a single by the membrane lipid fraction which contains protein band on disc gel electrophoresis. The toxin was cholesterol, and the addition of exogenous choles- activated by the addition of 10 mM cysteine, and stored terol to SLO inhibits toxin action. Shany and at -70~ SLO activity was assayed as previously co-workers (24) recently provided evidence that described (10). SLO does not adsorb to erythrocyte membranes Erythrocytes Downloaded from http://rupress.org/jcb/article-pdf/67/1/160/1266643/160.pdf by guest on 01 October 2021 which have been treated with alfalfa saponin or the polyene antibiotic, filipin, agents known to bind to Rabbit blood was collected from New Zealand white rabbits or purchased locally from a veterinarian. The cholesterol in the membrane. Despite these obser- blood was centrifuged at 2,000 g and the plasma and vations, it is not known how SLO produces the buffy coat were removed by aspiration. The cells were membrane alterations which result in lysis or death washed at least three times with phosphate-buffered of sensitive cells. saline (PBS; NaC1, 137 raM; Na2HPO,, 8 raM; When red ceils are treated with certain hemo- KH2PO,, 2 raM; pH 7.2). lytic agents such as saponin, filipin, or antibody plus complement, characteristic rings or holes are Analysis of Erythrocyte formed in the erythrocyte membrane (reviewed by Membrane Components Seeman, reference 22). The rings are readily seen Washed rabbit erythrocytes were suspended in PBS to in electron micrographs of negatively stained a concentration of 40-50%, and 0.1-0.2 ml of SLO membrane preparations, but their relationship to (500-2,000 HU) or control solution (consisting of Tris the lytic process is not clear. Freeze-etch studies on buffer plus cysteine) was added to 2-4 ml of the cell saponin-treated erythrocytes, however, suggest suspension. Other controls included the addition of that this substance produces an actual hole in the cholesterol-inactivated SLO, SLO neutralized by an- membrane (23). Several years ago, Dourmashkin titoxin, or heat-inactivated toxin. The cell suspensions and Rosse (9) reported that SLO produced "holes" were incubated at 37~ for 0.5, I, 3, 5, or 17 h; lysis of with a 50-nm diameter in erythrocyte membranes. suspensions treated with active toxin was apparent in less The toxin preparation which they used was not than 5 rain. After incubation, the erythrocytc membranes described, however, and the conditions necessary were isolated and washed in 5 mM Na2HPO~ buffer, pH 8, as described by Fairbanks et al. (l l). for the formation of the membrane lesions were not reported. MEMBRANE PROTEINS We have studied the effects of SLO on the major The washed membranes were solubilized in 2% sodium erythrocyte membrane proteins and lipids, and dodecylsulfate (SDS) at 100~ for 3 rain (16). A 0.l-ml have examined the lesions produced by the toxin sample of solubilized membranes was added to an equal on red cells, ghosts, liposomes, and cholesterol volume of a solution containing 5% (wt/vol) SDS, 160 dispersions. A model is proposed to account for mM dithiothreitol, 50 mM Tris-HCl (pH 8). 20 .g/ml the ringlike structures which are observed. pyronin Y, 50% (wt/vol) sucrose, and 5 mM EDTA, and the major erythrocyte membrane proteins were analyzed by electrophoresis on 5.6% polyacrylamide gels as de- MATERIALS AND METHODS scribed by Fairbanks and co-workers (11). Toxin Preparation In some experiments, the membrane proteins were cross-linked by incubating toxin-treated or control mem- The Richards strain (type 3) of S. pyogenes was used branes in 5 mM phosphate buffer with an equal volume for SLO production. Culture supernates (20-24 h) of this of phosphate buffer containing 0, 2, or 4 mM glutaralde- organism, grown in trypticase soy broth-yeast extract hyde. After 20 min at room temperature, the membranes (3:1) dialysate medium supplemented with 0.5% glucose were washed and solubilized by the procedure of Steck and Na~HPO, were harvested and brought to 70% (28). The proteins were analyzed on 3% polyacrylamide saturation with solid (NH4)3SO,. The precipitate was gels. DUNCAN AND SCHLEGEL Effects of Streptolysin 0 161 MEMBRANE LIPIDS dispersed over the air-water interface. A 400-mesh, Washed membranes of SLO-treated or control red Formvar-carbon-coated copper grid was gently applied cells were extracted in CHCl3-methanol with procedure to the surface of the drop for I min. Excess fluid was III of Ways and Hanahan (30). The final lipid extract removed from the grid by touching the edge with filter was resuspended in 1 ml benzene and stored at -20~ paper. The membrane lipids were analyzed by thin-layer GHOSTS: A 20-#1 sample of an untreated 50% red cell chromatography (TLC) on silica gel 60 plates (Merck), suspension was added to a 1-ml drop of water, and the by the procedures described by Skipsky (26). Phospho- ghosts were taken up on grids as described above. The lipids were analyzed with a solvent system of CHCls- ghosts were then treated with toxin by floating the grids methanol-acetic acid-H~O (25:15:4:2). For neutral lipids, on 20-#1 droplets of SLO solutions for 10 rain at 37~ the plates were run first in isopropyl ether-acetic acid LIPOSOMES AND LIPID DISPERSIONS: Liposomes were (96:4), then in petroleum ether-diethyl ether-acetic acid diluted 1:50 in PBS, and a 20-~1 sample was mixed with (90:10:1). The plates were developed by spraying with 40 #1 of SLO (200 HU) or control solution and incubated H2SO~ and charring at 300~ or 15 min. at 37 C for 10 min.