Alteration by cereolysin of the structure of cholesterol-containing membranes

Abstract

When erythrocyte membranes were treated with cereolysin, negatively stained and examined by electron microscopy, ring and arc-shaped structures were observed in the membrane. The outside diameter of the rings varied from 33 to 50 nm with a border thickness of 6.7 to 8.3 nm. The arcs varied in length from 33 to 170 nm with a border thickness of also 6.7 to 8.3 min. When right-side-out erythrocyte ghosts which had been treated with cereolysin were examined by electron microscopy after freeze-fracture, structures with a diameter of 31 to 63 nm were seen in the fracture face of the exoplasmic half of the membrane, but no alterations were visible in the fracture face of the protoplasmic half of the membrane bilayer. Thus the ring structures did not appear to form holes through the membrane. At cereolysin concentrations above 6 microgram/ml rings and arcs were seen when purified toxin alone was examined. At or below 6 microgram/ml toxin rings and arcs were seen only if toxin was incubated with free or membrane-bound cholesterol. Our interpretation is that cereolysin tends to aggregate into ring and arc-shaped structures, and that the tendency to aggregate is increased by cholesterol. Rings and arcs were not seen when erythrocyte ghosts were treated with low, but lytic amounts of cereolysin that significantly altered the premeability of the ghosts.