δ-Haemolysin from Staphylococcus aureus and model membranes

Solid-state 2H NMR and 31P NMR of 2H-enriched chains and polar head groups, respectively, of dipalmitoylglycerophosphatidylcholine/water dispersions were undertaken to investigate the action of δ-haemolysin from Staphylococcus aureus on biomembranes. When the lipid/toxin molar ratio, Ri is 10, the gelphase 2H powder patterns and the temperature of the gel–fluid phase transition, tc, are unchanged by the presence of the toxin whereas the 31P powder spectra of polar head groups are perturbed. At t > tc, a detailed analysis of methylene ordering indicates that δ-haemolysin orders the lipid chains near tc and disorders them for t≫tc. These findings are interpreted in terms of peptide location with regard to the membrane and suggest that the position of the toxin depends on the temperature relative to tc. Experiments carried out at Ri= 4 exhibit sharp, isotropic 2H-NMR lines, at t > tc, indicating that δ-haemolysin promotes the appearance of very small objects undergoing fast isotropic reorientation which average to zero the quadrupolar interaction. Below tc, one observes gel-phase powder patterns which indicate that the bacterial toxin is unable to form such small structures with ordered dipalmitoylglycerophosphocholine phospholipids. From comparison of the action of δ-haemolysin with that of melittin on same lipids [Dufourc et al. (1986) Biochemistry 25, 6448–6455] it results that both toxins perturb similarly fluid-phase lipids at elevated temperature, but they behave differently with gel-phase lipids, the former toxin being less efficient in membrane restructuring than the latter.