Abstract
The actions of bee venom melittin and delta-lysin from Staphylococcus aureus on membranes have been monitored by solid-state deuterium and phosphorus NMR and shown to differ depending on temperature and on the lipid-to-peptide molar ratio Ri. In the gel phase of phosphatidylcholine model membranes, for lipid-to-peptide ratios Ri>15, melittin induces isotropic lines interpreted as reflecting the presence of small discoidal structures, whereas deltalysin does not. These small objects are metastable, that is, within a time-scale of hours they return to large lipid bilayers. The kinetics of this process depend on the lecithin chain length. In the fluid phases, at temperatures greater than that of the gel-to-fluid transition Tc, analysis of the quadruplar splittings in terms of chain ordering indicates that both melittin and delta-lysin similarly disorder the membrane. At temperatures above but close to Tc, melittin preferentially orders the center of the bilayer, while delta-lysin promotes ordering throughoout the entire bilayer thickness. These effects are interpreted as reflecting different locations of the peptides with respect to the membrane surface. The addition of greater amounts of toxins, Ri=4, on phosphatidylcholine model membranes induces very small structures irrespective of the temperature in the case of melitin, but only above Tc for deltalysin. NMR spectral features similar to those characterizing the small fast-tumbling objects with phosphatidylcholine are also observed with egg phosphatidylethanolamine and erythrocyte membranes. The formation of small structures is thus inferred as a general process which reflects membrane supramolecular reorganization. This is proposed as a possible step for direct membrane lysis, on both phospholipid bilayers and biological membranes.
Highlights
Melittin and deJta-lysin are two peptidic toxins of 26 amino-acids, derived from bee venom and secreted by Staphylococcus aureus, respectively
nuclear magnetic resonance (NMR) of natural membranes is shown to be very useful in extending the conclusions reached with model membranes
Changes induced on DPPC by the toxins as followed by deuterium NMR
Summary
Melittin and deJta-lysin are two peptidic toxins of 26 amino-acids, derived from bee venom and secreted by Staphylococcus aureus, respectively. Originating from different species, these amphipatic peptides promote very similar effects on biological membranes, i.e. they lyse a wide variety of cells or subcellular compartments [1,2]. They have different efficiencies: for example, melittin is more active than delta lysin in the release of hemoglobin on sheep and cod erythrocytes [3]. Both toxins bind to phospholipids and are able to induce the release of molecules trapped inside vesicles (2,4,5). NMR of natural membranes is shown to be very useful in extending the conclusions reached with model membranes
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