Cryo-transmission electron microscopy was used in combination with turbidity and leakage measurements to explore and compare the membrane perturbing effects of
melittin and
alamethicin on POPC-based
liposomes of varying composition. The results show that the two
peptides, despite their differences in physico-chemical properties and proposed mode of action, induce similar structural effects on the
liposomes. Importantly, whereas low
peptide concentrations leave pure POPC
liposomes intact and seemingly unperturbed, POPC
liposomes supplemented with 40 mol.%
cholesterol change their shape,
rupture and fuse in response to the addition of both
melittin and
alamethicin. In the case of
alamethicin, but not
melittin, fusion is effectively prevented by inclusion of 10 mol.% POPG in the
liposome membranes. By means of a competitive binding assay we furthermore show that
alamethicin, in line with earlier findings for
melittin, possess high affinity for positively curved
lipid surfaces. Moreover, results from the present study show that
magainin 2 has a similar preference for curved surfaces.