T. Benachir et al., MELITTIN-INDUCED LEAKAGE FROM PHOSPHATIDYLCHOLINE VESICLES IS MODULATED BY CHOLESTEROL - A PROPERTY USED FOR MEMBRANE TARGETING, European biophysics journal, 25(3), 1997, pp. 201-210
Melittin, an amphiphathic peptide, affects the permeability of vesicle
s. This can be demonstrated using the dye release technique. Calcein,
a fluorescent marker, is trapped in large unilamellar 1-palmitoyl-2-ol
eoyl-phosphatidylcholine (POPC) vesicles and melittin-induced leakage
of the dye can be monitored directly by increasing fluorescence intens
ity. First, we characterized the effect of increasing cholesterol cont
ent in the membrane on melittin-induced leakage and our results reveal
that cholesterol inhibits the lytic activity of the peptide. Using in
trinsic fluorescence of the single tryptophan of melittin and H-2-NMR
of headgroup deuterated phosphatidylcholine, we demonstrated that the
affinity of melittin for phosphatidylcholine vesicles is reduced in th
e presence of cholesterol; this is associated with the tighter lipid p
acking of the cholesterol-containing bilayer. This reduced binding is
responsible for the reduced melittin-induced leakage from cholesterol-
containing membranes. The pathway of release was determined to be an a
ll-or-none mechanism. Finally, we investigated the possibility of achi
eving specific membrane targeting with melittin, when vesicles of diff
erent lipid composition are simultaneously present. Melittin incubated
together with vesicles made of pure POPC and POPC containing 30(mol)%
cholesterol can empty nearly all the cholesterol-free vesicles while
the cholesterol-containing vesicles remain almost intact. Owing to the
preferential interaction of melittin with the pure POPC vesicles, we
were able to achieve controlled release of encapsulated material from
a specific vesicle population.