M. Murata et al., FUSION OF DIOLEOYLPHOSPHATIDYLCHOLINE VESICLES INDUCED BY AN AMPHIPHILIC CATIONIC PEPTIDE AND OLIGOPHOSPHATES AT NEUTRAL PH, Biochimica et biophysica acta, 1152(1), 1993, pp. 99-108
Peptide E5 is an analogue of the fusion peptide of influenza virus hem
agglutinin and K5 is a cationic peptide which has an arrangement of el
ectric charges complementary to that of E5. We reported that a stoichi
ometric mixture of E5 and K5 caused fusion of large unilamellar vesicl
es (LUV) of neutral phospholipids (Murata, M., Kagiwada, S., Takahashi
, S. and Ohnishi, S. (1991) J. Biol. Chem. 266, 14353-14358). K5 cause
d fusion of LUV composed of dioleoylphosphatidylcholine (DOPC) at pH >
10, but not at neutral pH. In the presence of oligophosphates, such a
s 1 mM ATP, GTP, or polyphosphate, K5 caused rapid and efficient fusio
n of DOPC LUV at neutral pH without hydrolysis of oligophosphate group
s, but another anions such as citrate, acetate, AMP, phosphate, or EDT
A were ineffective. The peptide/oligophosphate-induced fusion behavior
s have been investigated by a fluorescence resonance energy transfer a
ssay for lipid mixing of LUV and negative staining electron microscopy
. At higher ionic strengths (> 0.3 M KCl) or in the presence of 5.0 mM
MgCl2, the fusion was inhibited. Even at the inhibitory conditions, t
he association of K5 with lipid vesicles at neutral pH was directly co
nfirmed by the Ficoll gradient assay method and by blue shifts of the
tryptophan fluorescence of the peptide. A nonhydrolyzable GTP analogue
, GTPgammaS, also induced fusion. These observations suggested that th
e electrostatic interactions between the positive and negative charges
of K5 and oligophosphate, respectively, induced complex formation, tr
iggering membrane fusion.