Abstract :
[en] Elucidation of the molecular mechanism leading to biomembrane fusion is a
challenging issue in current biomedical research in view of its involvement in
controlling cellular functions and in mediating various important diseases.
According to the generally admitted stalk mechanism described for membrane
fusion, negatively curved lipids may play a central role during the early steps
of the process. In this study, we used atomic force microscopy (AFM) to address
the crucial question of whether negatively curved lipids influence the
interaction of the simian immunodeficiency virus (SIV) fusion peptide with model
membranes. To this end,
dioleoylphosphatidylcholine/dipalmitoylphosphatidylcholine (DOPC/DPPC) bilayers
containing 0.5 mol % dioleoylphosphatidic acid (DOPA) were incubated with the SIV
peptide and imaged in real time using AFM. After a short incubation time, we
observed a 1.9 nm reduction in the thickness of the DPPC domains, reflecting
either interdigitation or fluidization of lipids. After longer incubation times,
these depressed DPPC domains evolved into elevated domains, composed of nanorod
structures protruding several nanometers above the bilayer surface and attributed
to cylindrical reverse micelles. Such DOPC/DPPC/DOPA bilayer modifications were
never observed with nontilted peptides. Accordingly, this is the first time that
AFM reveals the formation of cylindrical reverse micelles in lipid bilayers
promoted by fusogenic peptides.
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