Hemifusion and fusion of giant vesicles induced by reduction of inter-membrane distance.
Proteins involved in membrane fusion, such as SNARE or influenza virus hemagglutinin, share the common function of pulling together opposing membranes in closer contact. The reduction of inter-membrane distance can be sufficient to induce a lipid transition phase and thus fusion. We have used functionalized lipids bearing DNA bases as head groups incorporated into giant unilamellar vesicles in order to reproduce the reduction of distance between membranes and to trigger fusion in a model system. In our experiments, two vesicles were isolated and brought into adhesion by the mean of micromanipulation; their evolution was monitored by fluorescence microscopy. Actual fusion only occurred in about 5% of the experiments. In most cases, a state of "hemifusion" is observed and quantified. In this state, the outer leaflets of both vesicles' bilayers merged whereas the inner leaflets and the aqueous inner contents remained independent. The kinetics of the lipid probes redistribution is in good agreement with a diffusion model in which lipids freely diffuse at the circumference of the contact zone between the two vesicles. The minimal density of bridging structures, such as stalks, necessary to explain this redistribution kinetics can be estimated.
Heuvingh
J
J
Laboratoire de Physico-Chimie Moléculaire des Membranes Biologiques, URD-CNRS UMR 7099, IBPC, 13 rue Pierre et Marie Curie, 75005 Paris, France. julien.heuvingh@univ-paris5.fr
Pincet
F
F
Cribier
S
S
D022081:Cell Surface Extensions / Q000737:chemistry*; D004247:DNA / Q000737:chemistry; D004058:Diffusion; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D046911:Macromolecular Substances; D008560:Membrane Fluidity; D008561:Membrane Fusion; D008567:Membranes, Artificial; D008846:Micromanipulation / Q000379:methods*; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D013314:Stress, Mechanical
D008051:Lipid Bilayers; D008081:Liposomes; D046911:Macromolecular Substances; D008567:Membranes, Artificial; D004247:DNA