title: Direct observation of intermediate states in model membrane fusion.
abstract: We introduce a novel assay for membrane fusion of solid supported membranes on silica beads and on coverslips. Fusion of the lipid bilayers is induced by bringing an optically trapped bead in contact with the coverslip surface while observing the bead's thermal motion with microsecond temporal and nanometer spatial resolution using a three-dimensional position detector. The probability of fusion is controlled by the membrane tension on the particle. We show that the progression of fusion can be monitored by changes in the three-dimensional position histograms of the bead and in its rate of diffusion. We were able to observe all fusion intermediates including transient fusion, formation of a stalk, hemifusion and the completion of a fusion pore. Fusion intermediates are characterized by axial but not lateral confinement of the motion of the bead and independently by the change of its rate of diffusion due to the additional drag from the stalk-like connection between the two membranes. The detailed information provided by this assay makes it ideally suited for studies of early events in pure lipid bilayer fusion or fusion assisted by fusogenic molecules.
authors.affiliation: Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Andrea
authors.initials: A
authors.lastname: Keidel
authors.affiliation: Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA.|Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, New York, New York, 10065, USA.
authors.forename: Tobias F
authors.initials: TF
authors.lastname: Bartsch
authors.affiliation: Center for Nonlinear Dynamics and Department of Physics, University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Ernst-Ludwig
authors.initials: EL
authors.lastname: Florin
mesh_terms: D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008561:Membrane Fusion; D009038:Motion; D010713:Phosphatidylcholines / Q000737:chemistry*; D010714:Phosphatidylethanolamines / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry; D013500:Surface Tension; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D012822:Silicon Dioxide; C017251:1,2-oleoylphosphatidylcholine; D004134:Dimyristoylphosphatidylcholine