Membrane fusion intermediates via directional and full assembly of the SNARE complex.
Cellular membrane fusion is thought to proceed through intermediates including docking of apposed lipid bilayers, merging of proximal leaflets to form a hemifusion diaphragm, and fusion pore opening. A membrane-bridging four-helix complex of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) mediates fusion. However, how assembly of the SNARE complex generates docking and other fusion intermediates is unknown. Using a cell-free reaction, we identified intermediates visually and then arrested the SNARE fusion machinery when fusion was about to begin. Partial and directional assembly of SNAREs tightly docked bilayers, but efficient fusion and an extended form of hemifusion required assembly beyond the core complex to the membrane-connecting linkers. We propose that straining of lipids at the edges of an extended docking zone initiates fusion.
Department of Neurobiology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.
Javier M
JM
Hernandez
Alexander
A
Stein
Elmar
E
Behrmann
Dietmar
D
Riedel
Anna
A
Cypionka
Zohreh
Z
Farsi
Peter J
PJ
Walla
Stefan
S
Raunser
Reinhard
R
Jahn
D000818:Animals; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism*; D008081:Liposomes / Q000737:chemistry / Q000378:metabolism; D008561:Membrane Fusion; D011485:Protein Binding; D011487:Protein Conformation; D051381:Rats; D050600:SNARE Proteins / Q000737:chemistry / Q000378:metabolism*; D050988:Vesicle-Associated Membrane Protein 2 / Q000378:metabolism
D008051:Lipid Bilayers; D008081:Liposomes; D050600:SNARE Proteins; C494706:Vamp2 protein, rat; D050988:Vesicle-Associated Membrane Protein 2