Membrane fusion induced by neuronal SNAREs transits through hemifusion.
Synaptic transmission requires the controlled release of neurotransmitter from synaptic vesicles by membrane fusion with the presynaptic plasma membrane. SNAREs are the core constituents of the protein machinery responsible for synaptic membrane fusion. The mechanism by which SNAREs drive membrane fusion is thought to involve a hemifusion intermediate, a condition in which the outer leaflets of two bilayers are combined and the inner leaflets remain intact; however, hemifusion has been observed only as an end point rather than as an intermediate. Here, we examined the kinetics of membrane fusion of liposomes mediated by recombinant neuronal SNAREs using fluorescence assays that monitor both total lipid mixing and inner leaflet mixing. Our results demonstrate that hemifusion is dominant at the early stage of the fusion reaction. Over time, hemifusion transitioned to complete fusion, showing that hemifusion is a true intermediate. We also show that hemifusion intermediates can be trapped, likely as unproductive outcomes, by modulating the surface concentration of the SNARE proteins.
Department of Biochemistry, Biophysics, and Molecular Biology, Iowa State University, Ames, Iowa 50011, USA.
Xiaobing
X
Lu
Fan
F
Zhang
James A
JA
McNew
Yeon-Kyun
YK
Shin
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry; D008055:Lipids / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry; D008561:Membrane Fusion; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D009474:Neurons / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry; D050600:SNARE Proteins; D009435:Synaptic Transmission; D013997:Time Factors; D033921:Vesicular Transport Proteins / Q000378:metabolism*
D008051:Lipid Bilayers; D008055:Lipids; D008081:Liposomes; D011994:Recombinant Proteins; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins