Trans-SNARE pairing can precede a hemifusion intermediate in intracellular membrane fusion.
The question concerning whether all membranes fuse according to the same mechanism has yet to be answered satisfactorily. During fusion of model membranes or viruses, membranes dock, the outer membrane leaflets mix (termed hemifusion), and finally the fusion pore opens and the contents mix. Viral fusion proteins consist of a membrane-disturbing 'fusion peptide' and a helical bundle that pin the membranes together. Although SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes form helical bundles with similar topology, it is unknown whether SNARE-dependent fusion events on intracellular membranes proceed through a hemifusion state. Here we identify the first hemifusion state for SNARE-dependent fusion of native membranes, and place it into a sequence of molecular events: formation of helical bundles by SNAREs precedes hemifusion; further progression to pore opening requires additional peptides. Thus, SNARE-dependent fusion may proceed along the same pathway as viral fusion: both use a docking mechanism via helical bundles and additional peptides to destabilize the membrane and efficiently induce lipid mixing. Our results suggest that a common lipidic intermediate may underlie all fusion reactions of lipid bilayers.
Reese
Christoph
C
Département de Biochimie, Université de Lausanne, Chemin des Boveresses 155, CH-1066 Epalinges, Switzerland.
Heise
Felix
F
Mayer
Andreas
A
D007425:Intracellular Membranes / Q000378:metabolism*; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism; D050356:Lipid Metabolism; D008561:Membrane Fusion; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D050600:SNARE Proteins; D014617:Vacuoles / Q000737:chemistry / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000378:metabolism*
D008051:Lipid Bilayers; D050600:SNARE Proteins; D033921:Vesicular Transport Proteins