UNDERSTANDING CELL SECRETION AND MEMBRANE FUSION PROCESSES ON THE NANOSCALE USING THE ATOMIC FORCE MICROSCOPE - Life at the Nanoscale: Atomic Force Microscopy of Live Cells - page 106

complex involved in fusion of opposing lipid membranes. The structure and
arrangement of the membrane-associated full-length SNARE complex was
irst determined using AFM ( Fig. 5.5 ) . 20 Results from the study demonstrate
that t-SNAREs and v-SNARE, when present in opposing bilayers, interact
in a circular array to form supramolecular ring complexes each measuring
a few nanometers. The size of the ring complex is directly proportional to
the curvature of the opposing bilayers. 24 In the presence of calcium, the ring
complex helps in establishing continuity between the opposing bilayers. 21-23
In contrast, in the absence of membrane, soluble v-SNARE and t-SNAREs fail
to assemble in such speciic and organized pattern and do not form such
conducting channels. Once v-SNARE and t-SNAREs residing in opposing
bilayers meet, the resulting SNARE complex overcome the repulsive forces
between the opposing bilayers, bringing them closer to within a distance of
2.8-3 Å, allowing calcium bridging of the opposing phospholipids headgroups,
leading to local dehydration and membrane fusion. 21-23

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