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Cold preincubation can accumulate docked, fusion-ready intermediates. On warming, that population proceeds promptly to lipid mixing, whereas newly combined vesicles must first encounter, dock and assemble productive SNARE complexes. This explains the faster initial rise and larger signal at the displayed endpoint without requiring a different total amount of fluorescent lipid.

The original reconstitution experiments likewise distinguish docking from subsequent membrane fusion.^[ref]

A SNARE complex is an assembly of complementary SNARE proteins, commonly forming a four-helix bundle. A trans complex bridges opposing membranes and can promote membrane fusion; after fusion, its components occupy the same membrane in a cis complex. ATP-dependent disassembly permits component reuse. This distinction explains why detecting a complex alone does not determine whether it is a fusion intermediate or a product remaining after fusion. ^[ref]

A SNARE protein contributes a helical segment to a membrane-fusion assembly. Complementary SNARE proteins on opposing membranes form a SNARE complex whose assembly helps pull the membranes together. Syntaxins, SNAP-25 and synaptobrevin illustrate different components of the neuronal machinery. Purified components reconstituted into separate liposomes can promote fusion, showing that these proteins participate directly in membrane rearrangement. Cellular control additionally involves targeting and regulatory factors. ^[ref]

Synaptobrevin is a membrane-anchored SNARE protein associated with secretory vesicles, including synaptic vesicles. Its cytosolic helix joins complementary helices from syntaxin and SNAP-25 to form a SNARE complex. When the partners initially occupy opposing lipid bilayers, their assembly helps bring those lipid bilayers close enough for membrane fusion. The protein helps couple the membranes mechanically; it is not a pore through which the neurotransmitter simply leaks. ^[ref]

Reconstituting synaptobrevin and its complementary SNARE proteins into separate liposomes made fusion measurable outside a cell. The ability to accumulate docked intermediates at low temperature and trigger fusion on warming also distinguished membrane docking from the subsequent merger. Living synapses add regulation that this minimal assay does not reproduce. ^[ref]

Syntaxin is a family of membrane-anchored SNARE proteins that contributes a helix to a membrane-fusion complex. In neuronal secretion, syntaxin and SNAP-25 on the target cell membrane assemble with synaptobrevin on a synaptic vesicle. Syntaxin contributes one helix, synaptobrevin one and SNAP-25 two, producing a four-helix SNARE complex from three protein chains. Assembly across opposing lipid bilayers couples molecular binding to membrane fusion. ^[ref]

The membrane context matters. Reconstituted complementary SNARE proteins in different liposomes can promote fusion, while a complex assembled after fusion has its membrane anchors on the same lipid bilayer. Detecting a syntaxin-containing complex therefore does not by itself show that it is still bridging a vesicle to its target. ^[ref]

A t-SNARE is a SNARE protein or complementary assembly assigned to the target membrane in a particular membrane-transport event. It pairs with a v-SNARE on the incoming carrier to form a fusion-associated SNARE complex. The prefix describes the experimental transport arrangement; it does not imply that a given membrane is always a target in every trafficking pathway. The neuronal target assembly includes syntaxin and SNAP-25. ^[ref]

Coauthor of experiments on SNARE complexes as minimal membrane-fusion machinery. Reconstitution tested what selected molecular components could achieve without the full complexity of a living cell.^[ref]

A vesicle is a small compartment enclosed by a lipid bilayer. Its vesicle lumen can carry soluble cargo, while its lipid bilayer carries lipids and membrane proteins. In a transport pathway, budding separates a carrier from one compartment and membrane fusion joins it to another. Orientation matters: fusion of a secretory vesicle with the cell membrane connects its vesicle lumen to the extracellular space while incorporating its membrane proteins into the surface. ^[ref]

A vesicle is therefore more than a freely diffusing package. Recognition, movement and membrane fusion require distinct interactions. In a reconstitution experiment, complementary SNARE proteins placed in separate liposomes brought opposing lipid bilayers together and promoted fusion; the experiment isolated one part of transport from the rest of a living cell. ^[ref]

Vesicle docking brings a transport vesicle into close, stable association with its target membrane before membrane fusion. Recognition factors and SNARE proteins help organize the contact. Docking and fusion are experimentally distinct: a carrier can remain attached without exchanging its internal contents with the target compartment. Reconstituted liposomes bearing appropriate SNARE proteins allowed such docked intermediates to be distinguished from subsequent fusion. ^[ref]

A v-SNARE is a SNARE protein assigned to a transport vesicle in a specified fusion event. Complementary interaction with a t-SNARE on the target produces a membrane-bridging SNARE complex. Synaptobrevin is a familiar example in neuronal secretion. The label describes which membrane initially carries the component; after membrane fusion, both sets of components occupy the same membrane and must be reorganized for reuse. ^[ref]