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After warming, more labelled v-SNARE remains full length: lane 2 is approximately 80–85% of the reference signal, compared with about 40–45% in lane 1. Formation of a protected SNARE complex provides a consistent explanation: the susceptible part of v-SNARE is less accessible after complex assembly.

Protection is not itself a unique readout of membrane fusion. Some protein may face the vesicle lumen, and SNARE complexes can protect protein without proving that the two aqueous compartments have merged. The inference depends on comparing these alternatives with the detergent and partner-free controls.

In lane 3, detergent removes the lipid bilayer barrier while both partner preparations are present. Their binding regions can then encounter one another even if they originally faced inward or were on poorly apposed lipid bilayers. The strong remaining full-length signal is consistent with extensive formation of protected SNARE complexes.

Thus detergent does not prevent partner association under the displayed conditions; it removes the topological restriction on that association. This lane is the normalization reference, not a direct measurement that 100% of all initially supplied protein is active. The weak signal in the detergent-treated partner-free control also argues against detergent simply preventing all cleavage.

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]

SNAP-25 is a SNARE protein that contributes two helices to the neuronal fusion complex, partnering with syntaxin and synaptobrevin. Lipid attachment anchors SNAP-25 to membranes despite its lack of a conventional membrane-spanning helix. Assembly helps couple recognition of a secretory carrier to membrane fusion. Its two helical contributions explain why a four-helix SNARE complex need not contain four separate protein chains. ^[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]

Syntaxin-4 is a membrane-associated SNARE protein involved in fusion at the plasma cell membrane. In regulated GLUT4 delivery, it participates with compatible partners in the fusion machinery that exposes transporters at the cell surface. Its presence identifies a possible component of that machinery; productive fusion also depends on assembly and regulation of the whole SNARE complex. ^[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]

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]