SNAREs והתמזגות ממברנה

For a vesicle to fuse with the target organelle, the lipid layers of the two membranes must be within one point five nanometers of each other.

In this proximity, lipids flow from one bilayer to the other by displacing water molecules around the membrane. This energetically unfavorable process requires specialized fusion proteins called SNAREs.

SNAREs are transmembrane proteins with helical motifs that catalyze membrane fusion.

SNAREs exist in complementary sets in the vesicle and target membranes as v-SNARE and t-SNARE.

The helical domains of t and v-SNAREs wrap around one another to form a trans-SNARE complex that initiates membrane fusion. The energy released upon trans-SNARE complex formation locks the two membranes together.

As the cytosolic sides of the bilayers move  close together, they expel the water molecules at the interface. Now, lipid molecules freely flow from one leaflet to another, forming a connecting stalk.

During hemifusion, lipids in the outer leaflet mix to widen the zone of fusion. When the newly formed bilayer ruptures, fusion is complete.

SNAREs can remain in the membrane as stable complexes until they are needed for new rounds of membrane transport.

NSF, a hexameric ATPase, catalyzes SNARE disassembly. This ring-shaped protein feeds the SNARE complexes through its center to dissociate the t and v-SNAREs.