T-SNARES

T-SNAREs (Target-Soluble NSF Attachment Receptor) is one specific part of conglomerate of proteins that make up cell or organelle membranes, where these proteins are involved directly in membrane fusion between, usually, the membranes of a vesicle and the cell's membrane in the process of endocytosis. A T-SNARE is found on the target membrane in the endocytosis of a certain substance, where it is commonly made up of three proteins. These T-SNARES will combine with V-SNARES (Vesicle) to create a Trans-SNARE complex which is a four alpha helix bundle which is stable, this will then allow eventually the two membranes to fuse and a fusion pore to open, causing the vesicular contents to diffuse into the cell. The energy for this membrane fusion is thought to come from the conformational change when the helices, from either transport or vesicular SNAREs, combine to form a complex, releasing energy. T-SNARES usually have an inhibitory complex bound to them, therefore Rab proteins and their effector proteins are needed to rid of this inhibitor, so that T-SNARES and V-SNARES can bind together, however specific extracellular signals are what initiate the binding of the two SNARE types, Rab proteins only increase the rate at which they bind.

This process is constantly occurring in the nervous system where, for example in a cholinergic synapse, acetylcholine is being transmitted across the presynaptic cleft for transmission to the postsynaptic neurone, where on the vesicle there is the SNARE protein synaptobrevin, and on the target membrane there SNARE proteins SNAP 25 and Syntaxin.