In all eukaryotic cells, proteins are organized into organelle compartments. Numerous cellular processes depend on the sorting of proteins to the correct compartment. Vesicles play a key role in protein transport as their formation, docking, and fusion enable protein transport among a cell's many compartments. Proteins synthesized in the endoplasmic reticulum are transported via vesicles through the Golgi apparatus, to secretory vesicles and finally to the cell surface.
Proteins involved in vesicle budding and fusion are non-specific.
One set of vesicle budding proteins and one set of fusion proteins is common to many compartments. Specificity of transport is achieved by unidirectional docking of vesicles at the appropriate target compartment. V proteins are on transport vesicle surfaces, while T proteins are on target organelle surfaces. V proteins of vesicles originating from various compartments are believed to be structurally similar, as are the T proteins of various target compartments. VT protein interactions are specific enough to prevent inappropriate docking events.