Vesicle-associated membrane protein (VAMP) (or synaptobrevin), a type II membrane protein of small synaptic vesicles, is essential for neuroexocytosis because its proteolysis by tetanus and botulinum neurotoxins types B, D, F and G blocks neurotransmitter release. The addition of cross-linking reagents to isolated small synaptic vesicles induces the formation of 30 and 50 kDa complexes containing the isoform 2 of VAMP (VAMP-2). Whereas the 30 kDa band is a VAMP-2 homodimer, the 50 kDa species results from the cross-linking of VAMP-2 with synaptophysin. This heterodimer also forms in detergent-solubilized vesicles and involves the N-terminal part of VAMP-2. The implications of the existence of a synaptophysin-VAMP-2 complex in the processes of vesicle docking and fusion with the presynaptic membrane are discussed.

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