STXBP1 may participate in the regulation of synaptic vesicle docking and fusion, possibly through interaction with GTP-binding proteins. The protein is essential for neurotransmission and binds syntaxin, a component of the synaptic vesicle fusion machinery probably in a 1:1 ratio. It can interact with syntaxins 1, 2, and 3 but not syntaxin 4 and may play a role in determining the specificity of intracellular fusion reactions.