Review Question - QID 106957

A group of scientists discovered a neurotoxin that prevents neurons from releasing neurotransmitters. They performed a series of experiments to determine the protein that the neurotoxin affected. They used a fluorescent molecule that localizes to synaptic vesicles. In the control experiment, they observed the movement of vesicles from the cell body down the axon and finally to the synapse, and they saw movement from the synapse back to the cell body. When the neurotoxin was applied, the vesicles stopped moving down the axon, but movement back to the cell body still occurred. They also applied tetanospasmin and botulinuum toxin to see if these toxins exhibited similar behavior but they did not. Which of the following proteins is most likely affected by this neurotoxin?