In neurons, the synaptotagmin-1 protein is localized to presynaptic axon terminals. When activated, it facilitates the fusion of neurotransmitter-containing synaptic vesicles to the plasma membrane, leading to neurotransmitter release into the synaptic cleft. Which of the following would you expect to directly activate synaptotagmin-1 for this function?
A) Binding to Mg²⁺ B) Binding to Ca²⁺ C) Binding to phosphatidylcholine D) Binding to K⁺ E) Binding to the K⁺ leak channels