Question

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

Answer 1

Synaptotagmin-1 is activated by the binding to Ca²⁺ ions, which occurs when an action potential opens voltage-gated Ca²⁺ channels, leading to neurotransmitter release.

Step-by-step explanation:

Direct activation of synaptotagmin-1, which is crucial for facilitating the fusion of neurotransmitter-containing synaptic vesicles with the plasma membrane, is primarily initiated by the binding to Ca²⁺ ions. During neurotransmitter release, an action potential triggers the opening of voltage-gated Ca²⁺ channels, which allows an influx of Ca²⁺ into the presynaptic axon terminal.

The increased concentration of Ca²⁺ is the signal for synaptotagmin-1 to initiate the fusion process, leading to neurotransmitter release into the synaptic cleft, playing a critical role in neuronal communication.