Synaptotagmin

About SYT / Synaptotagmin:

Synaptotagmins (SYTs) are membrane-trafficking proteins. They regulate the speed and synchronicity of calcium-dependent neurotransmission. Eight out of the fifteen synaptotagmins directly bind to calcium. These are synaptotagmins 1, -2, -3, -5, -6, -7, -9, and -10 The other seven lack the necessary critical residues for calcium binding and hence operate indirectly.

SYT Function
It is believed that Synaptotagmin plays a role in exocytosis. Specifically, the calcium-binding synaptotagmins bind to the SNARE complex. This results in the fusion clamp effect of complexin being released and hence allows vesicle fusion to occur. By extension, Synaptotagmin is therefore believed to play a role in recovery from injury.
Synaptotagmin is also believed to have a significant influence on the development of neural connections and hence on the ability to learn. It has also been linked with bipolar disorder.

Synaptotagmin Structure
The Synaptotagmin-1 gene is located in position 21.2 of the q arm of chromosome 12 (12q21.2). The Synaptotagmin protein is formed as an N-terminal transmembrane region (TMR), a variable linker, and two C-terminal C2 domains - C2A and C2B.

SYT Interaction
Synaptotagmins interact with the intracellular loop I-II of neuronal voltage-sensitive sodium channels. They specifically interact with calcium either binding directly to it or acting as a sensor for its presence.

Synaptotagmin Mechanism of action
Although there is a large body of data on this subject, relatively little is known about the molecular mechanism of this highly regulated fusion machinery. It is, however, known that synaptotagmins react to Ca2+ influx by triggering the fusion of synaptic vesicles with the active zone in the presynaptic terminal.