Synaptotagmin 1 is a member of the Ca²⁺-binding synaptotagmin family of proteins that includes 16 members in vertebrates and is involved in regulated exocytosis and trafficking^1,2.

Synaptotagmins are type I membrane proteins located in intracellular vesicles and consist of a short N-terminal domain located in the vesicle lumen, a transmembrane domain and a cytosolic domain containing two Ca²⁺ binding domains^1,2.

Synaptotagmins are usually localized to distinct secretory vesicles and control their Ca²⁺-dependent fusion. Synaptotagmin I is predominantly expressed in neuronal cells and is an abundant constituent of synaptic vesicles^1,2.

Synaptotagmin I has a relatively low Ca²⁺ affinity and is able to bind Ca²⁺ mostly in the vicinity of Ca²⁺ channels pores. Indeed, Synaptotagmin I has been demonstrated to directly interact with selected Ca²⁺ channels. Synaptotagmin I also binds to the t-SNARE protein Syntaxin 1 in a Ca²⁺-dependent manner thus forming the prototypical Ca²⁺-dependent fast synaptic vesicle exocytosis protein complex that also includes SNAP-25 and VAMP^1,2,3.