The SYT9 gene encodes a member of the synaptotagmin family. Synaptotagmins are integral membrane proteins of synaptic vesicles. They contain a transmembrane domain at their N-terminal, followed by C2A and C2B domains. These proteins carry out calcium-dependent phospholipid binding through their C2A domain and are suggested to be involved in the calcium-dependent exocytosis of secretory vesicles. By carrying out its functions, the SYT9 protein mediates the release of neurotransmitters such as norepinephrine and maintains fast synaptic transmission. It is also believed to function as a calcium-ion sensor during vesicular trafficking.