Synaptotagmin family member which does not bind Ca(2+) (PubMed:7993622). Involved in neuronal dense core vesicles (DCVs) mobility through its interaction with KIF1A. Upon increased neuronal activity, phosphorylation by MAPK8/JNK1 destabilizes the interaction with KIF1A and captures DCVs to synapses (PubMed:29166604). Plays a role in dendrite formation by melanocytes (By similarity). Interacts with KIF1A; the interaction increases in presence of calcium and decreases when SYT4 is phosphorylated at Ser-135. Widely expressed (PubMed:7892240). Expressed in the brain (PubMed:7892240). Expressed in pituitary gland, cerebellum, cortex, hypothalamus and hippocampus (PubMed:7892240). Up-regulated by potassium depolarization, calcium ionophore, ATP and forskolin in culture cells (PubMed:7892240). Up-regulated by kainate in the hippocampus and piriform cortex (PubMed:7892240). Unlike in other synaptotagmin family members, the first C2 domain/C2A does not bind Ca(2+) neither mediates Ca(2+)-dependent phospholipid binding. An aspartate-to-serine substitution in this domain inactivates Ca(2+)/phospho-lipid binding. Phosphorylation at Ser-135 by MAPK8/JNK1 reduces interaction with KIF1A and neuronal dense core vesicles mobility. Belongs to the synaptotagmin family.