May be involved in the regulation of neurotransmitter release and synaptogenesis. Binds ATP with high affinity and ADP with a lower affinity. This is consistent with a catalytic role of the C-domain in which ADP would be dissociated by cellular ATP after bound ATP was hydrolyzed. Interacts with CAPON. Peripheral membrane protein localized to the cytoplasmic surface of synaptic vesicles. Expressed primarily in brain. The A region binds phospholipids with a preference for negatively charged species. Phosphorylation at Ser-9 dissociates synapsins from synaptic vesicles. Regulated by calcium. Belongs to the synapsin family.