Adapter protein involved in endocytic recycling of synaptic vesicles membranes. May act by mediating the retrieval of synaptotagmin protein Syt from the plasma membrane, thereby facilitating the internalization of multiple synaptic vesicles from the plasma membrane. Interacts with the second C2 domain of Syt. Colocalizes with synaptic vesicle pools. Colocalizes with the endocytic network within synaptic boutons. Present at synaptic connections both in the CNS and in neuromuscular junctions in the mature embryo (20-22h) and throughout larval development. In the third instar larva, it is expressed in all synaptic bouton types, including I, II and III boutons. The Asp-Pro-Phe (DPF) motifs, which are found in many presynatic proteins, are thought to mediate an interaction with AP-2alpha. StnB, which is involved in the same pathway, is derived from the same bicistronic transcript that encodes these two different proteins.