Synaptojanin 1 is a phosphoinositide phosphatase which exists in two tissue specific isoforms (170 and 145 kDa). The 145 kDa isoform is predominantly expressed in the nervous system. It has a three domain structure with an N-terminal part homologous to the yeast Sac 1p protein, a central inositol 5-phosphatase domain and a C-terminal SH3 binding domain. Synaptojanin is involved in clathrin mediated synaptic vesicle recycling and binds to endophilin and amphiphysin.
Six isoforms are described so far and two splice variants of the 145 kDa isoform. The predominant one contains a 16 AA insert at position 1140-1155.