Phosphatase that acts on various phosphoinositides, including phosphatidylinositol 4-phosphate, phosphatidylinositol (4,5)-bisphosphate and phosphatidylinositol (3,4,5)-trisphosphate (PubMed:27435091). Has a role in clathrin-mediated endocytosis (By similarity). Hydrolyzes PIP2 bound to actin regulatory proteins resulting in the rearrangement of actin filaments downstream of tyrosine kinase and ASH/GRB2 (By similarity). a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol-4,5-bisphosphate) + H2O = a 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol 4-phosphate) + phosphate Interacts with ASH/GRB2. Interacts with PACSIN1, PACSIN2 and PACSIN3 (By similarity). Binds AMPH, SH3GL1, SH3GL2 and SH3GL3 (PubMed:10542231). Interacts with MYO1E (via SH3 domain) (PubMed:17257598). Interacts with BIN1 and DNM1 (By similarity). Concentrated at clathrin-coated endocytic intermediates in nerve terminals. Isoform 1 is more enriched than isoform 2 in developing brain as well as non-neuronal cells. Isoform 2 is very abundant in nerve terminals. Binds to EPS15 (a clathrin coat-associated protein) via a C-terminal domain containing three Asn-Pro-Phe (NPF) repeats. The C-terminal proline-rich region mediates binding to a variety of SH3 domain-containing proteins including AMPH, SH3GL1, SH3GL2, SH3GL3 and GRB2. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Belongs to the synaptojanin family. In the central section; belongs to the inositol 1,4,5-trisphosphate 5-phosphatase family. Extended N-terminus.