PTPN9
PTPN9 encodes Meg2, one of the largest non-receptor tyrosine phosphatases, featuring an N-terminal FERM/Band 4.1-like module, a central PDZ domain, and a C-terminal catalytic domain. Meg2 associates with secretory granules and the cytoskeleton in epithelial and hematopoietic cells, where it regulates vesicle trafficking, SNARE-dependent exocytosis, and insulin secretion, and it modulates STAT3 signaling in myeloid cells. Expression is prominent in liver, pancreas, and blood cells. The PDZ domain mediates interactions with membrane and junctional proteins, positioning Meg2 at sites of polarized secretion. Its unusual modular architecture makes recombinant Meg2 a distinctive tool for studying scaffold-coupled phosphatase function among PTPN family members.
