A new layer of phosphoinositide-mediated allosteric regulation uncovered for SHIP2

The Src homology 2 containing inositol 5-phosphatase 2 (SHIP2) is a large multidomain enzyme that catalyzes the dephosphorylation of the phospholipid phosphatidylinositol 3,4,5-triphosphate (PI(3,4,5)P₃ ) to form PI(3,4)P₂ . PI(3,4,5)P₃ is a key lipid second messenger controlling the recruitment of signaling proteins to the plasma membrane, thereby regulating a plethora of cellular events, including proliferation, growth, apoptosis, and cytoskeletal rearrangements. SHIP2, alongside PI3K and PTEN, regulates PI(3,4,5)P₃ levels at the plasma membrane and has been heavily implicated in serious diseases such as cancer and type 2 diabetes; however, many aspects of its regulation mechanism remain elusive. We recently reported an activating effect of the SHIP2 C2 domain and here we describe an additional layer of regulation via the pleckstrin homology-related (PHR) domain. We show a phosphoinositide-induced transition to a high activity state of the enzyme that increases phosphatase activity up to 10-15 fold. We further show that PI(3,4)P₂ directly interacts with the PHR domain to trigger this allosteric activation. Modeling of the PHR-phosphatase-C2 region of SHIP2 on the membrane suggests no major inter-domain interactions with the PHR domain, but close contacts between the two linkers offer a possible path of allosteric communication. Together, our data show that the PHR domain acts as an allosteric module regulating the catalytic activity of SHIP2 in response to specific phosphoinositide levels in the cell membrane.