Catalytic inositol polyphosphate 5-phosphatase (INPP5c) domain of SH2 domain containing inositol polyphosphate 5-phosphatase-1 and related proteins
This subfamily contains the INPP5c domain of SHIP1 (SH2 domain containing inositol polyphosphate 5-phosphatase-1, also known as SHIP/INPP5D) and related proteins. It belongs to a family of Mg2+-dependent inositol polyphosphate 5-phosphatases, which hydrolyze the 5-phosphate from the inositol ring of various 5-position phosphorylated phosphoinositides (PIs) and inositol phosphates (IPs), and to the large EEP (exonuclease/endonuclease/phosphatase) superfamily that contains functionally diverse enzymes that share a common catalytic mechanism of cleaving phosphodiester bonds. SHIP1's enzymic activity is restricted to phosphatidylinositol 3,4,5-trisphosphate [PI (3,4,5)P3] and inositol-1,3,4,5- polyphosphate [I(1,3,4,5)P4]. It converts these two phosphoinositides to phosphatidylinositol 3,4-bisphosphate [PI (3,4)P2] and inositol-1,3,4-polyphosphate [I(1,3,4)P3], respectively. SHIP1 is a negative regulator of cell growth and plays a major part in mediating the inhibitory signaling in B cells; it is predominantly expressed in hematopoietic cells. In addition to this INPP5c domain, SHIP1 has an N-terminal SH2 domain, two NPXY motifs, and a C-terminal proline-rich region (PRD). SHIP1's phosphorylated NPXY motifs interact with proteins with phosphotyrosine binding (PTB) domains, and facilitate the translocation of SHIP1 to the plasma membrane to hydrolyze PI(3,4,5)P3. SHIP1 generally acts to oppose the activity of phosphatidylinositol 3-kinase (PI3K). It acts as a negative signaling molecule, reducing the levels of PI(3,4,5)P3, thereby removing the latter as a membrane-targeting signal for PH domain-containing effector molecules. SHIP1 may also, in certain contexts, amplify PI3K signals. SHIP1 and SHIP2 have little overlap in their in vivo functions.
Jiyao W et al.(2023). "The conserved domain database in 2023.",