Type I inositol 3,4-bisphosphate 4-phosphatase and Type II inositol 3,4-bisphosphate 4-phosphatase Pleckstrin homology (PH) domain
INPP4A (also called Inositol polyphosphate 4-phosphatase type I) and INPP4B (also called Inositol polyphosphate 4-phosphatase type II) both catalyze the hydrolysis of the 4-position phosphate of phosphatidylinositol 3,4-bisphosphate and inositol 1,3,4-trisphosphate. They differ in that INPP4A additionally catalyzes the hydrolysis of the 4-position phosphate of inositol 3,4-bisphosphate, while INPP4B catalyzes the hydrolysis of the 4-position phosphate of inositol 1,4-bisphosphate. They both have a single PH domain followed by a C2 domain. PH domains have diverse functions, but in general are involved in targeting proteins to the appropriate cellular location or in the interaction with a binding partner. They share little sequence conservation, but all have a common fold, which is electrostatically polarized. Less than 10% of PH domains bind phosphoinositide phosphates (PIPs) with high affinity and specificity. PH domains are distinguished from other PIP-binding domains by their specific high-affinity binding to PIPs with two vicinal phosphate groups: PtdIns(3,4)P2, PtdIns(4,5)P2 or PtdIns(3,4,5)P3 which results in targeting some PH domain proteins to the plasma membrane. A few display strong specificity in lipid binding. Any specificity is usually determined by loop regions or insertions in the N-terminus of the domain, which are not conserved across all PH domains. PH domains are found in cellular signaling proteins such as serine/threonine kinase, tyrosine kinases, regulators of G-proteins, endocytotic GTPases, adaptors, as well as cytoskeletal associated molecules and in lipid associated enzymes.
Jiyao W et al.(2023). "The conserved domain database in 2023.",