PEPP1 (also called PLEKHA4/PH domain-containing family A member 4 and RHOXF1/Rhox homeobox family member 1), and related homologs PEPP2 (also called PLEKHA5/PH domain-containing family A member 5) and PEPP3 (also called PLEKHA6/PH domain-containing family A member 6), have PH domains that interact specifically with PtdIns(3,4)P3. Other proteins that bind PtdIns(3,4)P3 specifically are: TAPP1 (tandem PH-domain-containing protein-1) and TAPP2], PtdIns3P AtPH1, and Ptd- Ins(3,5)P2 (centaurin-beta2). All of these proteins contain at least 5 of the 6 conserved amino acids that make up the putative phosphatidylinositol 3,4,5- trisphosphate-binding motif (PPBM) located at their N-terminus. 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.",