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Adaptor protein containing PH domain, PTB domain, and Leucine zipper motif Bin1/amphiphysin/Rvs167 (BAR)-Pleckstrin homology (PH) domain APPL (also called DCC-interacting protein (DIP)-13alpha) interacts with oncoprotein serine/threonine kinase AKT2, tumor suppressor protein DCC (deleted in colorectal cancer), Rab5, GIPC (GAIP-interacting protein, C terminus), human follicle-stimulating hormone receptor (FSHR), and the adiponectin receptors AdipoR1 and AdipoR2. There are two isoforms of human APPL: APPL1 and APPL2, which share about 50% sequence identity. APPL has a BAR and a PH domain near its N terminus, and the two domains are thought to function as a unit (BAR-PH domain). C-terminal to this is a PTB domain. Lipid binding assays show that the BAR, PH, and PTB domains can bind phospholipids. 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.",