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Adaptor protein containing PH domain, PTB domain, and Leucine zipper motif (APPL; also called DCC-interacting protein (DIP)-13alpha) Phosphotyrosine-binding (PTB) domain APPL 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. PTB domains have a common PH-like fold and are found in various eukaryotic signaling molecules. This domain was initially shown to binds peptides with a NPXY motif with differing requirements for phosphorylation of the tyrosine, although more recent studies have found that some types of PTB domains can bind to peptides lack tyrosine residues altogether. In contrast to SH2 domains, which recognize phosphotyrosine and adjacent carboxy-terminal residues, PTB-domain binding specificity is conferred by residues amino-terminal to the phosphotyrosine. PTB domains are classified into three groups: phosphotyrosine-dependent Shc-like, phosphotyrosine-dependent IRS-like, and phosphotyrosine-independent Dab-like PTB domains. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",