title: New insights into Dok-4 PTB domain structure and function.
abstract: The seven members of the Dok adapter protein family share a highly conserved phosphotyrosine-binding (PTB) domain. In the case of Dok-1, 2 and 3, the PTB domain binds to the lipid phosphatase Ship1, a key component of their inhibitory signaling mechanisms in immune cells. In contrast to most other Dok family members, Dok-4 is expressed widely but is poorly understood, largely because of limited knowledge of its partner molecules. We previously showed that, in contrast to the Dok-1 PTB domain (defined as aa 107-260), the homologous sequence in Dok-4 (aa 100-233) bound very poorly to Ret, a known Dok-4 partner. In the current study, we show that binding of Dok-4 to Ret requires residues C-terminal to the previously defined PTB domain boundaries (up to aa 246). These residues are predicted to form an extension in a critical C-terminal α-helix. We show that the Dok-4 PTB domain also binds the phosphorylated NPXY motifs in Ship1 but not Ship2. Finally, we found that a rare human single nucleotide polymorphism causing a R186H substitution in the PTB domain abolishes tyrosine phosphorylation of Dok-4 by Ret. In addition to providing a clearer understanding of Dok-4 PTB domain structure and function, our findings point to a potential mechanism for Dok-4 inhibitory signaling in T-cells and to the possibility of a rare Dok-4-related phenotype in humans.
authors.affiliation: Department of Medicine, Division of Nephrology, McGill University Health Centre, Montreal, Quebec, Canada H3A 2B4.
authors.forename: Erika
authors.initials: E
authors.lastname: Hooker
authors.forename: Cindy
authors.initials: C
authors.lastname: Baldwin
authors.forename: Serge
authors.initials: S
authors.lastname: Lemay
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000737:chemistry*; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D057809:HEK293 Cells; D006801:Humans; D000072181:Inositol Polyphosphate 5-Phosphatases; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry* / Q000235:genetics; D051379:Mice; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry; D010766:Phosphorylation / Q000235:genetics; D019000:Phosphotyrosine / Q000737:chemistry*; D020641:Polymorphism, Single Nucleotide; D017434:Protein Structure, Tertiary; D051096:Proto-Oncogene Proteins c-ret / Q000737:chemistry; D020798:Two-Hybrid System Techniques
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C486625:DOK4 protein, human; C432911:Dok4 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D019000:Phosphotyrosine; D051096:Proto-Oncogene Proteins c-ret; D010744:Phosphoric Monoester Hydrolases; D000072181:Inositol Polyphosphate 5-Phosphatases; C000606430:INPP5D protein, human; C000606433:Inpp5d protein, mouse; C000606435:Inppl1 protein, mouse; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases