title: Identification of the major autophosphorylation sites of Nyk/Mer, an NCAM-related receptor tyrosine kinase.
abstract: Nyk/Mer receptor tyrosine kinase is a new member of the Ufo/Axl tyrosine kinase family and is characterized by its neural cell adhesion molecule-like extracellular domain. By using a vaccinia virus expression system to express a constitutively activated form of Nyk, we identified the major sites of Nyk autophosphorylation in tryptic peptide IY749SGDY753Y754R. Tyr-749, Tyr-753, and Tyr-754 in this peptide lie in the activation loop of the kinase domain. We also studied a series of Nyk mutants in which the three tyrosine residues were replaced individually, in pairs, or all together by phenylalanine. Single mutations of Tyr-749 or Tyr-753 to phenylalanine reduced Nyk kinase activity toward exogenous substrate to 39 or 10% of that of the wild type Nyk, respectively, whereas the Tyr-754 mutant is completely inactive. All of the double and triple Tyr-Phe mutants reduced Nyk kinase activity to a level below the background. Similar results were obtained when Nyk autophosphorylation levels were examined. Our studies suggest that full activity of Nyk/Mer kinase requires phosphorylation of all three tyrosine residues in the kinase domain (Tyr-749, Tyr-753, and Tyr-754) and that Nyk kinase activity is modulated by the level of autophosphorylation in the kinase domain. Given the highly conserved nature of this region among the Ufo/Axl receptor family members, the information presented in this report may provide insight to the biochemical properties of other members of this family.
authors.affiliation: Department of Molecular Biology, Case Western Reserve University, School of Medicine, Cleveland, Ohio 44106-4960, USA.
authors.forename: L
authors.initials: L
authors.lastname: Ling
authors.forename: D
authors.initials: D
authors.lastname: Templeton
authors.forename: H J
authors.initials: HJ
authors.lastname: Kung
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D002522:Chlorocebus aethiops; D017931:DNA Primers / Q000235:genetics; D004789:Enzyme Activation; D015870:Gene Expression; D008969:Molecular Sequence Data; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D019006:Neural Cell Adhesion Molecules / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D017354:Point Mutation; D011505:Protein-Tyrosine Kinases / Q000235:genetics; D020794:Receptor Protein-Tyrosine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D019006:Neural Cell Adhesion Molecules; D011994:Recombinant Proteins; D011505:Protein-Tyrosine Kinases; D020794:Receptor Protein-Tyrosine Kinases